MMD-45 Mill Tight Spindle

[Oldneweng]

Yesterday I tried to use a new carbide milling cutter. I set the mill to the fastest speed of course. When I switched it on all I got was a hum from the motor. My first thought was a motor capacitor. I played around with turning power off and on etc with no change. I then started changing gears. I found that with a bit of hesitation it worked on the lowest gear and sounded normal. I then worked up thru the gears. With six gears, it worked on the lowest three and then with a bit more hesitation, the fourth gear. I have not been able to get the top two to work however.

I positioned the gear levers in a neutral position and turned the spindle by hand. It was certainly harder to turn than normal.

The spindle has always got a bit hot since new, but I have not checked it recently. I assumed it was just bedding in.

Any suggestions to assist with this issue would be greatly appreciated. Bearing Types? Adjustments?

Dean

[simonl]

Hi Dean,

If you find a "sweet spot" in-between the gears which would serve as a neutral then you can turn the spindle by hand to get a feel for how smooth and how tight/loose the spindle bearings are. It may take a bit of jiggling (especially if it's new and a bit stiff) to find an unofficial neutral.

So, the reason it stalls in top gear but just manages to turn in the lower gears may indicate that the spindle bearings are tight. It may also be one of the shafts from the gears that is also tight but given what you have explained, i'd be inclined to think it's the spindle or the final drive before the spindle or the final gear that has the slip shaft that drives the spindle.

Either way, it sounds like you will need to either take the mill back or (if you would rather) take the gear head apart, clean it, adjust whatever is not properly adjusted and re-assemble.

Be interested to see what others suggest.

Good luck.

Simon

[Oldneweng]

Thanks Simon.


If you find a "sweet spot" in-between the gears which would serve as a neutral then you can turn the spindle by hand to get a feel for how smooth and how tight/loose the spindle bearings are. It may take a bit of jiggling (especially if it's new and a bit stiff) to find an unofficial neutral.

Yes that is what I did.


So, the reason it stalls in top gear but just manages to turn in the lower gears may indicate that the spindle bearings are tight. It may also be one of the shafts from the gears that is also tight but given what you have explained, i'd be inclined to think it's the spindle or the final drive before the spindle or the final gear that has the slip shaft that drives the spindle.

I have no idea at this stage how it operates internally. That is the main reason for asking for advice, along with some suggestion as to what form of bearing I am likely to encounter.


Either way, it sounds like you will need to either take the mill back or (if you would rather) take the gear head apart, clean it, adjust whatever is not properly adjusted and re-assemble.

I will have to dismantle the head, which will enable me to do a couple of other things I have in mind including checking the inside for foreign matter.

Most results I have found on the net show tapered roller bearings at both ends. My top bearing is not a tapered bearing (visible on the top of the head) which leads me to believe it is different to these other mills. I should point out that there are many types of mill produced of this type and I have no illusions that any of this information is the same as mine. Having said that, the only parts breakdown document I have found is for a Grizzly G0463_pl mill and as they use a totally different naming convention I don't even know if it is the same size. For a start it is belt driven. This mill does use non-tapered bearings. They appear to be deep groove, and thrust bearings.

My first step will be to remove the lip seal from the top bearing and inspect it.

Dean

[steran50]

HI,
It does sound like the Spindle bearings are a bit tight, but the upper gear shafts may also be tight. I have a DM-45 Mill it is harder to rotate the spindle in the lower gears, because of the low gearing. It is however easy to rotate the spindle in the higher gears. These Links may help in Dismantling your Mill's Gearbox
http://www.graetech.com/index_files/Page878.htm http://www.metalworkingfun.com/showthread.php?tid=405 Good luck.

[simonl]

My top bearing is not a tapered bearing (visible on the top of the head) which leads me to believe it is different to these other mills.
Dean

Not necessarily. The top bearing that you see may in fact be the bearing of the shaft of the final drive gear. It has an internal spline to match the spindle. The spindle slides in and out of this when it moves up and down and transfers the rotational power to the spindle. I doubt you will see the spindle bearings from the top but I could be wrong.

Bare in mind, when you take the top off, it houses about 4 bearings for the shafts for the gears. Depending on how tight a fit, the shafts will either pull out from the bottom or from the head. They are pretty easy to put back when re-assembling. Easier than first expected.

Simon

[Oldneweng]

HI,
It does sound like the Spindle bearings are a bit tight, but the upper gear shafts may also be tight. I have a DM-45 Mill it is harder to rotate the spindle in the lower gears, because of the low gearing. It is however easy to rotate the spindle in the higher gears. These Links may help in Dismantling your Mill's Gearbox
http://www.graetech.com/index_files/Page878.htm http://www.metalworkingfun.com/showthread.php?tid=405 Good luck.

Thanks heaps for those links Stewart. They should make things easier to understand. I will study these carefully.

