View Full Version : Vee Bearing Tracking

10-29-2005, 08:23 AM
Hi Guys, I just noted on my PRT96 that my y axis, in 1 direction only (y negative) that 1 (and only 1) vee bearing is climbing the rail (a leading bearing). I have tried to loosen this side of the bridge and re-tighten it with everything seated properly... to no avail. It is putting my cuts in that direction out of z depth by approx. +0.1000". As soon as I travel in the y positive direction, all bearings are seated.
Any thoughts as to what I should try/look for next.
Thank you.

10-29-2005, 08:43 AM
Perry, my first guess is that the rails on the Y axis are not parallel. You do not say on which side the vee bearing climbs, outside or inside. I would bet the farm that the neg Y rails are either slightly closer together or slightly further apart than the distance at the other end. Sounds like the rails at the positive end are the correct distance apart.


10-29-2005, 08:43 AM
Opps, hit the enter key twice. Duplicate post

10-29-2005, 08:44 AM
Hmm. Once you have made a post I see you can't delete it.

10-29-2005, 09:09 AM
Perry, my guess is that a wheel (or hold-down roller) is not aligned to the rail - its axis is not perpendicular to the rail. Running one way it squashes the flexible rails together, but the hold-downs stop the movement. Running the other way it bends the rails open and nothing stops that. Or something like that.......

10-29-2005, 11:51 AM
Thanks guys for the posts. It gives a "new" starting point. I have a couple of jobs on the cnc right now I have to get out and this issue is not affecting the results for this job. Once I get caught up I am tackling this issue to try and resolve it.
Thanks again.

10-29-2005, 12:15 PM
Perry, your car may seat better if you remove the hold-down rollers altogether - we have run without them for a long time already.

10-29-2005, 02:47 PM
Gerald, where do you get your knowledge? You were absolutely correct. I stopped the jobs because it just bothered me to know that my PRT wasn't running well. I took a more careful look and low and behold (1) hold down roller wasn't running true. I loosened it away from the rail and the y axis is running proper again. I don't know what has happened or changed that instigated this, but I am glad for this community and the assistance that it provided in resolving this issue.
I also wish to thank Jay for his prompt return to my post. It is the individuals such as yourselves that makes Shopbot a truly united community.

12-06-2005, 02:41 AM
hi guys, i am having a problem with my prt . when running a program the x car gets stuck, sometime stopping completely othertimes missing steps , we have had the machine for a year and it only has started in the last month.

12-06-2005, 02:52 AM
A banana Shark!

Derek, if you loosen the turnbuckles, unhook the springs, swing the motors down free of the racks - does the x-car roll freely?

Does it always happen in the same spot? Maybe a chunk of dirt stuck between the rack teeth?

Are both of your x-motors driving? Maybe one is faulty and causing a load on the other. If this is the case, then check wires/cables for good connections. Then there is also the possibility that a driver is dying.....

You can call me at Cape Town 448 8872

ron brown
12-06-2005, 07:52 AM
Possibly clean and grease the rack.


04-03-2006, 12:13 PM
Does anyone know where to get the hold down roller bearings on the bottom of the channel? (On an older PR upgraded to a PRT)

There is no numbers on them and they appear to be patio door wheels??!!

Any help is appreciated!



04-03-2006, 12:33 PM
The early SB's did have patio door wheels. link (http://www.talkshopbot.com/forum/messages/28/1528.html#POST8917)

04-03-2006, 12:51 PM

As always, thanks for the help. I searched for lower roller bearing - just didn't put in patio door wheels!

Thanks Again,