BaronJ 1st April 2014, 06:08 AM Hi Guys,
Some of you will know that I've had various problems with my Chinese mill. Well I would like to solicit comments about this plastic gear from my mill. The gear in question is the duplex speed change gear that lives inside the mill head. From new, the mill has always made a slight ticking sound that varied as the spindle speed changed. Well the other day I was slitting some alloy bar with a 1 mm thick saw and the blade grabbed and the top plastic gear lost a tooth and ground it into the other teeth. I'm not overly happy about it but not too concerned either. Since replacing it is a 20 minute job. I'm more concerned about the other one. After removing the smashed gear I tried rotating the spindle by hand and found that it had a spot where it was hard to turn. Getting to this gear is a major job to remove and inspect. The pictures show what I found. So my request for comments.
The first three pictures are of the duplex gear. The damaged area is inside the red box. The other picture is the top driving gear. This one is directly driven by the motor. You can see where the initial grab took place and the place where the teeth were stripped off.
Thanks all.
Michael G 1st April 2014, 06:54 AM It looks like it will mesh but will be noisy, may jam in the future and will probably affect your surface finish. If it were me I'd be replacing it either with a maker's spare part or preferably with something made from a decent material (we used Nylatron for Simon's worm gear and that seems to be going really well)
Michael
nearnexus 1st April 2014, 02:08 PM Replace both gears.
The teeth are already weakened and will let go at some later stage - plus as stated it will be noisy and irregular.
I would ditch all those poly gears and use alloy instead. There's almost certainly a metal gear or belt kit available, given this is an obvious weak point.
Rob
BaronJ 2nd April 2014, 03:49 AM Hi Guys,
Thanks for the comments. I'm having difficulty getting the supplier to talk to me about supplying replacement gears. You know the old not here, send Email describing problem, run around.
Anyway that aside I do have access to a firm that makes gears ! and they have suitable replacements, in steel and bronze, in stock. OK I'm going to have to do a little massaging because the bores are unfinished but subject to their checking my measurements I'll have replacements tomorrow. Not expensive either so I'll know more later.
I'm still interested in any and all comments about my initial post.
Thanks Guys:
Toggy 2nd April 2014, 07:56 AM John
If those gears are a pair (meshing together) I would suggest one in steel and one in bronze unless the steel is hardened, to ease wear. I believe that dissimiliar metals cause less wear.
Ken
BaronJ 4th April 2014, 12:32 AM Hi Guys,
I've now got three of the four replacement gears. The last one is being posted out to me. So I have taken photos of the two main ones that make up the dual gear. These gears are in steel and are 1 mod with 42 and 62 teeth. One of the pictures shows how they will go when in place in the machine.
Since they need machining to finish the bores, I've some work to do. I've also included a picture of the machine just for reference.
Here is what I propose to do. Since the original dual gear slides on a keyed hardened steel shaft, I have obtained a short length of brass bar 25 mm diameter and 30 mm long. The hardened steel fork that is used to move the gear from high to low speed is 5 mm thick and runs in the 6.5 mm gap between them requires a 25 mm diameter surface. This works out perfectly for the 25 mm diameter brass bar.
I will turn down the ends of the brass bar to say 23 mm diameter with a 6.5 mm land in between and bore 23 mm diameter in each of the gears so that they are a good press fit onto the brass bar. I need to bore the brass bar so that it will slide freely on the hardened steel shaft and cut a 5 mm keyway so it cannot rotate independently of it. If I have got all this right then I should have a replacement gear that fits and runs properly.
Ken, mentioned using dissimilar metals to reduce wear on the teeth. Neither of the gears purchased nor the original spindle gears are hardened ! The advice from the manufacturer of the new gears is that it won't make any difference to the wear pattern and over time and that the gears will eventually bed in to each other, though it may take many years... Or a few weeks if they are not kept lubricated properly.
I could have had bronze gears from a wear point of view but those gears were more than twice the price even though the lubrication aspect would not be as severe but would still be necessary. So I chose the cheaper option.
Toggy 4th April 2014, 07:54 AM John,
sounds good. Your gears with some lubrication should last lots longer than the original crap. I am over chinese made machinery. Usually just cheaply made rubbish that has to be rebuilt properly. I now look for good old heavy cast iron machines and restore. Oh; and I do tend to over engineer.
