Trueing a bolt face on the lathe...

E

eww1350

Guest
What is your preferred method of fixturing and indicating a rifle bolt to true the bolt face and cut the locking lugs when blueprinting an action..??
Do you use the firing pin hole as the true center at the nose.??..what is the true center at the rear..??



Eddie in Texas
 
The body, the OD has to be indicated so the est of the bolt is concentric/perpendicular, etc.
 
Most bolts have an internal threads of 1/2-13. First, the extractor and ejectors, if present, must be removed.

On those I chuck a 1/2-13 threaded stud and true it up. Then I screw the bolt on that trued stud and run the area just behind the lugs in a roller equipt steadyrest.

This will accomplish setting up for bolt face truing. This will not allow access to the bolt lug faces on a fluted bolt.
 
JerrySharrett said:
Most bolts have an internal threads of 1/2-13. First, the extractor and ejectors, if present, must be removed.

On those I chuck a 1/2-13 threaded stud and true it up. Then I screw the bolt on that trued stud and run the area just behind the lugs in a roller equipt steadyrest.

This will accomplish setting up for bolt face truing. This will not allow access to the bolt lug faces on a fluted bolt.
Click to expand...

Jerrys hit it right, I would add make a false center center drilled on one side and faced then cutoff so parallel and use this against newly cut bolt face to cut bolt lugs.this will support without steadyrest for trueing cuts on back of lugs. george
 
Eddie, it depends upon how close to the center the firing pin hole is whether you can center on the firing pin hole or not. If you've indicated very many bolts in, you'll find they aren't very concentric and very seldom are you able to get a bolt indicated in any better than about .0005" or so. You just do the best you can with the bolt that you have and get it indicated in as close as you can front and rear. The photo below shows a jig I made for use when the firing pin hole isn't in the center. It presses against the end of the bolt nose and has four brass tipped 10-32 set screws to move the bolt head back and forth. You indicate in the rear of the bolt and with the live center in the firing pin hole or in a plug made to fit in the firing pin hole with a center cut into it, if the runout behind the lugs is over about .002", then I use the jig and get the bolt body running as true as I can get it front and rear. I use a threaded rod with a ball made into it at the rear that will let the rear of the bolt pivot. I used to do as Jerry said and chuck up on the bolt and true up the threaded rod and turn it around and chuck on the trued surface. After you do this several times on different bolts, you have to remake the threaded jig to hold the rear of the bolt. The ball on it serves the same purpose and doesn't have to be remade.

boltsetup2.jpg

Indicating in front and rear on the bolt body.
facelugs.jpg

Facing off the rear of the lugs.
boltfacetrue.jpg

Facing off the bolt face with the front of the bolt held in the steady rest.

The photos are old and were made on a lathe that I no longer have. My current steady rest is a roller bearing steady rest on not the brass tipped steady rest shown in the photo.

Trubore_thb.jpg

Current setup for truing receivers.

There are several schools of thought on truing actions. How much difference it makes, I really don't know. For the expense that you go to when building a custom rifle, it's pinching pennies to not have the action trued. I've rebarreled enough actions that have had their lugs lapped in by someone else to see that it's a lot better to have the receiver and bolt lugs trued by machine and then lapped to check than by just lapping the lugs. Quite often, lugs will have a taper lapped into them making the bolt close tighter on the go gauge the farther the bolt handle is closed. A properly set up action should close on the go gauge after the bolt cams over the same at the top of the stroke until the bottom of the stroke. If it gets tighter as the bolt closes, then a taper was lapped into the lugs. Some gunsmiths will sleeve the bolt at the rear and at the front of the bolt with the live center running on the firing pin hole and then turn the sleeves down for the clearance they want and face off the rear of the locking lugs on the same bolt setup. This makes the sleeves concentric with the firing pin hole and the lugs perpendicular to the sleeves. For the time that it takes to do this and resulting cost, now days, you're better off to replace the bolt with a Pacific bolt made to the diameter than you want, for instance, .703 or .704 on a .705 raceway.
 
