Is it safe to TIG weld on the lathe?

Even if you do everything right, there is still a good chance of damaging or destroying the spindle bearings. If your lathe has any solid state electronics, they are also at great risk.
 
I would never do any welding (either gas or arc) on the lathe. One errant BB and you are hosed.
 
I guess the question I'd have to ask is would this method actually be any more likely to keep things aligned than another method. As has been pointed out welding will always introduce a certain amount of distortion, will the lathe actually keep that from happening.

I've seen quite a few welding positioning devices but nothing that looks like a lathe.

If you have enough length to do it why not bore a close fitting recess into the larger piece and insert the smaller one into it? That's likely to keep it as straight as you're gonna get it. I've done this very thing and actually made the fit tight enough that all I did was heat up the larger part for a shrink fit.

Of course everything depends on the application, is this for a tractor repair or are you making prototypes for Space-X?

John
 
Here's the repair I did similar to what it sounds like you're trying to do.

www.hobby-machinist.com

Don't get overly eager

So over the weekend I finished and installed the replacement leadscrew and feed rod on my Bolton 13x40 project lathe. Apparently I got something wrong because the carriage stopped moving after engaging the feeds a few times. Hopefully I can straighten it out well enough to at least make a...
www.hobby-machinist.com www.hobby-machinist.com

John
 
Oh, please don't risk running current through the finer bits of your lathe.
If you must do it, clamp the parts in insulator block sleeves (I like linen/phenolic) and make sure your ground is secure on the larger of your rods.

Better yet to not use a lathe and clamp the parts in proper vee-blocks and shim the smaller to center on the larger.

If your rods are small enough, and you want to try something new, there's always friction welding.
 
Well there you go a simple but complex question, do or don't, lots of good advise. I would not do it if there are other options. One option would be to use 2 v blocks or angle iron, depending on the precision required, to center the 2 rods, shim the the blocks till the rods are centralized. Tack weld and turn 180 degrees, and weld, then finish weld all around. What's not mentioned is the size of the rods or the length. Are the rods 1/4 " or ?. Bigger the rod the easier this would be to shim to center. Then turn the weld down in the lathe.
Just my opinion.
 
In the shop I used to work in the welding was done off the lathe. They had some fancy powered rotary welding devices, they also had several sets of simple rollers, like the v blocks mentioned earlier but rollers to rotate the part easily while welding. Depending on the size of your part even some large washers could be made into a quick set of rollers. The lathe is a great place to straighten the part after it is welded. We did a ton of drive shafts and even though the yoke is a tight fit in a new tube it was always off a little after welding. Heating, cooling and peening the weld were out main methods of getting it to run true.
 
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