Tool Post Grinding

[Anorak Bob]

Anyone out there conversant with tool post grinders and how to achieve an acceptable finish with one?

I have a little Dumore 44 grinder and yesteday I was trying to grind a piece of 4140 bar. Close inspection of the ground finish revealed chatter in the form of closely spaced parallel axial lines, about .020" apart. It is hard to see in the attached photo.

The 2 1/2" wheel is a Dumore item, 60 grit aluminium oxide that I dressed insitu. The grinder spindle speed was 6600 rpm. The work piece was turning at 75 rpm. Axial feed was slow and I let the wheel spark out.

The lathe has a plain bearing head stock.

I will keep experimenting but any advice would be greatly appreciated.

Bob.

[Stustoys]

Hi Bob
Haven't used a tool post grinder but have used surface and cylindrical grinders.
Did you lock your gibs?
Did you make sure the wheel is tight?(Yes I know "they cant come undone", but they can, even on a Jones and Shipman)
After that I'm pretty much out of ideas sort of the bearings being shot.

Stuart

[Metmachmad]

Ensure that everthing is tight and that the centre of the grinding wheel is no higher than the centre of the work-piece, best to be a little lower rather than higher.

Also how did you dress the wheel?

[Anorak Bob]

Thanks very much for the replies, Stuart and Metmachmad.

I had not tightened either the cross or compound slide so that's the first thing I will do tomorrow when I have another go.

The spindle bearings were trashed when I bought the grinder. I replaced them with Barden angular contact bearings which have a speed limit in oil of twice the grinder's maximum of 38,500 rpm. Setting the bearing preload was guess work, so if I have that wrong there could be another source of chatter.

I dressed the wheel with a diamond tool in a less than perfect Dumore holder.
I will redress to wheel tomorrow in a far more rigid tailstock mounted holder.

I had the grinder spindle set on the lathe centreline.

I will report the outcome of my attempt tomorrow.

Regards Bob.

[Stustoys]

How much did the bearings cost?
Did you feel the bearing after your test? If they arent warm you should be able to tighten them up. Bearing life goes down pretty fast as preload goes past a certain point, but the bearings will warn you by getting hot. Also if the bearings are cheap enough even with alot of preload they will likely last more hours than you'll put on them as a tool post grinder(unless of course you plan on using it alot).
Good luck tomorrow
Stuart

[Anorak Bob]

Two hundred bucks cash for the pair.

They don't get hot. The rear bearing gets warmer than the front bearing because of the belt tension. I replaced the oiling wicks and felts within the spindle housing when I replaced the bearings.

The preload was based on maintaining the position of preloading device as installed against the original New Departure bearing.

Regards
Bob.

[Greg Q]

Bob, where'd you get the Bardens? Abec 7 or 9?

Greg

[Stustoys]

Two hundred bucks cash for the pair.

Ok so we go a little easy on the preload then :rolleyes:


Stuart

[Anorak Bob]

Greg,

The bearings were ordered in for me by Statewide Bearings in Perth.
They are FAG / Barden Aerospace 200HC bearings.

In their catalogue, they state that they manufacture spindle and turbine bearings to class ABEC 9 and instrument bearings to class ABEC 7. The box the bearing came in is marked B7200C.T.P4S.UL. The P4S refers to tolerances as per DIN 628-6. I haven't bothered to go there.

Given the cost, you'd think they would do the job.

Bob.

[Greg Q]

Bob...I did some comparative research awhile ago but it looks like I'll need to review.

A friend in the industry told me that they suspect that any bearings are only of stated quality in the factory until they go to shipping, then every step removes some of the fanciness from them. Barden is the only manufacturer that I saw listing the elusive Abec 9 bearings, (ultra precision in the 60's lexicon).

I need to get a pair of AC bearings for my lathe soon, hence the question.

I have the New Departure bearing handbook (50's?) that shows the relationship between life, accuracy and preload. The famous Moore Jig Bore machines of the day used ABEC 9 spindle bearings cranked down so tight they were in the annual replacement range.

Greg

Barden supplies what is supposed to be a pretty good spindle rebuilding video but I've had no luck getting a copy here.

[Anorak Bob]

Maybe I have a problem with the preloading.

