# Burning dovetail bit while joining 3/4 plywood



## sprior (Aug 31, 2008)

I'm practicing dovetail joints in plywood with the Porter Cable 4212 jig and noticed that I'm blackening my dovetail bit. Any tips on how to fix? Do I need to adjust the router speed or is it something else? The plywood I'm working with at the moment in cheaper import multilayer birch.

Thanks


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## phinds (Mar 25, 2009)

sprior said:


> I'm practicing dovetail joints in plywood with the Porter Cable 4212 jig and noticed that I'm blackening my dovetail bit. Any tips on how to fix? Do I need to adjust the router speed or is it something else? The plywood I'm working with at the moment in cheaper import multilayer birch.
> 
> Thanks


blackening is ususally a sign that the bit has dulled enought that it is scraping the wood instead of slicing and the heat build up will just keep making everything worse ... you need a new bit most likely.

if that's the case it sould be very easy to tell ... just touch the bit (CAREFULLY) right after cutting with it.


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## Leo G (Oct 16, 2006)

More than likely you are going way to slow with the routering. Is it a carbide bit.


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## sprior (Aug 31, 2008)

It's a carbide bit. I guess I'm going a bit slow and careful, but at the moment it's hard to imagine going faster. The bit isn't that old, I've mostly been practicing with it. Any kind of a guess how many 5" dovetail joints you'd expect to be able to do on a carbide bit?


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## Leo G (Oct 16, 2006)

Using Euro maple (9 ply 5/8" plywood) I get roughly 20-25 4 1/4" drawers before the bit breaks. I never discolor them. What brand is the bit?


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## sprior (Aug 31, 2008)

Whiteside.


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## Leo G (Oct 16, 2006)

Good bit, unless something was wrong with it, it seems to be your technique.


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## sprior (Aug 31, 2008)

Here's a picture of the bit. I'm assuming it's something I'm doing wrong (or something nasty in the plywood), but just don't know exactly what.


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## del schisler (Nov 5, 2009)

sprior said:


> Here's a picture of the bit. I'm assuming it's something I'm doing wrong (or something nasty in the plywood), but just don't know exactly what.


Run the bit at full speed Ply wood I don't use To much junk to keep it togother All this build's up on the bit I use a dove tail and pin And i get lot's of box's out of my bit Whiteside is a very good bit So i think it on your side


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## apprentice (Mar 31, 2010)

My dovetail bit ended up the same way after the first 2 or 3 cuts in hard maple, i've been dosing it heavily with WD40 with each new cut, which has helped a great deal, and trying not to feed the cut to fast. I should probably mention the router has been stationary set to a table, not hand held, and the bit is not carbide tipped.


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## jschaben (Apr 1, 2010)

sprior said:


> Here's a picture of the bit. I'm assuming it's something I'm doing wrong (or something nasty in the plywood), but just don't know exactly what.


That definitely looks to be a heat issue to me. Whiteside or not, I would say you need a new bit. 
Are you attempting to complete the dovetails in one pass along the comb? I've gotten into the habit of doing dovetails with 3 or 4 quick shallow passes along the comb and then a final cleanup pass. Total time isn't much more than slugging through each dovetail. JMHO.


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## sprior (Aug 31, 2008)

I will replace the bit, I'm trying to figure out how not to burn out the next one so fast.

I would do a climb pass to break the edge, then do each pin in one pass. It seemed that a lot of the sawdust was staying put instead of being ejected, in fact a bunch of sawdust almost caught fire once, but often the sawdust has been blackened.


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## jschaben (Apr 1, 2010)

sprior said:


> I will replace the bit, I'm trying to figure out how not to burn out the next one so fast.
> 
> I would do a climb pass to break the edge, then do each pin in one pass. It seemed that a lot of the sawdust was staying put instead of being ejected, in fact a bunch of sawdust almost caught fire once, but often the sawdust has been blackened.


