Plexiglass cutting

What dia. blade do you use and what width. You write of surface feed per minute but you don't mention what dia. of blade you use. The amount of teeth and size also make a big difference in the SFPM. Chip size is very important. The temperature of the plastic I have found does make a difference in the amount of chipping. I cut just fast enough to prevent any melting. I have also found that the sharper the cutting tool the more the tool will grab and dig into the work. I cut, bent and drilled the wind shield for my fly bridge last spring out of 1/4 stock. I didn't say my way was the best. I only said that was the way I did it. I was a machining engineer for years. I also sand the edges to remove any tool marks before flame finishing. Good thread Luckydave. I will try your ideas the next time I cut plastic. I use a heat gun and bend the plastic over a wood form covered with a clean cloth. You must remove the protective paper where you are bending. It does not stretch. But ONLY in the area you are bending. There is always that better mouse trap.



BILL

We use an ordinary 1/8" carbide tipped blade, and cut everything with it, even aluminum and bronze. If I want to cut plexi, I grab one that has been sharpened (a virgin, in other words) because the aluminum buildup on the sides of the blade, however small, tears up the finish when cutting plastic an rubs "dirt" into it, making for more sanding later to "clean" it. The bottom line is that it doesn't matter so much what type, or grind, of blade you use, what counts is how sharp it is.

My saw is a 17 horsepower monster (Delta Industrial, awsome saw) and turns a 20" blade, but that doesn't really matter, the feed rate on a manual table saw is established by feel anyway. The coarser (less teeth) blade you use, the slower the feed rate, and the easier it is to manually control. Another thing I didn't get into is that you want to raise the blade above the table only enough to cut through the part, plus 1/8"-1/4". (1/4" stock, raise the blade 1/2"). This aligns the cutting force as much as possible with the long dimension of your part, and makes for less chipping. In the same light, don't let the part vibrate (jump) on then table, hold it down against the surface for smooth cutting. This is true with any machining operation on plexi.

Sanding the edges before flame polishing is good practice, I forgot to mention it, (I can't remember everything when I'm typing fast). :D
The tiny "hairs" of plastic standing up on the surface melt into the scratches and actually give a better fnish than a smooth surface does when flame polishing, so sanding with coarse paper is fine. Clean any surface you want to flame polish beforehand, or you'll melt any dirt (including fingerprints) into the surface. Use windex.

Heat gun bending works just fine, it takes manual technique to heat the part uniformly so the bend is consistent, which gets us back to practice, practice, practice.

Once again I forgot something. I buy 140+ tooth blades in the 20" size, but we also cut plexi with a 10 tooth blade and a Skill saw, which works well also.

Yea those corners on Hatteras's are tricky. We would make what we call a " half bend " a heated bend Starting at the bottom, going half way up to the top, and then the rest would follow the curve at the top, the trick is getting that bend in the corner
PERFECT cause the slightest little bit out of wack it just does not look right.

I have to ask you this. Are you trying to construct a hard enclosure on your own??? You are asking for a HUGE HUGE HUGE headache!!!! There is a bit that goes into making one, so many things that have to be DEAD on!! when dealing with zippers they have got to be just right, teeth to far away from each other you are not going to get it zipped, to close together you will get them zipped, but they will get bound up, out of alignment and you are going to start breaking teeth ( you only have to break one, and the zipper is useless ). I have seen a few people try to do this, and they usually called us to finish ( well start over really ) or they just go to conventional vinyl windows. The reason all the zippers have to be almost perfectly matching too, is because the plexi does not shrink or stretch much at all. even when we went to install enclousures we had a portable sewing machine with us, and to sometimes move a zipper, or take out some material to make them fit. And I take it you will pattern it also??? Well after you take down the patterns and back to your shop, they have to be processed and there is a formla to that to make them fit right, unlike conventional soft enclousures.

I am not trying to discourage you from trying this, just giving you a warning. Call a canvas shop, they have came out with a " sewable" Lexan that can be used now without being a EZ2CY dealer,it is .060 gauge , and get a price on it. The glass has a five year warrenty on it, but after that you are on your not sure how long it will stay clear after that. Remmember what Capten on the Nimrod said, his enclousure is 12 years old now, and still very clear.

Hope this gives you some help on your desision.

Dan

About 15 years ago I fabricated sliding glass side windows P&S on my 1980 DC. Steve McPherson got me the metal extrusions and they worked out well.
(I'll not get into the side windows at this time - if anyone is interested, PM me with your phone # for more info) The stern was made up of 5 plexi panels, 2 bent corners, 2 slightly curved P&S and a 30" center door. The center door and the teak gate and dodger door were all made larger to accomodate the son of one of my friends on his wheelchair.

The arrangement worked out very well for years with the only problem being the 2 bent corners. I made a pair of forms for them, curved tops and tighter bend at the wood railing. The heating was done using several heat guns held by a couple of helpers. The result was acceptable but within a couple of years, they started to craze and eventually cracked. I guess the problem was that it was not stress relieved as stated earlier in this thread. The problem is how does one properly stress relieve such a large panel. Suggestions please.......

Walt

Just like heat treating any other odd shaped part, you have to build an impromptu oven out of whatever you have at hand.
For steels, I use firebricks and a natural gas burner.
For a large plexi part, I'd first obtain the manufacturer's recommended annealing temperature, then build an oven out of 2x4's, blankets, popsickle sticks, plastic sheet, duct tape, dirt, shipping foam for insulation, whatever. You could probably modify the thermostat in a small space heater to fool it into supplying the heat.
If you're technically savvy, use a universal PID digital controller's output to run a relay to switch the heater current on and off. The controller will require a thermocouple for signal.

Make sure you support the part in it's desired shape when annealing, as it WILL relax into a different shape otherwise. You will likely have to restrain it from moving when it's hot.

Think like a third world mechanic. They have no parts, no supplies, nothing but their brains, and they use them well. Make do.

This is a great thread. Lots of useful information. I think eventually it should be moved to the frequently asked technical questions section so it does't get lost in the pack and will be easier to find.

Mike