Best Speed To Run Dovetail Cutters?

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  • Last Post 02 February 2015
GBertolet posted this 27 January 2015

I am going to try my hand at cutting some pistol sight dovetails for a winter project of mine. I have purchased .370 X 65 and .330 X 60 carbide cutters. The cutter instructions  specificly warn of not going over 700 rpm. Is there an ideal speed to use? What speed do the amateur and professional gunsmiths on this forum like to use? I have a choice of 670, 470, 310, and 190 rpms on my mill.

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RicinYakima posted this 27 January 2015

I have only done this twice with my new mini-mill, before I just filed them by hand. For me the best speed appeared to be about 600 rpm, lots of cutting oil and a very slow feed. What I really had to learn is that the work piece had to be dead solid and not have any vibrations.

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Ken Campbell Iowa posted this 27 January 2015

try some cuts on easy cut steel before going to the real one. old gun barrels would work, 12l14, etc. if you need steel, i still have about a ton left of ezcut round ( g ) .

it is really a matter of chip load per tooth than either feed rate or rpm. in easy cut ( most gun steels included ) a minimum chip would be about 0.0005 per tooth. less could lead to work hardening, and more than o.002 per tooth may be too much load and break tool or start massive chatter.

for example, one flute at 1000 rpm at a chip of 0.001 max thickness ( feed per tooth ) is 1 ipm ( inch per minute ) infeed, or crank feed....

if your cutter is 6 flutes, 0.001 per tooth at 1000 rpm is 6 ipm, and 2 ipm at 300 rpm, and 1 ipm at 0.0005 chip. 1 to 2 ipm at 300 rpm is about what i would start with.

rotary cutters lead a much more violent life than a lathe cutter, so feeds per tooth are lower, especially for smaller hobby machines.

also, cut the square ( or rectangular ) meat out of the final dovetail first with a standard end mill; that gives chip clearance and smaller load for your delicate dovetail cutter. getting rid of chips is the biggest problem in cutting, also note there is very little metal at the end of the dovetail cutter tooth; carbide can chip easily if chatter starts. chuck up as close as possible on the cutter, and tighten the gibs on your holding fixtures as much as possible and still crank. and yes, more oil, lots of oil.

pm me if i can be of further help.

ken

edit: heh, thought i should add :  a dovetail is a one-pass deal, you can't cut in successive deeper cuts ( g ) .  that why you should run some practice trys in plastic, aluminum, or ezcut steel.  heck, all three !!

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TomG posted this 27 January 2015

As Ken sez the depth of the cut is a one shot deal but the width can be adjusted. My dovetail cutters all cut smaller on the width and you will need to take very light cuts to make it just wide enough for the sight to start into the dovetail. 

The last one I cut was a Novak rear sight cut on a 45 auto slide. As he says, make the major center cut with a straight end mill and just cut the corners out with the dovetail cutter. I think I ran it at around 500 rpm and kept the feed rate up by hand. I don't have a power feed on my old jap mill.  

Practice on an old piece of 4140 steel barrel if you need to and you can get a feel for the feed rate that works best. Carbide likes to run faster than carbon steel. Use a real good cutting oil and lots of it.  I like the old Rigid pipe thread cutting oil with sulfur in it. If you want to get fancy, you can cut a little taper into the dovetail to facilitate the sight entering the slot. The slot on a Novak is pretty shallow so you don't have much more than one shot to make it right.

Once you've done one you'll be an expert.

Tom

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TomG posted this 27 January 2015

I just thought of one more thing. If you don't know the depth of the cut, you can measure the sight and get it.  Measure from the bottom of the dovetail on the sight to the bottom the blade or frame of the sight above. You want about .010"clearance between it and the top of the barrel or slide in the end. Just subtract O10 ” to that dim. and you will be OK.  If you get it too short, you can always file a little flat on the barrel for clearance. Tom

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GBertolet posted this 31 January 2015

Thanks guys. My project was putting a Heinie Slant sight set on a Browning Hi-Power slide. I needed a .370 X 65 cutter for the rear sight, and a .330 X 60 for the front sight. I purchased carbide cutters for the task.

The measured drawing included with the sights was detailed and easy to understand, on where and how deep to make the cuts.

I ultimately ran the mill at 670 rpm, and cut slowly, adding plenty of oil. I finished up using the 60 and 65 degree triangular sight files to get the dovetails just right. For a beginner, I was really amazed on how well the job turned out. I was on pins and needles, having to make 4 different cuts for the rear sight, and was relieved when everything lined up perfect with the sight. I just hope Mr Heinie's selection of the proper front sight height for the Hi-Power, jives with the point of impact. We shall see.

 

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Ken Campbell Iowa posted this 02 February 2015

congrats !! don't you just love it when a plan comes together !!

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