Ckickety Clack

[Mayo]

I have a PRT4896 which I purchased new in 2001.
It's got the Vexta PK296A1A-SG 7.2 motors with gear boxes as supplied by Shopbot at the time. The motherboard is V2.07 but a couple years after getting the machine, a driver blew out and (hard to remember that far back...) I think a small circuit board was replaced - that the driver chips mount on? I know it did not get a 4G upgrade but the board that was replaced was not exactly the same as the original one and I did have to change unit values. Anyways...

I really can't say when the clickety clack noise started - I've just thought it was "normal" for this machine. But the other day I was positioning the gantry without my ear protection on and I realized it's not constant and it's sometimes louder than other times. So maybe it's not "normal".

The noise happens when I move the gantry in the X direction only.
I don't hear it when I move the Y motor.

I have made sure the set screws are tight which hold the pinion gear to the motor shaft. I have tried loosening and tightening the spring tension that holds the pinion gear against the track. I have tried loosening and tightening the motor mount which allows the motor to pivot against or away from the track. None of these seemed to make much if any difference in the noise.

How likely is it that it's one or both of the X motor gear boxes?

It's possible that the pinion gears are worn however 90% of my cutting is on EPS foam, so there's not a lot of stress on the motors, pinion gears or track.
After getting grease on my shirt for the XXXth time, I stopped putting grease on the track. I know shame on me. Doesn't anyone make durable nylon or synthetic pinion gears that don't need grease on them?

I'm thinking of making a video of the machine moving so that the noise can be heard and that way it would be easier to determine if this should be considered normal for this model of Shopbot.

I know a lot of you will suggest that I upgrade, but this machine does what I want it to do and my production level is such that I'm not needing to produce faster.

Any ideas about the noise issue would be appreciated!

[bleeth]

Hey Mayo:
Time for new pinions. Keep it greased. Be more careful about where you lean.
That may or may not be the "clack" but it is true no matter what else is going on.
Probably not the 7.2's but they are the straight gear type as opposed to the tapered hob type that came a bit later. They will wear eventually and since they are far from one of Oriental's more expensive motors not a super major deal even if it is.
If it is still cutting to your satisfaction then forget the noise but do do the pinions and grease.

[Mayo]

After I posted the info above, I ran a test where I dropped one X motor but left it electrically connected. The clacking sound was greatly diminished with just one X motor moving the gantry. Then I repeated the test with the other X motor and got basically the same result - much less to almost no clacking sound.
I then reconnected them both and jogged the gantry and the noise returned.

So this affirms what Dave suggests - the pinions need to be replaced.

Is it OK to just replace the pinion gears and not the track?
I would think the track is probably equally worn.

[jimmya]

The track is probably ok, the track is harder than the pinions.

Jimmy

[bleeth]

Jimmy is correct-Rack is much harder than the pinions.

[Mayo]

Thanks for the replies guys. Here's an update on how it went.

I had to order the pinion gears from a company other than Shopbot because Shopbot didn't have the 30 tooth ones that my machine uses. They were over twice the money that I would have paid if I got 25 tooth pinions from Shopbot instead but I didn't want to wind up with a machine that cuts 20% slower. I only got the two X pinions (30 tooth) and the one Z pinion (25 tooth) and it was over $100.00.

Having the machine as long as I've had it, I guess that's pretty cheap for maintenance anyways.

I installed the new pinions on the X motors and it reduced the clickety clack but it's not eliminated completely. Now it's more like a rattle sound.

Any tips on changing out the Z pinion? It looks like I'll have to completely remove the Z carriage to take off the plate which holds the router, and which seems to block the access to the pinion gear.

[Mayo]

The last couple weeks I was noticing the clickety clack was back with a vengeance so I did some experimenting.
The sound seemed to be from the X motor on the Y=48 side of the table.
I loosened the spring tension and lowered the motor so that the pinion was not making any contact with the rack. When I did so, I noticed a slight shift of the Y carriage. I did not unplug the motor because I wanted to hear it running while it was not against the rack.

I then ran a few X moves up and back with just the one X motor engaged and there was no clacking sound.

Then I lifted the previously disengaged X motor back into place and at first it was not meshing properly with the rack. It felt like it was hitting tooth to tooth but after 2 tries, it slipped into place. I then tightened the tension spring just enough to keep the motor in place but not the recommended number of turns on the turnbuckle.

I ran a few X moves again and this time there was no clacking sound!
Success at last! Then I tightened up the turnbuckle properly and all is still good.

So if your PRT happens to be plagued by phantom clickety clack sounds, it may be from the pinion being one tooth out of alignment. I can't believe I could have been cutting things this way for such a long time and not noticing things being "off" looking but then again, I'm not doing highly precise cuts and most of my designs are "off" anyways.