Full diameter action mandrels

[Taylor Stratton]

I’ve recently discovered how to check action straightness in actions I’m blueprinting with the old bushing and .500 mandrel and I’m commonly getting .0025-.005 runout right behind the action when it’s shouldered up on the tenon. I’m a little disappointed as I spend so much time indicating and taking light cuts to try and make them perfect. I’ve checked a few custom actions that were anywhere from .006-013!! I had no idea.

I’d like to try some full diameter mandrels to indicate actions in for blueprinting and to more accurately check the customs I’m working on (im hoping they aren’t really that bad). Where would you guys get these mandrels made? I would imagine you’d want them hardened and ground. What tolerance would you ask to be held on them? Thanks guys! I always appreciate your input and help.

 

[Alex Wheeler]

The solid mandrel is the only way to go. I had a bunch of they made up in .0005" increments. .0002" for diameter and straightness, ground and hardened. They were not cheap and there was very little interest in them. But I had to order enough of them so the price was affordable. I have them for Bats as well. Setting up an action for truing is tricky, you cant have any error, especially with tight fitting bolts on customs. What your finding is not rare. Not all customs are as good as everyone thinks are they....
Try JGS to see if they will make you a set, but be prepared to pay for a small batch.

 

[GenePoole]

Check your mandrel as well. I went through three from Manson that were not straight. Turns out they were grinding them on centerless grinders (I don't know who had that bright idea), but after talking with their head machinist, they made me one ground between centers as it should be. Check for the center marks on each end.

Here's the video I sent to Manson:

 

[DiffEQ]

they made up in .0005" increments. .0002" for diameter and straightness, ground and hardened.

Wow, talk about *tight* tolerances!

 

[Tucker65]

While it takes a little time I turned my own mandrels out of 4140 shaft. Probably not as nice as the ones Alex had made but I don't do the quantity of actions to justify having a set ground. Here is an action I trued up that was screwed onto a barrel shank that was just threaded. The mandrel just barely slides into the action without any resistance. Only has about .002 total indicator runout about 5" away from the tang. Plenty good enough for me.

 

[tobnpr]

Explain to me why it's preferable to have a solid mandrel, when the raceway is not of a consistent diameter, and the mandrel appropriate for the smallest ID must be used?

 

[Alex Wheeler]

Explain to me why it's preferable to have a solid mandrel, when the raceway is not of a consistent diameter, and the mandrel appropriate for the smallest ID must be used?

Thats exactly why its preferable. The bolt body is full diameter. Bushings do not account for all the variations in between them. A full diameter mandrel will find center of the entire inconsistent bore, bushings will find center between 2 points only. Rarely is an action bore straight, you cant account for that unless you use a full diameter mandrel. Not to mention stacking tolerances and out of round bushings. I'll go as far as to say the bushing/rod setup is terrible. A shop made turned mandrel would serve you better even if it was not perfect.

If the action bore is perfectly straight and the bushings have no run out, then it would work ok but with double the error due to two clearances needed. But the vast majority are not. Most know that the bore diameter is not consistent, but do not realize its warped as well.

 

[jkohler]

Maybe if there was enough interest in a set we could get a group buy.

 

[Taylor Stratton]

Maybe if there was enough interest in a set we could get a group buy.

I’d be interested in a group buy if we can get a few guys interested. Any idea on numbers we would need to reach to get better rate @Alex Wheeler?

 

[Alex Wheeler]

My sets were $400 I think I had to buy 6 sets. You would need to contact the manufacturer to find out but I would assume it would be more now. Thats if they are not too busy to do it.

 

[marazzi59]

I would like to buy a set as well, price pending. Please keep me in the loop gentleman

 

[tobnpr]

A full diameter mandrel will find center of the entire inconsistent bore, bushings will find center between 2 points only.

OK, this makes sense to me- but also consider this.
Exaggerating to make the point- consider an example where your smallest raceway diameter is in the center, and is .003 smaller than either end.

