X carriage motors

[GlenP]

Hi Everyone and Happy New Year. Lets all hope this is the Year of the Bot!
I have a question about tightness of motors to the gear rail. I have a 2 month old PRS 4896 and I can rock the x carriage back and forth around 1/8" of an inch when powered up. I try to move the Y carriage and it is tight as a rock. Should I remove the motor and try getting it up tighter with a clamp or is this a normal thing?? Other than that I love the machine, learning lots and hoping for a prosperious year.

[steve4460]

Check the screws on the gear that is attached to the motor are tight , and make shure it is pulled up against the rack before you tighten the mounting screws . check the manual for installation instructions.

Bot on

[srwtlc]

Glen,

Pulling them up with a clamp is going to be too tight and you'll notice more of a growl/vibration as you jog the X axis. Just good solid hand force has been the best for mine. A good greasing of the rack helps too.

One thing I found though that produced a similar situation was that where the ends of the rack are cap bolted through the rails, if they're pulled up tight enough that the double-sided tape compresses slightly, will cause the pinions to be loose at the ends of the rails if you tightened the motors away from the ends and just the opposite if you tightened them at the ends.

I pull/push mine up tight away from the ends and can notice just slightly more "backlash" at the ends of the rack, but that area seldom if ever gets used.

[fleinbach]

The most common reason for what you describe is loose pinion gears. Make sure both allen screws are tight.

The second possibility is if the mounting bolt for your motors is to tight or to loose. When properly tensioned the spring will hold the motor against the rack and you will not have any movement when pushing the car in either direction. The manuel calls for 2 1/2 turns after the spring begins to expand. If the mounting bolt is to tight when the car reaches a place along the rail that is slightly thicker the spring will not be able to compansate when it gets to a thinner section of the rail. If the mounting bolt is to loose the motor will twist from side to side allowing unwanted movement. To properly tighten the bolt without the the spring attached tighten the bolt enough to hold the motor from dropping. Then back off just enough to allow the motor to free fall. After that make your spring tension adjustment.

[pfulghum]

Pat's secret formula...

Tighten the allen screws on the pinion to a point where the allen wrench is just short of breaking.

Keep the rail greased and only 2.5 turns of tension on the spring.

[srwtlc]

The PRS machines, which Glen has, no longer have spring tensioners. They rely on you just pulling/pushing them up into the rack and tightening them down and the parallelness of the rails to rack. I think I would prefer some kind of spring loading though. Also, the pinions are keyed, but set screws should be checked anyway as if they are loose, you could start to wear the key.

[harold_weber]

Hey folks, wee need to have a consistent story on the number of turns to tighten the turnbuckles. Here are three different answers:

>My May, 2002 Edition of the PRT Assembly manual says to use 3 full turns.

> This ShopBot WIKI page says to use 4 full turns on PRT machines: http://shopbotwiki.com/index.php?title=X_and_Y_Axis

>Frank and Pat report above that 2.5 turns are required.

I don't care WHO is right, but I'd like to know WHAT is considered the best answer for PRT type machines. Does it matter whether its an Alpha or not? Does it matter what VINTAGE of PRT it is?