How to change M12 to 1/2" BSW drawbar thread?

Steve

I have arc welded tooling steel a few times in the past with home shop equipment when I could see no better alternative but rarely had that nice warm feeling that the job has gone well. Brittle fracture at the join seems to be a serious risk.

One unconditionally successful result was converting a J&S square 3/8 toolbit holder back to its proper bent form after some previous user had cut it and welded it straight. Having already got one bent and one straight one I needed the opposite hand bent one much more than another straight one. Besides it was free so fiscal risk was small.

A workable but less clearly successful job was to modify a No 4 morse taper and 5 to 4 sleeve to create a milling cutter holder for a monster pillar drill. Having no drawbar the unit had to be end retained via a collar fitted to the spindle with the collet, cutter holding gubbins and short drawbar arranged to be inside the drill spindle. Unit needed to be easily removable for cutter changes and reversion to drilling use. Although the various welds seemed solid I glad that direct tension and side loadings had been carefully avoided at the design stage as I was never completely happy that the joints were not brittle. In retrospect I should have made it from scratch but modifying seemed much easier.

Repairing the end of a Dickson parting blade holder turned into a real battle. Frankly if the thing hadn't already owed me best part of £40 as well as being hard to find in the first place I'd have scrapped it. The lower part of the blade support was cracked for around 1/4" to 3/8" at the front presumably due to heavy jam up at some point. I tried a number of things all of which failed in short order, fortunately only costing me part of the blade once. What eventually worked was to treat it like welding cast iron with an ordinary stick welder and ordinary rods by laying down several thin layers of weld of minimal thickness at minimum current to get a good joint before building up with larger rods. Finished off by diamond filing to shape. Phew! The initial low, but sufficient, current lay down of thin layers minimises any heat driven changes and thermal effects liable to change the structure. As ordinary welding rods are made to retain ductility when cooling it also provides a tiny bit of flexibly between the main body and the weld build up helping absorb thermal stresses during cooling. After all arc welding is fundamentally still a casting process so inherently tends towards being brittle.

By the time I did the Dickson job I'd upgraded to a Fronius Transpocket inverter welder which is a seriously good (and expensive!) example of the uber compact inverter breed. I suspect that its excellent arc control and ability to work with very low currents were important factors in in the eventually successful result. No chance with an ordinary low end AC buzz box from Halfrauds et al.

Clive.

What eventually worked was to treat it like welding cast iron with an ordinary stick welder and ordinary rods by laying down several thin layers of weld of minimal thickness at minimum current to get a good joint before building up

So you CAN weld cast iron? I'd always heard it was "impossible"

I've got a cheap buzz box with low amps and bog standard rods

Any major caveats apart from the general quality of the CI that you are aware of?

I'm thinking that carving away part of the cast  iron and rebuilding with weld would be part of sorting a cracked job. (Got a knackered vice I can practice on)

Edited By Ady1 on 01/09/2015 11:01:09

How to weld cast iron is described at http://www.lincolnelectric.com/en-gb/support/welding-how-to/Pages/welding-cast-iron-detail.aspx.

Nickel rods are stunningly expensive!

If you have access to oxy acetylene then sifbronze might be more attreactive

http://www.twi-global.com/technical-knowledge/faqs/process-faqs/faq-oxyacetylene-and-bronze-welding-of-cast-iron/

You do I grolly mine up else they drop out or cutter moves.
Have stripped several off the shelf studding welded to drawbars but never striped a HT bolt even an 8.8.

Sounds like something grossly wrong to me - maybe an inaccurate MT taper somewhere. John is quite right in my experience .... never had to do more than nip up the drawbar either on the lathe, or on mill (when I had an MT setup on it).

Even with the R8 taper I currently have on the mill, I don't tighten it very much. Certainly nothing like enough to strip a piece of studding.

Hi Clive and many thanks for the very interesting post on welding. Blimey - that Fronius welder sounds exotic. Apparently it has ' resonant intelligence' which sounds awesome and makes me want one. Even if I wouldn't know what to do with it!

Steve