Cutting a crown, reamer w/pilot or from outside?
- Thread starter thefitter
- Start date
jonbearman
I live in new york state,how unfortunate !
On a lathe.
Thefitter,
I'm interested to get some info on this too but no one has really answered your question yet.
Of course I cut them on a lathe, with a sharp carbide bit and I have also cut them with a piloted reamer from PT&G. I usually just cut an 11 degree crown and I really can't tell the difference on target from one methed to the other. I do run a cotton swab to make sure theres no burrs.
I dail the barrel in using Gordy Gritter's method and I would think, using a piloted reamer in a floating reamer holder, would give you the square'st cut you could get to the bore.
I'm interested to get some info on this too but no one has really answered your question yet.
Of course I cut them on a lathe, with a sharp carbide bit and I have also cut them with a piloted reamer from PT&G. I usually just cut an 11 degree crown and I really can't tell the difference on target from one methed to the other. I do run a cotton swab to make sure theres no burrs.
I dail the barrel in using Gordy Gritter's method and I would think, using a piloted reamer in a floating reamer holder, would give you the square'st cut you could get to the bore.
sailhertoo: I've had several experiences with one of my gunsmith's when he cuts the crown on one of my new barrels. If I request the 11 degree included angle, he will use the cutting tool (looks like a router bit/ shown in Brownell's catalog) to cut the crown. When I get the rifle home I check out the bore with my Hawkeye borescope, for the condition of the chamber, throat (both perfect with not a trace of a reamer mark in the throat), and at the muzzle end (not so perfect with cross reamer marks on the tops of the lands, for approx. 1" or so). This area will then copper foul heavily for the first 20 or 30 rounds. For this reason, when I now get a new barrel chambered I request, (in writing), the traditional 90 degree sunken crown, and the bore surface is free of any cross markings. This was my suggestion to "thefitter" to be considered when contacting his gunsmith. Some might say "find another gunsmith", but except for this one very minor problem, he is at the top of the list of my favorites--- way too good to stop using him.
The basic issue that needs to be considered is that the bore of the barrel is unlikely to be concentric with the barrel outer diameter. If you cut a 90 degree crown or recessed but still 90 degree crown this is the easiest and it does not really matter if you center on the OD or ID of the barrel. You could use a self centering 3 jaw, or a 4 jaw adjustable. Because you care cutting at 90 degrees there will be no consequence to any concentricity issues.
The problem comes in when you want an 11 degree target crown or any other none 90 degree profile. If you use a 3 jaw self centering (on the OD), and the bore is not concentric then your crown is not concentric, and it may create accuracy issues. The proper way is to use an adjustable 4 jaw with a pilot in the bore used to adjust for concentricity to the bore.
The last way is to use a PTG type cutter which pilots in the bore. It avoids the concentricity issues, but yes, you do have to be aware of any potential damage to the bore. But remember pilots are used to cut the chamber too...
The problem comes in when you want an 11 degree target crown or any other none 90 degree profile. If you use a 3 jaw self centering (on the OD), and the bore is not concentric then your crown is not concentric, and it may create accuracy issues. The proper way is to use an adjustable 4 jaw with a pilot in the bore used to adjust for concentricity to the bore.
The last way is to use a PTG type cutter which pilots in the bore. It avoids the concentricity issues, but yes, you do have to be aware of any potential damage to the bore. But remember pilots are used to cut the chamber too...
fdshuster said:
When you say cross reamer marks on the tops of the lands, are you talking about where the pilot slides into the bore?
The "live pilot", (only kind I use) , should fit tight and not spin when you cut the crown.
sailertoo: Yes! And that's the reason when I spec out a chambering reamer from PTG, it's always one with a floating pilot. When my 'smith does his usual excellent chambering with a proper diameter pilot, he leaves no reamer marks in the leade, so in that area no copper fouling from the first shot fired. I've never seen the 11 degree cutting tool, but from pictures doubt it has a floating pilot to make contact with the tops of the lands. Just one of the things I'm fussy about. Hate to clean out copper when it did not have to be there in the first place.
