Chinese milling adapters for a mini lathe

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philf:

--- Quote from: DavidA on March 22, 2011, 11:52:13 AM ---Jose,

Can't say that I agree with you entirely. I would expect (and get ) my old lathe to track square to less than 0.0005" across the face plate. And also checked with a dial guage. Maybe that's not dead square, but it's close enough and the lathe is about 50 year old.
If your trying to square the end of, say, a bit of 50 X 10 mm bar by clamping it on the cross slide then I was always told that you get the edge facing you to run true to the lathe centre line then you can clean up the end with an end mill using the cross slide. If your cross slide isn't somewhere near, then the end won't be square.

My concern was that you must also be accepting this error when you are facing off a job in the chucks.

If it works for you, then ok. Just me being picky. :D

Dave.

--- End quote ---

The recommended way of testing the squareness of the cross-slide to the spindle axis is to grip a parallel lightly in a 4-jaw chuck. You then clock one end of the parallel, rotate the spindle through 180 degrees and clock the other end. You then need to tap the parallel until, when rotating through 180 degrees, you have exactly the same clock reading. You can then set the parallel horizontally and run the clock along the parallel. The recommended limit is 0 - 0.0005" hollow or concave on a 12" diameter (or 0.015mm over 300mm dia.) for a tool room lathe.

I haven't tested my lathe but know that, just by clocking the faceplate, I would expect a much lower runout than 0.001" - this is because I machined the faceplate on the lathe. I expect that the faceplate is slightly hollow or concave which, if it's not perfectly flat, is how it should be. Just clocking the faceplate, therefore means very little unless you know that it's perfectly flat and rotates with zero runout.

A perfectly square cross-slide is fine but the difficulty in achieving this means that most will be made to turn a concave surface for practical reasons.

This level of out-of-squareness wouldn't be noticeable on a 10mm end mill held in the spindle of the lathe. You may notice problems with a 12" fly-cutter. It's analogous with most vertical turret mills which won't have the spindle tramming perfectly with the table.

Phil.

maybecnc:
I referred the out of square possibility because bigmini and myself have both small Chinese lathes. For many posts I have read on several related forums there are cases of out of square cross slide far from the worst spec you can imagine. If for a general purpose lathe is 0.02mm over 300mm, for a toolroom lathe 0.01mm over 300mm and for a Hardinge toolroom lathe 0.005mm over 230mm, one year ago I have read that one found on his small Chinese lathe 0.25mm over about 70mm of cross slide travel. In such cases it is a real problem for any milling work.

Mine has now about 0.015mm over 100mm and that will be fixed soon. And believe me, I would love to put my hands on a good old small lathe! Until that day I'll be improving the one I have as needed.

Jose

bigmini:
Thanks all for the responses. I guess I'll have to accept the limitations until the Minister for Finance says I can afford an X2 or an X3. :( Perhaps if I make her a steam engine :lol:. So far it's pretty much been tooling and mods for the lathe itself, and fixes for other stuff.

In the meantime, I did find early on (after breaking the tooth off a cutter) that climb milling was a no-no. I've never attempted to figure out how far out my cross slide is, but that's next. It would certainly explain the little row of circles I get when milling :). It does mean I need to check how flat the pieces I faced in the chuck actually were.

I can still get a reasonable result on aluminium, but 1020G steel seems to be a problem with anything larger than an 8mm cutter.

For making keyways and flats on small shafts, it's easier to remove my QCTP and clamp the whole thing on centre in the 4-way toolpost.

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