CNC / machining shop

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boep777
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CNC / machining shop

Post by boep777 » Mon Jun 13, 2016 6:46 pm

Hi, can somebody recommend CNC or regular machining shop for fabrication of high precision (0.1 mm) but very simple items from solid plastic, something like in the image below ? Dimensions are 16x6x0.5 inches. Thanks!
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sthone
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Re: CNC / machining shop

Post by sthone » Mon Jun 13, 2016 6:54 pm

If you're looking for something online you can try - http://www.emachineshop.com/ or http://www.protolabs.com/‎ They both do online quoting.
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ednisley
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Re: CNC / machining shop

Post by ednisley » Mon Jun 13, 2016 7:49 pm

boep777 wrote:fabrication of high precision (0.1 mm)
Remember that it's very hard to machine perfectly square inside corners, like those in the recess: you must generally allow for the radius of the milling cutter in each corner. If you really need absolutely square inside corners, that could get expensive.

If the thickness and flatness tolerances really are 0.1 mm, then you (probably) must machine the surfaces of a stress-relieved cast plastic slab, rather than using cheap as-extruded sheets, and anneal the part during / after machining. That surely depends on the plastic you want to use, too.

A 16 inch length of polycarbonate will expand / contract by 0.1 mm when the temperature changes by 4 °C, so you're looking at controlled-temperature machining. You must also specify the temperature at which the dimensions will be valid; the parts will fail inspection if the shop is much hotter or colder than your office.

It'll probably require a pocket fixture to maintain alignment when it's flipped over for the bottom features. I'd be tempted to use the existing holes for alignment pins, but, over that much length, two holes in one end won't hold the tolerance you want at the other end.

The tolerances seem tight for the overall dimensions and material. I'm sure you can get what you ask for, but be sure that's what you really need!

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