see **LINK** or https://www.youtube.com/watch?v=_CUGz0jXvWQ the machine just runs forward but as you move the head up the tapping head automatically reverses the direction. Torque on the tap can be set so you should not break taps and as a note you need to use machine taps. One problem is they can occupy a lot of the throat on small machines.

Bob

Edited By Bob Brown 1 on 02/02/2015 20:33:01

what size taps are you using?

Take a look here http://www.dormerpramet.com/en-gb/products/round-tools/taps-dies

Edited By Bob Brown 1 on 02/02/2015 20:56:10

I use Pollard tapping heads, mostly on my Pollard 15 AY drill. Like Andrew I have considerable affection for the beasts as they make tapping a simple process.

The Pollard versions have simple forward and reverse cone clutches controlled directly by feed pressure. As soon as you stop feeding the tap draws forward reducing clutch engagement pressure and rapidly interrupting the drive. Offhand I'd say no more than half a turn from stopping feed to loss of drive. My practice is to lubricate the holes properly before starting to tap and apply only enough feed pressure to drive the tap. Even on the big 15 AY its a quite sensitive process and its easy to feel if the tap needs too much drive power for any reason. If the tap does seem to want too much driving simply lifting the feed lever so it can reverse back clears the thread, just like manual tapping, so a second attempt usually allows the thread to be completed.

Proper machine taps are pretty much never any trouble unless blunt or the material unfriendly. Soft aluminium and phosphor bronze are my least favourites. Ordinary hand taps work well enough in most materials if you keep the speeds down and are careful on feed pressure. Second cuts from good brands have worked fine for me when needs must. Not a place for bargain basement no-names.

You should always set the depth stop so feed stops before the tap bottoms. Big gear driven drills like mine will snap a half inch, or even larger, tap like a carrot if it bottoms out. I suspect than anything under 3/8 is at serious risk in smaller belt drive machines. Remember its a square drive so the tap cant slip like a drill in a chuck. One of my Pollard No 2's came with a normal, decent quality, drill chuck instead of the proper square drive and allignment chuck assembly. Pretty much useless as anything over 5 mm slips at the slightest provocation. No worry to me as I got it in a job lot, for effectively less than nothing as the rest was worth more than I paid, as a spare parts source for the one I was using.

The morse taper needs to be a good fit lest the head be pulled out when you reverse. My spinde was somewhat bruised. The MT3 reamer went in approaching 1/8" before everything was properly cleaned out. It now grips like a bolshie badger with only modest fitting effort.

Clive

Edited By Clive Foster on 03/02/2015 00:09:43

Edited By Clive Foster on 03/02/2015 00:10:26