Welding in a lathe ??

cuslog · Dec 6, 2008

I know this probably makes some of you cringe but here goes anyway.
In the past, I've broken the drive ends off of 18" ship augers (1/2" hex ).
I welded a new piece of hex shaft on, using my lathe (chamfered both pieces, put one in the chuck and the other in the tailstock) for alignment.
I grounded directly to the work piece and it was TIG so no splatter.
I thought it should be OK as long as I grounded directly to the workpiece so no current is going thru the bearings.
Have I sinned ?

Pierce Butler · Dec 6, 2008

You are likely OK.

The only thing that can be real bad is if you weld on a modern car. I have seen guys destroy over $3000.00 worth of electronics on a car by not taking appropriate precautions.

9100 · Dec 6, 2008

I have done welding on a lathe, but it is to be avoided if at all possible. Proper grounding is critical. I did TIG welding on some stainless tubing for liquid helium transfer lines. I fitted a plug in the end and struck an arc while it was slowly turning, melting the material together without adding filler. Since it had to be rotating, I clipped a ground to the tubing, making an improvised rotating joint. One time I forgot the ground and blew a transistor in the speed control. Fortunately, the lathe is a plain bearing South Bend and at the low speed there was enough contact to avoid damage there. That would have been deadly on a ball bearing lathe. The little contact points weld, and that is the end of the bearing. If you are joining two pieces, put grounds on both. The current path through the tailstock back to the spindle can have the same effect. I have also done torch welding and silver brazing on round parts rotating in the lathe. If you do it, remember that any surface the flame or hot stream off the flame end touches will have a coat of rust the next day. If you must, immediately clean and oil any surface the flame comes near. Better yet, figure out another way.

Bill

John in CA · Dec 6, 2008

Do you do enough of this type of operation to maybe justify buying a beater lathe specifically for the purpose? One process pipe/ pressure vessel fab shop I worked in had several old lathes set up and modified expressly for pipe welding. Two had the beds completely removed to accomodate larger pipe sizes. Now that I think about it, I'll bet an old lathe with working powerfeeds could be modified to do a little "robotic" welding on plate, at least with 7018 stick or dual shield/flux core wire where no weave is required.;

register · Dec 6, 2008

As john said, many welding shops have a lathe simply for welding. The tolerances required (in terns of TIR, etc...) are nowhere near what the machine was designed for, and so even after significant wear it is still perfectly functional for the purpose.

I have seen most commonly leathers used over the ways, headstock, and tailstock. They were cut to allow a hole for the spindle and ram to protrude. This way, even the splatter of MIG or stick is not an issue.

As stated earlier, be sure to ground on both sides of the joint, and keep those ways covered.

dazz · Dec 7, 2008

If I was doing this, I would electrically isolate the work from the chuck. Inserting precision plastic shims (aka old cut-up credit card) between the work and the chuck jaws will prevent any chance of current passing through the spindle and bearings.

Is it possible to do friction welding on a standard lathe? Hold one part in a tailstock chuck, then press hard against the other part in the standard chuck until the friction is enough to weld???

FlatBeltBob · Dec 7, 2008

I have a junker old lathe for just this purpose . An old flatbelt convert that I put a 2nd moter and a gear reducer that is attached to the main moter with a v belt I can disengage . Then I wired up a foot operated on off switch . By using back gears , I can get the speed close enough . I always felt that building up worn shafts , or splicing 2 together by doing a "spiral "
build up , made a very weak , and stressed joint . I prefer to weld beads parallel to the shaft , and jump from side to side . This allows me to spread the stress over a larger area , and I can use the heat to my advantage to spring it straight by welding more on one side .
I did have a job that required a hard surface overlay on the circumference of a 1/2" thick X 36 " dia circle . I just drilled a 3/8" hole in the center , bolted it to a 1" shaft that I tapped the center of , Took off the tailstock and used a steady rest to support it , then let the disc spin outboard of the end of the lathe.

Robert Campbell Jr. · Dec 7, 2008

dazz said:
If I was doing this, I would electrically isolate the work from the chuck. Inserting precision plastic shims (aka old cut-up credit card) between the work and the chuck jaws will prevent any chance of current passing through the spindle and bearings.

Is it possible to do friction welding on a standard lathe? Hold one part in a tailstock chuck, then press hard against the other part in the standard chuck until the friction is enough to weld???

Yes. I've done this several times on a 12" Robling, (1952 German manual lathe.)

Workholding can vary widely so I wont address this.

I've always used the lathes top end, 2,500RPM.

Start the lathe, drive in the tailstock with force. In seconds sparking will start and rapidly turn to a glowing ring.

At that point, turn the lathe off while maintaining high pressure on the tailstock.

The lathe will come to a very satisfying quick stop. Done right and it's not that difficult, you'll end up with a very strong weld displaying a nice bulged ring the size of the glowing metal portion.

Two great advantages, nearly perfect concentricity, (you did set it up with precision didn't you?) and the ability to successfully weld a great range of dissimilar metals.

