Questions on machining weldments

T

tmihelick

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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 tatybypu.jpg

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True in the absolute sense? Unlikely. True enough for machining from roughout, certainly. You did not give your material selection, but after welding, most parts should be stress relieved prior to machining. If it is your intention to save material by welding in a stub, you're right, but you should have realistic expectations of what will happen at the joint regarding stress and possible cracking, etc.

Are you planning on finished bolt holes for the chuck mount? As long as you make them with adequate clearance, that shouldn't present a problem. But as far as concentricity, you wouldn't normally finish machine any part of such an assembly, such as the threads or registration surfaces.
 
Certainly, there are commercially supplied (cheap) chuck backing plates manufactured in this way. But they would be machined true afterwards. You could have the boss threaded before welding, then drill your bolt holes if you wanted to supply them that way, but the end user is really going to need to fit them to their own chuck register
Like Tony stated, it is not realistic to expect the plate to run true to machining standards after welding.

Cheers Phil
 
Yes, it can be done. I do things like this all the time but as Tony pointed-out, it will not be totally true after welding. Once welded, you'll need to mount it and face everything back to perfection.

Some caveats: The weld caps will be hard -as in very hard and it will give HSS bits a run for their money. The preferred method is that after welding, you completely normalize the part (in an appropriate oven). I've got many threads here on how to do that. Once normalized, it will machine like butter.

Second issue: To prevent complete warping during the weld, you must raise both pieces up to 500 degrees F then assemble and weld them. This will stop cracking and severe warping dead in it's tracks.

Once it's completely resurfaced, you can optionally re-heat treat it if it's made of metal that can be treated. If not, don't bother to harden it...

Hope that helps...

Ray
 
If the base material is steel, either 7018 stick or E70s6 wire will yield a weld that is easier to machine without subsequent heat treating. I would still stress relieve it before machining. If the material is a higher carbon content alloy, then other considerations come into play. We need to know your materials to be more specific. But the general idea is sound for what you are doing. I have made literally hundreds, if not thousands of parts from weldments. They can be very difficult, or pretty straightforward.
 
And to give the full story, one of the benefits of preheating the pieces to 500 F is that after it's welded, the whole part will cool down more slowly and evenly (and with less distortion). If the pieces are welded cold, the hot weld area will be more rapidly cooled by the colder, surrounding metal and that effectively is a form of quenching. Quenching metal that is up in the 1500 F range (such as with welding) hardens it. Anyhow, the main benefit of preheating is to control cracking and warping; secondarily, it helps keep the weld caps from becoming really hard but even so, the caps will be tough on HSS and since they're irregular in nature, will easily chip carbide.


Ray
 
Preheating the part is pretty easy to do with an outside gas grill. Gas grills can reach temps in excess of 500 degrees with the lid closed.
 
Preheat is more a condition of the type of metal. Low carbon steels are not prone to hardening if allowed to air cool from welding, especially if done with the proper filler. They need no preheat. Think of the thousands of pipeline welds that are done in less than ideal conditions, certainly without pre and post heat. This does become an issue with higher alloys, however. That's why we are kind of shooting in the dark here not knowing what material is under discussion.
 
xalky said:
Preheating the part is pretty easy to do with an outside gas grill. Gas grills can reach temps in excess of 500 degrees with the lid closed.
Click to expand...

Kitchen oven -just wait till the house is clear of the kitchen police.

EDIT: (of course, make sure the metal is clean)...

Ray
 
The preheat addresses and minimizes warpage and internal stresses, and hardening to a lesser degree. A slow cool down also helps with warpage.

- - - Updated - - -

Ray C said:
Kitchen oven -just wait till the house is clear of the kitchen police.

EDIT: (of course, make sure the metal is clean)...

Ray
Click to expand...
I was trying to keep peace in the house. I've been known to cure powder coating in the house oven too, when my wife wasn't around. :lmao: Don't worry, I did a self cleaning cycle on the oven before she showed up. She was so happy that I cleaned the oven:rofl:
 
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