# Questions on machining weldments



## tmihelick (Mar 4, 2014)

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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## Tony Wells (Mar 4, 2014)

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.


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## 12bolts (Mar 4, 2014)

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


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## Ray C (Mar 4, 2014)

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


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## Tony Wells (Mar 4, 2014)

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.


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## Ray C (Mar 4, 2014)

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


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## xalky (Mar 4, 2014)

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.


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## Tony Wells (Mar 4, 2014)

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.


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## Ray C (Mar 4, 2014)

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.



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

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

Ray


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## xalky (Mar 4, 2014)

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


 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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## Bill C. (Mar 5, 2014)

tmihelick said:


> 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
> 
> 
> 
> ...



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.


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## ericc (Mar 5, 2014)

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.


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## tmihelick (Mar 5, 2014)

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 (Mar 5, 2014)

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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