Richard, Ken 1 'n all. Thanks. Being fair, I have probably only made a couple of dozen jets all told. The 6" (Chinese) lathe is more accurate than my Unimat SL. (Which I guess must date from 1960s or earlier?). The Unimat must be at least 1 diameter off-centre for the 0.25mm drills. And trying to align the headstock with the tail-stock tells me the Unimat lathe just isn't true after a long life. I have had best results on the 6" lathe by threading the jet, drilling the "gas-side" 1mm dia for all bar 3mm of length - then parting-off. Reverse the jet in the chuck, face then strike a centre for the 0.25mm drill and do the drilling with tail-stock chuck holding the drill. On the Unimat, I have to swap the chuck and tail-stock (drill-chuck) so the drill is rotating, as I just can't find a true centre the conventional route with the drill in the tail-stock. - Through the magnifying glass you can see the drill bending as it wobbles off-centre. If I get a hole it is somewhere around 0.27~0.28mm I guess (smaller than my 0.30mm drills). I buy sets of 10 drills of E$@y for £2.50, so cheap enough, and I have a dozen or so shanks from broken drills - some with a mm or 2mm of drill left unbroken. I use these to strike the centre now, as nothing else is small enough in my collection of centre drills and spot-drills. When I get a true centre, the jet gives a gas flame exactly the same size as a commercial jet (cost £3.). I'm just a sucker for making it myself, rather than buying "mass-produced stuff at 10 times the cost". When commercially practical - I buy! - Then spend my time making the more unique stuff.
I would just like advice on the best speed for drilling? The drills are so femur that high speed definitely doesn't work for me. I seem to do best at 800rpm... but when you talk about it you seem to be at Dremmel high speeds of over 10,000rpm? (If I read you correctly?). When I tried that the drill bit simply broke-off the shank "to meet its maker". Glad I was wearing glasses! Perhaps you are drilling >0.5mm when the drills are strong enough for the speed? When I have tried simply holding drills with a steadied chuck that has less than a 70% chance of success, as my hands are not "stiff" enough. You can't feel the snatch - there isn't enough torque on such a small drill. But you can feel the drilling pressure, holding the chuck lightly 'tween finger and thumb mostly supported by the tail-stock, but without the taper jammed... (like Drawfiler's method). - I don't need pin chucks (mine are not accurate enough anyway) as the drill shanks are 3.2mm dia. I'll make a tail-stock sliding holder for a small chuck I have, and try that. It really does need the alignment from the larger lathe, but with the feel I guess I'll achieve with the sliding chuck arrangement? - I'm much like MRA with my hand skills, so need the machine to compensate! (Breaking 10mm taps is easy for me! - For hand tapping, my Push and Pull are not in-sinc most of the time!
).
Cheers lads! If I achieve more than 1 in 3 true jets I'll let you know... or if I ever reach more than 5 true holes with 1 drill-bit. My real challenge will be to buy some 0.2mm drills...
Did someone recount the tale that after WW2 the Americans sent the British a tube with a machined-hole that was smaller than anything supposedly available? - So the British sent it back with a tube inside it? Here's the latest! -
Smallest 'test tube' scoops world record
At work, we needed oil-spray bars for valve cam lubrication (400,000/year)... 0.5mm holes specified. The Japanese had very clever checking devices an cameras to check for broken drills, blocked or badly drilled holes, etc. and a 5% part reject rate. To make these in the UK I specified Laser drilling - 100% OK parts - and cheaper! (High capital cost recuperated in months).
I'll try not to stress you with my "simple" queries again!
K2
