Thread: Clamping screws

I'm not familiar with what you are calling hexhead chipboard screws but I don't think the type of head is as important as the threads. Coarse threaded drywall screws hold better than fine threaded ones so if the screws you've found have coarse threads I'd say use them.

I used small plywood "washers" to protect the surface when I built my Goat. After many use cycles I found that the bugle headed drywall screws pulled deeper and deeper into the washer, weakening it a little. So for my current build I obtained some washer-head screws with deep threads. They don't sink into the plywood washers at all and can even be used without the washer in low-stress assemblies.

The chipboard screws have a burr under the head that makes them cut a countersink hole for the screw head. Not ideal.

You can get around the problem by using small ply pads under the screw heads (take a strip of ply, wrap it in brown packaging tape then cut it into squares.

You can get drywall/plasterboard type screws with a flat head as well.

The pad method does reduce the damage from the screw whatever type of screw you use.

MIK

Because you need a screw that will see you through a number of cycles during your build, I suggest the Kreg type screws would be ideal. I used plasterboard/drywall screws and plywood pads, but found that after a couple of cycles that they pulled through the plywood, or caused a dent in the surface the wood underneath. This is because of the bugle shaped head which pulls into the ply pad. For a once-only use they are brilliant, because of their enormous holding power, but you can really only use them once with the same hole in the ply pad.

I got around the problem by making new holes in the ply pads, but this was a nuisance that cost me time, and time is your enemy when epoxy is setting up. If I were to build again, I would use panheads or better still, these Kreg-style screws which are used for Kreg jig joins. They cost about AU$15/100 for the square drive version, but well worth the expense for the multiple uses you get from them.

You can get these with a Phillips head drive, but believe me, the square drive is king because they are so much faster to use than any other screw and you can drive more screws per battery charge.

Attachment 140750

That is the style of screw I switched to for my Simmons build. Mine came from McFeely's here in the States. They have an auger point and dual-drive heads, square and phillips. They fit the #2 square drive bit so well it is like having a magnet holding them. Even though I use the square drive bit and screwdriver it is nice to be able to remove them with a phillips driver if it happens to be at hand.

Speaking of alternate bits, I couldn't locate a #3 phillips bit last week when I needed to remove some large screws. On a whim I stuck a #2 square drive bit into the screw heads and found it was a better fit than the proper phillips size! Try it, you'll like it!

Working with 4mm & occasionally 6mm ply, I use (and re-use, and re-use) a fair few
stitching screws. Stitching Screws
Either the yellow-zinced button-head or pancake-head ones.

I put them through 4mm ply pads & dont care if the thread strips out the pad hole.
The same 20 or so pads & screws have built 4 kayaks so far.

AJ

The common theme here is to use screws that are flat under the head. It doesn't matter that the screw strips the thread in the ply pad. In fact it's preferable that the screw does turn in the pad hole so that the pad doesn't spin around when you're driving it tight.

Square drives can be nice, but can be expensive because they are not common enough yet.

I do remember Chuck at Duckworks driving a long philips head screw into a piece of hardwood with no problems at all using a drill set on its impact setting. Was a pretty phenomenal demonstration.

He said no slipping or burring of the head in almost all cases. Good for extraction too.

Would get a screw with thread all the way up to the head too of course ... i think the one with the threadless part of the shank put up above was to show the head only?

MIK

Hi Mick, I agree square drives were once expensive and hard to find here in Australia. But now that Bunnings stock them they are more accessible and cheaper.

Countersunk screws, set in a properly countersunk hole will apply more pressure then a flat bottom type head (pan, button, etc.). Depending on what they are compaired against, but up to 40% more pressure.

For temporary screws, I do as Mik suggests and use pieces of scrap with pre-drilled clearance (and countersunk) holes. I have hundreds of them in a couple of cans and reuse them.

Thanks to everyone for their contributions. The variety of responses shows that (as I suspected) the cat can be skinned in several ways...so now I just need to go ahead and skin it!

What I propose to do while I have this surplus of csk chipboard screws is to make some (let's start with 50 and see whether I need more) washers with a clearance hole from scrap and see how I go.