Making grooves for 1/4" plywood

[Ellen Benkin]

I'm making something with frame and panel construction and the panels will be 1/4" maple plywood. I am now on a hunt for a slot cutter to make grooves for the plywood panels. I've tried a 7/32 cutter which is slightly too big and a 3/16 cutter which is slightly too small. I may use the 7/32 cutter and pin the panels so that they don't rattle but I wondered if anyone had a line on a cutter that would be the correct size with no additional "jigging" to make it work.

Rockler makes a router bit for plywood sizing but I find it easier to use a slot cutter.

[Wayne Lomman]

Run it twice with the 3/16 cutter, adjusting it for correct fit for the second run. This gets you the result without costing you another cutter. Cheers

[Jerry Miner]

Wayne's advice is good. You can also buy adjustable slot cutters (from Freud and others) to get the exact slot width you want in one pass.

[Lee Schierer]

Check out the Freud 99-036 Adjustable tongue and groove set (http://www.routerbitworld.com/Freud-99-036-1-3-4-Diameter-Adjustable-Tongue-p/freud%2099-036.htm). It is adjustable at .002 inch increments for stock thickness of ½” to 1-1/4” and groove widths of 7/32” to 3/8”.
364911

[Keith Hankins]

I bought "plywood" router bits. What a waste of money, since no one makes it identical, and it keeps getting thinner. How I do it is get it close (on the slot side) and shave the back-side of the panel with a router table, and make it a glove fit. Since Ply will not expand, its never an issue.

Works like a charm, and none of this fiddling with dado stacks etc. I've got a nice set of Forrest dado with magnetic shims, that I've not used in years.

[Curt Harms]

The ply may be 5.5 mm and even that will vary a little. When I was faced with oversized slots, I put masking tape on either side of the slot for a few inches either side of center then put a little silicone caulk in the groove, not too much so it doesn't squeeze out. That holds the panel but there is some flex. Never had a finishing problem and no rattle.

[Ellen Benkin]

Thanks for all the great suggestions. My first choice would be the adjustable cutters but they seem a little pricey for a one time project. I'm very lazy and I'm trying to avoid a lot of fussing around with this. I will probably try Curt's suggestion of masking tape and a little silicone caulk on a sample. If the tape and caulk seems problematic I will use the 3/16 cutter and making a second pass for a "perfect" fit.

[Wayne Lomman]

If you proceed with caulk, avoid anything containing silicone. It will be a polishing/painting disaster. Use a water based gap filling caulk or a polyurethane chalk, both of which are compatible with finishes. Cheers

[Jim Becker]

The ply may be 5.5 mm and even that will vary a little.
Bingo...most plywood these days is metric, but still has some variability as you note.

[Curt Harms]

If you proceed with caulk, avoid anything containing silicone. It will be a polishing/painting disaster.
<snip>


GE may beg to differ:)

http://www.caulkyourhome.com/ge-silicone-II-paintable-silicone.php

though it appears to be a blend. I don't know that polyurethane caulks were around when I was doing those panels. Does polyurethane caulk stay as flexible once cured as silicone? I've never used any polyurethane caulk but the PL construction adhesive seems like good stuff.

[Darrell Bade]

The ones I did recently I followed these instructions. Worked fairly well...........To quickly cut a perfectly centered ."
groove in the edge of a workpiece, set your
tablesaw’s fence to position the saw blade
just to one side of dead center. Cut a kerf, flip
the workpiece end-for-end, and cut another
kerf. Check the fit of the plywood in the
groove and adjust the fence if necessary. If
you use a thin-kerf blade (with teeth less
than 1⁄8" wide), you may need to adjust the
fence and make a third cut to remove the
middle material. Use a featherboard to
ensure consistent cuts, and always test your
setup in scrap before cutting the actual
workpieces.


To

[Brian Henderson]

I just make multiple passes, although I usually don't do it on the router table, I do it with a dado stack. Long ago, I took a piece of MDF and made slots with every possible combination of dado blades and shims. Now, I can just fit my wood to the slot, then I know how to set it up.

[lowell holmes]

Slot it on the table saw and you can size the slot by making multiple passes.

[Charles Wiggins]

Run it twice with the 3/16 cutter, adjusting it for correct fit for the second run. This gets you the result without costing you another cutter. Cheers

+1. You can actually get a more accurate fit this way. If you ply isn't exactly ¼" but your cutter is the panel is still not going to fit properly. I usually cut 3/4" dadoes with a ½" bit using the material as a guide.

You don't have to get this fancy - I just screwed mine together using scrap, but this video gets the idea across:


https://www.youtube.com/watch?v=7j4vGS4HY-8

[Rich Engelhardt]

The ply may be 5.5 mm and even that will vary a little. When I was faced with oversized slots, I put masking tape on either side of the slot for a few inches either side of center then put a little silicone caulk in the groove, not too much so it doesn't squeeze out. That holds the panel but there is some flex. Never had a finishing problem and no rattle.I substitute Space Balls for the caulk. Way less mess & no chance of squeeze out or silicone contamination.

[Curt Harms]

I substitute Space Balls for the caulk. Way less mess & no chance of squeeze out or silicone contamination.

If you're really cheap, people have laid thin lines of caulk on wax paper, let it cure then cut into short pieces. Homemade space balls. I think the risk of silicone contamination is pretty low when putting caulk in a masked slot. It's not like a sprayed liquid with attendant overspray. My thinking was that adhesive caulk adds some structural ridgidity while retaining enough flexibility to prevent joint failure due to wood movement. Whatever works.

[Robert Engel]

I suggest you consider running grooves and rabbets on the tablesaw.

This is my preferred method because its easier & no tear out issues you sometimes have with a router bit.

Use a flat top rip blade, run a groove, tweak the fence to adjust for panel, and you're done.

Another advantage is you can customize the groove allowance if you're finishing the panel prior to gluing up the door.

[Prashun Patel]

I do mine on the table saw as Darrell describes. It takes some tweaking of the width with a test piece, but there's no fiddling with the height.
I also get better fits this way because the featherboard maintains a straight groove better than the pressure of my hand if the rails/stiles are at all out of flat.

[Ellen Benkin]

Thanks Charles. I have the dado jig and it is great for making dadoes across the grain of the wood but I want to make slots with the grain. That's why I wanted slot cutters. I've also used a table saw with dado blades but I find it hard to start and stop a cut on a table saw.