CNC Bits - Discussion

General
#1

All,

I’ve done just a little research - don’t know if it’s what y’all are seeing or not but I thought I’d put a few thoughts out and see if it rings true with anyone… Or not.

  1. Metal cutting bits can be used for wood but they dull faster. Metal cutting is typically higher grade carbide but is probably too brittle for fast cuts in wood.
  • The bits I bought at AtlasCuttingTools are all for metal.
  1. Regular router bits - assuming they are designed to cut on the surfaces required (i.e. the ends) can be used.
  • CNC bits seem to be available at very high prices - which makes sense for lots of cutting. And you should probably go with that.
  • But, it seems, for general purpose router-like cuts, it’s okay to use a router bit (ensure you can plunge with the router bit if necessary!).
  • The CNC wood bits I could find similar in size to the metal ones I bought are about 50% more expensive than the metal cutting bits (wood ones seem to have more pronounced cutting edges)
  • However, end mills for wood of the same size as the ones I bought for metal seem to be about 2-8 times more expensive than their metal cousins…

So, it looks like I need a new source for wood material router bits. I’ve found:
a) NiagaraCutter.com (which requires you to call them or email)
2) cmtUtensili.com (which hooks you up with Amazon)

I’m liking these as my next reference standard:
http://www.amazon.com/CMT-191-008-11-Carbide-Spiral-Diameter/dp/B000P4HOEQ/ref=sr_1_5?s=hi&ie=UTF8&qid=1423634810&sr=1-5
http://www.amazon.com/dp/B001NIA9I6/?tag=cu0e-20

Thoughts?

Regards,
James

#2

This is a interesting subject!

Here is my $0.02 worth:

The trend for metal bits is the usage of high grade carbide for high speed or very high speed machining. This “technology” is better than the old steel one ONLY if you are using it a the correct speed AND with coolant. Mostly for this two reasons: The coating use on carbide bits is design to lubricate the cutting. This coating become active only above a given temperature. Using a coolant help to keep the bit at an acceptable temperature. So, on wood, the coating lubrication is useless and the bit is not cooled down by anything.

In addition, the carbide bits are very sensitive to any force that try to bend it. Remember Elly’s talk yesterday (Carbide is hard but not tough!). If you have any deflection on your bit it will brake immediately. Especially, when it is a small diameter and extra long bit like the one we used yesterday night…

I have in the past used steel bit on wood (most plywood or soft wood) with good results. I have also had very nice result with carbide bits designed for wood. Here is the like of the one I used:

http://www.sorotec.de/shop/Cutting-Tools/Milling-Tools/END-MILLS/END-Mill-WOOD/

I have also used router bits without any problem. the two mainly differences with (spiral) CNC bits are:

  • the plunge feedrate has to be much lower because the shape of the blade on the bottom is usually straight.
  • the feedrate has to be lower too because there is no spiral to evacuate the chip and there is a risk of clogging.
    To find the right feedrates (plunge and horizontal), I am using a router with approximately the same power. I take the same kind of wood and I try different speed when milling (routing?) 1 meter. One, I get the right settings, I measured the time of milling 1 meter and this is the invert of my horizontal feedrate!

For the plunge feedrate, I usually set it half of the one I use for metal and add a spiral plunge equal to 10-15 degrees.

However, we should expect a lot of broken bits before finding the correct settings of the kind of material we want to mill. Hopefully, we are a community and we will share our experiences and solve these issues quiclky!

Julien

#3

James,

I tried my first cuts today on my first project. I figured I’d use MDF since it should cut easier than the Oak that they were cutting last night. Unfortunately I got similar results and the MDF look really bad. See pic 1 & 2 below. I had to leave to get my kids in bed (they were with me) but I just couldn’t figure out why we were having all these issues. As I pulled into my subdivision I figured it out and think you will be happy with the answer. It wasn’t our bits at all, the spindle was spinning in the wrong direction. I messaged Jon and had him look at this and reverse the spindle direction. Picture #3 is the result, it has the same carving with an offset. I’m willing to bet this is why your bit broke yesterday. There are a lot of guys taking larger cuts in the Joes CNC forums than what you were trying.

#4

So I looked at the other 3mm endmill and if it is the same as the one that broke then we were definitely running it in the wrong direction.

Oops.

#5

Wow!

Considering we were running in the wrong direction the cutting was not so bad. Can’t wait to see milling in the correct direction!!

Julien

#6

oops indeed.

I’m guessing it didn’t smoke as much either…

Funny - I just had that conversation with my son about drill bits.

Righty tighty lefty loosey. or something like that.