repair Lexan

Perhaps check here for ideas:

Karl,

Are you sure the cover is Lexan (polycarbonate) and not acrylic (Plexiglas)? Polycarb is very tough - you can bend 1/4" thick material double before it will break.

As far as adhesives go, Loctite 401 makes extremely strong joints in polycarb. I've never used it on acrylic, but Loctite says properly made joints are strong as the base material.

As long as you don't overheat it (sharp, coarse tooth blade), you can saw, drill, mill, turn, polycarb with abandon. A table also saw works fine. Acrylic, being more brittle, is touchier. Both are sensitive to certain solvents(alcohol?), especially when stressed.

Ned Simmons

I don't know what it is. Smoky clear plastic. Will loctite 401 work just as well if its plexiglass?

Karl

Karl what is the form of the plastic in your guard? By this question I mean is the plastic just a flat sheet? Or is it molded somehow?

Lexan is very easy to work but there are a few design constraints to consider. One big thing is you never want to have a sharp inside corner. This will focus the stress and it will crack, but if you have a radius inside corner than the stresses are distributed.

As others have said Polycarbonate (Lexan) is almost impossible to break. Sounds more like acrylic. If the break can be fit back together tightly with few missing chips you can cement it back together with virtually full strength with acrylic cement. It is a mixture of Methyl chloride, methyl acetate and some other methyl. Fit the parts back together so the seam is tight and apply the cement in little drips using a polyethylene squeeze bottle fitted with a hypodermic needle. Don't use a plastic syringe because it is acrylic and will either cement itself together or melt.

The cement is drawn into the crack by capillary action and melts it back together.

I use the stuff regularly for building shields for my weird router jigs. Even built an underwater camera housing using it.

As I said, I've never used 401 on plexi myself, but Loctite says it's a good match.

If you're very fussy, which doesn't seem to apply here, 401 will frost the plastic near the joint line. If you're working with new material, you can minimize this by removing only enough of the masking paper to make the joint. There are also "low-blooming" cyanoacrylates that sacrifice some strength in a trade for cosmetics.

If you're familiar with the two materials it's pretty easy to tell them apart. If you make a mark with a sharp scribe it'll scratch acrylic mostly by removing material. On polycarb it's more likely to dig a furrow by pushing up the plastic on either side of the mark.

Ned Simmons

for acrylics (plexiglass) you want to use a solvent based adhesive - weldon makes an excellent one, the bottle I have sitting by my desk right now says "habond acrylic cement" but it's just a generic, I think.

"Karl Townsend" wrote in message news:2FH9h.3441$ snipped-for-privacy@newsread2.news.pas.earthlink.net...

"Karl Townsend" wrote in news:JuG9h.3064$ snipped-for-privacy@newsread1.news.pas.earthlink.net:

I'd just purchase a new sheet of lexan. Smoked is $185 a 4'x 8' sheet in

1/4" You can cut it with a jig saw, use a 10 TPi blade and slow speed. Edge trim with a knife or whirly-gig debur tool.

tape the broken halves together temporarily and use a soldering gun/iron to weld the halves together. will be messy and stinky but will work. For cutting I have always used the finest blade possible and LOTs of cooling water. I usually use a small spray bottle to spray as I am cutting It will commonly leave a "mound" of material on the cut edge but after it cools you can just crack it off with your thumb. Thin stuff bends pretty easy with gentle heat from a propane torch or heat gun just be careful it's easy to light it on fire or overheat it till it bubbles.

Bla

For polycarbonate, acetone is likely the worst of the solvents. The way a piece of polycarbonate crazes within seconds, upon receiving a squirt of acetone, is something to behold... on a piece you don't value. It's sort of like exposing Superman to kryptonite, except that with polycarbonate the loss of strength is non-reversible.

Usually, acrylic and polycarbonate are very clear, even with the coloured versions. If you mean "smoky" as not perfectly clear, but somewhat translucent, then it might not be either of those.. The "broke in two pieces" would strongly suggest that it is NOT polycarbonate.

However, transparent PVC is usually "smoky" and not perfectly transparent.. Then there's transparent ABS, which is not perfectly clear either..

You can see some photos of part made from transparent PVC here

the flow sensor.

For PVC, solvent based "welding" with Tangite or such will work wonderfully. It's used for making PVC pipeline connections.

For acrylic, there is glue based on acrylate that will make the two pieces one piece again.

Kristian Ukkonen.