I dun wrong

[Mark J]

OK, I did something wrong here.  In fact the photo does not do justice to how black this router bit is.

It is a Whitside 3/8 inch bit that I used to cut a number of 5/16 inch deep grooves in baltic birch plywood.  The project had a total of about 21 feet of groove, but the bit was burnt up after maybe 15 feet were done.  Shaft speed was about 21,500 rpm.

Was I spinning the bit too fast/slow?  
Pushing through the wood too fast/slow?
I think it should have been able to manage a 3/8 deep cut, but maybe that was too much?
Is this a plywood thing (adhesive)?

Do you think I can clean the bit and continue to use it or is this recycling?

[Eric.]

Plywood adhesive is nasty stuff.  It can gum up a bit with a quickness.  Soak that thing in pitch and resin remover, and if you didn't damage it due to extremely high heat, it should be fine.

[wtnhighlander]

Combination of resin be and cut depth. Maybe feed rate, too. With any luck, Eric's suggestion will get you going again.

[wdwerker]

Lack of chip clearance can add to heat too. Was the groove packed w chips after routing it?

I run a Whiteside 1/4" bit w a 1/2" shank in a router table with a power feeder and cut 1/4 X 1/4 grooves. I get a year or 2 out of a bit, thousands of feet. But I have a shop vac pulling chips out.

[gee-dub]

I have seen different rules of thumb for how much to remove in a pass with routers.  There are a lot of contributing variables and I give more careful consideration to anything greater than 1/4" x 1/4".

One of the variables is the material type and plywood is nasty stuff.  It is a bit of a catch-22 since sheet goods are a challenge to dado accurately on the tablesaw due to irregularities.  A router follows the surface better but a dado stack can be better suited to the job.  

Clearing the ships will keep your heat down.  An upcut spiral does a lot of this itself but, is not the best choice for veneered material like ply.  For a regular straight, downcut or compression bit a vac attachment can help you out.

Altering your approach when you first notice a problem can also save you some grief.  Fortunately straight bits are pretty easy to touch up.  Clean that baby up and do a little of this.

Stroke the flat face against the 'stone' drawing away from the cutting edge.  Equal strokes and pressure on each face.  Contrary to the marketing picture I hold the abrasive on the bench and stroke the bit along it.  Just a few strokes will do it; you don't want to change the diameter after all.

[estesbubba]

8 minutes ago, Mike. said:

From what I recall, Don (RIP) used to say you should limit your cutting depth to 25% of the bit diameter.  For a 3/8" bit that is 3/32".   The logic is the bit needs time to clear the chips.  A solid carbide spiral bit might do better, or one of those freud bits with 3 cutters.   They make smaller chips that can be cleared more quickly.  

Bit diameter or depth?

[Cochese]

10 minutes ago, Mike. said:

From what I recall, Don (RIP) used to say you should limit your cutting depth to 25% of the bit diameter.  For a 3/8" bit that is 3/32".   The logic is the bit needs time to clear the chips.  A solid carbide spiral bit might do better, or one of those freud bits with 3 cutters.   They make smaller chips that can be cleared more quickly.  

Wait, Don died?

[Cochese]

2 minutes ago, Mike. said:

Diameter - I know it seems awfully conservative.  I will say I have switched to monster bits and slow speeds for pattern routing and my results have improved dramatically.  Take it with a grain of salt, this is from the guy who thought you needed a shaper to cut a 1/16" roundover, lol.

I will see if I can find his posts.  

Have you seen him here recently? 

Last I saw he had retired from posting, but that was before my sabbatical.

[gee-dub]

9 minutes ago, Mike. said:

Diameter - I know it seems awfully conservative.  I will say I have switched to monster bits and slow speeds for pattern routing and my results have improved dramatically.  Take it with a grain of salt, this is from the guy who thought you needed a shaper to cut a 1/16" roundover, lol.

I will see if I can find his posts.  

Have you seen him here recently? 

Mike brings up a good point about template routing.  I always use the largest diameter bit that will follow the curve and run the motor speed accordingly.  There is no chip ejection issue when making a non-captured cut. 

Mark is cutting dados and just like drill bits, router bits have a happy-place in speed and feed rates.  Remember the first time you paid attention to drill bit speed recommendations and saw how much better the flutes clear spoil at the correct speed?  Wait, maybe that was just me

[Mark J]

Hey thanks folks I appreciate the advice.  I'll clean up the bit and see how it performs--I was going to toss it.  

The router was hooked up  to a vacuum, but I don't really recall how well the chips were being evacuated--I'll keep an eye on that in the future.

As to depth of cut, for that particular project I had established the correct depth by trial and error with test pieces and I did not want to change it once set.  So supposing you had to cut a "deep" groove, would you then want to slow the feed rate?  Would it be better to advance the bit, pull back, then repeat (presuming you are using a guide rail)?