Cross Slide / Facing Adjustment

MozamPete

MozamPete

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How do you typically adjust a lathe to face off square?
My lathe is levelled and can cut a diameter well enough without a significant taper (good enough for the tolerances I work to anyway), but it faces off the work with a noticeable convex which I would like to eliminate.
I assume it has to do with the saddle being slightly off perpendicular to the bed, but there doesn't seem to be any built in adjustment to correct this.
I see a lot of references to adjusting a lathe to cut a diameter without taper but haven't seen anything on how to correct a convex facing - only references to it being common as machines wear and that it is preferred to have it cut slightly concave to allow fit up of parts without rocking.
Does this require scraping of the dovetail opposite the gib to fix?
Or is it the bed wear that causes it and can only be fixed by a regrind?
Or am I overthinking it again and missing something simple?

My particular lathe is a Myford ML7
 
When I rebuilt old lathes,I sometimes had to remove the top part of the apron and re cut the dovetail till the lathe would face true. One lathe in particular had been used for years for polishing,and all the sliding surfaces were completely worn so badly that the lathe would NOT cut metal!

Your Myford must have been a bit defectively assembled. It is permissible to have maybe 1/2 thousandth CONCAVITY across a 10" face plate. Good for flange work. But,a lathe should NEVER cut a convex face.

On most Asian made lathes,you can rotate the headstock some to adjust the true turning or true facing cuts(you can't get BOTH to be perfect,though! I got lucky,mine does both perfectly.

I have not had a Myford,but have read a lot of English origin books where Myfords are used in the home shop. I'm pretty sure your headstock cannot be adjusted(rotated any). But,I could be wrong.

It might well be possible to remove the headstock and file the headstock casting where it fits between the ways of the lathe,then shim it till it faces true. But,that would change how truely it turns bars held in the chuck. if you aren't an experienced lathe adjuster,I would not recommend doing that. Plus,you didn't mention HOW ACCURATELY it will turn a bar held in the chuck. It is possible that an error was made machining the bottom of the headstock. NEED MORE INFORMATION on how true your lathe turns a bar.

Investigate how your headstock is attached to the bed. See if there are any adjusting screws that allow you to slightly swivel the headstock. If there are any,they may be on the backside of the bed. At least,that is where Asian headstocks are adjusted.
 
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I second Bob's comment. If the spindle is not aligned properly it would face the surface to a cone shape
 
This is a quote from another forum and it describes your problem and the fix.

"It is not desirable for the saddle to be square to the ways or the spindle center line. All new lathes have the saddle slightly offset, such as to ensure that the lathe faces concave. This offset is quite large for cheap lathes, and pretty small on an expensive precision lathe, but there always is this offset in concave direction. A lathe that faces convex is a worthless reject that cannot be sold.

You do not check this measuring the angle between the cross slide dovetails on the saddle to the lathe bed. You check this very simply with a facing cut, because a real cut takes into consideration every contributing error. And this is not something that you can adjust. The only way to change this is by taking off metal from the saddle, either from where it meets the bed, or from where it meets the cross slide."
 
Mac, I found your quote interesting. One of my lathes is a Sherline and one of its features is a movable headstock. You can turn it to turn tapers and reset it for standard use. If I get sloppy and don't set it right I can easily face a concave or convex pattern but if I pay attention I can face square and turn a 4" rod without any taper. Not all lathes have an adjustable headstock but it seems to me that its worth a try at shimming or otherwise attempting to correct any misalignment. Just a long winded way of saying I agree with Bob and the others.
 
mikey said:
Mac, I found your quote interesting. One of my lathes is a Sherline and one of its features is a movable headstock. You can turn it to turn tapers and reset it for standard use. If I get sloppy and don't set it right I can easily face a concave or convex pattern but if I pay attention I can face square and turn a 4" rod without any taper. Not all lathes have an adjustable headstock but it seems to me that its worth a try at shimming or otherwise attempting to correct any misalignment. Just a long winded way of saying I agree with Bob and the others.
Click to expand...
All head stocks are adjustable, just some require a scraper to do the work... For testing and setting up a lathe, the very first thing a lathe needs is a spindle adjusted to be lined up with the ways, in both axes. After that, you can start working on other things -- in the proper order. That said, to do a major reconditioning on a lathe usually follows almost exactly the opposite approach, starting with leveling the bed, then compound slide, carriage, tail stock as a template, ways, tail stock, head stock, final alignment of carriage.
 
My 13x40 lathe has opposing set screws to adjust the horizontal orientation of the headstock. To ignore that can lead to a bunch of unnecessary work.
 
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