Migrating Zero

[bandphillips]

Hello. I am having a problem with the Y zero changing as it goes through the cut file. I am cutting 22 holes in 9 blocks of wood at one process. The blocks are lined up in a row. I can get the zero in the right place to center the holes but they start getting off center and by the time it gets to the last block its moved over .060". Any ideas.

Bill

[srwtlc]

It would help to know a bit more about how you have these blocks setup to cut. Could you be getting some accumulative error due to the size of the blocks?

What model of machine do you have? If it's a standard, you could lose steps if cutting too aggressive.

A little more info would be helpful. Setup, cutting strategy, feedrates, part hold down, etc.

[bandphillips]

Hi Scott. It is a standard machine and I think I may be losing steps like you suggest. Would a sharp bit help with that. The bit doesn't feel dull. What else can make that happen? The blocks are pretty secure in the holders. If I am able to get these pics attached, you can see the recess cutouts to hold them in place. I have clips that hook the top of the block and springs pull down on them. Then I put wedges in between the blocks to to hold them tight. The cutting strategy may be a little aggressive. The plunge rate is 40 ipm. the feed rate is 30 ipm. I am using a zigzag ramping move. The holes are 3" deep. I did about 300 blocks without this happening. I got another order and it is now happening.

[jerry_stanek]

Have you checked if the gantry is moving the correct distance or could it be off. I measure the travel that my gantry moves in each axis. Here is a file that I use to see if my machine is square and moving the right distance.

[burchbot]

Your Y car could be racked.
Dan

[feinddj]

Just as a preference I would use a spiral ramp for circular holes like that. I would also check to make sure the reference board is parallel to the cut. I use a long strip of ply that I cut with the bot while it is screwed to the table. I make it wide enough to recut several times before it needs replacing.

D

[srwtlc]

Bill, A sharp bit is always good, but it sounds like yours might be ok. I don't see a bunch of burnt holes anyway. What kind of tool are you using (I think I see an upcut spiral about 0.5" diameter)? Feed rates are conservative, but if you're using a router at a lower RPM on a standard in hardwood, I wouldn't think that would cause it to lose steps. What's the depth per pass? You could use a chip breaker/finisher upcut that would be more aggressive and still give a good finish on the wall, but if you're using a router and a shallow depth per pass, it may not be worth it.

That's quite a jig/holding setup there! If it worked on the first 300 and isn't now, what could have changed in your set up? Location accuracy of the jig/machine off slightly if it was removed and replaced between runs? Those are some good size blocks, are you sure they're square and that the faces are parallel (not skewed)? As you work your way down the row wedging them tight, it seems that it could be easy to get some accumulative error in either direction, but I see you mention that it's in the Y and not X. That would make me think that the jig is not parallel to the X axis. Use the tool to make it's own locating pin holes in the jig and table first and then cut the pockets for the blocks. Next time you put it on the table it will be lined up properly.

As David mentioned, a profile inside with a spiral ramp would be a good choice for the toolpath, but if your hole diameter is larger than 2x the bit, you'll have to add another toolpath offset to the inside to take out the center which will take a bit more time.

Check the alignment of the jig with the tool at each end of the jig and that would tell you if you placed the jig back on parallel to the X as it was when initially cut and the first batch was ran.

As was mentioned by others, make sure your gantry is still square too.