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I've just got myself a Kreg Pocket Hole Jig, but I'm stuck because the measurements are imperial. I have a 35mm plank, but the jig only has 13, 19 and 38mm. I understand that 35mm is only a few mm off 38mm, but should I still somehow push the stop tabs back a little? I'm planning to use 51mm pocket screws.

Any advice appreciated. Thanks.

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    the stop collar would still be off right? Better to drill though a shim of cardboard into the wood to bring the total thickness to 38mm. Or just test as-is (39mm) on a scrap piece and see if it pokes through, I'm guessing it won't...
    – dandavis
    Aug 15, 2023 at 22:33
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    You probably won't drill through if you're using the 38mm setting on 35mm wood, but the hole might be deep enough that the screw will poke through the other side. You might need to use a shorter screw, but I'd also suggest migrating this to Woodworking, as you'll probably find more expertise there...
    – FreeMan
    Aug 16, 2023 at 14:03
  • I don't think you're going to be able to figure this out mentally. You could do a quick-and-dirty simulation flat on the bench with some scraps of wood and the screw, to see how things will work out but I think ideally you want to sketch this out on paper. Even a crude sketch might tell you what you need to know.
    – Graphus
    Aug 16, 2023 at 16:52
  • Agree with dandavis. Try it with a 4-5mm shim on some scrap. That seems like the easiest/quickest way to reach a conclusion.
    – gnicko
    Aug 16, 2023 at 19:28
  • @dandavis But if I place the jig on top of a 3mm shim of cardboard or mdf and drill through it into the wood, wouldn't the hole end up being closer to the surface of the wood than it should be? I think it needs a way to maintain the depth of the hole and just stop the drill bit from going in too far?
    – John M.
    Aug 17, 2023 at 8:03

1 Answer 1

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I understand that 35mm is only a few mm off 38mm, but should I still somehow push the stop tabs back a little?

Moving the "front" of the jig (where the drill bit enters the bushing) farther away from the edge of the workpiece moves the exit hole (where the bit pokes out) down, away from the face that the workpiece is clamped to. Moving the jig closer to the edge moves the hole up, closer to the face where the jig is.

So... if you've got a 35 mm-thick workpiece, you can use the 1 1/2" (38 mm) setting for the stop with a 6 mm shim between the edge of the work and the stop to set the position of the jig. Once the jig is clamped in place, you can of course pull the shim out of the way.

Remember that you may also need to adjust the stop collar on the bit slightly, not just to keep the thick part of the bit from exiting the hole, but to make sure that it leaves enough wood that the screw head won't easily pull through what's left. Ideally, the tip of the bit should just break the surface when the stop collar hits the bushing.

Alternatively, you can put a 1.5 mm shim between the jig and the face of the workpiece before clamping and just use the 1 1/2" setting. There's no need to change the stop collar from the 1 1/2" setting if you use this method.


Let me explain where I got the shim sizes. The second one is easy: the jig is set up to drill a hole such that the tip of the bit hits the center of the edge of the workpiece. The difference between 35 and 38 mm is obviously 3 mm, so if you want to keep the hole in the center of the edge, you'd move the jig away from the face by half the total thickness.

To calculate the size of a shim to use between the stop and the edge of the work, you need to know that the jig drills pocket holes at a 15° angle. If you think of a cross-section of a board with a pocket hole drilled in it, you can imagine a right triangle where the legs extend from the corner of the workpiece between the face and edge to the pocket hole, and the hypotenuse is the center axis of the hole itself. Since the angle of the hole is 15°, the ratio between the legs is tan(15°), or about 0.27. If you want to move the exit hole "up" 1.5 mm to adjust for the 3 mm difference in material thickness, you can do it by moving the jig 1.5/0.27 = 5.55 mm closer to the edge, and it's probably a little easier to just round that to 6 mm.

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