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which screw thread depth for pine?

3K views 26 replies 12 participants last post by  Al B Thayer 
#1 · (Edited)
Looking to buy nice screws for my wood bench project but curious how thread depth affects wood does anyone know from experience? Is tighter or wider thread depth less likely to cause splints or cracks? Any other tips on screws for a beginner? Thanks
 
#4 ·
Second that! Most importantly is to pilot drill & try to keep the hole away from end grain edge of wood to minimize splitting.
 
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#6 ·
Also try not to put two screws in the same grain. In other words offset the screws and predrill with a bit that's just a little smaller than the base of the screw. Another great tip is use High Performance Exterior Screws with the star drive tip. Trust me you'll go crazy driving cross tip screws, they slip. The star drive are a ton easier. Good luck.
 
#8 ·
#10 ·
So how much different is a countersink or counterbore going to finish compared to a spade bit? I like the countersinks that don't have the long drill on it because you can't really pick the size of it. They tried to make it one step when really it should always be two.
 
#14 ·
Echo'ing Hammer1 on the caution of using "cheap" drywall screws on anything remotely engineered.Heck,they're marginal for SR...duh.

Any flex within the pce will see them fail....may be sooner,may be later.Some would see this as overly complex(it's just a screw),and maybe it is?But do a set of deck stairs with some POS screw and get a dz folks on them,shakin their booty....that there would be flex.

Just remember....the more flex,designed/engineered into the project....the more critical the fastener.And there are charts for length's.
 
#18 ·
Coarse thread drywall screws work OK when they are installed correctly. Drill a piloted/countersunk hole, and drive the screw in slowly with a cordless drill. When near tight, just bump the trigger to tighten the screw. Screws snap, or the heads snap off from driving too fast, creating heat. When driven fast and then they seat, that's when they can snap.

There are drywall type screws, like #7's with larger diameter shanks. Their composites may differ, along with how brittle they may be.






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#16 ·
BobLongwood said:
so what is a cheap drywall screw and what's a high end drywall screw? I was thinking on using torx screws because they look better and would be easier to install with a hand ratchet.
I love those screws but I only use them for fixtures and jigs. I use the deck screw kind. But again only for fixtures.

Al

Nails only hold themselves.
 
#19 ·
It's not "cheap" vs "expensive" drywall screws, somebody just injected their personal take. It's the type of steel used to make drywall screws, at any price. For structural assemblies that can be subjected to shear forces, you want a mild steel that can bend, not a hardened one which can break off. There are some folks who use drywall or drywall like screws because they are readily available and easy to drive with a drill. They may not realize the screws can fail catastrophically. One major issue is in the construction of scaffoldings on job sites. People have used such screws in this type of construction and been hurt seriously. The type of drive head has nothing to do with it. You can get structural grade screws in all different styles of drive heads.
 
#21 ·
BobLongwood said:
Why is that because they are expensive or you don't think it would work well?
If this question was for me. As far as screws go. I built mostly furniture and don't use screws at all. The deck type will work great on any wood you care to use them on. Better than drywall screws because they will draw the two pieces together. Drywall screws would have to strip out in the first piece in order to draw the two together. I use one of those drill flip screw devices in my drill when using the deck screws even though they do have self tap threads.

Al

Nails only hold themselves.
 
#22 ·
Thanks I remember that happening the last time actually when I used lag bolts on my work bench.
The ones with the top third of the screw that has nothing on it are the preferrable ones? I also found these which seem to have a reversing pattern.


and then the original design

 
#23 · (Edited)
This has turned out to be quite the discussion, so I'll throw in a few more thoughts to consider.
As stated above the material & temper of the steel used in screws is very important for the application. However, keep in mind that regardless of the screw one uses, the purpose of a screw, wood or machine screw, is to draw the mating pieces together, and then to hold the pieces together from that point forward.

When using wood screws, it's easier to simply drive the wood screw through the first & second pieces in one operation, but this is not the correct way to install screws as the threaded portion in the first piece can prevent the second piece from drawing to the first piece.

To properly draw them they should be installed as follows:

  1. First use a pilot drill & line drill through both wood members to the final depth.
  2. Then use a body drill suitable for the screw & drill completely through the first piece of wood.
  3. This will allow the upper body of the wood screw to slide into the first piece of without having to "thread" it in.
  4. Countersink the first piece of wood to allow the head of the screw to sit flush, or just below the face of the first piece of wood.
  5. Assemble the wood pieces & then install the wood screw.
  6. This will allow the second piece to be freely drawn to the first piece, plus it facilitates dis-assembly or re-assembly.

Granted, this is more "work" than what most people are willing to do, so most use the easier method of just driving the screw into both pieces. In some cases this can add enough torsional load on the screw to cause it to snap off, or have its strength significantly reduced. Does anyone really want this?

Alternatively, if this is too much work, there are "screw drill bits" that are shaped & sized for individual screw sizes that have the body diameter of the screw built into the screw drill bit, or are tapered to suit.
 
#24 ·
When using wood screws, it's easier to simply drive the wood screw through the first & second pieces in one operation, but this is not the correct way to install screws as the threaded portion in the first piece can prevent the second piece from drawing to the first piece.
It may not be the threaded piece preventing a tight draw. An example would be if you were to screw two pieces of substrate together to get a 'double up'. Even with using a pilot/countersink combination bit, when the bit drills through the first piece it can create a bit of tearout, or debris around the hole, creating a blockage to the bottom piece.

A fix for that would be to align both pieces, mark the edges so they will align again for attaching. Drill all the holes for the grid pattern. Countersunk on the top piece, and piloted into the second piece. Then separate both pieces. Using a countersink bit, on the backside of the top piece, and the face of the second piece, drill a small countersink to clean off the hole area.

Then when attaching both pieces, the screws can seat completely, and there will be no debris between the pieces.

BTW...wood screws are technically tapered screws, and I don't use them unless they are with hardware.






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#25 ·
Something I just ran across. This should be helpful.
 
#26 ·
Cheap DW screws are made to keep prices down for that specific trade.

Any trade that is done by the "sq ft"..or "by the sheet" is susceptible to a downward spiral in materials quality.Look at the Chinese DW that came under scrutiny a few years ago.....do you think the industry looks for a "more expensive" product?Or do they look for cheaper alternatives?

So it is with the screws.When they first came out they were deffinately of better quality.......they have gotten progressively worse since.

Do you get what you paid for?Beats me......but ask anybody who screws DW all day and ask him how many heads pop off now...vs say 10 years ago.

So,anytime you are buying a product that's used in highly competetive,price point driven markts........as a hobbiest(and that can include folks at the HIGHEST levels of craftsmanship)you are swimming in shark infested water,just sayin.......don't let the price of materials be the "only" guide.This is a huge deal in the hdwre aisles.
 
#27 ·
BobLongwood said:
Thanks I remember that happening the last time actually when I used lag bolts on my work bench.
The ones with the top third of the screw that has nothing on it are the preferrable ones? I also found these which seem to have a reversing pattern.

and then the original design
Good deal. Those look like square drives. I've used those too. Anything but a standard flat head. I have a whole set of flat heads I will make anyone a good deal on. :)

Al

Nails only hold themselves.
 
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