Z Zero suddenly inconsistent by .028?!

[jTr]

Thought it was a fluke yesterday, but finishing a batch of material today and finding quite a variable of up to .028" too deep.

Checked a bit quickly by ZZero routine, then driving Z to 0 to verify at least by sight it is where it should be. That worked fine.

As I continued processing more sheets with multiple tool changes, I noticed on some sheets through cuts really plowing up the table, again by almost 1/32" of an inch. That is not such a big deal, but dados that should be leaving .50 of material are down to .472, meaning inside of boxes will be pinched, exposing ply edge and impeding drawer slide operation.

I zero to the bed, and have had remarkably accurate results for 3 years.

- High humidity right now?
- Age of ground wire?
- Software or hardware related?

Any hints/suggested remedies would be appreciated.

Jeff

[Ralph Balanik]

Hi Jeff,
Without knowing your setup or how you maintain your machine I might take a guess that something has changed recently and it might be mechanical. I would suggest using a dial guage and a mgnetic base on your spindle to check for any backlash up and down. I fought with my machine for over four years and could not get a consistant cut, some of my cuts were out 1/8 of an inch because I kept trying different things,and then I discovered that my gantry was out of square by 1/16 of an inch in four feet. After a very careful setup my gantry is less than .005 out of square in four feet. As soon as I set it up properly all my problems went away. There are many possibilties. It would be better perhaps to have a conversation so if you wish to call let me know.

[jTr]

Ralph,
Thanks for the input. I did recently go through a drill of re-alignment/squaring and resolved issues there. A month ago, I replaced all pinions, so double checked Z motor for loose grub screws and to check if motor crept a bit loose. Seems as though that may have been a pinch loose, so re-torqued down to the grub screws and back and will see what today's milling results are.
Will re-surface before doing anything.
Again, thanks for suggestions.

jeff

[bleeth]

Yesterday I had to cut 8 sheets of mdf that each had many small parts so each one took quite a while. By the time I got to the 3rd sheet I had to drop the z a couple thou to compensate for the loss of moisture from the vacuum holdown in the spoilboard decreasing the thickness of the spoilboard. Humidity fluctuation can easily throw things off

[bobmoore]

If you have more humidity than normal I would check a few different spots on the spoilboard. Sometimes a warp from an expanding bed or spoilboard will give fluctuating results. I have a 1 x 1 x 1.0 inch piece of corian block that I slide under the bit after it has retracted from the zeroing process. Not a precision gauge but a reality check that the zeroing is close. That could also help you clarify whether it is in your zeroing process or the router bed itself. Bob

[jTr]

Good points- living in the most arid region of the country, we are completely stunned at moisture levels right now. Had .50 inches of moisture from Jan 1 to May 1. Then, from May through June, we've added 6-8 inches total moisture in our area. BIG jump.

I discovered after re-surfacing that my ZZero block of 8/4 Alder attached to the table end was in need of very little leveling after a .020 shaving of the Ultralight during surfacing. I believe the ultralight swelling is what likely threw things off the most.

Final sheet cut yesterday after surfacing was doing much better, with accuracy back to normal +/- .003.

Bob - great suggestion- I'll see what I can come up with for a similar gauge block.

The simplest things are sometimes hardest to see, and being able to enlist a few more brains is very refreshing...

As always, appreciate the help!

Jeff