Pinion gear replacement

[seana]

Hi all,

I think I have come up with some of my chatter issue.
It looks like my pinion gear maybe worn out.
From what I can tell the tooth on the rack is bottoming out in the pinion gear.
So here is the question.
Do I have to replace the racks as well as the pinion?

Do I just order the pinion gears from shopbot?

FYI I have 18 tooth pinion gears.
Hey anybody have 3 of the 18 tooth (new or close to it) laying around?

Looking forward to the input of all the stuff that I didn’t even think to ask or realized was important.

Thanks,
Sean

[Brady Watson]

Sean,
The pinions wear at a much greater rate than the rack does. Replace your pinions. If you are running a PRT, you may wish to go to 25 toothed pinions like the current & newer PRT tools use. You can get replacement pinions from SB. They are around $15 ea. I typically replace pinions about once every year and a half depending on how much cutting I do. Chances are yours are due...and yes, warn pinions will definately contribute to chatter.

-Brady

[seana]

Thanks Brady,
Yes, i am running a PR upgraded to a PRT before i got it so i don't know if the pinions were ever changed out.
So will the 25 toothed pinions match up to my current rack?
Will they also help in cut quaility?

Thanks again

Sean

[Brady Watson]

Yes, they will match up.

At 1st glance, the 18T pinions offer more of a gear reduction than the 25T pinions do, but the 25T mesh more completely with the rack (more teeth engaged than a smaller pinion) and I do believe that you will gain some smoothness in your cuts due to reduced cogging that a smaller gear may cause. You will also pick up about a 25% increase in top speed, at the expense of some torque. You will have to change your unit values for the 25T, which should be standard PRT values. For $45 (2X, 1Y) you can experiment with the 25T ones and see if it makes an improvement on your machine.

-Brady

[dhunt]

Your switch to larger pinions may result in different or greater noise/sound of the machine at slower (Move) speeds.
I would be interested to hear more about this noise factor,
when you make the change,
so please 'keep an ear out' for it!

About 2 wks. ago I started a thread called "Noisy X and Y (M)oves"
to be found at URL
http://www.talkshopbot.com/forum/messages/7/14240.html
where someone came back with the suggestion that our brand new PRT96
may seem unusually noisy(compared to an older smaller-pinion PRT96)
because of our larger pinions:
- you might want to read what was said on the subject.

[Brady Watson]

Yes, you may get some increase low speed resonance. This low speed resonance is normal on a standard out of the box PR or PRT. Regardless of pinion size, you are going to get some resonanace on a PRT. SB3 runs a LOT smoother than the DOS version of the software that I started on with my PRT. I consider the PRT the VW Beetle of CNCs...easy to fix, run, afford etc & it has a unique sound


Just for clarity, I was speaking of mechanical smoothness in my above post, not electrical smoothness. I suppose that it would be helpful to know what Sean typically cuts on the PR, as this will influence the selection of pinions.

Personally, I would move to at least a 20T pinion to gain some mechanical smoothness without sacrificing low end gearing and resolution. Sean, if you cut a lot of very small parts in plastics or aluminum and you need high resolution, then I would keep the number of teeth small. If you do general cutting and cut larger signs and sheet goods, I would go with a 20T or 25T pinion to make better use of your router's power range to get your chipload right.

-Brady

[seana]

Thanks for all the input it gave me some good questions to ask when I talked to sb.
I cut a variety of material but mostly it is sheet goods for cabinet parts.

I went with the 20 tooth figuring that way I could get good results on all materials that I cut and not loose that much torque.

OK the real reason is that sb doesn’t have 18T for my rack anymore. But I was leaning towards the 20t. Really..

I can’t wait till they get here to see just how bad they were affecting the quality of my cuts.

Thanks again for all the input, this forum is priceless.

Sean