I use a pretty light duty router, 1-1/4 or 1 1/2 hp stone age Crapsman, which, may really be a good thing. Climb cut on ply is almost mandatory in my experience, otherwise the back of the pins are all but ripped off without a backer. Then, I make two or three regular passes, just getting into the side piece. The last pass, I finish each tail with circular cuts. Rotating around inside each tooth of the comb in a clockwise direction until I've evacuated that tooth and move to the next one. This action does a couple of things for me; taking shallower cuts helps reduce tearout and clears out the sawdust. I'm using the Rockler version of the 4212 with the dust collector and seldom see any sawdust except in passing as it goes down the hole. You can build up heat in a heck of a hurry with all the resins and stuff they use in the glues. Sounds like maybe you are getting sawdust and resins packed up in there aggravating the heat issue.


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## sprior (Aug 31, 2008)

Some good news. I brought the burned bit to the Woodworkers Club in Norwalk CT and showed it to them and asked for tips for what I might have done wrong. I had tried to use cleaning stuff to clean the bit, but he asked if I had soaked it (I hadn't). He then dropped the bit into a cup of cleaning solution and worked on it a little - after about a half hour all the stuff was off and the bit was almost as good as new, still sharp and no need to replace. This new picture is the same bit as the picture above. He said that the glue in the plywood was the problem and not my technique and suggested using Drano in the future to clean the bits. I bought a spare bit anyway.

Back to the basement...


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## sprior (Aug 31, 2008)

Here's the dovetail practice project I was burning my bit on. Yeah that's baltic birch plywood - I wanted to get some experience using the good stuff instead of the Asian import stuff I had been playing with before. I noticed the veneer layer didn't flake off nearly as much on the baltic.


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## jschaben (Apr 1, 2010)

sprior said:


> Here's the dovetail practice project I was burning my bit on. Yeah that's baltic birch plywood - I wanted to get some experience using the good stuff instead of the Asian import stuff I had been playing with before. I noticed the veneer layer didn't flake off nearly as much on the baltic.


That is good news:smile: Nice looking dovetails too:thumbsup: 
I wonder about using Drano on the bits though. I think it was Freud that published some tests some time back about harsh cleaners attacking the solder/brazing/whatever that holds the carbide to the bit. I picked up some of the CMT cleaner from Holbren last time I ordered from them. $10 for a 18oz bottle a bit pricey for soaking saw blades but not bad for router bits. I don't see why it can't be reused anyway, just haven't got organized enough to do that yet.


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## sprior (Aug 31, 2008)

I like the CMT cleaner for table saw blades, stuff comes off instantly. I tried it on this router bit and it didn't seem to take anything off, but I didn't try soaking in it. Like everyone else I first thought the bit itself was burned so I wasn't that serious about trying to clean it off.


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## sprior (Aug 31, 2008)

This is getting more and more interesting. Today I exchanged a few emails with Whiteside to get their perspective on the router bit burning issue. After hearing that I was talking about plywood he also mentioned the glue being the issue and suggested that I slow my router down to 16-18k RPM. The concept was that I was feeding the router too slowly for the RPM I was using. It'll be at least a few days before I can try it.


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## apprentice (Mar 31, 2010)

sprior said:


> Here's the dovetail practice project I was burning my bit on. Yeah that's baltic birch plywood - I wanted to get some experience using the good stuff instead of the Asian import stuff I had been playing with before. I noticed the veneer layer didn't flake off nearly as much on the baltic.


Nice "practice project". What was your jig setup?


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## sprior (Aug 31, 2008)

For the dovetail jig I have the Porter Cable 4212 so normal setup on that. For the inside groove I made the attached template out of masonite then used double sided tape to fasten it to the piece and more tape to fasten the workpiece to the table. Routed it out then took the pieces apart. For the round edge I just traced something round that was the right size, cut on the band saw, then disc sanded smooth.

The old paper tower holder was cheap plastic and didn't work well, so this practice project is nice to have.


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