Simon


Not necessarily. The top bearing that you see may in fact be the bearing of the shaft of the final drive gear. It has an internal spline to match the spindle. The spindle slides in and out of this when it moves up and down and transfers the rotational power to the spindle. I doubt you will see the spindle bearings from the top but I could be wrong.

Bare in mind, when you take the top off, it houses about 4 bearings for the shafts for the gears. Depending on how tight a fit, the shafts will either pull out from the bottom or from the head. They are pretty easy to put back when re-assembling. Easier than first expected.


Some more pieces of the puzzle to help me. Thanks again.

Now I have some concept of what I can expect to see inside.

Dean

[Oldneweng]

Ok. So the plot thickens.

I just went to have a quick (I'm watching tea cook) look at the top bearing above the spindle thinking to remove the lip seal. I forgot a torch as the light is not quite good enough that high. I did clean off some dirt and stuff. I tend to forget to replace the cover. Maybe I should put it on the table when I remove it so I see it before I continue.:doh:

Anyway I thought I should remove the milling cutter and the ER collet chuck before proceeding. I then turned the mill on. It was still in H-1 (Fourth gear). It took off without any hesitation. Switched to H-2. Same thing here and in top gear.:?

This is something I need to ponder. Tomorrow I will experiment with various attachments and see what result I get. The ER collet chuck was not over tightened. The mill was in H-1 as stated above and I did not hold the spindle. The draw bar released just with a quick twist of the spanner.

Dean

[pipeclay]

It would seem from your own results that something you have put in the spindle is the cause of your problem.
Have you used this collet chuck and drawbar assembly before?

[Oldneweng]

It would seem from your own results that something you have put in the spindle is the cause of your problem.
Have you used this collet chuck and drawbar assembly before?

The collet chuck was received in a fairly large order shipped from CTC on 28/12/12. It has seen extensive use. The drawbar was made by me shortly after receiving the order as the one that came with the mill had a 14mm thread which fits nothing I have seen except for what was supplied with the mill.

I have not used anything else in the spindle in the last couple of days.

I will have a look inside the spindle. It seems like it is pretty easy to remove.

Dean

[Oldneweng]

Today I first checked that the problem still existed (desperation I know). No Change. I tried varying the amount of pressure on the drawbar and found that this made a difference. Keep tightening it and at a point it stops turning in 2 top gears.

I then tried the drill chuck and 14mm drawbar, both of which were supplied with the mill from new. The same result. This at least confirms that the problem is in the spindle.

I have removed the spindle. Checking the taper, it looks and feels fine except it is not the finest finish I have seen. What one would expect. I have examined the MT4 tapers that have been used in the spindle and could not see or feel any imperfections. I have not dismantled the spindle, but I did check that the locking tab is engaged on the top adjusting nut.

I could just back off the adjustment a bit and see what happens, but I can't help thinking there is a problem further down. The spindle laying on the bench is still pretty tight. I struggle to turn it with my finger/thumb from the slots at the bottom. Gripping the spline it is quite firm to turn. It wouldn't hurt to clean it out and check the bearings while I have it out although it was a pretty easy job.

Dean

How tight should it be to turn?

[simonl]

Hi Dean. I think you should be able to turn it with your fingers reasonably easy. Based on the info you have given, I would suggest its way too tight. Its a bit late now but I should have suggested you run the spindle in a mid range gear for 15 mins and check the temp with your hand. I shouldnt be anymore than warm to the touch. In fact the owners manual for both my lathe and mill said to run the machine in each gear for 20 mins when new.

I would take the spindle apart since you got it out and clean and repack the bearings with grease. In fact I would replace them the quality japanese bearings and be done with it but thats just me and it could be unnecessary.

Simon

[Oldneweng]

Hi Dean. I think you should be able to turn it with your fingers reasonably easy. Based on the info you have given, I would suggest its way too tight. Its a bit late now but I should have suggested you run the spindle in a mid range gear for 15 mins and check the temp with your hand. I shouldnt be anymore than warm to the touch. In fact the owners manual for both my lathe and mill said to run the machine in each gear for 20 mins when new.

I would take the spindle apart since you got it out and clean and repack the bearings with grease. In fact I would replace them the quality japanese bearings and be done with it but thats just me and it could be unnecessary.

Simon

I will check the prices for the bearings as it makes sense to replace them while I have the chance to do it easily. I will certainly check the condition of the bearings if I can get them out. The 2 links provided by Stewart have a lot of useful information regarding disassembly, but there is information missing in both of them. Disassembly of the lower section of the spindle is one of these. There is a large threaded disk which obviously needs some sort of pin spanner to remove, but the holes (3) are tiny. I don't have any sort of tool to fit and don't really know what to use make one. Drill bit shanks? I can make up a disk to suit. The face is not flat, but has a taper. No real problem there. It would be good to have a working mill to position the holes!:D Can any one tell me if this disk will be tight to remove? (typically that is) I have found a picture. It seems to be only to keep carp out, but mention was made of needing to press the quill out of the bottom bearing so it needs to come off.

