Gunsmithing Want input on an idea... Action 'truing'

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May 2, 2008
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#1
OK, so I was doing a lot of thinking about truing an action but still being able to use either the barrel that was on it, or a take-off barrel that was already threaded on the tenon. I know I know, why waste the time truing an action if you aren't going to put on a brand new barrel. I agree for the most part, and think the PTG mandrel to true the action around the bore of the action is the way to go (thanks Robert). That said, I still think this idea might be viable for a low cost accuracy job on a factory rifle. I am hoping to get your input here.

So, My thought is that if I want to leave the thread size the same in the action, perhaps I could dial the action in to be concentric with the threads, and then face the action and lugs with this setup, and then lap the bolt lugs in. Below are pictures of a mandrel I had ground that should allow me to dial the action in concentric to the threads. What I do is put the washer in and then a spring, I then thread the mandrel into the action until it bottoms out, and then twist it slightly to back it out a little bit, this will allow the mandrel to bottom on the threads, and should allow me to perform the rest of the facing work concentric to the threads. Tell me what you think:

Mandrel, spring, washer, and action:
aeackw.jpg


Washer and spring in the action:
13zwrw4.jpg


Assembled:
2nslxeb.jpg


Of course I would take the trigger off before indicating in the jig
laugh.gif


DD
 
#5
Re: Want input on an idea... Action 'truing'

well, when you true concentric to the raceway, you are truing to a reference, what is different about truing to the threads? Couldn't you as easily 'true' everything on the action to the exterior of the action? Well, maybe not as easily, but it could be done...

I guess I think of 'truing' as making the critical areas of the action concentric to each other. So as I see it, the threads, the lugs on the bolt and action, and the bolt body itself. I understand the rear of the bolt can't bind or throw off the mixture which is why the raceway is so commonly used. If I used my method, and then turned the bolt raceway out until it cleaned up 100%, I would have everything concentric and have not started at the raceway. Does that make sense?

DD
 
#6
Re: Want input on an idea... Action 'truing'

i'm with mike.

if you true the internal lugs with it setup like this, you are running a high probability of causing them to be out of true compared to the bolt lugs, which are attached to the bolt body, which rides in the bolt raceway.


if it were me and i just wanted to do something to say i trued the action (which i wouldn't), i would stick your mandrel into the lathe and dial it in nuts. i would then screw the receiver onto it and make a facing cut on the front of it. remove the receiver and lap the lugs and call it done.
 
#7
Re: Want input on an idea... Action 'truing'

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: wnroscoe</div><div class="ubbcode-body">In the last photo, is the mandrel screwed in all the way?

If so, I see problems with this method.</div></div>

The plan is to screw it in until it bottoms out (the threads are tapered), and then unscrew it slightly so the area of contact between the mandrel and action are only on the face of the threads...
 
#8
Re: Want input on an idea... Action 'truing'

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: DebosDave</div><div class="ubbcode-body">well, when you true concentric to the raceway, you are truing to a reference, what is different about truing to the threads? Couldn't you as easily 'true' everything on the action to the exterior of the action? Well, maybe not as easily, but it could be done...

I guess I think of 'truing' as making the critical areas of the action concentric to each other. So as I see it, the threads, the lugs on the bolt and action, and the bolt body itself. I understand the rear of the bolt can't bind or throw off the mixture which is why the raceway is so commonly used. If I used my method, and then turned the bolt raceway out until it cleaned up 100%, I would have everything concentric and have not started at the raceway. Does that make sense?

DD </div></div>

if you set up the way you are describing, you would need to bore and ream the raceway to make it true to the threads and internal lugs if you true them in the same setup.
 
#9
Re: Want input on an idea... Action 'truing'

Robert,

I appreciate the input, and I agree to an extent. If I lap the lugs after the facing, then everything is still good to go, full contact, and face of the action is true to the threads of the action. The lugs might not be a perfect 90° to the bolt body, but are VERY unlikely to be at some kind of crazy angle.

What is the furthest out that anyone has found the threads to be? It is very difficult to tell when the procedure is to just cut them until they clean up 80-100%. With this method, I could put the PTG mandrel in and find out if the bolt raceway is out, or if it is just off-center compared to the threads. There should be no difference in the end product if you bored the raceway concentric to the threads, other than you now have standard threading in the action...
 
