Derek,
I normally don't use lube for cast iron, as there is a lot of free carbon in the metal itself to make it self lubricating.
But when I am doing a bit of thick stuff using a 14volt rechargeable drill, a touch of Rocol paste makes sure I don't run into trouble.
This is a 5" diameter 1/2" thick, cast iron rotary table clamping plate I made recently. To cut all the holes would have taken hours by hand, these 4mm ones were done in about 20 mins with a large battery drill. Straight thru with no stopping or backing off.
If you have the correct sized tapping hole (a major cause of tap breakage is the wrong sized hole), and a good sharp tap, there are no problems using power tools for getting the job done.
For aluminium, paraffin is always recognised as the cutting fluid to use. But nowadays, WD40 is classed as a better substitute. I buy it by the gallon and use a spray bottle, but for tapping, spray a bit into a small container and dip the tap in before starting a new hole.
If I break half a dozen taps a year, I think I am doing something wrong, and I tap thousands of holes a year, in all sorts of materials. I actually throw them away when they start to dull. I do buy in bulk, and if you buy 9 at a time, for standard smaller sizes, they work out at £1:40p (excl. VAT & postage, no minimum order, and delivered next day in the UK) each for high quality HQS taps, that cut thru stainless like butter.
http://www.tapdie.com/html/metric_taps_or_taps_metric__ta.htmlUsual disclaimer.
So for what FLJ is doing, tapping out thin ali plate with a powered screwdriver, as long as a bit of lube is used, there would be no complaints from me.
Anything to make life easier.
John
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