Hardening the pinions, (or the racks?)
 

Hardening Rack and Pinon:

Is it common to harden both or just the rack?

Nils, racks are very rarely hardened. I harden the pinions only. The pinions wear faster than the racks because they might only have 30 teeth compared to the over 600 teeth on the rack. An un-hardened pinion will give over a year or two of use, havn't worn out 2-yr old hardened ones yet. You might decide to save the rack and run with "soft" pinions - the hardening of the pinion is not essential.

A couple of questions.

1. Is it OK to drill clear thru the short z-rack when tapping the M6 threads. Or, should I stop before reaching the teeth? I'm thinking it should be fine as long as the screw does not interfere with the teeth and there are no burrs (clean teeth).

2. What's the DIY method for heat treating the pinion? Is it as simple as getting the pinion "red" hot and immersing in water? Is it really necessary?

I don't think it is a problem if you drill right through and clean off the burrs.

The normal hardening method for small gears is case-hardening, which isn't a typical DIY job. If you can't get an experienced company to harden the gears, then I would rather leave them unhardened.

Greg,

You can buy the gears hardened.

Thanks Gerald,

I only have a "thru" tap and don't want to wait a week ordering a "bottom" tap.

Again, great response time. I sure hope to repay the debt someday. :)


Nils,

Do they have the set screw already threaded?

I bought pinions from McMaster, but I would like your source and I'll get a set of hardened also.

Greg,

I have not actually bought. Boston Gear

For the Pinion the Catalogue page no is 30 and the item code is 46133.

http://bostongear.com/pdf/catalogs/P...penGearing.pdf

I hope that helps.

When I am ready to buy this will be the place.

Thanks Nils,

Yes, good information is always a help. :)

question on hardening gears
 

Since the rack will last quite longer than the pinion gear. Would it be adviseable to harden only the pinion gears and leave the racks unhardened?

It would not be hard at all to oil bath harden the pinions using temprature markers and Oxy/Acet. for heat. Not exactly the same as case hardening but it will bring the carbon to the surface and the quick cooling of the oil quench will hold the carbon on the surface.

But I wanted to ask first, and see what you guys think of that idea.
I am thinking that It would be a good idea.

I believe Gerald mentioned once in another post that is was a lot easier to replace a pinion than replace a rack. If you harden the pinion, then the rack will wear faster.

Gerald, Did I get this one right?

On the ShopBots, the pinions are unhardened - the general experience there is that the pinions last about a year while the racks go 5 years plus. The traditional thing for us mechanical blokes is to harden pinions, and our experience with our ShopBot supported the belief that the pinions should have been hardened. For our first MechMate gantry, we hardened the pinions and now have over 3 years without any problems. Bear in mind that the ShopBot pinions were only 20 teeth and had to do a lot of rubbing - 30 tooth pinions will have less wear.

So, hardening of the pinions is not essential. You can decide for yourself if a year's service is enough, compared to the hassles you might have to get the hardening done.

You might also want to experiment with various pinion sizes in the beginning . . .
(Hardened pinions have no effect on table performance)

The racks are definitely not hardened - they are too long and thin and will distort too much.

Heath, I think I remember reading that thread. Probably would be better not to harden either then, since the pinons are not big$$.

Oops I must have been writing while you were Gerald. Thanks guys for the help. I think that I will go ahead and harden them.