I'll try any combination and can't remember not getting a satisfactory joint, though I always test on scrap first.

Caution, watch brass closely, it wont get nearly as bright as most other metals at the fusing temperature.

Bob

jwatts · Dec 7, 2008

In light of the above, friction stir welding can obviously be done in a lathe. That said, I wouldn't want to do it to mine. One of the labs where I work does research on friction stir welding. For small spot welds about 1/2 inch in diameter, the plunge forces can be over 1000 pounds in steals. Maybe someone who knows more than I can chime in here, but that seams like more axial load than I would want to apply to the spindle bearings.

REAPER · Dec 7, 2008

cuslog,

As long as you properly ground to the workpiece ( close to the weld point), and your machine is well grounded, you should be ok for what little welding your actually doing. We periodically weld on a machine and have not had any problems of note.

Exptec · Dec 7, 2008

Many years ago I modified an old lathe just for TIG welding some instrument cases.
I added a commercial rotary ground contact to the backside of the spindle and I re-powered the lathe with a variable speed DC drive.

The main reason I mention this is because of a peculiar behavior I experienced when I first tried welding. I have the work piece I wanted to weld chucked up. I have the TIG torch positioned in the tool post. I turn the DC drive on and get the RPMs I want. Then I then put my face shield down and pressed the TIG pedal to strike the arc. I could see in the arcs light that the RPMs were much faster than I wanted. I took my foot off the pedal lifted my shield and things looked fine. I repeated the trial and it still looked fast. Eventually I figured out that I when I struck the arc, the DC controller went “crazy” and the lathe sped up. The quick fix was to run a ground from the lathe to a ground stake.

daredo222 · Dec 7, 2008

Spiral Welding

cuslog,
Thought you might like to see this photo, several more in the folder on webshots. The motor/gearbox drives the input shaft to the headstock. The headstock ratios can be used to give a choice of speeds. The welding earth clamp is attached to the aluminium bung in the end of the spindle, it just swivels/slides as the headstock rotates. The MIG torch is clamped in the toolpost & a coarse feed or a screwcutting ratio selected by trial & error. Once the parameters are set it repeats very good. See the results on the other photos.

http://good-times.webshots.com/photo/2790754710101259633NnxGYd

cuslog · Dec 8, 2008

daredo; Thanks for the pics.
I thought I would be OK so long as I kept the ground directly on the work piece.
I'm sure I saw someone (many years ago) in an engine rebuilding shop using a mig welder in a lathe to build up crankshaft journals prior to grinding. Seemed to work quite nicely. My setup was not nearly so sophisticated but it did work. This is something I do only a couple times a year.

scrapbin · Dec 9, 2008

about time!

finally,a real use for those chinese lathes.the sand from the casting that's in the bearings will isolate the rest of the machine.

what? the grease in the bearings will conduct the electricity? WHAT grease?

surplusjohn · Dec 9, 2008

I had sold a few old lathes over the years for this purpose, including a very old large Pond that was like 24 inch swing. They turned it into a very nice horizontal welding positioner

William462 · Dec 9, 2008

In the engineering department of the company I retired from, I saw a lathe used for metal spraying experimentation. They simply needed a rotary fixture. Rather than buying an old lathe, however, they had purchased a brand new lathe, about 16 inch swing by 6 foot bed . It was well encrusted with overspray, as little attempt had been made to mask parts of the machine. The sight gave me an uneasy, queasy feeling.

daveog · Nov 22, 2020

This is an old, old thread, but I thought I'd add my question to it anyway. I have a one-off TIG welding job with about a dozen 1/2" or so welds. If I use my chuck to hold the part while I weld it with the lathe unplugged and the work itself grounded, is there any risk of damaging the lathe itself?

Joe Gwinn · Nov 22, 2020

daveog said:
This is an old, old thread, but I thought I'd add my question to it anyway. I have a one-off TIG welding job with about a dozen 1/2" or so welds. If I use my chuck to hold the part while I weld it with the lathe unplugged and the work itself grounded, is there any risk of damaging the lathe itself?

I'd insulate the workpiece from the chuck, so no current at all passes through the lathe or any part of the lathe. Use an insulator that won't melt during welding, like vulcanized fiber sheet.

Actually, it helps if the lathe is turning, so stray currents are dispersed.

If the workpiece isn't turning, why use a lathe at all? Just rig up a rotatable fixture, perhaps with a wooden body for insulation?

Gordon Heaton · Nov 22, 2020

In my opinion, you have nothing to worry about with the setup you describe.

john.k · Nov 23, 2020

I used Delco starter motor brushes and holders ,onto a slipring at the back end of the lathe spindle.....from a Cummins starter,biggest ones I had ....starter brushes seem to be a mix of copper and graphite,and obviously have very low resistance,and high current capacity.....and the brushes and holders are free,if you have a collection of stuff.

Welding in a lathe ??

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