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| plastic intermediate gears or metal for mini-lathe? |
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| Woodsman22:
Hello everyone; This is my first post and I am new to model engineering/home shop machining (forgive me if this is not the right forum for this post but I am not sure where it should go). I have a Chinese 7 X 12 mini-lathe which I am converting to metal change gears and I am converting the spindle gears to metal as well. However, from what I have read online many people seem to think that going "all metal" is not so good and that it is best to keep the intermediate shaft gears as plastic. I am unsure of what I should do at this point as I have the lathe apart and have the complete set of metal gears, but if the lathe is going to be very loud then perhaps keeping the plastic gears for the intermediate shaft is a good idea? My primary reason for converting to metal change gears is that the plastic ones are variable in dimension (so I have been told) and therefore threads cut using them vary in tolerance. I want this little machine to be as accurate as possible. Having said that, I note that the intermediate shaft power take-off cog wheel is plastic as well and no metal version of it exists so far as I know. Does this affect threading quality? Please forgive the basic questions as I am a newbie. By the way, I am changing to taper roller bearings as well. I just got the whole headstock taken apart, so before I proceed I would greatly appreciate input/advice from those more knowledgeable than I (which is probably everyone! |
| Joules:
As your new to model engineering I would suggest you put it back together and get using it. The periodic error is going to be minimal especialy whilst you learn to cut threads. Start out with brass as its soft and forgiving, avoid alloy as its too easy to gaul and lock up if both parts are alloy. Treat the plastic gears gently and think if you break a plastic gear, what would have broken if that gear had been metal. Joules |
| Woodsman22:
Thank you for addressing my questions in such precise detail. Such generosity in imparting knowledge is surely the hallmark of a great teacher and mentor; one with much experience no doubt. :bow: |
| vtsteam:
No need for sarcasm. You asked for advice. That will likely come in a range of opinion. |
| NeoTech:
The small chinese machines will vary in accuracy, and the change gears will prob. be the least of your worries there. But yeah sure, changing them up is not a bad idea. I have a large chinese/german machine.. And welll lets say all the primary bearings (8 of them) is 6004-RS2 type.. thats what you find in wheel axles.. and the vibrations is horribad. The spindle bearing is the same type ford uses for their wheel mount. And the accuracy of that is.. not even funny to talk about. The drive screw on the machine leaves things to wish for. And i have been having todo modifications to the whole drive train to get into repeatable 1/100th of a mm. So just saying.. The change gears is your least problem when it comes to accuracy.. For material choice, well i would go with brass, its soft, doesnt expand to much from friction and is easy to make parts out of.. I do see this "i have a chinese machine and i want it to have a high accuracy" threads quite often on forums. And to be honest, learn on your chinese machine and if you get bit by the bug - buy a used machine from a known high accuracy brand. my 2 cents.. |
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