Cutting acrylic for portlights

[Cheechako]

I'd have them do it. Too fine a tooth blade and it melts the edge in a messy manner. You need to find a speed that doesn't melt, whatever tooth you use.

[AiniA]

An alternative to using goop is 3M VHB tape. Comes in a variety of widths, thicknesses, and colours. Put it on the acrylic and push into place. Make sure you position it correctly it is very hard to impossible to move. This tape is very strong and will give you a consistent thickness between the plastic and the boat. You will have a small gap at the edge of the acrylic. Fill it with a UV resistant goop. Use masking tape either side of the gap. The whole job will be much less messy than the traditional goop method.

[bcboomer]

Originally Posted by iansan5653

It's about time to replace the surface mounted acrylic portlights on my Freedom 21. They're crazed, cracked, leaking, and the screws keep falling out. I plan to forgo mechanical fasteners in favor of Dow Corning 795 sealant as described here.

I followed the Don Casey method you referenced. Worked well but I don't have as much curve.
The suppliers here are all fabricators so likely yours will likely be too. Ask them about the curve and heating it.
I took mine off and took them to the supplier at an agreed time and had the new ones in a couple of hours.
No polishing required and no chance for me to screw up.

[Mithril Bham]

You might want to hire a pro for this one.
I have had good luck cutting with a Fein Multitool.
Good luck

[Sailshabby]

Originally Posted by JPA Cate

Hello, Iansan,


We have rented a commercial pizza oven to heat bend acrylic (facilitated by eating there often enough).

Ann

I checked my dictionary, and found this definition under “win/win”!

[Cadence]

Jammer's suggestion of using a router is going to give you a cleaner edge than any saw. Used with a bearing to follow the old one as a templet will give an exact match but slightly larger.
Keep moving plastic melts.

[Tupaia]

Originally Posted by Cadence

Jammer's suggestion of using a router is going to give you a cleaner edge than any saw. Used with a bearing to follow the old one as a templet will give an exact match but slightly larger.

This shows a fundamental misunderstanding of the process. Both the existing and the new pieces are curved. It is impossible to lay one over the other and cut round it as this will neither account for the curvature or the thickness of the acrylic.

It may work for flat port-lights but even then having a result that is slightly larger is unlikely to be acceptable.

[LouK]

Originally Posted by Jammer

Oh, on mounting these, when I resealed my acrylic windows, I used VHB tape instead of fasteners. I had someone help hold it in place since you only get one chance to get it right, but it worked out well. The VHB tape was chosen to be the same thickness as desired for the silicone, then I put the tape on the inside of the bonding area and the silicone on the outside, and pushed the window into place. Worked great.


On bending, for significant curves you do have to use heat, if you don't then even if it looks OK at first it will leave latent stress in the acrylic that will lead to premature crazing over time and with temperature cycling.

+1 for the VBH tape, then seal the joint, works great!

[Cadence]

Originally Posted by Tupaia

This shows a fundamental misunderstanding of the process. Both the existing and the new pieces are curved. It is impossible to lay one over the other and cut round it as this will neither account for the curvature or the thickness of the acrylic.

It may work for flat port-lights but even then having a result that is slightly larger is unlikely to be acceptable.

Cut a slab larger than the original duplicate the curve or flatten the templet, clamp the two together then route. Just a suggestion.
I have seen thin acrylic scored and then snapped but on straight runs.
It would seem to be a job not for a novice.

[MicHughV]

As other's above, I have done this project myself. I can substantiate that it is a royal
PITA, such that, I will never attempt to do it again, not ever !!!

Do yourself a big favor and get a pro to do it for you.

[ohdrinkboy]

I would find a shop that can shape the plexi for you. take the old ones in for the mold. go with the tarp. blue tape will work and leave less residue.

[n5ama]

Originally Posted by Anders

Get a jigsaw blade designed to cut plastic and the job is easy but you will need to polish the edges if they are visible.
Buy cast acrylic, not extruded acrylic and not polycarbonate.

I concur with the above. I replaced the port lights on my Catalina 25 which had a modest curve, was long and +-7” high. The “cast acrylic” was a little more expensive and a little harder to find in the sizes I needed but was delivered within 2 weeks of placing the order.

My existing port lights were probably original to the boat (mid 1980s) and were severely crazed, and cracked across in several places. They were leaking a little but the main reason I changed them was limited visibility especially when the sun was shining on them. They were surface mounted with some sort of adhesive/sealer and also mounted with screws.

The hardest part of the project was removing the original material. Because of the crazing, the existing material came out in pieces that ranged in size from hand size to pinky size. Once removed, I also had to remove the adhesive with a chisel (major pain in the butt).

Since this came out in pieces, I couldn’t use the original stuff as a pattern. I took dimensions and cut a cardboard pattern oversize and slowly trimmed it to size until I got a perfect fit in the recess provided by Catalina to mount the replacement.

I ordered my cast acrylic and while waiting I taped covers over the exposed areas. Cutting the cast acrylic was easy after marking it with my pattern. I used a jig saw with a blade designed to cut plastics.

I placed the cut material in position before sanding the edge so I could see the original mounting holes, marked and drilled them. I also drilled a additional hole between these holes for more secure mounting. I then sanded the boat side edge for better adhesion. I used butyl tape for a seal and felt the shorter spacing would be helpful. I replaced the original screws with 316 stainless screws, flat washers, lock washers and nuts also packed with butyl tape.

The project took some time to do but the new cast acrylic is absolutely transparent and looks like there is nothing mounted in the port light.

BTW, the curve was not a issue on my boat.

[4runner]

Use LEXAN only

Cut it out with a jigsaw by tracing the old ones.

Smooth and slightly ease (round) the cut edges.

Install with 3M 5200

It’ll last 10-15 years

You can get a 24” x 60” x 1/4” thick piece for about $200 from acmeplastics.com

Good luck—

[Loons]

Our neighbours with a Hunter 45 called a glass shop who sourced, cut and installed the new windows. Looked good what they did. Similar to yours, large and shaped like a pilot house.

[capn ken]

Originally Posted by iansan5653

It's about time to replace the surface mounted acrylic portlights on my Freedom 21. They're crazed, cracked, leaking, and the screws keep falling out. I plan to forgo mechanical fasteners in favor of Dow Corning 795 sealant as described here.

I'm pretty sure I can handle this, but the only thing I'm stuck on is how to cut and prep the new pieces. They aren't simple shapes (see the attached image) and they are pretty long, so I think I have to just remove them and use the existing portlights as templates (as opposed to measuring them and sending dimensions to a fabricator).

If I pay someone to do this, I'll have to deliver them one of the current pieces for them to trace. That would take a couple days and there's always the risk of rain so I'd have to tarp over the opening. Then I have to deal with duct tape residue, the potential for theft, etc. Not really a good option.

So I think my only choice is to try cutting them out myself and get it all done in one weekend. I assume I can do it with a jigsaw (though I'll have to buy one) but I've never cut acrylic before and I'm nervous about ruining a large, expensive sheet of acrylic.

I don't really have a specific question here, but any general tips on purchasing, cutting, and finishing large acrylic pieces would be greatly appreciated!

After replacing the Port lights in my 1972 Cal 29, twice with acrylic I decided to go with automotive safety glass. Much heavier but doesn’t scratch. Be very generous with the beddingAnd best of luck. Lots of great advice, just be patient with yourself you can do this.