I am just going thru the learning process again with small drills (less than 0.010"). I have been involved with micro drills with my job many years ago, and industry provided the solutions then with super fast air bearing spindles and drives (over 100K RPM).
I was trying to recapture that somewhat with my small drill in my post here
http://www.homemodelenginemachinist.com/index.php?topic=7805.0
The reason I was going for speed rather than feel, because the smaller you go, the less feel you have, all because of the flexibility of the drill itself. With what I call a large drill, 1/32", you can actually 'feel' the strength and flex in the drill if you are using your fingertips and one of those finger chucks. If you try that with say a 0.010" drill or smaller, by the time you 'feel' it, it is already broken under the strain.
They reckon that if you spin a disk of normal writing paper fast enough, you can actually use it to abrade it's way thru steel, just like a grinding disk.
The same theory extends to drill bits, the faster you can spin them, due to the centifugal forces involved, the drill actually goes and stays more rigid, and thus the bending forces that leads to breakage is kept under control, even under heavy feed pressures.
I did some calculations a while back for the sizes of drills that I want to use, and the speeds involved are up in the 90K rpm range.
There is no way that I can reproduce those figures in my shop for more than a few seconds at a time, purely because of the cost of bearings to do continuous running at those high speeds becomes very prohibitive, and also the standard holding chucks might start to want to explode at constant hi revs. 50k was about my limit, but even at that low speed, I suspect that my drill bit attrition rate would fall dramatically.
With my newly donated commercial hi speed drill, I am now looking at making the cones for that to run at a constant 20K and put a super fine feed using a worm drive on the quill. A sort of compromise between reduced hi speed rigidity and keeping the feed rate down to prevent drill breakage.
My problem now isn't the drilling unit any more, but the high cost of the micro drill bits. I now have a person scanning drill factories in China to see if I can get the costs down to a reasonable level. I bought all my micro HSS bits a few years ago, at 10 pence each, they are now well over 20 times that price.
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I was trying to recapture that somewhat with my small drill in my post here
http://www.homemodelenginemachinist.com/index.php?topic=7805.0
The reason I was going for speed rather than feel, because the smaller you go, the less feel you have, all because of the flexibility of the drill itself. With what I call a large drill, 1/32", you can actually 'feel' the strength and flex in the drill if you are using your fingertips and one of those finger chucks. If you try that with say a 0.010" drill or smaller, by the time you 'feel' it, it is already broken under the strain.
They reckon that if you spin a disk of normal writing paper fast enough, you can actually use it to abrade it's way thru steel, just like a grinding disk.
The same theory extends to drill bits, the faster you can spin them, due to the centifugal forces involved, the drill actually goes and stays more rigid, and thus the bending forces that leads to breakage is kept under control, even under heavy feed pressures.
I did some calculations a while back for the sizes of drills that I want to use, and the speeds involved are up in the 90K rpm range.
There is no way that I can reproduce those figures in my shop for more than a few seconds at a time, purely because of the cost of bearings to do continuous running at those high speeds becomes very prohibitive, and also the standard holding chucks might start to want to explode at constant hi revs. 50k was about my limit, but even at that low speed, I suspect that my drill bit attrition rate would fall dramatically.
With my newly donated commercial hi speed drill, I am now looking at making the cones for that to run at a constant 20K and put a super fine feed using a worm drive on the quill. A sort of compromise between reduced hi speed rigidity and keeping the feed rate down to prevent drill breakage.
My problem now isn't the drilling unit any more, but the high cost of the micro drill bits. I now have a person scanning drill factories in China to see if I can get the costs down to a reasonable level. I bought all my micro HSS bits a few years ago, at 10 pence each, they are now well over 20 times that price.
Blogs
