I recently bought a 3/8 two flute compression bit from Spetool that I’m using to cut birch plywood. I started with the 15,000 RPM and 270 in/min feed rate as recommended in the Spetool charts. I experienced terrible screaming in the bit on corners and a couple cross cuts and it dislodged my sheet of ply even with it both brad nailed and vacuumed. So I’m clearly doing something wrong.
Any of y’all using a 3/8in bit? What are you running it at? Ive attached a photo of my settings in Mozaik and the chips with a 1/4in bit for scale in case that helps
One design note: you never want to have your corners in your design exactly match the radius of the tool you are using, you always want them slightly bigger than your tool. if it’s the same you engage basically the hole bit in the corner which spikes the load on the tool/machine/workpiece and leaves a bad finish.
not sure if this was the case on your design
Also with a 3/8” bit you want to really make sure it’s tight in the collet. might have been slipping.
Thank you! I’ll double check the design in the corners and decrease the feed rate a bit and see how it goes. Also go full sheet tabs until the vacuum is fixed. I have a session on Sunday so will let you know how it goes!
Do you know where on the mill the spiral switch happens? It’s often at a distance from the end equal to the diameter. If so, then it looks like your initial cut depth puts that transition point right at the top surface. Odd things can sometimes happen in that case. And you aren’t benefiting from the compression bit unless the depth of your first cut is greater than the length of the inverted section. I think you would also want to avoid ramping, since that delays reaching the proper cutting depth.
It could be a bigger issue, but typically to fix the vacuum pumps all you have to do is beat and blow out the filter that’s on them and then open the front electrical cabinet when the machine is off and reset the overload breaker(there are two right next to each other on the upper rightish.
The stem of one of the pressure relief valves broke so I believe it pulls no vacuum despite appearing to run fine, the replacement part has already been ordered.
I have used a 3/8” Amana Compression successfully at Feed 200 IPM, Plunge 100 IPM @ 18,000 RPM. It did feel a bit agressive, but cut well. I had a sudden bit slip, so definitely tighten up that collet and check between runs. My 3/8” Amana bit has a crazy 0.5” upcut section making it too deep a first pass for me to benefit from the compression bit, IMO. I will run a smaller downcut first to prevent breakout on the riftsawn oak ply.
