[JDona]

I've been getting this boundary lines that show up when face milling between passes. Now I have decided to find the root of the issue.

I've used my TTS Touch/digital dial indicator, dropped Z till the indicator is pre-loaded, Zeroed both the Z on PathPilot and the Dial Indicator, then checked both limits on Y by comparing the dial indicator number when the tool is at Z0 on both ends (is this a good way of seeing the Y tram? or am I missing something?). I can see only a difference of 0.0003 across 7". I have a 0.0005 across the entire table on the X.

Anyone had similar face milling issue?

Been reading about shimming but how lifting the bed will correct Y with Z if Z is also bolted to the bed base? Is it even worth the trouble for the 0.0003"? Considering the lines showing when face milling is actually 0.001 deeper than Z0, rest of the piece is Z0 level with only 1 thou deeper just on the lines. I don't mind the 1 thou, don't think my machine can do any better tolerance. But want to get rid of the lines?

What is the proper procedure to do the tram for 770? Seems the 770 base is much higher than the stand, anyone did the bolt/bar to lift the base on 770?


Cheers.

[Snecx]

It's going to take a lot of work to get it dialed in, but if you have the patience you can almost get it "perfect". You need to check every aspects of the mill individually. In your case, it is probably in the column AND spindle tram.

My 770 column for example, was not perfectly square to the table. It leaned to the left and it nodded down a little. In addition to that, the spindle was not perfectly parallel to the Z way too.

I started by leveling my base to remove any twist from the Y way with a machinist level + shims. Then I shimmed my column to get it square to the table in both X and Y. Lastly I trammed the spindle to be parallel to the Z in both X/Y directions. At the end I had shims all over my mill to get it sorted.

Now my column is square to the table <0.01mm (<0.0004") over 100mm (4") in both X and Y. My spindle tram is "spot on" <0.005mm (<0.0002") over the entire travel, about 350mm/14" in both X and Y.

Even with all these, and with tightened gibs, weight of the table at extreme travels will still affect the spindle tram a little. I had much better repeatability once I removed the machine arm from the right and put my monitor/controls on a separate rolling cabinet.

https://www.youtube.com/watch?v=3IC0lmQqu6k

[JDona]

Thanks for your input.

Cheers

It's going to take a lot of work to get it dialed in, but if you have the patience you can almost get it "perfect". You need to check every aspects of the mill individually. In your case, it is probably in the column AND spindle tram.

My 770 column for example, was not perfectly square to the table. It leaned to the left and it nodded down a little. In addition to that, the spindle was not perfectly parallel to the Z way too.

I started by leveling my base to remove any twist from the Y way with a machinist level + shims. Then I shimmed my column to get it square to the table in both X and Y. Lastly I trammed the spindle to be parallel to the Z in both X/Y directions. At the end I had shims all over my mill to get it sorted.

Now my column is square to the table <0.01mm (<0.0004") over 100mm (4") in both X and Y. My spindle tram is "spot on" <0.005mm (<0.0002") over the entire travel, about 350mm/14" in both X and Y.

Even with all these, and with tightened gibs, weight of the table at extreme travels will still affect the spindle tram a little. I had much better repeatability once I removed the machine arm from the right and put my monitor/controls on a separate rolling cabinet.

https://www.youtube.com/watch?v=3IC0lmQqu6k

[philbur]

I've been getting this boundary lines that show up when face milling between passes. Now I have decided to find the root of the issue.

What diameter/type of cutter are you using, what depth of cut and rpm, what material? A DTI only measures the no load condition. The root cause maybe that your machine is not sufficiently rigid to achieve what you are trying to do without flexing. A smaller diameter cutter will automatically reduce the step issue regardless of the cause.

Phil