Grizzlypeg
Aluminum
- Joined
- Aug 20, 2012
- Location
- Canada
When truing internal threads with a single point cutter, do you use only the cross feed to advance the cut deeper?
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truing internal threads
- Thread starter Grizzlypeg
- Start date
- Replies 25
- Views 5,303
LKeithR
Stainless
- Joined
- Sep 1, 2011
- Location
- Langley, B.C.
The most common--but certainly not the only--way to cut threads is to set the compound to 29-1/2 degrees and cut the majority of the thread by feeding the compound in deeper. The tool cuts easier because it's only cutting on one side. For the finish passes (.003" - .005") feed in with the cross-slide. This forces the tool to cut on both sides and normally leaves you with a nice clean finish...
J. Randall
Stainless
- Joined
- Jul 29, 2003
- Location
- Vici Okla. U.S.A.
wesg
Titanium
- Joined
- Nov 4, 2004
Me too. I want the whole thing cleaned up so I know where I am diameter wise. No guessing as to what's going on as I thread the barrel to fit.
If you're feeding at an angle you need to set the compound as you normally would for cutting an external thread and feed out with it. The back side of the thread is what matters. Consider that if you're grinding your own tool. The inserts I use don't seem to care which way they go.
If you're feeding at an angle you need to set the compound as you normally would for cutting an external thread and feed out with it. The back side of the thread is what matters. Consider that if you're grinding your own tool. The inserts I use don't seem to care which way they go.
Grizzlypeg
Aluminum
- Joined
- Aug 20, 2012
- Location
- Canada
Do you skim the tops of the threads afterwards so that they aren't so sharp? Do you measure the actual finished theads afterwards with a measuring instrument, or do you simply keep track of how much you cut and appropriately oversize the external dimension of the threaded part that goes into it?
wesg
Titanium
- Joined
- Nov 4, 2004
You should. And this is why I use full form inserts, so I don't have to worry about it.
I've done a couple by threadmilling, a Lee-Enfield and a Ruger no3, that weren't so easy to set up in the lathe. In both cases I had plug gauges I made ahead of time to figure out where I was on diameter so I could mill the minor diameter to correct size.
You could probably eyeball the flat to spec after cleaning up the thread and be good enough.
I've done a couple by threadmilling, a Lee-Enfield and a Ruger no3, that weren't so easy to set up in the lathe. In both cases I had plug gauges I made ahead of time to figure out where I was on diameter so I could mill the minor diameter to correct size.
You could probably eyeball the flat to spec after cleaning up the thread and be good enough.
Forestgnome
Stainless
- Joined
- Aug 2, 2008
- Location
- Californeeeah
I do this when cutting new threads, but when truing receiver threads I would think it would be better to use the crosslide to keep the cutting tool in direct alignment with the original threads.
Grizzlypeg
Aluminum
- Joined
- Aug 20, 2012
- Location
- Canada
How heavy of a boring bar do you use for holding the internal threading tool? Is 3/8 too light?
Kiwi 'smith Dean
Cast Iron
- Joined
- Jan 13, 2011
- Location
- Tauranga, New Zealand.
Way too light. Rule of thumb: Use the biggest size boring/threading bar that you can get away with.
Dean.
jim rozen
Diamond
- Joined
- Feb 26, 2004
- Location
- peekskill, NY
When cutting ID threads you do NOT put the compound in the same orientation as you would
for doing OD threads.
There's no reason to avoid putting the compound at 29 degrees when doing ID threads, this
is the way to set it up:
1) loosen the compound and swing it so the handle is pointing away from you - that is, directly
at the wall behind the lathe.
2) swing the compund 30 degrees to the right, then back it off a half a degree. It will then be
pointing to the rear, mostly and a bit right.
3) infeed the dial to larger numbers to increase the thread depth.
There are other ways, but this works well when running the spindle forward, and cutting
right to left.
for doing OD threads.
There's no reason to avoid putting the compound at 29 degrees when doing ID threads, this
is the way to set it up:
1) loosen the compound and swing it so the handle is pointing away from you - that is, directly
at the wall behind the lathe.
2) swing the compund 30 degrees to the right, then back it off a half a degree. It will then be
pointing to the rear, mostly and a bit right.
3) infeed the dial to larger numbers to increase the thread depth.
There are other ways, but this works well when running the spindle forward, and cutting
right to left.
