the real secret to hand cutting a dovetail

[yip]

 i've been cutting dovetails by hand for some time and have never found the secret to cutting them. seems i can't get the right width, the depth is no problem its the width, i find it all trial and error mostly error. is there a secret to this? times its tight and others is a little loose. i made them .050 deep on thin barrels and about .060 on larger barrels it all depends.

[Bill Raby]

Just cut it with the width too small and very slowly widen it out until it is the right size. Don't try for a perfect fit the first time.

[Steve_Rose]

Cut the square area to the minor width and depth of the sight, lug, etc. Then cut the dovetail to fit with your “safe file”. There is no real"secret" to the job.

Even when cutting modern gun dovetails on the mill for sights and such there is enough variance in the sight to do the final fitting at .001” per pass.

[Jerry]

In the past when hand filing a dovetail, I would always file them with a tapered width. That way I always got a good tight fit. Jerry

[Bob McBride]

All the advice you’ve gotten is perfect. Make it smaller than needed and SLOWLY work you’re way to a fit. Continually check fit from both sides as it’s darn hard to keep your safe triangle file perfectly square. As you get close check every few swipes with the file. Debur the dovetails on the lug/sight first. That’s the only secret I know of.

[tiswell]

In my opinion, all of the advice is correct. I think what Bob McBride shared is most insightful. The file can not make the interior corners on the female dovetail perfectly sharp. There is always going to be a slight radius or chamfer created by the file there. Deburring the exterior corners of the sight or tenon every so slightly will keep you from thinking you are getting sufficient contact on the angled surfaces when you may only be getting contact on the otherwise sharp corners.

[P.Bigham]

A sharp Chisel also helps to get in the corners of the dovetails. 

[WestBranchSusquehanna]

Yip, I have been posting about my Hawken Flint build and mentioned about a method that has really worked for me in cutting in dovetails:
First I mark out on the metal after having coated the area with Dykem or use anything to mark on.  Whiteout should work.  Taking my calipers, I measure either the sight or lug to how wide I want my cut to wind up and mark on the barrel.  Then taking the same calipers, measure the depth of the cut, i.e. the thickness of the base of the sight or lug and with the depth gauge of the calipers will use that to scribe the line on the barrel.  Most times I'll then use a hack saw and make as many cuts ALMOST to those lines as possible.  Then I clean up with a file and get to the lines.
Having made the main channel cut, I then use a triangular file and just start a grove in the bottom of the L on both sides,  Then I will take my jewelers saw and using a #8 blade cut into the grove about 1 1/2 blades thickness.  Take a chisel and form up the metal a little.  I will then go back to my tri-file and hit a few times to dress up the metal.  I then go back and form up with the chisel a little more.  Sometimes, particularly with a sight, the fromnt wedge may be longer than the back.  Cut and form as needed.  Once, I am close to fitting, I open up one edge a little with either the file or chisel to start the insertion.  Then little by little using any of the above, it will give you a tight fit. 
Finally, using a large pin punch, I'll form the metal over the wedge and sometimes it looks just like the sight was originally cut out of the barrel metal.

[Herb]

Here is how I did it.

https://americanlongrifles.org/forum/index.php?topic=11329.0#top

[D. Taylor Sapergia]

If there is a secret, I think it is this:  learn to file flat!!  Creating that first rectangular cut in your barrel is the hard part.  After that, the 60 deg. dovetails go in easily.  Filing flat is a skill that pays for itself over and over in this craft.

[B.Barker]

Flat filing is a very good skill and most folks can't use a file that well. I use a cold chisel now to do the under cut and it also lifts up a small amount of metal. The raised metal will help you make shallower cuts for barrel lugs.

[D. Taylor Sapergia]

Yes, and the raised steel can be used to gently tighten the dovetail.

[alacran]

This is one of those skills that require the right attitude. First off measure everything and be very careful laying things out. 2nd you are not on a clock.  As Taylor said flat filing is very important, you need to measure a lot to insure a flat surface that is parallel to the barrel flat.
I have been studying Flintlock Jaeger Rifles by Wolf. In the book you can see that even in these masterworks, there are sights installed that are not square to the barrel. Yes some of these guns were made 300 years ago but the sights were installed by the same techniques we are using today. On rifle #9 there is a good close up of the barrel's front sight dove tail. It is missing the sight. the dove tail is less than perfect. It is not filed very flat. Might be why the sight is missing.