I placed a tenth indicator on the spindle with the magnetic base affixed to the spindle housing. There is about .0001" TIR runout which could simply be wear on the shaft BUT with pressure exerted with thumb and forefinger, I can move the spindle radially, about .001". This is with the spindle cold.

Do I crank up the preload adjuster?

Bob.

[Dave J]

I would tighten it a little and then run it keeping an eye on the bearing temperatures. I had to do this with my mill recently and it's the only way to do it.
It should be warm to touch after around half hour, but not that hot you cant hold your hand on it.

Dave

[Stustoys]

Not that I disagree with Dave, but I came across this on the SKF site when looking for some info on preload "SKF angular contact ball bearings undergo a special heat treatment. When fitted with a steel, brass or PEEK cage, they can operate at temperatures of up to +150 °C. ".

Didnt come up with much about preload though :( some unlabeled graph I dont understand.

[Dave J]

Mine are different being taper bearings, but only getting them hot enough to touch by hand will be insurance that you don't cook them or do any damage as they are expensive.
I know the SKF site say so, but I personally I wouldn't run them up around 150 °C.

Dave

[Greg Q]

The topic of preload and how to measure it occupied me for quite some time a coupe of years back, and my figurative ears would perk up whenever the topic was mentioned. Absent any kind of torque setting (or a torque wrench adapter for that matter) I guess for us it boils down to temperature rise.

I thought had read about 65º for a target somewhere, but from what Dave posted I guess the temp maybe is limited more by the spindle application* than bearing life. (and lube too...mine are greased with Kluber Isoflex 15 which has a 130º max temp.)

* I wouldn't want my lathe spindle to grow that much in a facing operation for example. 150º means a lot of movement.

Greg

[Stustoys]

Aren't your greased Dave?
I didnt mean to imply that I would run them at 150 either. Just that if they get a little hot while adjusting them it shouldnt matter to much. SKF arent paying for the bearings after all . Besides what would be happening to preload as things heated up to 150C?

[Stustoys]

A thought that just crossed my mind.
SKF said "Its ok to run our bearings at 150C" not "preload our bearing until you get to 150C" that's two very different things

I guess there would be a big difference in bearing life between a bearing that was running with little preload in an environment heated to 150C from some other source and bearing that has enough preload on it to heat it to 150C. If the casting was big enough it might never get that hot.

I guess it comes back to nipping it up a little at a time until either you don't see an improvement in surface finish or the bearings start getting to hot for your liking.

[Garry Edwards]

There is a group on yahoo that is dedicated to Dumore Toll Post Grinders, they may be able to help as I am sure someone has struck the same situation,

Regards

Garry

[Garry Edwards]

There is a Dumore 44 manual on ebay, do a serch for tool post grinder and you will see it there.

Regards

Garry

[Anorak Bob]

All the Best for the New Year, Lads.

Thank you for your comments.

In my copy of the Dumore publication "Care and Operation of Portable Precision Lathe Grinders" under the heading "the features of Dumore quills" is this -

"Quills at times, have a tendency to run hot at the bearing ends. this is not harmful - it is merely heat being dissipated from the bearings and should cause no alarm. Heat may rise to 55 degrees Centigrade over room temperature. This is allowable because provisions have been made to take care of the expansion from heat.....

If a new quill is turned with the fingers it may seem to be stiff or in other words, it does not turn free. This is due to the quill being cold and a pre-determined amount of preload has been put on the bearings. After the quill is put in operation, heat causes expansion and the automatic preloading arrangement allows the quill to run perfectly free."

There is no mention of determining the amount of bearing preload, but it is obviously more than I have.

The Series 44 Parts List and Operating Instructions that I downloaded a couple of years ago from Dumore's website offers no more advice on the matter of preloading.

I searched the Yahoo User Group site and came up empty handed in regards to the 44.

Barden's catalogue discusses preload but not how much.

I'll slip up to the shed later on and start fiddling.

Regards
Bob.

[Anorak Bob]

OK. I tampered with the preloader to the point where there was a discernable drag on the bearings. Ran the grinder for a bit and the bearings warmed up. Attached the indicator back on the spindle and still had some radial movement. As before, about .001". That got me thinking that maybe the spindle was bending.

