Re: Sharpening Small Bits
Hi all, Have not posted much since 2009 and not sure if this is the best place for this question but: Considering making a sharpening jig but first, can anyone recommend an ideal geometry for .7mm drill bits used for drilling 12mm long holes, with the grain, in exotic hardwoods? The problem is that they often tend to follow the grain and get off center. Obviously I need advice on feed rate and spindle speed as well. Also, in a gang tool type setup, would a live tool help with the drilling of small diameter holes in wood? Many thanks in advance.
Re: Sharpening Small Bits
15:1 length to diameter. A challenge.
Wire twist drills, VERY sharp.
The wishbone sharpener is a must, (IMHO)
http://www.cnczone.com/forums/toolgr...tml#post500997
8000-1000 RPM (a guess)
Peck drilling 1mm steps
Feed.. Quite slow.
Some air cooling would help and let you run faster.
Re: Sharpening Small Bits
Quote:
Originally Posted by
C&Me
Hi all, Have not posted much since 2009 and not sure if this is the best place for this question but: Considering making a sharpening jig but first, can anyone recommend an ideal geometry for .7mm drill bits used for drilling 12mm long holes, with the grain, in exotic hardwoods? The problem is that they often tend to follow the grain and get off center. Obviously I need advice on feed rate and spindle speed as well. Also, in a gang tool type setup, would a live tool help with the drilling of small diameter holes in wood? Many thanks in advance.
A wood bit is somewhat different than what was being discussed here because the tip is ground completely different. The tip is ground to a needle point but the flutes are left long on each side but shorter than the needle point and sharpened on their leading edge to cut like an auger. The needle point guides the bit into the wood while the flutes do the cutting. You can use a conventional drill bit sharpened the usual 118° but you must run the drill as fast as possible and 'peck' the hole by feeding in .010" - .020" and draw the bit back out of the hole making sure that the flutes are clear of any swarf. That should get a deep accurate hole but small holes in hardwood are tricky. Pecking is best done on a CNC machine because of the accuracy needed on each peck - taking the bit in too far can cause it to begin to lead off - then you're done with accuracy with that hole. You need a CO2 laser to drill those holes....# 70 drill bits will be tough to grind for wood.
Bill C Haven't been here for a while either.
Re: Sharpening Small Bits
Thanks Bill and Neil, what do you think about a 60 deg angle, as is used for plastic/plexiglass drills? Yes, brad point would be great but the smallest I can seem to find them is 2mm. Pecking has worked very well for me for manual work, especially in plastics. I use a taig lathe with lever tailstock, but there is usually some substantial deviation with woods. Hoping to start some cnc production at some point and wondering how to manage this issue in that context. I also have a foredom type rotary hand piece set up in a drill press type arrangement, that works quite well at around 20,000 rpms and a moderate feed rate, but it is basically vaporizing the material and the bits burn quickly.
Re: Sharpening Small Bits
And now for a completely heretical solution.......you could burn the holes in grainy wood by heating the "drill" bit, which is just plain wire, and as long as the wire is not too hot the hole does not get too big in diam.
Ian.
Re: Sharpening Small Bits
Quote:
Originally Posted by
C&Me
Thanks Bill and Neil, what do you think about a 60 deg angle, as is used for plastic/plexiglass drills? Yes, brad point would be great but the smallest I can seem to find them is 2mm. Pecking has worked very well for me for manual work, especially in plastics. I use a taig lathe with lever tailstock, but there is usually some substantial deviation with woods. Hoping to start some cnc production at some point and wondering how to manage this issue in that context. I also have a foredom type rotary hand piece set up in a drill press type arrangement, that works quite well at around 20,000 rpms and a moderate feed rate, but it is basically vaporizing the material and the bits burn quickly.
Have you tried making/using a spade bit for this? A Ø 0.028" (#70) piece of hardened drill rod or carbide (special wheels for carbide as you probably know - green) - grind the sides away equally (cutter grinder would be great for this but you could off-hand it too) to form a basic tapered spade bit. Give the sides about .100" length at about .010" thick at the start. Spin it up, peck and relieve it often. Carbide - spin as fast as you can but feed slow. High speed - spin maybe 6 - 10K and relieve more often with moderate feed.
Spade bits are too dumb to lead off if they are not pushed and fairly accurately made. 60° is strictly for keeping plastic from heating and sticking to the drill bit - and still not so effective even then.
BC
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Re: Sharpening Small Bits
Thanks Bill, I have tried making a spade bit but never managed to get the geometry right. That is probably due to lack of a jig. I have been playing around with a simplified design, based on jigs I have used for sharpening gravers for hand engraving. The lip angle is set by the protrusion of the bit from the pin vise and the difference of the levels of the sharpening stone and the surface the jig rides on, while the clearance angle ( 12 deg) is determined by the angle cut in the bottom of the jig. Attached some mock ups below. Thanks for the burning idea Ian, some of the woods smell quite nice when they burn! Would the CO2 laser really work?
Hope you guys can advise me on this thread I just posted: http://www.cnczone.com/forums/vertic...26360-cnc.html
Many thanks