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DFMiller
12-13-2011, 07:00 PM
I am continuing to fine tune (Fix) the Z axis Gib on my KX3. :-(
It seems to me the length of the gib should be the length of the saddle minus the adjustment length of one screw. This would allow the gib to be adjusted so that both Adjusters are recessed in the bore that they run in. Am I correct in this assumption.

If you don't do this one of the adjusters is always not in the bore in the saddle as free to bend when tightened.

The Gib is currently full length and of course the screws are bent in a attempt to keep the gib from sliding around. When it moves it locks.

The gib also is steel not Cast iron so it does not slide that well.
I guess I am going to have to shorten the gib and maybe reduce the friction.

Thanks
Dave

Fasttrack
12-13-2011, 07:46 PM
Reducing the length of the gib won't reduce the friction (noticeably). Friction is not (to first order!) proportional to the surface area between the materials. This approximation is not so good when dealing with bearing surfaces that are coated in a lubricant, but in that case we typically expect a reduced surface area (i.e. smaller gib) to be a bad thing because the reduced area means you are exerting more pressure on the oil film.

Ok ... so that didn't answer your question. I think you should look at making a new gib out of cast iron. There are several people here who are more qualified to help in that endeavor than I, but when I get a chance, I'll post a summary of what Connelly has to say on the matter (from Machine Tool Reconditioning).

If I understand you correctly, the gib protrudes from the saddle as it is adjusted. Typically, a gib is made long and then trimmed to fit the component and adjusting screw.

DFMiller
12-14-2011, 01:50 AM
Fastrack,
Thanks for your comments.
The real issue and fault with the design is the adjusters screws are too flexible and will not hold the gib properly if the heads of them are proud of the saddle. The saddle has a bore that is 25mm deep on each adjuster. With the existing length of gib that means about 1 mm of adjustment either way before one of the screws is not supported in the bore and thus can bend a distorted and do not allow for good adjustment not locking the gib properly.

This is why I am thinking of shortening the gib to allow for some adjustment. I will try to post a sketch to make this more clear.


I have Connelly and will look at it but there is many knowledgeable people here.
Thanks
Dave

DFMiller
12-14-2011, 02:08 AM
Here is a real quick SW model to illustrate the issue
http://i560.photobucket.com/albums/ss47/ve7pke/Misc%20Machining/KX3section.jpg

Gray is column
Red is gib
Pink is saddle
Yellow is adjusters

Shorten gib and the adjusters will stay in the bores and not move around.

Dave

Peter.
12-14-2011, 06:45 AM
Seems easy enough to me - if the gib is being adjusted 'downwards' to compensate for wear, machine it at the bottom to bring the head of the adjuster up into the hole in the saddle.

DFMiller
12-14-2011, 05:31 PM
Thanks Peter,
Just looking for someone to tell me I am on the right track or wrong one.
It does seem to be very simple what need to be done. Just picked up some 30mm SHCS so I will make some adjuster screws first. Then hack away.
Thanks
Dave

Fasttrack
12-14-2011, 05:38 PM
I read your earlier thread. Clearly you know what you're about!

I wouldn't hesitate to cut the gib down a tad. Your bearing surface will be reduced by a little bit, but it should be a complete non-issue here.

DFMiller
12-15-2011, 01:51 AM
Thanks,
You have more faith than I do on this one. ;-)
Is hall report back.
Thanks for your suggestions.
Dave

Boostinjdm
12-15-2011, 01:55 AM
Shorten the screws. They're easier and cheaper to replace than a gib.

DFMiller
12-15-2011, 02:17 AM
Shortening the screws will not do anything. In fact if you shorten the screws given the length of the gib they won't even screw in. Shortening the gib is the only solution to this problem.
If you look at thei true the red is the gib. It's preventing the screws to screw into the bores.
Thanks
Dave

Boostinjdm
12-15-2011, 02:26 AM
You're pic doesn't show up well with my monitor problems. I thought the end of the screws were pushing on the gib. It sounds like its the heads doing the pushing. If that's the case, then just make the notch on the narrow end of the gib a little deeper.

DFMiller
12-15-2011, 02:31 AM
Sorry the picture was not clearer. Yes we agree on solution. I will do that after I make new adjuster screws as the originals are bent after my messing around.
Thanks
Dave