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Mini Lathe Speed Reduction Mod - Belt & Pulley Kit

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ehamady

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Taper roller bearings in my 7x14 lathe have significantly improved performance and finish, but I notice the rpm's still fluctuate while parting or taking heavier cuts, especially with 304 stainless steel which is my favorite material. I figured this was natural because of the lathe's size but decided to investigate possible solutions to increase torque at slow speeds. I first thought of trying a more powerful motor but didn't want to risk the lathe buckling from stress that it wasn't built to handle. Another possibility was to tweak the speed/torque pots on the circuit board but didn't want an "electrical" solution over a mechanical one. The jack shaft motor speed reducer mod seemed like overkill. I ultimately came accross this simple belt and pulley kit on eBay which lowers the gear ratio and decided to give it a try.

I made a key for the new motor pulley from 35 cent 1/8" key stock and spent a couple hours installing the kit, painstakingly adjusting belt tension and took my time leveling the motor in its mount. Max speed in low gear is now down to 660 rpm and 1550 rpm in high gear which I never use. The torque increase has done several good things, most of which I didn't expect - parting stainless produces smooth chips and the motor speed no longer dips or stalls, I get an excellent finish when taking heavy cuts, the lathe no longer labors to spin up the 5" 5C collet chuck, tapping and threading with my tap and die holders is much easier, no chatter when chamfering, the dartboard/pie chart ghost pattern when facing is gone, the metal headstock gears run a little quieter, I can now run the spindle as low as 20 rpm, and I like replacing plastic parts with metal ones.

Taper roller bearings have been the best upgrade and this increased torque mod is the cherry on top.
 
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mattthemuppet2

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nice work, sounds like you now have a very capable little lathe! Any pics of it installed? How much was the pulley and belt kit?
 

ehamady

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nice work, sounds like you now have a very capable little lathe! Any pics of it installed? How much was the pulley and belt kit?
I really like my Big Dog lathe. It's great for learning how a lathe works and the importance of torque, rigidity, and lubrication. A nice stepping stone before getting a much bigger lathe. I've just about got it dialed in.

The kit was $74 which I initially thought was steep. The ratio logic made sense so I was 90% sure it would work. I'm glad I got it and think it's worth it. I could have saved money by scouring the internet for each individual component, but the kit saved time and guaranteed that the pulleys and belt fit each other. Here's a pic of it installed:

I initially got the idea to try the gear ratio method of this mod here: http://www.mini-lathe.org.uk/torque_gear_replace.shtml

The kit's description that caught my attention:
Fits Mini Lathe 7x10, 12, & 14, Pulley/Belt Reduction Power UpGrade, Aluminum XL Pulleys & Belt, 3 to 1 Reduction instead of the OEM 1.82 to 1, 40% power increase, ideal for spinning 4 & 5 inch chucks, NOTE: This upgrade lowers Max RPM in Low Gear to Approx. 700 RPM, and 1600 RPM in High Gear.
 
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Chucketn

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Does the kit just replace the stock motor pulley, driven pulleya nd belt, or does it contain a jack shaft setup also?

Chuck
 

ehamady

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Does the kit just replace the stock motor pulley, driven pulleya nd belt, or does it contain a jack shaft setup also?Chuck
The kit is a direct replacement of the stock plastic motor pulley, plastic spindle drive pulley, and belt. I simply removed those 3 stock parts and slapped the 3 new ones on in their place. The stock motor pulley had the key formed into the plastic, so I had to make a key for the new aluminum pulley. I've read that some people don't bother with the key because the aluminum pulley has 2 set screws instead of 1. I think keys are important so I used 1/8" key stock from the hardware store and ground it into a nice press fit quickly with my table disc sander. I spent more time adjusting the belt tension and making sure the motor was optimally aligned than installing the kit. I'm a stickler for that stuff.
 
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ehamady

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Day 2 of running with the speed reduction mod. I decided to experiment in high gear on aluminum, brass, 303 & 304 stainless, 1018, 4140, and 12L14. Before the mod, high gear was way too high so I never used it. It would dull the tools quickly and immediately burn off cutting fluid and only produced a nice finish with super light cuts. I did a facing cut on each material at 750 rpm with indexable tools and HSS tools that I ground. Got an excellent finish on the AL, brass, and stainless with all the tools. The indexable tools produced a smooth finish on the rest although not as bright which I'm sure is due to the material itself which I thought was a bit "gummy". The ground HSS tools also produced a smooth finish on the remaining materials but was "liney" under the magnifying glass like a vinyl record because of the tools' sharpness - certainly good enough for making functional components that don't need to look like jewelry and would look better after stoning a larger radius on the HSS.

I'm going to stay in high gear for awhile to play with speeds and feeds for each type of steel. High gear is actually useful now and I can use low gear for thread cutting. I mainly cut brass and 304 stainless and high gear produced a better finish on those than low gear. I continue to be amazed at how much smoother and quieter the lathe is running now, even in high gear. The metal gears in the headstock used to clank like loose change in a dryer, but now I can actually hear the grease doing its job!
 
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mattthemuppet2

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well done, sounds like it was well worth the effort :)
 

DavidOulton

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I would like more information on the gear reduction you made on your lathe . I have a cummons 7x12 lathe . I live in Oakville Ontario Canada . Thanks any help in finding the parts and Pictures would be great. David Oulton . email davidoulton@sympatico.ca
 
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