Heat shrink problem

[Naz]

Hi, I'm making a tong rack for the shop and went a little overboard with the details.
I cut a piece of 3/4" round bar of what I think is brass and stamped my logo in.
I then punched a 3/4" hole in square stock at a yellow-orange heat.
Keeping the hole at a yellow orange heat, I inserted the brass disk hoping the metal would shrink around the disk traping it solid. It seemed tight until I quenched the whole thing. I heard a "tic", pulled it out of the water to realize it had gone loose.
Anyone know why that happened ?
It is possible that the hole was over 3/4" as I didn't have a drift and had to fight with the 3/4" punch to get it out, is this the only reason you guys can see or am I missing something ??


Thanks !
Naz.

[bigfootnampa]

It looks nice and you can just put a little super glue around it to fix it. As to why... methinks your metal shrank leaving the hole larger than it had been when hot. Think about it... the narrow band of metal around the hole shrinks becoming even narrower and thus the hole becomes larger. Half the shrinkage away from the hole and half (roughly) toward the hole. If the hole were in a large piece of plate I think that you'd have seen the effect that you expected (more or less).

[pkrankow]

I think you need to look up interference fit. There are tables published of differing metals and tolerances to gain the shrink fit you are after. You can do a shrink fit in several ways, either the way you did by heating the outer part, or you can chill the inner part, or both.

Phil

[MLMartin]

well the hole loots pretty chamferred and rounded. maybe next time punch and drift hold to 1/16 smaller than you need, then drill the hole to full size. also you can gently peen the edges of your brass spacer so that it will widen out in the hole and rivet itself in place

[BIGGUNDOCTOR]

Is that a crack in the lower left? Was the tic you heard possibly a crack?

If the hole was sized say .003"-.005" smaller than the disc when cold it should work. Size the opening cold, then heat, and drop in the cold disc. Let cool, or quench.

I used to shrink fit hubs at Jelly Belly for the big pans we used to build up the beans. I would weld and re-machine them with a .003" "press" fit. I would heat the hub to a dull red, and literally drop the shaft into the hub. Once it was cooled we would weld it on the end to the shaft. Done this way they didn't break, or work loose like they did from the factory.

[fciron]

I think that part of the problem might be the lack of control on the hole. If the disk is relatively thin and the hole is kind of tapered then I could easily see the disk flexing and popping out of the hole as the hole shrinks. You don't often see shrink fits on pieces that are smaller than the hole and perhaps this is why (usually parts are shrunk onto a piece that sticks out of the hole.) That popping out could also be the source of your ping noise.

I'm going to have to argue with bigfoot, the hole will shrink smaller because the metal also contracts lengthwise around the periphery of the hole and that amount of shrinkage is more than enough to overcome the thinning in the other dimension.

I've had good luck drifting the hole with the same size material as the plug will be and then just inserting the plug and quenching. If you drift it hot then you will end up with an interference fit after cooling.

[Frosty]

A couple things come to mind:
First, how thick is the disk? It should only be slightly (a couple hundredths max) thinner than the bar stock you wish to mount it in.
Second, as said, the hole as punched looks chamfered saying to me it's not clean enough and probably imprecise and uneven. Drift it to a few thousandths smaller than the insert piece, the more cylindrical the better and very slightly hour glass shaped is good.
Third you tried shrink fitting it at WAY too high a heat. Doing so at yellow heat means the brass stretched the iron rather than being trapped as the iron shrank.

Brass has a much higher expansion coefficient than iron so what happens as the two equalize in temperature, is the brass expands significantly while the iron is in a highly malleable state at yellow, orange or even red heat. To get the effect you want try drifting the iron to a few thousandths smaller than the brass insert. Then heat the iron to 300-400f and try dropping the brass into the opening periodically as you gradually heat the iron. Keep the brass cold even if you have to use ice water or alcohol and dry ice. (be careful of alcohol fumes as they are flamable!) When the brass inserts to the stop. The stop is just a piece of small bar stock clamped on the back side of the iron frame. As soon as the frame stock is warm enough the brass falls into the hole adjust the insert's depth, position and orientation and quench the iron frame. You can do this with the iron frame at room temp if you use alcohol and dry ice to chill the brass but it takes more precision in prep.

300-400f will expand iron sufficiently, to allow the brass to be inserted without the use of enough force to damage the insert or frame's finish but at a low enough temperature the iron frame will NOT be stretched. This is a low enough temp to be below iron or steel's elastic limit meaning it isn't permanently deformed, just stretched like the waist band on your shorts. Wagon tires were hot fit barely hot enough to make the wood wheel smoke, around 450f give or take. A red hot tire would slip off pretty quickly because it stretched.

Frosty the Lucky.

[bigfootnampa]

#39;m going to have to argue with bigfoot, the hole will shrink smaller because the metal also contracts lengthwise around the periphery of the hole and that amount of shrinkage is more than enough to overcome the thinning in the other dimension.

