A tool for cutting crowns

Pete Wass

Pete Wass

Well-known member
I am interested in grinding a HS steel tool for cutting great crowns. Looking for a shape that will enable me to cut a 45* chamfer without leaving burrs after I have cut the face. If someone could post a picture of theirs, I would appreciate it.

Thanks,

Pete
 

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Pete, if you are looking to cut a 45 degree bevel on your crown, rethink it. I've tried on probably 20-30 crowns, a sharp crown cut from the inside out, slow feed with a positive rake HSS tool works best.

Use the stem of a Q-tip to feel for any burr. The stem of modern Q-tips are some kind of cardboard and give a good feel if there is a burr. If there is a burr you will feel a drag when moving the Q-tip handle from the outside in. If your operation has left a burr, something is wrong with the grind on your tool, or you set it above or below center.

Ask Frank Green at Bartelin about crown burrs that break off a section of the muzzle bore. Even a 0,010" break-off will destroy accuracy. So much for the idea of shooting the burr off.

Granted, a bevel or micro-bevel makes a much more durable-to-wear crown but for benchrest use a sharp crown. You have a lathe, refresh the crown every 300-500 rounds.

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I like using a 3/8" shank Micro 100 boring bar. Turn it 45 degrees and make a few passes at high speed till you get your depth. Makes a clean fine finish.
 
rbfj49.jpg


Either HHS tool pictured will work.

Notice the extreme secondary clearance to allow clearance in the bore when machining from inside to OD.

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Yes!

JerrySharrett said:
rbfj49.jpg


Either HHS tool pictured will work.

Notice the extreme secondary clearance to allow clearance in the bore when machining from inside to OD.

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Click to expand...

What I was hoping to see. I was looking for a grind that would not be able to rub in any way in a .224" bore. I took a tool I had ground some time ago and relieved the area below the tip leaving just a small amount to support the edge. It has a very small radius on it and it cuts well but the two HHS tools you have shown here are more what I had in mind, I just couldn't seem to picture them myself.

Thanks Again,

Pete
 
Pete
I use a really small carbide boring bare. Insert is a CDCD . I cut 30 degree chamfers on crowns all the time. Good friend of mine just placed 7th in the two gun at the east west shooting one. i think its pretty safe to say, it will work. I see nothing wrong with a 45 Degree chamfer either. I actually think its a good idea. On my personal stuff i usually use an inside out, straight sharp crown. They shoot well, but as you know can be very delicate. Having the resources to re cut at any time, i dont worry much about it. Lee
 
Having my own range right outside my machine shop, i have done some pretty silly testing with crowns. One test i did was to simply chuck a barrel up in a 3 jaw and cut the crown at 11 degrees The crown and barrel shot a 3 shot zero right out of the gate. 6PPC. Perhaps the bore was pretty close to the outside diameter, or perhaps this was a fluke?? The barrel shot well, and still does. I didnt change it!!
I wouldnt go as far to suggest this by any means, but perhaps we over think things at times???? lee
 
skeetlee said:
Pete
I use a really small carbide boring bare. Insert is a CDCD . I cut 30 degree chamfers on crowns all the time. Good friend of mine just placed 7th in the two gun at the east west shooting one. i think its pretty safe to say, it will work. I see nothing wrong with a 45 Degree chamfer either. I actually think its a good idea. On my personal stuff i usually use an inside out, straight sharp crown. They shoot well, but as you know can be very delicate. Having the resources to re cut at any time, i dont worry much about it. Lee
Click to expand...



While there is no doubt that a angular bevel that breaks the sharp edge at the muzzle makes the area more durable, less subject to damage, by the cleaning process or use, I question if this intersection of a cylinder and cone are the best for extreme accuracy. Especially, if the bullet is a boat tail and the intersection of that cylinder and cone are not exactly on the same rotational axis. This, in my mind, could kick the bullet off its rotational spin, making it have a greater cross-section to the wind.
 
jerry
if dialed in properly why would there be any angular differences? am in not following what your describing properly? lee
 
This ad reminded me;

BG Gunworks said:
For most production crowning, piloted HSS cutter.
Otherwise, this work well for me with recessed target crowns and where a "non-standard" (other than 11°) is desired. I believe PTG sells it as well.

http://www.brownells.com/gunsmith-t...e-bits/barrel-crowning-lathe-bit-prod717.aspx
Click to expand...

Several years ago I was using a 30-284 short in HBR and it required rebating the heads. I had borrowed a custom ground tool to do them and returned it. A bit later I wanted to make more cases so went to a local machine shop and asked them if they could grind me a tool to enable me to cut them in one operation. They said yes and the next day called me saying the tool was ready. Much to my surprise, the bill was $50.! I was shocked a bit but paid without any comment and realized after that Fifty probably was a fair if not a great price for the work that had been done. Then I got to thinking, Old Son, you had best be learning how to use your bench grinder. :). The problem is, being able to conceptualize what a tool should look like and where to grind on it, and why I reached out here to see what others use. I greatly appreciate the pictures that were put up. I happened to have a tool that was mostly shaped for what I needed, all I had to do was relieve it a bit more.

Thanks again,

Pete
 
Pete
Is this the same tool you used in the guns you shot in Maine in the rim fire match today?
Thanks in advance
Gordon
 
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