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Which screws for clamping plywood in dado while glue dries?

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Forum topic by BinghamtonEd posted 05-12-2015 08:56 PM 1309 views 0 times favorited 12 replies Add to Favorites Watch
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BinghamtonEd

2281 posts in 1831 days


05-12-2015 08:56 PM

For my upcoming cabinet build, the carcasses will have the sides dado’d to accept the bottoms (for both base and uppers). Since the outsides will not be visible (well, one end will have a 1/4” applied finished panel), I want to use screws, from the outside, to provide the clamping power until the glue dries. Which screws do you guys suggest for this? Not that it’s a deal-breaker, but I would prefer square drive or torx. Cabinets are 3/4” plywood with a rabbet to accept a 1/2” back.

-- - The mightiest oak in the forest is just a little nut that held its ground.


12 replies so far

View Kazooman's profile

Kazooman

624 posts in 1414 days


#1 posted 05-12-2015 10:08 PM

I have to admit that I am not an expert at this, but I would just glue and clamp and be done with it. Screws into the edge of plywood aren’t very good, even for “clamping” while glue dries. If you really need to do it this way, then the main concern isn’t so much exactly what screw you choose, but how you prepare the pieces. If you want the screw to pull the pieces tight together then you need to be certain that there is enough clearance in the pilot hole on the carcass so that the screw threads do not grab. A screw with an unthreaded shank the thickness of the carcass would help. If the threads bite into the carcass and then into the end of the plywood, they will not draw it tight. Any small gap as the screw cuts in will remain. Avoid the allure of over tightening, it will likely result in the screw stripping out the plywood. Also, don’t expect the force of the screw to overcome an overly tight joint. The pieces need to fit together well without screws and should not reply on screws (or other clamps) to compensate for an incorrect fit.

If you don’t have enough clamps to allow assembly and curing of the glue for all the pieces you need to build, you could clamp one up, and then lock the joints in place with a brad or pin nailer and release the clamps for the next piece. Or…... This is a perfect reason for a road trip to buy some more clamps. You can never have enough clamps.

View joey502's profile

joey502

487 posts in 979 days


#2 posted 05-12-2015 10:13 PM

I used 8×1 1/4” for the same application when I built my cabinets (drilled and c sink). The ones I used were phillips head wood screws from Lowe’s. I also like the extra holding power the screws provide when tossing them around during the install.

View DalyArcher's profile

DalyArcher

72 posts in 581 days


#3 posted 05-12-2015 10:46 PM

since you are dadoing I think 8 by 1 1/4” is a good choice. As mentioned, pilot and countersink. Alternatively, I have in the past shot the carcasses together with a 15 gauge finish nailer. Even though the glue is likely sufficient to hold it is nice to have the fasteners in place for extra security when jostling the cabinets around during moving and install.

View Ghidrah's profile

Ghidrah

667 posts in 684 days


#4 posted 05-13-2015 02:11 AM

Glue, clamp and leave it alone till it cures, I never screw my carcasses together

-- I meant to do that!

View waho6o9's profile (online now)

waho6o9

7171 posts in 2038 days


#5 posted 05-13-2015 02:14 AM

GRKs or Spax work well for me and they’re torx I think.

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firefighterontheside

13458 posts in 1318 days


#6 posted 05-13-2015 02:19 AM

I use torx exclusively. I keep them in sizes from 1 1/4 to 3”. They’re exterior grade. That’s what I use for what you’re talking about too. Make sure to use a countersink and predrill.

-- Bill M. "People change, walnut doesn't" by Gene.

View MrUnix's profile (online now)

MrUnix

4211 posts in 1660 days


#7 posted 05-13-2015 02:26 AM

Make up a few of these and forget about using screws :)

(Credit goes to Izzy!)

Cheers,
Brad

-- Brad in FL - To be old and wise, you must first be young and stupid

View Mike Throckmorton's profile

Mike Throckmorton

124 posts in 1126 days


#8 posted 05-13-2015 02:27 AM

Kreg 1×1/4 coarse thread is what I have used, though I only do that if I have an exception alert during clamping.

I’ve also used them to dirve in and hold where I’ve clamped, then pull the clamp to use elsewhere, removing the screw and filling later.

-- You are never complete, you just draw a line where done is and stop at that line.

View lab7654's profile

lab7654

264 posts in 1708 days


#9 posted 05-13-2015 02:28 AM

+1 on GRK and Spax, contractor grade and pretty hard to strip out the head with torx or square. Self-drilling ones are nice for avoiding splitting.

-- Tristin King -- When in doubt, sand it.

View shipwright's profile (online now)

shipwright

7167 posts in 2259 days


#10 posted 05-13-2015 02:55 AM

If you want to screw them and not have clamps in the way as you go on there’s nothing wrong with that. I’d use drywall screws. They have a deep sharp thread and a very narrow core. They hold very well in plywood and your edges won’t split if the dados are snug.

-- Paul M ..............If God wanted us to have fiberglass boats he would have given us fibreglass trees. http://thecanadianschooloffrenchmarquetry.com/

View BinghamtonEd's profile

BinghamtonEd

2281 posts in 1831 days


#11 posted 05-13-2015 12:38 PM

Thanks for the suggestions, guys. Yes, the reason I’m looking to be able to screw these together instead of clamps is that I have 14 boxes to build, and I want to be able to more or less mass produce them instead of building one at a time. I’d rather drive a few screws and set them aside. I’m going to go take a look at the GRK screws, and run a couple into some test pieces.

The lowers will have a dado at the top to accept two rabbeted stretchers, so I’ll need two clamps on those, but I have enough clamps right now to put two on each box. The uppers will have the top and bottom panels in full-width dados, so those all get screws.

-- - The mightiest oak in the forest is just a little nut that held its ground.

View skipj's profile

skipj

88 posts in 1734 days


#12 posted 05-13-2015 01:07 PM

I use 3/4 prefinished plywood for my carcasses. With the tops & bottoms dadoed I nail it with one 18ga nail
to keep it from moving and use the 5mm,not the 7mm confirmat screws.no glue.

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