328526

Photo thanks to Graetech.com

The only info in the links provided regarding adjustment of the spindle bearings is


Install keeper plate and castellated nut. Tighten and back off about 1/8 turn. Set the keeper tab into the nut slot.

I guess that will be enough to work it out.

Dean

[pipeclay]

I have probably missed something here but doesn't the spindle rotate inside a top and bottom bearing?
And the tooling you use Is held in a taper in the spindle and if required retained by a draw bar?
If the spindle when in the machine was able to rotate in high gear with out tooling there must be something causing it to tighten or jam when the tooling is fitted.
Is there the chance that the spindle may have a small fracture and when you tighten the draw bar the crack is opening causing the spindle to tighten or jam on the bearings.

[Oldneweng]

I have probably missed something here but doesn't the spindle rotate inside a top and bottom bearing?
And the tooling you use Is held in a taper in the spindle and if required retained by a draw bar?
If the spindle when in the machine was able to rotate in high gear with out tooling there must be something causing it to tighten or jam when the tooling is fitted.
Is there the chance that the spindle may have a small fracture and when you tighten the draw bar the crack is opening causing the spindle to tighten or jam on the bearings.

Yes you are correct PC.

The first picture is the bottom spindle inner bearing race on the spindle and the mating bearing cone still in place in the quill. The thread just outside the bearing cone is where the spindle cover screws in. The second picture shows both bearing inner races on the spindle in relation to where they fit in the quill.

Sorry about the small sizes. Pictures are both thanks to Metalworkingfun.com Forum.



328546 328547


If the spindle when in the machine was able to rotate in high gear with out tooling there must be something causing it to tighten or jam when the tooling is fitted.
Is there the chance that the spindle may have a small fracture and when you tighten the draw bar the crack is opening causing the spindle to tighten or jam on the bearings.

There is always the possibility of something like this happening which is why I wrote


I could just back off the adjustment a bit and see what happens, but I can't help thinking there is a problem further down.

I do want to pull it apart and examine it carefully. Looking at the diameters it seems that the only place a problem like this can occur is at the bearing mount points. There appears to be a lot of clearance everywhere else inside the quill.

Dean

[BaronJ]

Hi Dean,



If the spindle when in the machine was able to rotate in high gear without tooling there must be something causing it to tighten or jam when the tooling is fitted. Is there the chance that the spindle may have a small fracture and when you tighten the draw bar the crack is opening causing the spindle to tighten or jam on the bearings.


This would be my guess as well ! I would pull the bearings, and fit the drawbar and a tool, tighten and see if you can see or measure any crack or out of round where the bearing fits. If you have access to someone who has crack testing equipment that may be a better bet. Though I hope that you find something silly such as a spacer that is binding and easily fixed.

[cba_melbourne]

It seems to be essentially a Taiwanese Rong-Fu clone. There are many factories in mainland China making these. One of the better ones is sold in the US as the Grizzly G0755. You can download the parts list from here and compare it to your mill: http://www.grizzly.com/products/Heavy-Duty-Mill-Drill-with-Stand-and-Power-Feed/G0755.
There is an exploded drawing of the head, and according to the parts list the main bearings are two taper rollers 30206P5 and 30207P5 (I doubt low cost versions of this mill use P5 class bearings, but the size is most likely the same).

These are usually the problems you will universally face with low cost Chinese machine tool spindles:
- bearing preload cannot be adjusted properly, because the inner cones are too tight a fit onto the spindle. The spindle journal needs to be reduced (ground, turned, or in a pinch at least polished with emery cloth) until the cup can slide on it (slide firmly but with hand force alone, no sledge hammer should be necessary).
- lots of casting sand left in craps and crevices that over time comes loose and contaminates lubricant and degrades bearings. It is advisable to completely strip such machines and clean out. Some of the better machines made in the more expensive factories may not suffer from this problem, but if unsure better take apart than be sorry.
- the most low cost factories may use inferior trailer bearings with excessive runout (making audible noise). Such bearings may initially get better after some hours running-in, but won't last for long. Replacement will be needed.

Notice that too much preload will cause the spindle to show excessive resistance when turning, this will cause the spindle to heat up excessively, and it will quickly ruin the bearings. Insufficient preload otoh will cause poor surface finish, and in more extreme cases chatter and inability to hold dimension.

[Oldneweng]

Thanks for the model number cba. As I had previously mentioned I had downloaded a parts list from Grizzly, but it was for the G0463 as I had no idea which one to choose.:2tsup:

I am pretty sure I have found the problem. When removing the locking nut at the top of the spindle I had to use a lot of force. I used the ER collet chuck spanner. I was just about to get a pipe extension when the bearing retaining nut cracked free. Yes I had released the locking tab.:D

I pressed the spindle out of the quill on my press. It did not take much force.

328612

It is obvious that the lower bearing is less than ideal. The upper bearing does not show any signs of damage tho. Now I need to get some prices.

