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Hi, anyone here used shrinking joinery before? My terminology might not be correct but by that I mean joinery where a cold piece of steel is hammered into a hole in a hot piece of steel and as the hot steel cools it shrinks and grips the cold piece. I don't think I've seen another thread about it.

 

How, where, when, why did you use it? Opinions, anecdotes and pictures all welcome. I go weak at the knees for a nice bit of traditional joinery!

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Yes I've done it now and then, it is not my preferred join but I guess you could include collaring with this too, which is a good way to join. However, I tend to use mortise and tenon joints more often than not, then either rivetting the tenon down or using a wedge through a hole in it. I'll be interested to read of the applications you have found where your method is most useful.

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Often referred to as an interference fit. Many times used when shafts have to get installed into rollers, collars on shafts, bearings installed etc.

 

 

Often the pieces that are supposed to go together  are machined to the "wrong" dimensions. The plug to go in a hole for example is .003" larger than the hole it's to fit in. Trick is to heat the hole to get it to expand while cooling the plug to get it to shrink. Once put together the pieces return to their normal size, and can no longer get separated. It's done very frequently with bearings on shafts.

 

Same idea applies to things with courser dimensions like you are talking about. Rivets would ab a classic example. A hot rivet when it cools, shrinks and pulls the pieces tight together. That's why rivets can be used to make 2 overlapping plates water tight like in ship construction. In this case the piece going thru cools vs the outer piece, but the same idea applies.

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I'll get a pic tomorrow after work of a knife guard I made when just leaning forging techniques and fitting steel together, first and only time I have done it though.

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About 25 years ago I shrunk fit a war hammer head onto a sucker rod handle (squared and twisted)  left the end a bit proud thinking I would rivet it over if it became loose---haven't had to yet.  I drifted the hole with a piece of the hand material that I ground down from the size it was *slightly*

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However, I tend to use mortise and tenon joints more often than not, then either rivetting the tenon down or using a wedge through a hole in it.

I think that's most commonly known as a "keyed" mortise and tenon.

I've not tried shrink joining yet but I'm going to give it a whirl. I expect a rivet would hold best if it had a square shank but the blind hole it was going into was round. I'd imagine tapering the tip a fraction would be required.

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I've set gear rings using that method . Bolts on N Reactors are said to set that way. Never saw it done but a friend did and was really impressed.

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We once bought a bearing heater on an auction that is used to heat bearings to fit over shafts. Some sort of induction heating, it was a long time ago.

 

Ended swopping it for something else

 

51VyWEL2jDL._SY300_.jpg

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I think that shrinking tyres on to wheels should count, and I suppose strakes too for that matter - they do pull the fellows together.

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Beat me to wagon tires and hub bands darn it. I used to use interference fitting on things that had to take a lot of force like drill extensions. A rotary soils drill uses an extension to run from the turn table to the top of the auger and when making one it's going to be under huge stresses. It wasn't uncommon for us to stall a 453 Detroit Diesel in low gear drilling, if the guy on the controls wasn't fast enough the back lash would make the engine run backwards.

 

It took some time to convince the heavy duty shop to stop making extensions from 2" HC hex bar, those things seldom lasted an entire hole. I used DOM mechanical tubing with an over thick female hex on the box end. On the pin end, I turned down 6" of the HC hex bar to about 0.004" larger than what I cleaned the ID of the Mech tubing. Then I heated the tubing to around 800f +/-, slipped them together and let it cool Once it was locked in I welded the join.

 

One of my extensions broke under pretty severe abuse but did so in the way I'd intended. The weld on the pin end broke. this is at the top of the extension right under the turn table and seeing as there was 6" of coupler IN the extension tube it couldn't go anywhere but around and shriek. If the coupler at the bottom had broken there would've been 5' of steel extension swinging around in a most violent manner. Even though, call him, Lewy was pretty smug about breaking one of my welds nobody got hurt, nothing got damaged and the lead driller took the controls for the rest of the job. I was happy with the failure mode.

 

Okay, enough of the windy ramble, here's a thing to remember about interference fits. You can get the female section TOO HOT. This is a perfect example of how wrong the old adage, "a little is good a lot is better," can be. You only want to expand the outside of the joint a couple few thousandths and a few hundred degrees is usually plenty. If you bring it to say bright red what will happen is, as it shrinks over the inside section it stretches and you lose the true interference fit. sure it'll probably be tight but it won't be a proper join.

 

Frosty The Lucky.

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With the proper fits, these joints can transmit a large amount of torque as well.  When runout is critical, shrink fit tool holders are often used to hold endmills and other tooling in CNC machining centers.  It's somewhat analogous to putting something in a collet. 

 

Steve

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They also used to use it when lining gun barrels on big guns like battleships. The old Washington Navy yard gun shop had a big pit specifically for heating barrels and shrinking them around the barrel liners.

 

 

 

The main structure would cover a shrinking pit, 16 feet in diameter and 18 feet deep, with horizontal re-heating furnaces abreast. Two traveling cranes would be set up, one of 100 tons and the other of 25 tons capacity, both with 50 feet hoist and a span of 60 feet. The east wing was the one planned to contain the tools for making the larger classes of guns, up to 16-inch caliber. For smaller guns the west wing would be used.

 

 

 

In construction, the system employed was essentially the same as is still used in making the larger number of the Navy’s guns. Guns consisting of concentric rings of steel forgings were built up by heat and shrinkage, the net result being to give strength to the finished product that it could never have if composed of a single sheet of steel.

 

 

http://www.history.navy.mil/library/online/navgunfound.htm

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I add one step to his process. after forging them together, I quench the joint. you can hear that sucker "snick" tight! very cool.

I've also drilled thru the round bar and added a rosette top and bottom. when quenched, I've never "had" to rivit, done it for the detail.

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