[CTOPS]

Does anyone have a recommendation for what type of clear plastic sheet material would be best for some sign boards I'm working on? These pieces average 36" X 60" with up to 300 5mm dia holes drilled in them.


The prototypes I've made have been fabricated using 1/8" plexiglass from one of the big box home improvement stores but the durability just isn't there. Too much spider cracking around the holes over time due to flexing of the material.

Any suggestions for material type and/or suppliers would be appreciated

Thanks!!

[trevis1st]

Are the holes where the spider cracking a mounting point? If so then is there a bushing of some sort to allow the acrylic not to bind? For something that size I would go with 1/4 or thicker material. Does the sheet need to be translucent or completely clear?

[CTOPS]

The design requires the use of clear material. The sheet floats within a grooved framework so there is no load from mounting screws etc.

The holes are for a plastic hangar bracket that is used to display sample chips. The hangar utilizes two holes spaced 1" apart and is unfortunatley designed for 1/8" thick material

[trevis1st]

How is it cleaned? I'm guessing the sample chips aren't very heavy. And the hanger bracket is fused or glued in place. Also how is it being fabricated? Flame polishing, lubrication? I had a customer come in with a 3/8 piece that had spider cracked around a hole. Turns out the lubricant he added was eating the acrylic. Cast acrylic would be more stable also. Sorry for the 20 questions

[CTOPS]

Thanks for your help!!

The piece is fabricated on our cnc router. The holes are peck drilled using an Onsrud drill designed for plastic (6000 RPM @ 50 IPM). No coolant or mist is being used during fabrication.

As for cleaning, we are using windex type cleaners to wipe off any dust. The hangar itself utilizes a pin and hook arrangement on the backside that clips into the two 1" spaced holes. No glue or adhesive is used for mounting. The front side has a 1-1/2" long X 1/8" dia rod that projects out for printed sample color chips to hang from

[trevis1st]

The Windex type cleaners can cause the spider cracking. Mild hand dish washing detergent and water is usually the best thing to use. Also a microfiber cloth. Another cleaning idea might be a lent roller. I use sign transfer tape to clean off dirt and dust from acrylics and polycarbonates.

[RomanLini]

I second that not using Windex or any window cleaner on acrylic! In most cases water and a soft paper towel works well, or the tinyest drop of detergent.

Another thing to try would be flame sealing the holes, as the drilling leaves microcracks in the material that will worsen over time and flexing. (Check with a micrscope).

Cyanoacrylic glue (like super-glue, crazy-glue etc) also do a good job of sealing the microcracks and you can paint that on before the product goes into use.

You could also get some cheap rubber or silicone grommets that will press in to the 1/8" acrylic and support the holes, reduce load, and even cover up cracks a bit once they start.

[RSTYLR]

Consider using polycarbonate or on of the new poly/acyrlic hybrids (sorry, can't remember the name). We buy from AIN & use the hybrids for store fixtures, brochyure holders & displays with good success.

[Flateric]

If you choose to flame polish/seal the holes try to allow the plastic to cool as slowly as possible. This will help greatly in resisting crazing (spider cracks). Cooling can be slowed by placing a non-synthetic (so it will not melt itself of course) type of cloth over the heated part immediately after heat.

Being sure to use the sharpest tools available to you generally help in most milling situations or machining of any kind also seems to lead to less crazing.