riggler

Acrylic spheres - motivation!
« on: November 02, 2012, 03:46:28 PM »
I gotta get rollin with this M50 mic idea. So I finally made the spheres!
I learned you need to make a good jig, cut slow, and you need to keep it cool.

I am going to make another set since now I know what I am doing.

I am going to fill in that extra gap around the capsule by cutting a ring from a balloon.
(My forstner bit is 1mm oversize!)

CHEERS!!
Why does it happen? Because it happens - Roll the bones...


Gus

Re: Acrylic spheres - motivation!
« Reply #1 on: November 02, 2012, 07:53:36 PM »
Are you using a round nose cutting tool?

I sometimes use water as a coolant when machining Plexiglas


JohnRoberts

Re: Acrylic spheres - motivation!
« Reply #2 on: November 02, 2012, 08:26:26 PM »
many moons ago when I worked in a machine shop (summer job) I once machined a steel ball joint on a lathe. Both the ball and the socket, were machined with a tool post that rotated on a pivot, so all manual feed, but simple and it worked as long as you go slow.

To make that part on a lathe, first I'd machine the round ball, then cut out the middle cylinder cavity, separating the ball from the stem.   

Actually nowadays it looks like a candidate for digital printing.

JR
Don't only half-ass tune your drums. Visit https://circularscience.com to hear what properly "cleared" drums sound like.

riggler

Re: Acrylic spheres - motivation!
« Reply #3 on: November 02, 2012, 08:59:00 PM »
Hi Gus and John,

I bought the spheres.

I figured out the most important thing was getting the jig right.
Placed one board on top of the other. Screwed them together temporarily with wood screws.

Marked a 3" square. And marked a center point for that square. Drilled 1/4" hole through both boards on each corner.

Drilled countersink holes into bottom board to clear carriage bolt heads.
Inserted carriage bolts. Knock them into place with hammer a bit.

Turn the whole mess upside down and position on drill press table.
So, now the threads of the carriage bolts are pointing up.

Line up 1.25" Forstner bit on center point on board. Clamp BOTTOM board (which is longer than the top one) down to table of press.

Put washers and wing nuts on the carriage bolts and tighten. Remove the temporary wood screws that held the boards together.

Now drill big hole through the first board and a good bit into the bottom board. You could go all the through I guess...

DON'T even think about removing the jig from the table!

Loosen the nuts, pull up top board, plop in the sphere. Tighten the nuts evenly!

Then I drilled a #29 hole, learned (at the end) to use a water / baking soda mix as a cutting lubricant. Then I rotated the piece 90 degrees and drilled another #29 hole. I got a perfect 90 degree rotation by running a rod through the first hole, which let me visually place it square. No need to ever mark the sphere!

Then drilled with forester bit the capsule recess.

Gonna try it again for a cleaner outcome hopefully. But it's DIY so whatever...
Why does it happen? Because it happens - Roll the bones...

Gus

Re: Acrylic spheres - motivation!
« Reply #4 on: November 03, 2012, 10:21:47 AM »
I would make a piece that fits in the top hole with a center mark on it.  This can help to center the holder if you remove it from your drill press.  Make sure the holder is clamped tight to the drill press table plastic can "Grab" a bit

Drills for plastic, here is a link http://www.plasticsmag.com/features.asp?fIssue=Sep/Oct-01

Be careful not to overheat the plastic when drilling Search for the MSDS of the plastic you are using.  Plastic can release bad stuff when overheated.  I Google etc the material I a need to machine with  "machining "the material" dangers"
here is a linkhttp://www.sawmillcreek.org/showthread.php?80652-Acrylic-fumes-safety-MSDS


« Last Edit: November 03, 2012, 12:19:41 PM by Gus »

sahib

Re: Acrylic spheres - motivation!
« Reply #5 on: November 03, 2012, 06:17:06 PM »
For cutting large holes onto plastic  I would use either a core cutter (hole saw) or an end mill.  And go very slowly. Lubrication is a must. Anyhow, it seems you've done good job of it. Congrats.

riggler

Re: Acrylic spheres - motivation!
« Reply #6 on: November 04, 2012, 09:02:04 PM »
GUS, good idea!