I have one and yes, it has a floating pilot! You can interchange the pilot bushings for the correct fit.
Larryh128
Silver $$ Contributor
A floating pilot would work fine, the problem as most well know are fixed pilots. I have seen some crowns that I couldn't possibly describe in words suitable for a forum. Most were done with a hand drill & a piloted cutter. Can you say chatter?
Any lathe can be made to accurately cut crowns. Some need a 4 way spider to help adjust the chuck, some don't. It's also possible to set up a concentric crown using a steady rest but that would be my last choice. Whatever method you use, higher rpm's will equal a better surface. Even though I use TICN coated inserts, I still use a coolant such as Cool Tool. If you have any specific questions regarding how to- feel free to PM.
Any lathe can be made to accurately cut crowns. Some need a 4 way spider to help adjust the chuck, some don't. It's also possible to set up a concentric crown using a steady rest but that would be my last choice. Whatever method you use, higher rpm's will equal a better surface. Even though I use TICN coated inserts, I still use a coolant such as Cool Tool. If you have any specific questions regarding how to- feel free to PM.
Here is how I cut many crowns.
1. Cut the barrel in a bandsaw (long by .250")
2. Chamfer and clean muzzle with nylon bore brush.
3. Dial in the barrel in a 4 jaw chuck and cat head (through the head stock).
4. Determine bore by bushings or pins. (to .0001)
I select a bushing that is not to tight (bushing stays as reamer spins but can slip with a little resistence)
5. I use PT&G piloted 79 degree counter bores, dish radius, or 90 degree cutters in a floating reamer holder.
6. With a clean muzzle bore I squirt(1 from pump bottle) 20-30 weight non detergent oil in the bore.
7. I carefully move the tail stock forward and insert the bushing to just clear of the cutter flutes. I use Vipers venom or heavy dark cutting oil and 105-125 rpms to cut the crown.
I clean and keeping the cutter well lubricated.
8. I then use a lathe bit to chamfer the OD of the barrel and a file to clean it up.
9. Some times I polish the crown with 400, 600, 800, 1200 grit emmory paper to a mirror polish.
10. I inspect the rifling and the crown with a 20 power bore scope and run a cotton swab in and out. No scratches, and no burrs and as little stress as possible. No in or outward lathe tool bit presure to cause stress or work hardening in the crown.
My customers success speaks for itself.
Nat Lambeth
1. Cut the barrel in a bandsaw (long by .250")
2. Chamfer and clean muzzle with nylon bore brush.
3. Dial in the barrel in a 4 jaw chuck and cat head (through the head stock).
4. Determine bore by bushings or pins. (to .0001)
I select a bushing that is not to tight (bushing stays as reamer spins but can slip with a little resistence)
5. I use PT&G piloted 79 degree counter bores, dish radius, or 90 degree cutters in a floating reamer holder.
6. With a clean muzzle bore I squirt(1 from pump bottle) 20-30 weight non detergent oil in the bore.
7. I carefully move the tail stock forward and insert the bushing to just clear of the cutter flutes. I use Vipers venom or heavy dark cutting oil and 105-125 rpms to cut the crown.
I clean and keeping the cutter well lubricated.
8. I then use a lathe bit to chamfer the OD of the barrel and a file to clean it up.
9. Some times I polish the crown with 400, 600, 800, 1200 grit emmory paper to a mirror polish.
10. I inspect the rifling and the crown with a 20 power bore scope and run a cotton swab in and out. No scratches, and no burrs and as little stress as possible. No in or outward lathe tool bit presure to cause stress or work hardening in the crown.
My customers success speaks for itself.
Nat Lambeth
PALarson
High Power Competitor, XC and Long Range
I really shutter at the thought of cutting a target crown with anything other than a sharp tool bit and a 4 jaw chuck. Dial each end using the bore for centering. Once the barrel is chucked up and the bore is true any degree of crown can be done accurately. AS has already been said faster turning speeds are better, lots of lubricant, and a final polishing is always nice.
Paul Larson
Paul Larson
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