Forestgnome
Stainless
- Joined
- Aug 2, 2008
- Location
- Californeeeah
I still think straight into the thread would be the best way. You're trying to centraliize the thread concentric with the bore while cutting the least material possible. In my mind skimming all features of the thread at once would minimize the cut needed to achieve this. Just my opinion though. I know it's done all the time on Rem 700's. Would like to hear about any testing done on concentricity of stock receivers.
wesg
Titanium
- Joined
- Nov 4, 2004
The absolute minimum would be to just shave the inner face that's loaded when the barrel is torqued in. Cleaning up both would seem to require enlarging the PD by twice as much.
Jim's setup is correct for cutting a new thread. Using that method to recut an existing thread in an action will NEVER clean up the inner face of the thread no matter how much you take out. You need to go the other way, or straight out.
I've seen several that are crooked enough that simply centering the tool at one point will find it well off center 180° out. So you need to play a bit there and compromise so you take roughly the same off each side.
As for checking alignment, I thread each one onto a freshly threaded dummy barrel stub and check at the tail end with a mandrel. The best I've seen was about .003 TIR on a M-70. The face was as near dead nuts as I could hope for, so I didn't bother touching anything on it. Remingtons ... good lord ... I think the best one cleaned up with the thread about .020-.025 oversize. Some of them are beyond the .080 range of my Interapid indicator at the tail end. Makes me wonder just what you're getting with a piloted .010 OS tap, that is flexing as well. I'd love to run some tests some day.
I also check them again after truing. I consider anything under .003 TIR to be 'perfect'. It's really easy to be worse than that if you get carried away tightening the screws in your truing fixture and spring the action while you're setting it up. These things are so flexible it's really hard to keep them straight once the screws hit them.
The Ruger no3, BTW, was pointing 'down' at about 3/4°, visibly crooked by eyeball, and I took it all the way out to a nominal 1-1/16" thread to get it straightened out. The Lee-Enfield was better than most of the Remingtons I've seen ;-)
Jim's setup is correct for cutting a new thread. Using that method to recut an existing thread in an action will NEVER clean up the inner face of the thread no matter how much you take out. You need to go the other way, or straight out.
I've seen several that are crooked enough that simply centering the tool at one point will find it well off center 180° out. So you need to play a bit there and compromise so you take roughly the same off each side.
As for checking alignment, I thread each one onto a freshly threaded dummy barrel stub and check at the tail end with a mandrel. The best I've seen was about .003 TIR on a M-70. The face was as near dead nuts as I could hope for, so I didn't bother touching anything on it. Remingtons ... good lord ... I think the best one cleaned up with the thread about .020-.025 oversize. Some of them are beyond the .080 range of my Interapid indicator at the tail end. Makes me wonder just what you're getting with a piloted .010 OS tap, that is flexing as well. I'd love to run some tests some day.
I also check them again after truing. I consider anything under .003 TIR to be 'perfect'. It's really easy to be worse than that if you get carried away tightening the screws in your truing fixture and spring the action while you're setting it up. These things are so flexible it's really hard to keep them straight once the screws hit them.
The Ruger no3, BTW, was pointing 'down' at about 3/4°, visibly crooked by eyeball, and I took it all the way out to a nominal 1-1/16" thread to get it straightened out. The Lee-Enfield was better than most of the Remingtons I've seen ;-)
B
butchlambert
Guest
wesg,
I have read a little about how you cut threads. How do you accurately indicate a 17 Enfield receiver prior to straightening threads?
I have read a little about how you cut threads. How do you accurately indicate a 17 Enfield receiver prior to straightening threads?
jim rozen
Diamond
- Joined
- Feb 26, 2004
- Location
- peekskill, NY
"...Using that method to recut an existing thread in an action will NEVER clean up the inner face of the thread "
THat's right. Taking skim cuts on an ID thread, trying to bring it to axis, is a tough one. Having full engagement
of both sides of the tool when you pick up the thread, is a recipe for springing the tool. If doing this then the
biggest boring bar possible and the most rigid setup is a must-have.
THat's right. Taking skim cuts on an ID thread, trying to bring it to axis, is a tough one. Having full engagement
of both sides of the tool when you pick up the thread, is a recipe for springing the tool. If doing this then the
biggest boring bar possible and the most rigid setup is a must-have.
wesg
Titanium
- Joined
- Nov 4, 2004
Hi Butch,
This was a British Enfield, .303. I started by milling an aluminum block with a nest for the bottom of the action. Bedded the action into it with Devcon, then added the front guard screw and a plate in the tail end with a screw to secure it. Then I turned a mandrel to fit the bore, and squared the aluminum block from that. From there it went into the machining center in a vise standing on edge. Indicated the mandrel in, and then thread milled it. I made a series of plug gauges in .005 increments over the 1-14 thread it had.