How would you do a BAT action bolt, as it does not have the treaded bolt shroud?
I have a Model 'B' which is PPC bolt face and I need to open it up to 308

Thanks
Michael
 
I've made a plug before that's a tight fit into where the bayonet mount goes with a allen head set screw that tightens up against the inside of the bayonet area of the bolt. You have access to the allen head set screw through the area where the cocking cam is on the bolt body. Then you can run the front of the bolt on the steady rest and open up the bolt face.
 
JerrySharrett said:
Most bolts have an internal threads of 1/2-13. First, the extractor and ejectors, if present, must be removed.

On those I chuck a 1/2-13 threaded stud and true it up. Then I screw the bolt on that trued stud and run the area just behind the lugs in a roller equipt steadyrest.

This will accomplish setting up for bolt face truing. This will not allow access to the bolt lug faces on a fluted bolt.
Click to expand...

All well and good, but how do you true up that 1/2-13 bolt? Every one that I have worked on needs to have that bolt screwed in and tightened and then trued up due to the excessive runout. I indicate the lug end in first, then run the handle end in the steady with the bolt in place and single point a 60 deg center in it. I then remove the steady and insert the tailstock center into the bolt end. With both ends now running true, I take a light cut on the back side of the lugs (lug end still in four jaw). Next, turn it around and put the bolt head in the four jaw and lug end in the steady. Indicate in the handle end and your have the bolt running true to cut the face. The thing of it is, the threads in the bolt do not run true.
 
Jkob said:
All well and good, but how do you true up that 1/2-13 bolt? Every one that I have worked on needs to have that bolt screwed in and tightened and then trued up due to the excessive runout. .
Click to expand...

The only bolts I have trued are Remington 700/600/xp100 series. The threaded bolt is true because I machined it in a 6-jaw chuck that runs within 0.0005". I marked the bolt so it goes in the same jaw orentation each time. What kind of bolts are you truing anyway? Sounds like Chilean Mausers or such??

If you are truing the OD of the bolts then you need to sleeve them back to a decent fit within the action.
 
JerrySharrett said:
The only bolts I have trued are Remington 700/600/xp100 series. The threaded bolt is true because I machined it in a 6-jaw chuck that runs within 0.0005". I marked the bolt so it goes in the same jaw orentation each time. What kind of bolts are you truing anyway? Sounds like Chilean Mausers or such??

If you are truing the OD of the bolts then you need to sleeve them back to a decent fit within the action.
Click to expand...

I understand that, kind of a cheap shot on the Mauser reference! I was referring to Remington Bolts

It sounded as if you were insinuating that the threads in the back of the bolt were concentric with the OD of the bolt. You did not indicate whether you trued the bolt when it was in the six-jaw, it sounded like You set it up with the bolt running as if it were true. If, after you inserted the half inch bolt in the bolt body you indicated it in in the six jaw, I would not question you procedure.

I am not questioning or doubting your abilities, your reputation prededes you, onl;y trying to clarify for the OP

I don't true up Mauser bolts!
 
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I true them as Mike Bryant does, studied his pics. I was very skeptical at the steady rest install but then surprised at how well it works if you are careful. To help pivot at the chuck when dialing in, I took an inner tie rod end off a truck and cut it apart, don't have a ball cutter and a used tie rod end was in the scrap steel bin. The ball is part of the shaft and I threaded it 1/2x13 for about 1 1/2" so I could put a nut and washer on it plus install it in the bolt. The tool used to hole the bolt head in the pic should have four adjusting screws as Mike's does, not three like mine does.
 
Not too long ago in a similar discussion it was "turn a fitted collar to slip over the barrel to "center it" inside the headstock"......

I happen to be with Jim on this, 3-dimensions of axial adjustment is (marginally) adequate for any setup.

I'd prefer four.

I don't trust ME, and I certainly don't trust anything else :)

And I certainly would never waste the time to turn and thread a spindle for this application. There's a whole lot more wrong with it than the fact that the threads might (WILL) be eccentric with the bolt body.

al
 
OK, so with the threaded 1/2" stub, how does one tighten up to stop? Against a shoulder? Against a nut? How do you take the play out of the threads without sucking up to SOMETHING? Even if you're driving off the bolt hannle, or a dog, you can't just let 'er FLOP......And once you're sucked up how are you not indexing off the rear of the bolt? In other words, compare it to a threaded barrel shank, I think we'll all agree that even with perfectly machined threads if one were to have the stop shoulder off 90degrees it would point the barrel in a new direction, right? And how do we face off the rear of the bolt? I'm just not getting any sense of this, even with a buck chuck that bolt's gonna' be in a bind to my mind.....