#10
Re: Want input on an idea... Action 'truing'

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: 300sniper</div><div class="ubbcode-body">

if you set up the way you are describing, you would need to bore and ream the raceway to make it true to the threads and internal lugs if you true them in the same setup.</div></div>

You are correct, but I think if I lap the lugs on this setup, I can 'get away with' NOT truing the raceway. It would allow full contact of the lugs, and maintain the original thread dimensions of the action... making it possible to install a pre-threaded barrel onto a 'trued' action.
 
#11
Re: Want input on an idea... Action 'truing'

personally, i wouldn't touch the lugs in this setup. i have not measured the actual runout of the receiver threads when dialed in off the raceway. i know that it is usually quite a bit by listening and watching the the treading tool though. i am going to make a mandrel that looks similar to yours before i do my next one so i can measure how far out they are.

i don't want to crap on your idea but the only thing i see it being useful for is truing the receiver face. if you are going to use it for that, you might as well stick the mandrel in the lathe chuck and dial it in and then screw the receiver onto it.
 
#12
Re: Want input on an idea... Action 'truing'

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: wnroscoe</div><div class="ubbcode-body">That being the case you're relying on the receiver thread / mandrel thread datum lines to provide lock up, bad mistake.

OEM receiver threads are never concentric, some have taper and some are off set. Receiver threads are the least important part of the equation, why allow them to dictate the outcome? </div></div>

I am curious how you determine the the threads are never concentric? Are you speaking of concentric to the raceway? How do you determine that they are tapered? I am just asking, because if you are only going by the bolt raceway, then lapping lugs and/or reaming the bolt raceway will take care of those issues...

The reason to let the threads dictate the outcome is because you could true an action and use a take-off or the original barrel again. Of all the things that are matched to a particular action, the barrel is the most often removed/replaced/swapped... The threads of the action dictate which barrels you can use and try. If you are using new barrels only, then yes, I like the PTG raceway mandrel method. Even if you have to do other work to a barrel in the chamber, shoulder, or bolt recess area, the threads are un-changeable without cutting the entire tenon off
 
#13
Re: Want input on an idea... Action 'truing'

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: DebosDave</div><div class="ubbcode-body">well, when you true concentric to the raceway, you are truing to a reference, what is different about truing to the threads? Couldn't you as easily 'true' everything on the action to the exterior of the action? Well, maybe not as easily, but it could be done...

I guess I think of 'truing' as making the critical areas of the action concentric to each other. So as I see it, the threads, the lugs on the bolt and action, and the bolt body itself. I understand the rear of the bolt can't bind or throw off the mixture which is why the raceway is so commonly used. If I used my method, and then turned the bolt raceway out until it cleaned up 100%, I would have everything concentric and have not started at the raceway. Does that make sense?

DD </div></div>

I understand and appluad your ambition, but I envision your process actually taking the action in the direction of being more untrue than it was before you started. The idea is to make the bore of the barrel concentric to the centerline of the bolt way and have the lugs, receiver face, bolt face and threads be square with this reference. If you use the threads as a reference, you're going to take the lug abutments, receiver face and bolt face further away from the centerline of the boltway and bore of the barrel.
 
#14
Re: Want input on an idea... Action 'truing'

I guess if I dial in an action with this mandrel, and then measure how far out the PTG raceway mandrel is out, perhaps it will change my vision on this?? But if it is only out a couple thou, then it would work well in my opinion. Also, when folks are 'blueprinting' actions, they are many times enlarging the raceway and sleeving or ordering a new PTG bolt anyway... so that wouldn't take away from this method at all

Thanks for all the input, I appreciate it greatly, and will do much thinking and playing with it...
 
