10 x 22 lathe cross slide dovetails not parallel(?)

[Mac McCaskie]

Hey All,
I was adjusting my cross-slide gibs, again, with hopes to relax the friction I get when cranking it all the way out. I had just put it back together after honing the gibs and dovetails, hoping to remove stickiness. Now, I think the dovetails are not perfectly parallel. Am I right or should I check for something else that could be causing a jam?

It's a Grizzly G0752

If it's the dovetails, Is this normal?
Can it be fixed, and how likely would it be for me to make it worse? I have a SX3 mill.
If I do fix it, is this a good time to convert to tapered gibs? It's not like I I know how to do that, yet.

Thanks,
-mac

 

[ShopShoe]

How heavily has this lathe been used? Is there a location in the cross-slide distance where it is more worn in and thereby moves more easily?

Like other Chinese-Made lathes, I would look at the seating of the gib on the adjustment screws and the condition of the screws themselves.

I would also look at the condition of the cross slide leadscrew and the location and adjustment of the cross slide leadscrew nut.

These things are what make these lathes projects themselves. The good thing to say is that by the time you get all of this right (to your liking) you will learn an awful lot about precision fits and machine tool adjustments.

--ShopShoe

 

[Mac McCaskie]

ShopShoe, Thanks for the notes.

In spite of the fiddling, I'm enjoying this Chinesium lathe kit.

What should I look for on: "seating of the gib on the adjustment screws". The screws and nuts are in good shape (er, new), not tight but slight pressure. Each has a little rod, or plunger, that pushes against the gib. The middle screw fits into a vertical groove in the gib.

The lathe is essentially new, I purchased it this last Spring and hasn't seen much use yet. The sticklyness gets heavy on the last two inches moving out, or toward the operator.

I tested the alignment of the lead-screw by loosening up the gibs and moving the slide from end to end, it was very easy with no friction. I broke off the backlash adjustment "tang" on the lead-screw nut (Doh! as Homer would say.) so that is not a factor.

PS, one day I'll have the nomenclature down and will keep up.

 

[kiwi2]

Hi Mac,
I guess you have one of two problems.
The first is the possibility the dovetails are worn or not parallel. To check this get two short (say 15mm) lengths of round stock of a diameter such that they protrude slightly beyond the dovetails when placed in the dovetail angles. Starting at one end, measure across the outsides of the round stock - preferably using a micrometer or a good quality vernier gauge. Repeat say 6 times at regular intervals down the dovetail. If all the measurements are the same, the problem is not in the dovetails.
The second possibility is that the gibs are not adjusted correctly. I used to have trouble adjusting the gibs to give a consistent fit over the whole range of movement of the cross-slide until I followed a procedure showed by Tubal Cain on YouTube. The key is to take the screw out and move the slide by hand over the full range of movement while tightening the set screws for the gibs until you get a consistent resistance to pushing it back and forwards over the whole range. Pushing it by hand gives much more sensitivity than using the screw as well as being much easier.
I hope this helps.
Regards,
Alan C.

 

[TonyM]

A simple first test is to move the cross slide to where it starts to get tight. Undo the mounting screws for the leadscrew and wind it out a bit until the mounting is well clear of its location. Move the slide manually through the last couple of inches and see if it is still tight. That will eliminate(or not) problems with the leadscrew and nut and their respective locations.

 

[goldstar31]

The second possibility is that the gibs are not adjusted correctly. I used to have trouble adjusting the gibs to give a consistent fit over the whole range of movement of the cross-slide until I followed a procedure showed by Tubal Cain on YouTube. The key is to take the screw out and move the slide by hand over the full range of movement while tightening the set screws for the gibs until you get a consistent resistance to pushing it back and forwards over the whole range. Pushing it by hand gives much more sensitivity than using the screw as well as being much easier.
I hope this helps.
Regards,
Alan C.

I more than agree with Alan's suggestions but would go further to suggest that this problem has been flogged and flogged- without much success. I have a SiegC4 which has THREE 5mm gib screws to secure the saddle whilst my little Quorn tool and cutter grinder has a perfectly fitting 3 or 4 inches of a bar of 1" diameter and the intended cut on the little machine can take a whopping cut of 1/4 of a thous. Takes some believing doesn't it?
If my Sieg was to be fitted to the same standard, it wouldn't have a gib at all, it would be scraped in --- to fit.
Yes, I made the Quorn.

