Engraving depth rises???

[plastics]

I am engaving benchs made of recycled plastic. The last couple of weeks as the bot is running the depth of the engraving gets shallower. It is engraving on a 2x4 and 2x6 flat boards that are clamped down well. The table is also level and the z axis shows the same depth during the whole part file. Any help or suggestions would be appreciated.

[ken_rychlik]

You Z move speeds may be to fast. What do you have it set at? If it tries to go down faster than the machine likes, it may loose steps. The machine thinks it went down, but really didn't. The way to check is after a file runs, move the z to zero and see if it is still at the right spot. Also make sure the bit is not slipping in the collet.

Kenneth

[geometree]

Check your material thickness with calipers. Whenever we machine Azek, we have that problem, the thickness varies a lot in the same sheet. Usually have to run it thru the wide belt sander to flatten it. Its amazing how much 0.010"-0.020" will effect the depth/width of flutes and v-carving.

[eaglesplsh]

I second Shawn's suggestion - if you're zeroing to the table check your material thickness.

Even if you're zeroing to the top of the material, the problem may still lie with your supplier. I've tested/used recycled plastic from several of the largest manufactures. There is very little control over thickness, width, or density. The sides/top+bottom surfaces are rarely flat. Sometimes the cross-section looks like a football, other times the center has sunk in like an hourglass.

[clueless]

Your vacuum system can pull the table down in the center as well. I've seen it pull .020" down in the center of the table.

[navigator7]

I hope this is not considered off-topic.....
This summer I was doing some custom Trex Decking on a deck over the water.
It was a fan shape with boards similar to a 1x6.

Trex to me is recycled plastic which is what jogged my brain synapses.

I made a jig and fixture to make the taper shape and it worked terrific. To our horror found that our cuts were more accurate than the factory edge. We did a lot or bullnosing on boards that were somewhat sun faded. A weed burner brings it all together.

While I'm discussing Trex has anybody tried to machine it?
Talk about a stable product!
Responds to heat and might be the ideal material for a curved surface insert.