Old School Mandrel?

[Shooting in the wind...]

Seems like everybody these days are using purchased mandrel with bushings to find "center line" of an action. What happened to making a mandrel on a lathe and threading it into the action? Now pardon my ignorance, but iam i in the wrong mind set to think this would work? Threads all have clearence in them so if the reciever face is trued then theoretically the reciever should screw on flat to the action if the clearence within the threads is sufficent.
How how perfect is too perfect, i mean that anyone would even notice? I have done countless hours of research and i can see where madrels with bushings that ptg sells would be benifical especially for truing the threads and lug abutments but there soooo expensive.
Is ther a way to true a reciever without having to spend an arm and leg, especially for only doing a few a year? I know you can make a straight mandrel and machine your own bushings, but seems like maybe this whole process of truing a action is over thought to a certain degree? Am i wrong?

 

[hoz53]

Seems like everybody these days are using purchased mandrel with bushings to find "center line" of an action. What happened to making a mandrel on a lathe and threading it into the action? Now pardon my ignorance, but iam i in the wrong mind set to think this would work? Threads all have clearence in them so if the reciever face is trued then theoretically the reciever should screw on flat to the action if the clearence within the threads is sufficent.
How how perfect is too perfect, i mean that anyone would even notice? I have done countless hours of research and i can see where madrels with bushings that ptg sells would be benifical especially for truing the threads and lug abutments but there soooo expensive.
Is ther a way to true a reciever without having to spend an arm and leg, especially for only doing a few a year? I know you can make a straight mandrel and machine your own bushings, but seems like maybe this whole process of truing a action is over thought to a certain degree? Am i wrong?

Well I am planning on trying to make some mandrals. Not gonna thread them for Tenon thread though. Probably just make them strait and ill find another way to fasten them to the action. It will be an exercise in seeing how close a tolerance I can work to. I figure Ive invested in the lathe ect so why not try to get the use out of it. If i cant do it ill buy some.

 

[Shooting in the wind...]

Well I am planning on trying to make some mandrals. Not gonna thread them for Tenon thread though. Probably just make them strait and ill find another way to fasten them to the action. It will be an exercise in seeing how close a tolerance I can work to. I figure Ive invested in the lathe ect so why not try to get the use out of it. If i cant do it ill buy some.

Thats where i am coming from, i have invested in both a lathe and mill, so why not use them? I understand that a ground rod will be held to a closer tolerance than a machined rod. But there has to be more than one way to true an action the right way, if you get where i am coming from. Some say the accuracy gained can be minimal to decent by truing, but going to the extent of having everything indicated to .0000 seems alittle much. I have read that the only places that really need trued are the action face and bolt lugs, bolt face, and lug abutments. Just seems aslong as the barrel fits squarely to the action is what is most important. I believe that also doing the lugs and bolt will help, but as to what extent is out for debate, each action will react differently.

 

[Dusty Stevens]

If the threads were concentric to the bolt centerline and the action face that would work. But then again if that was the case we wouldnt need to true them in the first place

 

[tobnpr]

No reason at all you can't turn your own mandrels.
The reason some of us (myself included) use bushed mandrels is to avoid purchasing/machining multiple ones to fit when dealing with larger quantities of receivers.

Every action (mass produced) is going to have variations in size- including one end being different than the other which is where the bushings add value. Otherwise, you need to turn to the smaller diameter and have a "loose" fit at the large end.

Also, you need to make sure your lathe's bed is dead-nuts "no twist" and tailstock precisely aligned to turn without any taper on the mandrel.

Now, JMO...and I'm confident many will disagree...
Single-pointing receiver threads oversize, reaming the bolt raceway- very little return on your time/investment unless something's really wrong with the receiver or you're building a benchrest competition rifle.

Truing the receiver face is a must, for the same reason you must have a perfectly perpendicular shoulder on the barrel. Get those two surfaces to mate perfectly, ensure even/full lug contact (usually lapping will accomplish, sometimes a VERY light cut on the back of the lugs). Avoid any more than a very light facing cut on abutments/lugs or you'll need to re-time the bolt.

That little bit of work on the receiver- with a perfect chambering job (THIS is where you want to spend your time) will build a rifle that shoots better than most can drive them.

 

[Tucker65]

If you're not going to true the threads make sure you have enough clearance in the threaded joint that it's not binding when the shoulders come up tight. You're better off with too loose of a thread fit than too tight. If everything is true with each other than the fits can be alot closer.

John

 

[Dusty Stevens]

I cant imagine trying to turn a bar that long in a home shop size lathe and hold the tolerance needed to make the bar useful

 

[shortgrass]

I cant imagine trying to turn a bar that long in a home shop size lathe and hold the tolerance needed to make the bar useful

I've been machining since '74. I spend every working day in a machine shop ( a job shop). Much of that time is spent with 'hands-on' a 20 x 96 engine lathe. Some 'parts' have to be 'sanded in' to size, so they fit as they should, but they're not 8" - 12" long or need the tolerances needed for a mandrel for action truing.

