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1-800miner
03-28-2013, 11:11 AM
I am getting an old Sebastian with no change gears at all.
I can get my hands on 3/8" plate acetyl for a good price.
Do you think it will hold up for change gears?

tylernt
03-28-2013, 12:16 PM
Acetal and even nylon has been used to make lots of gears. The question is, how much torque are they going to experience? Not sure about a Sebastian, but my 7x mini-lathe's entire change gear system is all plastic and I've never heard of anyone breaking/stripping them except when the carriage is power-fed into an obstacle.

On the other hand, the plastic gears in the X2 mini-mill are notorious for stripping/breaking, but that's usually when people try to take too big of a cut -- especially with a flycutter that hammers the gears with shock loads. Change gears on a lathe should be comparatively light duty.

Abaker
03-28-2013, 01:37 PM
I would give it a try. Sheldons with a QC gearbox came with fiber reinforced plastic end gears. Those gears do seem to go missing or get damaged.

What size is the Sebastian? 3/8" face width might be a little little light for a 15" lathe.

See if the leadscrew has a taper pin somewhere. On some lathes that pin was the safety fuse - made of brass and designed to shear and leave the gearing intact.

JohnAlex141r
03-28-2013, 02:19 PM
Hi baker,

I had an old Sebastian that was about 9" dia swing, originally foot-powered, so they did make a bunch of different sizes.

Just a friendly FYI;

John A. Stewart

Evan
03-28-2013, 04:29 PM
Acetal will work fine for change gears.


On the other hand, the plastic gears in the X2 mini-mill are notorious for stripping/breaking,...

I am pretty sure they are Nylon 66. It doesn't have the same impact resistance as acetal.

The Artful Bodger
03-28-2013, 04:44 PM
Do you need high impact resistance for lathe change gears? If not, various plastics such as ABS can be easily pressure formed to create the gears.

RussZHC
03-28-2013, 10:44 PM
Is there any difference for this use between a sheet/plate and a round of acetal?

Ask since IIRC, some plastics are sensitive (in terms of durability) if cut from a flat or cut from a round...could have something to do with fiber reinforcement...Tufnol?

darryl
03-28-2013, 10:49 PM
Someone suggested that acetal/acetal is not a good combination for gears- that acetal/nylon would be better. I've thought about trying a mating gear in pvc, though somehow I don't think it would have good impact resistance or strength either. Maybe brass for a mating gear?

Evan
03-28-2013, 11:13 PM
Acetal on acetal works fine. Change gears are really slow running and not that heavily loaded either. The plate vs bar is no issue, they have the same characteristics. There is no directional difference as there is with PTFE.

_Paul_
03-29-2013, 10:23 AM
I wonder could you use Acetal in place of the ABS used to make a gear as shown in this post from Madmodder Easy way to make a plastic gear! (http://madmodder.net/index.php?topic=3487.0)

The Artful Bodger
03-29-2013, 04:43 PM
I wonder could you use Acetal in place of the ABS used to make a gear as shown in this post from Madmodder Easy way to make a plastic gear! (http://madmodder.net/index.php?topic=3487.0)

That is my post you linked to and I am afraid acetal is difficult if not impossible for that method. The problem is that if the material has too much resilience it does not form and adding heat requires that metal 'cheeks' be on each side of the blank to stop the blank deforming. Maybe with some means of temperature control.