Extension table Stuck!

[EdinPA]

My problem was solved. I received an email from a Shopsmith engineer who suggested I use a heat gun to heat up the casting, then hit it with a rawhide mallet. I heated up the casting, but the mallet did nothing. However, i was able to use a bar to lift each tube in succession. A sixteenth of an inch at a time and it finally came free! Took a little over an hour to ease it up. It is rather beat up, so I ordered a new tube assembly, which will be here tomorrow. Thanks to Shopsmith for the assist!

[RFGuy]

My problem was solved. I received an email from a Shopsmith engineer who suggested I use a heat gun to heat up the casting, then hit it with a rawhide mallet. I heated up the casting, but the mallet did nothing. However, i was able to use a bar to lift each tube in succession. A sixteenth of an inch at a time and it finally came free! Took a little over an hour to ease it up. It is rather beat up, so I ordered a new tube assembly, which will be here tomorrow. Thanks to Shopsmith for the assist!

Glad you got this solved, but Shopsmith's solution seems counter-intuitive to me and could have only exacerbated the problem IMHO. Heating up the casting would have caused expansion of the metal. This expands the outside of the casting, but ALSO the inside of the holes that the table extension is stuck inside of. Now, if you had cooled down the casting and/or the extension table supports, then I could see that helping you to be able to remove it. Would appreciate others chiming in here with their opinion to potentially help others in the future that encounter this problem. Does anyone agree that Shopsmith's solution makes sense??? Am I missing something here?

[jsburger]

I think you are missing that by heating up the casting the holes also get larger not smaller. I worked for the Air Force as a civilian (after retiring from active duty) at Hill AFB doing depot level repair on aircraft generators. If a generator main stator required rewinding for repair it had to be removed from the round housing. The housing was a shrink (interference) fit to the stator. The entire assembly was put in a 300º oven for a certain amount of time depending on the particular generator. The coefficient of expansion is different for the housing (aluminum or magnesium) and the iron stator stack. When you hit the sweet spot (time) the iron would fall out. Same thing for installing the stator iron. Heat the housing and drop the room temperature stator in.

Pretty much the same procedure we use for interference fit bearings

[RFGuy]

I think you are missing that by heating up the casting the holes also get larger not smaller. I worked for the Air Force as a civilian (after retiring from active duty) at Hill AFB doing depot level repair on aircraft generators. If a generator main stator required rewinding for repair it had to be removed from the round housing. The housing was a shrink (interference) fit to the stator. The entire assembly was put in a 300º oven for a certain amount of time depending on the particular generator. The coefficient of expansion is different for the housing (aluminum or magnesium) and the iron stator stack. When you hit the sweet spot (time) the iron would fall out. Same thing for installing the stator iron. Heat the housing and drop the room temperature stator in.

Pretty much the same procedure we use for interference fit bearings

John,

Thanks. I thought about the difference in coefficient of expansion between the tubes and the casting being different metals. I guess the part I am stuck on is I thought that metal would expand in all directions when heated. So, I assumed that the outside of the casting would expand outwards and the inside of those holes in the casting would expand inward making a smaller ID for the holes the tubes insert in. IF you are saying the inside of the holes will expand as well when heated, then that is something new I learned today. Just curious and wanting to understand. Thanks.

[jsburger]

I think you are missing that by heating up the casting the holes also get larger not smaller. I worked for the Air Force as a civilian (after retiring from active duty) at Hill AFB doing depot level repair on aircraft generators. If a generator main stator required rewinding for repair it had to be removed from the round housing. The housing was a shrink (interference) fit to the stator. The entire assembly was put in a 300º oven for a certain amount of time depending on the particular generator. The coefficient of expansion is different for the housing (aluminum or magnesium) and the iron stator stack. When you hit the sweet spot (time) the iron would fall out. Same thing for installing the stator iron. Heat the housing and drop the room temperature stator in.

Pretty much the same procedure we use for interference fit bearings

John,

Thanks. I thought about the difference in coefficient of expansion between the tubes and the casting being different metals. I guess the part I am stuck on is I thought that metal would expand in all directions when heated. So, I assumed that the outside of the casting would expand outwards and the inside of those holes in the casting would expand inward making a smaller ID for the holes the tubes insert in. IF you are saying the inside of the holes will expand as well when heated, then that is something new I learned today. Just curious and wanting to understand. Thanks.

Yes that is exactly what I am saying and it is true. Anytime you have something stuck on a shaft, if all else fails, you heat the something to expand the hole in the something.

[HopefulSSer]

When making wagon wheels, the iron tire that goes around the outside is heated to expand it, then dropped over the wooded wheel. Once in place, water is poured over it to shrink it tight to the wheel.

[jsburger]

Exactly how they used to put the steel "tires" on the cast iron steam locomotive driving wheels.

[RFGuy]

Yes that is exactly what I am saying and it is true. Anytime you have something stuck on a shaft, if all else fails, you heat the something to expand the hole in the something.

Thanks John. I believe you and trust you, but I am still intrigued. It must have something to do with the geometry involved. I mean if I think of a piece of flat bar stock. Say, I heat it up, it is going to expand outward in all directions, right? Now, this is thin, flat bar stock. Let's say I had drilled a hole in the middle of the bar stock and then heat it. I am just surprised that the metal would expand outward on all sides, but then that hole would expand and get larger and not smaller. Thinking of flat, thin bar stock to constrain the problem to 2 dimensions (or near 2 dimensions) instead of 3 dimensions. I trust you are right, but I am having a hard time understanding the why. It just seems so counter-intuitive to me that metal when heated will expand outwards, but if a hole is drilled in it, then that hole will expand in ID, rather than contract. Why doesn't the metal push into that drilled hole when heated? Thanks again.

P.S. My example here is one piece of metal. Not discussing something inserted into the hole.

[jimbeaux]

I asked Google and here's the AI Overview explanation why the hole expands instead of contracts:

Yes, a hole in a piece of metal will get bigger when heated.
When metal is heated, it expands in all directions, including the space within a hole. This is because the atoms in the metal gain kinetic energy and move further apart, increasing the overall size of the metal object and any voids within it.

Thermal Expansion:
Metals expand when heated due to increased atomic vibrations.

Hole as a Void:
A hole in a metal object is essentially a space where there is no metal. When the surrounding metal expands, it pushes outward, increasing the size of the hole.

Analogy:
Imagine a rubber band with a hole in it. If you stretch the rubber band, the hole will also get bigger.

Applications:
This principle is used in various applications, such as fitting metal rims onto wheels. The rim is heated, expanding the hole, then placed on the wheel. As it cools, the rim contracts, creating a tight fit.

A YouTube video that gives a more technical explanation:
https://www.youtube.com/watch?v=A5EyqV4C304

[RFGuy]

A YouTube video that gives a more technical explanation:
https://www.youtube.com/watch?v=A5EyqV4C304

Thanks. The AI explanation was useless IMHO. That video was rough, at least for me, but maybe that is just because his accent is so thick. It did bring me to a much better video which I am linking below. The conceptual explanation in the video below makes sense and does seem to confirm it is geometry dependent I believe. In other words, metal is going to expand out in every direction that it is NOT constrained when heated. So, it is about boundary conditions. Thus around the hole, or void, it can't expand without putting areas into contraction. So, to uniformly expand it dictates that the hole will increase in size as the metal expands outwards making the hole larger in diameter. I do wonder what interesting shapes and/or different configurations of voids in a metal could create interesting effects when the metal is heated. Anyway, I am satisfied now and thanks for helping me to understand.

https://youtu.be/Lr2NIyebdfI?t=263