Ken
BaronJ 5th April 2014, 06:38 AM John,
sounds good. Your gears with some lubrication should last lots longer than the original crap. I am over Chinese made machinery. Usually just cheaply made rubbish that has to be rebuilt properly. I now look for good old heavy cast iron machines and restore. Oh; and I do tend to over engineer.
Ken
Hi Ken,
I would hope they do.:U:U:U I expect to have good use of this mill for a few years yet ! Even if I have to completely re-manufacturer it. :o
BaronJ 5th April 2014, 06:54 AM Hi Guys,
Next instalment or the work I managed today...
The photographs show the work carried out in turning and boring the brass bushing, the small gear that will be pressed onto it and the plug gauge that I made in order to make sure I got it right. There are also pictures of the gear being bored out on the lathe and the soft jaws used to make certain that I didn't damage the teeth on the new gear and that the bore was concentric with the teeth. One of the pictures shows how the original gears were set up in the machine and the shaft with the key that the dual gear slides up and down on.
I'm sure that I will have forgotten to mention various things. So all comments welcome.
PS. Sorry about camera shake on a couple of pics.:(:(:(
simonl 5th April 2014, 03:39 PM Hi John,
Nice work with the gears. Thye will last longer than the rest of the machine!
WRT the soft jaws, did you make them purpose built for the job? I assume it's not a co-incidence that the radius of the jaws is exactly that of the gears?
Simon
BaronJ 6th April 2014, 01:49 AM Hi John,
Nice work with the gears. They will last longer than the rest of the machine!
WRT the soft jaws, did you make them purpose built for the job? I assume it's not a co-incidence that the radius of the jaws is exactly that of the gears?
Simon
Hi Simon,
Thanks. See today's post.
Those soft jaws were made just for this job. Oddly enough they were made from an old aluminium belt drive gear that I had kicking about. Those teeth on the outside have nothing to do with using slices from the gear as soft jaws. The hole is conveniently 16 mm in diameter with a 2 BA grub screw. The grub screws were just sawn off from a 50 mm long bolt with a hacksaw cut across the end. They are very easy to make and throw away when finished with.
As a point of interest the large gear won't go into the 4" chuck. Before anybody says anything, I don't know where the other set of jaws is, they disappeared a very long time ago. :doh: So I have four ways around this problem !
1/ Use a larger chuck. I do have a 5" one but I will have to make soft jaws for it. I don't want to mare the teeth of my new gears and I do want the bore to be as concentric as it possibly can be.
2/ Use the faceplate and clamp the gear to it. OK I will have to clock it and make sure that it is running true.
3/ Same issue with clocking if I use the four jaw chuck. (Preferred option) Use soft packings under the jaws to protect the teeth.
4/ Clamp a sacrificial aluminium plate to the faceplate and turn a recess into it to take the gear as a press fit then clamp the gear down so it won't move.
I think I've got all options covered. :U
BaronJ 6th April 2014, 02:10 AM Hi Guys,
More got done today. Finished turning the brass bushing and got the small gear pressed onto it. I warmed up the gear in a pan of boiling water. Still had to press it on but it didn't take much effort. Skimmed the very slight protrusion off the brass bush where it came through the other side. Put the gear back into the chuck and checked the bore for being true. I surprised myself. Not a flicker on a .0005" test gauge. Then I turned .050 of the diameter ready for the gear on the other end.
(See previous post)
There are photographs of the other two gears that I am going to use to replace the two primary drive gears. One goes on the end of the original shaft that drives the dual gear discussed earlier. The other is to replace the bronze gear on the motor shaft. As you can see there are straight toothed gears and not helical as the original ones. The 7.5 degree helix tends to pull the motor shaft down when running in the normal direction and pushes it up when in reverse.
So using straight gears won't produce this effect and should make no or very little difference to the smooth running.
These two gears are also stainless steel ! That wasn't intentional. Simply that these gears had the right teeth numbers and the correct PCD. Whilst a little more expensive, not as much as bronze.
Michael G 6th April 2014, 07:59 AM As you can see there are straight toothed gears and not helical as the original ones. The 7.5 degree helix tends to pull the motor shaft down when running in the normal direction and pushes it up when in reverse.
So using straight gears won't produce this effect and should make no or very little difference to the smooth running.
You'll have to see but it may. With a properly specificed helix angle there is always a tooth in contact with a tooth of the other gear. This makes things quieter (no micro-bang as individual teeth contact initially - gears need clearance) and the transmission a little smoother. It may not be noticeable but going from plastic helical gears to metal straight cut I suspect that you will find things a little noiser.
