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View Full Version : How to sort this? Tapered jib adjuster.



Peter.
08-18-2010, 06:14 PM
I have had the x and y slides off my Herbert mill. I've been chasing a problem with the y-slide sticking in one direction, and when I stripped off the table I found that the slot in the gib was .015" wider than the shoulder on the adjusting blt, so when winding the bed towards me the gib was pulling into the taper and making the movement tight. I've sorted that out by turning a .015 shim on my lathe and using that to pack out the clearance in the adjuster.
My problem is, the x-slide jib slot is also a loose fit but only a few thou. I can't make a spacer that thin so how will I take up the slack? I had thought about 'bruising' the gib either side of the slot with a center-punch (on a part that doesn't contact the ways) but this seems like a bit of a cowboy fix, so I'm looking for better ideas.

DannyW
08-18-2010, 06:47 PM
Peter,

The setscrews for the gibs should have a sharp point instead of being flat.
Also the indentations in the gib should match the pointed setscrews.
I take it that yours are flat bottomed and wiggling around in the gib due to play, so the gib pulls itself tight?

Danny

Toolguy
08-18-2010, 06:50 PM
Make a new adjusting screw with the head a close slip fit to the gib slot.

Peter.
08-18-2010, 07:02 PM
DannyW - the gib isn't adjusted by opposing set-screws, it has a single bolt with a collar on it that works in a slot in the gib, the same as the adjuster on some boring heads.

Toolguy - I'll give that some thought, though my lathe only does metric screwcutting and the mill is all-imperial.

Lew Hartswick
08-18-2010, 07:02 PM
Peter,

The setscrews for the gibs should have a sharp point instead of being flat.
Also the indentations in the gib should match the pointed setscrews.
I take it that yours are flat bottomed and wiggling around in the gib due to play, so the gib pulls itself tight?

Danny It's not that type of gib. He has a tapered gib and a "push-pull"
screw that moves it in-out.
...lew...I see Peter beat me to it.

MuellerNick
08-18-2010, 07:09 PM
The setscrews for the gibs should have a sharp point instead of being flat.


The OP was talking about a tapered gib. That's a different game.
And good adjusting screws for flat gibs are not pointed. They do have a pin that is sitting flush on the gib. This pin is adjusted with a corn screw.



the x-slide jib slot is also a loose fit but only a few thou.

Adjusting screws for tapered gibs usually have one screw at each end (better design) or they have a single one (your design).
Now, if you have a 0.02 mm play and consider that the gib's taper is normally 1:50 you'll find out that this minimal difference in width (0.02 mm / 50 = 0.0004 mm) is absolutely neglectible.
BUT! You might have much more longitudinal play in the thread.

Say you want to accept 0.001 mm in width (and that is really a low value), you can have an added up play (slot and thread) of 0.05 mm. Even 0.1 mm won't hurt you.

Hope you know now what to look for.

Edit:
Right answers while I opened my beer. :)

Nick

DannyW
08-18-2010, 07:18 PM
It's not that type of gib. He has a tapered gib and a "push-pull"
screw that moves it in-out.

K, got it. New set screw it is then.
Or you could persuade those "few thou" to move over, closer to the bolt flange.
:rolleyes:

Danny

Peter.
08-18-2010, 07:31 PM
The OP was talking about a tapered gib. That's a different game.
And good adjusting screws for flat gibs are not pointed. They do have a pin that is sitting flush on the gib. This pin is adjusted with a corn screw.




Adjusting screws for tapered gibs usually have one screw at each end (better design) or they have a single one (your design).
Now, if you have a 0.02 mm play and consider that the gib's taper is normally 1:50 you'll find out that this minimal difference in width (0.02 mm / 50 = 0.0004 mm) is absolutely neglectible.
BUT! You might have much more longitudinal play in the thread.

Say you want to accept 0.001 mm in width (and that is really a low value), you can have an added up play (slot and thread) of 0.05 mm. Even 0.1 mm won't hurt you.

Hope you know now what to look for.

