Source of Error

[sm38240]

All,

I have CNCRP Pro4848. I am using VCarve 9.5 and Mach 3. I am making some replacement 3' x 5' Festool MFT table tops from 3/4" MDF. Basically, the design consists of a series of holes on a 96 mm spacing grid pattern. 13 rows, 8 columns. I cannot machine all the holes in one pass as the board is larger than the Y axis range on my Pro4848. So, I machine 10 of the 13 rows, then index the board down and finish out the last three rows. In Vcarve, I run two sets of g-code, one for the 10 rows and one for the 3 remaining rows. I also machine in two reference holes on the first pass. I use the offset feature in vcarve to offset the machining of the final three rows.

The grid pattern on the first run is spot on. All the holes are correct and the spacing is consistent. But the last three rows (machined on the 2nd run after the board has been moved and dowels reinstalled) is off by about 15 thou in the x direction. Basically, if you insert a machined dowel in two holes made on pass one and another dowel in one of the last holes, then extend a straight edge across all three, the last dowel has a 15 thou gap between it and the straight edge....All this to ask....

How do you accurately machine a grid like this when your piece exceeds the x or y travel of your cnc? The part has to be moved, regardless.

Thanks,

Stan

Similar Threads:

• Need Help!- Has anyone ran into this error? Parasolid ® Kernel Interface Error: KI Error Code:58
• Need Help!- Fixed BMDC Error, now have overactive feed error. Help needed.
• New Machine Build- Strange error in machine defintion manager (Error occoured in IOF chook: )
• Cincinnati Sabre 750 850SX spindle error 16541 Fanuc error AL 12
• Yaskawa Servopack error: A.D1. Motor Load Position Excess Error

[Goonk]

Hmm. I've done similar using 1/4" ground pins as references. One issue I had was that my circles were not circles. I had to sneak up on the diameter to get just the right fit. I was milling a two sided project and used the dowels to flip (holes were all the way through). But I've also used the pins for other projects for re-locating without any issues. I haven't measured the error, but I've never noticed any by eye either. How accurate are my eyes? Dunno! I have a CNCRP standard. I did tweak until I got rounder circles. Someone hear taught me to use a smaller bit to make a specific diameter hole (ie 1/8 to mill a 1/4"). Good lesson.

For something that big, I wonder if three locating pins would help? Could the "flatness" of the panel come into play? 0.015" ain't much really - especially over a long span. Is your machine tweaked? Just thinking out loud here.

[sm38240]

Thanks for the thoughts. The grid pattern is 104 holes on 96mm centers. The hole diameters are 20.1 mm. I use two of these holes as the reference holes, bored into my spoil board. I am using my Festool tracsaw track as a straight edge. All the holes on the first run are dead on parallel and straight. Only when I move the board to finish the last set of holes is the error introduced. You are right, 15 thou is not much, but enough to potential introduce additional error into boards you are cutting when using the MFT. I made three of these boards, trying various options to secure in addition to the reference pins, but the error was always there and on the same side. That should tell me something, but not sure what.

[mactec54]

Thanks for the thoughts. The grid pattern is 104 holes on 96mm centers. The hole diameters are 20.1 mm. I use two of these holes as the reference holes, bored into my spoil board. I am using my Festool tracsaw track as a straight edge. All the holes on the first run are dead on parallel and straight. Only when I move the board to finish the last set of holes is the error introduced. You are right, 15 thou is not much, but enough to potential introduce additional error into boards you are cutting when using the MFT. I made three of these boards, trying various options to secure in addition to the reference pins, but the error was always there and on the same side. That should tell me something, but not sure what.

Sounds like your machine is not square, have you checked to see if the first lot of holes are square, they may line up but still out of square