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Author Topic: Big ultrasonic drilled holes  (Read 850 times)

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lithicbeads

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Big ultrasonic drilled holes
« on: July 28, 2018, 09:04:32 PM »

A few of you folks know I am a stone bead maker but few know about the thousands of hours of my life I have spent in front of an ultrasonic drill making bead holes. ultrasonic "drill" is a bit of a misnomer as the machine cuts the hole using a very high frequency small amplitude up and down motion using very hard fine (220) silicon carbide grit in a hammering action. The correct mix of grit , water and the proper hand motions , a bit up and down to wash out the spent grit and ground up stone and a small bit of rotation to maintain hole symmetry vary by type of stone drilled , how deep you are in the hole and how much the bit has worn.Practice makes the motions and choices second nature but recently I have decided to makes huge beads with 10mm holes , a far cry from the 4mm biggest holes of the past. the hole cores are big enough to drill out themselves with a 2.5 mm bit for smaller beads.I practiced with a slab of relatively soft limestone to practice various strategies and then drilled some jade,jasper and grossular garnet. My drilling efficiency improved dramatically after this practice. Eventually these big holes will be drilled in the same mindless intuitive manner that has served me so well over the years. If you look closely at the drill cores picture you will see some square glass cores as I am practicing making square holes again as well.Bead on!!!
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bobby1

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Re: Big ultrasonic drilled holes
« Reply #1 on: July 29, 2018, 01:13:29 AM »

Our club recently bought a drill for the Modesto Junior College lapidary shop. I have been practicing with it so I can show others how to do it. As per your advice I have turned down the power on new bit in order to not break the bits off at the tip of the horn. It has helped me get faster hole drilling but I find as the bit gets shorter the speed slows down a lot. Also, I find the bit gets jammed in the hole frequently and the unit stops vibrating. Is there a cure for this? I notice you move the bit up and down frequently as well as rotating it. I will try this procedure.
Where do you get your bits from especially the very large and square ones?
Any other helpful tips?
Bob
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bobby1

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Re: Big ultrasonic drilled holes
« Reply #2 on: July 29, 2018, 01:14:55 AM »

We got our unit from Highland Park and they recommend 500 grit for the machine. Is 220 better?
Bob
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55fossil

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Re: Big ultrasonic drilled holes
« Reply #3 on: July 29, 2018, 06:37:21 AM »

    looks interesting, very good holes too.  Could you show what a bit looks like?
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hummingbirdstones

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Re: Big ultrasonic drilled holes
« Reply #4 on: July 29, 2018, 07:53:24 AM »

That is so very cool.  Thanks for showing us, Frank.  Please post some of your big beads when you are done with them.  I miss seeing pics of your beads.  Pics of the square holes would be interesting to see, too.

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Robin

lithicbeads

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Re: Big ultrasonic drilled holes
« Reply #5 on: July 29, 2018, 09:16:36 AM »

 As the bit shortens you usually need to up the frequency  and as the bit gets deeper in the hole you usually need to increase the frequency.My machine is quite powerful so it will use bigger bits than most.The overall mass of the bit is the limiting factor. I used 90 grit for over 20 years but Imahashi now says to use 220.It works quite well making for  a very smooth hole. 500 sounds very fine to me but they probably have had best luck with that grit. Every machine is quite different.The best way to make square holes and keep the mass of the bit down is to get brass L shaped rod at the hardware store. Cut a short(possibly very short) piece and solder it to the horn. If it wont vibrate take the horn off and grind the bit down with a smooth diamond hard wheel. If you can get it to vibrate and still be a useful length drill through your preform or slab then rotate the rock so you cut the other half of the square.Square brass stock can be used but it takes a powerful machine to use it .I do both and find the L system makes a better hole as the brass stock is less likely to deform while cutting it to length.I will post a bits picture later.
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