How about some advice on lost motion :)

1992 fadal 4020, I'm trying to find where my lost motion is coming from, other then the thurst bearings. My question is, to check motor couplings can I grab the end of the screw (I'm working with the Y axis) and twist back and forth? Should it move at all? It was a trick to convert the little motion it has into set numbers, but this is how I (think) I did it.

I took a indicator holder (just the holder) and clamped towards the end of the ballscrew. Theres a flatspot on the holder which is the surface I indicated on using a .0005 test indicator, mounted to a magnetic base and placed on the y axis boxway. (Both the holder and indicator are positioned perpendicular to the screw.) When I would twist the screw, the flat spot on the holder would actuate the indicator. I figured my high number from twisting one way and the low number when twisting the other way. I then jogged the Y in tenths until the same differance was achived from the hand twisting technique.

I came up with .0004, which accounts for the extra lost motion.
.0016 at the table and at the ball screw
.0011 on the end of the screw (thrust play)

I hope my "test" is somewhat understandable. Does anyone have another way to check for lost coupler motion?

If I put bearings in and then did the old push and pull technique and came up with no movement in the table but had .0004 backlash when jogging or running a BL program, that would more or less tell me its the coupling or motor, right?

I would like to test the Z somehow but with the weight of the head, I doubt my test would work well.

Thanks, Andrew

you need to put the indicator on the lead of the ball thread, take the handwheel, and rapidly reverse table travel directions or come up against resistance going both ways. The indicator from the table to the ball lead should be within 0.0001-0.0002( sometimes get this much flex off a mag base ) or your ball nut is on its way into history. The coupler,,, never had to test one,,,,,, but if you make a 2 pc shaft collar with a flag on it, clamp it on the ballscrew, inicator on the flag from mahine base, should be able to go +/- on handwheel and repeat readings pretty well.

Andrew,
Tools needed: test indicator .0001" and a mag base with an fine adjusting screw.
Start at the sourse of power and follow the movement.
Check the motor coupling to ensure it is tight.
Then, mount the indicator on the slide so you can look at the thread of the lead screw.
Use the handwheel and move the axis plus and minus while observing the indicator.
(This would be checking the ball nut and or the attachment of the ball nut to the slide.)
You should see very little indicator movement, less than .0001 or at the most .0002".
Then mount the Mag base to the base of the machine and indicate the end of the lead screw.
Again using the hand wheel move the axis plus and minus. At the point of reversal, you should see no movement on the indicator. A reading here would indicate bad mounting bearings on the screw.

Another method for this would be to mount the indicator the same places but try to move the slide with a prybar. I sometime use a precision grade wooden 2 by 4. Using the 2 by 4 saves scratching up the paint on the machine.

Don't let lead screw reversal error comp muddy up the water.

Many times, ye old 2 by 4 method works best on a slide that has a counter balance..
Keep in touch.
Regards Walt...