I did try the drill chuck in the taper after I had loosened the bearing retaining nut and then retightened it. I gave it more tension than it should normally be adjusted, but no where near as much as it had originally. I tightenened the draw bar a fair bit tighter than I would normally. There appeared to be no difference when turning the spindle.

The lower cover ring I was asking about was a problem. It was cross threaded. Its only plastic so I managed to get it off without totally destroying it.

Dean

[Oldneweng]

Some initial results from bearing research. The bearing sizes required are 30206 and 30208. The Grizzly list has a 30207 istead of the 30208.

The following bearing is available on EBay. It is a spindle bearing from a Myford 10 Lathe. It is rated at P6. The Grizzly parts list shows a requirement of P5.

http://www.ebay.com.au/itm/NEW-HIGH-QUALITY-NSK-TAPER-ROLLER-BEARING-HR-30206-JP-TAKEN-MYFORD-STORES-/111356375243?pt=LH_DefaultDomain_15&hash=item19ed5b70cb

The local CBC store says there is only 1 grade for these bearings as listed in their books. The grade is unknown, but at $30 for the larger bearing it is unlikely to be very high. He did say he could try a search for better bearings, but who knows how much they would cost. Cost is a definite issue for me and I need to balance this with the benefits obtained considering that it is just a Chinese built machine.

Is the CL7C classification of any use in this situation? It was mentioned in a thread on Prac. Mach. in relation to a manual lathe. A quote from the thread which came from SKF originally.
The tolerances for CL7C specification bearings correspond to Normal tolerances except for the running accuracy which has been tightened ...

There appears to be a shortage of higher grade bearings available.

Dean

[cba_melbourne]

Some initial results from bearing research. The bearing sizes required are 30206 and 30208. The Grizzly list has a 30207 istead of the 30208.

The following bearing is available on EBay. It is a spindle bearing from a Myford 10 Lathe. It is rated at P6. The Grizzly parts list shows a requirement of P5.

http://www.ebay.com.au/itm/NEW-HIGH-QUALITY-NSK-TAPER-ROLLER-BEARING-HR-30206-JP-TAKEN-MYFORD-STORES-/111356375243?pt=LH_DefaultDomain_15&hash=item19ed5b70cb

The local CBC store says there is only 1 grade for these bearings as listed in their books. The grade is unknown, but at $30 for the larger bearing it is unlikely to be very high. He did say he could try a search for better bearings, but who knows how much they would cost. Cost is a definite issue for me and I need to balance this with the benefits obtained considering that it is just a Chinese built machine.

Is the CL7C classification of any use in this situation? It was mentioned in a thread on Prac. Mach. in relation to a manual lathe. A quote from the thread which came from SKF originally.

There appears to be a shortage of higher grade bearings available.

Dean


Hi Dean,

in this case common automotive grade bearings (precision class P0 or PX, or no suffix at all) are probably the best choice. But choose them to come from a reputable "western" maker like SKF. Stay away from fantasy maker names that you have never heard mentioned before, you do not want to install boat trailer grade bearings. P5 and better bearings would be overkill, because the spindle of this mill is itself probably only manufactured to 0.02mm runout tolerance.

When installing the new bearings, make sure that the top inner cone is a sliding fit onto the spindle. Meaning that if lightly oiled, you can just slide it up and down with hand force only. If its too tight, you will not be able to finely adjust the bearing preload, because the cone will only move in "jerks" when tightening the adjuster nut, and it wont release preload when loosening the adjuster nut (you will need to use a hammer on the spindle to loosen preload).

Next, do not overfill the bearings with grease. If you do, they will run hot and the oil will separate out from the grease, leaving just gunk behind that is not a good lube. Remember, a machine tool spindle requires a much higher preload than a car wheel and thus will run hotter. Use a good quality bearing grease, you do not want to take that spindle out regularly to re-grease.


Disclaimer: I am no bearing expert and do not claim to be one. I am just a hobby user happening to have some experience with bearings inside hobby machine tools.

[Oldneweng]

Hi Dean,

in this case common automotive grade bearings (precision class P0 or PX, or no suffix at all) are probably the best choice. But choose them to come from a reputable "western" maker like SKF. Stay away from fantasy maker names that you have never heard mentioned before, you do not want to install boat trailer grade bearings. P5 and better bearings would be overkill, because the spindle of this mill is itself probably only manufactured to 0.02mm runout tolerance.

When installing the new bearings, make sure that the top inner cone is a sliding fit onto the spindle. Meaning that if lightly oiled, you can just slide it up and down with hand force only. If its too tight, you will not be able to finely adjust the bearing preload, because the cone will only move in "jerks" when tightening the adjuster nut, and it wont release preload when loosening the adjuster nut (you will need to use a hammer on the spindle to loosen preload).

Next, do not overfill the bearings with grease. If you do, they will run hot and the oil will separate out from the grease, leaving just gunk behind that is not a good lube. Remember, a machine tool spindle requires a much higher preload than a car wheel and thus will run hotter. Use a good quality bearing grease, you do not want to take that spindle out regularly to re-grease.


