Best router bit for cutting dados in hardwood plywood?

[butzla]

I recently acquired a OF1400 and am anxious to try some dados in an upcoming cabinet project.  Before, I've always used a table saw with stack dado cutters for all dados.  Question is what type & brand of straight bits do you have good luck with?

 

[Tim Sproul]

For the absolute cleanest cut use a down cut spiral bit.  Even an upcut spiral bit will generally give better edge quality than a standard straight bit.

A less expensive alternative to spiral cutter is to use a downshear straight bit.  You can mount bearings on these if that is how your dado jig works.

 

[butzla]

What's the difference between down and up cutting spirals?  I'll be using an MFT and guide rail to cut dados.

 

[Tim Sproul]

Upcut: 

--> rotation \ angle of cutting edge - this forces chips to be ejected up and out towards the collet. 

downcut or downshear:

rotation or

 

[webfarmer]

If you have not already done so, check out the great website at "woodshopdemos.com"  They have a wonderful demonstration of accurate and repeatable dado cutting with Festool routers.

If have used an up-spiral Festool bit in the past with fine results, although the veneer fibers needed sanding at the edge of the dado, there was  no tear-out.  Down-spiral would no doubt be cleaner.

Good luck,

Brett

 

[butzla]

Thanks for clearing that up Tim.  That makes sense.  You said either the down shear or the up shear bit will work well, leaning towards a down shear bit.  I imagine the OF1400 has good enough dust extraction for this bit?
Webfarmer,  I saw John Lucas's brilliant method using playing cards as shims,  a long time ago.  It was one of the big reasons I had for scoring an OF1400.  Here's the link to his article: http://www.woodshopdemos.com/fes-dado-1.htm

Any brand name tips out there?  And where to buy?  There's a myriad of choices out there. 

 

[Tim Sproul]

You said either the down shear or the up shear bit will work well, leaning towards a down shear bit. 

IME, spiral bits work the best but they are also the most expensive.  A downcutting or downshear spiral cutter is the best.  Surprisingly, I find upcut spiral bits are better than regular straight bits.  That said, the most cost effective bit is a downshear straight bit.

You can get very good results with a straight bit.  Use an undersized bit (1/2 inch for 3/4 inch dado).  Plow out the majority of the waste, staying away from the edges of the dadoes.  Go back and make climb cuts on the edges - this helps a lot with minimizing the fuzz/tearout of the veneer.

 

[woodshopdemos]

Jeez, they stole my thunder. Actually I am glad they gave you the URL...saves me looking. You can get lucky and find a bit that is exact thickness of the ply, but it is purely by chance. Even those sets that describe themselves as "undersized" are for today's plywood, I find will not fit exactly. The problem is the ply...it can vary from minute to minute. That is why I would rather get a bit that is always undersized. I can then use my method of making the second pass.  "up" and "down" spiral bits can be a bit  confusing. "Up" is the one you want. I will keep the dado clean in that it draws the chips "up" an dout of the cut.  For a 1/2" or less dado, you can make the first cut iin one pass, and then move router and make 2nd cut. It should be t otally clean dado at that point.

 

[robtonya]

I have had good luck with the CMT plywood bit set. I've only used them once, but the fit for me was tight.

 

[butzla]

Jeez, they stole my thunder. Actually I am glad they gave you the URL...saves me looking. You can get lucky and find a bit that is exact thickness of the ply, but it is purely by chance. Even those sets that describe themselves as "undersized" are for today's plywood, I find will not fit exactly. The problem is the ply...it can vary from minute to minute. That is why I would rather get a bit that is always undersized. I can then use my method of making the second pass.  "up" and "down" spiral bits can be a bit  confusing. "Up" is the one you want. I will keep the dado clean in that it draws the chips "up" an dout of the cut.  For a 1/2" or less dado, you can make the first cut iin one pass, and then move router and make 2nd cut. It should be t otally clean dado at that point.

My bad, John, I should have posted your link in my original post.  I like your method a lot even though I haven't tried it.  It's also my experience that plywood is always different thickness, even in the same lift.  I've never cut dados with a router but I always make my cabinet drawers out of 3/4" birch plywood using a lock miter bit.  I find I have to check bit height every time I switch to a new sheet.

Rob,  I've seen the set you have pictured but am not sure about it for the reason mentioned above.  Have you had success with it with different types or sheets of plywood?  Thanks for posting the picture and sample.

 

[josephgewing]

Whiteside and  Eagle America make good bits in a wide variety of sizes.javascript:void(0);

 

[robtonya]

Rob,  I've seen the set you have pictured but am not sure about it for the reason mentioned above.  Have you had success with it with different types or sheets of plywood?  Thanks for posting the picture and sample.

Actually, I've only used it on oak veneer plywood from woodcraft, but I had some baltic birch in the building, and tried it for you, and there some play in the baltic birch, not a good fit, but with the oak veneer ply, I had to use a scrap of wood to tap it in.

 

[minimal]

Jeez, they stole my thunder. Actually I am glad they gave you the URL...saves me looking. You can get lucky and find a bit that is exact thickness of the ply, but it is purely by chance. Even those sets that describe themselves as "undersized" are for today's plywood, I find will not fit exactly. The problem is the ply...it can vary from minute to minute. That is why I would rather get a bit that is always undersized. I can then use my method of making the second pass.  "up" and "down" spiral bits can be a bit  confusing. "Up" is the one you want. I will keep the dado clean in that it draws the chips "up" an dout of the cut.  For a 1/2" or less dado, you can make the first cut iin one pass, and then move router and make 2nd cut. It should be t otally clean dado at that point.

Hope this is related enough to stay in this thread: what is the dimensional stability of plywood (in ALL dimensions)?

The reason I ask: I'm building a table out of strips of euro-ply glued together so that the "plys" are exposed. In other words, the width of the table is composed of plywood glued in it's "height" orientation. This table will have an inlay of a material that is totally stable (i.e. no measurable expansion/contraction) and so I have to leave enough gap so that the table doesn't come unglued if it shrinks over the inlay.

Technical, I know. Thanks in advance!

Oh yeah, I'll be cutting the inlay field with a router and the bit recommended here (downcut spiral): thanks for the advice. I promise to post pics when done...

 

[Les]

Any brand name tips out there?  And where to buy?  There's a myriad of choices out there.   

You can try this link and this link. I buy from both.

Festool offers metric straight and spiral bits which some say plywood is now sized to. Hard to say exactly because as Mr. Lucas said, ply varies. I use both 1/32" under size and metric bits. Whichever works best and hopefully I can make it in a single cut. But if not, it's not a big deal when using the router on a guide rail with the fine adjuster. Just move a little and make second cut. Bit of a PITA since it adds time.

 

[poto]

As for the bit manufacturer, the only bits I've been really disappointed in were PC. The Amana and Whiteside bits I've used are great. Rockler are fine, too.

 

[dltflt]

I have had good luck with the CMT plywood bit set. I've only used them once, but the fit for me was tight.

I have that same set and they have worked well every time.