# Mini lathe headstock herringbone gears



## Masterjuggler (Aug 3, 2020)

I'm about to put in a 1/2hp 3ph Baldor motor on my 7x12 mini lathe, and I fully expect the plastic spur gears in the headstock to break even at that relatively low power. I might still have to buy the metal gear set eventually if this ends up not lasting, but I decided to 3d print my own set of gears out of nylon. I designed them with a herringbone tooth geometry to make it quieter and stronger than spur gears.

Initially I was going to just make helical gears, but I didn't want any axial thrust messing with the shift lever position. And because herringbone gears don't slide axially, I had to keep them all stationary and make a selector collar like in a car's manual gearbox.

I stuck them in the lathe, ran it for a bit, and made a few test passes on some steel. So far I'm calling it a success in that they didn't immediately explode on startup and they're definitely quieter than the spur gears. I included a recording of each set of gears.

Hopefully they work well with the more powerful motor, but time will tell. If worse comes to worst, I'll just get the metal spur gears and deal with the extra noise. Honestly the change gears are far more noisy than the headstock anyway lol. I might just have to print them all with herringbone teeth too....


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## silence dogood (Aug 3, 2020)

I like the herringbone gears,  May I suggest that you add a shear pin somewhere in the drive train.  A number of lathes have a pin mounted in the lead screw.   I suppose that you could make one out of aluminum or plastic.


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## Masterjuggler (Aug 3, 2020)

That's a good idea, and if I end up getting the metal gears I'll definitely include something like a shear pin. For now I highly doubt a crash would break the lathe before the printed gears, so I'm pretty comfortable with how it is.


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## Masterjuggler (Aug 3, 2020)

I with I had some kind of dynamometer setup, but I somehow gained quite a bit of torque with this gear change. I kept the tooth ratios the same, so I'm not entirely sure why. Before I could only go about 10 thou into 1" diameter 12L14 before it stalled, now I can go 20 thou.

Still, I'm working on putting the better motor on it because I want to really turn some steel lol.


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## AssassinXCV (Jun 1, 2021)

Hello,

Would you be kind enough to share the .STL files for these gears? I'm looking to upgrade the gears for my lathe but twice now the metal gears have gotten lost in shipping from China.

Thank you.


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## foleda (Jun 1, 2021)

Masterjuggler said:


> I'm about to put in a 1/2hp 3ph Baldor motor on my 7x12 mini lathe, and I fully expect the plastic spur gears in the headstock to break even at that relatively low power. I might still have to buy the metal gear set eventually if this ends up not lasting, but I decided to 3d print my own set of gears out of nylon. I designed them with a herringbone tooth geometry to make it quieter and stronger than spur gears.
> 
> Initially I was going to just make helical gears, but I didn't want any axial thrust messing with the shift lever position. And because herringbone gears don't slide axially, I had to keep them all stationary and make a selector collar like in a car's manual gearbox.
> 
> ...


Note that 1/2 hp is about 373 Watts, less than 10% more power than the 350 W motors commonly installed on mini-lathes.

Torque is the more relevant parameter for deciding if gear teeth will survive.  I don't know enough to say which would produce greater torque in your application.  The answer will depend on speed and the details of the motor/controller design.

Regardless of the above, herringbone gears are a great idea.


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## Masterjuggler (Jun 1, 2021)

foleda said:


> Note that 1/2 hp is about 373 Watts, less than 10% more power than the 350 W motors commonly installed on mini-lathes.
> 
> Torque is the more relevant parameter for deciding if gear teeth will survive.  I don't know enough to say which would produce greater torque in your application.  The answer will depend on speed and the details of the motor/controller design.
> 
> Regardless of the above, herringbone gears are a great idea.


In an ideal world you'd be correct, however there is no possible way that piddly little DC motor was putting out anywhere near its rated spec. I could run it on low gear and stop it with my hands. The 3ph motor on the other hand is a true 1/2hp, which is way more than enough for this thing and many larger lathes.

I've been using the herringbone gears but the teeth have gotten sort of smushed over time. Maybe I'll try printing them out of carbon fiber nylon at some point. For now though, steel gears are working well, if a bit loud.



AssassinXCV said:


> Hello,
> 
> Would you be kind enough to share the .STL files for these gears? I'm looking to upgrade the gears for my lathe but twice now the metal gears have gotten lost in shipping from China.
> 
> Thank you.


Sure. You'll probably have to play with the shaft hole tolerances a bit, so I uploaded the step files for them instead. If you end up getting it working too, make sure to post pics and let us know!


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## Firstram (Jun 1, 2021)

I have a 2.5 hp treadmill motor on my 7x10. I ran the belt to a reduction jack shaft and I have broken lots of gears! I use the metal gear on the spindle and buy plastic drive gears 3 or 4 at a time. This way it's still quiet and I don't have to pull the spindle every time. I did make a banjo to hold extra gearing so my feed is only 25% of the factory's lowest rate. When it is tuned up and happy I have taken .050" doc in 2" aluminum, it needs a new gear now.


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## Masterjuggler (Jun 12, 2021)

Firstram said:


> I have a 2.5 hp treadmill motor on my 7x10. I ran the belt to a reduction jack shaft and I have broken lots of gears! I use the metal gear on the spindle and buy plastic drive gears 3 or 4 at a time. This way it's still quiet and I don't have to pull the spindle every time. I did make a banjo to hold extra gearing so my feed is only 25% of the factory's lowest rate. When it is tuned up and happy I have taken .050" doc in 2" aluminum, it needs a new gear now.


Out of curiosity, how do you have your motor connected? Right now I have an intermediate pulley mounted where the original motor used to be, with a v-belt between it and the motor, and the timing belt still to the drive shaft.

Also could you go into more detail about your banjo, maybe with some pictures? One thing I've been contemplating doing for a long time is mounting a window or windshield wiper motor to the leadscrew with a potentiometer control, but gearing sounds more consistent.

I'll have to see what my max comfortable DOC is for kicks lol.


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## Firstram (Jun 13, 2021)

Masterjuggler said:


> Out of curiosity, how do you have your motor connected? Right now I have an intermediate pulley mounted where the original motor used to be, with a v-belt between it and the motor, and the timing belt still to the drive shaft.


 I don't have any pictures and I'm working away from home for 2 months.

The TM motor sits behind the lathe and turns an intermediate jack where the original motor was mounted. Sounds like you did the same. I can't find a link to the banjo. If I was going to do it again I'd go with a motor on the lead screw, infinitely adjustable and *quiet !!*


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## Masterjuggler (Jun 13, 2021)

Firstram said:


> I don't have any pictures and I'm working away from home for 2 months.
> 
> The TM motor sits behind the lathe and turns an intermediate jack where the original motor was mounted. Sounds like you did the same. I can't find a link to the banjo. If I was going to do it again I'd go with a motor on the lead screw, infinitely adjustable and *quiet !!*


Good to know I'm on the right path then lol.

The intermediate pulley mount I made is a little too flimsy having been made out of bed frame angle iron, still only mounted with the two bolts the original motor used. Absolutely horrible to work with when I need to take it apart. Because it has some flex, I shredded the timing belt more than once and got a 5 pack off aliexpress in case it happens again. Seems to be synonymous to your plastic gears.

I didn't have a 2" piece of aluminum, so I chucked some 2" mild steel and it seemed pretty alright with 100 thou off the diameter, or 50 thou off the radius, in back gear at 350rpm. Also using the 80 tooth change gears, the lowest it can go stock. The carbide insert I had in it was happier than I've ever seen it, breaking chips into grains of rice. I don't think I'd want to go much deeper just due to bed rigidity though.


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