Disclaimer: I am no bearing expert and do not claim to be one. I am just a hobby user happening to have some experience with bearings inside hobby machine tools.

Thank cba. In that case I will probably just get the local bearings as I could afford them. He did say there were also used for industrial purposes? I just need to get there. I will try a much more local/closer industrial "everything" type store. At least I go past regularly. They may be expensive tho.

I will check the fit of the top cone as suggested.

Half full or so of grease is what is mentioned in the repair threads have mentioned before.

I may have trouble removing the bottom bearing cone. There is very little room. It appears to be only a shallow shoulder and then a taper. There is not much to grip on because of the taper. I was thinking of a disk with a taper to roughly match. Another disk which fits inside the cone and bolts to the larger disk then cut the larger disk into pieces so I can fit it in position behind the cone and lock in place with the smaller disk.

Dean

[Oldneweng]

The LOML talked me into taking her into town. I decided to try the Industrial Shop there for the bearings. (Not the town I was thinking of) This shop caters primarily for agricultural equipment supplies. No matter, "Blue" (he has red hair) went straight to the boxes and whipped them out.

CBC price for both $49.70.
ATI price for both $36.60. (The ones I bought)

I am happy except for working out how to get that lower cone out.

Dean

[cba_melbourne]

............
I am happy except for working out how to get that lower cone out.
Dean

On these spindles the cone journal often grossly oversize. To make matters worse, the journal is often only turned or coarsely ground instead of being precisely ground to a fine finish. Then at the factory they use brutal force to get the cone on. Which btw distorts the cone and ruins the precision..... Anyway, they can be very hard indeed to get off. One method is to carefully grind a slit into the cone with an abrasive disc, then split it with a center punch. The cones are hardened and usually very brittle. Or you can grind a flat onto the cone, and as you come very close to the spindle give it a punch and the cone will break and spring open. If you have an acetylene torch all you need is a fine pointed hot flame to heat the cone only (not the spindle) and it will pop loose. Before putting the new cones on, measure the spindle and compare to the required installation tolerance from the bearing website or catalog. It the spindle journal needs to get smaller, put the spindle in your lathe and use fine emery cloth over a file, 400 grit then 600. This method is a big "nonono" for precision spindles. But given these spindles are not made very accurately to begin with (about 0.02mm tir is normal for Chinese hobbylathe and hobbymill spindles) and most of those low cost spindles are not hardened, the emery cloth method is an appropriate shortcut. You typically only have to take off a few 0.001mm from the journal diameter to bring it into the bearing maker tolerance for a loose interference fit. Do it by trial fit if you do not own a micrometer capable to resolve 0.001mm - a common 0.01mm micrometer is not good enough to measure/make a bearing fit.

Removing the outer races are easier. Just weld a bead to the inside and they shrink and pop out.

[Oldneweng]

On these spindles the cone journal often grossly oversize. To make matters worse, the journal is often only turned or coarsely ground instead of being precisely ground to a fine finish. Then at the factory they use brutal force to get the cone on. Which btw distorts the cone and ruins the precision..... Anyway, they can be very hard indeed to get off. One method is to carefully grind a slit into the cone with an abrasive disc, then split it with a center punch. The cones are hardened and usually very brittle. Or you can grind a flat onto the cone, and as you come very close to the spindle give it a punch and the cone will break and spring open. If you have an acetylene torch all you need is a fine pointed hot flame to heat the cone only (not the spindle) and it will pop loose. Before putting the new cones on, measure the spindle and compare to the required installation tolerance from the bearing website or catalog. It the spindle journal needs to get smaller, put the spindle in your lathe and use fine emery cloth over a file, 400 grit then 600. This method is a big "nonono" for precision spindles. But given these spindles are not made very accurately to begin with (about 0.02mm tir is normal for Chinese hobbylathe and hobbymill spindles) and most of those low cost spindles are not hardened, the emery cloth method is an appropriate shortcut. You typically only have to take off a few 0.001mm from the journal diameter to bring it into the bearing maker tolerance for a loose interference fit. Do it by trial fit if you do not own a micrometer capable to resolve 0.001mm - a common 0.01mm micrometer is not good enough to measure/make a bearing fit.

Removing the outer races are easier. Just weld a bead to the inside and they shrink and pop out.

Thanks for this excellent information and particularly for the bead welding trick. I had totally forgotten that one.

The inner cones were quite easy to press off. I hope to only need a little touch up of the spindle to acheive a neat slide fit as as you have mentioned.

I forgot to mention in the previous post that both bearings were NSK.

Dean

[cba_melbourne]

........
I forgot to mention in the previous post that both bearings were NSK.....
Dean

I am surprised. NSK is a very reputable maker. I would have expected a much cheaper no-name bearing in there. This means they must have ruined that bearing when installing it. Maybe they used a too heavy mallet to adjust the preload. Or maybe there was more than usual casting sand contamination in the grease they used. Maybe condensation water collected inside the quill whilst in transit...

