3rd broken cutting bit.

[jeff412]

I have just broken my third cutting bit since going to 1.133. I was watching it when it broke. It looked like the board was feeding too fast. I just checked for software updates and it says that 1.134 has a fix for the board feedrate issue. Is that what may have caused my bits to break? I've attached the MPC. I had it set to minimum .25 per pass and it was a simple cutout. It broke half way through the first pass.

[cnsranch]

Jeff, I looked at your mpc, and can't find anything wrong - it's pretty simple.

At .25 per pass, feed rate shouldn't be a real problem - the cutting bit should be able to plow through - pretty shallow.

I had a cutting bit come loose last week, and drop down during a cut out. It didn't come all the way out, the set screws were in far enough that they held at the top of the groove in the bit - but the bit really "chattered" - I didn't realize the problem until the cut was done. Believe it or not, the bit did not break - some kind of miracle.

I assume you're placing the new bits into the same adapter as you replace them - if so, a tip form MTyler (I believe) calls for snugging one screw before snugging the other, then tightening both - trying to make the sets even can result in a tiny bit of wobble - and I think that wobble can be the culprit. Also, I'm assuming that you're using loctite on the set screws.

Breaking a bit can only happen when there's undue stress applied to the bit - if it's not set right, or the board is hanging up (not moving properly due to warpage or set too tight against the bar) or too deep a pass (being able to set the depth is the fix for that).

Finally, make sure you don't have any of the dreaded bb marks on the adapter - if you do, that could be the cause.

Wish I could be more help.

[Digitalwoodshop]

2 things I would do is use masking tape on the brass roller part of the board and replace the sand paper belts if they are worn.

You may be right on with the feed rate in 1.133 and 1.134 may be your fix.

AL

[jeff412]

Two of the bits were broken on this project. Both bits were brand new. I reset the set screws with locktite when I received them. The first one broke, but I was cutting all the way through, so I took the blame for that. But with the second one everything was cutting accurately, but fast. I almost stopped it when I saw how fast the board was moving, but I didn't. I watched as $40 vanished. So far this pro bono project has cost me $80.00. Not a real good return on investment.:( Hopefully 1.134 will fix the problem. I have two new bits on order.

Jeff

[mtylerfl]

... if so, a tip form MTyler (I believe) calls for snugging one screw before snugging the other, then tightening both - trying to make the sets even can result in a tiny bit of wobble - and I think that wobble can be the culprit. Also, I'm assuming that you're using loctite on the set screws.

Breaking a bit can only happen when there's undue stress applied to the bit - if it's not set right, or the board is hanging up (not moving properly due to warpage or set too tight against the bar) or too deep a pass (being able to set the depth is the fix for that).

Finally, make sure you don't have any of the dreaded bb marks on the adapter - if you do, that could be the cause.

Wish I could be more help.

Hello,

Jeff Birt had the tip about the setscrew tightening method.

Another cause for broken bits is that the board leaves the rollers. Projects with cutouts should always be kept captive under the rollers. Not saying this was the cause in this case, but thought I would mention it just to cover another base...

[jeff412]

It was kept under the rollers. I actually had about 12" extra board length and I centered the project on the board.

Jeff

[mtylerfl]

It was kept under the rollers. I actually had about 12" extra board length and I centered the project on the board.

Jeff

Hello Jeff,

Other possible causes...

- cut path kerf binding on the bit due to high moisture or high pitch content (use dry wood)

- board with slight warp, twist or cup can cause binding (use flat, straight wood)

- sliding plate too tight against the board can cause binding (use two playing cards stacked together as a "spacer" when snugging up the sliding plate against the board)

- board sides not parallel can cause binding (verify board width is the same at ends and middle)

- bit adaptors if not fully seated, can cause run out and stress the bit (check with a mirror and flashlight that the red indicator marks are touching/overlapping)


By the way, it is my understanding that the feed rate issue was not to do with the standard Cut Path. Feed rate came into play when a user was creating a MANUAL cut path (assigning a bit to an outline and creating their own manual tabs). The software feed rate should have been ok if you were using the actual Cut Path tool.

[jeff412]

Hello Jeff,

Other possible causes...

- cut path kerf binding on the bit due to high moisture or high pitch content (use dry wood)

- board with slight warp, twist or cup can cause binding (use flat, straight wood)

- sliding plate too tight against the board can cause binding (use two playing cards stacked together as a "spacer" when snugging up the sliding plate against the board)

- board sides not parallel can cause binding (verify board width is the same at ends and middle)

- bit adaptors if not fully seated, can cause run out and stress the bit (check with a mirror and flashlight that the red indicator marks are touching/overlapping)


By the way, it is my understanding that the feed rate issue was not to do with the standard Cut Path. Feed rate came into play when a user was creating a MANUAL cut path (assigning a bit to an outline and creating their own manual tabs). The software feed rate should have been ok if you were using the actual Cut Path tool.



It's possible that I messed up somehow. I've just never broken a bit before and since going to 1.133 I've broken 3 cutting bits. 1 using a manual cut path and two using the cut path tool. I did use the cut path tool on this project, so it sounds like the feed rate issue isn't what caused my problem. I have two bits on order. I will be extremely attentive when I finish this cutout.