Indicating on the plug gauge afterwards showed it off center by a thou or so. Don't know where that came from. And don't really care much ;-)
With the huge socket on the rear for the buttstock it looked like a giant PITA to set up in the lathe. I figured I'd need the same block, and an angle plate mounted to a face plate. The P-17 would probably be ok with a large enough truing sleeve to clear the sight ears. The only other thing with those is the locking lugs are helical, so a bad idea to true them up while you're in there.
It's one of those dumb 'why am I doing this?' projects. True it up, add a Kreiger barrel in .30 cal chambered for a slightly improved .303. Bury the light Palma profile under the original handguards, machining the muzzle to fit the original front sight, etc. And then go and shoot 600yd prone matches with what looks like a no4 mk2 in .303.
Senseless, really. I must have SOMETHING better to do with my time?
This was a British Enfield, .303. I started by milling an aluminum block with a nest for the bottom of the action. Bedded the action into it with Devcon, then added the front guard screw and a plate in the tail end with a screw to secure it. Then I turned a mandrel to fit the bore, and squared the aluminum block from that. From there it went into the machining center in a vise standing on edge. Indicated the mandrel in, and then thread milled it. I made a series of plug gauges in .005 increments over the 1-14 thread it had.
Indicating on the plug gauge afterwards showed it off center by a thou or so. Don't know where that came from. And don't really care much ;-)
With the huge socket on the rear for the buttstock it looked like a giant PITA to set up in the lathe. I figured I'd need the same block, and an angle plate mounted to a face plate. The P-17 would probably be ok with a large enough truing sleeve to clear the sight ears. The only other thing with those is the locking lugs are helical, so a bad idea to true them up while you're in there.
It's one of those dumb 'why am I doing this?' projects. True it up, add a Kreiger barrel in .30 cal chambered for a slightly improved .303. Bury the light Palma profile under the original handguards, machining the muzzle to fit the original front sight, etc. And then go and shoot 600yd prone matches with what looks like a no4 mk2 in .303.
Senseless, really. I must have SOMETHING better to do with my time?
Dave W
Aluminum
- Joined
- Jan 10, 2007
- Location
- central Arkansas
Scrubbing the oven, watching Oprah, darning socks, doing a stealth wildcat Enfield... jeez, hard decision there...
B
butchlambert
Guest
wesg,
So you do not ream the bore of your receiver before putting your mandrell in to indicate?
So you do not ream the bore of your receiver before putting your mandrell in to indicate?
wesg
Titanium
- Joined
- Nov 4, 2004
No, I don't ream them. I have a couple mandrels with journals on them that just hit the bearing surfaces in the receiver. The journals are about 1/2" long. I usually have to lap a little bit to get them to fit. So in effect, 'reaming' the bore on a small scale, but not anything close to fully cleaning everything up like you'd do with a reamer.
These are primarily match rifles that have to be shot rapid fire, and a hunting rifle or 2. So no tight bolts, and they're more than loose enough to begin with. I don't want to make that worse. If these were benchrest rifles I wouldn't bother with any of this. Same with my long range rifles, all custom actions.
These are primarily match rifles that have to be shot rapid fire, and a hunting rifle or 2. So no tight bolts, and they're more than loose enough to begin with. I don't want to make that worse. If these were benchrest rifles I wouldn't bother with any of this. Same with my long range rifles, all custom actions.
B
butchlambert
Guest
OK,
I thought you were going to the trouble to really square them up, my mistake. Good enough for a hunting rifle. Looks like you are enjoying yourself.
I thought you were going to the trouble to really square them up, my mistake. Good enough for a hunting rifle. Looks like you are enjoying yourself.
wesg
Titanium
- Joined
- Nov 4, 2004
Yeah, I suppose I am. At least when I have time to actually get anything done.
So how true are yours when you finish? I asked for data on the BR forum years ago and nobody even bothered to reply. I assumed that meant they never bothered to check and were happy deluding themselves.
Not trying to be a dick, I really want to know. My M-70 did come out a bit better than average after lapping the bolt bore straight. About .002 TIR at the tang. God what a mess that thing was when I got it. No comparison to my 1st Barnard though. The second hasn't made it to the lathe yet. Come to think of it, I don't remember if I bothered to check the Borden.
So how true are yours when you finish? I asked for data on the BR forum years ago and nobody even bothered to reply. I assumed that meant they never bothered to check and were happy deluding themselves.
Not trying to be a dick, I really want to know. My M-70 did come out a bit better than average after lapping the bolt bore straight. About .002 TIR at the tang. God what a mess that thing was when I got it. No comparison to my 1st Barnard though. The second hasn't made it to the lathe yet. Come to think of it, I don't remember if I bothered to check the Borden.
