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Table moves slightly when locked

mtdave

Plastic
Joined
Oct 19, 2017
I am seeing movement of .0005 - .0015" of movement of the table when I lock the table or saddle. After its locked, there is no movement.

The machine is an older series 1 that's been rebuilt. The gibs are adjusted and the leadscrew nuts have been taken up. Any thoughts on why i'd see this movement?

Thank you.
 
TADT

when trying to be fussy it usually takes a few tries to get it to stay at zero. This of course does not account for actual movement against the gib since the readout cannot see that
 
The machine is "older", and the gibs may be adjusted, but as they (and the table ways) are likely worn in the areas of heaviest use, no amount of adjusting will eliminate this issue. Whether the rebuild addressed these issues should beunderstood. I have a 1958 J-head with 36" table, and I frequently see movement in the DRO display when I lock the table up. On my other BPort (1990, chrome ways, 42" table) almost nothing
 
I've noticed that mine does the same thing. It seems to be most likely when there's a higher load on the screw, like when near the limits of travel in X or Y. My solution is to slightly slack the screw before locking the gibs. It's not infallible but it seems to help.
 
I am seeing movement of .0005 - .0015" of movement of the table when I lock the table or saddle. After its locked, there is no movement.

The machine is an older series 1 that's been rebuilt. The gibs are adjusted and the leadscrew nuts have been taken up. Any thoughts on why i'd see this movement?

Thank you.

I'm not familiar with BPs but whatever does the locking is not square to the locked thing. On a dirt cheap clone of mine the screw ends cause some of this by grabbing while being rotated. Bit of a knock with the dead blow and it's fine.
 
It's not going to help you because it's an aspect of machine design, but I've seen this addressed on precision machines by having the lock "float" perpendicular to the locked axis, while still rigidly restraining the locked axis. When you tighten up the lock, it places no (signficant) force on the restrained part.
 
Thank you for the replies. I'm relieved that it's somewhat "normal" for a slightly worn machine. I've been going nuts trying to figure out what was wrong. Thank you.
 
I am seeing movement of .0005 - .0015" of movement of the table when I lock the table or saddle.

Are you sure? Do you have a laser that you check that with? It's a DRO on a BP, if you want something closer, buy a CMM. Actually, a half thou is pretty good. A change of 0.001" on a DRO is quite common. Mine has done that since new.
JR
 
I'm inclined to agree with JR on this. A BP shouldn't be expected to hold position within .0005 like other machines that are better designed and more expensive. While it may be possible to hold a milling operation to +/- .001 it's not a good practice to expect it. The tram of the head, wear in the table/saddle, and even taper of the cutter are all working against the accuracy. Don't get me wrong, I've used BP's for many years and like the speed/versatility of a knee mill. But don't expect more out of it than it is capable of. For truly accurate positioning you'll want a better machine if you need sub .001 positioning. Something with ball screws (in good condition) or a jig bore can do this. You can also use different strategies to achieve the final level of accuracy like bore the hole and then use a surface grinder to final edge-to-center dimension if that's possible. There's also the time consuming option of using "toolmaker buttons" to achieve a higher level of accuracy where center-to-center distance is critical. The BP in my shop is certainly not capable of positional accuracy better than +/- .003 I just don't expect it to and use other methods for achieving a tighter tolerance when needed (jig bore). I like my BP but I also bear in mind that in some circles a BP is referred to as a graduated drill press.
 
I am seeing movement of .0005 - .0015" of movement of the table when I lock the table or saddle. After its locked, there is no movement.

The machine is an older series 1 that's been rebuilt. The gibs are adjusted and the leadscrew nuts have been taken up. Any thoughts on why i'd see this movement?

Thank you.

.
i have used a old jig bore every time i turn the motor spindle on it moves .0005 to .0010 seen on the DRO. a lot of old machines are like that
 








 
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