Router Bit Problems

[Tom Winship]

Today, using a 1/2" carbide spiral upcut bit in a Makita 3612 router, the noise level change and the bit came out. Upon examination of the bit, the shank had seperated a disc about 1/32" thick. Later, using another similar bit, the same thing occurred. I'm thinking maybe it is a problem with the collet, which is allowing the bit to vibrate at a high frequency. Your opinion?

Can the two upcut bits be salvaged by having a shop grind them back square?

[glenn bradley]

Not sure I understand "separated a disc". Do you mean a little cross section of the shank came off the butt end? Are these bit made by the same manufacturer? Pictures would help immensely.

[Tom Winship]

Yes, just a little cross section on each. One of the bits is a Bosch; the other a Freud.

[Tom Veatch]

...
Can the two upcut bits be salvaged by having a shop grind them back square?

I never seat a bit deeply enough that the end rests against the bottom of the recess. And, IIRC, most everything I've read about router operation recommends against bottoming out the bit, so I'm wondering why it would be necessary to square off the sheared surface.

[Tom Winship]

Thanks for the info. I noticed that the instructions for my router (20 plus years old) specify bottoming the shank out. Might try it your way.

[Myk Rian]

When you bottom the shank, the collet tries to push it further in as you tighten it, keeping it from tightening fully. Put an O ring in the bottom of the shaft so it won't happen again.

[Bill Huber]

I agree with all on this, never ever bottom the bit out. I learned this the hard way with my first router table. The bit walked up and wiped out a very costly chunk of wood.

You can drop a space ball in the router or just make sure you pull it up from the bottom before you make the last tightening.

[Greg Hines, MD]

Can the two upcut bits be salvaged by having a shop grind them back square?

I would not trust them now. Chalk it up to experience, and replace them. Carbide is very brittle, and once broken, I doubt that it would be safe to use them, reground or not.

Doc

[harry strasil]

The bit shank delaminated, in steel its called Lamalear tear and the end pieces of plate steel has this because when its rolled to size the ends overlap and it forms a cold lap as its called in forge welding.

I would returrn it to where I bought them and see if they will replace them, I believe solid carbide bits are formed under great pressure from carbide granules and it may have been a bad batch of bits.

[John Terefenko]

Alot of times you can't bottom a bit out because the shaft is not long enough so that is one of those miscalled terms. The reason you do not bottom a bit out is because where the shaft meets the cutter body there is a slight bevel for transition. If you lock your collet around this bevel you are now contacting a very small portion of the bit and when the bit vibrates when cutting this bevel will slide up thus causing the bit to come loose and become a dangerous projectile. Now some collets do wear out over time so that will also cause a bit to become loose. Just wanted to point that out in case there were those that did not realize this. Take a lok at a bit next time you go to use one. You want that collet to secure around the solid part of the shaft. I think what some books or manuels state is to bottom the bit out and then raise it about 1/16 to 1/8" as you tighten the collet. Have a great day.

[Tom Winship]

Thanks to all who responded. Two points I would like to make are:

1. Makita's instructions say to "insure that the bit is seated all the way into the collet cone". To me, this means "bottomed out".

2. These bits are probably 10 years old and I have normally used them this way. (This might be like running through and intersection on red 10 times also.)

I will not bottom in the future and I will not reused the two bits.

[Bill Huber]

Thanks to all who responded. Two points I would like to make are:

1. Makita's instructions say to "insure that the bit is seated all the way into the collet cone". To me, this means "bottomed out".

2. These bits are probably 10 years old and I have normally used them this way. (This might be like running through and intersection on red 10 times also.)

I will not bottom in the future and I will not reused the two bits.

What they are saying is correct, all the way in the collet, not all the way to the bottom of the hole in the router. If you take the collet off you will see that there is space below it.

[Tom Veatch]

...Makita's instructions say to "insure that the bit is seated all the way into the collet cone". To me, this means "bottomed out"....

Need to check my router's manuals to see what, if anything they say, but my interpretation of that instruction is to make sure the bit is inserted far enough that the collet's entire bearing surface (cone) is in contact with the shank of the bit. I concur that the instruction is ambiguous enough that either interpretation can be justified.