Polishing a plastic sliding hatch

[peaman]

Before I reinstall my sea hood, I'd like to remove some light scratches from the smoked Lexan (?) sliding hatch. I have some Shurhold Buff Magic Compound that I used with a buffer on the hull, and that seemed to work okay on a test patch on the hatch, but I wonder if others could recommend a better product or method for polishing the hatch?

 

[Loren Beach]

Just do not buff too hard or too 'hot'. Your slider is most likely acrylic. It should look a lot better/clearer after having the surface restored.

 

[peaman]

So I had very light scratches across the entire surface, plus a few heavier scratches. The Buff Magic compound worked well for the light scratches, but seemed to make the heavier ones more noticeable, so I decided to get more aggressive. Wet sanding with 1000 grit wet-or-dry paper, worked pretty well for eliminating or minimizing the deeper defects. Following that with 1500 grit wet to remove swirl marks from the first step left a uniform haze on the plastic. Next, I used a rubbing compound from an auto parts department, applied with my MaxShine M8SV2 buffer at the minimum speed setting. And finally, I brought the finish to like-new with the Shurhold Buff Magic. Not counting the testing to figure out the right procedure, the whole effort took maybe 90 minutes, and the hatch looks great.

I bought the buffer (MaxShine M8SV2) last fall based on a recommendation from another boater, and I recommend it for anyone who needs a buffer. It has replaced a buffer I bought previously which was too heavy and too much to handle with its 7" wheel. This one is very comfortable and efficient.

 

[Afrakes]

I worked with casting acrylic plastics forty years ago. After the final polishing, the castings were annealed to relieve the surface stress and prevent crazing.

 

[Prairie Schooner]

I worked with casting acrylic plastics forty years ago. After the final polishing, the castings were annealed to relieve the surface stress and prevent crazing.

Huh. I've messed around with acrylics here and there for over forty years and didn't know about this. I'm self-taught, definitely not a pro. In the web searches I did this afternoon I didn't come across a good explanation of the science, though it's certainly a thing. Is this for maximum life? I've had things shatter while working, but if I got it successfully made, they seemed to last. Were the things you made from cast sheet or were they cast forms, like sculptures?

 

[Angel D.]

Very interesting, thanks for sharing!

 

[Afrakes]

I should have said 50 years ago. We were casting large sculptural forms from raw materials, acrylic powder and monomer. Castings were placed in an autoclave and subjected to pressure and heat. The forms were then finished by machining, grinding and polishing. Annealing was the last step in the process. I was an art department graduate assistant at SUNY Albany then.

 

[Prairie Schooner]

I should have said 50 years ago. We were casting large sculptural forms from raw materials, acrylic powder and monomer. Castings were placed in an autoclave and subjected to pressure and heat. The forms were then finished by machining, grinding and polishing. Annealing was the last step in the process. I was an art department graduate assistant at SUNY Albany then.

You were about five years ahead of me. My undergrad work was in metalsmithing and sculpture at the U of Northern Iowa and I remember folks doing resin casting and fiberglass work. For some reason I just never did any. Welding, clay, and foundry were my thing.
A couple links from my search:

Meisner Art Casting | Resin Castings | Full Service Foundry

Seeking exceptional acrylic or resin casting services? Our skilled artisans specialize in creating durable, visually captivating pieces with limitless customization options.

www.meisnerartcasting.com

Bruce Beasley - The Bathysphere Story

Bruce Beasley is an internationally aclaimed sculptor based in Oakland, CA

www.brucebeasley.com

I can see where the large volume and varying thicknesses of a sculpture would create a lot of stresses. You would think any standard sheet you bought would have already been annealed. I'm startled that machining can introduce that much stress. When we had our hatches rebuilt last year they didn't say anything about annealing the panels after machining. From what I read, the cycle of sustained heat and cooling takes hours. Apparently just bonding sheets together can induce stress. But how would polishing create that much? You'd need a big oven to anneal something like a display case. I wonder if this sort of treatment is necessary mainly for building things with extreme technical demands like MilSpec products and sculptural forms and deemed not worth the cost for consumer products like boat hatches. Could the crazing we find in our hatches be because they were never annealed in the initial manufacture? I think I'm just going to proceed as I always have and not worry about annealing for the kinds of things I've been making.
Jeff

 

[Prairie Schooner]

Minimize Impact of Stress on Acrylic Sheet Through Heat Treatment | Grandview Acrylic

Grandview acrylic has a complete process of thick acrylic panel cutting, bonding, bending, annealing and polishing for underwater acrylic pool window, floor and acrylic aquarium

www.gvacrylic.com

Public Aquarium Acrylic Window & Tunnel

Public Aquarium Shark Tank windows, Aquarium Acrylic Tunnels, Acrylic Cylinder tank

www.gvacrylic.com

I suppose if you're building a 200K gallon aquarium, you'd want optimum performance out of your acrylic.