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

[Aukai]

Yes sir...

 

[woodchucker]

Where is the z axis DRO attached? The mill DRO's that I have installed are attached at the bottom of the spindle so the DRO is separated from the work by only the length of the milling cutter.

I've never seen that. I didn't know that was done.

 

[RJSakowski]

I've never seen that. I didn't know that was done.

Actually, I misspoke. The pickup for the DRO scale is attached to the head of my RF30 clone and the scale is attached to the bracket for the depth stop rod which is mounted on the quill about 2.5 inches above the end of the spindle. I did a similar mount on a Grizzly G0755. Sorry for any confusion.

While I was down in the shop, I lowered the quill about 4" and zeroed my z axis DRO. Then I heated the quill with a heat gun to about body temperature. This would be comparable to the temperature rise due to extended milling. My DRO reading changed by 1.4 thousandths. When the quill cooled back down to room temperature, the DRO returned to zero.

 

[WobblyHand]

Actually, I misspoke. The pickup for the DRO scale is attached to the head of my RF30 clone and the scale is attached to the bracket for the depth stop rod which is mounted on the quill about 2.5 inches above the end of the spindle. I did a similar mount on a Grizzly G0755. Sorry for any confusion.

While I was down in the shop, I lowered the quill about 4" and zeroed my z axis DRO. Then I heated the quill with a heat gun to about body temperature. This would be comparable to the temperature rise due to extended milling. My DRO reading changed by 1.4 thousandths. When the quill cooled back down to room temperature, the DRO returned to zero.

Neat experiment! Was going to say cool, but that wasn't right! Definitely learned from this thread!

 

[mmcmdl]

Man, the tooling pool is sooo deep.

It most certainly is !

 

[erikmannie]

I've noticed that even locking the z-axis gibs on my PM25MV, the head drops a tad after use. By a tad, I mean 0.01 mm. This is after 5-10 minutes. For what I do, most of the time it doesn't matter, but sometimes it does. Here is an example of what happened.
View attachment 409789
You can see slots in the surface. I didn't change the z axis, it was locked. The R8 collet was tight. The quill was locked. What can cause this? What is the technical term for this effect? Is there a fix for it? For what it is worth, it doesn't always happen, but it happens frequently enough that it's annoying, and can spoil the appearance of a piece.

I had this same problem on my PM-25MV. I removed the two stock locking levers (on all axes, by the way), and replaced them with socket head cap screws. That sure fixed the issue!

If, after this, the z-axis is still slipping, you can crank the SHCSs more.

As a bonus, the SHCSs take up less space. The locking levers for the x and y axes were often in the way.

 

[Christianstark]

Oww! I had a dovetail cutter pull out from the R8 collet, much not have been tight enough. Ruined the work piece as the cutter made a downward slot, more like \ rather than ---. But my vise was unhurt, but I was chastened.

Are the z-axis locks just longer handles? Or did you also go with bigger diameter screws?

Yes. Longer handles.

The handles are over twice as long lever wise from the ones that came on my PM 833-TV

 

[graham-xrf]

Many machinists will ruin their machines for ten or so minutes before starting any actual machining to minimize this effect.

I know it was just a typo, but it was of the sort that continues to be valid in a sentence I love these!

Regarding the way you experimented to reveal expansion using a DRO. Is it that the only part that can falsify the cutting position readout is the expansion of the length of the milling cutter, and the relatively short length parts that grip it?

 

[RJSakowski]

I know it was just a typo, but it was of the sort that continues to be valid in a sentence I love these!

Regarding the way you experimented to reveal expansion using a DRO. Is it that the only part that can falsify the cutting position readout is the expansion of the length of the milling cutter, and the relatively short length parts that grip it?

Thanks for catching the typo @graham-xrf

The little experiment concerning thermal expansion exclusively measured the growth of the spindle/quill. any change in length of the milling cutter would be in addition. The quill lock on my RF30 clone is about 2" above the bottom of the head so there was about 6" of quill length contributing to the DRO reading change. For a 10ºC temperature change, a 6" length of grey cast will grow about .0012" which is consistant with my empirical observation.

 

[graham-xrf]

Thanks for catching the typo @graham-xrf

The little experiment concerning thermal expansion exclusively measured the growth of the spindle/quill. any change in length of the milling cutter would be in addition. The quill lock on my RF30 clone is about 2" above the bottom of the head so there was about 6" of quill length contributing to the DRO reading change. For a 10ºC temperature change, a 6" length of grey cast will grow about .0012" which is consistant with my empirical observation.

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.