Cross slide not square to spindle

[David Pollard]

Hi Guys,
I have a 10” Atlas lathe will a milling attachment.
I had a fly cutter in the spindle, when taking a standard flat cut across a piece of metal in the vice I noticed the back rotation of the tool was taking a significant trailing cut. The tool was set at about a 3” diameter. From this I deduce that the spindle isn’t at 90 degrees to the crosslide.
Is this adjustable at all?
I have not removed the head from the bed since I have owned it but who knows what has happened in the past.

I suppose I could take a facing cut across a workpiece in the chuck then run a dial indicator across the full face and see what it reads.

Or should I just ignore it?
David

 

[ddickey]

Mount an indicator on or near your chuck and check your cross slide any deviation from zero. I believe this will tell you if your cross slide is square.
If it is square run it along your vise of your milling attachment.
My cross slide isn't square and there is no adjustment as far as I can tell. I thought I also read somewhere that lathes are supposed to cut slightly concave across a face.

 

[British Steel]

HI David, and welcome!

It's normal for a cross-slide to be minutely out of square, we have manufacturing tolerances to thank for that...

A lathe should be constructed to make a slightly concave facing cut, so that faced parts won't rock on a central raised area, the degree of concavity is down to the quality of the lathe - a Toolroom lathe will produce less concavity (at least from new) as more attention (read time, wages) will be put into accuracy - people often refer to Schlesinger's limits for Engine Vs Toolroom lathes.

Correcting alignment isn't a trivial task, I'd recommend reading The Books first - "Machine Tool Reconditioning and Applications of Hand Scraping" by Edward F Connelly and "Testing Machine Tools" by Dr. Georg Schlesinger, possibly also "Foundations of Mechanical Accuracy" by Wayne R Moore to get an idea of what you'd be letting yourself in for... You may find them in the "files" section of one of the machinist web sites, or may have to exercise your GoogleNinja skills...

Dave H. (the other one)

 

[magicniner]

Cross slides on older lathes were commonly set up to give a very small amount of "concavity" on facing cuts, I have seen this explained as a way to ensure close mating of faced parts which might otherwise be affected by anything less than a perfect surface finish, it kind of makes sense but I have not found any conclusive manufacturer documentation.
I learned very early to use small cutters when milling on my Myford to avoid the problem David describes, with the addition of a vertical milling attachment for the lathe the problem went away and the vertical attachment convinced me to put together a separate vertical milling machine,
Regards,
- Nick

 

[British Steel]

In Schesinger's book, starting about page 56 (in my copy...) are tables of accuracies, not a bad point to start from.

Dave H. (the other one)

 

[TeaBagofHorror]

There are younger data in the German DIN 8605 and 8606.
If someone needs them - just send a message.
Written in German language, of course, but nevertheless I think it is understandable.
They are from 1976, but still current status.

 

[benmychree]

With an Atlas lathe, there is not much to be done about the problem due to the flat ways. On a lathe with vee ways, the carriage can be re scraped to correct the problem, not so for flat ways. If you tried to attack the problem by re aligning the headstock, the lathe would not turn or bore straight.

 

[mikey]

Seems to me that you need to determine if you really have a problem. The milling attachment may not have been precisely aligned so how a fly cutter cuts is not really a good indicator of an issue. You would be better off facing a work piece mounted in the spindle and seeing if the cut is really off and by how much. Then you can decide if you have something to worry about.

 

[magicniner]

Seems to me that you need to determine if you really have a problem. The milling attachment may not have been precisely aligned so how a fly cutter cuts is not really a good indicator of an issue.

It really is.
When you surface a face with a cutter the orientation of the work or attachment is irrelevant for (X Axis) cuts involving cross slide movement on a lathe, on a mill the OP's reported problem would indicate "Out of Tram" but you cannot tram a lathe X axis (cross slide) as the orientation of the head stock and cross slide are fixed,
Regards,
Nick

 

[wa5cab]

With an Atlas lathe, there is not much to be done about the problem due to the flat ways. On a lathe with vee ways, the carriage can be re scraped to correct the problem, not so for flat ways. If you tried to attack the problem by re aligning the headstock, the lathe would not turn or bore straight.

Actually, that isn't correct. Although I doubt that anyone would go to the trouble to do it, it would probably be less trouble to do an Atlas carriage than to do one of the single-vee types. For one thing, you only need to scrape one surface instead of two. And for another, the included angle that you would be working up against is 90 degrees instead of I assume 60. The reason only one surface would need to be done is that the gib screws would take care of skewing the carriage around to match the front. So there would be no need to do anything to the carriage gib.