Lathe replacement gear

[Douglasr]

Guys, if I wanted to increase the torque of a 7 x 12 lathe, would a drive gear with fewer teeth be the best way? If so, is there someplace that sells the gear pre made or would if have to fabricate one? Thanks for your ideas

 

[road]

I may be wrong here but changing the drive gear will change the rpm range.
changing to a higher hp motor will increase torque.
Depending on the model mfg'r you may be able to look at LMS site for an upgrade motor or switch to a sewing machine motor. .

 

[Privateer]

Decreasing the gear size on the motor will decrease the RPM in the gear ratio, and increase your torque. Bear in mind that you'll have to recalculate your RPM chart at the end. As was mentioned above, a higher HP motor would likely better serve you, as you wouldn't have to bother with any calculations.

Terry

 

[fgduncan]

Guys, if I wanted to increase the torque of a 7 x 12 lathe, would a drive gear with fewer teeth be the best way? If so, is there someplace that sells the gear pre made or would if have to fabricate one? Thanks for your ideas

You might want to be a little thoughtful about increasing the torque on a light duty machine! They were designed for limited duty and trying to increase the torque is going to increase pressure on the entire drive train as well as the carriage and tool post. The gears may be made out of white metal and in which case they will wear more quickly or even worse, break. If the bed is not a sturdy V way design, then it will tend to flex causing the tool post to rotate slightly and the tool to dig in. I think that I have outlined a number of considerations for you to be very thoughtful about trying to re-engineer a machine to do something for which it was not designed. You may get away with it-for a while. But is the need for extra torque great enough to risk losing the machine, or at least its services for a while? Perhaps taking lighter cuts in the short run will serve better than replacing parts in the long run.

 

[kd8wdave]

I think fg.. is correct. You have to be very careful when you do this sort of thing.
Changing HP will also change the torque for the same speed, and Torque will be
your enemy if you apply more than your gears, equipment is able to handle.
If I remember correctly;
HP = Torque * RPM / 5252 or Torque = HP * 5252 / RPM
Run a spread sheet of this basically formula and you will what happens when
you have speed range say 50 to 1500 with varying HP size motors. You
will get the picture.

I have made gears for my little 109 craftsman, and went thru the calculatons
and can use the lathe, but I have to take much smaller cuts so as not to
overstress the components. I had bought a few gears on-line, only to discover
that the 'seller' was a little less than forthcoming as to quality and condition.
I'll just make my own from now on. My little lathe works, but I do baby it. After
all its a 'baby lathe' and I do this as a hobby, not for profit.

Have fun playing

 

[SEK_22Hornet]

If you are talking about the typical 7 x 12 mini lathe like a Harbor Freight or Grizzly, most of these have a plastic gear train in the head. You most likely have a lever on the back of the head to shift between high and low speeds already, which will give you a slow speed with more torque. The rest of the drive train is a plastic cog pulley on the motor and a toothed belt driving a pulley on the internal jack shaft that has the sliding gear for the high / low speed selection. The Little Machine Shop sells steel replacement gears for the two speed headstock. Their own version of this lathe has a single speed drive using a brushless DC motor that they claim gives better torque over a wider speed range. I have seen a belt drive conversion that bypasses the internal gear train somewhere on the net, but don't recall exactly where. I think I would spend the money to upgrade to a heavier lathe - maybe a 9 x 20. I have made the mistake of thinking that I can make do with a smaller machine to save money, only to end up damaging the machine by trying to do more than it was intended to do. I've come to the conclusion that I'm much better off buying more machine than I think I need.