As soon as a set screw is placed through the action to bear on the mandrel, it will bias the mandrel off center/at an angle to the raceway so that the action raceway cannot be precisely parallel to the mandrel due to clearance being present on both sides.

 

[Taylor Stratton]

OK, this makes sense to me- but also consider this.
Exaggerating to make the point- consider an example where your smallest raceway diameter is in the center, and is .003 smaller than either end.

As soon as a set screw is placed through the action to bear on the mandrel, it will bias the mandrel off center/at an angle to the raceway so that the action raceway cannot be precisely parallel to the mandrel due to clearance being present on both sides.

I’m no expert but I’ll give my thoughts. Your point makes sense but we aren’t putting any set screws against the mandrel. Secondly. The middle of the action is where the ejection and load ports are cut and so the likelyhood of it being the smallest part is very very unlikely. So. Have you ever welded 4 pipes together into a square? If you go in a circle it will not be flat any more. The action has a port on bottom and side with thick metal on one side so chances are it’s going to warp towards the ejection side, material would play a part as well but I just don’t think you’d see the scenario you stated. However I have nothing to back this up at the present moment, just thoughts.

 

[tac284]

I would be willing to put my name down for a set. Maybe it’s a given but I would highly recommend that JGS Reamers be the supplier.

 

[Alex Wheeler]

OK, this makes sense to me- but also consider this.
Exaggerating to make the point- consider an example where your smallest raceway diameter is in the center, and is .003 smaller than either end.

As soon as a set screw is placed through the action to bear on the mandrel, it will bias the mandrel off center/at an angle to the raceway so that the action raceway cannot be precisely parallel to the mandrel due to clearance being present on both sides.

That would be an issue, but I have never seen an action like that. All the good custom actions hone the bores. Even though they are not always square to the face and lugs of the action the bores are usually very straight and consistent. On factory actions with magazine cuts, you dont even have a bore in the center. and based on my experience if you could find a factory action like you describe, the bore would be warped as well providing a snug fit on each end still. You can come up with hypothetical scenarios to create an issue with any method, but in practice the full diameter mandrels work very well and fix many of the errors involved with other methods. The other scenario guys always come up with is, what about an action thats looser on one end. Well, since its rare to find a remington with a bore thats not warped the looser end will still fit up snug since the rod you are going to use will be smaller than either end due to the warpage. I went away from the multi piece setup years ago, been using these for a while now so Im not hypothesizing, it did improve my work.

 

[DaveTooley]

I've turned down a few actions to go in sleeves. The middle of all the action was warped going to the outside. Never to the inside.

 

[tobnpr]

Alex, appreciate the input- I'm sold on the idea.

I shot an email to Meyer Gage (these are basically big azz gage pins) to see if they'd be interested and what the cost would be for a set from .700-.705 in half-thou increments. I'll post back when I hear from them in case anyone else is interested.

 

[Alex Wheeler]

JGS made mine. Regardless, your paying for tolerances. Spin them in v blocks and mic them when they come in. I can say JGS hit the specs on all of mine as usual. Would be interested to hear what they can do them for. Found the original ad for reference on price. I didnt buy them to make money, I just wanted a set and had to buy enough to get the price down so I sold the rest. Actually had a couple sets sitting around for quite a while.... https://forum.accurateshooter.com/threads/precision-action-truing-mandrels.3910417/

 

[RDA72927]

I’d be interested in a group buy if we can get a few guys interested. Any idea on numbers we would need to reach to get better rate @Alex Wheeler?

Count me in for a set

 

[Taylor Stratton]

@Alex Wheeler, having been using these for a while now, what sizes do you recommend we order? I’d like to make sure I cover every size I’d need but I don’t want to order bars I will most likely never use. Also if you have any recommendations for other sizes for the actions that have bigger bores like .725 bolts I believe.