Gib Strip

[ptjw7uk]

Hi All,
Been making chips this weekend both in material and cutters! Busy enlarging the slot in my new QCTP holders when at the end of one cut the cutter grabed the holder, stopped the cutter and blew the fuse to the motor. The y axis was then very sloppy. So I cleaned all the chips cleaned everything and then readjusted the jib strips so all were snug, I then noticed that the gap behing the gib strip was wider than the gib strip itself. I remember in the past that all the lathes I have ever used the gib strip was quite thick and did not have a lot of clearance behind it. I realise that metals are getting scarce but the 1/16 inch strip is a bit penny pinching.
So should the gib strip be quite substantial and fill most of the gap in the slot.
Peter

[pcarpenter]

Details? What kind of lathe? Has it been apart before such that a filler strip could be missing? Is it a tapered gib or straight gib that has multiple screws for adjustment and locking?

Paul

[ptjw7uk]

Sorry it is my little X1 milling machine with straight gibs.
Peter

[pcarpenter]

So are you saying that the gap is perhaps bigger than it should be both front and rear(as opposed to just one end)? If that's the case, I would consider making a new, thicker gib. The trouble with that gib design is that reasonably you must have little indents in the back of the gib strip itself for the adjustment screws to ride in. On a thin gib, this can make it even thinner and make that a spot prone to breakage. I suppose that anohther possibility is to make a backer strip with the indents in the backer to go behind what you have. In a sense it would be a gib for your gib

If the gap is different at one end than the other, there is the possibility that you broke the gib during the crash.

I have it on a list of things to do to get or make some plastic insert type locking set screws for gib adjustment on my little lathe and mill. This takes out the hassle of adjusting for correct fit and then attempting to hold the screw carefully while you tighten a locking nut. With a sort of locking set screw which is under friction all the time, you can more carefully adjust for good fit.

Paul

[ptjw7uk]

Yes the gap looks to be very excessive in that it looks as if it could pivit on the adjsuting screws, I suspect that the Y axis divetail has been cut under size.
I will have to machine a thicker gib have to think about this as the dovetail is 55 degrees not 60.
I have bought a spare Y axis unit so I could invert that and hold some gib material in that.
Peter

[John Stevenson]

Peter, no reason why you can't get a bit of thicker cold rolled, file two angles on the edges so it slides in and holding the strip with one screw drill through the others to indent the strip.

Fit a simple stop on the drill bit of a piece of bar with a grubscrew in the side to stop it going too deep.

Then fit a screw into a indented hole and do the original screw hole.

Carefully deburr, cover the face with a marker pen or layout fluid, fit and adjust, move the table, then undo the screws and remove the gib strip and check for rubbing.
Remove any high spots and repeat until it marks along the whole length.

.

[ptjw7uk]

John,
Thanks for that I will give it a go, I assume gib strips would be just plain old mild steel (thats all Ive got)
Peter

[Sparky_NY]

Its a pretty common mod on a X1 to make new gibs from brass by the cnc boys.

Here is one link to a X1, converted to cnc, with a custom made brass gib and pictures of the gib.

http://www.embeddedtronics.com/micromill.html

[pcarpenter]

Typically, gibs are made of cast iron which leaves them a bit brittle. This is the reason that your rather thin gib concerns me from a durabilty standpoint. However, you could remake it from bronze as mentioned. In the ideal, they should be scraped in to match the mating face of the dovetail, but given the original manufacturing method, I would advocate that if you mill it carefully that should be good. You could lap it on a piece of carborundum paper on glass, but you risk imbedding grit in the soft brass or bronze that way. I think I will just mill it and then stone it with a flat stone and let it wear in.

Paul

[ptjw7uk]

Finally made the new gib strips - used mild steel as the brass strip I ordered has not turned up.
A bit of strenuous exercise with a file and I mad the first one, had to make another as the first had shrunk(used the y axis as a measure and not the base?)
Upon screwing the adjustment screws in I found just where all the movement had come from. The 3mm screws used for adjustment had one end turned down to 1.5mm with a rounded end it was one of these ends that had bent so giving all the slack. Just another bad design I will replace these with some cap head screws when I can get some.
I looked at my lathe and the gib strip on that is 1/4" thick so thats not going to move.
Peter