I clamped a short length of 9.5mm stainless rod in my vise and set up an indicator to measure any deflection. With a 40mm protruding past the jaws ( matching the Dumore spindle diameter and projection outboard of the bearing ), I was able to deflect the rod about .003" with my fingers. Maybe preload is not the problem.

The Dumore operating instructions emphasize the importance of using balanced wheels. The three grinding wheels I have used so far have all had a noticable axial wobble.On the largest wheel I used (3") there would have been about 1 mm total wobble. I guess that would contribute to vibration, causing chatter.

Wheels for the grinder, 3" OD (max.) x 3/8" ID x 1/2" thick are few and far between on Ebay. Local suppliers don't carry that size or much of anything else with a 3/8" bore.
Maybe I will have to buy some Dumore wheels.

The last couple of snap shots are of the latest attempt. I used a different wheel, dark brown in colour, that was harder and had a finer grit the the white aluminium oxide, 60 grit Norton wheels of the previous attempts.

The chatter is still there, only finer.

Am I hoping for too much?

BT

[Greg Q]

Just out of idle curiosity Bob, is your lathe 3 phase powered? How about the grinder? Not that I'd expect motor torsional vibration to be the culprit; I have heard that single phase motors can telegraph a pattern in turning operations, was wondering about grinding.

Your wheel runout figures are dismaying. Good luck finding some good ones.

Greg

[Bryan]

Bob I was wondering how your lathe spindle bearings are? Probably impeccable. But I guess this is the process that will show up any imperfections. Maybe one slightly flattened roller could do that, I don't know.

[Stustoys]

To add to Bryans idea. Do you know someone with a lathe nearby that you could try it on? Is it the lathe? is it the grinder?

Have you tired changing the the spindle speed?
Does your lathe have back gears?

Stuart

[Anorak Bob]

Hello Greg,

Both motors are single phase. The grinder motor does vibrate. It's 110 V running through a transformer.

I did mount the grinder on my other 9" Hercus, again single phase, but thought that the spindle roller bearings may have contributed to the poor finish I obtained in my earlier grinding attempts. In reality, they most probably would make no difference.

I wasn't too eager to continue grinding on that lathe given the lathe shows minimal evidence of wear, something I am keen to prolong.

Genuine Dumore balanced wheels aren't too expensive. The trick is knowing what one to get.

BT

I

[Anorak Bob]

Sorry Boys,

I was laboriously typing a response to Gregory's post when you asked your questions.

The latest experiments were done using my plain bearing 9" for reasons outlined in my response to Greg. Backgear was engaged to acheive a spindle speed of about 60 rpm. I ran the spindle at the next higher speed of 81 rpm but there was no discernable difference.

I might try installing a piece of rubber sheet between the grinder motor and it's mount to isolate the motor vibration.

The answer might be in the wheels.

Grist goes everywhere with one of these things, hence the drop sheet shroud.

I can't see too many invites coming my way for a trial on another machine.

BT.

[Greg Q]

Bob, I am wondering if there's something in the lathe's leadscrew which is giving you a periodic error. If the defects aren't exactly spaced, then forget that idea.

Next, how about the grinder's drive belt? Maybe it has a hard spot causing a thump in the wheel?

The motor vibration doesn't sound good either. I would have thought that a grinder would have to be as close to perfect as you could get it to get a good finish. It is my understanding that visible flaws are often in the 0.0001" range.

(sorry for the imperial measure)

Greg

[Greg Q]

Bob...I was just reading some hits from a google search on this problem. PM and other forums have had discussions way back on these grinders.

One tidbit that I just read was running the same size pulleys on the motor and shaft causes chatter problems. There are others but its bedtime for me...

Greg

[Pete F]

Wheels for the grinder, 3" OD (max.) x 3/8" ID x 1/2" thick are few and far between on Ebay. Local suppliers don't carry that size or much of anything else with a 3/8" bore.
Maybe I will have to buy some Dumore wheels.

