Hi Steve, just my beginner input.

Is the MT3 arbor part of a tool already or is it a blank arbor? If it's just a blank arbor it would be cheaper to just buy another with the correct thread rather than threading kits.

Ed.

#2 for Timesert & high strength Loctite. Drill is fraction larger than the helical one so gives, to my mind at least, a slightly cleaner fit. The timesert also has a slight flange round the head which fits into a countersunk recess cut by a tool included in the kit which gives a clean end and proper tapered lead in to the thread. Always assuming you can get BSW timeserts.

As a helicoil is basically a spring expanded into the hole by a combination of its own resilience and the component being screwed in rather than a positively fitted device I always feel that it's potentially less reliable when faced with multiple screw in / screw out cycles. Especially if end thrust when loose, as required by the extraction effect, is involved. Probably more prejudice than engineering but thread problems with a tightly inserted arbour and captive drawbar are not pleasant to contemplate. Definitely puts the in in inaccessible!

On reflection I see no reason why you couldn't make your own Timesert type device. Thin "top hat" ended sleeve with any convenient thread on the outside, cut a whisker oversize for a good fit, and a not quite finished thread cut with a taper or second cut tap inside. Fit with the highest strength loctite you can find making sure that the rim of the tophat sits cleanly down on the end of the arbor. Run a well fitting bolt down it to expand the base ensuring that all is stable. I've done similar before now and expanding the not quite finished thread really does help stability. OK I found that out by accident as first time was a desperation, 11 pm and "got to get to work in the morning", vehicle fix. Only a taper tap in the box and not enough clearance to go right through so things just got wound in. Found out latter that there was an official fix using helicoils but reliability was said to be iffy. My fix lasted at least 15 years!

Clive.

Hi Steve,

Why not just run an 11mm drill down the existing threads then re tap 1/2" BSW?

Peter.

Is it possible to just shorten the MT3 taper and then fit a homemade conversion into the end to regain the correct length. I'm assuming that there will be enough grip left in the remaining taper and the conversion extension is made smaller od than the existing taper so no need for clever matching up.

Try putting a file down the thread to see if its hard.

Ian S C

Remember you don't need to tighten the drawbar very much especially for MT collets. A length of studding will be just fine, more than strong enough.

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.

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/