Taper Gib

[groundhog719]

Trying to get play out of the Z axis On my used X4+. When adjusting the tapered gib it seems like it is either loose or locked. Not much in between.

The adjusting screws for the Z tapered gib were all bent to hell (from previous owner). I made 2 very thick washers to use instead. I can't really see a reason for the top screw to be able to move the gib up - you can do that with the bottom screw. Also, the gib didn't appear to be thick enough and needs to go down further than the stock screw would allow. Please correct me if I'm missing something. See first 2 pictures.

On initial inspection there was no contact on the wide part of the gib. Just on the narrow part that contacts the column. That didn't seem right to me. (Didn't take pictures of initial inspection). So I started sanding the narrow side down to force the wide side to contact the column. As you can see in the pictures I am finally getting pretty good contact on the wide (tapered) side. Still have contact on the narrow side however. And still don't have much leeway between loose and solid.

My questions are; am I on the right track? (I was pretty sure at first, but starting to question myself). Do I need to keep sanding the narrow side or is it always going to make some contact with the column? Should I be able to get all of the play out of the head (if I put a screwdriver between the table and the spindle I can pry the spindle and entire head assembly up 0.020 or more.









Thanks!
Groundhog719

[neilw20]

Are you saying the yellow bit moves relative to the dark bit? It shouldn't.
The top and bottom screws have a purpose.
You loosen one, move the gib with the other, then lock the first one.
Bottom one moves the gib up. Looser I think, top one moves it down.
Once in the correct position the screws make the gib captive.
The gib should never be able to move up and down.
My SX3 Z moves about 0.002" max, and when adjusted gets close to 0.001".
I measure by moving the head down, touching the DTI, then zero the DTI and the the Z DRO.
Now jog up in very fine increments. (ctrl and arrow keys - setup with TAB key) The head will keep moving DOWN !
Once it stops moving down, the indication on the DRO is how much I measure.
I really am measuring the head 'bob' and the smaller that is the better it is. The more play in the gib, the worse it will be.
If the gib is too tight, then you start to measure other deflections as it is getting stuck.

This is a FEATURE of this column arrangement.
I just program the measured error into my Z moves for finish cuts.
I repeat to 0.0001" all day, once machine is warm.
I cheat by a factor of 20. The top of the column is solidly attached to a brick wall. Without that, it is a bit ordinary.

[groundhog719]

Guess my post is confusing.

The gib and head move together. I am using the top and bottom screws to move/adjust the position of the gib and then to lock it to the head (yellow). What I meant by loose and locked is the head relative to the column. It was impossible to get the head to move without much play - it would either move freely with play or was locked tight to the column. Either way the gib had no movement relative to the head.

The first thing I saw when using dye was that there was no contact between the tapered (wide) side of the gib and the column. The last picture shows this (wide or tapered) side, only the picture it shows good contact area. The only contact was on the narrow side (3rd picture) - (the side facing you, not the top side in the picture).

The old top screw (because of being bent and deformed) would not allow the gib to be adjusted downward enough to tighten the head. The new washers correct that.

So, my question is; should the narrow side of the gib (3rd picture) contact the column at all? It seems to me that this contact might be stopping the tapered side of the gib (last picture) from contacting the column with 100% of the force needed to properly adjust the play between the column and head. In short, should I keep sanding the narrow side of the gib until it shows no contact with the column?

Sorry for being such a long post & thanks for the help

Groundhog719

[neilw20]

Is the column damaged? It needs a really good surface that is parallel.
Putting the head right down or up, you can put some ground rollers in the groove and measure from side to side with a micrometer.
Use short rollers, and measure in lots of places up and down the column.
It will get stuck if it is not smooth, flat or out of parallel.
You need to get rid of any damage without making it out of parallel.
Or get carried away and use Turcite B.
http://www.mtsandtg.com/specialty/products
If you use that stuff, you can actually have preload on it and it still moves. It is Teflon. Maybe a strip on the gib. Might work. I'd like to know if it does on that column.
Fair bit of work to implement though without some precision grinding capability.

[Ed from NY]

On initial inspection there was no contact on the wide part of the gib. Just on the narrow part that contacts the column. That didn't seem right to me. (Didn't take pictures of initial inspection). So I started sanding the narrow side down to force the wide side to contact the column. As you can see in the pictures I am finally getting pretty good contact on the wide (tapered) side. Still have contact on the narrow side however. And still don't have much leeway between loose and solid.

I think only the wide side is supposed to make contact. It is also strange that the adjusting screws would be bent -- hopefully it is not damaged. I would take the head off the column and inspect the surfaces on the column and head as well as the bits and bobs of the gib adjustment. You can use a straight edge to check if any surfaces are bent or warped. To see if the column ways are parallel you would need a pair of gauge pins (about 3/8") and the right size micrometer.

[groundhog719]

Ed,
I took the head off & checked most everything initially. Didn't check to see if the column dovetails are parallel. I might do that this weekend if all else fails.
I took some more off the narrow edge and it is improving. I don't think I will ever get rid of the narrow side rubbing a little, just from the way the adjusting screws push on it from one side. (Might be interesting to make something to push on the whole end of the tapered wedge instead of just a corner?)
It looks like the screws were bent by the PO trying to adjust the wedge by tightening the top screw without loosing the bottom screw. I didn't try to straighten them as I figured they would just break when straightened.
Anyhow, I think that the narrow edge making contact with the column is/was not allowing the tapered side of the wedge to move into position to adjust the play. I'll update this post when I find out for sure.
As for turcite, we have several hundred turcite bushings on a ski lift where I work. As far as I'm concerned it isn't any better than a properly lubricated bronze bushing and while it is harder it is far more brittle. The only advantage I see is that is does not need to be lubed.

Groundhog719

[groundhog719]

Follow-up if anyone is interested.

The gib was definitely bottoming out with the narrow side against the flat part of the column, not allowing the tapered (wide) side to be adjusted against the dovetail.
After removing material from the narrow side, the tapered side is contacting the dovetail properly (as I see it anyway).
The end result is that the head is now adjusted (more or less) properly as to play and movement.

Groundhog

[neilw20]

That should work better.