If you stand back and look at things objectively, the gib is held by the points( or dumb ends) of the three little screws and there are air gaps where the gib doesn't fit neatly.

My two little Myfords have not only rounded ends to the gib screws but Myfords supplied laminated shims in an effort to get a better bit and in the case of the Super7B, the 'gib' is in two solid sections whereas the Sieg can only sport a bit of flimsy steel strip. However, my cheap and much despise d mill drill has gone even better that Myford and put in two solid but tapered gibs.

It should make one think of the simple improvements possible.

 

[ShopShoe]

-mac,

What everyone has said is good advice.

To clarify my point about the seating of the gib, what I meant was that sometimes these gibs are made so that the places where the points on the screws push in are located so that you have to be very careful to make sure the points of the screws contact the gib where they are supposed to. It is also possible that poorly-made or damaged screws have eccentric points, so that the point of contact moves up or down as you rotate them. I found both of these things on my lathe*, although it is NOT the brand and model of lathe you have. Screws are cheap to replace, even on an experimental basis.

Since your lathe is basically new, you may also look for edges not deburred in places you can not see when the lathe is assembled. Be careful if you decide to remove or "touch up" any metal as it is harder to put it back than take it off.

--ShopShoe

*P.S.: In re-reading this I think I need to explain further: On my lathe one of the gib adjusting screws was found to raise and lower the gib when turned in and out, rather than only adjusting the pressure of the gib (in and out). I was able to find that there was a very fiddly way to seat the gib when assembling things so that this no longer happened.

--SS

 

[goldstar31]

The Gospel of Saint George Thomas, the Divine in his wonderful Model Engineers Workshop Manual gives advice of using rounded ends of gib screws- and pinning the gib into the bargain. I as the Devil's Advocate added extra gib screws. I have a vertical slide from a possibly pre-War Perfecto lathe which has a pinned gib. I have also one of these U2/3 Deckel clones which someone else suggested that I scrap the rubbish gib and substitute a home made locking gib which will not-drop out.

In Ian Bradley's book on the Myford 7 series his Myford top slide has additional gib screws as well.

Of course, there are 'other' views

Norm

 

[larryg]

A simple first test is to move the cross slide to where it starts to get tight. Undo the mounting screws for the leadscrew and wind it out a bit until the mounting is well clear of its location. Move the slide manually through the last couple of inches and see if it is still tight. That will eliminate(or not) problems with the leadscrew and nut and their respective locations.

This was my thought also. Not to say the dovetails aren't the problem but it could be the lead screw centerline is not in the center of the dovetails or the nut is off center so that when the slide approaches the bearing end of the leadscrew the side forces from the misalignment get greater. Do take the leadscrew out of the equation and get the slide to move freely by hand and then introduce the lead screw back into the problem.

Confirm also that the flats of the dove tails are on the same plane. If one of the casting warped after machining...

lg
no neat sig line

lg
no neat sig line

 

[Mac McCaskie]

Thanks all for the replyies, I checked the dovetails for parallel and found the bottom slide was spot on according to my dial calipers. The top slide was off a bit. I worked a coarse eze-lap in the side with the adjusting screw holes and after a bit noticed high spots near those holes. The high spots were in identical patterns for two holes, like it was a manufacturing defect. Feeling brave, I grabbed my small flat bastard and took the worst of the high spots down, then polished with the eze-lap.

End result is the sliding is much better, not perfect but good enough for now (for me).

Thanks for the tip! Removing the lead screw sure made it easier to adjust and check. When I re-attached the lead screw I found cranking the top slide all the way out, before tightening down the bolts, helped prevent mis-alignment. Not that most of you guys didn't already know that.

I'll check the nibs (that little bar in front of the screw) on the adjusting screws when I get a chance. If I remember correctly it looked like they were sheer cut and semi polished. At least the locking nib was, maybe the adjusting nibs where better.

 

[ShopShoe]

Mac,

Congratulations on staying with it and getting things improved.

I'm glad to hear things are getting better.

--ShopShoe

 

[SmithDoor]

This is not first time I heard some like this.
Check head stock
Some times the lathe was to over

The other problem is worse the lathe was made in China oops.

Dave

FYI Prof read when posting

 

[Wizard69]

I’m glad to see that you have resolved the problem to your satisfaction however to prevent future grief I’d suggest learning to scrap bearing surfaces. I cringe everytime I hear about uncontrolled lapping of bearing surfaces. This especially if geometry corrections are needed.