Pocket Inconsistency

[sevans]

Hello Everyone!

I am working on a couple of signs (Identical). Long story short, prismatic lettering with the background removed at 3/8". The signs are app. 4ft wide X 5ft high. On the first sign, in pocketing, there were areas toward the middle of the table that were slightly higher than others, as though it did mill them down, but not quite to 3/8". I cut the same exact file today on a new sheet of HDU (by the way, I'm cutting HDU), and I had areas like this sporadically in different places than the first cut, but still in the same places as the first. I know this may sound confusing but I'm trying as best as I can to explain. I did surface the table before beginning. My bit is fairly new as is the collet. Any suggestions would be most appreciated. Over and Out, Sarah

[Gary Campbell]

Sarah...
What are you using to hold the material down?
Gary

[harryball]

I saw something similar when I first got my bot, even though I would have sworn it was tight it turned out that the set screw on the pinion was loose. When I actually pulled the Z and checked it was was able to pop it free with a pair of pliers. I realigned it and made sure it was tight and all was good.

Make sure your collets and bits are sawdust free when you tighten them down. I doubt this is your problem since bit slippage is generally a change that never corrects. i.e. once you are cutting too shallow, it finishes the job cutting too shallow.

If the pocket is gradual without sharp edges, you might check your table surface for a dip. If it is a vac table, cover it with plastic and turn on the vac, then check for dips while it's under stress.

Of course, pinion wear could be an issue too, or the spindle mount bolts a little loose etc... Just go over the Z real close looking for any movement and check all the bolts and set screws.

/RB

[sevans]

Thanks guys! I am using a vacuum system for hold down. I really don't believe it to be hold down at this point. The reason I went vacuum was in an attempt to solve this problem. This is all much needed advice and much appreciated. Thanks much.

[Gary Campbell]

Sarah..
The reason I asked is that when you surface the table, if the bleeder is not glued down, you can experience varying height levels when cutting a material that is less porous.
Robert gives some great points to check above, as it sounds like you had the problem prior to using vacuum.
Gary