universal chuck for hollow bits, coolant-through. Sherline, drill press.

[runcyclexcski]

I have these hollow-core diamond bits that I use to drill precision holes in glass, on a Sherline mill. The bits are 1-3 mm OD and 0.5-2 mm ID (quite fiddly and expensive). I find that I get much better results with these holow-core bits than with solid core burrs. But I would like to get even more consistency (and longer life) by running the coolant through the core non-stop. Is there a small unversal chuck into which I could feed a tube with a coolant in it? Apart from the Sherline, I can get access to a bridgeport. I also have a 1 HP dirll press. Basic DIY solutions would work, too.

At the moment, I drill in a water bath, and each bit lasts only 3-5 holes, 3 mm deep, 2500 RPM (borosilicate)). Also, the hole diameters vary to within 0.1 mm, probably b.c. I cannot control the amount of ground glass floating around (but this still much better than I used to get with solid burrs). With the coolant running through, I thank I could continously wash the bits and the diamonds away and prevent the hole from expanding sideways uncontrollably.

Thank you in advance!

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[skrubol]

Such things exist, they're called coolant inducers, however they are a bit pricey, and I've never heard of one that would be small enough for a Sherline.
Most mills that need coolant through the tool use through spindle coolant. It's a feature typically in large VMC's though.
If you had more time and inclination than cash you might try that method and build an inducer to run water through a hollow drawbar.

[runcyclexcski]

Such things exist, they're called coolant inducers, however they are a bit pricey, and I've never heard of one that would be small enough for a Sherline.
Most mills that need coolant through the tool use through spindle coolant. It's a feature typically in large VMC's though.
If you had more time and inclination than cash you might try that method and build an inducer to run water through a hollow drawbar.

Thanks for the up! Well, I have time, but not unlimited amounts of it... I can sure connect one of my 0.04" bits to a silicon tube, feed it to the top, and hope the centrifugal force from the tube is not too high to induce vibration. Then attach the tube to a spinning beaker of some sort, but it would have to be in sync.

[skrubol]

I can't see how that'll work. Spinning a container large enough to hold enough water to get you through a hole would be a bad idea. You'll need a rotary coupling of some sort. You could build your own with shaft seals:
https://www.mcmaster.com/#mechanical-seals/=19mzcxu
But if you don't have a lathe, you'll probably have quite a bit of leak trouble.

[runcyclexcski]

Yes, shaft seals is what I have in mind. I could drill through the bolt that holds the Sherline chuck in. The bit is tiny, so I would not need to hold an entire bucket 'up there'.

Regarding the container: I could just use a fatter tube as a 'funnel', and feed it by gravity drip by drip. My holes are 0.04", i.e. tiny. That said, it could be that gravity may not provide sufficieng cooling anyway.

[skrubol]

Height will only get you about 1/2 PSI per foot, so yeah, that may not be enough to get the chips out of the way. Good luck.

[RCaffin]

I drill in a water bath, and each bit lasts only 3-5 holes, 3 mm deep, 2500 RPM (borosilicate)).
You are very seriously doing something very wrong there, but I am not sure what.

By way of explanation: borosilicate glass is SOFT, between 5.5 and 7.5 Moh. I am machining granite and basalt, which are harder. I can snap a drill off by bending it, but I have yet to wear a drill out when running in water. A close-up photo of the tip of the drill (the wear surface) might be useful.

I have drilled in a water bath, but it can be difficult setting that up. Most of the time I machine with a low-pressure jet of water flooding the tip of the drill. Not a problem.


First thing: can you get higher RPM? Core drills 1 - 3 mm OD can be spun fairly fast since the radius is so small.
Second: how fast are you down-feeding? If you go too fast downwards you will just tear the diamonds out of the matrix.
What sort of core drills are you using? Bought where and for how much? There are different sorts.

Cheers