Michael
simonl 6th April 2014, 08:26 AM It may not be noticeable but going from plastic helical gears to metal straight cut I suspect that you will find things a little noiser.
Michael
Well if that's the case, welcome to the (noisy geared head mill) club, John! :U
They are looking good. The soft jaw idea worked well! I would have been a little lazier and just used a 4 jaw with copper sheet in-between each jaw.
Simon
BaronJ 7th April 2014, 01:42 AM Well if that's the case, welcome to the (noisy geared head mill) club, John! :U
They are looking good. The soft jaw idea worked well! I would have been a little lazier and just used a 4 jaw with copper sheet in-between each jaw.
Simon
Hi Simon, Guys,
Yes I do believe that the mill will be a little noisier. But that was the excuse I was given for the use of plastic gears.
Michael. Thanks for the information about helical gears. That is something that I didn't know about. :( However all is not lost because if push comes to shove I can go back to using a plastic helical gear and the original bronze one. That of course assumes that I can actually get one !
Simon, I'm going for option three with the big gear.
More in the next post.
BaronJ 7th April 2014, 02:10 AM Hi Guys,
Got a little further today. I used the same soft jaws that I used to machine the smaller of the dual gear, to machine the larger of the two stainless steel gears. The one with the red marker on it in the last set of photographs. For stainless steel it machined remarkedly well. which surprised me a little since I've not had too much success machining it in the past.
I've also included photographs of the soft jaws now that they have been finished with and also the boring bar and shims that I have used to machine the bores to size. You can see the grind from the pictures of both ends of the tool. There are pictures of the intermediate shaft this gear drives. Its a hand tight push fit. I did very lightly run a tool over the surface just to take the lip off the sides of the groove for the keyway. No problem getting the plastic gear off but there was no way that the bearing was going to come off over the haridge on the edges, and I couldn't push the gear down by hand over it. The key looks as if it was put in with a hammer because the shaft was several thou bigger where the key fitted.
One of the problems that I am going to have to face is putting a 5 mm keyway slot into these parts.
Later !
simonl 7th April 2014, 10:52 AM Hi Simon, Guys,
Simon, I'm going for option three with the big gear.
Awesome! You're certainly not a one trick pony! :cool:
Gears are looking fan bloody tactic!
Simon
BaronJ 8th April 2014, 06:46 AM Hi Guys,
Well I chickened out on setting up the four jaw to machine the big Gear. :B Got the four jaw out and then changed my mind and put it back in the cabinet. I decided to do the small one instead. I snipped off a short length of 1/2" wide aluminium strip and wrapped it around the gear so that I didn't damage the teeth in the chuck. Measured how long the gear had to be and then parted 6 mm off the boss end of the gear. Since the motor shaft is 10 mm diameter and the bore was 8 mm, I ran a 9.5 mm drill through and then bored it out to 0.392 thou. cleaned it up and took the boss OD down to 0,7" so that it clears the bearing housing.
The pictures show the setup in the lathe and the original bronze gear. Also how the two gears sit when the thing is re-assembled. This gear has a 4 mm wide by 5 mm key so I'm going to struggle with cutting that one as well as the others.
Anyone have any suggestions about lubrication for these gears since they are virtually inaccessible after the machine has been put back together. I had thought about oil and making some kind of oiler but I not sure about what I should do. The original was smothered in green goo very little was on any of the gears.
I will have a go at the big gear tomorrow...
kwijibo99 8th April 2014, 10:26 AM Anyone have any suggestions about lubrication for these gears since they are virtually inaccessible after the machine has been put back together. I had thought about oil and making some kind of oiler but I not sure about what I should do. The original was smothered in green goo very little was on any of the gears.
G’day Baron,
I use motorcycle chain lube on the change gears of my lathe, works a treat and sticks to the gears where it’s needed.
Cheers,
Greg.
Stustoys 8th April 2014, 11:16 AM Hi Baron,
Looking at the second picture. Is that the top of the motor? (are they vents for the windings?)
Stuart
Oldneweng 8th April 2014, 06:33 PM I have to concur BaronJ. That is awesome work. :2tsup:
Dean
BaronJ 9th April 2014, 01:40 AM Hi Baron,
Looking at the second picture. Is that the top of the motor? (are they vents for the windings?)
Stuart
Hi Stuart,
No ! Its the fan blades that you can see. The motor end plate has been removed so that the bearing can be seen along with the keyway.
The motor is a permag type and the only windings are on the armature.