Edit:
Right answers while I opened my beer. :)

Nick

Thanks for the explaination Nick, if that's the case I'll leave it alone, the x-gib never gave me any sticking problems at all, but the y-gib with it's 15 thou play and steeper taper certainly stuck every time I tried to wind it out.

oldtiffie
08-18-2010, 08:21 PM
I have had the x and y slides off my Herbert mill. I've been chasing a problem with the y-slide sticking in one direction, and when I stripped off the table I found that the slot in the gib was .015" wider than the shoulder on the adjusting blt, so when winding the bed towards me the gib was pulling into the taper and making the movement tight. I've sorted that out by turning a .015 shim on my lathe and using that to pack out the clearance in the adjuster.
My problem is, the x-slide jib slot is also a loose fit but only a few thou. I can't make a spacer that thin so how will I take up the slack? I had thought about 'bruising' the gib either side of the slot with a center-punch (on a part that doesn't contact the ways) but this seems like a bit of a cowboy fix, so I'm looking for better ideas.

Peter.

I agree with Nick generally.

If the taper in the gib is 1 in 50 then in theory the "side-play/clearance" between the gib, the apron and the dove-tail will be 1/50 of the end-play.

There has been no taken account so far of the back-lash/end-play between the gib adjusting screw and where it screws into the apron, but it, like the end-play in the gib is of no real concern.

When a "Y" slide wears (both sides) and the wear is "taken up" by the gib (which is all "one-sided") the alignment between the lead-screw, the lead-screw nut and the bored hole for in the apron for the "Y" lead-screw tends to get mis-aligned.

This will cause some "jambing/tightening" between the lead-screw and its bearing/hole in the apron as the "Y" nut "walks up" toward the bore/hole as the "Y" slide causes the table to move out toward the operator.

The gib should have been set with the lead-screw removed. Any change with the lead-screw installed should have been caused or attributed to the lead-screw.

If there lead-screw is rubbing excessively in its hole/bearing it will be working against the gib and its adjustment.

I'd suggest either removing the lead-screw or slackening-off the lead-screw housing and pushing and pulling the table forward and back in the "Y" direction and see if it makes any difference.

If it does, and if it seems that the lead-screw is binding in the bearing/hole you will have to make a judgment call as to whether you ease/adjust the lead-screw clearance in its hole/bore or just put up with it.

It may be possible to loosen the lead-screw nut and to re-position it to get a better fit and feel.

After a bit of normal wear and tear, a slide and its gib will wear with most wear where the most use is or was - normally about the middle of the slide. In that case, gib adjustment can only achieve a compromise between being "tight" at the ends of the table/apron travel and a bit looser or "slacker" in mid travel.

The same applies to lead-screws and nuts.

djc
08-19-2010, 07:12 AM
...the x-slide jib slot is also a loose fit but only a few thou. I can't make a spacer that thin so how will I take up the slack?

I see you are sorted now, but one option is to reduce the thickness of the shoulder on the adjusting screw such that it suits a wider shim that you do have. Conversely, make the slot in the jib wider...

Buy a set of cheap feeler gauges; these make excellent shimstock. Drill inside or turn outside while sandwiched between two pieces of thicker material.

Duffy
08-19-2010, 10:52 AM
Just a thought. I have noticed, particularly on Off-shore machinery, that the tapped holes for adjusting screws are often a "toss fit" with the screw. Would it help, since a new screw is proposed, to drill and CAREFULLY tap for the next larger thread size, for the gib adjusting screw?
I have a Tiawanese mill/drill and it seems that there is about a half turn of slack in the gib adjuster screw threads.

Peter.
08-19-2010, 01:44 PM
Thanks for the replies guys - sorry I haven't kept up but I've bee at work all day.

Tiffie: I did just what you said when re-fitting the slide, left off the leadscrew nut and adjusted the gib by sliding the apron by hand. It does as you said get a little tighter at the ends but not enough to get 'sloppy' in the middle - I'm quite satisifed with it's operation now the screw is shimmed for a good fit.

djc: I did check the clearance with feeler gauges, I find they are useful for many things. Thank you for the idea of increasing the slot width or thinning the shoulder - that would work perfectly well in making the clearance large enough to make a shim from bar stock

Duffy: The thread on the adjuster screw is pretty good, it's quite a coarse British thread. The mill itself is British and made in 1952, not an 'offshore' model (I like that term - very diplomatic :))

Thanks for the ideas again!

duckman
08-19-2010, 01:59 PM
Some times you just have to get down and dirty, we have in the past where the customer didn't want to spend a lot of $ we would drill and tap the end of the gib and put a small set screw in to push on the edge of the gib screw there is no slack then. ;)

Andrew_D
08-19-2010, 09:23 PM
I see you are sorted now, but one option is to reduce the thickness of the shoulder on the adjusting screw such that it suits a wider shim that you do have. Conversely, make the slot in the jib wider...


That's what I was going to suggest...Oh well, maybe I'll win the race next time...

Andrew