Drilling hard materials

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Chasper

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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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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
 

johncrane

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howsitwork

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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.
👍
 

Chasper

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Success, I did get the pen turned and assembled. The first photo shows the blank with two layers of tongue depressors glue on. that held it together during drilling. I drilled pilot holes with a 7 MM bit, re-sharpened it twice while drilling each section. then drilled the holes larger to the final diameter, that took two more bit sharpening jobs for each section. I turned it with a carbide cutter. The cutter has four sides. I started with a new cutter, used three sides to turn the thicker section, used the fourth side then re-sharpened the cutter and dulled all four sides again before I got the thinner section turned. I filed out the inside of the tubes so there was no pressure on the tube during assemble. Then I used epoxy to glue the parts on. I was concerned that any pressure in assemble would fracture the hard coral.

I turn a lot of pens, I'm accustom to spending hours building a blank, but spending hours turning is unusual. Total turning time for the two sections combined was about 4 hours. Making a pass with the turning tool was like removing a light layer of dust, it was slow work. I normally spend 2-3 minutes turning each section of a pen like this, half that time if it is going well..

It turned out well, I'm not happy that on the finial end where there is no coral, but I didn't make the blank, that is all the coral there was to work with. I glued a block of wood on the bottom of the tongue depressors so I could drill through all the way through the bottom of the blanks and into the wood.
Coral 2.jpg
coral 3 (2).jpg
 

magpens

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Glorious !!!!!

Thanks for showing the result, plus some intermediate stages .... Well done !!!!

I like the nice pattern matching across the center band also !!!!
 
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Chasper

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Coral 1.jpg
Here is another photo I should have shared earlier. What I want to point out here is the little blocks of wood on the bottom of these two sections. I like to stop short of drilling all the way through and cut to length later. I didn't have enough length to do that here, I glued on the block to. the bottom so when the bit went through the bottom it went into the wood to prevent a blow out. Even if I had enough length to stop short and cut it off, I didn't want to do that, I destroyed one band saw blade just cutting it in half. I squared the ends with a Rick Harrell sanding jig.
 

ramaroodle

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It turned out well, I'm not happy that on the finial end where there is no coral, but I didn't make the blank, that is all the coral there was to work with.

LOL Another one of those things I never would have noticed if you hadn't pointed it out. Gorgeous! I'm a diver. Never thought about casting coral. Gotta do it!

Was the blank made with bleached coral and colored resin? If so do you think it would have held together going slowly using plenty of DNA to cool the bit without wrapping it??
 
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KLJ

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Great work and some good tips. We had some metal that had been hardened for a knife blade. A good set of dewalt bits wouldn't hardly scratch it. Got a solid carbide bit and it drilled it no problem. It was expensive and they are brittle ( you don't want to force it or bind it) but it drilled it with ease. Beautiful pen.
 
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