Harder than I thought!

[IanTParticipant @iant]

Problems drilling and tapping a blank arbor!

[IanTParticipant @iant]

Decided to finally stop watching YouTube and finish something (for a change). Was feeling a bit idle so I chose a nice easy project – an MT1 slitting saw arbor for my EW lathe. I had [some time ago] purchased a few blank MT1 arbors and turned the body and cap a week or so ago, so I thought it would be a fairly quick job.

The body is a chunk of free-cutting mild steel I'd bored to fit outside the MT1 blank arbor and Loctited onto it. Today I just had to fit the cap and drill through and tap the body for a lock screw. I drilled through the cap no problem but as I entered the end of the blank arbor behind it, I started to get severe chatter.

I decided to try a larger drill but the chatter was even worse. The end of the arbor had been chemically blackened and since I hadn't turned the arbor body itself (but the sleeve) I started to wonder if I had some very odd material and had managed to work harden it or something similar. A quick cut across the arbor face into the blackening however didn't reveal anything odd and it cut OK. I tried drilling again but the drill was by now really leaping around.

Something clearly wasn't right, so I removed the work and had a good look under the light. I could see a shiny bit and the end of my drill didn't look too good either. The end of a sharp (and hardened) pick found that the area around the hard bit could be 'dug out' and two small holes appeared either side of the shiny bit. I was then lucky, as with some thin nosed pliers, I managed to pull the villain out. A piece of 3mm drill, broken off in what I assume was the centre hole. Once removed, I was able to drill the arbor without too much trouble, although the material still seemed gritty and I didn't really get nice curly cuttings (but the drill had probably had it's edges dulled).

I then tried to tap it M6 and found that I just could not turn the tap. Given the problems drilling the arbor, I started to think the body material really was something odd. Fortunately, I decided to go and have a cuppa and think about it. Now when I tap things, I usually just look up the tapping size in Zeus or Tubal Cain. This time I hadn't bothered, as for metric (and I'm mostly using BA) I have an inexpensive set of taps (and matching tapping drills) from Lidl The drill with the 6mm tap was 5mm. Stopping to think about it, that sounded a bit small. Sure enough, Tubal suggested 5.3mm (at 65%) for a 6mm coarse thread. So I drilled out to 5.3mm and now I could just about tap it (although not as well as the free cutting steel I've grown used to).

I've now checked all the drills supplied with the set (Powerfix Tap & Wrench Set M3-M12). All of the tapping drills are smaller than those given as being 85% engagement by Tubal. This may explain why I managed to damage my thumb tapping some fairly thin plate M8 yesterday (I used the drill supplied [6.8mm] when a 7.1mm would have been much easier.

I've finished the slitting saw arbor but decided to stop there whilst I was still ahead! I'm sure the broken drill bit was just bad luck but I should have been much smarter thinking about the tapping drill supplied in the set. Always dangerous to make assumptions.

Regards,

IanT

[IanTParticipant @iant]

That hadn't occurred to me John – I was trying to avoid having the screw head sticking out and causing an obstruction. The 'washer' is quite thick, so I will have a look at countersinking it for a standard cap screw instead. Thanks for the advice.

I'm also going to run a drill into the two other MT1 blanks later this morning – to make sure I haven't received any other unwanted factory 'extras'. I'm not sure how the 3mm drill would have gotten in there when making a blank arbor but maybe it was intended to be something else when the drill broke, so they "re-assigned" it. Very naughty if true – but hopefully a one-off

A label listing 'Tubal's' tapping drills (for the metric tap set) will also get stuck on the box front (as an aide memoire). The Powerfix taps and drills seem to be good enough quality by the way, I'll just swop the undersized drills out over time for "65%" ones. It is handy to have them in the one place.

Regards,

IanT

[roy entwistleParticipant @royentwistle24699]

Ian I hope you've got a draw bar holding your arbor in the mandril also I would advise not using a key to stop the blade revolving it's better to get a slipping blade than a smashed one

Roy ( Just a couple of thoughts )

[IanTParticipant @iant]

Good thinking Roy – and yes, I've made one from a 2" knurled 'washer' I've had in the scrap box for a while. Silver soldered it to piece of brass and attached it to a length of 10mm rod (rescued from a scrap printer). A 6mm stud loctited on the other end finished the job. Nor quite 'Schaublin' standard but it will do for my little EW just fine.

Drilled into my other two blank arbors just in case – all OK.

Took John's advice and used a 10mm slot drill to make the countersink flat at the bottom of the retaining washer and fitted a normal cap screw. Discovered in the process (I was going to holds the arbor in the tailstock and the slot drill in my ER chuck) that the MT1 arbors are too short for the tailstock (e.g. loose in it). However, managed by holding the slot drill the drill chuck and was careful! A bit annoyed, as I intended the other arbors to be usable in both ends. Have to have a re-think.

So better get on and use the bits I have done. Thanks for the advice Roy & John.

Regards,

IanT

PS – I always like seeing photos on this Forum (as I don't always understand things otherwise!) – so here's another one.

 

Edited By IanT on 28/01/2014 16:22:43

[Anonymous]

I always use keys on slitting saws, if they have a slot for one. With any sort of decent depth of cut and feedrate you're going to break the saw if it slips anyway, so one might as well use the key and minimise the chances of it slipping in the first place.

Regards,

Andrew

[John Stevenson 1Participant @johnstevenson1]

Anything under an 1/8" I don't use a key.

If you keep your eye on it and first chance of it slipping, helped by a marker line on the arbor and saw bang the estop.

At least you see the slipage, with a key it's already too late and you are wearing it.

[IanTParticipant @iant]

Thanks for the warning/advice guys.

Generally (on the EW) if I have a 'dig-in' the belt slips, as I don't have it that tight. I'll be cutting some brass angle into sections shortly but I will take it easy.

Regards,

IanT

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