Drilling hard materials

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Chasper

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Mar 22, 2007
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I need to drill a 37/64 hole in a 3/4 blank, not much room for error. The blank is coral cast in resin, very hard and very brittle. I think I will need to wrap it in fabric and soak in CA to hold it together while drilling. Maybe I should suspend it in a bigger mold and pour clear resin around it to hold it together when drilling. Should I start with a small hole and work my way up to the full size?

I've been looking for granite/marble/glass bits that come in obscure sizes like 37/64, not finding anything. Maybe I could use a 9/16 bit and then file it out a little larger with a rat tail file, but still would need to find a 9/16 bit to drill stone. I'm looking for ideas
 
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FGarbrecht

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Most coral skeleton (calcium carbonate) isn't very dense and not very hard actually. As Kyle says, go slow and avoid heat. If the coral is completely encased in resin I wouldn't anticipate any particular problems drilling it out. If there are any unsupported areas, the brittleness of the material will cause it to turn to dust.
 

magpens

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Lemme see … 37/64 hole in a 3/4 ( = 48/64 ) blank … that leaves a wall of 0.5*(48 - 37) = 0.5*11/64 = 0.086 inch ….

…. Yikes ! …. You're right …. not much room …. especially for a fragile material !

Does the blank have a round cross-section so that you can hold and drill it in a lathe chuck ? ( …. delicately ! )

I think you are pretty brave to attempt this.

But I hope you are successful, and I hope you will show us the resulting pen !!
 

FGarbrecht

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Lemme see … 37/64 hole in a 3/4 ( = 48/64 ) blank … that leaves a wall of 0.5*(48 - 37) = 0.5*11/64 = 0.086 inch ….

…. Yikes ! …. You're right …. not much room …. especially for a fragile material !

Does the blank have a round cross-section so that you can hold and drill it in a lathe chuck ? ( …. delicately ! )

I think you are pretty brave to attempt this.

But I hope you are successful, and I hope you will show us the resulting pen !!
0.086" = 2.18 mm. Sounds small but I routinely turn kitless with wall thickness of 1 mm. Agree it could be touch and go with a crumbly material in resin. Again, go slow, use sharp tools, do the drilling on the lathe (I would never try this on a drill press). Also question whether you're going to get enough coral structure left in the 2 mm wall to be even visible; I'd be interested in seeing pics along your journey to creating a sea-pen.
 

magpens

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2 mm wall in a homogenous resinous material is one thing …. but in a hybrid blank ?
And don't forget that the drilled blank still has to be turned down a bit and shaped. . (Yes, I know that there is brass support tube to go in.)

I would also like to see a couple of "progress pictures" … very interested in this challenge.
 

johncrane

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Jan 17, 2006
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Melbourne, Victoria, Australia.
this takes time, CA glue wooden ice cream pop sticks too the 4 sides about 8 sticks if its 3/4, now if you can to drill on the lathe use a center drill on the ends of the blank then turn the blank round between the lathes dead center and live center when the blank is round wrap the blank a few times with string and soak with CA and spray the hardener,you can make it as thick as you like it's up too you, use a mask and eye glasses string and CA gets alot of fumes coming off, once the string sets its tough as nails
 

howsitwork

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Jul 9, 2016
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Thirsk
brilliant idea . I’ve used string and epoxy to reinforce / firm a pleasant handgrip on tool handles but never though of CA to reinforce section of blank.
👍
 
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