Screw size for DIFFERENT sized lumber

[Steve Gronsky]

I seem to recall from a previous post somewhere that when choosing your screw size you should select the screw for the "receiving" piece of lumber rather than for the drilled piece.

e.g.  when joining a 2x4 to a 3/4 thick piece you should use the 1 1/4 inch screw.

as opposed to joining 2 2x4 to each other - you would use a 2 1/2 inch screw.

Have I got this correct? 

[Dan]

That is correct, the jig setting is for the piece you making the pockets holes in. The idea is to get the screw to come through the center of the edge of the wood, which is the strongest point. At first is was easy to understand when using two pieces of wood that were the same dimensions. However, when it came to using 2 different dimensions then it got a little confusing. I am now using the charts AND sample pieces whenever there is any doubt on which screw size to use.

[Ron davey]

Thanks for the info Dan. There has been discussion about a chart for all this. Where can I obtain this chart? I would post it right next to the jig if I had one. Also, if I'm understanding this, it would be better to put the pocket holes in the thicker of the two pieces whenever possible. Is this correct? It is a little confusing, but I think I understand the concept of it all. So, after all this, the screw length is the only deciding factor to consider when joing two different pieces of stock of a different thickness. Thanks for your help.

Dan said:

That is correct, the jig setting is for the piece you making the pockets holes in. The idea is to get the screw to come through the center of the edge of the wood, which is the strongest point. At first is was easy to understand when using two pieces of wood that were the same dimensions. However, when it came to using 2 different dimensions then it got a little confusing. I am now using the charts AND sample pieces whenever there is any doubt on which screw size to use.

[Dan]

The chart is in an excel file that I attached in this thread - about the 8th reply. The placement of the pocket hole depends on the situation, but as I understand it, it's best to put the pocket hole in the piece that goes in the direction of the grain, and have the screw go into the wood across the grain whenever possible.

[John Vinson]

Thanks for the chart. Settings worked right the first time I used it. I joined 3/4" to 1/2" using the 5/8" setting and 1" screws with no break-out and enough bite to hold a tight joint.

[Jens Jensen]

Now it sounds like if the pieces are edge joined ,how about face to face like say 3/4 to face of 1/2 inch,like drawer cases.I have not tried but it seems to me it will protrude out the back side. Tell me I'm wrong b4 I go out and run a test on it

[John Vinson]

Actually, mine was edge to face (3/4" pocket mounted vertically to 1/2" face). It was a shelving unit. The 3/4" shelf was being attached to a 3/4" side that already had a 1/4" rabbit leaving the 1/2" thick face. It did not break through using the 5/8" settings and the 1" screw.

Jens Jensen said:

Now it sounds like if the pieces are edge joined ,how about face to face like say 3/4 to face of 1/2 inch,like drawer cases.I have not tried but it seems to me it will protrude out the back side. Tell me I'm wrong b4 I go out and run a test on it

[DeWayne Demland]

This is great information, but I am doing something a little different. I am attaching a leg to a table top. The leg is a 2 inch square and the table top is 3/4" thick. The table top is attached to the wall, and the leg is for stability only. I was thinking of two screws, one on opposite sides of the leg. Since the Kreg can only be set for 1 1/2" will that work? Should I still use 1 1/2" screw as the chart shows for the 1 1/2"? Any suggestions would be great.

[Dan]

For me, I take all the markings and measurements of the Kreg Jig as a strict "guideline". They will be just want you need for most all of your joints, but in some cases you'll have to experiment. Keeping in mind there are 3 things to consider.
1 & 2. The size of the lumber you are drilling the hole in, the size of lumber you are connecting to, and the length of the screw. The objective is to drill the hole so the protruding screw exits in the middle of the stock AND that the hole is drilled deep enough to form the "pocket", but not too deep to weaken the joint by having too small of an anchor at the bottom of the hole. By anchor I mean the amount of wood left between the bottom of the hole and the rest of stock left beyond the hole.
Drill the hole too deep and you could pull the screw through the anchor. This is where the setting on the jig, in combination with the setting the collar on the screw is considered. Having the screw come out of the stock in the center is determined by the jig setting.
3. The length of the screw needs to be considered so it is long enough to have enough meat left after passing through the anchor to get good grip on the stock you are joining to. Too long of a screw will cause the screw to protrude through the receiving stock, which is not good. Also, keep in mind that the "length" of the screw can also be determined by the depth of the hole you drill. The deeper you drill, the longer your screw will get, and vice-versa.
As you can see all three considerations work in unison. It may seem confusing, but it's actually not that complicated. The best thing you can do is to use a piece of test stock to see how it all works with different settings, especially if your using stock out of the Kreg variables.
In your case, I would use the 1 1/2" settings and a 2" screw to see how close you get, then make adjustments. In my experience, the screw exiting in the center of the stock is the best thing you can 'fudge' on.
Sorry, didn't mean to get to long winded, but I hope this helps.

[DeWayne Demland]

Thank you I do understand and it makes sense.

DeWayne

[erik hinds]

I have found that when joining two 2 x 4's (actually 1 & 3/8ths thick) that you should use the 1 3/8 setting for depth and a shorter screw than 2 1/2. Mine keep poking out the otherside. Not sure if I should really be using a shorter screw versus a shallower setting...

[simpleman]

Exactly what I am doing!

John Vinson said:

Thanks for the chart. Settings worked right the first time I used it. I joined 3/4" to 1/2" using the 5/8" setting and 1" screws with no break-out and enough bite to hold a tight joint.

[Brian VanOrder]

I got the chart, which will help. What will help even more is knowing whether the dimension of the piece "being drilled into" is listed on the top or the side of the chart. Trivial why they left that out :)