Lee Valley ½ Dovetail Router bit mystery

[Brian Knodel]

For two evenings I’ve been trying to make a series of dovetail cuts using the Lee Valley ½ dovetail bit (part number 16J17.52) I’m making the cuts on a Jointech router table with the incremental positioning fence. Any ways the cuts were coming out like this and I couldn’t figure out why.
51809
Cutting dovetails using the Jointech system is based on centering and if you’re out a little bit I would expect to see off centered cuts as in the photo. I re-centered numerous times and always came up with the same cut and then out of desperation I measured the router bit and found it was 1/64 short of 1/2. Knowing this I know re-centered and came up with better cuts like this.
51810
Question is are all ½ inch dovetail bits actually just under ½ or is it just my bit, in any event I suppose doesn’t really matter unless you use a Jointech or Incra systems, and I’m in no way upset with Lee Valley as maybe that’s just the way things are … but I measured my ¼ inch bit ant its one quarter right on the money.

If you all don’t mind could you measure your ½ router bits for me?

Just curious

Brian

[Gary Keedwell]

Brian,
Just measured mine with dial calibers. Woodcraft=.502.....Freud=.500 Unnamed Taiwanese= .496


Gary K.

[Bill Boehme]

Sounds like it might actually be a 12 mm bit.

Bill

[John Lucas]

Brian,
I wonder if it is something else. Centering. If you are using their centering device, it may be a little off. Try the "old way" . Rather than try to describe it here, I found the page that shows it...it is with Incra but of course the same method other than Jointech is now using the centering jig which is cool but your first picture is out of balance and that isnt bit size. Fact is, if bit is 1/64 small, you should be able to adjust for it (raising bit height).

http://www.woodshopdemos.com/incr-c35.jpg

Here ispage: http://www.woodshopdemos.com/incr-ch2.htm
Let me know what you find out.

[Brian Knodel]

Thanks all for the help and John thanks for the link and I would like to address some things you were talking about, but first, although I am using a Jointech system I am using Incra’s templates and I also have Incra’s instruction manual so I am familiar with Incra’s Centering technique although you do it a bit different than shown in the manual with the board standing on end. I like your way better. I haven’t tried your method yet as I had to work today but I did give your post a lot of thought.

With the Jointech centering method you have the fence touching the furthest edge of the bit and then set the centering device (rabbit) to the appropriate width of cutter, in my case ½ and I think that is where the problem arose, as the cutter is smaller by just a hair and so the cut was off by just a hair. By adjusting the centering device (rabbit) to the actual diameter of the bit I could achieve better cuts so this tells me that the centering device is working properly. I recently built a spice box with 9 drawers with varying heights and the centering system worked perfectly for every drawers but I was using a ¼ inch bit.

The height of the dovetail cut shown in my first post is the final depth of cut and now cannot be adjusted up or down as then the dovetails will not fit like they do now ( I think I’m right on this) Once the depth of cut is found no further adjustment is required.

Fact is, if bit is 1/64 small, you should be able to adjust for it (raising bit height).
I don’t follow how this would work as by raising the bit not only would the depth of cut be off but your piece of wood is in the same position, tight to the fence and clamped to the slider. Would not raising the bit just make deeper cuts in the wrong place?

John if I’m wrong just say so and put me in my place … I’ve been put there before.

BTW I measured the bit tonight and it measures .491. Does that sound a little small? Or is it just me?

Thanks

Brian

[Jim Becker]

BTW I measured the bit tonight and it measures .491. Does that sound a little small?

.491" is not .5". Close, but not 1/2". I don't know how or if that would be affective to the cutting method you are using, however. On regular half-blind jigs, bit height is the critical measurement for fit. I'm not sure of the relationship when using the Jointech or Incra systems.

[John Lucas]

Brian,
You may be right on the loosen..I always have to check the book when it is that time. As to centering, how ever you do it, your cut end should be symetrical.
Measuring router bits, very difficult since th carbide cutters are a little off center. Measure the cut and you will be better off. I still think you can have success with the corner.