#15
Re: Want input on an idea... Action 'truing'

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: DebosDave</div><div class="ubbcode-body">I guess if I dial in an action with this mandrel, and then measure how far out the PTG raceway mandrel is out, perhaps it will change my vision on this?? But if it is only out a couple thou, then it would work well in my opinion. Also, when folks are 'blueprinting' actions, they are many times enlarging the raceway and sleeving or ordering a new PTG bolt anyway... so that wouldn't take away from this method at all

Thanks for all the input, I appreciate it greatly, and will do much thinking and playing with it... </div></div>

Not a bad test....Dial the receiver in using the bolt way as a reference and then screw in your contraption and see how it compares....BTW, a couple thou may as well be an inch
grin.gif
 
#17
Re: Want input on an idea... Action 'truing'

What Roscoe said....and...

Exactly what are the washer and spring for ?
Is it supposed to do something more than just sit on the lugs ?

You'd be better off having it contact on the outside of the receiver (like a lathe does) then you could actually find the true centerline.
I just can't see this method getting anything even close to precise.

Don't take that wrong...I mean no offense (and I understand very well that I am almost always misunderstood).

You would need 2 cup shaped pieces to go over the outside of the receiver with a small hole in each that holds your arbor....but...I really see no way even that could be precise enough and be able to spin a cutter or tap, or whatever tool you propose to use.

But yea, I think I understand what you're trying to do here (think being the operative keyword).

Just, please, don't put a cutter on it yet
smile.gif
 
#18
Re: Want input on an idea... Action 'truing'

If you wished to true the action without re-cutting the action threads simple use the same receiver truing fixture most everyone is using and simply don't cut the receiver threads. Do the action face and lugs. Do the bolt work, then lap the lugs.

I do something similar to factory Remington Police or Varmint rifles along with spinning the factory barrel back and re-cutting the chamber when the factory headspace is off. 99.9% of the time this will markably help the accuracy in these factory rifles.

I have also did some experimenting over the years with custom barrels were the receiver shank was cut undersize, or the action threads were cut oversize, among other things, and found in most cases you can get away with more then one thinks without effecting accuracy.

Would one want to do this as a normal course of business building rifles for others? No, but it showed what can be done. Barrel quality and Chamber work is more important then what is done to the factory action.

I don't like the set up as shown for many reasons, some have been already stated.


 
#19
Re: Want input on an idea... Action 'truing'

Would it be better to make a mandrel that sits in the bolt raceway and sit on the lugs so you can turn between centers or use it to dial in the receiver and cut the front of the receiver so the barrel would be pointing in the same direction as the bolt and the action(just a thought)
 
#20
Re: Want input on an idea... Action 'truing'

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Thorax</div><div class="ubbcode-body">What Roscoe said....and...

Exactly what are the washer and spring for ?
Is it supposed to do something more than just sit on the lugs ?

You'd be better off having it contact on the outside of the receiver (like a lathe does) then you could actually find the true centerline.
I just can't see this method getting anything even close to precise.

Don't take that wrong...I mean no offense (and I understand very well that I am almost always misunderstood).

You would need 2 cup shaped pieces to go over the outside of the receiver with a small hole in each that holds your arbor....but...I really see no way even that could be precise enough and be able to spin a cutter or tap, or whatever tool you propose to use.

But yea, I think I understand what you're trying to do here (think being the operative keyword).

Just, please, don't put a cutter on it yet
smile.gif
</div></div>

The spring and washer just load the mandrel onto the face of the threads. I tighten the mandrel down until either the tapered threads on the mandrel bottom in the action or until it bottoms out on the spring. I then reverse it slightly to make sure it isn't bottomed out any longer. This gives me the most 'load' or the tightest fit, but still allows the mandrel to be only loaded onto the face of the threads. The same side of the threads that the barrel will be loaded onto after the shoulder hits the face of the action. This then puts the mandrel shaft perpendicular and true to the threads. I could then true the entire action around this point. If the raceway bore was indeed out more than a couple thou or the threads were offset more than a couple thou I can see the issues as described above. Clearly, I need to do a lot more work on these to learn why this idea is no good at all.

I had just done a lot of thinking based on how everyone was/is truing actions, and came up with this thought. A factory Remington rarely doesn't shoot well with everything as it comes from their process. I think I can see why people choose to use the raceway as the reference to true an action around, but was always curious how folks determined which was out of concentricity, and it is always the face and the threads and the lugs, but to what I have read or heard no one really knows how far they are out. The threads are just determined to be out or offset or tapered once the action is indicated via the raceway and then cut to clean up. IIRC when Remington makes an action, they aren't doing these processes at the same time, but who says the raceway didn't get bored in slightly 'out' before the threads were ever cut into the action? What reference point do they use when their CNC mill threads these tubes?

