Struggling to tap some stainless.

[MachineTom]

All good ideas already, so another. 303 hardens easily, notice the chips color, and if you get a piece like a cap, as the drill breaks through. That cap means the last bit of material was over heated, and is now hardened. Two things to do, First use a piece of ALas a backer, this will pull heat from the final surface as the drill breaks through, second, drill a pilot hole then a tap drill hole. There are taps designed just for SS, in addition, I love spiral flute taps, designed for blind holes they tap through holes just as well.

When caught in the no more turn on the tap, back out, change taps, the list should be, starter tap, then plug tap, then spiral, then bottoming, then starter...This way you only cut a bit each change of the tap, but it is usually just the last couple threads.

Broken enough taps to learn.

 

[yadnom1973]

Thanks for all the advice guys, I wasn't able to answer for a while there but I've been working on the problem.
Yes I'm in the UK so I bought a pot of Molyslip Tap Compound, it has similar ingredient to the Moly Dee. I also bought a good quality set of German HSS-E Serial Form Taps. I tried them in a 5mm blind hole to start as I had some test holes drilled already. It went in so easily that when I hit the bottom I thought it had started cutting the thread and turned till I stripped the hole. I don't know if it's the serial taps or the compound but I tapped a few more and it's amazing how easily it goes through.

Drilling the holes is still a *****. 3mm or smaller and the bits go through nicely but larger ones don't, as I push the quill down the bit always slips in the chuck before it bites.
To solve this I put the drill bit in a collet and fed the whole head of the mill down and it seems to work well like this but this will only work with drills that fit in the collet and that's only a 5mm for the M6.

Normally I drill a starter, then a pilot hole and if I need an accurate hole I'll drill about 1mm under then come through and finish with the final bit to bring it to size but with this stuff, if its anywhere near the same sized hole as drill bit it takes the bit straight out of the chuck. This happens with a 3mm pilot hole for my 5mm holes for example. In the end, I just gave up with the pilot hole of any kind.

I have an M5 to do too so this is a 4.2mm or 4.3mm bit. Not sure how I'll drill this, I'm hoping it's small enough to just go through. I'll see. Tomorrow at least I'm feeling confident enough to start tapping all the M6's on the parts.