Bedding under the shank of a barrel?

[akajun]

Well my wife works at Nasa and she says the sky is green. Thats a fact. ;D
I have tested this (barrel bedding). What you say? An actual test? Not an Opinion? I originally bedded a 1000 yard gun with the chamber bedded. It was a rem clone with a 30" hv barrel. I shot it well for 6 months then ground out the chamber bedding and shot the barrel out. I saw no difference. For this reason I no longer bed the chamber. No benefits, only possible problems.

Well my wife is a nurse and she says yall are all retarded.... Well maybe just me.

Ill throw this in there, when chambering service rifle barrels, I like the gas block/FSB area to be a tight fit so that there is friction on the fsb when adjusting the windage on the FSB. Because of that I like to make that dimension .7502. Triying to machine that dimension while the barrel is warm will result in that dimension being undersized when the barrel cools as I found out. Therefore I started allowing the barrel to cool to room temprature before removing the last .0015 and havent had a problem since.
As far as bedding under the barrel, I dont care for it, but I have no data to back it up, I just dont care for it and was taught not to bed there.

 

[STS]

Well my wife works at Nasa and she says the sky is green. Thats a fact. ;D
I have tested this (barrel bedding). What you say? An actual test? Not an Opinion? I originally bedded a 1000 yard gun with the chamber bedded. It was a rem clone with a 30" hv barrel. I shot it well for 6 months then ground out the chamber bedding and shot the barrel out. I saw no difference. For this reason I no longer bed the chamber. No benefits, only possible problems.

Exactly. I've never seen any advantage, only potential for problems.

 

[logger3006]

We're talking about a barrel, not a solid. Completely different animals. From my resident structural engineer: "You guys are dealing with a rifle barrel that is not a solid. To believe the OD of the barrel is expanding from introducing heat, you would have to believe the rigidity of the barrel steel forces the OD expansion to make the bore diameter larger also".

I have watched a few flywheels assembled. The flywheel was heated to a certain temperature, then the ring installed. When it cooled, the ring was tight. As I stated earlier, we heat the enormous turbine shafts (actually performed by Cooper, a specialty contractor) wrapped with an induction type blanket with about 3 zillion wires attached for a 72 hour period. Once it has contracted to the correct dimension, we have a 30 minute window in which to lower the bearing onto the base of the shaft with the crane, before the shaft starts to expand as it cools.

I have never heated a flywheel to install a ring. It the ring I heat. If I ever saw someone heating the flywheel In my shop they would be fired. Granted the only person in my shop would be me. Also installing bearing on my skidder winch the bearings need to be heated to go on the shaft. Found this out the long way around with a hammer and no progress till heating the bearings..

 

[JRS]

Sorry, but you need to hire a new engineer. Tubes expand exactly as solids. If your engineer every had any advanced math tell him to review Green's theorem. The expansion of the ringlet at 1" diameter is not dependent on the ringlet at .5". And if he thinks that heating a tube causes the inside diameter to get smaller, then keep him out of the field.

If you don't believe me try this gedanken experiment. Think of each segment of the barrel as a circle, just as you draw on a paper. The elements of the circle are caused to expand by 1%. Thus the length of the line becomes 1% longer. That line is the circumference of the circle. So the circumference grows by 1%. Divide the circumference by 2pi to get the radius. Thus the radius grows by 1% also. Hopefully this helps.

--Jerry

We're talking about a barrel, not a solid. Completely different animals. From my resident structural engineer: "You guys are dealing with a rifle barrel that is not a solid. To believe the OD of the barrel is expanding from introducing heat, you would have to believe the rigidity of the barrel steel forces the OD expansion to make the bore diameter larger also".

You need to learn to read The bore diameter would get "larger". Another point you are missing: a rifle barrel is not a tube. It is a piece of solid stock with a hole bored through it. You apparently don't understand the google search you performed regarding Green's theorem!
Try this: weld a piece of pipe, or tube, onto the center of a base plate. In which direction does the plate move? Curls up towards the heat, doesn't it? That's called contraction. If it were expanding, it would curl down, away from the heat.

 

[Pappy42]

"When one finds himself in a hole; then one should stop digging"

 

[JRS]

Here's a really simple one: Neck turning brass. If heat is causing the brass to expand, why is the brass getting tighter on the mandrel, even though it is lubricated?

 

[Tim Singleton]

"When one finds himself in a hole; then one should stop digging"

Well said.

As to brass neck turning.
I think that's the reason some use carbide mandrels. They expand less than steel ones

The mandrel is expanding when it gets hot
http://www.benchrite.com/cscart/index.php?dispatch=products.view&product_id=29824

 

[JRS]

If the mandrel were expanding, you would have to constantly back off the cutter because the brass would be forced into the cutter, causing the cut to get deeper with every turn carbide is the better choice, due to it being much slicker, thereby mitigating the galling effect you have with steel as the BRASS heats up, tightening itself against the mandrel

 

[Tim Singleton]

If the mandrel were expanding, you would have to constantly back off the cutter because the brass would be forced into the cutter, causing the cut to get deeper with every turn carbide is the better choice, due to it being much slicker, thereby mitigating the galling effect you have with steel as the BRASS heats up, tightening itself against the mandrel

The first sentence in the above is what happens if you turn to fast on a steel mandrel the friction causes heat the mandrel and the brass expand against the cutter causing variances from pc to pc.