At any rate, if nothing else comes out of this mandrel, I will be able to compare the relationship of the threads and the raceway before I need to cut anything. I can then make the decision how or where to cut.

I am very new to this stuff, and I greatly appreciate everyone who has tried to explain why this mandrel won't work. Don't worry, I won't make any cuts with it yet, but will use it to educate myself on the relationship between the threads and the raceway. I appreciate all of you taking the time, I believe what has been said has sunk in, and makes more sense now.
 
#21
Re: Want input on an idea... Action 'truing'

my take on this, If you fail you are out the cost of a action, plus another action and a full blueprint job, if you succeed you have just opened one hell of a can of worms for all other smiths who do this the oposite way by recutting the threads. me personaly i am still stuck on the whole issue over what really needs to done in truing a action, threads or no threads, does it matter or not?, how far out are the threads on average? Why do benchresters use custom actions and not blueprinted actions? how is there accuracy? .250-.500 means they lose! Benchreseters a more fussy, maybe ask out on 6mmbr as well! if i had a action to be blue printed i would pay someone to BluePrint a action for me. Why not just go buy a custom action for a few dollars more than you would spend to send the action off and have it blue printed along with adding a new ptg bolt. also at the end of the day if you have one blue printed you still have a remy action vs. a custom action! i am also just giving my opinion and not trying to stir up a hornets nest guys
 
#22
Re: Want input on an idea... Action 'truing'

I'm still reading, trying, and learning myself on all this lathe work but let me see if I'm thinking right, please correct me if I'm wrong.

Just as an example to give a real numerical value here, assume the threads are 1 degree off from a perfect action center line.

If you set the action up with the method and tool shown by the OP, you wind up setting up the action in the lathe being 1 degree from center. Basically a wobble for the action but the threads would be straight inline with the lathes rotation. So now you go to cutting. The face gets cut straight, the threads are already straight, and the lug surfaces get cut. Now the lug surface, face, and threads are all true to the lathes rotation. But the action as a whole is 1 degree from this new center line.

Now removing the action from the lathe, and inserting the bolt. As the bolt rotates, this where the 1 degree off is going to show a problem. Its impossible to have full contact across the entire lug surface as the bolt rotates against the action since their surfaces are on two separate planes, exactly 1 degree off. Even if the rear of the lugs were machine in the lathe with the same 1 degree of tilt, their two surfaces (the rear of the lugs and the action) would only become perfectly parallel at one and only one point in the rotation. Even if one was to plan for this, you want that 1 degree of tilt to match on the action and bolt when the bolt is in the closed position.

Again, please correct my thoughts if they are incorrect, but this is why you would true an action based on the bolt raceway. Because its the centerline of rotation. The bolt rotates so all surfaces need to be either inline with that rotation or be perpendicular to that rotation. If you have multiple surfaces perpendicular to that rotation then you have surfaces that are also parallel to each other and they will be parallel to each other at all points as its rotated, not just at one point.

Or am I staying up too late on the computer again?

Mike
 
#23
Re: Want input on an idea... Action 'truing'

I don't want to keep beating this to death, but if you think of how much clearance or tolerance there is between the bolt raceway and the bolt body at the rear of the action, well, my guess is there is more than 1 thou. So if you did it by my method and the threads are only out 1 thou, you will still be fines especially when lapping the lugs. If you consider that you have just taken apart a rifle that was already 1/2 MOA capable, then do you really think truing around the threads will cause additional problems? There was already tolerance or clearance that allow the parts to work together. I may do some setups and see how far out the threads are. With what I have read and been taught, I think truing around the raceways is the way to go.

Thanks
 
#24
Re: Want input on an idea... Action 'truing'

Dave,
I say give it a try. My example was just a far out measurement to make it easier to imagine/visualize a worse case scenario. You might be able to get everything close enough that it wouldn't matter the difference between the raceway and the surfaces. Maybe take a few examples of actions and measure the thread run-out and see what you are working with.

