# Adjusting Dovetail Jig



## michiganmike (Jan 8, 2008)

I recently purchase a Porter Cable 12" dovetail jig w/ the halfblind jig or template. When I join the two pieces I've routed there is a gap, about 1/16 of an inch, in each of dovetail joints. Otherwise, the fit is fine.How do I adjust to eliminate this?


----------



## vapochilled (May 2, 2007)

practice! it is all a simple case of adjusting the bit height, work on scrap pieces first.

welcome BTW


----------



## bobj3 (Jan 17, 2006)

Hi michiganmike

Here's a little trick you can try, pull out a 3/8" drill bit, move the dovetail bit up or down till the top of the router bit is the same height as the drill bit, use a block of wood for a quick jig to set the bit,,put the block of wood on the drill bit and on top of the bit then adjust the bit...to match the drill bit..

Once you try it out and it's just right make a setup block, so you have one the next time you want to use the dovetail jig......
To make a setup block you will need to put a 1/2" slot in 1st. (for the brass guide) then just slide the dovetail bit in the slot,,, then mark the block and save it..
Note **** don't remove the bit to make the setup block, if you don't have a router table just drill a hole or two on the edge of a scrap board..then slide the dovetail bit in..



==========



michiganmike said:


> I recently purchase a Porter Cable 12" dovetail jig w/ the halfblind jig or template. When I join the two pieces I've routed there is a gap, about 1/16 of an inch, in each of dovetail joints. Otherwise, the fit is fine.How do I adjust to eliminate this?


----------



## curiousgeorge (Nov 6, 2006)

Old dovetail addage:
Heighten to tighten, lower to loosen.
In other words if the fit is loose... raise the bit. If it's tight... lower the bit.


----------



## michiganmike (Jan 8, 2008)

This is Michiganmike again. I think I need to be more specific. The 1/16" gap I mentioned is on the side of the joint, not the depth. I went overkill and used a digital readout depth gauge and the depth of the cut is perfect. No gap there. The gap I mentioned is on the sides or shoulders (one gap per dovetail joint). Like a gap between two teeth. It is consistent for each individual dovetail joint. I double checked the depth of cut, as I said above, and also experimented with the offset of the two boards. That only offset the two boards, leaving one high on one side, and inset on the other, in relationship to the other board. Ever seen this? Any ideas how to correct it? 

Thanks again,

Michiganmike


----------



## bobj3 (Jan 17, 2006)

Hi michiganmike

Because the dovetail bit is on a angle ( 14deg. the norm)

"Old dovetail addage:
Heighten to tighten, lower to loosen"


==========



michiganmike said:


> This is Michiganmike again. I think I need to be more specific. The 1/16" gap I mentioned is on the side of the joint, not the depth. I went overkill and used a digital readout depth gauge and the depth of the cut is perfect. No gap there. The gap I mentioned is on the sides or shoulders (one gap per dovetail joint). Like a gap between two teeth. It is consistent for each individual dovetail joint. I double checked the depth of cut, as I said above, and also experimented with the offset of the two boards. That only offset the two boards, leaving one high on one side, and inset on the other, in relationship to the other board. Ever seen this? Any ideas how to correct it?
> 
> Thanks again,
> 
> Michiganmike


----------



## Mike (Nov 22, 2004)

Mike, this could be caused by a couple of things. Let's try the simple one first; measure the diameter of the dovetail bit and make sure it is actually the correct diameter. Bits are often undersized from sharpening or poor quality control. If your bit checks out ok then what you are seeing is an improper depth adjustment. By raising the bit slightly the wedge shape moves up and eliminates the gap. If your joint had been too tight you would lower the bit to loosen the fit. It is important that the wood you use for setting up your joints is the same thickness as the stock you will be working with. Any change in thickness throws off the geometry. Once you have your bit set to the correct height and are getting good cuts you should make a set up block as BJ suggested. This should be a piece of hardwood or HDPE; simply make a partial cut into the material. The next time you do your set up you slide the block onto your bit and use it to set the height... perfect in seconds every time.
If you are near the Detroit area send me a PM and I will give you directions so you can join us for our next "Sawdust Saturday".


----------

