Weird triple flute drills

[RainbowsParticipant @rainbows]

Got a big ole bunch o big drills. Going to move the MT3 ones on since my machines are MT2. Found two odd ones in the batch though. Anyone know what they might be for?

1 5/32" dormer

63/64" dormer

[RainbowsParticipant @rainbows]

[Ian ParkinParticipant @ianparkin39383]

I’ll have some of your mt 3 drills rainbows?

What sort of price you looking at? I’m in sheffield S7 where are you?

Ian

[david sanderson 3Participant @davidsanderson3]

i think they are core drills for drilling castings

[Clive FosterParticipant @clivefoster55965]

Three flute drills are said to be better at opening out holes than two flute. Especially cored ones in castings which are pretty much inevitably less than accurate unless high end pressure techniques are used. Probably a stability issue.

Clive.

[egaParticipant @ega]

Core drills need a pilot hole but are otherwise excellent. I think they come in four flute style as well.

[SillyOldDufferModerator @sillyoldduffer]

I read about multi-flute twist drills recently whilst researching better ways to drill straight deep holes. I think it was on the web. From memory, they were invented by Brown & Sharp at the same time as the conventional twist drill. They cut rounder holes than a two-flute and are less inclined to wander off axis. The downside is they are expensive to make and easier to break. The more flutes the weaker they get.

They don't seem to be easy to buy. I did find this example.

Dave

[Neil WyattModerator @neilwyatt]

Posted by SillyOldDuffer on 20/10/2017 16:44:47:

They don't seem to be easy to buy. I did find this example.

Dave

Blimey I would say that's cheap for Guhring!

[geoff adamsParticipant @geoffadams14047]

core drill to drill cast holes to true up used them on cnc mill back in the 80s on precision barometers when I worked

for negretti aviation

[MWParticipant @mw27036]

Indeed this is a core drill my friend, and they're quite unusual so i'd hold onto them, they are quite expensive and limited to purchase.

They are the tool for opening out holes already drilled, hence the blunted end. The idea is that the hole ends up being less "triangular" than the variety twist drills often do and therefore more circular, the more flutes you've got the better it gets, (not sure how much better).

Michael W

[egaParticipant @ega]

Posted by SillyOldDuffer on 20/10/2017 16:44:47:

…"The more flutes the weaker they get."

I would have been inclined to agree but one authority points out that "The end of the [core] drill … does not come to a point, as in the case of the ordinary drill. For this reason the web can be made thicker, so that a stronger drill results."

[Nick HulmeParticipant @nickhulme30114]

Two flute drills have a tendency to cut a tri-lobal hole, three flute drills don't have the same tendency.

[RainbowsParticipant @rainbows]

Posted by Ian Parkin on 20/10/2017 16:21:21:

I’ll have some of your mt 3 drills rainbows?

What sort of price you looking at? I’m in sheffield S7 where are you?

Ian

Im at S2, near the football stadium.

Im thinking of £4 for the good drills, £3 for the drills that need a slight touch up and £2 for the ones where it needs a fair regrind. Got 6 of the first, 2 of the middle and 2 of the last. Mostly Dormer with a Cleveland and a Guhring with it. Could send an exact list of the sizes if you are interested?

[Ian ParkinParticipant @ianparkin39383]

Let me have your number so I can call you I,m probably 200 yards from You or so

[Raymond AndersonParticipant @raymondanderson34407]

Neil, I would agree that the price of the advertised drill you linked to would be cheap for Guhring, but… the drill advertised is Walter [ Titex ] and as prices go are more expensive than even Guhring. It is sold as new but must be old stock, as I checked the Walter prices and the drill is from a series that is mega spendy. Certainly a specialized drill.

Cheers.

Ps, unless you meant  that would be cheap if it  "were " a Guhring

 

 

Edited By Raymond Anderson on 21/10/2017 05:41:06

[not done it yetParticipant @notdoneityet]

Buy 'em quick. They are cheap, even for normal Dormer drills!

Edited By not done it yet on 21/10/2017 06:31:54

[Dinosaur EngineerParticipant @dinosaurengineer]

Have used 3 flute carbide in the past – they produce straight holes to reamer limits.

[Swarf, Mostly!Participant @swarfmostly]

Hi there, all,

Does anyone have any experience of, or comments on, the business of sharpening core drills?

Best regards,

Swarf, Mostly!

[John ReeseParticipant @johnreese12848]

I have a number of 3 and 4 flute core drills. I sharpen on the same equipment I use for 2 flute drills. In a pinch, they can be sharpened by hand. The clearance angle would be the same as on a 2 flute drill.

[John HaineParticipant @johnhaine32865]

Core drills great for opening out holes to then bore out. They don't grap and turn funny shaped lobed holes. Well worth having.

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