Router Bit Pop Quiz

[John Moorhead]

Folks -

Okay, I am cutting DTs in some oak veneer ply using the Stott's setup... I have two routers, one with the DT bit, the other with the pattern bit, and everything is adjusted so the joints slide into place with magnetic attraction - beautiful.... they won't be exposed, which is good - because of tearout in the ply.

I am revisiting this issue from an earlier post a few days ago. Both bits are new. I am taking a pull-saw and cutting on either side of the pin to make things easier, but am still getting fractures between the veneer laminations..

I got to thinking about it, and what I need, I think is a spiral (for a hand held router would that be an upcut bit??) pattern bit. Does anyone make such a beast - I've poked around in MCLS and Price Cutter but haven't seen anything.

My reasoning is that a spiral bit would give a smoother cut and place less stress on the thin ply layers than the straight cutting edge of a regular pattern bit.

Anyone heard of such a thing? Does my logic check out? I'd appreciate your feedback.

John Moorhead

[woodworker88]

I have heard of using the spiral upcut bits for cutting mortise and tenons, and they are probably the right bits for the job. This problem has some parallels in metal machining, and they make roughing end mills with a spiral fluting that does the job magnificently. As for a source, I would try the Whiteside line of bits marketed by Woodcraft (and probably others). Check in the Woodcraft catalog.

[John Moorhead]

WW88 -

Spiral bits, no problemo - what I *need* is a spiral *pattern cutting* bit - a half-inch bit, quarter inch shank, with a bearing at the top of the bit.

Any ideas?

John

[Edwin Pawlowski]

Spiral bits are all solid carbide AFAIK. Also, the largest diameter shown for 1/4" shank is 1/4".

cut do the job? The flutes are not straight.

[John Moorhead]

Ed -

Boy, thanks for the link.... Got some good info, but alas.... They have a "downshear" template bit, unfortunately.... the minimum diameter for a top-bearing downshear bit is a 3/4" cutter, and I need 1/2"... I just may be talking out my.... hat and it just doesn't exist... but I think that my theory as to why I am getting the "fracturing" of the plies is correct. I only have 4 more to cut, and DTs in ply are pretty rare work for me, so it may be just as well. Even tho' the joints won't show, and even tho' it'll be plenty strong and all, I just don't *like* having a crappy joint in a project. Now I'll probably start thinking about ways to patch in for the damaged pins, but that'd be over the top.

Again thanks for the site, I am going to keep those downshear bits in mind next time I need to replace a larger pattern bit.

[charlie b]

Since you're using Stotts, is it possible to make your pattern oversized to compensate for a "guide" (I should go out to the shop and see what's on my PC set to use the right term). Then you could use whatever bit you wnat as long as it has a corresponding "guide".

Or, you could sandwich your ply between sacrificial pieces of ply to avoid tear out.

Just thinking "out loud".

charlie b

[George]

That's the key. I won't use any but spiral bits in my Leigh, even though I had to fiddle and mark to get the settings. The shear does a good job, even, with slow approach, in plywood. Box joinery too.

[Robatoy]

Keep it down over there, will ya? I can't hear myself think!

[Mark & Juanita]

Not sure if they exist, but also not sure that this would solve your problem. The problem with ply is the alternating grain; if you have ply with voids, that's going to exacerbate the problem further. You could try a non-pattern spiral bit, if you've got one, just as an experiment to confirm or deny the theory. You *might* have better luck trying to set up things such that you could use a backer board on all cuts. I'm trying to picture how one could make this work on a dovetail jig and I'm not sure it will work. The Leigh DT jig manual gives specific warnings about trying to DT plywood, citing the specific problem you describe.

+--------------------------------------------------------------------------------+ The absence of accidents does not mean the presence of safety Army General Richard Cody +--------------------------------------------------------------------------------+

[Morris Dovey]

John...

I've seen spiral bits with pilor bearings (at the end) but can't remember where (or whether they were up or down spiral - but will guess they were up spirals.)

If you're cutting all the way through the plywood, you might try a compression spiral (which is an upcut on the bottom and a downcut at the top).

If you're not cutting all the way through the plywood, you'll probably get best results with a down spiral because there is less opportunity for layers to move at the cut boundary. A straight bit should do /almost/ as well, and an up spiral will maximize tearout. That's been my experience, anyway.

Morris Dovey DeSoto Solar DeSoto, Iowa USA

[Prometheus]

Depending on what router you've got, a set of guide bushings should work with any spiral bit- then you don't have to go digging for a pattern bit.

Aut inveniam viam aut faciam

[Joe User]

Someone does, because I've seen David Marks use one on Woodworks.

Whiteside seems to make 'em: