Not sure what the technical term for this is, but the head settles in use

[WobblyHand]

In my case, I was hogging out material and making the mill work. The head temperature did increase during the several hour session. Think I will definitely switch to hogging end mills for that kind of work to reduce the head heating. I did check the belt tension and it was a little tighter than it should have been. Loosened it slightly. Hope doing those two things will help some.

When you think about it, it's just physics in everyday life. Sometimes we just need these things to be pointed out and then it becomes obvious.

 

[RJSakowski]

This should not be a problem for anyone who is milling like normal folk. It's OK to be trusting the DRO if the milling operation is done with both the quill and ambient temperature about the same at the beginning of the operation as at the end.

I suppose if one touches off, and zeros the DRO at 5am in February before the heating came on, and stayed with it until 10C extra soaked in, and then added in some more machine friction spindle heating from working it to blazes, still without a DRO setting, that's not smart! Come to that, if the end if the thing you are milling is a few inches high, and you have a big fat Kurt under it, the work will rise up some under the cutter. We are allowing for a bit of temperature effect all the time, like stopping a few tenths oversize when turning, though this time, I agree that it's about the internals of the machine getting bigger.

With an ambient temperature change, the entire mill is changing dimensionally so the work should actually get further from the head due to the collumn growth. A good reason to let everything stabilize temperature wise before attempting any critical machining.

In the old days, prior to TTS, I would load a tool into the appropriate collet or chuck and zero it on the work just before using it so any change in length would be minimal. Nowadays, I have a whole bank of tools loaded into TTS holders, for which tool length compensation has been preloaded into my tool table, sometimes months in advance.

When I load up a piece of stock for a project, my first operation is to reference the work. I do this with my edge finder for x and y and my dial indicator for z. If I reference my work first thing in the morning and some other project comes up and I don't get back to this one until mid afternoon, any ambient temperature change will affect my previous reference. Fortunately, my basement shop is fairly stable, temperature wise. especially short term as in over the course of a day. Also. most work starts with blank stock and a few thousandths difference on my reference won't be problematic.

As to the issue of spindle growth, the Tormach mill doesn't have a moveable quill but rather a cartidge for the spindle. The cartridge is fixed at the base of the head which is the location of the lower spindle bearings so any spindle growth is above that position and will not affect tool positioning. The main effect of reference shift will be due to tool length growth sue to heating from aggressive milling. Use of flood cooling will keep tool temperature rise to a minimum.

The RF30 clone is a different matter. However, I don't use it very much any more and it is usually for short duration work at relatively low spindle speeds so spindle/quill growth isn't an issue.