Compression bit newbie question

[dima]

Hello and my apologies in advance if I have overlooked a post that answers this question. (I have searched and looked around for a while.

I am cutting 3/4" Birch Plywood (imported from china) with a centurion 1/4" compression bit. I am using a shopbot alpha with a spindle labeled as maxing out at 18k rpm. I initially tried a chipload calculator, onsud's feed rates, and tips from the forum and settled on 13k rpm/100ipm/0.32" pass (to get up and down parts in each pass - divided feed rate in half for this.)

At that speed the bit was making a high pitched scream. Slowing down feed rate to 60ipm and 50ipm did not change anything. At the end of a cut or two, the bit also appears to have some gunked on material.

Am I missing something here? Should the compression bit just sound like that?

Thanks in advance for any tips!
-Dima

ps - I've seen posts for cleaning really dirty bits in everything from mineral spirits to brake cleaner. What should I be using for just regular ole cleaning?

[harryball]

While I've found Centurion bits to be a good value for the money I've noticed 2 things, the bit geometry differs order to order and sometimes they are very loud, sometimes they are fine. The last batch of 1/4" mortise compressions I got I had planned to use at the Maker Faire in Austin. They cut fine but the screetch was so loud I couldn't use them. I tried several cut speeds but nothing helped. I changed to my previous Centurion mortise compression and the noise was acceptable.

I use a bit cleaner and pitch remover. I'll get the brand when I get back to the shop.

/RB

[Gary Campbell]

Dmitriy...
First problem... Chineese plywood is in my opinion... JUNK! Havent found anything that cuts it well...just OK. Dont get me started on the delamination.

I would probably cut with that bit near 4 ips (240 ipm) that will cool it an keep it cleaner. I would run that bit at 12K rpm , start at 180 ipm and increase till the scream stops. If getting too much deflection, decrease stepdown, but keep feed speed up. You bit will live much longer.

For cleaning we use spray carb or choke cleaner. Does the best of anything on removing gum from saw, shaper or router bits.
Gary

[gabepari]

I would start at 5 ips (300 ipm) and 13K rpm. I would cut .65" deep on the first pass in the climb direction, and then .010" into the spoiler in the conventional direction. Of course the material will dictate where I ended up, but that's a start. Should be just dandy until you smack a nail or screw that seem to be indigenous to core of chinese birch ply.

[dima]

Thank you so much. I'll also give the bam carbide bit I just got a try tomorrow and will get some choke cleaner. Also will stop in at a proper lumber yard and see if they have some better baltic birch.

I'm also confused - I thought the high pitched squeal was a sign of moving too quickly. Is that not necessarily correct? The bit was generating very fine (sea salt/sand) consistency bit - does that sound right?

[Gary Campbell]

Dmitriy...
You should be generating small chips... slightly elongated, chips.. not dust. When chipload is correct, you should be able to actually measure the thickness. You also will have a bit that is barely above room temperature.

Compression bits by nature seem to squeal more than most, and the amount varies by mfgr. Use the keyboard to raise/lower the move speed to see if you can reduce the squeal, I would increase until deflection is noticable, then back off.
Gary

[dima]

Thanks gary - sorry again for the newbie questions but what does deflection actually mean?

Also, when you say adjust speed with the keyboard, do you mean hit "S" to stop, insert command and alter speed in the shopbot software interface?

[Gary Campbell]

Dmitriy...
Deflection is the bit "bending" as it is pushed very hard. (happens when cutting aggressively with our PRSalpha)

You can increase/decrease the tools move speed with the keyboard combination of [Shift] [<] (slower) or [Shift] [>] (faster)
Gary

[myxpykalix]

I have used regular old oven cleaner to clean my bits.

[wberminio]

Jack

I've also been using oven cleaner for years.
From saw blades to router bits/cutters.

[khaos]

You can modify the cut speed on the fly with shift < or shift >