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| Drilling! - small holes on the mill and centre drills |
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| jim:
centre drills are only realy used when a centre is needed. spot drills tend to used for HSS drills and to provide a start for thin (say up to 4mm dia) or long carbide to prevent wandering. a centre drill is no where near as strong as a spot drill! in fact we often run an M00 (stop in program) to check centre drills |
| Rob.Wilson:
--- Quote from: JimM on July 18, 2010, 03:14:42 PM ---John / Rob can you recommend anywhere that sells (small) spotting drills at a sensible price ? Cheers Jim --- End quote --- Hi Jim I get mine off Ebay ,,,,,,,,,,,, about a fiver each ,,,,,,,,,sometimes you can pick up some good deals ,,,,,,,,,,, cheap as chips http://cgi.ebay.co.uk/6MM-NC-SPOTTING-DRILL-90-DEGREE-COBALT-SPOT-DRILL-NEW-/140418151078?cmd=ViewItem&pt=UK_Home_Garden_PowerTools_SM&hash=item20b192f2a6#ht_1259wt_1137 Regards Rob |
| AdeV:
Fascinating stuff... I learned my early machining knowledge (before I found this forum) from Darrell Holland's videos on how to run a vertical mill; and he used centre drills, just as Lew describes. As a result, I bought a set of 8 centre drills - in various sizes - for 20 quid, not long after I bought the Bridgeport. And yes, I've snapped 3 nibs off, so far... usually because I've plunged into the work too fast for the drill. I'll definitely be looking at spotting/stub drills from now on, & will keep the centre drills for lathe work. Qs: Why are spotting drills so much more expensive than stub drills, and - seeing as I'm only an amateur machinist - is there any reason to buy a spotting drill in preference to a stub drill? |
| John Stevenson:
Personally I don't think so. On those dividing plates I do there are literally 1,000's of holes, one has a 127 row right on the outside and it's just possible to fit this row in with 12 thou between holes. If you get a drill wandering it stands out like a sore thumb two holes will be broken together and another two will have a large gap between them. I buy good quality stub drill, usually Guhring, from J&L in quantity and change the drill every 4 plates, that's about 2,000 holes, if I do this I get no problems, any more and it's pushing it. I do regrind drills but I have a precision Swiss drill grinder that fits in a shoebox and cost £9,000 when new and no I didn't pay that. I only do this not to save money but a correctly ground drill will do 6 plates, remember drills are produced on production equipment to the best economical shape, not the ultimate shape. This is why Meteor and Christian are still making drill grinders that cost up to 15K and fit in shoe boxes. If there were no demand they would go out of business. John S. |
| AdeV:
--- Quote from: John Stevenson on July 18, 2010, 06:25:03 PM --- This is why Meteor and Christian are still making drill grinders that cost up to 15K and fit in shoe boxes. If there were no demand they would go out of business. --- End quote --- Do you have a piccie or model number of your grinder? I've been a'googlin', but nothing jumps out as being super-exceptional & shoebox-sized (let alone £15k...). Would your machine deal with a 5/8" x 600mm bit....? :wave: |
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