[Oldneweng]

I am surprised. NSK is a very reputable maker. I would have expected a much cheaper no-name bearing in there. This means they must have ruined that bearing when installing it. Maybe they used a too heavy mallet to adjust the preload. Or maybe there was more than usual casting sand contamination in the grease they used. Maybe condensation water collected inside the quill whilst in transit...

Oops, my mistake there.:doh:

I should have been clearer. The bearings I bought were both NSK. Sorry about that.

Dean

[pipeclay]

Was very clear to me what you meant,but then I am pretty simple and don't over think things to much.

[Oldneweng]

It turned out to be a bit of an anticlimax to finish up with.

The top outer cone was accessible with a bar thru from the other end. There was enough edge showing. I used a square piece and tapped it round and round the cone. Movement was soon visible. I was not using much force. I soon had it right out.

What the heck. I made an impact puller from all thread with a thick domed washer welded on one end. In the lathe I tapered the edge of the washer to fit into the narrow gap. It was about 2mm at the edge. Initially I had to use it angled out slightly, but again I soon managed to get my fingernail behind the cone. Proof it had moved. I soon had it out as well. I only used a small weight and did not use much force. Just lots of round and round the ring. This cone had P6 marked on the outer diameter! What are the chances?

Now all bearings were off.

As per cba's suggestion, I put the spindle in the lathe with copper protection under the jaws, the live centre in the other end, and polished up the upper bearing locating surface with emery paper and.......... a parallel:roll:. A little bit at a time. I was finally satisfied with one of those not really wanting to go on, but then a slow slide and click experiences. Perfect. I also polished the other bearing locating surface as well because it looked a bit rough. It had lines running axially from bearing contact/pulling off. Only a short polish had it looking very clean tho. Maybe a result of heat?

The quill has had a very good wire brushing and clean inside on the cast surface and both new outer cones have been put in. Both of them actually tapped in most of the way with my small soft face hammer and gentle taps around the ring. I pressed in the last bit just to be sure.
I was very careful to use the new ones, and put them in the right way round!:D

I am now ready to reassemble the rest.

A couple of queries tho.

There are 2 holes drilled on an angle to exit internally just above the bottom bearing, entering from the external surface of the quill, just above the depth rod mount. These would appear to be oil holes. They are about 4mm diameter. Any comments about this? Oil or grease? This is the first time I have seen them. They are hidden under the rubber bump ring which protects the bottom of the quill if you let go and it flies up.

On a similar note, the spindle end cap which I have mentioned before (plastic and cross threaded) has about 7mm clearance between its centre diameter and the spindle end diameter. This appears somewhat pointless to me. I was wondering whether I could mount a metal end cap and proper seal here. Would it be worth it?

Dean

[BaronJ]

Hi Dean,

Is the conclusion that the lower bearing damage was the culprit for the spindle tightening up ? Or haven't we got there yet...

[Oldneweng]

Hi Dean,

Is the conclusion that the lower bearing damage was the culprit for the spindle tightening up ? Or haven't we got there yet...

I don't recall the spindle ever being very easy to turn although I did not try turning it in a neutral gear position specifically to see, that I recall. I have turned it in a neutral gear position for other reasons.

My best guess based on the force required to release the bearing locking nut is that over tightening of this nut caused the problem. A bit(?) of extra pressure to line up the next locking tab?:no:

The damage to the lower bearing appears to be heat related. I cannot feel any variation in the surfaces. I would have thought that in order for this bearing damage to tighten the spindle to that degree, there would be other visible changes to the bearing. Other than the surface discolouration it looked and ran fairly normally in the hand.

The spindle has always run pretty hot as well. Guess I should have investigated this sooner.:doh: I have never owned a mill before. If I had realised how easy it was to remove the quill I may have been tempted.

Dean.

[Oldneweng]

My mill is fully back together and working just great. It is a bit quieter now. I made a few minor improvements. I only backed off the bearing adjustment nut slightly from contact. There is limited options with the locking tabs. The next tab was too far away for my liking. I will pull the quill out and recheck the adjustment after I have used the mill for a while.

It took about an hour to set up to press the bottom bearing onto the spindle and about 9 seconds to actually do it.

I lost one of the roll pins that holds the gear levers on. I had it partly in the lever and knocked it out so I could set alignment with the holes and haven't seen it since! Luckily I had already decided to use grub screws to secure them anyway. The holes for the pins were terrible. One shaft had 2 holes in it and the hole actually used was at a ridiculous angle. The levers were already drilled and tapped M6 with a steel central ring for strength. All I had to do was pop in a couple of grub screws. This meant I could adjust the lever with 3 gear ratios to align with the numbers better. Later I will file a bit of a flat at the contact point.

Dean

[cba_melbourne]

....... I only backed off the bearing adjustment nut slightly from contact. There is limited options with the locking tabs. The next tab was too far away for my liking.........

