Stacking plastic

[coach]

I got a request to cut circles from some form of plastic. The outer ring is 2" inner ring is 1"
the material is 60" x 48" I figured about 400 parts per sheet.
The customer told me a guy used to clamp them and cut 10 sheets at a time.
Am I getting smoke puffed up my shorts?
I was told he clamped them. How could you clamp something that used every square inch of material?
Any ideas guys?

[navigator7]

I'm visualizing a fixture full of .99" dowels.
Maybe wood or UHMW...cept that stuff ain't round.
After your 10 plastic sheets have a 1" hole machined, remove the sheets, install the fixture, add the plastic over the fixture dowels. Every third dowel or so could support a screw and washer.

My thoughts lean towards building a mold and casting the parts.

I don't know what your specs are on the plastic but it sounds like you are making a lot.
Talk to George at Farwest Materials:
http://www.farwestmaterials.com/joomla/index.php?option=com_docman&Itemid=53

Smoothon has plastics that will knock your socks off and you have the perfect machine to make molds or to make molds of molds.
http://www.smooth-on.com/Urethane-Plastic-a/c5_1120_1156/index.html

The killer thing about doing a mold...is you can purchase a starter kit, make a small prototype mold, proof your product with the customer and keep your machine free for other stuff.

Waaaay less scrap and waste.

[gene]

seems to me when you cut the first stack parts are going to be flying everywhere. What happened to the other guy? cut samples FIRST then prociede with caution, plastic is a funny material to work with

[rb99]

Only way I could see stacking is completely covering the sheets with 2 sided tape...but the cost and time to do so would be way more than just doing one sheet at a time.

How long can it take to cut one sheet? Have you run a test file through to get a time?

RIB

[dana_swift]

Chuck- that idea is really good.. using 0.99 dowels. I can imagine cutting a male "hold it" fixture with the bot. 0.99 would be no trick at all, and it would hold the material nicely. It could also use a high-vacuum system with all-star adhesive tape and no parts would go anywhere.

Also thanks for the links to the mold able plastic vendors. Info like that comes in handy so often that even though I have no use for it now, I love reading the forum.

Such a wealth of techniques!

D

[navigator7]

Dana,
More thinking along these lines....
.99 dowels formed on the bot would be cool but I was considering the law of unintended consequences.
Supposing the perforated plastic goes on easy but the collection of chips prevents easy removal effectively locking your plastic to the table?

Another idea might be fabricating a "Met-Wrench" shape for the dowels. Yeah the chips could get in but you could blow them out too.

An blow gun might help removing the panels too.

Also.....when you cut the washers loose, if they spin, I think you will have scrap. Something on top of the dowels has to hold the stack of washers securely.

What application does your customer have for so many washers?

[oddcoach]

you could get a tool made that would machine te center away and cut the outside at the same time.

5009
you could even make the center out of a forstner bit
this makes it a drilling operation and not a profile or pocket you would do 1 sheet at a time but in a fraction of the time. then a simple vacuum fixture would do the hold down. you could even put some foam in the tool where it is not cutting to help with the parts flying

[widgetworks_unlimited]

I've done something similar to Chuck's idea and it has worked well for holding small parts (single layer). I bet it will work well for multiple layers.

Instead of doing a fixture with protruding dowels/washers, I'd cut a bunch of "mushrooms" with .99" diameter stems. Push the mushrooms through the holes in your stack of plastic and secure to your spoilboard with a screw through the center.

Because the mushrooms can be installed/removed individually, they should be less likely to bind. I'd size the mushroom heads to closely match your OD - which may help with vibration and/or thin materials lifting.

I make most of my clamping fixtures for small parts out of MDF. I've found that you get a lot better grip on your parts if you cover the pressure points on the clamping surface with a layer of Gorilla Tape. Could help to add this on the underside of the mushroom caps.

[coach]

I quoted 15 cents each. They wanted 10 cents. The parts would take about 80 minutes a sheet. Not to mention clean up and part handling. about 400 parts per sheet.
Parts were small and probably need tabs too.
I don't mind working less than shop rate but not that far below.
Thanks for the great input.
There are some sharp guys around here.

[gabepari]

I missed how thick the parts are, but the following assumes .060" thru 1/4" thick acrylic (cast, extruded, polycarb, etc.) I would have quoted somewhere between 25 and 35 cents, depending on how many sheets and whether I liked the guy or not. I could cut those in about 20-25 minutes per sheet, plus 3-4 minutes to clean the table and change sheets. I cut stuff like this all the time and I'm told that I'm about 1/2 of what other guys charge. One sheet at a time is the way to go, I use a 15hp vacuum and some magic sauce that will hold those down without tabs. No need to make any fancy fixtures, just suck baby suck!

10 cents would be a "good guy" rate. Tell 'em to walk unless it's an ongoing project and you can get some low dollar help to run the bot during slow times. Shove the job to the back burner for higher priority/paying jobs. Just tell them "Cheap, Good, Fast..... Choose two"

Good Luck,

Gabe Pari
www.socalteardrops.com (http://www.socalteardrops.com)

[rb99]

How much would the bit cost? At 10 cents each it would take 500 units to pay for a $50 bit. Then there is the other stuff like power for the Bot and vacuum...

Pretty low margins.

RIB