Is pinning the rail to receiver a good idea?

[TRA]

Dowel pins purpose.....are for alignment purposes. The shear or rigidity of an assembly is taken up by friction created by the proper placement and torque of the fasteners. I've built connecting rods for high performance applications with out out serrations , pins, hollow dowels, or tongue and grooves. If the two parts are properly finished they will not move. Just the rod bolts create enough clamp that the rod and cap will not move.

Heavy duty trucks will sometimes have bolt patterns or flywheels out of round and the procedure is to remove the alignment dowel and with an indicator tram the Flywheel back in true. Then pitch the pin into the excess parts bucket. 4000-5000 hp tractor engines same deal.

Using dowels as stated above would provide a good chance for accurate repeatability if the assembly were to be removed and replaced.

 

[carlsbad]

Yes, another application of dowels is alignment. That is not the design purpose in this case. Good luck with your tractors. --Jerry

 

[ntsqd]

According to a mfg of said pins: https://www.huyett.com/getmedia/91e92ffa-e74b-4fe8-89f3-f174fe650e03/pins-Dowel.pdf.aspx?ext=.pdf
"Dowel pins are used as locking devices, pivots, hinges, shafts, jigs, or fixtures to precisely hold or align parts within machinery. Designed to achieve maximum holding power with increased shear strength to absorb lateral stress, (emphasis mine) they can manually align multiple work-pieces, install flush to produce a smooth surface or protrude beyond the work-piece to ease alignment of mating parts."
This is how I was taught to treat dowel pins, both for shear stress and for location of mating parts. Doesn't mean that they can't be exclusively used for one or the other per the design intent, but it can't be said that they can only be exclusively used for one or the other purpose.

At 6k lbf shear they're not 18-8 SS dowels unless they're 5/16" OD.

And at 4000-5000 HP they're not really "tractors". They're the tractor equivalent of an F-Class rifle, only vastly more intricate and complicated.

 

[carlsbad]

ntsqd,
I'm going to ignore you now. thanks, Jerry

 

[ntsqd]

Jerry, You're welcome to undo that at any time, or not as it won't make me loose any sleep either way. Your tone in the posts above brought it on, otherwise I wouldn't have bothered to post.

thom

So, does the OP feel that the question has been answered? Or at least enough valid & polite opinions have been expressed to form their own conclusion?

 

[gunsandgunsmithing]

ntsqd,
I'm going to ignore you now. thanks, Jerry

Looks to me like you made some nifty little recoil lugs out of dowel pins. Simple, easy and effective. To answer the op's question again, yes, they are a good idea. At the very least, they won't hurt anything but will add strength and precisely locate the rail.
Maybe not necessary, but I don't see a down side. Call them whatever you want Jerry. In this application, it matters not what the manufacturer calls them. They serve the intended purpose. I'm not sure why that isn't apparent and we have to define the purpose of a dowel pin here.

 

[carlsbad]

Mike
As you know, alignment pins have to have about .001" clearance to go on an off. These pins have about .0007" interference fit so that the rail now has become a structural member of the action. This is an engineered solution rather than something I read on a vendor website. --Jerry

 

[ntsqd]

What makes the biggest determination as to their intended use is the install of the pins. Are they press/press (shear + location) or are they press/slip (simple location)? And if they're simple location are they both round or is one a correctly oriented diamond as it should be if easy R&R is required?

 

[gunsandgunsmithing]

Mike
As you know, alignment pins have to have about .001" clearance to go on an off. These pins have about .0007" interference fit so that the rail now has become a structural member of the action. This is an engineered solution rather than something I read on a vendor website. --Jerry

Thats a lot of interference for such a small pin but I get it. It works, I'm sure. Tight little bugger, huh?

 

[carlsbad]

It may be more like .0005. The pins are .1250 +0 -.0001. I think some may be a bit undersized at I found the .1247 reamer not quite as tight as I wanted it. To be a structural member, yes I want it tight. --Jerry

 

[TRA]

Even with the spin in force, I for the life of me fail to see nor have ever seen a dowel used as an "engineered structural member".

If your customers are not having scopes falling off their rifles or you have some way of verifying your claims, then it seems to me this is an "engineered solution" looking for a problem. But then is that not what engineers do?

BTW, we, (my company) consult with engineers on a daily basis. I'm not just attempting to be argumentative, just that when I hear claims and numbers thrown about without some sort of validation, I question how the conclusion was made that such a modification was necessary. I'd be interested, as to what effect all this pinning has on the harmonics of the rifle.

 

[alinwa]

StiffnessView attachment 1069699

So IMO that is just frickin' awesome wikkid.

I have a Bridgeport with DRO's all over it, two hands and feets down below my knees.... and I'd like to try this. It just looks too simple to be true!