I'm new at all this and have only done work for myself on a borrowed lathe so I'm certainly no expert. These threads and discussions just help me and others learn whats acceptable, whats to look for, and maybe, ways to make the work a little easier. Either way, thinking outside the norm should be rewarded. Thanks for sharing your idea.

Mike
 
#25
Re: Want input on an idea... Action 'truing'

If the threads were out, say .002" with angular runout, and you trued the rest of the action based on the thread running true, then you would wind up taking one bigass cut by the time you got to the bridge. Better to true the short section of threads, indicated off the long section of raceway. Since the threads center themselves to a great extent when the barrel is screwed in, .002" oversize on the action threads is essentially disregardable, as long as the face is true.
 
#26
Re: Want input on an idea... Action 'truing'

m1k3 you have the point. Square is what you want but it has to go hand in hand with dead center. Center to the bore line and bolt. That's what the blueprint is for.
 
#27
Re: Want input on an idea... Action 'truing'

i would really like to see some actual measurements of how far out the treads can be. i know from the ones i have done, they are quite a bit out just by listening to and watching the threading tool.

i did a quick cad drawing with the threads being just .1° out of line from the raceway centerline. assuming the angle the threads were out was vertical and you cut the internal lugs this way, this would put one of the bolt lugs .00148 to .00175" off of the internal lugs (assuming the bolt lugs were square with the bolt body).

again, this is just with an angle introduced. now imagine that combined with axial runout or a worse angle.

i honestly think if you touch the internal lugs in this setup, you are creating more problems than you are fixing.
 
#28
Re: Want input on an idea... Action 'truing'

Thanks JW, I just wanted to confirm that my thinking was sound.

Not trying to bash the idea at all, I justed want to exam the locations where a problem could occur.

300sniper, good work on the math! The other thing would be that the bolt lug that was in contact with the internal lugs would only contact on the outer edge of one lug. As you pointed out, the other lug would have a gap between it and the internal lug surface. As Dave pointed out, perhaps the runout of the bolt raceway would cover that imperfection.

Now get this! The Savage bolt head WOULD make this up with its floating head. Perhaps that is something that Savage stumbled across. Again, the bolt face would have a pitch to it but maybe the brass would make that up. I understand tolerances are playing a large part here with "what if's" but I think that the problem with stacked tolerances may add up here. Either way, if you are going to go through the trouble of all that work to machine out the threads, lugs, face, etc, why not center the whole thing on one centerline.

Mike
 
#29
Re: Want input on an idea... Action 'truing'

To check thread runout, what if you would make a "gage". say thread a piece, as you would a barrel, to a squared shoulder, then you could indicate your reciever, on it's jig/mandrel then screw in the gage and indicate off the gage to check run out of the threads.
 
#30
Re: Want input on an idea... Action 'truing'

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: 300sniper</div><div class="ubbcode-body">i would really like to see some actual measurements of how far out the treads can be. i know from the ones i have done, they are quite a bit out just by listening to and watching the threading tool.

i did a quick cad drawing with the threads being just .1° out of line from the raceway centerline. assuming the angle the threads were out was vertical and you cut the internal lugs this way, this would put one of the bolt lugs .00148 to .00175" off of the internal lugs (assuming the bolt lugs were square with the bolt body).

again, this is just with an angle introduced. now imagine that combined with axial runout or a worse angle.

i honestly think if you touch the internal lugs in this setup, you are creating more problems than you are fixing. </div></div>

I knew 300 couldn't resist doing the drawing and I couldn't agree more with his findings.
 
#31
Re: Want input on an idea... Action 'truing'

<div class="ubbcode-block"><div class="ubbcode-header">Quote:</div><div class="ubbcode-body">I knew 300 couldn't resist doing the drawing</div></div>

laugh.gif
 
#32
Re: Want input on an idea... Action 'truing'

ARshuter, not sure if that would indicate more on the face of the action or the threads? The tool that Dave come up with looks like it could possibly be more accurate as far as dialing in the threads since it doesn't appear to come in contact or rest on the action face.

