Chinese Spot Drills

This topic has 10 replies, 7 voices, and was last updated 20 June 2017 at 19:52 by JasonB.

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19 June 2017 at 11:17 #303147
Colin Whittaker
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@colinwhittaker20544
It's only cost me a few dollars so it's no big deal …

I decided to buy some spot drills for use in making accurately located holes in brass for a clock. The set of Chinese bits that arrived from AliExpress do not come to a conical point as I would expect. From one side the bit does come to a point but when rotated 90 degrees there is now a large flat profile that doesn't look as though it will deliver the wanted hole precision.

Who's confused about what a spotting drill should do/look like? Me and/or the Chinese supplier?

Thanks, Colin
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19 June 2017 at 11:17 #25311
Colin Whittaker
Participant
@colinwhittaker20544
What kind of tip facet should I expect?
19 June 2017 at 11:20 #303149
JasonB
Moderator
@jasonb
All mine have a straight bit between the two ends much like you get on a twist drill, depending on make the size of this does vary.
19 June 2017 at 11:40 #303150
JasonB
Moderator
@jasonb
On the left is an unbranded Chinese one (actually it may be Interstate) on the right a branded keo one that I got from MSC and that is the make I buy now as they cut better. Keo one probably cost more than a whole set from Aliexpress but if you want precision you need to buy decent things.
19 June 2017 at 13:29 #303167
John Flack
Participant
@johnflack59079
I have in the past purchased c/drills from Drill Services these range from O to 4/O the smallest having a tip of 0.010". I paid about a fiver then,but being double ended halves the cost. No ides how this compares with info above

John
19 June 2017 at 14:08 #303170
Colin Whittaker
Participant
@colinwhittaker20544
Sounds like I do have the real thing.

Thanks for the intelligent answers to my stupid question.

I guess I'd better give my supplier some positive feedback.

Cheers, Colin
19 June 2017 at 14:59 #303182
ChrisB
Participant
@chrisb35596
The Dormer stub drills I have all end up with a pointed tip with almost no web. Compared to a stub drill a normal twist drill has a much larger web.
19 June 2017 at 15:02 #303184
Mike
Participant
@mike89748
I've always used centre drills rather than spot drills. When both ends are no longer capable of being sharpened, you are left with a useful cylindrical bit of HSS which can be ground into other tools. Yes, I am stingy! My chart lists 12 drills, from sizes 00 to 10 (0.125 to 1 inch, although sizes 0 to 4 will perform most tasks in my workshop.
19 June 2017 at 18:47 #303257
I.M. OUTAHERE
Participant
@i-m-outahere
I have a nice carbide spotting drill , split point geometry , well that was until i dropped it on the concrete floor chipping the point 😭 .

While i'm here and as i will eventually get around to fixing that spotting drill i am interested in everyones thoughts as to the type of grind i put on it with my T&C .

Split point ?

Four facet ?

Ian.
20 June 2017 at 19:35 #303453
Neil Wyatt
Moderator
@neilwyatt
Expect an article on web thinning in the next MEW.

As far as I can see Jason's better drill has the web thinned, perhaps the other drill could be ground to match.

Spotting drills are a use for broken jobber's drills, as long as they haven't bent.

Neil
20 June 2017 at 19:52 #303465
JasonB
Moderator
@jasonb
Keo site says their spot drills have a constant thickness thin web that does not require web thinning if sharpend See page 18 of cataloge

Edited By JasonB on 20/06/2017 19:55:55
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