BaronJ 9th April 2014, 01:55 AM Hi All,
Well I'm on the home run. I got the large gear set up properly in the four jaw. +- 1/2 thou on the bore it was a little rough so the test gauge needle flickered about a bit. Bored it out to .940 and cleaned it up. It press fitted comfortably onto the brass bush. I would have liked it to be a little more tight. I had to warm up the gear on the other end. But I can't twist it or pull it off by hand, so it stays...
Yes those marks on the smaller gear teeth is where I caught it with the hacksaw when sawing off the boss.
I know, I know... I should have parted it off in the lathe. :-:-:-
Tragedy *$%^& :((:((:(( Put in your own expletives. See next thread
Pictures below.
BaronJ 9th April 2014, 02:33 AM Hi Guys,
After setting up the large gear in the four jaw, I dropped my "Spot On" 1/2 thou test gauge !
Well it hit the drip tray, bounced and then landed on my rotary table which was sitting on the floor, ricocheting under the bench. I've had that gauge for more than thirty years. It was given to me by a very generous old friend, now departed, when I took an interest in his work. I learnt a great deal from him even though it was years later before I could make use of the things he taught me.
Anyway the crystal had got cracked and a tiny piece ended up inside the dial. The lever was jammed and didn't move anymore. I also found the the tension adjuster for the spring had cracked and no longer held its position.
After I stopped kicking myself for being so clumsy, I decided to try and repair it ! It took very little to take it apart. The moving arm had jumped onto the worm and it just clicked back when I removed the cover. The plastic lever for the adjuster had cracked and lost its tension. I decided to photograph it after I had shaken the broken crystal chip out of the dial and taken it apart. I thoroughly cleaned the parts (note the fine threads around the plastic lever) and made a new tensioner for the spring from a sliver of thin phosphor bronze strip 5 thou thick, salvaged from a scrap wall switch. Luckily for me it already had a 2 mm hole in it which fitted nicely over the spring adjuster spindle. A bit of teasing over some 5 mm rod shaped it to form a spring replacing the adjusting lever. Putting it all back together I now have a working test gauge, though it does have a hole in the glass crystal.:2tsup:
I'm still annoyed that dropped it. Especially since I have a new one still in its box, though its a different brand.
Sorry I didn't take any pictures after I did the repair.
Michael G 9th April 2014, 08:09 AM Good save there. If you can work out sizes you might be able to fit a replacement crystal (ask Stuart)
Michael
Stustoys 9th April 2014, 04:06 PM http://www.woodworkforums.com/attachment.php?attachmentid=309653&d=1396899664
This is the picture I mean. Which way does the air move through the motor?( I assume the motor can be reversed. so both?)
Just wondering about chain lube etc getting into the motor.
Good save there. If you can work out sizes you might be able to fit a replacement crystal (ask Stuart)
What he said.
Great name for a DTI, I wonder if they had a cheaper model "nearenuff" :D
Stuart
BaronJ 10th April 2014, 06:47 AM http://www.woodworkforums.com/attachment.php?attachmentid=309653&d=1396899664
This is the picture I mean. Which way does the air move through the motor?( I assume the motor can be reversed. so both?)
Just wondering about chain lube etc getting into the motor.
What he said.
Great name for a DTI, I wonder if they had a cheaper model "nearenuff" :D
Stuart
Hi Stuart,
That picture is effectively upside down the motor is above not below. The fan couldn't blow the dust off the blades if it tried. I have modified the motor cover with an external fan that forces air up through the motor. The other gears are in a totally enclosed space so grease couldn't get into the motor from there.
BaronJ 10th April 2014, 07:02 AM Good save there. If you can work out sizes you might be able to fit a replacement crystal (ask Stuart)
Michael
Hi Michael,
must confess that I'm tempted to leave well enough alone. I've had a crystal come out before and it was a pig to get it to go back into place.
Last photograph of the gauge showing the tension lever spring that I fabricated.
BaronJ 10th April 2014, 07:31 AM Hi all,
Didn't get much done today. Hospital appointments n all that.
Anyway I decided that since there was the possibility that the gears might slip on the brass bush to lock them in place. I've only had time to do one of the two gears.
I used a 4 mm slot drill and drilled two holes opposite each other into the joint line between the brass and steel parts. I then tapped the holes 2 BA and screwed in a 1/8" x 2 BA Allen grub screw. There is no way now that the gear will rotate on the bush or come off.
I note how the photographs show the distortion of the brass due to threading the holes.
