How does this work.?

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What is the reason / physics behind this working.?

no idea but im going to try it

would it be because 1 cutting edge is cutting before the other causing the shaped hole and putting a rag bit in there levels out the cutting edges to stop wander?

Dunno but I'll bet he discovered it when his shop coat got caught in the drill.

The cloth gathers the swarf and it doesn't get the chance to damage the hole?

Does it work fine without cloth at higher speeds? (lighter swarf)

Edited By Ady1 on 14/01/2016 01:10:03

This "trick" is as old as the hills. I was taught this by an old toolmaker in the mid 50's ! The emery cloth puts a small chamfer on the edge of the hole before the drill starts cutting and it stops the drill from biting too quickly. Also the cloth supports the drill between the 2 cutting points and minimises the drill wandering from the proper circular path. 3 flute drills are much better at drilling thin material as the drill is supported by 3 points and not 2. The method shown does result in a hole slightly bigger than the drill because of the extra material taken out by the emery. Clamping some thicker scrap material on top of the thin material to be drilled will give the drill better support and minimise any "wandering" by the drill and gives better hole dia. control..

Doesn't say (or look like) emery cloth - just a bit of thing cotton sheet perhaps.

As ASF suggests , I guess it's damping out the vibrations that result from the bit dancing about while cutting a non-circular hole. Just enough drag to dampen its enthusiasm. The drill centre must be jigging about nicely when it's making those trianguar holes.

Edited By Muzzer on 14/01/2016 08:29:48

Edited By Muzzer on 14/01/2016 08:33:52

.

I've not tried it with normal drills, but that certainly calms-down chattering countersinks.

MichaelG.

Edited By Michael Gilligan on 14/01/2016 08:49:23

I would concur with the last two posts with the additional comment:-

It's about getting an accurate start to the hole. Once that has been achieved the hole progresses correctly. Basically it stops the tips of the cutting edges grabbing and throwing the drill off centre. Once this has happened the drill follows the odd shaped hole all the way through.

regards Martin

Just drill hole a bit undersize and finish with a slot drill.

That was one of the first things shown to me when I started my tool making apprenticeship in 1963. We never questioned how it worked, just applied the method of a bit or worn emery cloth.

I've always assumed the cloth or emery cloth fills the flutes up, so creating a "solid" tip that works a bit like an end mill.

The method will work with ordinary cloth but works better with fine to meduim emery cloth.

Edited By Dinosaur Engineer on 14/01/2016 15:44:52

It fills the flutes and stops the web wandering when it starts to bite, use worn out emery tape folded double with the grit faces inwards, the resulting hole will be round but slightly oversize.

I was shown this trick many years ago,the method was to use a small piece , rag folded over and over to get 8 thicknesses, works well on thin sheet ,the rag fills up the flutes and makes the drill work like a reamer,