The Hourglass

JimDawson

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My son was tasked with building the hourglass for the Wicked Witch of the West castle scene for my granddaughter’s drama class production of the Wizard of Oz. The drama instructor deemed unacceptable, the first rendition of the hourglass made from two 2-liter soda bottles . This is a high school production BTW; not a Hollywood production, but the drama instructor wants what SHE wants.
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I can’t decide if this is the drama instructor or the Witch.
:dunno:


So on to plan B…..

My son found some wine bottles that had about the right shape when stacked neck to neck, but the necks are about 2 inches too long, so the problem is how to cut the bottles down to size and get them exactly correct.

Here is what we came up with:

We have a milling machine, and it's just glass, right.
:thinking: First mount the MDF backing plate on the mill

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Mill a pocket 0.125 deep to locate the bottle base. Vacuum up the MDF dust as it’s cutting

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Pocketing the hole for the plywood bottle hold down. This one had to manually vacuumed because of the next operation. Just a couple of deck screws securing the plywood to the MDF base for this operation. 20 IPM, 0.25 DOC, and 3500 RPM. Straight flute, ½ inch carbide router bit.
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Plunge milling the mounting holes 1 ½ inches deep, using the router bit. The vacuum head would not clear for this operation.

I had already set Y-axis to zero on the center of the T-slot, so no danger of milling into the table.
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The completed bottle holding fixture
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To get tool clearance we had to shorten the bottle neck a bit, so we scored the neck about ¼ inch long with a diamond wheel in the Dremel, and just popped it with a steel rod to knock it off.
We got lucky, it didn’t shatter and broke about where it was suppose to. :phew: The real challenge was trying to figure out where the center was in a out of round bottle neck.
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The HF air die grinder mounted in the endmill holder.http://www.hobby-machinist.com/show...ill-Spindle?highlight=50,000+rpm+mill+spindleThe diamond is the 5 for $5 HF wheels. It worked great, as well as the $17 Dremel wheels.



The blast shield, ¼ inch Lexan.
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We ran a profile routine to make the cut, using a 0.004 stepover. The tool was never working hard, and the wheel was like new after cutting two bottles. Feed was 10 IPM, and the wheel was spinning at maybe 30,000 RPM or so. At about 90% through the cut, the piece popped off and we let it finish to polish the top, and take off a couple of high spots. Mist coolant is WD-40. This also kept it wet so there was no glass dust flying around. It took about 20 minutes to make the cut.

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Setting up to do the bottle pocket in the top and bottom base. I love my laser edge/center finder for non-critical work. It’s good to +/- a couple of thou.

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Just to illustrate the hold down for this operation. A deck screw in each side ‘’clamp’’ is enough to hold the part.
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Pocketing 1/8 deep for the bottle base. 20 IPM, 0.125 DOC, 3500 RPM, 0.200 stepover

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Turning the acrylic plug to go between the bottles. This will be siliconed in place on final assembly. There is a tapered hole through the center for that sand to run through. This will be a fully functional hourglass, complete with Wizard of Oz red sand. I haven’t heard yet what the time specification is so we made the hole a bit small, and can adjust it later.

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The plug installed. And yes, the necks have different ID’s so that step is not the camera angle.

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Stacked bottles, about 15 inches high

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And the finished product, almost. Still needs a little paint

Photo Nov 09, 5 52 48 PM.jpg

Photo Nov 09, 5 52 48 PM.jpg wwotw.jpg IMG_0396.jpg IMG_0397.jpg IMG_0398.jpg IMG_0400.jpg IMG_0401.jpg IMG_0405.jpg IMG_0403.jpg IMG_0407.jpg IMG_0415.jpg IMG_0416.jpg IMG_0417.jpg IMG_0421.jpg IMG_0424.jpg IMG_0412.jpg
 
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nice work Jim,
Bit overboard for a school production though. The PET bottles would have been fine.

cheers Phil
 
nice work Jim,
Bit overboard for a school production though. The PET bottles would have been fine.

cheers Phil

YOU tell that to the drama instructor. She's the one with the green face :rofl:
 
YOU tell that to the drama instructor. She's the one with the green face :rofl:
You can bet I would have! She was waaaay out of line. Should make it herself if she didn't like the original. Maybe she had some idea of what his dad could do?
 
Very nice work!

Just send the Wicked Witch the bill for all of the machining at $200 an hour, sit back, and watch the fireworks.
 
Or constantly remind her of who owns the hourglass.

When it is not returned after the performance, have some fun with the local law enforcement searching her home and car for it.
 
Or constantly remind her of who owns the hourglass.

When it is not returned after the performance, have some fun with the local law enforcement searching her home and car for it.


I love it. Maybe at the very least I can get comped a couple of tickets to the performance. That should make my time worth about 50 cents / hour.
 
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I think you're being a little selfish. You should have ran out to the shop, built a kiln, melted glass, and blew an hourglass for her.


Beautiful job.
 
Re: The Hourglass UPDATE

UPDATE: My son sent me a note that the drama teacher loved the new design. :victory:
 
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