Yes, that sucker did smell terrible before I started lubricating with water/baking soda. I don't always have access to an end mill, but I do always have access to a drill press. So that's what I made these on.

I made initial prototypes on a 3D printer, but since I could not verify the electrical properties of that material, and also because the acrylic is transparent, I went with that as my plan.
Why does it happen? Because it happens - Roll the bones...

leswatts

Re: Acrylic spheres - motivation!
« Reply #7 on: December 12, 2012, 11:28:37 AM »
Acrylic machines horribly. Have to use it sometimes though. Whenever possible I use delrin (acetal). It mills, saws, turns,
and drills beautifully. Many of my microphone parts are made from it. Not transparent though.

Les

zayance

Re: Acrylic spheres - motivation!
« Reply #8 on: December 12, 2012, 12:24:43 PM »
Acrylic machines horribly. Have to use it sometimes though. Whenever possible I use delrin (acetal). It mills, saws, turns,
and drills beautifully. Many of my microphone parts are made from it. Not transparent though.

Les


+1

Marik

Re: Acrylic spheres - motivation!
« Reply #9 on: December 12, 2012, 06:00:12 PM »
Acrylic machines horribly. Have to use it sometimes though. Whenever possible I use delrin (acetal). It mills, saws, turns, and drills beautifully.

The only problem is you cannot glue it.

Best, M
Samar Audio & Microphone Design

www.samaraudiodesign.com

The Art of Ribbon Microphones


Gus

Re: Acrylic spheres - motivation!
« Reply #10 on: December 12, 2012, 06:51:34 PM »
Delrin can out-gas  formaldehyde when heated the white seems to worse that the black when machining it.

http://www.practicalmachinist.com/vb/cnc-machining/machining-delrin-173503/

http://www.eng-tips.com/viewthread.cfm?qid=246808

http://www.ifa.hawaii.edu/instr-shop/MSDS/Delrin.pdf

As I posted before I look up a MSDS and dangers of machining any material I need to machine.

riggler

Re: Acrylic spheres - motivation!
« Reply #11 on: December 12, 2012, 11:05:32 PM »
I found that using a lot of the baking soda / water mixture kept it cool, and I had zero problems. In fact, it didn't really smell either.
Delrin I suspect has the best insulating properties of them all.

On a side note, I was contemplating drilling spheres from wood, then cutting  an epoxy mix with alcohol so it is very fluid, almost water. Then paint the cut part with it and let dry, to help harden and stabilize the wood from moisture absorption.

Not sure if it would work, but have done similar things for model airplanes.

Gus, this practical machinist site is wonderful! Wow, so much good information here.
Why does it happen? Because it happens - Roll the bones...

leswatts

Re: Acrylic spheres - motivation!
« Reply #12 on: December 13, 2012, 06:45:08 AM »
Delrin can be glued if plasma treated. We usually don't though. We have a hand held little tesla coil designed for that.

It can outgas at high temperatures. Common grades of homopolymer and copolymer are stabilised though. I notice no smell
at all in normal machining. Nothing.

One thing...it doesn't like chlorine . There have been law suits from acetal plumbing failing just from the chlorine in tap water.

It's an excellent engineering polymer with very good mechanical and electrical properties though. Machine some and you'll ask yourself
why you shouldn't use it for everything! It's not for everything though of course.

Les
L M Watts Technology

sahib

Re: Acrylic spheres - motivation!
« Reply #13 on: December 13, 2012, 11:52:31 AM »
+ 1 on acetal. No such smell during machining either. Machines beautifully.

Most machine shops who normally work with metal do not know how to work with plastic properly.  Few times I subcontracted out my parts to outside machine shops. When I went to collect the parts they had a shock to discover that the sizes were all over the place.  Sticking the material into a CNC and running all the operations in one go do not work for plastic. Acrylic is worse.

We normally do the rough machining and then leave the parts for a day  to settle down. Then go back and do the finishing. For very ciritical parts we would even do it in three stages.


 

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