I came across a problem while carving my latest project in HDU that I’ve not experienced so far.
I’m using the same settings, same depths, same speeds I’ve been using for almost every project over the last several projects (and by several, I mean probably 20 signs).
Any thoughts on this from anyone?
Might be time for a fresh bit.
I thought the same thing, and I’m going to, but I tried two different bits 
Are you using the same material?
Yes. Same HDU from the same company.
Is this only happening on the edges of the pocketed areas? If so I would think the bit has lost a tad of its tolerance on the corner of the flutes? Was this just a pocketing tool path or did you offset with stock to leave and come back with a second bit for the final cut?
Never seen anything like that. Didn’t know HDU could do that. Admittedly it’s my least common material.
Using Advanced VCarve in the design. After I saw it, I tried a clean up pass and it helped but still left 1/3 of the fuzzies
Hmmmm……. It seems like there is a small offset between the v-bit and the pocketing bit leaving some fuzzies?
I would run a small test cut on some scrap you have with one new bit at a time and then both to see the difference.
In HDU or PVC, or other soft foam material, I cut the V-bit first, then the pocket.
It will still leave some fuzzies, but the come off easy with a stiff nylon brush.
I kind of looks like is bunched up and rolled over . Like is was still wet.
Was the dust pattern the same as always ?
So…I usually use an endmill first and then the Vee, which I did in that pic. But on the other side of the sign, I did Vee first just to see. I could immediately see that it was still fuzzing. 
I’m starting to lean toward a bad batch of hdu.
I did one last finishing carve using the same tool path which helped clean it up some, but those dang (pardon my French) fuzzies were still there some and sticking.
Tonight I will try out an old piece of hdu and see if the environment of the shop is somehow causing the issue.
There’s another view on some details.
That was the next question, potentially a different batch of HDU?
It seemed to be. Just seeming to struggle cutting it.
So since this post, I’ve carved another sign in some of my original HDU. Everything worked just fine using the max speeds and feeds using my “old” bits.
Before that, I purchased a Jenny 30 degree vee. Woooooweee! That’s a NICE bit! Heavy for a 1/4" shank vee bit. I carved that sign on one side with my regular “old” bit and the other with the new Jenny bit. Though I love the new bit, I saw little to no difference.
I also contacted my supplier to discuss. He recommended a drop in RPMs from 18000 to 12000 (his exact response when I told him how fast I was running the cnc was, and I quote, “Whoa!”). I told him I’d always used them as a supplier for the 1 1/2" hdu and he said they DID make a change in their formula about 6 months ago. Hmmmm…
So, my next step is to try a side by side sample of the old and the new HDU with both the 18,000 rpm and the 12,000 rpm to see what happens.
While the problem is not solved, at least I’m making some progress!!
Thanks for updating us on the issue. Seems the formula change might have something to do with it.
Which brand of HDU are you using ?
It comes from Jasper Plastics in Indiana. I called the manufacturer directly and unfortunately they had zero advice. Upon completion of another sign with this material running the spindle at 12000 RPMs , I’m about to take a trip to Atlanta to purchase another brand. The mess it’s leaving is making it almost unusable.
Check out Grimco in ATL.
Got “accepted” in Grimco today. Woohoo!