I guess you could use it on an action to see if the threads need to be chased or not. Say if they are within so many degrees of dead center then there would be no need to chase them?


Mike
 
#33
Re: Want input on an idea... Action 'truing'

For the record, I have learned a lot through asking this question. I think you could 'COULD' true the entire action around the threads, but on many actions you would end up with a bolt raceway that was oversized to the point that there wouldn't be adequate lug engagement surface left.

I appreciate all the input and the continued discussion, but I won't be using the mandrel I showed to do any cutting work. I may thread it in and see how far out threads are, but will likely use the best methods as detailed above, indicating the action in via a raceway mandrel...

Thanks again
 
#34
Re: Want input on an idea... Action 'truing'

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: DebosDave</div><div class="ubbcode-body">... but will likely use the best methods as detailed above, indicating the action in via a raceway mandrel...
</div></div>


oh it may just be the best way we can think of now. some day someone may think of something that is better, easier or faster with the same end results. although i didn't agree with your idea here, i applaud you for trying to think outside the box.
 
#35
Re: Want input on an idea... Action 'truing'

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: DebosDave</div><div class="ubbcode-body">For the record, I have learned a lot through asking this question. I think you could 'COULD' true the entire action around the threads, but on many actions you would end up with a bolt raceway that was oversized to the point that there wouldn't be adequate lug engagement surface left.

I appreciate all the input and the continued discussion, but I won't be using the mandrel I showed to do any cutting work. I may thread it in and see how far out threads are, but will likely use the best methods as detailed above, indicating the action in via a raceway mandrel...

Thanks again </div></div>


Howdy there bud!I'm new here but I've been a professional machinist and gunsmith for the last 20 years,in that time I've trued more than a few actions similar to what you want to do and built a few actions from scratch.What you are trying will work,with a couple of mods.Firstly that washer needs to be surface ground on both sides as IT is what will set the reference from lugs to mandrel.If you've already had that done great,not obvious from the pics.Secondly lose the spring,you'll screw yourself.Next,if your mandrel was turned and GROUND true great,in any case set it up between centers in the lathe and check it.Make absoulutly sure the mandrel is square from the thread OD to the mandrel face that will contact the washer.If you haven't learned to do this contact me and I'll talk ya through it.Next those threads shouldn't be tapered,just a very good fit.What you want is to drop in the washer then screw the action down tight by hand with the mandrel threads undercut ahead of the action so you can reach the face with the tool bit.Now a word on setting up the mandrel,if you chuck up more than about 3/8-1/2 inch of the mandrel shaft you will never get it true,even useing soft jaws and pecking it around.The easiest bestest way to do this is as follows.I don't know if you have a steady rest that has ball bearing rollers if so great,if not do this have the small OD of your mandrel ground to a standard bearing size closest to its current size.This diameter should be from that large shoulder back maybe 3 inches,the diameter from there to the end of the small OD should be about .002-.010 smaller so you can slide the bearing to it's seat.Next chuck up the small end of your mandrel,no more than 1/2 inch indicated dead nuts.Put your tailstock center into the center drilled hole that should be in the face of the large end.Set up your indicator and check the runout of the threads,the closer the better but .0005-.0007 is fine.If you know how to correct this runout with shims cut from aluminum cans great if not holler and I'll explain.Now set up either your ball bearing steady rest or set up your steady rest on the ball bearing I told you to have the mandrel ground for.If using the ball bearing method get the highest precision class bearing you can,that will minimize runout.Next Screw your action onto the mandrel and trim it.Truing the action may not make much difference,in most cases it is really to remove any mechanical variables to accuracy so that load and technique can be concentrated on.I hope this helps,if so and if I can explain any of the above PM and I'll give you my cell number.If not I apologize for the long windedness and bid you good luck.
 
