Tormach 770 - Face Milling Issue

[wmburke]

Hello everyone,

I am encountering an issue when my tool path runs along the x-axis while facing off parts. I run Tormach 770 with a 1.5" Tormach face mill. As I diagrammed in Picture 1, an approximately 0.0005" step is raised along the bottom side of the tool path. I am reaching out the community to find out if anyone else has had this problem or if there are suggestions for further investigation. My theory is that this condition is caused by one of two things.

1) The vise is not sitting flat - This doesn't seem like it would be the primary issue as I would think that the steps would go away if multiple passes were taken. This does not occur, these steps show up no matter how many Z level passes are taken.

2) The mill head or bed is canted in the Y direction (Spindle pointed slightly towards back of mill) - This scenario seems more likely to me since when milling parallel to the Y-direction, no steps are left behind (See Picture 2). That step seems to be being "scrubbed" off as the cutter moves off the edge of the part.

As I mentioned any tips on next steps is greatly appreciated!

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[sharmstr]

Did you ever tram your mill? 99% of us have to. Simple process and several videos out there.

[popspipes]

The "nod" in the head on my machine I corrected by adding a shim between the bottom head bolts and the colum. (.0005 or less)

The nod will get worse as the Z gib gets loose, tightening the gib helped but didnt get rid of all of it.

[syscore]

As someone mentioned, first make sure that you level and tram the mill properly. On my 1100, after leveling, everything is square, but I do have a slight cantor in the head, so that with a. 3" Superfly cut, there is a few tenths step in each pass. I measured the Z axis movement (up/down) and it is very orthogonal to the table. Less than 0.0002" deviation across an 8" square, on both the X and Y axis. So the cantor is in the head, not the column. Shimming the vise will not work because while it will make the passes flat, they would still step because now the work would be at an incline. However, you could compensate for that in G-Code by lowering or raising the head on each pass. I guess the fix in my case would be to shim the head. However, the steps in my case are not that big, and the largest facing I need now is 4", sometimes 5". What I may do instead is create a larger fly cutter.

In any event, make sure that you understand where the error is before you start chasing fixes. Level and tram the mill well and measure the Z axis perpendicularity.

[philbur]

From the manual:

If you do decide to make an adjustment, do not assume where the error is from. The error could be attributed to a specific problem, or from the combined effect of several problems. Mistakenly making the wrong adjustment can make matters worse. As a practical example, if the Z-axis gib is too loose, it will cause the spindle head to tilt slightly downwards, toward the column. It would be fairly easy to incorrectly assume that the issue is with the column and base connection (often referred to as tram), and make an adjustment by inserting shims between the column and base. Instead of correcting the real issue, this adjustment causes the column to slant back to correct for the head leaning down. Now, the mill is running in a slight parallelogram in addition to a loose head.

1) the column gib may be loose.
2) the column maybe leaning on the base.
3) the head may be leaning on the head carraige.
5) there may be a combination of all of the above.

Adjust the wrong one and you will be further into the long grass. Use the test certificate to work out which test is appropriate for each possibility, then measure each at least three times, then come up with a strategy for correcting any errors.

Phil

PS: The smaller diameter the cutter the less the problem.

[tmarks11]

Look at post #78:

http://www.cnczone.com/forums/tormac...ml#post1645434

Well, we finally solved our issue. It took longer than i would have hoped to get an opening on the machine but this weekend we got it all straightened out.

We started by loosening the base bolts to the table (which we had tightened the S*** out of initially - not good). we trammed the table and the measurements changed so it looked promising. We then removed all of the shims we had put under the base. Then we lifter the front of the mill and supported it with a .75" aluminum block in the center. This holds the table in a three point support and can't flex it at all as many on here have said to do. We then trammed in this position (still with all base bolts loose). It actually looked much better, but when we would get to a certain point the measurement would jump. It turns out the Y gib was now loose (no longer pinched from the base flexing), so i checked the X gib (did not need adjustment) and re-adjusted with Y gib, all while still supporting the mill in three points.

Once all gibs were re-adjusted it was time to re-tram the table...and WOW what a difference it made. We saw 0.0005" across the entire 18" X travel, and no noticeable change in the Interapid indicator across the 9.5" Y travel. we were ecstatic to say the least!

Now it was time to set it back on all 4 feet. We removed the block that was supporting the front in the center and set the mill back on all 4 feet. We trammed the table and saw about 0.0015 across the 18" of X travel and about 0.0006 Across the 9.5" of Y travel. We wanted to do better. Our approach was to lift the front and insert a shim under ONE of the feet and then set the mill back down and re-tram. We guessed the foot right the first time but the shim thickness was too thick (0.030") and it twisted the table the other way. You can tell by the direction of the indicator when you tram the Y on the left edge of X travel vs. the right edge of X travel, we reduced the shim thickness to a 0.010 shim and it was much better, but we wanted perfection. So we changed to a 0.007" shim and that was the one! we have 0.0005" in the Y direction on the left edge, 0.00125 across the 18" in the X direction (both top and bottom of the table), and no real noticeable change in the Y direction in the center and right edges. We decided NOT to tighten the base bolts, and just left them finger tight.

The machine has been running since saturday and i just re-checked it last night and it still trams as good as it did when we adjusted. I will check it again in a few months to make sure.

In addition the center T slot came back to life also, the FRONT edge (the ground one) measures with no noticeable error until the far right hand side two inches, and then it changes by 0.0005", so it looks like we can just set vices and fixtures on for standard tolerance work. and henceforth i will return to calling the center slot a "Precision center slot"

I was so used to working with the crooked table that everything we have made since has seemed like cake, many of them coming out within +/-0.001 in Z depth across the entire thing (usually 10.25"). So at the very least i may have gained some skills trying to compensate for the crooked table for the last several months lol

Sorry if this was long winded but i wanted to document what we found and hopefully our struggles and what we learned will be of use to someone in a similar situation in the future.

Thank you again everyone for all of the helpful input and suggestions while we were trying to figure this out.

Also watch this video series, which shows that adjusting under the base feet can have a big effect on mill tram:

[joshetect]

Is the facemill, the superfly?

Whats your DOC? Are you doing a light final pass? It could be tool deflection.

I make sure to have my CAM software not stop/raise the cutter until its off the work piece.