Cutting polycarbonate blanks to size

[grooveguy]

I'm really blown away by the techniques that fredbissnette and others use for turning-out blank discs. Their methods make the process look awfully simple and fast. "Hey, I can do that," I told myself, so here is my marginally-successful means of making blank records, and the problems I ran into.

The guys who are doing this successfully seem to be using a band saw, with some sort of jig to hold the disc in place for cutting. That's how I approached this, too, but I don't have a band saw. After this exercise, however, I think I'm going to invest in one. A band saw is a very handy tool to have around the shop.

First, here's a sort-of photo illustration of the steps I took to bang-out a blank. A description for each "slide" in the slideshow is below.

Composite.jpg

1. Starting with a 12" square of Lexan off eBay or Amazon, find the center by drawing intersecting corner-to-corner lines.
2. Drill the center hole. A 'step drill' makes a clean hole in this material, and a piece of masking tape above the 9/32" step shows where to stop with the drill.
3. Using a home-made compass (more about this later), index the center hole and draw a circle 11-3/4" in diameter. This is the RIAA-specified diameter for a 12" record.
4. Rough-out the circle with aircraft snips, which are great for making any cut that is other than a straight line. Cut outside the line by a 16th or so.
5. Using a special jig that attaches to the belt sander table, pop-on the cutout and slowly turn it to create a nice edge. Well, almost nice.
6. Use a deburring tool to knock off the 'smear' on the back of the disc. The belt sander leaves this, a band saw shouldn't.

This gives you a pretty good blank, although deburring it adds a hands-on step that sort of defeats the hoped-for simplicity. That's one drawback to this method, but there's another.

Here's a closeup of the compass I made specifically for marking the outline circle. It has a stubby 9/32" rod sticking out the back to engage the center hole. The marker is the cut-off end of a ballpoint pen filler.

7 Compass Close-Up.jpg

But note my hand after making one disc, and the other hand is just as bad. This grinding process creates a LOT of polycarbonate dust. Actually, 'sand' is a better descriptor. And the worst part is that everything is charged with static electricity. It's virtually impossible to wipe or brush off all this grit that's clinging to the blank. Thank goodness the protector sheets are still on the two faces of the disc; I'm going to have to find some way to discharge the static and get these discs cleaned up before I strip them and try to record.

Yes, a band saw or perhaps some sort of rotary shear is called for here.

[grooveguy]

Woops, typo in that; OD of disc is 11-7/8.

[fredbissnette]

i got a ryobi band saw on sale for 165cdn and i use a 14tpi blade

if i get any burring i just put a sanding drum on my drill press(i got this used too uber cheap)

i can cut a disc in about 25 seconds and if i need to smooth the edges its about 10 seconds on the sanding drum

cheers

9/32 basic bit to cut center holes

[grooveguy]

Fred, you're an inspiration to us all. If you can bang-out a blank in 25 seconds, you ought to make a video tutorial for those of us who must be missing something. Perhaps 14 tpi is the secret. I'd be inclined to use a finer blade, but maybe that just generates heat as it cuts, instead of knocking out 'chunks' to give an actually-smoother edge. I've noticed that my belt-sanded blank shows a bit of warp, which again might be from heating it as it grinds.

There are some cheap rotary shear type of cutters on eBay that will take sheet iron up to about 1/16". Any idea whether something like this might have application, and whether it would cut a circle if the center of the disc is maintained at a fixed distance?:

Snap2.jpg

Thanks for the tips!

[fredbissnette]

https://www.youtube.com/watch?v=95n3TqEck50

[grooveguy]

Very good, Fred; it doesn't look as if you get nearly the amount of Lexan 'sand' that I do grinding. Your other videos show good results with your recordings, too. What's your stylus, and what groove pitch do you generally use for these?

[fredbissnette]

i have no idea what my lpi is i have two gears one makes a microgroove and one a 12'' disco type groove

im using tungsten

one of my latest
https://www.mediafire.com/?navx345yajc3lit

[ROLANDJAYS]

I use to do it similar to these ways . now i just my big honking machine

[fredbissnette]

jealousy

[grooveguy]

Now, THAT machine looks like more than a polycarbonate blank cutter. It ought to cut the blank, add the grooves, and wrap for shipping. Probably makes coffee too.

[fredbissnette]

i have been cutting my own blanks a while now and i have found a 24 tpi blade works well
im using a tungsten needle and i have no idea what pitch im at but it works
i get 11 min per side at 45 rpm on a 12''

https://www.instagram.com/p/BUIPiy_j13E/?taken-by=madstyluspressure&hl=en

[Fela Borbone]

Instead a pencil, a cutter blade. Not fast as Fred's but I have no rooom for big machines!
You can cut a pile of labels too.

[grooveguy]

Both you guys are doing great with this blank-cutting business. I think maybe I'm trying too hard, need to be more laid-back and basic instead. Fela, what blade do you use, and how many passes (revolutions) do you have to make to cut all the way through? And what's the poly thickness and how had do you bear-down? Thanks!

[Fela Borbone]

Band saw is the best, I think. My method is a second choice. I Use x-acto blade. Great for 0.7 mm. thicknes, for 1.5 make some turns one side, and then flip the plastic. No need for sanding.

[grooveguy]

Thanks, Fela. Your 0.7mm material is fairly thin; .028 inches by my calculation. I'd been working with much thicker material, .060 in., which is your 1.5mm. I think a saw is the best way to go for the thicker stuff, but when I used my belt sander to clean up the edges I had polycarbonate dust everywhere, and it clings to everything, too. (It got all over my wife's car; I thought she was going to kill me.)

Not long ago I replaced the plastic 'lenses' below the strip lighting fixtures in the kitchen. The local DIY store had the textured material in sheets about 0.75m X 1m, a bit too big to fit the frames. They also sold a cutter, nothing more than a high-carbon steel knife, that did a pretty good job of trimming these pieces down to size.

Snap2.jpg

Snap3.jpg

I don't know what the plastic lens material is; not polycarbonate because it yellows with age, maybe just acrylic/styrene plastic. About 1.5mm think, I would say. By bearing-down hard, you can make a quite clean cut, scoring over and over maybe 10 times. It's not easy, but it is a clean operation. I wonder how a red-hot piece of nichrome wire would cut this stuff. The trouble is a 'horn' at the edge that still needs to be ground or sliced off. Cutting rollers would be ideal. Maybe I'll invest in one of those eBay roller cutters pictured in my Mar. 6 posting to the thread.

Here's a question that came to mind, thinking about thin material to record on. Do you guys use a turntable mat with any 'give' to it, like cork or rubber, or is it best to emboss against a hard surface? The thin material. especially, might need a solid backing.

[Fela Borbone]

15 seconds!


https://youtu.be/j0EOLmj36oQ

[Soulbear]

15 seconds!


https://youtu.be/j0EOLmj36oQ

Rápido!!!! Te He!!
Soulbear

[fredbissnette]

i like the saw because i have to cut 100 or more at a time and i can get that done in an hour or so with the saw and a jig