#36
Re: Want input on an idea... Action 'truing'

Allow me a moment to talk out of my ass..... One reason, already mentioned by xs hedspace is that by taking the short plane of the threads and applying it to the length of the action, you are going to multiply the runout by the time you get done cutting the rear of the bolt raceway. If you are .002" tir over 1" of thread when compared with the raceway and you base your cuts on that, if the raceway is say 6", you'd be cutting .012" by the time you got to the back. I don't know how round it'd be at that point. The thing about trueing to the raceway is that you aren't really indicating to the raceway itself, but to the centerline of the raceway. The raceway isn't going to be any more perfect than the threads are, but the centerline is the centerline and everything else can be compared to that imaginary line. You are basically taking all the imperfections that exist and averaging them out, minimizing the amount of metal needed to be removed to bring everything into true.
 
#37
Re: Want input on an idea... Action 'truing'

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: jwSubMOA</div><div class="ubbcode-body">

Howdy there bud!I'm new here but I've been a professional machinist and gunsmith for the last 20 years,in that time I've trued more than a few actions similar to what you want to do and built a few actions from scratch.What you are trying will work,with a couple of mods.Firstly that washer needs to be surface ground on both sides as IT is what will set the reference from lugs to mandrel.If you've already had that done great,not obvious from the pics.Secondly lose the spring,you'll screw yourself.Next,if your mandrel was turned and GROUND true great,in any case set it up between centers in the lathe and check it.Make absoulutly sure the mandrel is square from the thread OD to the mandrel face that will contact the washer.If you haven't learned to do this contact me and I'll talk ya through it.Next those threads shouldn't be tapered,just a very good fit.What you want is to drop in the washer then screw the action down tight by hand with the mandrel threads undercut ahead of the action so you can reach the face with the tool bit.Now a word on setting up the mandrel,if you chuck up more than about 3/8-1/2 inch of the mandrel shaft you will never get it true,even useing soft jaws and pecking it around.The easiest bestest way to do this is as follows.I don't know if you have a steady rest that has ball bearing rollers if so great,if not do this have the small OD of your mandrel ground to a standard bearing size closest to its current size.This diameter should be from that large shoulder back maybe 3 inches,the diameter from there to the end of the small OD should be about .002-.010 smaller so you can slide the bearing to it's seat.Next chuck up the small end of your mandrel,no more than 1/2 inch indicated dead nuts.Put your tailstock center into the center drilled hole that should be in the face of the large end.Set up your indicator and check the runout of the threads,the closer the better but .0005-.0007 is fine.If you know how to correct this runout with shims cut from aluminum cans great if not holler and I'll explain.Now set up either your ball bearing steady rest or set up your steady rest on the ball bearing I told you to have the mandrel ground for.If using the ball bearing method get the highest precision class bearing you can,that will minimize runout.Next Screw your action onto the mandrel and trim it.Truing the action may not make much difference,in most cases it is really to remove any mechanical variables to accuracy so that load and technique can be concentrated on.I hope this helps,if so and if I can explain any of the above PM and I'll give you my cell number.If not I apologize for the long windedness and bid you good luck. </div></div>


so you think it is important to surface grind the washer but you are going to tighten it between the threaded mandrel and the internal lugs which are almost guaranteed to be out of whack compared the the threads? i'm just a garage hack and have never been a machinist or gunsmith but to me, that doesn't seem like the best way, or even a good way to go about truing an action. maybe you can correct my thinking.
 
#38
Re: Want input on an idea... Action 'truing'

jwSubMOA, that's a heck of a first post. Welcome.



So now we have gone to the indicating the run out of the threads to indicating the run out of the internal lugs?

But if the threads are tight with the action, you're probably still going to show run out of the threads. Which, if solid against the internal lugs, could skew that reading as well depending on the threads mating surfaces.

The spring idea from Dave kind of eliminates any inconsistency with the internal lugs but still provides force on the tool against the action's threads. It could be the best way to measure thread runout.

Mike
 
#39
Re: Want input on an idea... Action 'truing'

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: jwSubMOA</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: DebosDave</div><div class="ubbcode-body">For the record, I have learned a lot through asking this question. I think you could 'COULD' true the entire action around the threads, but on many actions you would end up with a bolt raceway that was oversized to the point that there wouldn't be adequate lug engagement surface left.

I appreciate all the input and the continued discussion, but I won't be using the mandrel I showed to do any cutting work. I may thread it in and see how far out threads are, but will likely use the best methods as detailed above, indicating the action in via a raceway mandrel...

