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What is the purpose of centre drill and how does it work?

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NJH15/08/2011 12:33:07
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Surely a bit inconvenient though Chris? With a range of 1mm each you would always be changing collets.
I like keyless chucks especially for these small sizes - much quicker!
 
Regards
 
Norman

Edited By NJH on 15/08/2011 12:33:49

JasonB15/08/2011 13:24:37
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Not to mention that I was always tought not to grip a drill by its flutes.
 
pbrgff, a spotting drill only has very short flutes, you could only really use it to drill sheet, maybe half the drill dia max without the risk of filling the flutes with swarf. Stub drills are just liek a jobber drill thats been cut off and resharpened, you can probably drill about 5 times diameter. For individual 4 facet Stubdrills have a look at J&L's virtual catalogue page 19 the Dormer "A022 split points"
 
Whoever asked about stub drill sets Dormer do sets of their A022 four facet ones but they are not cheap, I think Greenwood do them and J&L definately do. I have just bought the common sizes and keep them in a little stand.
 
J

Edited By JasonB on 15/08/2011 13:25:44

pgrbff15/08/2011 13:36:43
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Thanks, I'm glad you explained the diam. to depth ratio as I had ordered a 6.1 A022 for the 6mm shaft clearance hole. I'll have to look again for something more suitable, a plain jobber bit? Does that mean I can't drill a 4mm clearance hole 6mm deep with the A022? Would it be bad practise to drill a bit at the time, reversing out to clear swarf?
I have saved an order at J&L's with A022 series bits which seemed reasonably priced. 3.3 for the 4mm tapped, 4.5 for 4mm clearance, 3.5 for 3.5 clearance and the 6.1 which I will remove.
What a shame I went to a posh school that didn't let you get your hands dirty with things like woodwork and engineering, I might have found a job I enjoyed!
 
chris stephens15/08/2011 16:06:48
1049 forum posts
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Hi Norman,
I find my ER32 collet much more convenient than a keyless chuck, granted it can take a little longer to change drills but as I am limited on quill to table height, the collets win hands down. In truth I have not used my R8 mounted keyless 5/8" for several years, although I do sometimes use a 0-10mm keyless that is fitted with a short 1/2" stub for mounting in a collet.
 
Hi Jason,
I would totally agree about not holding a drill by its flutes in an ordinary chuck but with a collet the gripping area gives more than enough support without the risk of damaging the flutes. As you know a collet grips over almost the entire circumference and not just the three points of an ordinary chuck. I therefore see no good reason not to do it , when the need arises.
 
Hi pgrbff,
Re. your last sentence, I am with you there but just think, could you afford to set up a workshop, in retirement, if you had a menial grubby fingernail job.
chriStephens

edits needed to counteract alzheimers, dyslexia and senility and a touch of more haste less speed.

Edited By chris stephens on 15/08/2011 16:11:28

Edited By chris stephens on 15/08/2011 16:16:05

JasonB15/08/2011 16:18:23
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If you look in the J&L catalogue it gives the flute length of the stub drills, this is approx the max you should really use them for. Can't see a 6.1 listed but the 6.0 has flutes of 28mm which is roughly what I said 5xdia (5x6 = 30)
 
If you do change to a jobber then the normal length Dormer equivalent split point is the A002 series page 35.
 
Just opened the latest J&L flyer and if you want reasonable spot drills as well the solid carbide Hertel ones are on special
 
Jason
Bogstandard15/08/2011 16:42:39
263 forum posts
Spot Drills at a good price
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