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seana
08-16-2006, 05:50 PM
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
08-16-2006, 11:58 PM
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
08-17-2006, 01:35 AM
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
08-17-2006, 01:59 AM
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
08-17-2006, 07:53 AM
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
08-17-2006, 12:53 PM
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
08-17-2006, 03:39 PM
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