 

[DaveTooley]

One of the very first things I made was a mandrel to true receiver faces. It is butt ugly as you might imagine. It's a mandrel with a cone and treads on one end. The cone centers up on the action bore at the lugs. Doesn't sound like it would be all that accurate. I've checked actions over and over again and only get runout in tenths. Go figure. Back then I used a piloted lap to true action lugs. I still us that method on some actions.

 

[tobnpr]

^^^
The cone on the mandrel is a great idea. Same as using tapered bushings..

 

[Shooting in the wind...]

One of the very first things I made was a mandrel to true receiver faces. It is butt ugly as you might imagine. It's a mandrel with a cone and treads on one end. The cone centers up on the action bore at the lugs. Doesn't sound like it would be all that accurate. I've checked actions over and over again and only get runout in tenths. Go figure. Back then I used a piloted lap to true action lugs. I still us that method on some actions.

Do you have a picture of the mandrel you made? Im having a hard time visualizing what it looks like.

 

[paperpuncher]

I cant imagine trying to turn a bar that long in a home shop size lathe and hold the tolerance needed to make the bar useful

Agree it could be done but Im not sure the juice is worth the squeeze. Then factor in that you will need multiple sizes in say .0005" increments and the task becomes monumental.
Now if you had an OD grinder at your disposal

 

[Roeder]

I cant imagine trying to turn a bar that long in a home shop size lathe and hold the tolerance needed to make the bar useful

I have made up a number of mandrels, the first ones I did on my lathe and to get around the issue of trying to turn 10 inches to a near perfect diameter I just turned the areas that actually engage the front and rear sections of the bolt raceway to size and turned the rest of the mandrel a little undersize. I use a small machinist clamp to lock the receiver in place in the set up. Later when I had access to a cylindrical grinder I made a few pretty looking ones at exactly .7015 and .702. Those are actually a little more troublesome to use but they look pretty.

 

[Rich S]

One of the very first things I made was a mandrel to true receiver faces. It is butt ugly as you might imagine. It's a mandrel with a cone and treads on one end. The cone centers up on the action bore at the lugs. Doesn't sound like it would be all that accurate. I've checked actions over and over again and only get runout in tenths. Go figure. Back then I used a piloted lap to true action lugs. I still us that method on some actions.

I made mine similar. A cone on one end and bushings on the tang end. It has worked well. Its made of 4140 PH. I wish it was hardened but for the few I do its ok.

 

[Shooting in the wind...]

I was just looking for a way to get similar results without having to spend a fortune on a mandrel and bushings. I do think a mandrel could be machined to an acceptable tolerence, maybe one day ill do a study to see how much variables in machining can effect accuracy. That will be a deep rabbit hile to go down.

 

[DaveTooley]

Loose threads mean square shoulders. Just saying

 

[hoz53]

One of the very first things I made was a mandrel to true receiver faces. It is butt ugly as you might imagine. It's a mandrel with a cone and treads on one end. The cone centers up on the action bore at the lugs. Doesn't sound like it would be all that accurate. I've checked actions over and over again and only get runout in tenths. Go figure. Back then I used a piloted lap to true action lugs. I still us that method on some actions.

Like this or this idea anyway. Thanks Dave

 

[hoz53]

I have made up a number of mandrels, the first ones I did on my lathe and to get around the issue of trying to turn 10 inches to a near perfect diameter I just turned the areas that actually engage the front and rear sections of the bolt raceway to size and turned the rest of the mandrel a little undersize. I use a small machinist clamp to lock the receiver in place in the set up. Later when I had access to a cylindrical grinder I made a few pretty looking ones at exactly .7015 and .702. Those are actually a little more troublesome to use but they look pretty.

The way you describe how you made your lathe turned mandrals is what I was thinking of doing. Thanks for this info.

 

[hoz53]

Agree it could be done but Im not sure the juice is worth the squeeze. Then factor in that you will need multiple sizes in say .0005" increments and the task becomes monumental.
Now if you had an OD grinder at your disposal

Well I was thinking of making them as I go so I wouldn’t need to do them all at once. It wouldn’t take to long to make one, and I’ll if I can’t get them accurate enough I’ll just buy some.

 

[Roeder]

Well I was thinking of making them as I go so I wouldn’t need to do them all at once. It wouldn’t take to long to make one, and I’ll if I can’t get them accurate enough I’ll just buy some.

The nice thing about doing it this way is that you can make them different diameters from the front to back. It seems like the front of the receiver raceway tends to run a little larger than the rear more often than not. If a receiver will take a .702 gage pin at the rear and a .703 at the front you can make your mandrel to match. You'll likely encounter another that fits those dimensions soon enough.