The Sequel - Oh Blimey I bought a CNC Lathe (Beaver TC 20)

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tom osselton:
That was lucky with the probe they are expensive for what they are I snapped one on the Haas doing a reading. I just bought some ridged tap collets Friday 1/4, 3\8, 1/2” as we were always wondering about tap slippage.

awemawson:
Today's job is to remove that broken tap, but first I wanted a 'sanity check' that the circle of 12 mm mounting stud holes are accurately placed. There are 12 threaded holes in the lathe spindle, the chuck uses six of them in three pairs to avoid the jaw mechanism, my adaptor uses six, but evenly spaced.

Sitting my adaptor on the reverse of the original chuck I could check three at a time and I'm glad to report that they are bang on. This will allow me to temporarily mount the adaptor on the spindle to turn the outer diameter concentric to the PCD of these studs, and I can pick this diameter up on the manual lathe to get concentricity when turning the female A2-6 recess.

OK let's work out how to get that tap out. I need to make a hollow copper electrode 8.5 mm (M10 tapping size ) for the Sinker EDM machine. This is easy. But the next step isn't - that's getting it accurately set up co-axial with the existing hole. The hole is blocked by the broken stub of the tap that I will have to shear off to see the target hole. Or possibly I can make a jig using the co-ordinates used to drill the holes in the first place. All a bit of a pain in the nether regions. So . . . . .

Think outside the box - revert to car mechanics techniques - weld a nut on the broken tap and wind it out (but it IS in pretty solidly!). And even if this doesn't work it will probably shear off the top of the tap which I need anyway.

There is not quite enough room for a 10 mm nut to turn fixed to the tap and clashing with the adjacent shoulder - probably about 20 thou interference. But I reasoned that after welding the nut will be dead soft - the shoulder is the EN19T hard stuff, and we should be OK. A good spraying with anti-spatter juice, a good heavy current Mig weld and . . .

. . and sure enough - we are :clap:

pycoed:
On the plus side, not only do you have your adapter(nearly), but also a useful M10 thread cleaner :clap:

awemawson:
Very good :clap:

During swarf clean up I found that one of the 16 welded on nuts had come adrift on the billet hold down plate. This probably happened when the big roughing cutter jammed cutting the first side of the chuck adaptor plate. Not particularly critical as the other nut on this set screw had held. No more heavy milling needed on the billet just drilling and tapping so no real problem.

I got the system to present me with the tap holder that still holds the stub of the broken tap, and sure enough it is of the extensible type as it should be.

When the replacement M10 spiral flute machine tap arrives I will mount the billet up again, drill the 8.5 mm holes much deeper - in fact probably all the way through, then clench my teeth and tap the holes.

awemawson:
The replacement M10 tap arrived by this mornings post so I could proceed but firstly I modified the program to drill deeper holes. It means that they project into where the A2-6 female taper will be turned but I don't think that will matter much apart from giving me an interrupted cut.

I bought some spare M10 spiral flute taps as they are a common size that I use

Next stage is turning tapers :thumbup:

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