Thanks again </div></div>




Howdy there bud!I'm new here but I've been a professional machinist and gunsmith for the last 20 years,in that time I've trued more than a few actions similar to what you want to do and built a few actions from scratch.What you are trying will work,with a couple of mods.Firstly that washer needs to be surface ground on both sides as IT is what will set the reference from lugs to mandrel.If you've already had that done great,not obvious from the pics.Secondly lose the spring,you'll screw yourself.Next,if your mandrel was turned and GROUND true great,in any case set it up between centers in the lathe and check it.Make absoulutly sure the mandrel is square from the thread OD to the mandrel face that will contact the washer.If you haven't learned to do this contact me and I'll talk ya through it.Next those threads shouldn't be tapered,just a very good fit.What you want is to drop in the washer then screw the action down tight by hand with the mandrel threads undercut ahead of the action so you can reach the face with the tool bit.Now a word on setting up the mandrel,if you chuck up more than about 3/8-1/2 inch of the mandrel shaft you will never get it true,even useing soft jaws and pecking it around.The easiest bestest way to do this is as follows.I don't know if you have a steady rest that has ball bearing rollers if so great,if not do this have the small OD of your mandrel ground to a standard bearing size closest to its current size.This diameter should be from that large shoulder back maybe 3 inches,the diameter from there to the end of the small OD should be about .002-.010 smaller so you can slide the bearing to it's seat.Next chuck up the small end of your mandrel,no more than 1/2 inch indicated dead nuts.Put your tailstock center into the center drilled hole that should be in the face of the large end.Set up your indicator and check the runout of the threads,the closer the better but .0005-.0007 is fine.If you know how to correct this runout with shims cut from aluminum cans great if not holler and I'll explain.Now set up either your ball bearing steady rest or set up your steady rest on the ball bearing I told you to have the mandrel ground for.If using the ball bearing method get the highest precision class bearing you can,that will minimize runout.Next Screw your action onto the mandrel and trim it.Truing the action may not make much difference,in most cases it is really to remove any mechanical variables to accuracy so that load and technique can be concentrated on.I hope this helps,if so and if I can explain any of the above PM and I'll give you my cell number.If not I apologize for the long windedness and bid you good luck. </div></div>

OMG!!!! Where can I find the "face palm" pictures? Maybe even the "double face palm?"
grin.gif
 
#40
Re: Want input on an idea... Action 'truing'

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: m1k3</div><div class="ubbcode-body">jwSubMOA, that's a heck of a first post. Welcome.



So now we have gone to the indicating the run out of the threads to indicating the run out of the internal lugs?

But if the threads are tight with the action, you're probably still going to show run out of the threads. Which, if solid against the internal lugs, could skew that reading as well depending on the threads mating surfaces.

The spring idea from Dave kind of eliminates any inconsistency with the internal lugs but still provides force on the tool against the action's threads. It could be the best way to measure thread runout.

Mike
</div></div>


Hello there!Unless the reciever is solidly set on the mandrel your just asking for movement.If you surface grind the washer and the mandrel is a good thread fit and square between the threads and mandrel face once you lock it down your good.I know that some actions are way out compared to others but,if you use his mandrel the way I described to face the action it duplicates the seated position of the barrel.Of course the barrel shoulder face needs to be checked for runout and trued if required.I have a large reciever truing fixture I made years ago that works in the typical way,allowing truing of the lugs,raceway and reciever face.I was simply describing the way to get the most from his rig,not a blanket statement about action truing.Think about your typical action mandrel,it actually locates off the threads or lugs depending on the action type.If the bolt raceway is running out enough to touch the mandrel shaft,you will not be accurate after machining.The BEST way is the reciever fixture,indicated on the raceway and truing face,threads and lugs.What he wants to do will work for the manner he intends.Nice talking to you guys.
 
#41
Re: Want input on an idea... Action 'truing'

I may be way the hell off in left field here but it seems like the mandrell can be made to make everything true off of the threads instead of the raceways correct. In my thinking everything gwould still be true to each other but just using a different point as center. Using Daves mandral the bolt may actually be crooked to the raceways but still be true to the lug embutment and threads, correct?
 
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