How Strong Is Acrylic?

[crokett]

specifically Silmar 41. I do wine glasses as gifts where I cut off the bottom part of the wine glass and turn a replacement. I'm considering casting either some or all of the replacement. I would probably start with a wooden foot and cast stem. The finished piece the stem would be 1/2" diameter at its narrowest. I could add something like a dowel in the casting if I had to. Is acrylic strong enough to stand up to casual use?

 

[monophoto]

There are a number of manmade materials that have properties similar to glass - acrylic, polyurethane, and polycarbonate for example. Acrylic is often used as a substitute for glass where greater strength (and break resistance) is required. Acrylic and polyurethane are both available as casting materials. Polycarbonate is extremely tough (although not as scratch-resistant), but I don't know if it is available in a form suitable for casting (but then I'm not a casting expert).

Thin acrylic is a bit flexible and can shatter. For example, the plastic cups used by airlines to distribute tepid soft drinks are made of acrylic; they hold up very well (my wife has some she has been reusing daily for years), but can wear out quickly if you squeeze them hard enough. Superglue (cyanoacrylate, or CA) is acrylic, and when glues are compared, CA joints are often described as 'brittle' meaning that a CA joint can fracture if it receives a physical shock, while other glues are described as 'resilient'.

I would think that a final thickness of 1/2" would be pretty strong. But then, I don't know what you mean by 'casual use'.

 

[ed4copies]

Cast a few half inch rods and drop them onto concrete.

Silmar 41 is polyresin, not acrylic, so any information you get is not necessarily going to help. The drop test will answer your question.

Oh, also do this at different ambient temperatures I believe cold will make it more brittle--an iced drink will cool the stem.

 

[jttheclockman]

You have a few things going on here. First off much depends on thickness and abuse. Then there is amount of drops of catalyst used. The more the brittle it is. Not enough and it is too soft and does not cure. Not an exact science. but for making pens we can focus better because the numbers are fixed more or less. Next all plastics are not the same example the code on the bottom is different. Has to do with mixture of ingedients and flexibility and strength.

Then there is the idea of adding a dowel or reinforcement. Well Silmar does not stick well to other things because it shrinks as it cures so you run the risk it pulls away from the reinforcement. The use of epoxies is the cure for that. Now there are so many different grades of epoxy and they do cure clear and strong. Now you would need to talk to the supplier when asking those questions.

So bottom line is I am of no hope but threw some thoughts out there to consider.

 

[Ed McDonnell]

OK, You want to replace the stem on a wineGLASS with something else.

Let's look a the big picture. Polyresin (e.g. silmar 41, aka PR) can be brittle (especially when cold), but so can glass. If you drop a wineglass on the floor I would be surprised if you expected it to survive, whatever the stem is made from. A 1/2" rod of PR acting as a stem on a wineglass sitting on a counter is not going to be any more susceptible to breakage than the glass it is attached to. Just my opinion. Feel free to disagree.

As far as attaching the new stem to the glass portion, I would expect you to use some sort of rubber adhesive between the glass and the new stem (in this case cured PR). I would expect there to be little difference in adhesion to any cured resin (PR, epoxy, urethane). and would expect PR to work as well as anything else. If you were thinking about somehow letting the uncured PR stem attach itself to the glass then John's concern about shrinkage and delamination is a major issue that wojuld likely lead to failure.

As far as casting objects within Silmar 41. PR shrinks as it cures and something has to give. If it sticks to your object better than it does to your mold then it will pull away from the mold as it cures and will remain tight to the embedded object. Using a release agent in the mold goes a long way to solving this problem.

As far as attaching a PR stem to a wooden foot, I would suggest a mechanical joint / fastener rather than relying solely on the adhesive properties of PR (which are minimal). Or make the entire stem / foot out of PR.

Ed

Opinions...everyone has one and there is little chance that they will all be the same.....

 

[jcjc]

The only acrylic resin I've ever heard of is Weld On 40 (and a couple of it's close relatives from the same company) and is amazing stuff but also expensive and noxious. I've used it quite a bit when working with various thicknesses acrylic sheet and is also the stuff that acrylic fish tanks are built with.

 

[crokett]

thanks for the correction on acrylic vs polyresin. To me it's all some form of plastic. A drop test is a good idea. I have some Silmar that's been sitting for about a year so I think I will cast some of that and if it turns out ok see how strong it is. I will also see about casting it directly to a wood base vs casting a separate piece and epoxying it down. I was thinking I could counterbore the base and use a dowel + undercut the counterbore to create a dovetail of sorts for the resin when it was cast.

by casual use I mean how you would normally use a wine glass.