Hi Mike, welcome aboard. I do not have anything to prove, was thru with taking tests a long time ago, but will throw my thoughts out there. I am not expert at any technical stuff, but there some that drop by this board that do have a lot of technical knowledge. There fore the following is just my observations and what I think. First, joining two different size objects that way will never look exactly like the one in your picture. If you make the transition gradually and smoothly enough it would probably appear just about the same to the less discering eye, or perhaps have the illusion of just a very slight taper depending on the length of the two pieces. You did not say how strong it has to be, but since you are talking about paste or putty, the asusumption would be that strength is not a critical factor. The joining of two different metals can sometimes be a bit of a problem, if they were both copper, soldering would not be hard to do, then you could file or grind and buff the seam to a smooth transition, perhaps. I do not know what would work best for copper/aluminum. Other thoughts would be that when you have it joined in a manner that meets your satisfaction with regards to stability and strength, you could grind down the larger piece, feathering it gradually to about the size of the smaller piece, then paint
Other possibilities that you may or may not have thought of or tried, superglue it in place, then try some auto bondo or other products that they use to repair dents small tears etc in their shops. Technology keeps advancing and some are pretty darned durable nowdays.
This board is fairly new, sometimes a little slow, but someone else will probably be along before long with other thoughts and ideas. If we do not prove ourselves to your satisfaction, bye bye.
Bill P.

Sorry, I didnÂt mean to come off pompous or arrogant. I was just speaking of forums in general. I meant, if the forum proves to be helpful and informative, I would definitely be posting a lot. No one has to prove anything to me. Bondo -
thatÂs what I was looking for. If anyone has any advice about bondo, donÂt be shy. I have only heard the name. I have no idea what it is or how it works.

Bill, thank you for mentioning strength. The copper and aluminum I am using are way too delicate to create a lasting final product. As soon as I can get some pictures up, of what I am working on, I will definitely be seeking advice on how to recreate it using harder metals.

Sounds like you just need a good grade of body putty.
If you want something better try Titanium Putty...

MC MAster Carr sells it...

Hi icup
Grainger Supply has a product made by Devcon , Aluminum Putty that might work for you. Have you thought about welding the two aluminum ends together, that would get your #3 results. It would also be an excuse to get a Chirstmas gift.(a GOOD WELDER)

Grainger's web site is www..geainger.com
Good luck Bill Z

epoxy paste could be used to secure the aluminum rod into the copper tube. Both the tube and the rod would have to be clean to assure a good bond. However, a thin layer of epoxy on the aluminum rod, adjacent to the joint, would likely flake off, if the rod is flexed. I'm not sure how to make the joint invisible.

Well, the best way to get a seamless connection is to use an aluminum rod that is the same diameter as the outer diameter of the copper tubing. Then turn down an inch or so of the end of the aluminum rod so that it fits snugly. That will leave a very minor seam that could be filled in with bondo or other filling compound of your choice.

If you choose two similar metal that are solderable, then you could use solder to secure the joint and then sand that down before painting.

The only rub I can see here is that if the aluminum rod is at the end of a long coil, it won't fit into a lathe for turning. But if you could get a straight length that is, say, no more than a yard long, it should fit into most lathes, although you may need to stabilize the other end.

There may also be ways to turn the end of an object that can't be easily rotated. Like a grinding die of some sort.

When this metalworking forum first began, there was a question asking what kinds of metalworking tools were in their shops. I replied, discussing my collection of holesaws. Now Spam here, just gave a good suggestion about turning down the end of the aluminum to fit the tube for a flush fit. Since a lathe would be a little pricey if you need to buy one for this operation, and since the stock is already formed into a shape, I would suggest looking for a holesaw that would cut the same external sise on the aluminum stock as the internal size of the copper. You may need to chamfer the end of the alumimum stock to allow the holesaw to start without jumping off, but this should be the ticket for you. At least it will give you another option to work with. If need be, a little JB weld will hold it in place if the fit isn't quite right. Of course if you're going to powder coat it, you need to consider any deterioration from heat, so a press fit would be best. Keep us posted on your success

GG

mike
Not an engineer, but you did say 7/32"(ID, OD, wall?) copper tubing and aluminum, assumming it's 7/32 ID copper then weightand or stress load can't be very high, and as mentioned in your second post you plan to consider harder materials(why?).
Any number of choices are available to join these, but I think I would consider the end product specifications first because changing materials can cause big changes in processing the final product, which obviously increase costs and time.
I was also wondering what painting the item does for it, hide defects, add color or prevent corrosion? For any light weight material in stressful applications its easy to have the coating(paint/adhesive) seperate under repeated stress and over time.
And remember if it works to well or lasts to long even at a bargain price, it won't fit into our throw away society, you'll either not be able to produce enough or you'll have to many. LOL

Oh by the way, Where are the pictures?

DED