Dovetail bits/jigs

[vaking]

I have made couple dovetail drawers before. They came out OK, nothing spectacular, not very ugly. I see a fare quantity coming soon, so I decided to improve my technique and setup and that got me thinking. I want nothing fancy, decent joint reasonably fast, simple and repetitive.
As a general rule I prefer router bits with 1/2" shank over ones with 1/4". All typical jigs are similar in design and yet there are differences. MLCS jig, for instance, uses 5/8" OD bushing. This bushing I believe allow use of either 1/2" or 1/4" shank. I have a Jet jig and it needs 7/16" OD bushing. With this bushing 1/2" shank is out of the question. What bit do you use for half-blind dovetails? How important is size of the shank?
Regular 1/2" 14-degree dovetail bit is very common. Most are double-flute and that is what I used so far. Recently I got a better quality bit but it is single-flute. What effect will it have on the cut? Do I need to increase router rpm or decrease speed at which I move it?
Finally - I am also considering sliding dovetail on the front of drawers instead of half-blind. Is it more complex or not? What is your experience?

[JimD]

Alex,

I have three inexpensive half blind dovetail jigs but the one I actually use is from Harbor Freight. I ususally use a Grizzly template guide on it to get 7/8 inch dovetail spacing rather than the 1 inch the guide that came with it gives. The Grizzly guide is also smoother than the cast aluminum HF guide. My jigs all require 1/2 inch diameter at the big end dovetail bits with 1/4 shanks. The one I am using at the moment came from CMS. It works well. I have broken inexpensive bits of this type so now I buy from one of the "better" brands. Other than that, I have had no issues with the 1/4 shank bits. I prefer 1/2 shanks too but that is not what my jigs can use.

I typically use my PC690 router for this although I have used my old Ryobi R-500 which is now dedicated to my router table. I might try my Bosch Colt at this someday but haven't so far. Full speed is what you want and I also make a back cut (climb cut) at first to minimize chip-out.

Sliding dovetails probably take a little less time than what I consider "normal" dovetails but you need to cut the slot on one side of the drawer front using a climb cut. I do not like doing such a long cut going the wrong way when a slight slip can ruin a good piece of wood. So I do not use sliding dovetails much.

I have my HF dovetail jig on a base which raises it and also gives me more side support to help with aligning the drawer pieces. Once the setup is right, it takes so little time to cut half blind dovetails I normally do it on the back as well as the front. If you search for my prior posts, you should be able to find my base for my dovetail jig. Cutting all the dovetails for a drawer has to take me well under half an hour. Maybe 15 minutes. I consider the appearance and strength to be well worth it. Getting your setup time down and you consistency up is what really helps dovetails be worthwhile. My base really helped me on these points.

Jim

[vaking]

Thanks Jim,
I found your post with description of a base - impressive work. Also noticed that HF jig in the pictures look exactly like Jet jig that I have (except the color). Same aluminum template, cams that secure the wood, etc. What made you switch from HF template to Grizzly? How important is the fact that grizzly is smoother? Or is it the spacing that attracted you?
Thanks again for posting - I am looking forward to making my setup better now.

[Black wallnut]

One small note that is worth mention. For 1/2" 14° dovetail bits the weakest point of the bit is usually the same diameter in both 1/2" and 1/4" shank models. It's simply a nature of the design.

I have the PC 12" jig and it allows me to use the 1/2" shank bits. More and more I'm thinking that the steeper angled dovetails look better.

IMHO for drawer fronts sliding dovetails are a weaker joint as there is very little of the wood between the dovetail and the edge of the drawer. Overlay drawers that are not rabbeted would be an exception. I do like sliding dovetails for other applications such as table leg to apron joints and corbels on my couch tables. Rising sliding dovetails are fun for the wooden mallet ala Woodwright shop. Sliding dovetails are also fun, really in the square dovetail puzzle......

[LCHIEN]

One small note that is worth mention. For 1/2" 14° dovetail bits the weakest point of the bit is usually the same diameter in both 1/2" and 1/4" shank models. It's simply a nature of the design.

I agree with BW, there's probably no real difference in use between the 1/4" shank and 1/2" shank for the common 1/2" 14° dovetail bits, because the lower diameter of the bit is fixed at 1/2" and the specified angle and the required cutting height results in a very narrow neck at the top of the angled dovetail section. When you push this bit too hard it will break there, not in the shanks. Nothing can be done about it.

So there's no real advantage in my mind to using the 1/2" shank version. I'm not sure but there may even be some fit issues using the 1/2" shank bits with some template systems. (As VAKING noted with the Jet template an 7/16" bushing).

[JimD]

I went to a Grizzly template due to the spacing. I made a couple bedroom sets from Woodsmith (PlansNow) plans. They assume 7/8 dovetail spacing. I have used the guide the HF jig came with and it works but the sides of the fingers being a little rougher is not exactly a good thing. I can't say it affects the resulting joint that much but it is a little tougher to keep the router where it is supposed to be. The 7/16 guide on the router just fits into the openings of a 7/8 template, however, so there it is always going to be easier to guide the router along. It is probably more than just the smoother surface.

Jim

[vaking]

I agree with BW, there's probably no real difference in use between the 1/4" shank and 1/2" shank for the common 1/2" 14° dovetail bits, because the lower diameter of the bit is fixed at 1/2" and the specified angle and the required cutting height results in a very narrow neck at the top of the angled dovetail section. When you push this bit too hard it will break there, not in the shanks. Nothing can be done about it.

So there's no real advantage in my mind to using the 1/2" shank version. I'm not sure but there may even be some fit issues using the 1/2" shank bits with some template systems. (As VAKING noted with the Jet template an 7/16" bushing).

I agree with the fact that weakest point on dovetail bit is the same for 1/4" or 1/2" shank. I might even accept that 1/4" shank is stronger because it has less sharp transitions and those transitions weaken the bit.
The main reason to use 1/2" in my opinion is heat dissipation. Bigger bit is much heavier and much harder to burn, so it can go on longer. In my experience most bits get ruined not by pushing too hard but by running too long and making it too hot. Dovetail might be different though, because once you cut one joint you must stop to replace the material and that will give the bit time to cool off.

In order to use 1/2" bit the shank must be able to fit through the bushing. I believe 5/8" OD bushing is the smallest that has ID still bigger that 1/2" (by a hair). So the only jigs that can use 1/2" shank bits are those that use 5/8" bushings.
And also - I read somewhere that the best angle for dovetails is 14 degree if joint is made of softwood and 9 degree for hardwood (from strength perspective, not aesthetics). I believe most people use hardwood for dovetails, so why 14 degree joint is so popular escapes me. But the fact remains that it is the most popular type and I am looking for practical easy-to-produce joint only. I don't want the best or the most politically correct type.