It seems somewhere along the line of all this. from what you've said above. You have decide heat does expand not contract. That's forward movement

The hole is dug so deep now I can't see down in it. I'm out

 

[JRS]

Nope! The brass is NOT expanding. It's contracting with heat. If it were expanding, (moving outward) it would be getting looser on the mandrel, not tighter. If the mandrel were expanding, it would be forcing the brass tighter against the cutter, causing a different and thinner neck with each subsequent pass. If the brass were expanding along with the mandrel, it wouldn't continue to get tighter on the mandrel. Would it ??? Considering the brass is hollow, and quite thin, and the mandrel solid, which do you think is heating up first and quickest? If you'll re-read my statement above, at no time did I say the brass was expanding. What I did say is that if the mandrel were expanding, the brass would be FORCED into the cutter I will concede to Dusty, regarding the railroad track scenario. With enough heat, you CAN lengthen the steel

 

[dantiff2]

JRS,

I think it's time to call it quits on this one

I can't believe I even fell so low into your world to even bother with this but I did. I took a steel pin that measured exactly .110" in diameter at room temperature (68.2°F). I then heated this pin to a slight orange tint with a torch. It was difficult to get my temp gun to read on it but I did manage a 850° reading after a few tries. I then measured out to the fourth decimal. My recorded measurement was..... wait for it...... .1126". Can you please explain to me what just happened??


Thanks
Dan

 

[JRS]

Sorry, but, no I can't. Perhaps the tool you used to measure is off that much? After all, the tools we use are +/- a certain amount. I have never chambered a barrel, but would imagine that reamer gets pretty warm. Does the reamer cut a bigger chamber than it's dimension because it gets hot? I seriously doubt a rifle barrel will reach 850 degrees. I have had drill bits smoking hot, but the holes were always the same size. Can you explain that?

 

[CJ6]

Try these examples. The SR-71 Blackbirds fuel tanks leak like sieves when sitting "cold" on the ground, only when heated by air friction "at speed' do the tanks finally seal (heat expands). 2) tubes/barrels when heated expand IN BOTH DIRECTIONS (internally and externally) to fill the void created by the bore hole and the external surface. If heat "contracted" steel the bore would get LARGER in diameter and the OD SMALLER in diameter the hotter it became .

 

[dantiff2]

Your holes with a smoking hot drill bit are certainly not the same size. Unless measured with a rule or tape. You would need to use an air gage to confirm this. My measuring instruments are professionally calibrated every month by our quality department

And the hole gets deeper 8)


Dan

 

[jrm850]

We run our lathes until the bearings heat up so they can get looser? This is going to be a big time saver for me.

JRS, I hate to pile on, I really do, but you have been taught wrong on this one. They heat rivets because it makes them malleable. Weld beads get laid at greatly expanded states and shrink as they cool. Just like putting a bead inside a stuck bearing race and watching it fall out as it cools.

Google, NTE or negative thermal expansion and see what materials you can find. There are very few.

Or you can go to matweb.com and look up the different material properties. Materials that shrink when warm will have a negative number for a CTE.

 

[JRS]

Holes were the same size. A base plate machined to a zero tolerance to accept the 6" pins that the base of a turbine shaft sits on. The pins are an extremely tight fit. After looking at a temp chart, at 850 degrees, that pin was getting reasonably close to a point of distortion. That could quite possibly be the difference in dimension. Thanks for responding to the drill bit portion And the chambering reamer question?

 

[JRS]

We run our lathes until the bearings heat up so they can get looser? This is going to be a big time saver for me.

JRS, I hate to pile on, I really do, but you have been taught wrong on this one. They heat rivets because it makes them malleable. Weld beads get laid at greatly expanded states and shrink as they cool. Just like putting a bead inside a stuck bearing race and watching it fall out as it cools.

Google, NTE or negative thermal expansion and see what materials you can find. There are very few.

Or you can go to matweb.com and look up the different material properties. Materials that shrink when warm will have a negative number for a CTE.

You'll quickly get lost talking to me about welding. It happens to be a very large part of the work I performed at the nuke plants. Stick, innershield, and tig. FYI: Welds don't shrink. They stretch to the base metal during cooling. We use fillet gauges to check our welds before QC inspection. If it calls for a 1" weld, we make sure it is. Hours, sometimes days later, when QC checks the weld, it remains 1". Behind QC comes QA. Same thing takes place again.

 

[Tim Singleton]

We run our lathes until the bearings heat up so they can get looser? This is going to be a big time saver for me.

JRS, I hate to pile on, I really do, but you have been taught wrong on this one. They heat rivets because it makes them malleable. Weld beads get laid at greatly expanded states and shrink as they cool. Just like putting a bead inside a stuck bearing race and watching it fall out as it cools.

Google, NTE or negative thermal expansion and see what materials you can find. There are very few.

Or you can go to matweb.com and look up the different material properties. Materials that shrink when warm will have a negative number for a CTE.

You'll quickly get lost talking to me about welding. It happens to be a very large part of the work I performed at the nuke plants. Stick, innershield, and tig.

I had to take a 550 word physc test to work at a Nuke plant 20 years ago. Do they still do those?
Those tests only had a few base questions. They just asked them 10 different ways.
This thread reminds me of those tests. Any way you look at it the sky is still blue.

 

[jrm850]

You'll quickly get lost talking to me about welding. It happens to be a very large part of the work I performed at the nuke plants. Stick, innershield, and tig.

Probably. Wish I was better at it. I was taught Oxy/Acetylene in school and and bought a Miller Econotig 18years ago to teach myself. Didn't know enough then to realize that it started at 15amps was not very good for gunsmithing. I still have it and it is still not very good for gunsmithing. What I did learn it that if you poke yourself in the calf with a 5000 degree tungsten, it will not bleed. ;D

 

[Pappy42]

What I did learn it that if you poke yourself in the calf with a 5000 degree tungsten, it will not bleed. ;D Quote

Did you happen to measure the diameter of the electrode before and after you quenched it? ;D