Box Joint Mystery

[Raymond Fries]

I am using a Freud 3/8” straight bit in a DW625 router bolted to an Incra Unilift to cut box joints with the Incra positioner. I also bought an Eliminator chuck to use as well. I have a Starrett caliper and it says the bit diameter is right at 3/8” and all fasteners are tight.

The slots always cut right at 1/64” wider than the 3/8” bit. I do not get it. I have tried the cuts with the stock collet and get the same result as with the Eliminator.

Does anyone have an idea what could be wrong? :confused:

[Lee Schierer]

What are you measuring th cuts with?? Try using the caliper on the cuts if that isn't what you are using. For best accuracy always use the same measuring device for all measurements. My apologies if you are already doing this.

How tight does your guide fit in teh guide slot. 1/64 is not a lot so looseness in the guide bar fit could also be a cause.

[Dave Falkenstein]

I'm not sure what an "Incra positioner" is, but I'll assume it is one of the Incra fences. Are you using the sled that rides on the fence? Are you clamping the work pieces to the sled? Are you cutting several pieces at the same time? I am theorizing that the material might be moving slightly as you make the cut, allowing the cut to widen.

[Raymond Fries]

I have also tried not using the guide with the pieces clamped vertical to cut the slots. I run the bit up 3/8" above the table and push a piece of stock against the fence and still get a wide slot.

There is no vibration in the router and it appears to be clamped tightly in place. The fence is locked and cannot move as well.

[Rick Hutcheson]

I would check the runout on the router. Does the same thing happen with other bits. Maybe your bit shank is bent.

[Bill White]

My first thought was voiced by Rick before I could post. RUNOUT?
Bill

[Raymond Fries]

Well we put the bit in a Bridgeport Mill and used a Starrett dial indicator to check it out. It turns out that one of the blades is .0015 further from the center than the other. Is this within Freud specs? Bad bit?

This means the bit will cut at .378 instead of .375. The shaft is straight and bit runs true.

The slot cut by the bit is right at .4 so the above only accounts for a small part of the error.

[Mike Marcade]

Have you checked the perpendicularity of the router bit with your router table top?

I checked mine by chucking a dial indicator into the router collet and sweeping the table surface. Mine turned out to be around .020" out due to bad machining on my router base. I shimmed it to the table to get within .001".

This may cause some of your problem as well. Just my .02

[Alan Trout]

I would check the runout with the eliminator chuck. I bought one not to long ago and could not get the runout to what I felt were acceptable numbers. I went back to the collet and everything works great.

Good Luck

Alan

[Mike Vermeil]

0.003 is negligible when it comes to wood. I'd keep looking for runout somewhere else.

[David Epperson]

Well we put the bit in a Bridgeport Mill and used a Starrett dial indicator to check it out. It turns out that one of the blades is .0015 further from the center than the other. Is this within Freud specs? Bad bit?

This means the bit will cut at .378 instead of .375. The shaft is straight and bit runs true.

The slot cut by the bit is right at .4 so the above only accounts for a small part of the error.
When the bit was in the bridgeport, was the shank gripped at the same point as the collet on the router? Why not use the dial indicator in the bit while the entire router is held stationary, as it could be some runnout in the router collet itself.

[Gary Keedwell]

When the bit was in the bridgeport, was the shank gripped at the same point as the collet on the router? Why not use the dial indicator in the bit while the entire router is held stationary, as it could be some runnout in the router collet itself.
My thought was as David above me was. You might either have a bad router collet or it just wasn't seated right in the collet.
Gary

[Raymond Fries]

Thanks for the ideas. I brought the bit to my day job because I knew we have a good way to verify measurements. I have not actually used my dial indicator at home yet but will do so tonight.

The router and lift are new and this was the first use for them. I just assumed it was the bit. Well it is more than the bit as the numbers now show. I'll keep you posted.

[Bill Wyko]

Incra has approved bits for their system. I don't think the Freud bits are in that group.