# Plastics that approach brass and aluminum for strength?

This question is asked out of ignorance, not trying to ask a trick question.

Is there a plastic almost as strong as aluminum or brass, not easily deformed, resistant to flexing, that could be used to mold the device shown in the image?

It needs to be a true 90 degrees, plus or minus a tiny fraction of a degree. The thickness of the vertical section is 2mm. The thickness of the bottom plate is 3mm.

• Ordinary plastics will never be strong in that shape. How much bending is allowed for a given force? is the shape negociable (can gussets be added)? Commented Sep 15, 2022 at 0:54
• Plastics also can't hold tolerances as tight as metals and "true 90 degrees, plus or minus a tiny fraction of a degree" does not say very much. You would be surprised how truly 90 degrees something can truly be, but if you meant to say you want it to be eyeballed at 90 degrees then say that, not that you want +/- a tiny fraction of a degree. Typically squareness is not measured in terms of degrees but how far out from 0 distance you are from where you should be at some fixed distance away from the 90 degree corner. For example, +/-0.005" at 4" out which is equivalent to 0.07 degrees. Commented Sep 15, 2022 at 2:00
• Otherwise this seem like an XY question. What are you actually trying to do? Because the geometry of that part seems deeply flawed to begin with. Commented Sep 15, 2022 at 2:05
• @DKNguyen : The top of the vertical section can be 0.15mm out of plumb.
– Tim
Commented Sep 15, 2022 at 12:05
• @DKNguyen : The part would serve as a kerf splitter for older table saws that lack riving knife and splitter devices. It would mount into the bottom of a zero-clearance throat-insert. If the vertical plate is too far out of plumb, it will fall outside the kerf and the wooden piece being sawn will collide with it.
– Tim
Commented Sep 15, 2022 at 12:14

Plastics, by definition, are flexible and deformable:

adjective Capable of being shaped or formed: synonym: malleable.

With the dimensions provided, it's going to be tremendously difficult (possibly impossible) to find something to rival aluminum. Aluminum at that thickness isn't going to be particularly resistant to bending. Some alloys of aluminum may have the strength you require, but you are asking for something other than aluminum.

The part of the question where you ask "to mold the device shown in the image" implies that you wish to pour/cast this object. That is also going to be a task nearly impossible to accomplish. Some resins used for molding would certainly pour into a form, but will not have the same strength as an injection molded part, but still not be as strong as aluminum.

The best non-aluminum option I would consider is an epoxy resin carbon fiber composite. It can be "molded" but not poured, although I suppose chopped carbon fiber in a low viscosity resin might qualify. Laid-up carbon fiber ply with vacuum bagging will give you something that excels the strength and stiffness of aluminum. The joints would have to be radiused, though, not dead-square nineties as shown in the image.

• Thanks for this helpful information. You bring up alternatives I did not realize were available, and you have helped me to clarify my question. The intersection of vertical and horizontal plates can have a small radius, but the vertical plate needs to be very close to perpendicular with the horizontal. The top tip of the vertical plate can be out-of-plumb by 0.15mm at most. I suspected that requirement would make plastics a no-go and it would have to be milled from metal.
– Tim
Commented Sep 15, 2022 at 12:09

Aluminum and brass alloys have a wide range of strengths. Pure aluminum is quite weak. There are some two part epoxies which are comparable in strength to the weakest of the aluminum alloys. An example is linked here. If you reinforce the epoxy with particles or fiber, you can get significantly higher strength than the epoxy alone.

Why are you interested using a plastic in the first place? If you are looking for strength and stiffness with reasonable fracture toughness then metals are typically the first choice.

I suggest using Ashby plots as a starting point for any materials selection. You can see the book by Ashby "Materials Selection in Mechanical Design" for some plots of common materials properties. See this link for a paper containing a plot that may be useful. By Nicoguaro - Own work, CC BY 4.0, https://commons.wikimedia.org/w/index.php?curid=42861211

• I hate that the author of that diagram chose to use pastel colours. Not only that, the legend colours don't even match the colours used. So I can tell the difference between the legend colours but then can't match up them with pastel colours, or tell the difference between the pastel colours. Commented Sep 16, 2022 at 4:48
• It's not pastel colors. The legend is solid but the graph has transparency. The colors are different though to easily tell them apart. Not the worst I have seen.
– CR.
Commented Apr 26 at 9:16