Cutting a good crown

R

rain164845

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I am having a lot of trouble with cutting a good crown. I have used a boring bar with carbide insert, I have also tried a hss boring bar and both are pushing a burr into the bore. Does anyone else have any ideas? If you grind your own, would you mind posting a picture?
Thank you.
 
I would not use a boring bar to cut a crown.

The proper method is single point facing with a sharp, positive rake tool ground from either a cemented carbide or high speed steel.

I use a 1/2 inch shank 883 grade cemented carbide ground with a curved chip breaker and a very slight nose radius, just enough to keep it from chipping.

I run it at 1000 rpm and hand feed, the final just taking .001 inch from the face..

http://benchrest.com/attachment.php?attachmentid=19164&stc=1&d=1488857111

The best way to cut a convex crown such as found on factory barrels is to use a sharp form tool to cut the convex shape, and then sing point a small counterbore just a few thousandths larger than the groove diameter to insure you have not pushed metal and formed a burr and also maintain the cosmetic appeal of the crown.
 
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I too like using a micro 100 boring bar for the crown. It's sharp and makes a super finish. I use a 3/8" shank and the shortest bore depth they make. I just simply angle the tool post so it makes roughly a 45 degree angle for my recessed crown. They also make nice tenon counter bore and cones. If you want a pic...I can post one up
 
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I might be wrong, but I would venture that the OP does not have a full CNC capable machine that he is doing his barrel work on.

Your procedure is totally impractical for the multitudes of Hobby/Gunsmiths who are working with small 13-14 inch manual machines doing just a few barrels to satisfy their own, or perhaps a few friends, needs.
 
jackie schmidt said:
I might be wrong, but I would venture that the OP does not have a full CNC capable machine that he is doing his barrel work on.

Your procedure is totally impractical for the multitudes of Hobby/Gunsmiths who are working with small 13-14 inch manual machines doing just a few barrels to satisfy their own, or perhaps a few friends, needs.
Click to expand...

I did my crowns the exact same way on a 13x40 manual machine for years. I was using Circle M solid carbide boring bars then because I didn't need focused coooant. The ops were the same.
 
This is what I use...
picsay-1488897740923.jpg


IMAG3154-picsay.jpg
 
http://benchrest.com/attachment.php...eason?? I accidentally ground the tool wrong.
 

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Tools

Here is what I am working with.
I am not sure why the pictures are rotated 90 degrees to the left, but tilt your head and you can see my setup.
The first picture was the boring bar that I was initially using.

The second picture is the Warner HSS insert on their general turning tool. I am getting good results with this, but the flat on the crown doesn't look great. The actual crown is burr free though.

3rd is a lapping tool I made from brass. Since I am cutting 90 degree crowns, I chucked the brass rod in a collet, faced the end, center drilled, slit the end, then faced again. I am not sure I'll use this on the finished barrel since I am getting good results from the Warner tool.

20170307_202423.jpg
20170307_203216.jpg
20170307_203523.jpg
 
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