X Axis Gib Strip

[digitalmdj]

Today I decided to check my Gib strips for straightness. Well it seems it is bowed like a banana. I cant understand how they could have adjusted the gibs with this wear strip. The quality is showing with ever piece I inspect.

[dahui]

My gib strip was probably the worst thing on the machine. I don't even know how you could get it so bent! I just started over and made my own.

However, this brings me to a question I can't figure out. When I was going through my "x axis rocking" dilema everyone said check the gib and make sure it's straight!

I can't, for the life of me, figure out why it really matters if the gib is straight or not. The adjusting screws only touch at each end. The gib is so thin I'm sure it's easily flexed by adjusting the screws. So, if it's bowed in the middle, wouldn't adjusting it mean that it's touching at each end and that's all that matters? The travel might not be very smooth with a bowed gib, but having each end of the gib adjusted to touch the ways should eliminate the rocking (if that was/is the issue of course). Any armchair (or professional) engineerists out there that can explain this one? We are also talking about a shoptask, not some swiss high speed mold making machine.

[digitalmdj]

Lets start with the basics. A gib strip is acually a bearing surface. And that surface rides on a film of oil. The more surface area the more support for the table and the smoother your table will ride on the film of oil between the gib and the ways. If you have a bent strip the lack of oil surface causes drag. And you will have to tighten the adjusting screws much tighter to keep the table up against the ways. Now you have friction causing heat and tight spots in your X Axis .

[fastlanecafe]

Digitalmdj is right about that. If it is bowed in the center, your table will rock until you tighten the adjusters tight enough to take out the bow- by then you will hardly be able to move the table. The gib is made of a much softer material than the ways, so the wear will always be on the replaceable part. I bought my machine used and the strips were pretty good, but after a while I found they began to bow a bit- I suspect it was from tightening the lock handle too tight. I took them out and laid them on the mill table and used a feeler gauge to measure the bow- then I just used a little hand pressure to bend them back a bit- After I was close I used a belt sander to get them flat. I also noticed that the serial number stamped on them had caused the surface to raise a bit and the sander took care of that. Now I use a little caution when tightening the lock.

[digitalmdj]

My gib strip had to be straightened out using a press. There was no number stamped on it also. It is has taken several days of sanding with 220 grit on a granite lapping block to get it close to being straight. I had to lap both sides so I can check it with a micrometer. It is still thick in the center by a few thousands.

[sharpshooter90]

Part of the problem may be that they are making these out of hot finish material. If they only grind the side that slides along the bed, the surface tension of the unground side will eventually pull it into a bow. I would suggest you straighten it as close as possible and then take it to a surface grinder and do both sides. That will relieve any surface tensions and it will most likely remain flat.

[dahui]

Ah I like that last part about surface grinding both sides. How about stress relieving in an oven? Okay new shopping list: surface grinder, heat treat oven.

So yeah, a bowed gib will not be smooth, but for arguments sake, you should be able to adjust out any rock even with it bowed right? As in...a bowed gib that has been adjusted should not rock, irrespective of how smooth it runs. Not a big deal. I just have an obsessive compulsive need to understand how things work.

My gib didn't have a serial number so you got me beat there but all the countersinks were drilled on an angle that was not parallel to the gib itself. I'll bet that didn't help. Did anyone else make a new one? I thought it was a pretty fun project.

[mixdenny]

In principal it should be possible to flatten the gib using the adjusting screws and remove any slop, at the expense of high effort. If the gib is not a constant thickness that also presents an issue.

By the way, the set screw dimples are supposed to be at an angle, so they accept the tip of the adjusting screws properly. I replaced my adjusting screws with cone point set screws from McMaster-Carr and also changed the lock nuts for good quality thin ones. I think you have to buy a box of 10 each, but they are cheap anyway.

The gibs on my 2000 Eldorado were dead flat and quite smooth, guess I got a good one. I did have a bit of a tight spot on the ways, but I was able to smooth that with a small stone on the underside of the ways. I still have a bit of tightness when the carriage is all the way towards the headstock, but I hardly ever work there.

John Stranahan's rebarreling/Shoptask book goes into his methods of finding where the ways are high and scraping them to be level.

Dennis

[digitalmdj]

I finally got my gib strip flat and polished. It took quite some time to get it just right. I already bought new adjusting screws from the bolt depot awhile back and some hardened nuts. I can shape the tips if necessary with a tool grinder to get the right pitch. I just checked my Y axis gib strip. It is bowed in the center also. I believe the strips were adjusted wrong and the center is the lock down for the table. They must have over tightened it causing it to bow the strip.