Very much a beginner question - Page 1
Forum section: electronics / general

author: DrG
author_rank: Super Contributor
timestamp: May 04, 2021, 04:01:03 pm
content: 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.fromhttps://us.amazon.com/Copy-Stand-Tabletop-Desktop-9x12/dp/B003OAF2BAThe 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?

author: tpowell1830
author_rank: Frequent Contributor
timestamp: May 04, 2021, 04:54:47 pm
content: 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...

author: DrG
author_rank: Super Contributor
timestamp: May 04, 2021, 05:02:34 pm
content: Quote from: tpowell1830 on May 04, 2021, 04:54:47 pmIt 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/B071X6V2C1Of 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 ?

author: tpowell1830
author_rank: Frequent Contributor
timestamp: May 04, 2021, 05:15:54 pm
content: Quote from: DrG on May 04, 2021, 05:02:34 pmI 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.

author: bdunham7
author_rank: Super Contributor
timestamp: May 04, 2021, 05:17:54 pm
content: 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.

author: DrG
author_rank: Super Contributor
timestamp: May 04, 2021, 06:22:16 pm
content: Quote from: bdunham7 on May 04, 2021, 05:17:54 pmI can't disagree.

author: DrG
author_rank: Super Contributor
timestamp: May 04, 2021, 06:34:15 pm
content: Quote from: tpowell1830 on May 04, 2021, 05:15:54 pmI went to the ACE and picked up a properly sized punch (so that I would not mangle anything). Working slowly and deliberately, the pin did come out easily - it did not fall out, but moved out with a few taps. The brass fitting was in a little tighter, but with a pliers on the rim (not on the thread), it came out fairly easily.Here is what it looks like now:The pin, the brass fitting and the aluminum tube where the fitting goes.I have no idea what the piece of, what looks like cellophane tape and grease, on the brass fitting is for. I had nothing to do with that.I wonder if it extended up to the threads (like with that plumber's tape stuff).N/M that makes no sense as the threads are on the other side of the fitting. It feels like grease not adhesive. Don't know, but now I will clean everything as you said. I have a number of solvents for de-greasing, including acetone and ethanol.I purchased some Loctite, two-part epoxy (just regular $7 type) that says that it works on metal. Following the cleaning, it will get smeared on the sides of the brass fitting. Then re-insert the pin. Then, let it sit (20 min firm, 24H full).Then, reassemble the unit and see what it feels like. Will let you know and thanks again.

author: Gyro
author_rank: Super Contributor
timestamp: May 04, 2021, 06:55:52 pm
content: That insert is pitifully short for the length of of tube it is supporting. It looks as if they wound it with Kapton tape and then maybe a little lubricant to help forcing it in. Ultimately it is dependent on the pin holes in the outer tube not stretching and becoming oval.High quality epoxy adhesivemightmanage to bond it, but you will probably get one decent shot at it. Mechanically keying the surfaces will hopefully improve bond strength.

author: DrG
author_rank: Super Contributor
timestamp: May 04, 2021, 07:00:10 pm
content: Quote from: Gyro on May 04, 2021, 06:55:52 pmBy "mechanically keying", you mean to abrade the bonding surface (with a file or something similar)? I can do that - both the aluminum and brass surfaces?Edit: BTW in that last shot, you can see the inner aluminum tube. It is in the fully shortened position and I can't go up to it with epoxy or it will no longer extend.

author: Gyro
author_rank: Super Contributor
timestamp: May 04, 2021, 07:08:36 pm
content: Yes, I was thinking in terms of coarse grooves on both surfaces rather than anything that further compromises the difference in diameters (like filing). Ideally you would machine knurl the insert in a lathe as this would have the effect of slightly increasing its diameter at the same time.Edit: Ah yes, I understand. That's probably why the insert is so short. Can you extend the tube first, before epoxying, and accept that it won't shorten quite as far afterwards? The extending operation is maybe where the grease has come from?

author: DrG
author_rank: Super Contributor
timestamp: May 04, 2021, 07:19:00 pm
content: Quote from: Gyro on May 04, 2021, 07:08:36 pm"Ideally you would machine knurl the insert in a lathe as this would have the effect of slightly increasing its diameter at the same time." - hehe *damn* I forgot to pick up a lathe at the hardware store. I am kidding, but look, baby steps that is what I am trying to do here...baby steps with knowledgeable folks looking over my shoulder....and I really do appreciate the guidance.As for the tube length. It is not the end of the world if I compromise a small amount on the inner tube such that it can't fully shorten, but if I just put epoxy on the brass fitting, it should not be an issue.I will not full-on file but roughen the surface a bit asymmetrically. Yes?

