Plug and feathers help please?

[Pitlamp]

Had you thought of using Simon's method from reply #6 above?
10mm cold chisels would be about right and they are not expensive.

Simon really knows his stuff!

It's for use whilst diving, hence the need to hand-drill using a star drill. This is quite laborious so I'd want to use the most effective tool for the job, to get the best result from the minimum number of holes.

Purpose made plugs and feathers have all components made with a very shallow wedge shape, such that the force is exerted eually all the way down the hole. Simon's method would (I suspect) concentrate the force at the lip of the hole. If a bit spalls off the hole would then become unusable for a second attempt (no problem with a chunky 36 V electric drill available but a bit of a personal disaster if it means having to drill another complete hole by hand).

I suspect the angle of the chisel blade would be steeper than the angle of the plugs and feathers as well, so less force exerted (= more holes needed).

Come on fellow potholers; where do half inch plugs and feathers grow at the right price?!

 

[alanw]

Entirely by coincidence, this second hand 19/32" star drill arrived from eBay a couple of days ago.

It's just over 9/16", would it be any use to you? Your need seems to be greater than mine.

At least in our dig we can hit large boulders with a sledge hammer, should we come across one, and we could borrow and lug in an electric drill should we need one.

 

[Pitlamp]

Thanks for the offer alanw.

I'm tempted but I have a number of half inch star drills which are new (and sharp). That's why I want a set of plugs and feathers to match the drills. Although only marginally smaller, these will probably drill quite a bit more efficiently. (If you've ever tried bashing a star drill endlessly in a sump, you'll know where I'm coming from here.)

Hang onto that star drill of yours; they're not that easy to come by these days.

If the situation does change though, I might just ask you!