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Mini Lathe gear.  

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MartyS
(@martys)
Trusted Member
Mini Lathe gear.

Was cutting some brass on my mini lathe and brass being brass it grabbed the tool and brought the little lathe to a halt.  Breaking one of the teeth on the high-low plastic gear, and of course it was the gear on the spindle requiring the most amount of tear down possible to replace it.

Grabbed an stl of the gear off thingy and printed it in polymaker PC max, took about 5 hours, should be stronger than the original.

If this one ever breaks I'll break down and spend the $70 for a set of metal gears.

 

Printed mini-lathe hi-low gear

Posted : 04/09/2021 6:41 pm
AndersK, dothuhuong, karl-herbert and 1 people liked
karl-herbert
(@karl-herbert)
Illustrious Member
Mini Lathe gear.

May the plastic wheel outlast the machine 👍

POM (Polyoxymethylene) would be the suitable material for such applications, but it can be more easily molded or milled than printed.

wbr,

Karl

Statt zu klagen, dass wir nicht alles haben, was wir wollen, sollten wir lieber dankbar sein, dass wir nicht alles bekommen, was wir verdienen.

Posted : 04/09/2021 9:27 pm
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MartyS
(@martys)
Trusted Member
Topic starter answered:
Re: POM

The original gear does say POM, but I can see odd patterns in the surface from when it was molded so not sure how good a gear it was to begin with.

One way to be sure the printed gear lasts forever would probably be to order the set of metal gears now. 😋 

Posted : 04/09/2021 10:43 pm
eewoz
(@eewoz)
New Member
RE: Mini Lathe gear.

Hey Marty,

That is very cool!  Was it hard to get the inner diameter of the gear to match the shaft diameter?  Did you make it a little undersized and then drill it out or did it come off the printer with a suitable ID?

Posted : 26/11/2021 12:45 am
Antimix
(@antimix)
Estimable Member
RE: Mini Lathe gear.

Hello Karl,

I recently started to be interested in mini lathes, and I bough one very very small, more a toy than a real lathe, but I had no choices due to lack of space at home, and problems of noise. I plan to use it rarely when I need to do small works that can not be done differently.

I have read that many people are replacing specific original metal gear on the lathe, with plastic 3D printed one. This because (they said)  something like what happened to you, can damage much more metal parts in the lathe gearbox, causing an astonishing amount to pay for replacement parts. So they decided to replace a strategic gear in the box, with one that they 3d printed, very cheap, that SHOULD IMMEDIATELY BREAK in case of issues, saving the lathe gearbox. They called it SACRIFICIAL GEAR. The annoying fact that they have to replace this plastic gear after few days of usage is not seen as a problems, since they prints lots of "consumable" 3d printed gears.
You could also design the gear shape, and then sent it to LASER  CUT a POM block.

Regards

 

Posted : 26/11/2021 4:49 pm
MartyS
(@martys)
Trusted Member
Topic starter answered:
RE: Mini Lathe gear.

 The STL was properly sized, perfect fit on the shaft.  My MK3S is pretty good at eliminating elephants foot but I still had to shave off a bit on the bottom edge.  I didn't trim the elephants foot off the gear so it was a bit noisy at first in the low range but with use it has gotten back to normal sounding.  So far the printed gear is holding up fine even under high torque.  Haven't had a tool catch and stop the lathe again so it hasn't been fully tested.

Posted by: @eewoz

Hey Marty,

That is very cool!  Was it hard to get the inner diameter of the gear to match the shaft diameter?  Did you make it a little undersized and then drill it out or did it come off the printer with a suitable ID?

 

Posted : 28/11/2021 5:11 am
Durahl
(@durahl)
Estimable Member
RE: Mini Lathe gear.

 

I didn't even know elephants' foot was a thing to begin with after using an i3 MK3S as my first FDM Printer until I switched over to a 350 sized Voron 2.4, ABS ( and now ASA-X ) instead of PLA/PETG as my goto Material and SuperSlicer to allow for more granular settings while remaining in the familiar PrusaSlicer UI.

If you're designing your own parts, then just adding like a 0.3mm Chamfer along the edges of the surface later contacting the Print Bed can mostly deal with EF on 0.2mm Layer Height prints in a pinch though realistically you should dial in your printer better to fix it without relying on such mesh modifications.

Posted by: @martys

My MK3S is pretty good at eliminating elephants foot but I still had to shave off a bit on the bottom edge.

Posted : 06/01/2022 1:42 am
MartyS
(@martys)
Trusted Member
Topic starter answered:
RE: Mini Lathe gear.

Everything is dialed in really well on my printer, but we are talking machine part tolerances here, and poly-carbonate (very high bed and nozzle temps), so while all parts look great visually and even feel good something like 100 microns (just a guess) of elephants foot was enough to make the tight fit of the gear on the steel shaft too tight for that bottom millimeter (and I didn't want to hammer it past and cause stress).

Posted : 06/01/2022 3:41 am
jmshaffer1973
(@jmshaffer1973)
Active Member
RE: Mini Lathe gear.

Were you threading when the gear broke?  Nice looking result by the way.  Too bad the lathe wasn't running or you could have turned the ID down a little eh?? lol

Posted : 27/01/2022 10:15 pm
MartyS
(@martys)
Trusted Member
Topic starter answered:
RE: Mini Lathe gear.

No, I was making a brass collar from some scrap brass casting (part of an old faucet).  Combo of brass being "grabby", the casting not being gripped as strong as a normal part, and me being a bit to aggressive lead to the catch and sudden halt.

The old gear still worked fine when in the high speed range but you are right that when I had the original gear out to compare with the 3D printed one I had no working lathe.

The new gear is still working great, I've only cut threads in plastic and aluminum with it but I have cut some steel parts, so I'm sure it will be fine next time I cut threads in steel.

Posted by: @jmshaffer1973

Were you threading when the gear broke?  Nice looking result by the way.  Too bad the lathe wasn't running or you could have turned the ID down a little eh?? lol

 

Posted : 28/01/2022 12:16 am
jmshaffer1973
(@jmshaffer1973)
Active Member
RE: Mini Lathe gear.

Personally on these mini lathes, the plastic gears don't bother me so much because I'd rather have plastic break than metal.  Which lathe do you have? I got the Grizzly 7x12 recently.  Pretty neat to be able to print working parts and also have a lathe to use in conjunction.  Have fun with it. 

Posted : 28/01/2022 3:42 am
MartyS
(@martys)
Trusted Member
Topic starter answered:
RE: Mini Lathe gear.

I've got the Central Machinery version, all those 7x 10,12,14 lathes are pretty much made from the same parts.

The high/low gears are such a pain to get to those are the only ones I'd consider switching to metal, pretty sure the relatively small motor on these would stall before breaking metal gears.  I've also 3D printed some larger change gears to slow down the feed rate, 100 tooth gears slow it down nicely but then you can't put the cover back on.  I did have one change gear break during threading so had to 3D print a replacement for that one.

Took a few weeks of modding and adjusting to get it working like a "real" lathe but I'm pretty happy with it for about a year now.  I added the cam lock from Little Machine Shop on the tail stock, 3D printed a smaller hand wheel for the carriage to get finer control, added stops, etc...

 

 

Posted : 05/02/2022 7:18 pm
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