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Old 03-11-2018, 10:16 AM
kenk kenk is offline
 
Join Date: Feb 2012
Posts: 271
Default Kreg Jig Screw Penetration Depth Formula

For those of you who use a Kreg (Pocket Hole) Jig, yesterday I did some ciphering (as Jethro Bodine would say) and here is the formula using Excel (or Google Sheets) format to calculate the screw penetration depth into the receiving material - at a right angle to the material surface - not along the path of the screw:

PenetrationDepth =SIN(RADIANS(75))*(ScrewLength-(0.073/SIN(RADIANS(75)))-0.48)

The ScrewLength and PenetrationDepth are in inches.

The ScrewLength is the distance from screw tip to the flat base of the screw head (the side toward the tip).

This assumes that the Kreg drill bit stop collar is locked in place using the 'nickel method' rather than the on-jig guide. This is done by placing a U.S. nickel on the jig base, inserting the Kreg drill bit with a loose stop collar into the jig letting the drill bit tip gently rest on the nickel. Slide the stop collar down until is meets the top of the jig and lock the collar in place.

I find the nickel method to provide a safer (less likely to drill through the base!!) and more predictable drill tip location relative to the jig base.

The formula assumes that the nickel thickness is 0.073 inches (measured using a 1976 nickel; a newer style 2013 nickel measured 0.075, and was notably lighter in weight!! Maybe my 1976 nickel was a bit worn from use over the years - I know I am. This value is easy to change in the formula as desired.

The formula aso assumes that the distance from the Kreg drill bit step shoulder to the tip is 0.48 inches. I couldn't find a published length, and your own measurements may be different, but again, this is easy enough to change in the formula.

If using the Kreg Micro Jig, you would need to measure the Micro drill bit tip length and replace the 0.48 value with that distance. I haven't yet taken the time to do that measurement on mine. Remember to use the nickel method of drill bit stop collar placement!!

If using the Kreg Jig HD on a Kreg Jig base, you would need to measure HD drill bit tip length and replace the 0.48 with that distance. Remember to use the nickel method of drill bit stop collar placement!!

If using the Kreg Jig HD off of a Kreg Jig base, you will likely to need both the 0.073 and 0.48 constants to be changed, since you can't use the nickel method of drill bit stop collar placement. Sometime in the future I'll try to do those measurements using the recommended drill bit stop collar placement.

The published angle between the jig 'fence' and the drill/screw direction is 15 degrees.

I compared my calculated values with some published depth values and they are close but not exactly the same. This may be related to the method used for screw bit depth collar placement.

Oh, and I don't think the screw penetration depth has anything to do with the thickness of the materials being used - either the material receiving the pocket hole or the material receiving the screw. Of course if the material receiving the screw is too thin then the screw will come out the other side - not good. I suppose I should determine the formulas for the horizontal distance of screw travel which would be important if doing edge joining.

The thickness of the material receiving the pocket hole is used to determine the Kreg Jig's height setting - so that the screw will exit the bottom of the pocket hole material at the center of the material's thickness. That location - for different thicknesses of material - is marked on the base of my Kreg K4 Jig.
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Old 03-11-2018, 10:32 AM
kenk kenk is offline
 
Join Date: Feb 2012
Posts: 271
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OK, here is the formula for the horizontal screw travel distance from the point where the screw exists the pocket hole material - the point where the screw enters the material that receives the screw - toward the direction away from the Kreg Jig base fence.

HorizontalScrewTravel =(SIN(RADIANS(75))*(ScrewLength-(0.073/SIN(RADIANS(75)))-0.48))/TAN(RADIANS(75))

The distances are in inches.

Again, this formula uses Excel and Google Sheets format.

If the HorizontalScrewTravel is greater than half of the thickness of the material that receives the screw, then screw is predicted to exit the material on the side opposite the Kreg Jig base fence.

Fun with trigonometry!!

Ken
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