Mini-Lathe Repair

[Neil WyattModerator @neilwyatt]

The metal vs nylon debate is interesting.

I think my gear lasted around 12 years or more, and was subjected to awful abuse. I am pretty sure that when they go it is because they are subjected to loads well beyond what the original designers anticipated for the lathe, such as crashing a tool into the chuck jaws or taking deep interrupted cuts trying to 'round off' irregular work.

They seem to fail either quickly in the hands of a beginner or after a decade or two. What probably saved my gears from my beginner's errors was having the toothed belt a bit loose so it would slip with a terrifying howl rather than break a gear.

Looking at the the cost of replacement gears, the difference for a pair is about £14, so I imagine it would add no more than this to the cost of a machine.

I also am sure the factories would happily fit them as standard if requested by importers.

It's worth thinking about how frequent broken bull wheel gears are on secondhand Myfords – probably mostly caused when changing chucks – to see damage in this area can be.

Neil

[egaParticipant @ega]

I think someone mentioned Nylatron. I have successfully used gears made from this material in a larger lathe.

[JasonBModerator @jasonb]

Gears are Acetal according to ARC site. Who also suggest a light application of grease.

[Anonymous]

Looking at the picture posted by Ron the problem, as has been pointed out, is one of fundamentally poor design. The gear that has broken has a very thin boss which clearly wasn't strong enough. It's not easy to tell but the gears also appear to be 14.5 degrees PA, which is also bad, as the teeth will be thinner, and weaker, at the root.

I'd disagree with SoD on a number of points. There's nothing wrong with cost reduction exercises but they have their limits, and I doubt the factories churning out mini lathes pay much attention. If you're going to provide a weak point you don't do it where you have to dismantle half the machine to get to it. You put in a simple, accessible, shear pin.

The late, great JohnS took the view that one of the big problems with the old Myford company was old fashioned, and expensive, manufacturing techniques, reliant on old school skilled workmen. The odd thing is those techniques are often venerated on this forum, but judging by the response on the has anyone bought a new Myford thread far fewer people are, or were, prepared to pay for them. As for many of the manual industrial lathes of the past, industry has changed and very few are now required. So a shakeout was inevitable.

Andrew

[JasonBModerator @jasonb]

I think it is a modified form due to being a 12T gear, if you look at the photo on ARC's site the larger one looks more like 20pa as do the pair it runs with rather than being 14.5pa.

 

They have not helped themselves by putting the keyway between two teeth where the gear is at it's thinnest

Edited By JasonB on 07/12/2018 13:27:50

[JasonBModerator @jasonb]

Ron, the other option is to bypass the layshaft entirely and pop a big 3-phase motor on it that drive sthe spindle directly like this bodger has

[Chuck PickeringParticipant @chuckpickering45941]

Has anyone needing these gears tried 3d printed ones? I

I used Fusion 360 and it's spur gear add in to design and print every gear in my 7x lathe.

My 7x is almost 20 years old, and I haven't broken any of the headstock gears, so haven't tried 3d printed ones there. But, I have printed various change gears, including a 90/20 combo gear for extra fine feed and a custom banjo to accommodate it, and a replacement motor pulley that work fine.

[Ron LadenParticipant @ronladen17547]

Posted by JasonB on 07/12/2018 13:35:50:

Ron, the other option is to bypass the layshaft entirely and pop a big 3-phase motor on it that drive sthe spindle directly like this bodger has

Wow, that is some motor, its a bit too scary for me though, plus 3 phase and associated electrickery that scares me even more.

[Ron LadenParticipant @ronladen17547]

The plot thickens !

I was about to order a replacement set of the plastic gears, I was on the Amadeal site (they supplied my lathe) when I noticed that their metal gear set looked different. Looking at the spec they had quite a lot more teeth than the plastic ones, 50% more in fact, so I gave them a call. They said that their metal gear sets have had the number of teeth increased to reduce the noise associated with the old set which were just a copy of the plastic ones. They claim that the new metal set is still not as quiet as the plastic ones but not far behind and a vast improvement over the old metal set.

The plastic layshaft gears are 12T/20T and the spindle gears 21T/29T which in the Amadeal new metal set have become 18T/30T and 31T/43T. So thats put the cat amongst the pigeons as I am thinking of giving them a try, though I wouldnt do it without the mod to the belt drive.

[Neil WyattModerator @neilwyatt]

Posted by Ron Laden on 07/12/2018 14:16:40:

Posted by JasonB on 07/12/2018 13:35:50:

Ron, the other option is to bypass the layshaft entirely and pop a big 3-phase motor on it that drive sthe spindle directly like this bodger has

Wow, that is some motor, its a bit too scary for me though, plus 3 phase and associated electrickery that scares me even more.

And look at the state of that welding!

[Ron LadenParticipant @ronladen17547]

Would anyone know of a source/supplier for the multi vee belts and pulleys, it is only a small belt 102mm diameter/320mm long. I was thinking a J2 section which from what I,ve read is 2.34mm rib centres and 4 ribs would give me a belt approx 10mm wide. I found a couple of belts at near enough the right length but they are only 2 ribs which is too narrow. From what I,ve seen so far pulleys could also be a problem but I guess I could make my own.

Just wondered if anyone knows of a supplier that offers a good range of belts and pulleys in the smaller sizes.

[JasonBModerator @jasonb]

13" may be the closest, slightly larger dia pulley would take up the slack if you can't move the motor enough

[Ron LadenParticipant @ronladen17547]

Posted by JasonB on 07/12/2018 21:00:32:

13" may be the closest, slightly larger dia pulley would take up the slack if you can't move the motor enough

Brilliant Jason, thanks a lot, there is plenty of motor adjustment so I think that belt will be ideal.