BT

Bob, sorry I can't help at all with the finish issue you're experiencing, however if you're after wheels maybe try Enco. I've found their service excellent and the freight to Australia very affordable. Unfortunately I think many US retailers feel selling internationally is all too hard and insist on very expensive couriers (I just got a quote for some lousy side-winding trailer jockey wheels from Harbor Fright for example; almost $400 for 4 jockey wheels!! :oo: ). In contrast Enco seem to want to help in that regard.
Enco - Guaranteed Lowest Prices on Machinery, Measuring Tools, Cutting Tools and Shop Supplies (http://www.use-enco.com/CGI/INPDFF?PMPAGE=514&PARTPG=INLMK3&PMITEM=893-1539)

[Anorak Bob]

Thank you Pete. I will check out Enco. Some of the large distributors in the states carry Dumore products, they may be one of them.

I do have another option. My little brother has lived in New Jersey for 22 years. Now and again I will have stuff posted to him and then he sends it on to me. After his comment a few months back that his home was becoming a "warehouse", I've become hesitant to ask for more favours.

Regards Bob.

[Anorak Bob]

Greg's comment about the motor vibration got me thinking.
Dumore state " they produce a grinder motor that is practically free of vibration and gives the smooth performance necessary for precision grinding". Definitely not the case with mine.

A few years back I bought a second, older No.44 grinder from the States. The seller, as is the nature of most sellers, described it as being in good condition. I bought it because with it came the pulleys, wheel guard and wheel dressing attachment missing from mine. It also came with a copious amount of rust as I later found out.

Dumore's list price for the largest and second largest pulley is a total of $202 US. The wheel guard, another $109. Quickly adds up.

Anyway, back to the motor. I knew the fan blades were distorted and I thought that there may be a chance that the fan from the older motor might be interchangable.

With both motors apart I noticed that some of the balancing inserts were missing from the newer armature. It turns out that I was able to install the old armature in the newer motor housing after swapping over one bearing. I will replace both motor bearings.

Turned it on and there was virtually no vibration. With new motor bearings and balanced wheels I might end up with the result I was hoping for.

Greg. My grinding was done without power feed. I have three belts. Two are Dumore, the other made locally. The original belts are old and jointless. The local belt has a join. I need to buy a fresh Dumore belt along with the wheels. What a great hobby!

BT

First photo shows the bent fan. The other shows the where the balancing inserts are missing.

[Pete F]

Bob I'm not sure if Enco sells the "real deal" but when you mentioned that size was difficult to obtain out here I thought I recalled Enco having them, and indeed they're listed at the bottom of the page I linked to. Almost certainly they're out of Asia, however they may give you a few more options regarding grit etc. At 10 bucks a go they're not that expensive and the good thing about wheels this size is they're not super heavy, so freight doesn't so readily become a deal breaker.

Good luck with it, for what it's worth the finish looks superb in the photos!

Pete

[Anorak Bob]

Hello Pete,

Enco's website is down at the moment, preventing a search for bargains.

The photos lie.

To the naked eye, the finish looks good. Seen through a 2 1/2X jeweller's loupe. the finish is lousy. A lot of irregular depth and spaced grinding marks.

As an unfair comparison, viewing a ground surface on my Schaublin dividing head with the same loupe, reveals perfection. Not that I would ever expect the liitle grinder to acheive similar results becase it just couldn't but with some more fiddling I should be able to improve on what I have done so far. Fingers crossed.

Had it not been for the observations and comments of interested forum members, I would have placed the thing back in it's box, having abandoned, yet again, the idea of being able to use the thing properly.

Bob.

[neksmerj]

Came across this article you might find interesting, if you have to replace the power cord.

Projects In Metal » Blog Archive » Rewiring (Replacing the Power Cord) on a Dumore Tool Post Grinder for the Lathe. (http://www.projectsinmetal.com/rewiring-replacing-the-power-cord-on-a-dumore-tool-post-grinder-for-the-lathe/)

Ken

[Pete F]

Bob, I am wondering if there's something in the lathe's leadscrew which is giving you a periodic error. If the defects aren't exactly spaced, then forget that idea.

Further to Greg's suggestion, I'd suggest it doesn't need to be in the leadscrew either, if there is ANY damage to either the gear on the back of the spindle or the tumbler gears on a Hercus, that will be transmitted through to the finish by moving the spindle slightly at regular intervals. When I first got mine it would actually turn considerably out of round for this reason when power feeding due to some damaged tooth profiles. I understood you used two separate lathes on your tests, which would imply that's not the problem, but if using the leadscrew maybe try feeding manually and see if the pattern is identical.

