How to assess the accuracy of a milling machine?

Hello all,

To cut a long story short, I had the opportunity to buy a little used from new Tom Senior M1 mill with S type head for a cheap price from a workshop manager I know who was urgently clearing out. I snapped it up after doing some rudimentary checks, like table traverse binding and rocking.

Now it's home, I want to take my time to properly assess it's accuracy. Therefore please can experienced mill owner talk me through a few test I can do to check the state of all three axes.

Also is run out from the horizontal arbor socket a potential problem in the same way as the mandrel of a lathe is checked?

I'm encouraged to do similar checks after another member helpfully explained how to check the state of my Myford ML7 bed: under 5 thou in bed shear difference is acceptable.

I have clock gauges (both plunger and finger), a magnetic stand and parallels at my disposal.

Any help gratefully received.

Probably the best place to start is adjusting all gib strips then tramming the vertical head in the normal manner (dial indicator swung in spindle, bearing on the table at four points). Then try machining some blocks of metal and measure how they come up.

Not a lot you can do if they come up out of spec without a major rescrape etc. But if it is little used, that should not be a problem.

If your arbor socket is running out of true, it might throw the arbor out enough so that cutting is all on one side of the cutter when cutting grooves or steps etc. Probably no big deal when facing. How much out of true is it running?

Maybe there is a small piece of swarf stuck in the arbor socket ? How did you check it for runout ?

Any chance of some photos ?

As Hopper has stated if it has seen little use , has no apparent damage , looks like it has been lubed properly i would set it up and use it and if it machines accurately leave it be .

No, any potential, which might be found when you measure up, will result in the oversize cut (if important) and as stated, the cutter may cut on one side more than the other, but it cannot present tapering problems, like on a lathe. You are not cutting cylindrically, as on a lathe. Setting up the workpiece will be the important factor in achieving a parallel and square finished article.

Important cuts in this context might be boring holes or making slots.