Tips on cutting a dovetail?

[MtGun44]

I have a brand new dovetail cutter from Brownells and would like to
cut a front sight dovetail in my Colt SS Commander. Never cut a dovetail
before. I am using a nice little BenchMaster knee mill, so the equipment
will be fine. It is the operator that is in doubt!

So far, I've planned it this way. I will do a piece of scrap first, the real
slide will be the first real part, but not the first trial cut.

Set up slide level in the mill vise. Take a very, very slight flat cut on the sight
area to make a pad for the sight blade, which overhangs the dovetail a lot
front and rear. Since the dovetail is supposed to be 0.060" deep, zero the
scale on the knee after the fine cut and moving the slide out from under the
cutter. Crank the knee up until I have the 0.060" deeper setting. Making sure
to be at low speed (Brownells says under 700 RPM, I will use slower) and
very slowly feed the slide past the cutter. Seems too easy.

Any hints, "must do's" and "don't do's" or shortcuts will be GREATLY
appreciated.

I wonder if a roughing cut with a straight 1/8" mill cutter to remove the center
stock down to maybe .050" deep would help or just more risk of a screwup?

Thanks.

Bill

[Morgan Astorbilt]

Here's how I cut a standard 3/8" dovetail in a round barrel using a 3/8" 60º dovetail end mill in my Bridgeport. The same method will work for the dovetail you're cutting.

The dovetail on a round barrel is .090" deep. I Make my first "roughing" cut with a straight 1/4" end mill, .090" deep, by raising the knee. This is to make the actual cut with the fragile dovetail cutter easier. It also allows me to vary the depth, which can't be done with the dovetail cutter. After making the 1/4" cut, I change to the dovetail cutter, and bring it down to just touch the bottom of the cut made, on one side, lock the quill, and make the cut in one pass using the cross feed. I also use a reduced diameter dovetail cutter for some jobs where a 3/8" cut won't do, using multiple passes. You can vary the size of the "roughing" mill to fit the slot width you're cutting.

A good way to determine depth, is to bring the cutter(power off) down on a piece of saran wrap on top of the slide, 'till it just grabs. Move the slide over, and bring the knee up to the depth you want, then make the cut.
Hope this helps,
Morgan

[dubber123]

I am getting ready to attempt this also, and everyone I have talked to suggested the straight cut to help out the fragile dovetail cutter. Most also preferred an undersize cutter, so you can "sneak up" on your final cut, which isn't possible by making a single pass.

Keep us posted, I am interested.

[GabbyM]

What Morgan said.
I never heard of using saran wrap. Gosh I can't even get that stuff over a jar without making a balled up mess. I've just used 20 lb paper and allowed for the thickness.

As long as you don't do something like forget to lock your quill it will come out fine. Not familiar with your mill but you may need to lock your tabel down on one axis too.

As in most jobs on a mill. Once you get the work holding solution you're half done.

Decreasing the rpm on your cutter will just increase the load.

[Morgan Astorbilt]

Gabby, I mentioned saran wrap as a generic description. If truth be told, I usually tear a small square of any thin plastic bag laying nearby, and use that. Any light touch on that with a cutting tool, brings the tool to within less than a thou., if not actually touching the work piece. No need to mike the paper and add the thickness.

Another trick, if you're re chambering a standard caliber that headspaces on the rim or belt, to an "improved" version, such as a 7mm Rem. to a 7mm STW, is to coat the existing recess for the rim or belt, with Dykem, and as you're finishing the chamber, just advance the reamer, 'till it removes the Dykem, without actually cutting into the metal, thus retaining the original headspace.
Morgan

[MtGun44]

Morgan,

Thanks VERY much. Sounds like what I wanted to do, just helps a great deal
to have someone that has done it verify that this is the correct sequence of
operations.

On my little BenchMaster, the knee is the only vertical feed, so no problem with
the quill moving!

I'm going to do a practice cut on some aluminum round stock to avoid dulling
the dovetail cutter. The saran wrap deal sounds great, too.

Bill

[Rustolium]

At work we use either scrap paper(around .003") or magic marker to color the part for touch off. Just go till the cutter grabs the paper or removes the marker and allow for the thickness on the paper. Good luck!