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| Mini lathe transmission replacement |
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| loply:
Afternoon folks, I got my mini lathe all tuned up (jibs sorted, etc) a few months ago, and about 4 weeks ago started working in earnest on my first real part - ball bearing handle for the compound. Why take 4 weeks to make such a part? Well, first the headstock gear broke, so I had to stripnit and replace... Decided to put tapered bearings in whilst I was at it, and to increase motor pulley ratio for better torque. A day later.... BANG! Electrics blown, motor runs at full speed only. New electric board fitted, I'm almost finished my rather swanky new compound handle when.... CRUNCH! Headstock gear completely gone again... Was only taking a light pass in alu. I think the whole gear has shattered as both high and low are completely gone. I'm pretty sick of this but determined to fix it properly. I had already been thinking of making a whole new transmission which provided 3/4/5 speeds and bypassed the headstock gears all together, and was also thinking of bypassing the electronics and using just full speed motor (if I have 4 or 5 ratios...) Of course to do this I will need a lathe, which I no longer have, so I will doubtless have to repair using another gear made from recycled plastic bags in order to make the new transmission. Anyway! I'm looking for ideas or advice on how to do this. I have a pair of V belt step pulleys with 2/3/4/5" pulleys on each one, which could potentially give me a speed range of 150 to 1000-odd RPM without the need for the toy electronics. Looking at the lathe I'm thinking to mount one of the stepped pulleys directly onto the back of the spindle, and not use the layshaft at all. I will then reposition the motor and create a system for tensioning and un-tensioning the belt so that speed changes can be made. This will require some kind of spindle extension to be made so that it's long enough to take the pulley, which is about 70mm through it's bore. I can then remove the whole gadget box on the front and build a much simpler on/off system, and put a tool holder there instead! Does this sound like a plan? Anybody have any better ideas or done anything similar? Thanks, Rich |
| loply:
Well, head off, here's the result... Sure enough the smaller of the two gears has completely blown itself to pieces! Luckily the larger gear, which is harder to replace, is more or less intact... The low speed end has lost one tooth, the high speed end is okay. I may not have to pull the taper bearings off the shaft therefore, if I can make my new transmission using only high speed ratio anyway :coffee: |
| John Swift:
Hi Rich , during the last 12 months I've fitted new brass gibs , tapered bearings and metal headstock gears to a clarke CL300M lathe all from arc euro trade :- http://www.arceurotrade.co.uk/Catalogue/Machine-Spares/C3-Mini-Lathe-Spares note - the metal spindle gears are in 3 parts and you need to check the key will drive all of them !! I can see how changing the pulleys to increase the torque will break the plasitic gears more easily , a mod i've thought about doing , but not done yet John PS look here at one version of what you are thinking about :- http://tool20895.homestead.com/treadmill.html |
| andyf:
Sounds like a plan, Rich, but you will only have 4 speeds with two 4-step pulleys unless you can arrange for one pulley to slide along its shaft into a position where (for example) the belt can run from one 5" pulley to the other 5" pulley, and a tensioner which can take up a lot of slack (when running from one 2" to the other 2"). If you could perhaps remount the motor so you could move it closer to or further from the spindle to take up the slack, you would get 12 ratios (2" to 2", 3" to 3", 4" to 4" and 5" to 5" all being effectively 1:1, so you wouldn't actually need 5" to 5"). Without the gears in the headstock changing the direction of rotation, the spindle will run in reverse when the switch says forward and vice versa. Some of these little DC permanent magnet motors only run at half speed in reverse (which with your pulleys would have the spindle going forwards) so it might be beneficial to transpose the wires to the motor. Hope this makes sense! Andy |
| picclock:
FWIW replace both of the headstock gears with metal ones (ArcEuro). If the lathe stalls or jams the motor just buzzes or the belt slips. I have never had mine blow the fuse yet. I've geared mine down to allow very large diameter turning of 5" plus steel with no problems and lots of use. Some info at http://s917.photobucket.com/albums/ad19/picclock/ If you need any other help post or PM me. The 7x12 forum is very good for stuff on these lathes. http://groups.yahoo.com/group/7x12minilathe/messages Best Regards picclock |
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