Choosing/using router bits to dado/rabbet and groove for/into under/nominal sized plywood??

[bent]

I've been chasing my tail trying to find the right place (/person) to cut up some ¼", ½", & ¾" plywood so I can make some built-in cabinet drawers with front lock joints, rear dados (or even possibly rabbet and dados), and grooved bottoms.

I learned that Baltic Birch (BB) is a company and their products are .750" if you buy 3/4". Same for 1/2" = .5"

I understand that if you are lucky enough to be using BB you can use a 1/2" straight bit to cut dados to join a 1/2" rear into a 1/2" side drawer joint, and the product will slide in with little (sanding maybe?), or no adjustment for a TIGHT dado joint.

But it looks like I'll probably not be so lucky as to be getting BB cut up, so I need to know what to do with the ¼"(double flute straight, & double flute upspiral), ½"(double flute mortising-plungable) straight router bits I have to deal with the fact that the plywood pieces I have cut to the right sizes will not be ½", but likely say 1/16" or 1/32" less than .5". They are titanium carbide bits and brand new, so I assume great cutting performance.

HERE IS MY QUESTION

I have a router table and I need to know how to make a TIGHT dado for nominal ½" birch (not BB) plywood pieces. If I used my ½" straight bit the joint would not be tight. I guess I could use my ¼" bit and move it over to the right width; say 15/32". Or should I ensure I buy BB (.5") in the first place, so I only have the ¼" depth to deal with in my routered dados. I am not a practiced woodworker, but I do have knowledge of cnc machining in metal, and know how to use woodworking tools. What am I looking at layering wise? Two width cuts and three depth, and in what order?

Freud's router bit catalog lists 3/8", 7/16", and ½" straight bits only in that order. Do I need another bit greater than my 1/4"s, & which one?

Whoops, Freud have a 15/32" "undersized plywood" bit on the next page. Is this what I need. Is all undersized plywood the same under-size, and should one setup produce a TIGHT joint?

END QUESTION

For the ¼" bottom grooves, I am assuming that it is fine to use a 1/4" straight bit for the ¼" nominal bottom plywood, because it will be floating (and expanding/contracting) in this groove anyway, and only supporting.

For the front lock joint I will be using my table saw, and will have to deal with a 1/8" thick combination blade to make the ¼" wide cuts. To be dealt with later.... I do not want to buy a stacking, or wobble blade, really; may not keep the TS.

[Edwin Pawlowski]

Freud and most every good router bit has them.

are good sources.

You may want to consider this:

[David]

Either buy plywood bits (a set of odd size router bits for undersized sheet stock) or get a good dado blade set for your TS. Or get both. (The one who dies with the most tools wins.)

Dave

[bent]

w/r/t lock joint or mitre lock joint router bits, would you recommend one over the other. I'll have 1/2" or ~1/2" sides and 3/4" or ~3/4" fronts. Is one any stronger than the other. I have already read the setup of the mitre lock so far. Not planning any overlay

[bent]

Infinity has a 31/64" straight bit. Do I need to borrow a caliper? - I lost my Mitutoyo.

[bent]

ok, so what is it like to try to get a 1/4" wide by (I'm gonna say 1/4" deep cut b/c I don't feel like digging out notes) out of a 1/8" wide combination table saw blade in order to make a lock joint?L

[Tyke]

I would not buy a dado blade if you are using only 1/4in dado. I would just make two passes with my 1/8in blade.

Here is a link showing how to make the joint with a table saw.

Paine.

[Secret Squirrel]

"bent" wrote in news:gridnQWd7vgingzenZ2dnUVZ [e-mail]:

Another alternative in some cases it to use a smaller dado, say 3/8" for your nominal 1/2" ply. You'd then need to rabbet the play to create a tongue 3/8 thick which would then fit tightly into the dado.

[David]

the closest I can come to 1/2" BB, is 12 MM. Are you sure you are getting BB that is exactly ONE HALF inch thick?

