Leave screws in or take em out?

[bean438]

Since you cant see inside the box, if I leave the drywall screws in will they ever cause problems, i.e come loose and rattle?

The exterior screws I will take out. Do these need to be filled with PL, or is wood filler good enough?

Obviously anything straight through a panel needs to be air tight, but not sure about a screw hole perpandicular through a panel.

[Harley]

Since you cant see inside the box, if I leave the drywall screws in will they ever cause problems, i.e come loose and rattle?

What sort of "box"

[bean438]

I am building a THT.

[Harley]

if I leave the drywall screws in will they ever cause problems, i.e come loose and rattle?

Well, if you you are screwing where you've glued the joint and bedded the countersink head into the wood, and used the minimum size pilot hole, it won't come loose

The exterior screws I will take out. Do these need to be filled with PL, or is wood filler good enough?.

Get yourself a tin of auto-filler. It's about 1/4 or 1/8 the price of wood fillers and does just as good a job. You may call it Bondo-Fill over there. PL is a glue, not a filler. Bondo-fill is a filler not a glue - don't substitute one for the other.

Obviously anything straight through a panel needs to be air tight, but not sure about a screw hole perpandicular through a panel.

If I am reading you right, you are wondering if the hole you leave in the panel you are screwing ( in other words clamping ) the top panel ( the panel that takes the countersink ) onto by pulling the screw out needs sealing ??? Strictly speaking no if you've used enough glue, however it's not worth the risk, so make sure the bond-fill is packed in tight into the hole and Bob's your uncle.

[bean438]

Hi Harley.

Yes the screws are where I have glued the joint. Screws were used to pull tight and hold. Screws are countersunk into the wood. Dont know for sure if I used the minimum pilot hole. I used whatever bit came with the countersink. Big enough to pilot but small enough for the screw to hold I guess?

I guess I will leave them in. Cant see em any way so i dont know why people would take them out?

I will get some Bondo.

Yes you did read correctly. For example I screw the final side piece into all the panels, then take the screws out because I dont want them to show.

I am confused though, you say PL is a glue/bondo a filler, and NOT to substitute one for another, but you also say to not take the risk and pack the bond fill in tight. Wouldnt it be prudent to pack it tight with PL to prevent air leaks?

[Harley]

I am confused though, you say PL is a glue/bondo a filler, and NOT to substitute one for another, but you also say to not take the risk and pack the bond fill in tight. Wouldnt it be prudent to pack it tight with PL to prevent air leaks?

PL will expand to fill gaps when you are gluing two pieces of wood together and yes it has sealing qualities to a certain extent for larger gaps. However how I have had it explained to me here by a manufacturer of the same type of product - 100% expanding polyurethane ( PL is a brand name ) - this glues uses moisture to cure and although there seems little present in dried ply, there's enough to set it off.

That's why it creates such a strong bond, it seeks the moisture and penetrates into the microscopic cracks of the play then cures. Although the US PL product does not ( apparently ) say so on the packing, if you slightly moisten the joints beforehand, you'll get an even stronger bond.

When two bits of ply are under compression ( screwed or clamped ) with the PL in-between, there is little room for the PL to expand freely so it has no option but to penetrate the ply, and the excess oozes out the sides as you know.

Now when you have gaps, the PL seeks moisture from the air to cure and provided the gaps aren't great, PLUS you have lots of wood-to-wood contact in any case, the joints will be strong.

However, spread a little PL on a flat piece of tin and let it cure and see what happens. The PL won;t adhere all that well to the tin because it has very few pores to penetrate and expand in, plus thee's damn all moisture apart from the air. Look carefully at the part that cures in the air and you'll see lots of little bubbles in the structure. It's also quite weak. Next - try to sand it and get a smooth finish - horrible right?

Now let some bondo-fill cure in a lump in free space. You'll see that it forms a real solid clump and although there might be the odd tiny bubbles, it's sandable and will be as smooth as the sandpaper grade you use. Then use the bond-fill to glue two bits of ply together and let it cure. The tray an pull it apart - it will crack and part a lot easier than PL under compression + moistened.

I hope that explains the difference.

[Greg Plouvier]

Assuming you're using a router on the edges, be sure screws are sunk deep enough so the router bit won't hit them, or remove screws around the edges.

[Harley]

Assuming you're using a router on the edges, be sure screws are sunk deep enough so the router bit won't hit them, or remove screws around the edges.

He was taking these edge ones out as I read it but leaving the internal ones in.

[Greg Plouvier]

Assuming you're using a router on the edges, be sure screws are sunk deep enough so the router bit won't hit them, or remove screws around the edges.

He was taking these edge ones out as I read it but leaving the internal ones in.

Guess I didn't have enough coffee in me this morning

[bean438]

Harley is correct. The ones I will leave in are inside of the tht folded horn. No one will see them, and why take em out and fill the holes if I dont have to.


I just glued panel 6 in place. One of the screws "spins" so I will take that one out and fill with PL and push it in with a putty knife. Although it spins, it is holding the panel tight.

I will only take out the visible screws.

I might even switch to my brad nailer if I gain confidence.

[Harley]

Guess I didn't have enough coffee in me this morning

Know the feeling...know the feeling

I might even switch to my brad nailer if I gain confidence.

Make sure you clamp well before nailing and angle nail rather than nail perpendicular...oh and keep your fingers at least twice the distance of the brad length from the business end of the nailer...those brads have a mind of their own particularly the 18g ones and they can come through that wood quicker than a greased fart

[bean438]

I may use a brad nailer for the access cover screw flanges. I can clamp them easily.

I might even try brads with panels 8, 9, and 10 as I can clamp those easily as well. Apply PL, clamp tight, set the brads, and I can take clamps off right away right? Brads should hold tight?

The final side piece I think I will stick to screws. I have no way of clamping the middle, unless 300-400 lbs of weights on top will do?

[AntonZ]

The final side piece I think I will stick to screws. I have no way of clamping the middle, unless 300-400 lbs of weights on top will do?

It can be done but is quite cumbersome. Lay a block of wood or something in the middle. Then something like a 2X4 or 4x6 (longer than cab width) across that, clamp at the sides. I think sticking to screws is easier.

[bean438]

I will stick with screws. For good measure, I shoot some PL in the pilot hole, and put a bit on the threads before I shoot the crew in,

[Tom Smit]

For good measure, I shoot some PL in the pilot hole, and put a bit on the threads before

Not really needed. You only need to lay a bead on the upright panels which will be less work and just as effective.

before I shoot the crew in,

YIKES!!!!