Are these spot drills?

[AdrianRParticipant @adrianr18614]

I got these drills for £1 each at a steam rally, by the colour they look to be carbide. They are 4 facet and the angle is larger than a normal drill. Are these spot drills?

[AdrianRParticipant @adrianr18614]

[old martParticipant @oldmart]

No they are not spotting drills, but if they are carbide (compare the weights with similar size drills in hss), they could be used as such, as they will be stiffer than steel. A spotting drill will normally have only about 1 diameter of flute length, these have a very slow rate of helix, I can't remember the reason for this.

[Stuart BridgerParticipant @stuartbridger82290]

I would say slow helix stub drill, rather than spot drill.

[JasonBModerator @jasonb]

Possibly slow helix sheet metal drill

[Anonymous]

Bottom is a carbide spot drill, top is a slow spiral drill for brass and bronze:

Years ago I'm sure I remember straight flute drills for brass, but i'm darned if I can find any reference to them now. Did they exist, or have I lost my marbles? On second thoughts don't answer that!

Andrew

[AdrianRParticipant @adrianr18614]

Hmm, slow flute for brass now that tickles a memory. Well if nothing else I have some nice drills for all the brass I bought today.

[Michael GilliganParticipant @michaelgilligan61133]

Posted by Andrew Johnston on 27/05/2019 20:42:39:

Years ago I'm sure I remember straight flute drills for brass, but i'm darned if I can find any reference to them now. Did they exist, or have I lost my marbles? On second thoughts don't answer that!

.

Yes they did … and they still do

Wikipedia confirms the traditional use, on Brass & Copper

but I note that carbide versions are advertised for use on hard steels, etc.

MichaelG.

.

https://en.wikipedia.org/wiki/Drill_bit#Straight_fluted_bit

https://www.drill-service.co.uk/products/drills/straight-flute-drill/dcsf-carbide-drill-straight-flute/

Edited By Michael Gilligan on 27/05/2019 20:59:54

[JasonBModerator @jasonb]

Andrew, this is from Chas A Strelinger & Co reprint originally from 1895 though I did not think you would remember that far back.

[Neil WyattModerator @neilwyatt]

Spotting drills usually have a 90-degree tip angle.

Sheet metal drills often have a tip angle greater than the usual 118 degrees, to reduce grab (supposedly).

If you have a step drill, they work very well on sheet, no doubt because of the straight flutes.

I've seen those straightaway drills with a small notch on each cutting edge. They are supposed to work well on hard materials.

Neil

[old martParticipant @oldmart]

Most of my spotting drills have a 90 degree tip, except a 5mm solid carbide one with a 120 degree angle. That shallow angle actually makes it harder to line up because it is difficult to see the tip

[Anonymous]

Posted by Michael Gilligan on 27/05/2019 20:55:05:

but I note that carbide versions are advertised for use on hard steels, etc.

That's what confused me. Drill Service list straight flute drills but all for very hard materials, not brass.

The picture posted by Jason is what I remember, athough not from 1895. The drills would have been in my fathers toolbox when I was a kid. So I expect them to be from the 1940s, and almost certainly carbon steel.

The slow spiral drills are good on brass but what would be really useful on the Britan is left hand, slow spiral, stub drills. But you don't seem to be able to get them either.

Andrew

Edited By Andrew Johnston on 27/05/2019 21:53:07

[Michael GilliganParticipant @michaelgilligan61133]

Posted by Andrew Johnston on 27/05/2019 21:51:36:

Posted by Michael Gilligan on 27/05/2019 20:55:05:

but I note that carbide versions are advertised for use on hard steels, etc.

That's what confused me. Drill Service list straight flute drills but all for very hard materials, not brass.

.

Hypothesis:

Straight flute used on Brass, etc. improves the work

Straight flute used on hard materials protects the drill

MichaelG.

Edited By Michael Gilligan on 27/05/2019 23:24:59

[Former MemberParticipant @formermember32069]

[This posting has been removed]

[JasonBModerator @jasonb]

Industry seems to like a 90deg spot drill that if sized correctly will put a slight chamfer on a finished hole in one operation or if taken to extreams will countersink the hole before it is drilled by going in deep enough with a large spotting drill so that there is no need to follow up with a CSK bit.

You can do the same if it is a tapped hole by using a larger spotting drill that the nominal thread diameter which will prevent the metal being pushed up around the hole by the tap which can happen in soft materials or when using thread forming taps.

But as you say a drill can jump about a bit as it enters a spot drilled hole until the point is in the metal, less of a problem with stub drills which I tend to use in the common sizes if only to save winding up the head on the mill.

[SamsarandaParticipant @samsaranda]

I have a number of different sizes of straightway drills in my drill collection, cannot remember where I got them from but now I know what they are used for, often wondered.

Dave W

[Former MemberParticipant @formermember32069]

[This posting has been removed]

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