Router Bit for Box Joints

[Paul Fitzgerald]

I've got a simple question that I wasn't able to find an answer to by searching the forum: Which would be better for box joints, a spiral bit or a standard two-flute bit?

I've had good results making a couple tulip poplar test boxes using a 1/4" PC up-spiral, but am concerned about strength and longevity. I'm planning on making fifty 3-1/2" square boxes from cherry. That's 2600 passes through the bit if I did my math right.

Thanks,

Paul

[Peter Quinn]

Solid carbide spirals are tough. 1/4" box fingers, so 1/4" material? 2600cutsX.25"/12=54LF! I think a carbide spiral is good for about 1500LF! Should work. If you think its over heating, take a beer brake half way through.

[Paul Fitzgerald]

Solid carbide spirals are tough. 1/4" box fingers, so 1/4" material? 2600cutsX.25"/12=54LF! I think a carbide spiral is good for about 1500LF! Should work. If you think its over heating, take a beer brake half way through.

Yep, 1/4" material. You're calculations are spot on.

I'm wondering if a down-spiral would be better than an up-spiral.

Paul

[Peter Quinn]

I think down shear (down spiral) makes a clean bottom cut when plunging, up spirial rougher bottom cleaner top, better chip ejection when plunging. I made some finger joint boxes in 1/2 inch qrt sawn white oak with 1/2 up spiral...no problems. Try a few test cuts in the cherry cause poplar behaves way different. They also have combination up/down bits (dual compression bits they are called I think?) Claim to give you best of both worlds, slightly slower feed rate when plunging. Check Infinity Tool, amana, or Onsrud if interested. Onsrud makes great truly industrial stuff, not much different price for basic bits. Expect to pay $20-40. I'd try to get the shortest bit that will work for your setup, puts less stress on router's bearings, and your only using the first 1/4 inch any way. 2 flute or 3 flute mortiser with sheer angle would probable work well to, might save you some money.

[Peter Quinn]

Looked at my jig. Been a while since I used it. Had problems with chip out on face of stock going into bit, right side of each cut. Made 1/4" MDF template to slip over face of stock, back supported by jig. Might be easier on the TS with dado or box cutters over that quantity of cuts, no?

[Paul Fitzgerald]

Looked at my jig. Been a while since I used it. Had problems with chip out on face of stock going into bit, right side of each cut. Made 1/4" MDF template to slip over face of stock, back supported by jig. Might be easier on the TS with dado or box cutters over that quantity of cuts, no?

I don't have a dado set or decent table saw... just a cheap $99 Ryobi with non-standard miter slots and horrible runout. It will be replaced, but probably not within the time frame I have to get these boxes done in.

Paul

[Peter Quinn]

no dado then. are you using dovetail type jig or table sled? I made mine using Yeung Chen style sled. Makes dam fine boxes cheap. pretty easy to build/set up. check out:

http://www.infinitytools.com/products.asp?dept=1053

[Paul Fitzgerald]

no dado then. are you using dovetail type jig or table sled? I made mine using Yeung Chen style sled. Makes dam fine boxes cheap. pretty easy to build/set up. check out:

http://www.infinitytools.com/products.asp?dept=1053

My jig is like the one Norm made on the two-part jigs show. It's just a piece of MDF with an indexing pin made from 1/4"x1/4" hard maple. The whole jig is attached to my miter gauge.

Paul

[Dave Falkenstein]

Depending on how you are making the box joint cuts, I would sure figure out a way to gang cut a bunch of the material in one pass, instead of making 2600 passes. When making boxes, I cut as many pieces as I can safely stack at one time. I use an Incra fence on my router table. With that many boxes to make, perhaps you could justify upgrading to an indexing fence and sled like an Incra or Jointech.

[Anthony Whitesell]

Good catch Dave. I hadn't thought about stacking them. I'm sure you could get 4 or 6 pieces at a time (2-3 box side pairs). Homemade sleds for the Incra Jig are cheap and simple. You'd be able to make 2-3 sleds out of scrap for nothing.

If you don't want to go the Incra route. Either the latest or last issue of Wood magazine has an article/plans for puzzle boxes. As part of the plans, there is a cheap way to make an "indexable fence". Just another idea.

Back to your question. I would stick with the spiral up bit. It would pull the chips out of the piece and into the router table. If you're getting tear out, then I might try a spiral down or a compression bit. Personally I haven't had good luck with the 1/4" straight 2-flute bits, I don't think they can clear the material/chips out fast enough. Getting the shortest bit possible with a cutting length long enough for the thickness of your material will help with bit strength (more solid shank, less fluted area).

[Dave Watkins]

The one time I made box joints I used an upspirial bit, pretty clean cuts. I don't think you would want to do down spirial, you want to clear them out for a cleaner cut and less heat buildup.

I made the jig that the Router Workshop guys use, except I used MDF for everything except the guide runner (hard maple), went together really fast and did a nice job once setup.

I also ganged the pieces to speed things up. Only problem I had was myself - didn't tighten the bit enough in the collet so the spirial made the bit climb thus messing up the depth of some of the later cuts. Luckily I wasn't locked into the final dimensions so I crosscut the pieces down a tad and recut, good practice I guess.

Good luck and enjoy,

Dave

[Paul Fitzgerald]

Thanks for the info guys. I'm going to stick with up-spiral bits.

Paul