Would it be fair to say that you screw the base down, ie "fasten it down conventionally" and then stick it in the mill, index/sweep everything into line and then punch the holes using a square endmill right down thru the base, thru the angled rollover of the action in one fell swoop? Would you mind sharing the size/shape/type endmill used if this is the procedure?

 

[carlsbad]

Perhaps you haven't seen my posts but I am an engineer with 35 years of power plant experience and throw numbers around a lot. I know people will check and challenge me so I make sure they are always right. If you see a number from me, you can take it to the bank. You do seem a bit argumentative but I am used to that from outsiders who think they know more that the engineers. So I will try once to explain.

To stiffen an action against a barrel vibrating up and down, the scope rail would be subject to compression and tension. the deflection is extremely small but small deflections cause big errors at 1000 yards. So if a member bolted to the side of the action is to be effective in resisting these harmonic forces, there must be no freedom of movement.

In the automobile (or tractor) industry and many other manufacturing applications, dowel pins are often used for locating. These dowel pins have .001 to .005" clearance to allow assembly and disassembly and get the part into the right place but don't prevent tiny amounts of relative motion.

I designed the pinning details on this rail to allow no motion. They are an interference fit and cannot be disassembled without driving out with a punch. I also used 2 pins per end and moved them away from the center of the rail to allow longer engagement length. The increase in stiffness is considerable, so long as the pins retain a zero clearance fit. The 1/8" hardened pins are rated at 2600lbf shear strength (10,400 for 4) but that is higher than the yield strength of the action steel so the 6000 lb number I used is my estimate of when the action will yield allowing some minor motion.

So as you see, this has nothing to do with the scope. I have seen pins on rails with clearance fits and don't consider them useful. that answer was given several times in the first 5 replies to this thread.

I use interference fit ins a lot on jigs and fixtures including my barreling spider which I bolted and pinned to a D1-5 chuck backplate.

Jerry

 

[carlsbad]

So IMO that is just frickin' awesome wikkid.

I have a Bridgeport with DRO's all over it, two hands and feets down below my knees.... and I'd like to try this. It just looks too simple to be true!

Would it be fair to say that you screw the base down, ie "fasten it down conventionally" and then stick it in the mill, index/sweep everything into line and then punch the holes using a square endmill right down thru the base, thru the angled rollover of the action in one fell swoop? Would you mind sharing the size/shape/type endmill used if this is the procedure?

Al,

If you figure out what you need to do rethread 6-48 to 8-40 screws and make sure they are perfectly aligned with the action, then you will know all you need to know to do this pinning. (I already told you what interference fit I use).

It wouldn't be fun if I just gave you step by step instructions, would it?

If you have any questions PM me.

--Jerry

 

[TRA]

Engineered? You drilled 4 holes reamed and pounded in the pins.

The 1/8" hardened pins are rated at 2600lbf shear strength (10,400 for 4) but that is higher than the yield strength of the action steel so the 6000 lb number I used is my estimate of when the action will yield allowing some minor motion.

"Estimate"? Sorry but what I see is a number from a reference sheet and a estimate.

I've seen plenty of your numbers you throw around. The fact remains to engineer a solution an engineer needs to know what exists, what is needed to fix the problem, then come up with the solution, not a published number and a guesstimate.

I think this is more of an easy out for not wanting to drill and tap 4 holes to a larger diameter. OR, that the proper equipment is not present.

The necessity for your pin fix remains to be seen.

If you are at liberty to say, what actions are these?....700's..... and what on earth would the application be for them to hang such a large barrel on them?

 

[carlsbad]

Al, Do you have one of these? --Jerry

https://rifleshooter.com/2015/02/making-a-remington-700-action-v-block/

 

[alinwa]

Al, Do you have one of these? --Jerry

https://rifleshooter.com/2015/02/making-a-remington-700-action-v-block/

Yes

 

[alinwa]

Al,

If you figure out what you need to do rethread 6-48 to 8-40 screws and make sure they are perfectly aligned with the action, then you will know all you need to know to do this pinning. (I already told you what interference fit I use).

It wouldn't be fun if I just gave you step by step instructions, would it?

If you have any questions PM me.

--Jerry

Yeahh, I'm fine Jerry.... thanks

 

[dolek]

Engineered? You drilled 4 holes reamed and pounded in the pins.



"Estimate"? Sorry but what I see is a number from a reference sheet and a estimate.

I've seen plenty of your numbers you throw around. The fact remains to engineer a solution an engineer needs to know what exists, what is needed to fix the problem, then come up with the solution, not a published number and a guesstimate.

I think this is more of an easy out for not wanting to drill and tap 4 holes to a larger diameter. OR, that the proper equipment is not present.

The necessity for your pin fix remains to be seen.

If you are at liberty to say, what actions are these?....700's..... and what on earth would the application be for them to hang such a large barrel on them?

Can we some of your work please ?

 

[dolek]

I'm with Jerry , I know for a fact he knows what he speaks of .