Off Topic Hobbies > Mechanical Engineering

Very much a beginner question

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DrG:
I'm reaching a bit, but I am trying to solve a problem the right way and not rely on glue or tape (which doesn't work).

I have an old copy stand - pretty much identical to this one.

from https://us.amazon.com/Copy-Stand-Tabletop-Desktop-9x12/dp/B003OAF2BA

The problem is that after many years of use, there is a little bit of 'rocking' in this part.


That is where the arm meets the base and I am showing you both sides of the aluminum tube with the brass fitting. There is a small amount of play between the brass and the aluminum that developed over the years. This may seem trivial, but for a copy stand, it is not.

There is no amount of tightening of the aluminum post or anything that fixes the problem. That brass fitting, with what looks like a pin in it looks like the culprit. I don't know what that pin is that seems to hold the brass fitting in place - I have no idea what those are called but my thinking is to go get a replacement, a punch, remove it using a hammer and put the replacement in its place. A little voice is telling me that it is that kind of thinking that frequently gets me into mechanical trouble.

Any help please?

tpowell1830:
My guess is that the part of the brass fitting is supposed to fit very snugly into the aluminum, and aluminum will stretch over time, especially that thin of a wall. The stretched aluminum will allow play, even a small amount of stretch. I would remove the pin by knocking it out with a punch, remove the brass fitting and then put epoxy on the outer diameter (OD) of the brass part that fits inside the aluminum. Push the brass part back into the aluminum and install the same pin that came out. Don't worry about a new pin if the pin is still  tight, and it should still be tight or it would have worked it's way out if it had been loose.

If for some reason you need to remove the brass part again after gluing, just use a small propane torch and heat right over the aluminum at the brass fitting. This should break the glue enough to remove.

This is how I would fix this problem, there may be other opinions.

Hope this helps...

DrG:

--- Quote from: tpowell1830 on May 04, 2021, 04:54:47 pm ---My guess is that the part of the brass fitting is supposed to fit very snugly into the aluminum, and aluminum will stretch over time, especially that thin of a wall. The stretched aluminum will allow play, even a small amount of stretch. I would remove the pin by knocking it out with a punch, remove the brass fitting and then put epoxy on the outer diameter (OD) of the brass part that fits inside the aluminum. Push the brass part back into the aluminum and install the same pin that came out. Don't worry about a new pin if the pin is still  tight, and it should still be tight or it would have worked it's way out if it had been loose.

If for some reason you need to remove the brass part again after gluing, just use a small propane torch and heat right over the aluminum at the brass fitting. This should break the glue enough to remove.

This is how I would fix this problem, there may be other opinions.

Hope this helps...

--- End quote ---

It does help, thanks. Looking around more (searching on "pin type brass fitting"), I see lots of examples of grease fittings like,


and they all seem to have a 'nipple' on top. I see nothing that looks exactly like the part in question.

For the epoxy, when I search on epoxy brass to aluminum, I find this product -
https://www.amazon.com/Henkel-Loctite-1360700-Pack-Bonding-Compound/dp/B071X6V2C1

Of course it is high priced (and about half the value of the stand itself). Do you think that other epoxies would work as well or ?

tpowell1830:

--- Quote from: DrG on May 04, 2021, 05:02:34 pm ---
--- Quote from: tpowell1830 on May 04, 2021, 04:54:47 pm ---My guess is that the part of the brass fitting is supposed to fit very snugly into the aluminum, and aluminum will stretch over time, especially that thin of a wall. The stretched aluminum will allow play, even a small amount of stretch. I would remove the pin by knocking it out with a punch, remove the brass fitting and then put epoxy on the outer diameter (OD) of the brass part that fits inside the aluminum. Push the brass part back into the aluminum and install the same pin that came out. Don't worry about a new pin if the pin is still  tight, and it should still be tight or it would have worked it's way out if it had been loose.

If for some reason you need to remove the brass part again after gluing, just use a small propane torch and heat right over the aluminum at the brass fitting. This should break the glue enough to remove.

This is how I would fix this problem, there may be other opinions.

Hope this helps...

--- End quote ---

It does help, thanks. Looking around more (searching on "pin type brass fitting"), I see lots of examples of grease fittings like,


and they all seem to have a 'nipple' on top. I see nothing that looks exactly like the part in question.

For the epoxy, when I search on epoxy brass to aluminum, I find this product -
https://www.amazon.com/Henkel-Loctite-1360700-Pack-Bonding-Compound/dp/B071X6V2C1

Of course it is high priced (and about half the value of the stand itself). Do you think that other epoxies would work as well or ?

--- End quote ---

I don't know what those items in the picture are, but obviously not what you need. The brass part is probably made specifically for this purpose and simply has a press fit hole for the pin that goes through all. The pin is simply a straight brass rod that is sized specifically for the through hole so that it is a press fit. Just guessing, but to my machinist eyes, that is the case. The brass fitting should just pull out of the aluminum fairly easy after the pin is knocked out. The brass fitting will simply have a smaller OD that fits snugly into the aluminum (or rather is supposed to fit snugly i.e. however the aluminum stretched a bit). The smaller OD on the brass part will probably be twice as long as the distance from the end of the aluminum to the center of the hole where the pin is located.

Any epoxy should do okay. You could even probably use a strong Gorilla glue. If you find the Gorilla glue gets loose again, just remove the brass again and go with an epoxy.

That would be my approach.

EDIT: It goes without saying, but clean the inside of the aluminum and outside of the brass thoroughly with a degreaser, such as alcohol or acetone before applying the glue.

bdunham7:
I think the key here is how long those brass inserts are.  If they are short, say shorter than the width, then it is a pretty bad design and you should find a way to extend them.  A thin epoxy resin will work if you take off the other end and pour it in and let it seep through and fill all the gaps.  Then after it sets, you can pour some more in, install the top part and invert it and let the same thing happen. 

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