Hey I think you are right, I didn't think about the shrinkage of the diameter.

[fciron]

I know, because I've been there. ;)

[MLMartin]

O another thing that just came to kind, how about making the iron hole the same way as before, then cut your brass slug, but cut it just a little longer than the with of the iron, insert the slug and lay the whole assembly on the anvil, then set a flatter or set hammer over the slug and give it a good hit or two, this will slightly stretch the edges of the brass slug and rivet the whole thing in place, lastly take your touch mark and stamp your name

[Frosty]

Sure, that'll work, pein it like a rivet.

Frosty the Lucky.

[Naz]

Thanks for all replies !
Once again i'm loaded with new information as I plan to experiment some more with combining different metals.

Frosty, I like the "waist band on my shorts" comparition, that's taking a lot of technical, valuable information and putting it at my level of understanding! Haha !!!

I'm a self-thaught blacksmith hobbyist with absolutely no background in metals, welding, or anything that has to do with blacksmithing. For me, being able to post a question and getting answers from experienced blacksmiths is one of the most valuable tools I have !

Thanks for taking the time to answer !

Naz.

[double_edge2]

I think you need to look up interference fit. There are tables published of differing metals and tolerances to gain the shrink fit you are after. You can do a shrink fit in several ways, either the way you did by heating the outer part, or you can chill the inner part, or both.

Phil

what he said,,prepare the outer to perfect and the inner same, chill one and clean heat the outer and dont deform the hole on th way in.

[Frosty]

It goes both ways NAZ. Nothing gets a person thinking and learning like a good question.

You're not the only one who's mostly self taught, I'm in that club though I do have a lot of schooling in other areas of metal work. First was Dad's metal spinning shop, we worked with darned near every exotic metal used in the aerospace industry(Ever hear of Mumetal?). Then there were years and years of classes from jr and high school shop classes to trade schools. No, I did NOT want to become a metal spinner, it was a brutally hard profession with maybe a 13 year career if you were careful.

Blacksmithing on the other hand was something Dad and every shop and trade school instructor discouraged as a dead trade, so I had to teach myself. Heck, I'm thinking it was the early 80's before I discovered a smithing book, "The Art Of Blacksmithing," by Alex Bealer and the mid or late 80's when I went online before I discovered living breathing practicing blacksmiths to sponge info from.

So, don't feel alone NAZ, sharing what we know benefits us all, I know I've gained WAY more than I've shared.

Frosty the Lucky.

[Naz]

Well said Frosty !

I see your wisdom doesn't stop at blacksmithing !

I salute you from douwn here montreal ! (Rarely can I say "down here" Montreal !)

Take Care !
Naz.

[Frosty]

Oh shoot Naz, I appreciate a good joke all round too, eastern one.

Frosty the Lucky.

[Nakedanvil - Grant Sarver]

Well, here's my take: The brass got hot, tried to expand and either pushed open the hole (as Frosty said) or in trying to expand was forced smaller. Then when everything cooled, the brass shrunk more due to it's higher expansion rate.

Some of the suggestions got me to thinking. Why not cup it like an old soft plug, put it in the hole and whomp it flat thus expanding it into the hole?

[Naz]

As most times, there seems to be more than one right answer.
Next time, I'll put my punch mark as the last step. That way if I need to "whomp" or expand the insert, I won't have to worry about messing up anything.
Here's the finished piece: ( I needed the rack for a new arrival of over 75 pairs of old, rusted pairs of tongs I haven't had time to clean or adjust, as seen in photo).
Funny thing is after I put the tongs on the rack, the rack seems to disapear in the picture.
Good thing is, I learned something about heat expansion.

Thanks !
Naz.

[Frosty]

Looks darned fancy for a tong rack to me NAZ but I like a guy with style.

Heat expansion?! I must be getting hotter!

Frosty the Lucky.

[Naz]

Looks darned fancy for a tong rack to me NAZ but I like a guy with style.

Heat expansion?! I must be getting hotter!

Frosty the Lucky.

Isn't that in the dictionnary? (expansion)?
Thanks Frosty !

Naz.

[Frosty]

Isn't that in the dictionnary? (expansion)?
Thanks Frosty !

Naz.

I could find nary a word about my waist in one Naz.

Frosty the Lucky.

[nuge]

Another way of setting the disc into steel would be to use a jewelers approach to setting stones and make a bezel. Make your hole a bit undersized and then make a "seat" for the round. You could do this by drilling or an accurate punch would also do the job. Make sure to leave a lip. All thats left to do is squish the lip over your setting. A fly press would excel at this, but you could get by with a blunt chisel or even a ball peen hammer. This is a "gypsy" setting.

[nuge]

Did my idea today. I cheated a bit for the shelf and filled some of the depth of the hole with a slug and tigged it on the back.

[Naz]

Nice, I like it !
Opens the door to all kinds of ideas !
Thanks !
Naz.