Problem with interpolation

[Waynno]

Hello there

Im am having an interpolation problem

Machine VMC 15 control CNC88 HS year 1999

I picked up this machine earlier this year, noticed this problem a while back

I scrapped a part due to this problem a while back, Today it almost bit
me again

Simplified scenario

Bore a rather accurate hole in a block of aluminum

Setx

SetY

Write a simple program with cutter to follow the bore wall

Run program, cuts out of bound approx .005 +X .005-Y direction

If I open up the interpolation program enough to clean 100% of the
hole, It make almost perfect diameter bore, but off center 5 and 5thou

Im not new to this, I originally assumed my software was creating the problem
but after further investigation today, it looks like a problem with machine

I took the job off the machine, and put it on my older Fadal (VMC40) that
has some noticeable backlash, and the part in question came out good

so back to the problem machine, Things I have considered and done to
attempt solution

Did a "RI" and zeroed everything maybe some corrupt data somewhere
of an offset table im missing, but nothing

Check backlash on both axis

look at backlash page to see if there is any odd numbers in there to
fiddle with things,
x 5,5,5
y 9,6,6

not much in my eye to cause .005 problem

Linear guide
Indicator placed different directions and hearty tap with very large soft mallet
to see if anything is loose, No noticeable movement in indicator ( also
spindle cover off and hammered pretty good on the quill)

So, Im open for suggestions, the machine seems tight overall, holds
tolerances good, but this interpolation off center thing has me baffled

I talked to tech today, he was working on a machine, and Im hoping will get back
as promised, but I figured I would try here as well.

The following pic is the milled wall, it is round within tenths, so, machine is mechanicly functioning,
but I suspect there is something in the control throwing things off, Again, I been at this 22 years,and seen grossly
worn machines, but this deos not seem to be a wear problem

Any suggestions?

Wayne

[Waynno]

Some clarification

See attached pic

I write a program to mill a simple square with .25r corners

Square part is accurate within tenths

mill hole with same cutter, same program

The hole comes out perfectly centered to square, so Interpolation is not the prob, its a positioning problem

After machine finishes the hole and square, it returns to home position

I put indicator in spindle, Hole indicates off .01 tir in X .005 in Y

So what the heck is the problem? If I do the exact same routine in my
VMC40, everything returns and dials in within a thou?

[Neal]

Waynno--
It sound like some mechanical lost motion. Check Gibbs, straps, motor tuning, and don't over look slop in the couplers or ball screw thrust bearings. I have seen this many time before during my 16 years with Fadal.

Neal

[Waynno]

I think I figured it out, extreme tram problem

Here is vid I just took, 1 inch bar in spindle, Indicator clamped in vise

So in theory, Part is indicated in 5 inches difference in relation to where cutter actually ends up in Z as shown in vid to indicator level, I think that is were my error is

[nomedia="http://www.youtube.com/watch?v=9QZjabqAC9c"]YouTube - ‪Indicator‬‏[/nomedia]

So now I study machine before I attempt to adjust or call a qualified tech to
tram this thing in, or is that even an option?

Wayne

[alex gitzel]

The tram is easily fixed by setting is easily fixed by setting the z axs gibs.if the machine was properly installed and leveled off of the ways it should come out with in .0005 (spec. on install).As the head gibs wear the head starts to sag down in the front and it can rock side to side.adjust the top strap gibs to fix the sag and the top and bottom center gibs to fix the rocking.the bottom staps are set last all they do is hold the bottom to the ways.if the tram is still off then the leveling needs to be checked.after that the last to things would be the head turcite is worn or the spindle was not properly shimmed at install.when tramming use a 10'' circle (spec.) mark 10''spots in the 4 quadrants and mount the indicator solid to the side of the spindle and take readings at the 4 points to get the table squareness and write readings down,then sweep the 4 points with the indicator in the spindle and write it down,you need to account for the table readings to get the true tram reading.if the table is high in the back adjust the number of your sweep.

[Waynno]

The tram is easily fixed by setting is easily fixed by setting the z axs gibs.if the machine was properly installed and leveled off of the ways it should come out with in .0005 (spec. on install).As the head gibs wear the head starts to sag down in the front and it can rock side to side.adjust the top strap gibs to fix the sag and the top and bottom center gibs to fix the rocking.the bottom staps are set last all they do is hold the bottom to the ways.if the tram is still off then the leveling needs to be checked.after that the last to things would be the head turcite is worn or the spindle was not properly shimmed at install.when tramming use a 10'' circle (spec.) mark 10''spots in the 4 quadrants and mount the indicator solid to the side of the spindle and take readings at the 4 points to get the table squareness and write readings down,then sweep the 4 points with the indicator in the spindle and write it down,you need to account for the table readings to get the true tram reading.if the table is high in the back adjust the number of your sweep.

This is a linear way machine, Im fearful to play with these adjustments
until I get some more feedback from either here or maybe speak to tech

It sure looks like something that if ya dont know what ya are doing,
the guides can be put in a bind and cause damage in the near future

I fully understand the concept of tramming in a machine, but these linear
guides have me concerned

Its mostly off on the X axis direction, so I am assuming this machine suffered a pretty good crash at some point

thanks for the input

Wayne

[alex gitzel]

for some reason i did not see the 1st post,the linear ways cannot be adjusted.the only options you have are to adjust the rear leveling screw to jack up the low side,it may not have any weight on it now with the tram being that far out,make sure all the screws have weight on them.if the machine is out more can be put on the low side but the high side needs a little bit ,the casting may be tweaked a bit if it has been out of level for some time,it will correct itself over time if you keep extra weight on the low side.the other option is to shim the spindle to tram it in loosen the bolts on the flange and slip the shim in.this machine sould not have the dowfrost system on it so will not need to worry about leaks.the spindle flange bolts get tourqed to 25 ftlbs.go around starting at the high side and then tourqe to 55 ftlbs. same way.then retest tram.

[Waynno]

Spent most of today fiddling with the adjusters on the bearing blocks, and got it
pretty close, X direction spot on, Y is off about a thou.

There are adjusting screws on the Bearing blocks, and access holes inside the column to get the blocks loose enough to move them a bit

Acceptable for now, Thanks for replies, I did some test parts, Its much closer than yesterday

Thanks

Wayne