Machine tool spindles need a very firm preload. If you adjust preload like a car wheel (slightly from contact as you say) you will get chatter and poor surface finish, and you will find it hard or near impossible to hold close tolerances.

Also, tabs are bad news to adjust preload. I assume you are talking a tab washer locking onto a hex nut? That would only let you fix the adjuster nut every 60 degrees? That is unacceptable, the difference between a too loose setting and a too tight setting is more like 20 degrees - sure it depends how fine the thread is, but they usually use a fine pitch like 1mm or 1.25mm or 1.5mm for the preload adjuster nut. It is usually a castellated nut (a nut that is tightened wit a hook-spanner). And it is common practice to have a grub screw radially threaded into this castellated nut to lock the nut at any random position, with a brass or copper plug between grub screw and spindle to protect the spindle thread from being dented. A bit less common is to use two nuts tightened against each other to lock.

Some machine makers give a torque figure in the maintenance manual for how much to tighten the lubricated preload adjuster nut. But this is not common with smaller machine tools and certainly not with hobby lathes or mills. Adjustment at the factories is more an empiric instruction like tighten to contact, then add 1/8 of a turn. Or on a lathe with standard chuck installed "spin as fast as possible by hand, and the chuck should spin for between 3/4 and 1-1/4 revolution". The latter method depends a lot on the grease used, and requires the spindle to be first run-in for a few minutes to distribute the grease first.

There is a more accurate method to adjust the preload. You observe how the spindle warms up. In the case of a mill with taper roller bearings and grease lubrication, the quill should become warm to tough after about 10-15 minutes running at maximum rpm. But themperature should not rise any further, regardless if running at max rpm for several hours. If it does not get about 40-50 degrees after 15 minutes, the preload is insufficient. But if it ever gets hot to touch, preload is excessive. You will find out that after about one or two hours running, you can slightly increase preload. That is because a bearing is invariably overfilled with grease - even if you think you only filled it to 40% as specified. It is in the nature of most people to always err on the generous side with grease. The excess grease causes excessive heating by grease churning. After about an hour running most excess grease is pushed up the quill and/or through the bottom seal.

Is it worth the time and trouble to adjust the preload by temperature rise? It is up to you and how you plan to use your new mill. I think yes it is worth it, even if it is not expensive precision bearings. Others will say I am overthinking it again, and will be working "good enough" if treated like a trailer wheel bearing.

[Oldneweng]

Also, tabs are bad news to adjust preload. I assume you are talking a tab washer locking onto a hex nut? That would only let you fix the adjuster nut every 60 degrees? That is unacceptable, the difference between a too loose setting and a too tight setting is more like 20 degrees

The nut is a hook spanner adjusted nut. Every 60 deg? Maybe if you are lucky. One of the tabs is bent around in the plane of the washer. Looks like manufacturing defect.


It is usually a castellated nut (a nut that is tightened wit a hook-spanner).

No it is not a castellated nut. It is a bearing adjusting nut. A castellated nut has the slots going right thru and is secured with a pin of some type. The "castellated" section is usually of a reduced diameter. The reason I know this is that one of the web pages I was reading, to work out how to fix the mill originally had the same admonition when someone used the term "castellated nut".:D

I had to put that in.:rolleyes: I don't care what its called. I know what you mean.


And it is common practice to have a grub screw radially threaded into this castellated nut to lock the nut at any random position, with a brass or copper plug between grub screw and spindle to protect the spindle thread from being dented.

Funny you should mention this. It was my intention to investigate this avenue.

Regarding the preload, the only mention I have seen up to now regarding adjustment of the bearings came from one of those web pages. This method was tighten to contact and then back off 1/8 of a turn. :o I realised this was wrong. Maybe they meant tighten 1/8 of a turn?

I will play around with preload later on, but I am a bit nervous at over tightening for obvious reasons.

Thanks for your assistance

Dean

[Michael G]

... it is common practice to have a grub screw radially threaded into this castellated nut to lock the nut at any random position, with a brass or copper plug between grub screw and spindle to protect the spindle thread from being dented.

Never seen that one. This is what I commonly see for locking up preload on bearings -
328886
You have 17x4 locking opportunities, so a little over 5 degree increments.

Michael

[BaronJ]

Hi Dean,
Without a torque wrench setting preloads is very much subjective. Does the bearing manufacturer have any notes in this regard ? Run the machine for a while and try to get a feel for how the spindle behaves. You can always adjust for more if you get any chatter. The spindle on my machine runs slightly warm and since replacing the plastic gears is much easier to turn and the motor gets nowhere near as hot as it used to. The surface finish is much better as well.

[cba_melbourne]

Never seen that one. This is what I commonly see for locking up preload on bearings -
328886
You have 17x4 locking opportunities, so a little over 5 degree increments.

Michael

Hi Michael. I have never seen one of those washers used on any hobby machine. Probably because it requires a slot in the threaded portion of the spindle, which would add to manufacturing cost. Hobbymachines need to be low cost, or nobody can afford to buy. The whole 300kg mill in question here, costs less than the naked spindle bearings of a Bridgeport or about $1700.

