action truing fixture

[bigngreen]

This is my latest jig. Only holds the action by the front ring, no possibility of tweaking an action, the action sits in a split bushing and the jacking screws have pivoting feet. It repeats to the tenth on the spindle. Also using precision ground mandrels from Wheeler Accuracy that are ground in .0005 increments and are ground to .0002 accuracy over the length and the repeat very good compared to using the bushings and small mandrel.

 

[Hired Gun]

Thanks for the compliment Gary. I'll have to get some current pictures of it as it is now.

bigngreen, have you ever noticed distortion right ahead of the lug abutments and in the thread bore by holding pressure directly over the threads? Even holding it as light as we dare we noticed it with a dial indicator behind the threads ahead of the abutments and in the threads when taking the first couple cuts. At first we thought it was just poor machining from the factory with egg shaped threads or high and low spots but further experimentation found that they are not near as bad as they first appeared. To get around it we purposely hold our actions back about the back edge of the lug abutments or right over the bushing so if there was any distortion it doesn't show up in the threads. Now most everything cleans up 100% with just a few thousandths clean up. I'm certain it wouldn't hurt anything but being the nature of the internet and these forums we can't risk someone dissecting one of our builds and being able to find any room for improvement.

A general observation not aimed at anyone. I often notice that a lot of the spiders, people are using bolts with large flat brass pads to hold actions and barrels. We found that even with flat pads as small as 3/8" those pads would try to bend the barrels, and actions to a lessor extent, to conform with the ends of the bolts. Like using a 4 jaw without a pivot wire or round pivot insert. Letting the jaws lay flat holds the surface of the barrel or action end flat to the jaws and then dial in the other end to center. On barrels held by large jaw flats or large contact pads dialing the muzzle end is just adding a curve to the barrel. No way to align the internal bore if that is your intent. To solve it we sharpened our brass contact points up to about an 1/8 round tip. The small tips allow us to hold tapered barrels without the bolt tip faces trying to bend the barrels. I hope that made sense.

 

[bigngreen]

Ya, I've seen the egging of an action, it's amazing how flexable actions are really and that is one reason I got away from holding the rear bridge also, I went back on two actions I have previously carefully trued with my older jig and they were out a little when in this jig. My split sleeve is very thick so it have a lot of support on the action and it has no issues, also with the ball swivel feet so they don't bias the action, like you said even a small flat will hold things straight.

I also don't touch an action now unless I can remove my mandrel and have it repeat in the tenths, found so many issues with the bushings, my buddy had one that was 6 thou out, with the solid hardened and ground rods the bolts are in the center every time!!

I see it in the barrels as well and with my current set up I have to watch it a little on light barrels that I'm not forcing the bore, I'm going to build a front chuck for barrels with swivel feet and mini v blocks, my buddy build one and it's amazing how well it holds a barrel and yet puts no stress into the set up.

 

[Danny1788]

Is there any good reason to not build one of these that threads onto the spindle?

I just finished an outboard spider, but one of these would be great for Contender and Encore barrels as well as actions and bolts!!


Gary

Like this one?

 

[Pdvdh]

Interesting thread. I have nothing to contribute, as I've never operated a lathe. Observed. Guess I'm observing now too, in a way, by reading these posts.

 

[Hired Gun]

I think the jig threaded directly to the spindle or connected directly to a cam lock plate is a lot better than trying to hold one in a 3 or 4 jaw. The stiffer the better.

 

[Trickymissfit]

This is my latest jig. Only holds the action by the front ring, no possibility of tweaking an action, the action sits in a split bushing and the jacking screws have pivoting feet. It repeats to the tenth on the spindle. Also using precision ground mandrels from Wheeler Accuracy that are ground in .0005 increments and are ground to .0002 accuracy over the length and the repeat very good compared to using the bushings and small mandrel.
View attachment 75171

I knew a guy that built one off a mandrel that used expanding sleeves like they use on grinders (think they came from Hardingh Brothers). Extremely accurate and extremely repeatable. He had a set of sleeves that were in .005" steps for different bore diameters, and worked off the bolt raceway. How well did they work? I saw him do a Remington PS action in about an hour and a half. Then turned a male master thread for the recut thread. Used that to cut the barrel thread off of three wires. Once he had the first barrel cut, he could cut a dozen for a switch barrel without ever doing anything else. His PS in .308 shot a comfortable mid threes, and his loading setup was pretty flakey.
gary

 

[Trickymissfit]

Thanks for the compliment Gary. I'll have to get some current pictures of it as it is now.

bigngreen, have you ever noticed distortion right ahead of the lug abutments and in the thread bore by holding pressure directly over the threads? Even holding it as light as we dare we noticed it with a dial indicator behind the threads ahead of the abutments and in the threads when taking the first couple cuts. At first we thought it was just poor machining from the factory with egg shaped threads or high and low spots but further experimentation found that they are not near as bad as they first appeared. To get around it we purposely hold our actions back about the back edge of the lug abutments or right over the bushing so if there was any distortion it doesn't show up in the threads. Now most everything cleans up 100% with just a few thousandths clean up. I'm certain it wouldn't hurt anything but being the nature of the internet and these forums we can't risk someone dissecting one of our builds and being able to find any room for improvement.

A general observation not aimed at anyone. I often notice that a lot of the spiders, people are using bolts with large flat brass pads to hold actions and barrels. We found that even with flat pads as small as 3/8" those pads would try to bend the barrels, and actions to a lessor extent, to conform with the ends of the bolts. Like using a 4 jaw without a pivot wire or round pivot insert. Letting the jaws lay flat holds the surface of the barrel or action end flat to the jaws and then dial in the other end to center. On barrels held by large jaw flats or large contact pads dialing the muzzle end is just adding a curve to the barrel. No way to align the internal bore if that is your intent. To solve it we sharpened our brass contact points up to about an 1/8 round tip. The small tips allow us to hold tapered barrels without the bolt tip faces trying to bend the barrels. I hope that made sense.

I've seen this issue several times in the past, but with tool room work. The small set screws exert a lot of pressure, and the wall thickness is not great in that area. Not enough room to use a D4 head with a collet. Really think a lathe is not the solution, but not sure what would be best. I'll think about it.
gary