# Welding Stress Question



## rustydog (Oct 25, 2012)

I need to produce 6 specialized v-belt pulleys for a pilot project. Being as overly thrifty as I am, I'm going to use 6 disks of free machining steel from the scrap box. The problem is that the hole in the center of the scrap box disk 1" and I need 5/8".  The 2 smaller holes near the rim of the disk are not a problem and will be left as they are.  The picture shows the disk and both a solid plug example and a pre-drilled plug example.

The plan is to turn plugs to fit into the 1" hole and weld them into place. The 5/8" hold will then be drilled through the plug piece. I'll chamfer both sides of both the plug and the scrap box disk before welding and then finish the plug / disk pair level after welding.

Questions
1) Should the plug be a tight or loose fit to minimize resulting stress.
2) Should I use a solid plug or a plug with a pre-drilled hole to reduce stress?
3) Are there other considerations I need to deal with?
4) All thoughts and critique welcome.


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## Tony Wells (Oct 25, 2012)

If these are idler pulleys, there's not going to be much torsional stress on the weld. As far as fit, they shouldn't necessarily be press fits. I'd cut them to about 0.0010 loose and go right ahead. If the bored bar is the same material, I'd use it, for sure. Save drilling time. If you're really worried about stress from welding, preheat to about 400°f and weld it out on both sides, and toss it in some vermiculite or something to slow cool it. Anything but a quench. Even a little rosebud after the weld will help relax things. I don't think you have anything to worry about though, even if you didn't do anything special.


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## bonneblktrk (Oct 26, 2012)

I agree with Mr. Wells.  Also welding on both sides of the plug will tend to counteract the contraction of the weld on opposite side, should balance out the stresses side to side.  Post heating would stress relieve.

What welding process are you going to use TIG, MIG, Stick?


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## rustydog (Oct 26, 2012)

bonneblktrk said:


> I agree with Mr. Wells. Also welding on both sides of the plug will tend to counteract the contraction of the weld on opposite side, should balance out the stresses side to side. Post heating would stress relieve.
> 
> What welding process are you going to use TIG, MIG, Stick?




Ihave both Mig & Tig (as well as gas and arc).   My eyes are getting old and I have trouble seeing when doing Tig even with cheaters and all the rest of the aids.     If I have time I'll practice with the Tig and use that.  In the end it will probably be Mig.   Your both sides remark makes sense and I'll do that.

Either way, I'm assuming stitching would be best.  Correct or?

I'm thinking welds all the way around would be over welded - thoughts?

Playing off the rosebud idea  - it occurs to me that maybe gas might make sense after all since it will be all heated.  What thinks ye?.


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## OldMachinist (Oct 26, 2012)

You said free machining steel. Do you mean like 12L14,1215 or 1117. These materials are not considered good materials for welding because of the additives(lead, manganese and sulfer) that make them easy to machine.


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## rustydog (Oct 28, 2012)

I probably miss-spoke.  Like most inherited scrap box material I don't really know much more than is mystery steel.  
I mentioned the free machining attribute based on the nice shavings which pealed off when I turned one ridge off each of the 6 pieces.

Both the plug and puck will be chamfered and welded in the chamfer.  They will be turned mostly smooth after welding and will not be in site.

Aside from the appearance is there likely to be a problem?  I'll do a pilot first..


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## OldMachinist (Oct 29, 2012)

Depending on what the material is there are different reasons why free machining steels are not recomended for welding.
Sulphur will make a weak slag filled weld.
Manganese causes post weld cracking.
Lead has a low melting point and will be forced to the middle of the weld and the weld will crack during cooling.
Lead and sulpher are a fume inhalation hazard at welding temps.


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## AGCB97 (Feb 2, 2020)

If this is a idler pulley, I'd just make it a close slip fit and use retaining compound (Loctite or other).


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## Cadillac (Feb 2, 2020)

Yeah oversize your plug by a .001-.002 heat your larger piece and drop in the plug. She won't go anywhere. To make it permanent take your tig and just fuse acouple spots on the seam.


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## kb58 (Feb 2, 2020)

The OP never said whether torque has to go through the assembly. If not, I'd just do a press-fit, and if you want a bit more stalking, drill a couple small holes right at the interface and push in a couple pins. I've had enough welding heat warpage to want to stay away from welding when not really needed. In this case though, we have no idea if it matters. Application?


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## savarin (Feb 2, 2020)

silver solder the plug in?


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