14 degree dovetail bit

[Gerry S. Wojtowicz]

I am trying to work with an old Reliant half blind dovetail jig. The instructions, which are not very clear, call call out for a 1/2 inch dovetail bit.
The comb spacing is 1/2 inch. If I use a guide collar the instructions call out for a guide collar of 7/16 OD. If I use a 1/2 inch dovetail bit with a bearing guide is the bearing guide itself less than a half an inch (like the 7/16 guide collar).

Does anyone know if a 1/2 inch dovetail bit with a bearing guide will fit between the fingers of this jig (which I assume is like most jigs, if not as well made or designed).

Thanking you in advance.

[Lee Schierer]

I don't see how they could make a 1/2" bit with a 7/16 O.D. bearing above the cutter that would be cost effective. They would have to machine the shank down to fit the bearing I.D. and then shrink fit an elongated bushing over that small shaft to get up to 1/2".

I use the Rocker dovetail jig that uses a similar guide busing and the 1/4" 14 degree bit works quite well.

[Ethan Melad]

I believe they are calling for a 14º cutter with a 1/2" cutter diameter (at the widest point), not a 1/2" shank. A 1/4" shank will fit fine through the 7/16" guide bushing. I think I have used both Freud and Wood River bits, would recommend Freud or Amana over the Wood River.

[Gerry S. Wojtowicz]

Lee, the 7/16 was not the diameter of the dovetail bit with a bearing guide, but a guide collar that attaches to the router (no bearing guide needed on the actual dovetail bit).

I assume they called out for that diameter because the spacing of the comb is .5 inches.

That's why I was trying to determine the diameter of the bearing guide on a 14 degree dovetail bit with a bearing guide. If the diameter of the bearing guide was .5 inches and the spacing on the combs was .5 inches would the guide actually be able to travel down the combs.

I assume if they are both .5 inches, the tolerances would be so loose it wouldn't be a problem. I was just trying to confirm that before I bought the bit.

[Gerry S. Wojtowicz]

Ethan,

I tried to use a guide bushing, but on my router ( a Freud) the bushing protrudes to the point where it interferes with the comb. That's why I wanted to try a dovetail bit with an inherent guide bushing.

[Lee Schierer]

My dovetail jig came with a shorter guide bushing. I also have the Freud bushing set with the taller bushing. You could shorten the bushing you have with a saw or have a machinist mill it down so it is slightly shorter than your comb.

[Lee Schierer]

That's why I was trying to determine the diameter of the bearing guide on a 14 degree dovetail bit with a bearing guide. If the diameter of the bearing guide was .5 inches and the spacing on the combs was .5 inches would the guide actually be able to travel down the combs.

I assume if they are both .5 inches, the tolerances would be so loose it wouldn't be a problem. I was just trying to confirm that before I bought the bit.

Unfortunately they rely on the play between the bushing and the comb to cut the right size pins and tails. If the .5" bearing went into the slot on the comb your slots for the tails would be narrow and the tails would be wide and they wouldn't go together.

[Gerry S. Wojtowicz]

Unfortunately they rely on the play between the bushing and the comb to cut the right size pins and tails. If the .5" bearing went into the slot on the comb your slots for the tails would be narrow and the tails would be wide and they wouldn't go together.

I'm not too sure what you're saying Lee. The .5 bearing would have to go into the slot on the comb, would it not? How else would the dovetail bit contact the wood?

[Myk Rian]

I don't see how they could make a 1/2" bit with a 7/16 O.D. bearing above the cutter that would be cost effective..

You have it wrong. A 1/2" dovetail bit with a 1/4" shank is a standard size.
I see no reason why a 7/16" bearing wouldn't work. It's the same size as the recommended guide bushing.

[Lee Schierer]

I know this sounds crazy, but a line to line fit won't work. If a hole and a shaft are the same exact size, you cannot put a .500" shaft in a .500" hole. There has to be a tiny bit of clearance. The way the dovetail jig works is the bit is guided by the bushing in the comb. The fact that there is 1/16" clearance between the bushing and the comb slot means that you need to follow the contour down one side of the opening and out the other as you do the cutting to make a dovetail that will actually go together. If the bit stays perfectly centered, which it would if the bearing were .499 and the comb opening was .500 the resulting dovetails wouldn't actually fit together. Since wood has fibers, you actually need to machine a bit of clearance in the dovetails so they will fit together without binding that clearance is created by the 1/16" diameter difference.

[Lee Schierer]

You have it wrong. A 1/2" dovetail bit with a 1/4" shank is a standard size.
I see no reason why a 7/16" bearing wouldn't work. It's the same size as the recommended guide bushing.

What is the Inside Diameter of a 7/16" bearing? That is the problem. It has to slide down the shaft to get in place just above the cutter. Since you have an outer race, balls and an inner race that all have some size your resulting shaft gets quite small.

[Gerry S. Wojtowicz]

I know this sounds crazy, but a line to line fit won't work. If a hole and a shaft are the same exact size, you cannot put a .500" shaft in a .500" hole. There has to be a tiny bit of clearance. The way the dovetail jig works is the bit is guided by the bushing in the comb. The fact that there is 1/16" clearance between the bushing and the comb slot means that you need to follow the contour down one side of the opening and out the other as you do the cutting to make a dovetail that will actually go together. If the bit stays perfectly centered, which it would if the bearing were .499 and the comb opening was .500 the resulting dovetails wouldn't actually fit together. Since wood has fibers, you actually need to machine a bit of clearance in the dovetails so they will fit together without binding that clearance is created by the 1/16" diameter difference.

I understand and agree with what you are saying Lee. That's why I started my inquiry about the diameter of the guide bearing on a 14 degree dovetail bit. If the bearing and the fingers are indeed the same diameter i couldn't see how the whole system would work. I'm hoping there is enough of a clearance between the finger width and the guide bearing to allow the system to work.