Dave

[bent]

So thats why one would do that (me).

And apparently gluing surface is king.

[bent]

No, but I understand (since like weeks ago) this is one thing you can say about Baltic Birch.

BB is always singled out. For plys, thickness, strength. It comes from one place and/or one source.

|12mm| is less than |1/2"| by about 14 thou. I always remember that one

1/32" is approximately 1/33". 32s or 33s, who cares. And I know 1/33 divided by 1/33 is .99999... (1.0000...). So a 1/32" (1/33") descrimination is like .033..."

14 thou is less than one half of 1/32". Less than a 1/64". Actually it is

1/7257143152"

Pretty good size, but will it fit? Maybe for a bottom. A 3-ring piece of paper is about 3 thou. Five pieces may just hold the weight of itself from falling out. I bet you the entire combined tolerance of the 75, 000 thousand machined parts in a Stealth fighter is less than that.

I haven't measured any sheets. I bet they are all different from each other. Freud has an undersized plywood bit of 15/32". Infinity 31/64". One guy said to use a sharpening service and a 1/2".

I love going to Home Depot and determining if you'll have to reverse engineer your project when some guy sets your cut once on the wrong line. He tells you if you're cutting an 8 foot long piece of ply four times combined it's gonna be off by the thickness of the material. You ask, and he says no problem. So he takes the first cut, lays out the tape measure and exclaims PERFECT. Perfectly closer to the next closest line. Thats a buck. Do you want the next fifteen?

I figured the panel saw out. For cutting horizontally there are two platforms, and two reference rules. The rules don't move. One is to the lower rest, the other to the upper rest, depending on the width of the sheet and convenience. Absolute dimentions from bottom to top. No adding or subtracting. No factoring in the blade. Because of gravity I draw all my rips from bottom to top. The machine isn't set to measure the other way. Maybe some employees would assume a perfect 48" and subtract if a drawing is made that way. All dimensions should be contiguous, not combined, because the top piece is removed after each cut. The thickness of the blade is zero set. The rule never moves. 1/8" is set when the machine is built. That is, with the needle pointer at 15-15/16", thats what you get. If you were resting on the lower platform, say 30" away, use the other rule. It is offset by 30" It would read 15-15/16", The machine cuts straight as an arrow and perfectly normal. With vertical cuts, the blade is slid over to a lock position and rides up and down. The wood is slid side to side to a stop block. Accuracy of consecutive cuts just depends on moving the wood over to lightly touch the stop block. The rule for the stop block starts at zero and works both ways. The blade is accounted for, the rules origins start .250" appart (two 1/8" saw kerfs). The stop block is a steel fixture with a cam clamp that rides on a rail. It is a bit figetty, but done firmly and right its all over. The V and H rules are the same. and the indicating pointers are the same. There is no paralax error to worry about. Pointer to rule is a fractions of a millimeter. White steel rule with black graduations. Black spring steel pointers. There is no operational errror introduced.

[Juergen Hannappel]

[...]

No. 1/2"=12.7mm, 1/2"-12mm=.7mm approx 28 thou approx 1/36"

[bent]

ya. so a dozen sheets. I was using the decimal remainder from a 6mm vs.

1/4 BBvc pw source I found today for drawer bottoms

[CW]

[Odinn]

On 12/13/2005 9:53 PM CW mumbled something about the following:

Especially on a stealth plane such as the SR-71 Blackbird. The component parts of the Blackbird fit very loosely together to allow for expansion at high temperatures. At rest on the ground, fuel leaks out constantly, since the tanks in the fuselage and wings only seal at operating temperatures.

[CW]

You are confusing tolerance (allowable variation from the ideal) with designed fit. They are not interchangeable though they each have a bearing on the other.

[Odinn]

On 12/14/2005 8:55 PM CW mumbled something about the following:

I'm easily cornfused, what's new :)