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Discussion Starter · #1 ·
So, I FINALLY found a place to buy cheap 1/4" acrylic (which I don't know the difference between it and lexan, but I'm assuming they're relatively similar) for the plate for my 3 axis skull!

My question is about tapping for the screws. Is it completely necessary to tap for the screws that will attach the plate to the skull? Has anyone NOT tapped and had success? I just don't want to have to run to Harbor Freight and grab a tap set if I don't think I'll ever use it besides right now. If anyone sells cheap pre-drilled Lindberg plates, let me know!

Also, if someone's already done the work of compiling a parts list for the Lindberg 3 axis, that'd be nice. Thanks, guys!
 

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I had bought a tap for mine when i did it, but it snapped halfway though, i didnt want to buy another so i used a screw to tap the rest, i had good results, going in a tiny bit, backing out and going in agian, it kept the screw from heating up and sezing up in the plate.
You can but just the 4-40 tap at a hardware store and and the holder so you dont have to buy an entire set, you can also pick up the entire set on ebay for about 10-15 dollars (not a great set but it gets the job done, mine only snapped because i didnt have any oil to keep it cool and friction free.)
 

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When you tap plastic it is really inportant to only turn the tap about 1.5 turns and then back it out and repeat the process going in another 1.5 turns. This backing out process cleans what you have cut off the threads and keeps the tap from binding up. Also, realize you will have to drill deeper than you want to tap. The tap will not create threads all the way to the bottom. Hope this helps. Keith
 

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Discussion Starter · #4 ·
Interesting... you learn a little more each day. So, joshua, it sounds like tapping it with a regular screw works - just that I need to do it really slowly and back it out, clean out the threads, then do it again. I guess I could give it a shot on some scrap plastic... :)
 

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When you tap a hole make sure to use a cutting oil or lube also. the oil helps A LOT. You might be able to use a sheet metal screw, they do not need tapped threads. There is a self tapping screw that is made to cut the threads as it goes in, but most of them have a large hex head that is hard to hide.
The advantage to threading the hole is the threads stay and you can disassemble it and reassemble it often, a sheet metal screw is meant to go in and stay. Also, a better quality tap is a good invenstment.

As before, slow and easy, back it out, clean out the hole, then back in, little more oil each time.
 

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Wild Fandango
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Acrylic is brittle and can crack or shatter, Lexan is polycarbonate and is called "unbreakable". It will bend under stress rather than splintering like Acrylic. Of course you can break it if you try hard enough but it's definitely much tougher than acrylic sheets.
 

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Discussion Starter · #7 ·
So, Xane, do you know anywhere that sells 1/4" polycarbonate? I haven't been able to find anywhere cheap. I'd prefer local so I don't have to deal with shipping.
 

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Wild Fandango
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In my area I know sign shops, boat hull and interior remodeling shops, and straight-up "plastics" shops sell acrylic and polycarbonate by the rod and sheet. Sign shops may not be quite as willing to tell you where they get their supplies if they don't get it themselves, though if you explain what you're looking for they may be more likely to talk. You'll just have to call around in your area and see if someone is either selling or can tell you where to find it. If you're lucky they may have scrap pieces that were damaged or from unpaid projects they'll be willing to sell cheaper or for free.

Or here:

http://www.usplastic.com/catalog/default.aspx?catid=704&parentcatid=795

Both the 9034 and Makrolon are sold in 12" x 12" x 1/4" sheets. The Makrolon is UV resistant to be tougher and is about $2 more than the $8.33 9034.

If you already have the acrylic and aren't planning on using the skull as a football just be gentle with it when tapping. I tend to rush things so I have a bad habit of shattering acrylic whenever I try to work with it. Polycarb is harder to cut but also harder to accidentally snap the wrong way and stab you if your score line isn't deep enough.
 

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Discussion Starter · #9 ·
Sweet! Okay, well, that's a lot of good information. Thank you everyone for your help!
 

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Obssessed Haunter
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I happen to have a couple lexan plates already cut for a Lindberg skull. The holes arent drilled but the plates are cut into shape. Let me double check that they fit properly... if so I could possibly send you one of them. I am not planning on making another 3 axis skull so I thought about just throwing them away.

PM me if interested.
 

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Bucky Brain Surgeon
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We tap everything on the plate 4/40. I makes disassembly and reassembly much easier and faster than using nuts and bolts. For the holes through the skull I drill them slightly larger than 3/32 so that the 4/40 bolt has a little play. This makes it easier to line up the threads when securing the plate into the skull. Early on we used some small self tapping wood screws but these tended to split the plastic plate with repeated use. I recommend tapping. I'd also recommend getting some 4/40 tap kits at a place like Osh. They come with a 3/32 drill bit and a 4/40 tap.
 
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