Questions on machining weldments

[Bill C.]

I am fairly new to this site so if this is in the wrong place please correct me. I am looking for advice on welding 2 turned pieces together and having them run true. I would like to make a chuck adapter plate like in the picture. I will use a piece of plate and a round bar. I plan to machine my bolt circle on the plate and press a small piece of bar into it. And weld. Also I plan to turn some 45 deg chamfers in to get a better weld after I do the weld I plan to machine this true I know the first thing everyone will say is to buy one, but I would like to try this out. I think if I can pull it off I will use this technique a lot. Also I have a hair brained scheme to turn it but I wanted to wait till I could get some pictures to demonstrate my idea and I will make a new post for the project

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I would like to add my two cents, They have given you good advice.

If I was doing it I would likely use HRS plate for the hub and solid round stock or heavy wall boiler pipe for the threaded piece. You are on the right track about the chamfers. I would bore the hub to a slip fit. I would tack weld in four places then weld one inch beads leaving gaps. Let them cool down to room temperature then clean off the slag then finish welding the remaining areas. I would strongly recommend normalize or stress relieve the weldment.

If you only have a three jaw chuck I would bore the inside diameter to the desired diameter. Then remount the weldment, so the outer hub is against the jaws, by chucking the inside diameter and turn all the outer diameters and cut the threads. By doing this all the diameters will run true to each other. Finally remount the weldment so the back hub is facing outward then machine the faces. Finally transfer the bolt holes. Like they said HSS bits will take a beating but they are easier to regrind compared to carbide. Good luck, I like your project.

 

[ericc]

This is the way they did it in the old days. Also, the piece was often forged close to dimension, then machined to final size. Surprisingly little would be cut off. At one of the blacksmith meets, there was a forging to dimension competition. No dividers, rulers, scales of any sort were allowed. The top 3 were within 0.010" on all measurements.

The key is uniform heat and lots of it. The big problem with welding is that the cooling bead contracts and only pulls in one direction. If you heat the whole weldment to a good red heat, or even better, a forging heat, the bead has nothing to pull on, or the pull is in all directions. Tiny amounts of peening and straightening are very useful since it prevents localized upsetting and pulling of metal around a spot heated area. Unfortunately, it can be difficult to heat a large object uniformly. Two things that have worked well for me are a stack of firebricks and a propane weedburner or a "ground forge", which is just a pile of charcoal in a hole in the ground with an iron pipe blowing air in.

 

[tmihelick]

Thanks for all your advice. I'm pretty sure I will use all mild steel. Because that's all I think I have. Using scrap also I only have a MIG welder at the moment. I got the idea to press it first BC I used to be on a collage robotics team and we made a driveshaft from a piece of pre-made shafting and a Dewalt cordless drill drive shaft. The depth it pressed in was about .75-1in deep and it was tig welded by our shop advisor. It was surprising how great it came out. Also it was balanced to the point no one could tell otherwise in the aplication. He insisted on the press fit first but he is also the kind of guy who would demand perfection when and where it isn't critical

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[tmihelick]

We press fit the two shafts together. One was half an inch od. The other was about 1/4in od. I didn't think bout how hard that was to picture from my poor description. Also I'm pressing a lot more shallow comparatively if you take size as a factor.

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