Custom Jig Settings

[Mark J Kristan]

I set the piece that sides up and down, and the position of the step on the bit, differently than the width of the workpiece.  For those who hate reading and want to get straight to the question, it is, does it really matter if the bit goes all the way through the work piece, and drills a hole in the other side?  There are other details that I figure are relevant but if reading too much makes your head hurt or something, above is the short version.

I am extending the depth of my router table to accept an Incra LS jig.  I face-joined two boards to come up with the width of the existing table top and am trying to attach the two parts using the Kreg jig.  I fashioned three 15/16" thick by about 1.25" tall strips of teak to use as runners for this purpose.  The first problem I had was, with the short height, when I set the part that slides up and down the Kreg jig and the step on the bit, to 15/16", rather than enter the wood at a point on the side of runner, the hole started at the top.  I can't see how this would really matter so I'm no too worried about that and proceeded to drill some holes into an identically-sized scrap piece.   What I thought was a bigger problem is, when I used a 1.25" screw (the next longest one I have is 2.5") it did not go very far through the other side, maybe about half an inch.  So I played around with the bit step and the piece that slides up and down, and used spacers between the edge of the workpiece and the jig body, to try to make the hole come out around the middle and to allow the screw to penetrate farther into the mating piece.  When I figured I had it set acceptably well, I drilled four (out of a total of seven) holes into one runner;  those four holes do go all the way through that workpiece, I'm wondering whether this is really going to be a problem, in terms of the strength of the jig (not sure how much stress there will ever be on the joints - I don't think very much). I'm trying to decide if I should re-do that one runner, or if this is really not that big a deal.  I decided I'm going to find 1.5" screws and drilled the other seventeen holes with the jig set for  15/16" work piece.

If anyone thinks that a pic of what I'm doing would be helpful, I could attach that in a future post.

TIA.

Mark

[Hugh Clare]

If I understand your explanation correctly, you have two problems with the way you set up the jig. The first is that your screw won't exit the work piece in the center of the thickness. The second is that you reduce the amount of wood between the screw head and the joint, increasing the risk of tear-out.

[Mark J Kristan]

Hi Hugh, thanks for the reply, but that isn't exactly my problem.  One of the two issues I mentioned I really don't think should be a problem so I'm not going to worry about that but my question really is about the significance of some of the holes being through holes.  The jig is designed so that, if you set the bit step and the sliding piece to the thickness of your workpiece, the bit doesn't quite drill all the way through, so the screw bites into a bit of the workpiece the holes are drilled into.  Four of the seven holes on one of the runners are through holes, I'm wondering if this may significantly reduce the joints' strength.  Even those four holes come out pretty much in the centre of the piece.  I played with the settings to make the screws go farther into the runners before contacting the piece because not very much of the screw was coming out the other side, but I'm just going to buy longer screws to deal with that.  What I want to know is should I be concerned about those through holes, or for a fairly light duty application like this should I be okay.

[KregCS]

Mark,

When using the jig you will not want the bit to come through your material.  The drill but should stop just short of coming out your piece.  This allows for the screw to still have threads in the piece allowing you to have a stronger joint. 

 

With your situation, you will want to set everything up for 7/8" settings and then use a 1 1/2" screw.   If you have any other questions please let us know. 

[Mark J Kristan]

KregCS said:

Mark,

When using the jig you will not want the bit to come through your material.  The drill but should stop just short of coming out your piece.  This allows for the screw to still have threads in the piece allowing you to have a stronger joint. 

 

With your situation, you will want to set everything up for 7/8" settings and then use a 1 1/2" screw.   If you have any other questions please let us know.

Thank you, this is what I was asking, will those four through holes significantly reduce the joints' strength - I will replace that one piece that has some through holes.   It is curious why you say to set things to 7/8", though\, I mean 15/16 is a difference of only .0625" so I guess it is probably inconsequential, but I set the step bit and the piece that slides to about half way between 7//8" and one inch for the seven holes in each of the other two runners (all fourteen of those holes are non -through).