Y calibration

[bobbyc]

This machine is driving my crazy. I have been working with tech support via e-mail and telephone but so far no resolution. The problem is that the Y axis makes all of its cuts 1/16 inch short. It is consistent. The X axis is right on the money. I have cut 1 inch, 3inch and 10inch lines and they are all short 1/16 of an inch on the Y axis.

I have checked the following.
set-screw is tight.
rails on both the X and Y are equal distance along the entire lenght.
I am using a new 1/4 two flute end mill from Onsrud. I am cutting solid surface.
I have loaded the newest version of the software.
Any ideas???
PS I purchased the machine in March. It is a 48X48 PRT. I believe it may have been doing this from the inception. My initial cuts were outlines and it did not show up but when I tried to cut a 1 inch circles the top and bottom of the circle were somewhat flat. Its then that I cut the straight line and measured the two axis.

[steve4460]

Hi Bob

Check your unit values if you have an alpha the X,Y and Z should al be 1273.2395

bot on

[Brady Watson]

Bob,
If I had to guess, I would point fingers at the Y axis pinion. From what you are describing, it sounds like you have eliminated most of the common culprits. I would however, completely remove & replace (with new) the pinion on the Y axis, just to be certain that it isn't somehow defective. If you are out 1/16" on EVERY cut, then it sounds to me like the pinion is not seated properly and not completely tightened. You can think that it is tight...when it really isn't. The best way would be to remove it & replace, being sure to really crank down the set screws...this is why they give you 3 wrenches with a new tool...You should be ruining each one with the torque applied to the grub screws.

-B

[fleinbach]

Bob,

You did not mention how deep or how fast you were cutting. Due to the fact that the Y car has only one motor, there is slight flexing in the Y axis direction. This is most apparent when deeper and faster cuts are made. To see if this is the problem try making a very shallow cut in the Y direction. Just enough to score the surface of the wood so you can make a measurement.

Another way to make sure the Y car is moving the exact distance you are telling it to would be to make the measurement without cutting at all. You can make a reference mark of the Y car position using a piece of tape. Then move the Y-car say 10 inches. Now measure and see if the Y-car moved 10 inches. This will determine whether cutting forces or the tool itself is the culprit.

[bobbyc]

I am cutting 1/4 deep at 1 inch per second.
Brady, I like your idea about replacing the Y pinion. I will call shopbot today and order one.

[harryball]

If unit values were wrong the error would scale, i.e. at 1" of travel you'd be out 1/32" at 2" 1/16" and so on. I don't know if you tried that test.

If it's always 1/16" error I'd go with slop in the carriage like the loose pinion suggestion.

Also, don't forget to check the actual gear rail for damage or if it is somehow loose and sliding.

Robert

[fleinbach]

If you checked for tightness of rack and pinion and there is no detectable movement when manuly trying to move the Y-car, then measuring the actual distance the Y-car moves when not affected by cutting forces will clear up any software issues. If the Y-car moves the proper distance when not cutting and everything else is tight it can only be deflection from cutting forces.