Edit: on hobby lathe spindles you do not see this type of washer, because the threaded part has the thinnest wall thickness anywhere along the spindle. An axial slot here would seriously weaken the spindle. Whilst for commercial reasons, every manufacturer seeks to maximize the through-spindle bore diameter. Buyers often base their machine choice on this diameter.

[cba_melbourne]

Hi Dean,
Without a torque wrench setting preloads is very much subjective. Does the bearing manufacturer have any notes in this regard ? Run the machine for a while and try to get a feel for how the spindle behaves. You can always adjust for more if you get any chatter. The spindle on my machine runs slightly warm and since replacing the plastic gears is much easier to turn and the motor gets nowhere near as hot as it used to. The surface finish is much better as well.

I am not aware of any hobby machine, lathe or mill, costing below $10k, that would use a torque wrench for preload setting (I have not seen them all though). I can see two main reasons for this:
- to use a torque wrench, the bearing journal on the spindle would have to be very finely ground to the same finish and the same tolerance band as the bearing cone itself is made to. This means just a few microns diameter tolerance for a tight sliding fit to the cone. To manufacture such an accurate spindle would alone add some $500 to the cost of a machine and price it out of the market. If you look at these Chinese hobbylathe/mills, the journals are often not ground at all, just turned. And if you see them ground, its a very very coarse finish. They make the journals on purpose oversize, because they can not hold the tight tolerance that a sliding fit would need. But without a sliding fit, any torque wrench would simply max out to get the cone moving on the spindle in jerks. No precise torqe adjustment is feasible.
- the same is true for the thread on both the spindle and the adjuster nut, these would have to be of tight tolerance and good finish, otherwise the uncontrollable friction would render any torque specification inaccurate. If you look at these on a Chinese hobbymachine spindle, you understand instantly what I mean.

There must be more reasons why even more upmarket hobbymachines (Emco maier, waabeco, myford...) do not use torque wrench specifications to adjust preload. There are probably just too many variables with such small machines.

[Oldneweng]

Michael's picture is almost right. The lock washer only has 6 tabs on the outside. 3 on each side, one of which is the bent one mentioned. The central tab locates in one of the spline slots so no extra machining is involved except one of these slots is slightly longer, presumably to fit the tab. I found the washer fitted better facing the other way anyway which meant it could fit in any slot. The tab is bent at 90 degrees so it sits along the bottom surface of the slot.

328903

This one only allows for quite large increments.

This mill appears to be different in some regards to the run of the mill (:D) mill. It weighs in the vicinity of 380 kg and the bearing journals seemed to be a ground finish. Not only that, the spindle shaft between bearing journals was ground.

328905Sorry about the low res. This picture came from the net, but it almost shows the finish.

The bottom section of the spindle was hardened where the slots are to grip the spindle. I did not investigate how far up this hardening went. The reason I know it was hardened is that the bottom face of the spindle was very very rough and not level. I cleaned it up in the lathe to allow it to sit upright to press the bearing on.

Dean

[Pete F]

Hi Dean,
Without a torque wrench setting preloads is very much subjective. Does the bearing manufacturer have any notes in this regard ? Run the machine for a while and try to get a feel for how the spindle behaves. You can always adjust for more if you get any chatter. The spindle on my machine runs slightly warm and since replacing the plastic gears is much easier to turn and the motor gets nowhere near as hot as it used to. The surface finish is much better as well.

I can't say I've ever seen torque of the pre-load nut quoted, either by an equipment manufacturer or bearing manufacturer. What they will sometimes quote is the torque to begin to move the spindle from rest. An easy way to set up to do this is to wind some string with a weight on it around a pulley etc on the spindle and hang a weight on it. Nice theory at least :roll: Never done it that way and never will. Oh, and obviously the spindle needs to be horizontal unless you use a spring scale. All in all, rather impractical, although it is indeed the "correct" ie most accurate, way to set spindle pre-load.

In practice what I do is adjust the pre-load so I can feel a little "stiction" when I try to turn the spindle by hand, but once rotating there isn't any undue resistance. It's one of those things that is hard to describe, but when you feel it you'll know. It's very subtle and the differences between properly adjusted spindle bearings and ones improperly adjusted is only a few degrees on the adjustment nut. I'm surprised some of these Chinese manufacturers are using such agricultural settings for pre-load, the likelihood of falling on a point where the tab was just right to lock it would be about the same as winning a chook lotto at the local RSL (ie it happens but don't count on it!). By default, you'd pretty much guaranteed to have to run the spindle at lower than ideal pre-load. If it were my machine I'd ditch the lock washer and cross drill the locking nut for a grub screw and brass plug.

[Michael G]

Michael's picture is almost right.

I prefer to think that your machine maker almost has it right :U

Michael

[Oldneweng]

I prefer to think that your machine maker almost has it right :U

Michael

I will pay that one Michael. It is more accurate?:roll:

Dean