Thanks, I will.
Clint
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Thanks, I will.
Clint
I know that this is an old thread, but this problem resurfaced for me today. Luckily I caught it. This is a 1/8" Carvewright cutting bit, first time using it. It is the same configuration helix angle as when I first had the problem. What I don't know is if this was a bit that I purchased years ago, or more recently. I thought I had gotten rid of all of the problematic bits by returning them to Carvewright at the time.
If you have purchased a 1/8" cutting bit from Carvewright recently, could you check the configuration? Just count the number of spirals - the problematic ones show 7 as you count top to bottom of the bit. 4 flutes. If I order more bits from Carvewright, I'd like to know what I'm getting. I don't want any more of these bits in my shop.
Attachment 87352
It's hard to see but almost looks like the secondary relief is higher than the primary cutting relief (the cutting edge) Meaning the 2nd relief area is rubbing behind the cutting edge. May be wrong but the guy who resharpens bits would be able to for sure tell you.
Great eye or point to bring up at the least. most people would not even thinking that the cut on a bit would have this issue. That would definitely cause the affect that is seen here.Quote:
Originally Posted by CarverJerry
Mugsowner, over my 40+ years in the machine shop and doing some of my tool grinding which included end mills, our bits are nothing but an end mill, one is tapered with a ball nose, one is a standard 1/8" 4 flute end mill. I can see where maybe during a batch of tools made the secondary relief got missed or just not ground enough, and that would cause issues. At least it's only in wood where I would have seen a lot bigger problem being used on metal. I forget the guys name who will resharpen our tools, but I'm willing to bet he would take a look at these and be able to tell you. I hope DickB can get this figured out so he can get his clock gears cut out. There are many of places on line where we can buy our tools from. Any questions I'll try to answer them, PM me as I don't always check our forum everyday.
Interesting theory, but I don't believe that it is the case. Here is a photo, using my PC microscope, of the offending bit:
Attachment 87354
I see a nice curve away from the edge.
Let me recap the original problem, and the conclusion to which I came. The offending bit is a 4 flute Carvewright 1/8" cutting bit with a helix angle of about 28 degrees. Carvewright had changed the helix angle specification on this bit.
Attachment 87355
Previously, the bits had a smaller helix angle:
Attachment 87356
I note two characteristics of these bits. First, if you draw an imaginary line down the center of the bit and count cutting edges, the "bad" bit has about 7 edges, while the "good" bit has about 5. Second, the gap between flutes to eject sawdust is tighter on the "bad" bit.
Now, here is a Kennemetal bit that I used while Carvewright looked into the problem and subsequently changed specs again:
Attachment 87357
Note that while the helix angle is greater, it is a 2 flute design. So, there are fewer cutting edges, and the opening to eject sawdust is less twisted and larger.
My conclusion is that the burning is a result of the number of flutes and helix angle. The offending bit left more sawdust in the slot which I am guessing can cause more friction. Likewise, it has more cutting edges which I also assume causes more friction.
The reason for my recent post was to simply find out what is the configuration or specs of the 1/8" cutting bits now being shipped by Carvewright, as I was unsure if my "bad" bit was new old stock in my personal inventory, or a new bit. So, I asked anyone who had purchased a bit recently to look and report. Still asking.
I have since reviewed my inventory, and I believe that the most recent bit that I have purchased is the one pictured with about a 22 degree helix angle. I am still curious to learn what others have in their personal inventory, and if possible when purchased.
(BTW I went back to the Kennemetal bit to rerun my project with no incident.)
The difference in the helix angle is like threads on a bold, the coarser one 22° would pull the wood chips out better than the finer 28° one. The 2 flute one would do an even better job as they are made for roughing work and the 4 flute are more for finishing. Just more of my 2¢ worth.