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adjusting gib on machine vice

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Frank Small18/11/2010 20:07:34
25 forum posts
3 photos
Hi Guys,
I have a Deckel lookalike milling machine with its own excellent vice 
The gibs on the vice need adjusting as the workpiece tilts badly when vice is tightened. There is multiple set screws for the gib and wonder if there is a good way to carry out the adjustment
Thank you for your interest
Regards
FS
Steve Garnett18/11/2010 22:44:55
837 forum posts
27 photos
Well, in the absence of anybody else telling you about gib adjusting, I'll tell you what I do - others may be able to improve on it though:
 
With any gib adjustment at all, the idea is to keep the force applied by the adjusing screws even along the gib, so that it's not just a close fit at the ends, but in the middle as well. In my experience, you need to slacken them all off, readjust them till they just nip, and then very gradually increase the force on each one in turn until you still have reasonable movement available without having to apply undue force to achieve it - and that sometimes takes a few goes until you get it right!
 
The other thing about gib strips is that the smoother you can get the gib and its mating surface, the easier it is to have a reasonable grip but still be able to move the slide. So it's worth polishing both by the best means available to you. I use a fine stone on gibs, and then buff them afterwards. The other thing to consider is lubrication. Some say grease, but the instructions that came with my lathe say that light machine oil is what you need.
 
Other people's mileage may vary!
Andrew Johnston18/11/2010 22:55:07
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7061 forum posts
719 photos
I'd second the use of oil for lubrication; use slideway oil. Grease is much too thick, and the swarf will stick to it like s**t to a blanket.
 
I used to spend ages adjusting the gibs on my machine vice to minimise jaw lift, and then it was stiff to operate. In the end I bought a vice that doesn't have the problem, or at least I can't measure it.
 
Regards,
 
Andrew
Clive Foster18/11/2010 23:43:21
3630 forum posts
128 photos
Its far easier to feel what's going on when adjusting gibs if you can remove or disengage the screw letting you test by sliding back and forth by hand.  Gives a much better feel for WTHIGO, especially if there is a sticky bit.
 
Especially with an unknown history component I'd advise doing the strip, clean, careful inspection and make sure it all fits right without binding thing before trying to adjust gibs.  In particular remember that the old, gone off oil, dust, stuff, swarf and gremlin poo mixture which builds up everywhere that isn't positively swept out can take a deal of removing.  Keep your thinking cap jammed on tight and visualise where the nasty stuff gets swept to during the operation of the slides.  On small lathes I've often found that alleged "lots of play 'cos its worn out" is actually due to only part of the travel being covered by back'n forth movement allowing  thous of "stuff" to build up in the rarely traversed areas.  Darned hard too.  Vices suffer in the same way although its harder to feel.  Usual symptom is holds nicely over part of the travel but pants where you normally use it.  I like to undercut the dovetail sharp corners a fraction with a couple or three strokes of a saw blade or three square file and remove the sharp edges from gibs.
 
Check the gib to see if its straight and flat and inspect the pressure point dimples where the screws act for smoothness and clean shape. Similarly inspect the ends of the screws.  Bent and battered screw ends working in manky dimples destroy any chances of good adjustment.  If you find such damage it is perfectly acceptable to comprehensively curse the perpetuators.  Seems to be a Gib Screw Over-tightening Fellowship out there. Also inspect the alignment of the gib where it rides on the adjustment screws.  Its not uncommon to find one or more screws a touch out of line or a slight skew on the gib so it drags on the top of slot.
 
Don't be afraid to re-make a damaged gib, not difficult as the material isn't critical.  Flat with a decently hard surface are the main criteria steel, brass, bronze are all fine, but it does need to be as thick as possible.  Ideally all but filling the gap so it is stiff to slide in.  Best way is to get ball ended adjusting screws and use the common slocombe centre drill operating through the screw holes to make precisely aligned conical recesses for them to work in.  Carefully shape the top edges of the nascent gib and push it tight up into the top of the slot when drilling.  Good idea, if you feel up to it, to add a dowel to stop any tendency of the gib to float back and forth on the screws.  The dowel works fine with the usual pointed gib screws but their condition and alignment must be beyond reproach.  A carefully re-made, fitted and doweled gib with ball ended screws can run at rather tighter clearances than the usual variety. 
 
Clive 

Edited By Clive Foster on 18/11/2010 23:46:15

Frank Small19/11/2010 09:58:03
25 forum posts
3 photos
Hi Guys,
Many thanks for you interest.
The history of the vice is unknown and hence the clean, stripdown inspection and repair is important. Without your input I would probably have spent a lot of time just trying to carry out the adjustments.
Regards
FS
 

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