Plexiglass cutting

I need to cut from 1/8 to 1/4inch plexiglass for my bridge windows. There is a curve to the windows so no straight line. I have the origional windows removed so there is a templet. ANYONE have a surefire way to cut plexiglass easily without cracking or splintering the edges?
thanks
Rian

Use a sabre saw with a fine tooth blade. Not a a real fine metal cut.ting blade, but a relatively fine wood cutting type. Rub it with a wax candle and continue to do that while cutting. Use a slow speed and keep the preassure on. Don't let it get hot and melt the plastic. If yo have a tight turn, switch to a blade that is narrow front to back. You can block sand the edge smooth after cutting to eliminate any stress cracks.

I can help you with this, being my old line of work, all we did was cut plexiglass all day. You can do it by hand, and is really the safest way.

Put your old window on the new sheet and trace it out. And then get a plexiglass cutting tool ( you can get one of these at Lowes or Home Depot ) and with the first cut, slowly score just inside of your line the first time, and then do it again, and as you get deeper with your cut, you can increase the speed and the pressure on your plexi. If you are using 1/4 inch, this can be done in about 5 or six passes. Then Bring you scored line to the edge of the table, and start at one end, and just start snapping it all the way across, Then to preety up your edge, use a propane torch in the rough edge, not to close, and just heat it till it is smooth, just keep the heat moving.

The glass you buy comes 4x8 sheets or you can buy a half sheet. Just utilize the piece you buy, and if you have to draw it out a couple times, ( might just mess the first one up ) then you can try it again.

Or you can just take it to a glass/ plexiglass store which specializes in car's , bathrooms etc etc, and take them the piece off the boat, and have them do it for you.

Good Luck

Dan

Dan .... what is the best way to bend .080 plexi? The supplier told me that it takes 280 degrees of heat to make the plexi bendable. Thanks.

EZ,

This is what we used to make 90 degree bends

http://www.professionalplastics.com/...ending-acrylic

and for other kinds of bend, we used a heat gun. Just make sure you keep constant heat and distribute it evenly along the place you want to bend!!

I have hear of a household oven being used, like for making the bends in a Venturey windshield on a boat, coarse it can't be too big, unless you use a pizza oven at Domino's or something....LOL.

What are you wanting to bend???

And I highly recommend anyone who wants to do any work with the acrylic, try to get the " Acrylic Plus " as I spoke off in the EZ2CY thread, if you can get yours hands on a sheet. Cyro Plastics is the manufacture of the " Plus " but if you get in touch with Cyro, and get the name of the closest distributer to you, they will probably sell you a single sheet if you do the footwork.

Hope this helps

For cutting straight lines I use my table saw with a fine blade running backwards. For rounds configurations I use a fine blade and I warm the plastic where I plan to cut. For bends I use the oven and only heat what I need to bend and bend it over a form.


BILL

To table saw plexi use a SHARP blade going forward, not backward. You want to cut the stock, not friction saw it. The number of teeth isn't that important, just remember that you want each tooth to cut about .001" of an inch chip load. If you multiply the number of teeth by the rpm of the saw, times .001", you'll see that you want to feed the stock pretty fast through the machine (cut across a 48" wide sheet in ~15 seconds). If the plastic is melting, you are feeding it too slow. The stock shouldn't be warm after cutting, if it is, speed up the feed rate. Properly done, a table saw cut is ready to flame polish without further sanding or smoothing.

To band saw plexi, use about a 10 tooth per inch blade, and don't feed the stock too fast, or you'll get chipping on the bottom edge, but feed fast enough to cut, not rub.

Drilling plexi is done with spade drill bits, or if you don't have access to those, "dub" the leading edge of the drill on a grinder so the leading edge of the twisted flute is parallell with the axis of the drill (similar to cutting brass). Feed rapidly enough to avoid melting the plastic, use a coolant to lubricate the cut and keep the drill cool (water is ok) and back off the feed rate when you cut through the back side to prevent chipping out the back of the hole. If your drilled hole has a rough melted appearance, you let the drill get warm. You MUST keep it cold.

Machining is done with very sharp end mills, kept wet with oil. Don't try to cut plastic with a dull one, you'll get a terrible finish. If you have to cut with a fly cutter, grind a large radius tool (+.25r) to prevent chipping of the surface, and hold down the feed rate. If the flat surface is chipping out, slow down the feed. High surface speed (rpm) is fine. The same is true when turning. High speed tools diamond honed by hand work best, carbide turning tools aren't sharp enough.

Flame polishing is best done with an OxyHydrogen flame, but you can also do it with a butane or propane flame. For best results use a "blazer" micro butane torch (sold at hobby stores) and adjust the air control for hottest flame. the object is to melt the surface as quickly as possible without heating the underlying material. Practice with the torch on scrap. Like welding, flame polishing is an aquired skill. If you move too slow, the surface will take on a bubbled appearance. Practice, practice, practice. With enough practice, scratches in the middle of panels can be flame polished out.

Forming is done at 150F, the slumping temperature. If you form or machine (and then glue) plex without annealing it first, you will get crazing. the annealing temperatue is low, usually about 115F for 8 hours.
Gluing is accomplished with methyl methacrylate. Fit the parts with .002" clearance, and admit the solvent with a 5cc syringe with a 25 1/2 guage needle. For small parts use a 3cc syringe. The idea behind the small syringe is to give more control over the amount of solvent applied. Remember, that you are not gluing plex per se, but rather solvent welding it. For larger joints, fit the parts with .005" wires every few inches as spacers holding the joint apart. Insert the solvent, wait 20 seconds, and pull out the wires, closing the joint. This will allow time for the solvent to melt the stock, and closing the joint will push out any air bubbles.

Sorry for the long post, but I've been fabricating plexi (acrylic) and Lexan (polycarbonate) scientific parts for 30 years.

Wow! These are fabulous posts. I'm going to be a lot more confident working with these materials with this info.

Thank you all very much.

Ted

Dan ... thxs for the reply. I'm thinking about using plexi for the curved aft corners of my enclosure (1979 43DCMY). These are about 42" high and 14" at top and 18" at bottom. It will be tricky as the top is rounded and the bottom angled to conform to the teak cap rail. I'm thinking about using the heat gun as the sheet will be too large for an oven.

I'm also thinking about using the plexi for the large side curtain panels (appx. 42" high by 38"wide). I'll either use plexi or Stratoglass for the panels at the boarding gates as they need to bend some.

My panels are currently bordered with vinyl. I've done some tests with hot glue and it appears to adhere the plexi to the vinyl well ... or I may just use 5200 sealant adhesive.

I forgot to address edge treatment. To get a nice smooth rounded edge to your panels, use a router table with a bearing supported radius cutter. Don't feed the part past the cutter too slowly, or once again you'll melt the part instead of cutting it. Follow up with flame polishing.

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