Ron

[Ron LadenParticipant @ronladen17547]

I have ordered the new type metal gear set and a poly vee drive belt to replace the timing belt. I will need to make a motor drive pully and the layshaft pully. The motor pully is fitted with a grub screw and the layshaft pully has a keyway and secured with a circlip, I plan on copying that on the two new ones which will save any mods to the layshaft.

Having no experience of multi vee belts or cutting keyways, this is what I am thinking but please shout if I have it wrong. I am guessing that the depth of the rib grooves in the pully will need to be cut just shy of the depth of the belt rib, too deep and the belt at the base of the ribs will contact and the ribs wont..?

The keyway on the existing pully is 3.9mm wide and 1.9mm deep, I was thinking of drilling a 3.9mm hole before I put the hole in for the shaft and positioned to give a depth of 1.9mm from the edge of the shaft hole if that makes sense..? After the shaft hole is in I would then use a square needle file and square out the keyway, it will be around 13mm long and the material is 6082.

Ron

[Neil WyattModerator @neilwyatt]

> The keyway on the existing pully is 3.9mm wide and 1.9mm deep,

Not 5/32" wide and 5/64" deep by any chance?

Imperial bits sneak into the oddest places

Neil

[Ron LadenParticipant @ronladen17547]

Posted by Neil Wyatt on 08/12/2018 10:41:50:

> The keyway on the existing pully is 3.9mm wide and 1.9mm deep,

Not 5/32" wide and 5/64" deep by any chance?

Imperial bits sneak into the oddest places

Neil

Probably is Neil, I just measured it with the vernier in metric.

 

Edited By Ron Laden on 08/12/2018 10:49:59

[Geoff TheasbyParticipant @geofftheasby]

What a timely thread! Or the cause of my trouble… A harbinger, in fact (Dic. one who harbingers) My super mini lathe has just stripped the leadscrew gear. Removing it reveals a jammed leadscrew, so I slept on it. My task, should I accept it, is to take down the leadscrew and find out why. The carriage moves freely.

[Ron LadenParticipant @ronladen17547]

Oh dear Geoff, I hope this thread is not a harbinger of doom and start a spate of mini-lathe problems..

In your case the good thing is you should quickly find the problem, at least you dont have to strip down half the machine to find the problem…good luck with it.

Ron

Edited By Ron Laden on 08/12/2018 11:13:18

[HOWARDTParticipant @howardt]

Geoff, with regard you jammed lead screw, I had similar on my SC3 and found it was the idler gear assembly. The idler gears are mounted on a steel bush running on a steel shaft Needless to say if not lubricated frequently the two seize. They are a bugger to get apart, but judicious use of a wedge(flat screwdriver) and hammer will separate. Then just try and remember to lubricate frequently. Of course alternatively could be just one of the bearing supports seized.

[Stuart Smith 5Participant @stuartsmith5]

I have recently had a similar problem with the leadscrew gear on my Amadeal cj18 lathe. I have been thinking of fitting a motor to the right hand end of the leadscrew and was trying out options and forgot to tighten the retaining screw on the end. When I started the lathe the collar tightened up and seized the leadscrew. There was a bang and the plastic leadscrew gear shattered.

Luckily easily fixed. I ordered a replacement from Amadeal (£7 inc postage) and it came in the post the next day.

[Geoff TheasbyParticipant @geofftheasby]

Update:

It's the LH leadscrew bearing. Seized. Can't imagine why, it's had the same lubrication as the other end bearing. Maybe it was tight to begin with. Anyway, now soaking in penetrating fluid (Brake fluid + 3-in-1)

[Ron LadenParticipant @ronladen17547]

A picture of the metal gear set I have ordered, not as coarse as the original metal gears there is 50% more teeth. So fingers crossed that these will run well and not be too noisy, they are said to be much quieter than the old set.

Edited By Ron Laden on 08/12/2018 20:25:28

[Geoff TheasbyParticipant @geofftheasby]

Success! Bearing freed off with a combination of brute force and persuasion.

After soaking all night in penetrating fluid, (The shaft, not me!) it moved a little, but not much. I then warned up the bearing with a butane torch, and heard a 'crack' noise, which was promising. Then, resting the shaft vertically in the vice, loosely, not gripped, so the bearing rested on the jaws, I whanged it with a lump hammer, protecting the end… A sliver of light showed where the leadscrew was shouldered next to the bearing. Thus encouraged, I applied my 75 mm gear puller to it, and it began to move! Then I just wound it off. The bearing area was black, suggesting lack of lubrication, so I polished it, made sure the oil holes were clear and, feeling & seeing no obvious problems when held up tho the light, reassembled it in the reverse order, as the Haynes manuals say.

Now, before I was so rudely interrupted, what was I doing?

[Howard LewisParticipant @howardlewis46836]

My mini lathe did not have ball oilers in the bearings for the Leadscrew! . So when making an outrigger bearing for a Handwheel for the Leadscrew, fitted a ball oiler to that and to the one at the Headstock end.

Copied what Neil did with the Apron on his mini lathe, to keep swarf out of the gears. Made a cover, and fitted a ball oiler to that as well. HJaving sealed the perspex cover to the Apron,the gears now run in an oil bath.

Howard

[Neil WyattModerator @neilwyatt]

I greased my gears

My mini lathe leadscrew has a ball oiler at one end and a simply oil hole at the other.

The SC4 has so many ball oilers I worry about not getting them all… I'm not 100% convinced they are all needed although having them on things like the tailstock barrel does no harm and means I don't have to extend it to blob some oil on once a year

Neil

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