author: DrG
author_rank: Super Contributor
timestamp: May 04, 2021, 09:21:02 pm
content: Cleaned and roughened.This epoxy syringe is not a joy to work with and the the pin was a little stubborn and I had a few mis-whacks, but got it together in ~1 min, well before 5-min set time.Tomorrow, I will re-assemble and test.

author: DrG
author_rank: Super Contributor
timestamp: May 05, 2021, 09:31:25 pm
content: Re-assembled everything and.......it's tight! No detectable wobble.Not sure how long it will last, but I think I will be able to get some additional use out of this old copy stand. Much thanks for the guidance.

author: coppercone2
author_rank: Super Contributor
timestamp: May 16, 2021, 07:04:46 am
content: I had this problem with a kitchen fruit stand and the solution that someone came up with is to bang on it with a hammer to deform it back around the thread (I was going to do something complicated) and its perfectly stable. So you might be able to tighten it and press it against some kind of anvil and bang on it with a hammer around the circumference to rejoin the pieces without play.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: May 16, 2021, 07:57:46 am
content: That was my first thought, hammer the pins until they mushroom into the tube, locking it once again -- though this obviously discourages future disassembly, and will eventually wallow out as the aluminum is softer.The epoxy solution is excellent -- I would guess, if the surface prep is good, it'll be more reliable, and may even be stronger than the original! (And even if the surface prep isn't great, it'll still fill the gaps, making it a lot harder to wiggle loose.)Tim

author: DrG
author_rank: Super Contributor
timestamp: May 16, 2021, 04:29:42 pm
content: I chuckled reading these last two responses, not because they are wrong necessarily, but because I know myself better than those authors. Believe it or not, the suggested "hammer" fix, or some derivation of it, did occur to me. I can, with high confidence, tell you that it would not have worked. I would likely have had a deformed aluminum tube that simply wobbled even more. Further, I would likely have broken the pin which is not brass but rather, "pot metal". I believe this because it bends too easily, something I saw when I reinserted it into the brass fitting. In fact, I am happy that I went and purchased a correctly sized punch rather than used a nail, which is what I would have done. At least that is what occurred to me.If you are into photography, search on "copy stand" - these can be very high priced. That little table top stand was low priced and came with a light table that used a cold-cathode fluorescent lamp. It eventually dimmed and I did find a replacement bulb but it was about $35 and I ended up buying a much nicer table brand new. Granted, the new one has the typical digital PWM dimming which is fine for tracing a pattern but basically useless in photography.I still have that old light table and may use LEDs with it if I can ever figure out to dim it without PWM.I replaced the copy stand with this one:Look at that bad boy - rock solid - not cheaply made - not elegant, but it does what it is supposed to do quite well and has worked for years. An $bay purchase and the seller was the manufacturer. It was something like $45 and I admire that design. I have searched on DIY copy stands and I have yet to see one that I felt that I could build as cheaply that is as solid and works as well.That left the old table-top with the option of tossing or fixing. It will now get some limited duty.For me, this one was a clear win, thanks to the help I received..

author: coppercone2
author_rank: Super Contributor
timestamp: May 16, 2021, 07:26:40 pm
content: thats what I thought but its been holding grape fruit for 1 year without a problem and its quite loaded for a 1/4 inch shaftI think the stuff work hardens when you peen it to deform it so it gains some strengthI was thinking about helicoils when I first approached the repair but I never used them before, no idea if its appropriate for a pedestal type structure.I did the glue thing with a ring stand before and it did not work very well, a glassware stand had a wobbly shaft and I tried to fill the thread with normal 2 part epoxy and it gave out after a while.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: May 16, 2021, 09:11:38 pm
content: Ah, I thought the pins might've been steel. That's definitely a nonstarter then.Tim

author: G7PSK
author_rank: Super Contributor
timestamp: June 26, 2021, 02:49:11 pm
content: Locktite bearing retainer 638 will solve the problem. I have used it to fix loose drive shaft flanges on truck gear boxes, originaly it was as an emegency road side repair but it was so strong that nothing else was required since then I have used it for all sorts drive sprockets/pullys etc and similar items to the one youy have there.