Pete

[C-47]

Bob, have you tried Siegling belting in Weshpool. I had some belts made there for a Waldown TP grinder, just ask them to scarf join the belt, seems better than the usual lap joint. Alan.

[Anorak Bob]

Hello Ken,

Thanks for that. I did have to replace the cable on the grinder. I did not remove the stator. The machine had no switch when I purchased it on Ebay from Dave "Tissuescars" about four years ago.

If I recall correctly, the machine came from BHP Engineering in Sydney and it had been modified for a particular job. Dave had two No.44 grinders up for auction at the time. He correctly stated that this one was in need of repair.

I installed a cheap toggle switch bought from Jaycar. The conical shroud was formerly a cast aluminium pulley. The original Dumore switch and shroud were cheap enough, less than twenty bucks, but getting hold of them was another issue.

I connected to the internal wiring by soldering and covering the joints with three layers of heat shrink tubing. It all works well.

Bob.

[Anorak Bob]

Hello Pete,

I should say that any attempts at grinding on the ARL were half hearted. I had not adopted the use of the plastic dropsheet to cover the entire lathe. I was using sheets of newspaper and old rags. The dust gets everywhere.

The results I achieved were poor enough to quickly abandon the thought of continued trials on my prize lathe. I thought, probably erroneously, that the roller bearings may have contributed to that finish.

The older plain bearing A runs very smoothly, with no discernable vibration. The cast iron legs appear to provide more rigidity than the sheet metal pedestals of ARL.

I will continue my experiments after replacing the motor bearings. I have a crank handle that I fit into the rear of the spindle for hand threading. Using it to rotate the spindle at Dumore's recommended 50 rpm might reveal whether the back gear train is influencing the finish.

Bob.

[Anorak Bob]

Hello Alan,

I had a belt made by Habasit in Malaga. You can feel a slight increase in thickness at the joint as you can on the two Dumore belts. I'm sure that the belts cause some vibration but the greatest reduction in vibration has come as a result of swapping the armature.

Tell all of us more about your Waldown TPG.

Bob.

[Dave J]

I would like to see it as well if you have time.
I am watching with interest as I want to make one myself because they are to expensive to buy.Their are lots of guys that have made their own and are getting good results with them.
I did use a dremal to true up a coaxial indicator shaft as it was all I had and it turned out ok, but a proper tool post grinder would be superior.

When I was down at H&F's before christmas they had 2 tool post grinders on the damaged/shop soiled section at $500 each instead of the $1200 odd they are new. They where a bit to big for my lathe but I notice they don't have them on their website anymore so maybe their where problems with them.

Dave

[C-47]

OK, attached I hope are some staged photos of the Waldown - 0 on a Colchester lathe. Don't use it much now due to having a cylindrical grinder, however when I did use it surface finish was never the best, I'm sure due to rigidity of the entire setup and also not using coolant. OK for the odd touch up job a the time though. The motor at 12,000 rpm sure makes a noise. Also the internal spindle in 1 of the photos, never got to use it though. Bob I'm sure the scarf joint belt would help a bit as this is what I had to do on a surface grinder as the join was pantographing through to the surface. Alan.

http://i87.photobucket.com/albums/k139/Alan_045/TP%20Grinder/TPgrinder1.jpg

http://i87.photobucket.com/albums/k139/Alan_045/TP%20Grinder/TPgrinder2.jpg

http://i87.photobucket.com/albums/k139/Alan_045/TP%20Grinder/TPgrinder3.jpg

[Anorak Bob]

Alan,

There is no snap shot.

Bob.

[C-47]

Bob, pm sent. Alan. OK they have now shown up, a bit big but better than nothing I suppose. Ah! DJ I now see it, thanks for doing whatever magic was required. Alan.

[Anorak Bob]

Alan,

Great photos. I was told by one of the blokes at Hughans Saw Service in Osborne Park that Brobo Waldown had ceased the manufacture of their TPG's a few years back. It's a shame because they appear to be a nicely designed and made tool. In reality, I guess TPGs fit into the Jack of All Trades, Master of None category.

