Box Joint are too tight - help!

[Jim Broestler]

Trying to finish up Christmas gifts and I'm having a problem. Making some canisters using box joints, but the fit is really tight - have to use a rubber mallet to put them together, and they still won't quite seat all the way. Here's the set up I'm using:

Incra jig (original), mounted on a 3/4 piece of MDF, held by two C-clamps to my router table top. 1/4" spiral upcut bit to make 1/4" box joints. Material is 4" wide ash, 1/4" thick. I move the fence in exact 1/4" increments. All fingers seem to be equally tight fitting, so I've ruled out discrepancies in body position and hand movement as I move the pieces along the fence using the right angle jig that comes with the Incra set.

I've checked the bit with a set of calipers, and it's 1/4" dead on. I'm wondering it it's the type of bit I'm using, but spiral up-cut seems to be the type mostly commonly used for this operation. I'd really much rather do this on the router table than the TS just because of the precision factor, but I'm actually wondering if that's part of the problem: too little tolerance. I don't have time to order Rockler's box joint jig for the router table. Basically I want to stick with the method I'm using, but need to figure out why it's not 'working like the video'. Thanks.

[roman fedyk]

When I make box joints on my Akeda jig I use straight bits and they work fine. My Leigh also provides straight bits for this purpose. I guess you should try those as well.

[Jim Broestler]

Yeah, I was a bit worried about tear out, but with the backer board it should be okay. Hate to change the set up, but no big deal really. I'll see how that works and let you know.

[roman fedyk]

If you use a 1/4" straight bit you probably won't have to change the set up...

[Anthony Whitesell]

How wide are the fingers? How wide do your other spiral bits measure versus their stated size? It definately sounds like "too much precision" or the router bit is just a hair undersized.

[Jim Broestler]

tried a 1/4" straight bit and it works great! Imagine that - a cheap Skil bit ends up working better than a pricier Amana. Maybe it's just the type rather than the brand.

[Jim Broestler]

just the router height. no big whoop, though.

[roman fedyk]

Good deal.....now those gifts can get out on time....do you need my address??

[Jim Broestler]

For only $25 + S&H, I'd be more than happy to send you a set! Thanks for the tip. Looks like I'll be buying a straight bit tomorrow. The Skil bit probably won't be able to handle the 1,100+ cuts I'll have to make.

[Gary Chester]

Could you adjust the fence a couple of thousands and run the pieces thru again? That would open the joint just a bit...

[Jim Broestler]

Problem is it's an Incra jig. Only adjusts in 1/32 increments. I could use a conventional fence, but that costs me the precision that makes the router table preferrable to me over the TS jig method. The bit change seems to have solved the problem with resorting to a lot of trial and error fiddling. If it was only one or two boxes, probably wouldn't matter. I'm making 18. That's 1,152 cuts!

[roman fedyk]

If you can find Whiteside locally, they are excellent bits.

[Rod Sheridan]

Trying to finish up Christmas gifts and I'm having a problem. Making some canisters using box joints, but the fit is really tight - have to use a rubber mallet to put them together, and they still won't quite seat all the way. Here's the set up I'm using:

Incra jig (original), mounted on a 3/4 piece of MDF, held by two C-clamps to my router table top. 1/4" spiral upcut bit to make 1/4" box joints. Material is 4" wide ash, 1/4" thick. I move the fence in exact 1/4" increments. All fingers seem to be equally tight fitting, so I've ruled out discrepancies in body position and hand movement as I move the pieces along the fence using the right angle jig that comes with the Incra set.

I've checked the bit with a set of calipers, and it's 1/4" dead on. I'm wondering it it's the type of bit I'm using, but spiral up-cut seems to be the type mostly commonly used for this operation. I'd really much rather do this on the router table than the TS just because of the precision factor, but I'm actually wondering if that's part of the problem: too little tolerance. I don't have time to order Rockler's box joint jig for the router table. Basically I want to stick with the method I'm using, but need to figure out why it's not 'working like the video'. Thanks.

Hi Jim, I make box joints on a table saw, and the jig has an adjustment to vary the spacing of the fingers.

For example if I'm making 1/4" box joints, I set the dado blade (bit size) to 1/4", and adjust the jig so that it cuts a finger every .248".

(OK, that's a guess, however by cutting the fingers less than .250" apart, it means that the fingers are very slightly smaller than the slots they fit into.

That way when I put a PVA glue on them, and they swell, they're still hand tight.

Regards, Rod.

[Anthony Whitesell]

How big does the straight bit measure?

[Ken Higginbotham]

I have found that the fit of the box joints are a function of the distance between the key and the blade. In other words moving the key closer to the blade will make the fit tighter and moving it away from the blade make the fit looser.