BaronJ 12th April 2014, 02:19 AM Hi Guys,
This will probably be my last post on this subject. I've now got the gears slotted with the keyways and am ready to put this thing back together.
I've decided to make an oil feed from the side of the machine into the cavity where the main gears are housed. I will drill and thread a hole to take an oil nipple in the side of the casting just below the inside of the top of the casting. On the inside I will put a pair of 1/8" bore copper tubes Siamesed together and formed into a "Y" so that lube can be applied to both sets of gears from the one nipple. I've made a 4 mm polythene key to go into the driving gear as a shear key so it will be interesting to see how that holds up.
Once the oiler has been made this bad boy can be used in anger again, and I can get back to making my tool grinder.:U:U:U
Abratool 12th April 2014, 09:35 AM Well done on the repair of the"Spot On" indicator.
What a great name.
Hope it still gives years of service, sounds like it has some good memories for you.
regards
Bruce
BaronJ 13th April 2014, 02:35 AM Well done on the repair of the"Spot On" indicator.
What a great name.
Hope it still gives years of service, sounds like it has some good memories for you.
regards
Bruce
Thank you Bruce,
Yes it has :) The chap, Stanley, who gave it to me was very much a mentor, not just in engineering but life in general. To a great extent he was a father figure ! He always had time for me, which very few others did.
BaronJ 13th April 2014, 02:53 AM Well the mill is back up and running. I've not done anything more than switch it on and run the motor, and change the speed gears.
Ok there is no real load on it but it certainly sounds different. I wouldn't say its any noisier but the rhythmic chugging has gone. I did find another problem but it was easy to solve.
The speed change knob on the side moves the dual gear up and down to select high or low gear. In the low position it moves the gear upwards. I found that it didn't move the gear far enough to engage the teeth fully. There was always movement of the knob past the ident position, but it never stayed there. I rotated the plate with the three ident dimples in it 180 degrees. Blued it and refitted the knob moving it to each extreme took the knob off and the plate. Then drilled three more dimples. One at each end of the mark and one in the middle. It now moves the gear up enough to engage the teeth in both gears fully.
So at the moment I'm a happy chappie.
Thanks Guys for all the kind words and good advice.
Steamwhisperer 13th April 2014, 06:08 AM Well done BaronJ,
I have enjoyed this entire thread.
The easy part is the advice, the hard part is putting it into practise. :2tsup:
Phil
BaronJ 14th April 2014, 02:42 AM Hi All,
I used the mill today to finish off the job that started this whole thread. Anyway the slitting saw had a crack in it !:oo: I hadn't noticed it before. Then it broke into three pieces as I tried to get it off the arbour. Not having another slitting saw I pressed an old 125 mm circular wood saw blade into service. I had to turn up a suitable arbour for it and put it in the drill chuck to use it. Job done. :U:U:U
One thing that I have noticed, the mill runs on a lot longer than it did before when you cut the power. I assume that this suggests less losses in the new gears.
Now where did I put that chunk of 80 mm cast bar...
Oldneweng 14th April 2014, 08:44 AM It is great to hear that it is working so well after all the work you have done. Just reward for your efforts.
Dean
simonl 14th April 2014, 10:01 AM Hi All,
I used the mill today to finish off the job that started this whole thread. Anyway the slitting saw had a crack in it !:oo: I hadn't noticed it before. Then it broke into three pieces as I tried to get it off the arbour. Not having another slitting saw I pressed an old 125 mm circular wood saw blade into service. I had to turn up a suitable arbour for it and put it in the drill chuck to use it. Job done. :U:U:U
One thing that I have noticed, the mill runs on a lot longer than it did before when you cut the power. I assume that this suggests less losses in the new gears.
Now where did I put that chunk of 80 mm cast bar...
Good work!
I dare say that the reason your mill runs on longer is because of the angular momentum embodied in the mass of the spinning gears as opposed to the plastic?
Could be wrong, but it was the first thing that came into my mind.
Cheers,
Simon
BaronJ 15th April 2014, 05:44 AM Good work!
I dare say that the reason your mill runs on longer is because of the angular momentum embodied in the mass of the spinning gears as opposed to the plastic?
Could be wrong, but it was the first thing that came into my mind.
Cheers,
Simon
Hi Simon,
Yes you are probably right. When it had the plastic gears the spindle was always heavy to turn by hand. Now you can feel the motor being turned and its a smooth motion with no tight spots even in low gear.
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