Whilst we see few Waldown TPGs for sale here, there is always an abundance of Dumores on offer on US Ebay.

I'd love to get hold of a small tool and cutter grinder ( along with everyone else! ) But how often do they surface!

Bob.

[Anorak Bob]

Pete F asked whether I had resolved my problem with surface finish using the Dumore. To eliminate the motor as being a possible cause of chatter, I swapped the rotor. I removed the bearings this afternoon. The drive end bearing is a Fafnir 202 KDD, a standard size, single row radial ball bearing 15 id x 35 od x 11 thick but with C4 clearance. Things do get hot as a result of belt friction but I am not sure it would require a special bearing.

The other bearing is a Nachi WBC 202 W1WZNSL. Again 15 x 35 but 12.7 thick.

The Fafnir is knackered. The Nachi, not perfect. I will try to buy new bearings tomorrow.

If there is a problem with the availability of the Nachi, what are my chances of removing the synthetic rubber seal, flushing, regreasing and refitting the seal?

BT

[Greg Q]

I guess that depends on how much of the roughness is dried grease. I've done it before, but I think its a crap-shoot. Anyway, what's the downside except time? If you have an ultrasonic cleaner that's any good you might want to give it a half hour in a container of solvent suspended in the water, then another solvent rinse.

Let me know if you can't find one- I have a fweind in wome.:cool:

[ecobbman]

I've solved this issue in the past with my Dumore grinder by shimming the hole in the grinding wheel with 1 mil thick copper film. The very small amount of clearance in the hole was allowing movement of the wheel around the shaft, even when the wheel was well tightened on the shaft. It doesn't take much movement to make these chatter marks. Obviously you need to true the wheel after shimming and mounting.

[rusty steel]

I remember a few years ago I was using a Waldown TPG and I was getting a poor finish. I slowed the speed down by using a variac and I achieved a much better finish. Perhaps it is worth a try.
Russell

[Anorak Bob]

I do need to reassemble the 44. I obtained a new set of motor bearings but to install one of them requires the machining of a simple spacer. The original 1/2" thick bearing was not readily available, so I purchased a pair of 11mm thick bearings. They have been sitting in the swarf tray for the past 5 weeks. One excuse for the inactivity is that I've sidetracked myself milling cast iron.

Another is the fear that even after reassembly and the incorporation of the last two helpful suggestions, the finish will not be markedly improved.

I have a question for those who have used these machines. What quality of finish can you expect from a tool post grinder? It's a lightweight grinder on a lightweight lathe.

BT

[Stustoys]

BT,
What direction are you running the spindle in?

*edit* the lathe spindle that is, I assume you have the grinder spindle running so the sparks go down.
Stuart

[Anorak Bob]

Forward, anti clockwise.

[Stustoys]

That could be your problem.
Can't say any more than that as I've never run a grinder in the same direction as the work.
Certainly worth a try. Granted it would have been more help 6 months ago :(

A quick google gives me wiki "This effectively means the two surfaces will be moving opposite directions when contact is made which allows for a smoother operation and less chance of a jam up."
Cylindrical grinder - Wikipedia, the free encyclopedia (http://en.wikipedia.org/wiki/Cylindrical_grinder)

Stuart

p.s. Its that assumption woman again ;)

[Dave J]

I have seen this discussed on a few forums and it seems most people run with the work and some run against.

Dave

[Stustoys]

Got some links Dave? If they are handy, could be an interesting read.
Centerless grinding the work and wheels turn the same way so I guess its not a huge issue. Maybe you can use the lathe rotation to adjust surface speed?(as long as you dont spin it fast enough to get a surface speed of 0 ):)

BT what rpms were you using?

Stuart

[Dave J]

Sorry Stuart no links as it was just something I read last year. I think it was either PM or HMEM. It was an interesting read and I will have a look latter to see if I can find it for you.

Dave
PS
I think you gave me your flu though one of your PM's, LOL

[Stustoys]

I think you gave me your flu though one of your PM's, LOL
Can't have been me...... I still have it lol

Stuart

[Dave J]

Can't have been me...... I still have it lol

Stuart

Serves me right for not having anti virus on the computer, lol

Dave