'Course I'm open for correction, I too realize deeply that Jerry was making chips when my parents were playing spin-the-freakin'-bottle.....

al
 
alinwa said:
OK, so with the threaded 1/2" stub, how does one tighten up to stop? Against a shoulder? Against a nut? How do you take the play out of the threads without sucking up to SOMETHING'Course I'm open for correction,

I too realize deeply that Jerry was making chips when my parents were playing spin-the-freakin'-bottle.....

al
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Where does it stop?

Where does it stop Al? Think of the threaded thingy as a partially threaded stub arbor chucked in a precision 6-jaw chuck. The thingy is slid back into the chuck jaws to where the rear of the bolt butts up against those 6 jaw faces. Since the thread faces are machined surfaces, they provide the opposite surface for the workpiece loading, i.e. a stop. I may have some photos that I can post, right now it is coffee time in Tennessee.

Spin the bottle? Has it been that long? Could be, I guess. My first machining experience was in 1956 in a course at VA Tech titled Machine Shop Practices for Engineers.....that long??

Where does it stop, Butch. You state Jcob (apparently afraid to use his real name) called my bluff?? Where and when was I bluffing? I don't bluff, Butch. I don't have time to!!!!
 
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The 700 bolt that never was!!

Like this, Al.

22nvcm.jpg


A comment, on a non-fluted bolt such as this the lug faces can also be remachined.
 
Thanks Jerry,

so there it is.... I didn't even consider threading clear up to the chuck. I'd thread it OUT, me :) I'm chicken!

The bolt is indexed off the rear surface. So before the steady goes on you should be able to snug 'er up and there will be no wobble out at the locking lugs.

I certainly can't answer to that, never tried it. Maybe they are that good? is that a reference surface? Is the front of a good 6-jaw that good?

So now... we tighten 'er up enough to drive and we take all the driving load on the first 3-4 threads in the split portion of the bolt body... on the unsupported side.??

But hey, that's all speculation. IF IT WORKS, if you can snug 'er up and get a wobble-free bolt every time, "within .0005," Who am I to say?

If there's no jacking with the steady...

al
 
alinwa said:
Thanks Jerry,

so there it is.... I didn't even consider threading clear up to the chuck. I'd thread it OUT, me :) I'm chicken!

The bolt is indexed off the rear surface. So before the steady goes on you should be able to snug 'er up and there will be no wobble out at the locking lugs.

I certainly can't answer to that, never tried it. Maybe they are that good? is that a reference surface? Is the front of a good 6-jaw that good?

So now... we tighten 'er up enough to drive and we take all the driving load on the first 3-4 threads in the split portion of the bolt body... on the unsupported side.??

But hey, that's all speculation. IF IT WORKS, if you can snug 'er up and get a wobble-free bolt every time, "within .0005," Who am I to say?

If there's no jacking with the steady...

al
Click to expand...

Al, I suspect that just from the working clearance of the threads would allow runout at the bolt face. I've never actually checked because when I scoot the bolt up against the jaw faces I am doing it with the talistock center in the firing pin hole and the steadyrest rollers are set at this time too. Use care not to put wnough pressure on the center in the firing pin hole that could damage the edge of the hole/face intersection.
 
JerrySharrett said:
Al, I suspect that just from the working clearance of the threads would allow runout at the bolt face. I've never actually checked because when I scoot the bolt up against the jaw faces I am doing it with the talistock center in the firing pin hole and the steadyrest rollers are set at this time too. Use care not to put wnough pressure on the center in the firing pin hole that could damage the edge of the hole/face intersection.
Click to expand...

But you do drive off the threads and the rear surface of the bolt right? You don't dog to drive off the bolthandle?

al
 
alinwa said:
But you do drive off the threads and the rear surface of the bolt right? You don't dog to drive off the bolthandle?

al
Click to expand...
I'm driving off the threads but there would be runout at the bolt face if it were not for the steadyrest. Make the setup yourself, then you'll understand better.
 
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