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Hi All,

I need to make an "t"  beam out of 2 pieces of 1/8" by 3/16" styrene.  The joint must be strong and must help stiffen the "t" beam.  This "t" beam is connecting a switch motor to the throw bar over a distance of about 15 inches.  

Or should I just make the beam 1/4" by 3/16"?

Am I correct is thinking that epoxy will be better than MEK?  Any other suggestions?

And, "Yes", I did check with "This to That".

Thanks,

Ed

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The best cross-section for a beam is an "I" with a vertical web that joins two horizontal flanges (top and bottom). Without doing any beam theory analysis, it seems to me that a square 3/16" (solid) cross-section should carry the loads to move the switch rails. Your beam will have a tension load when moving the switch in one direction and a compression load in the other. I suspect it will carry the tension load without any problem. However, a long beam with a small cross-section is subject to buckling in compression, so that's what you need to avoid. Trial-and-error should be sufficient to determine an adequate beam cross-section.

MELGAR

Last edited by MELGAR
@Ed Kelly posted:

Am I correct is thinking that epoxy will be better than MEK?  Any other suggestions?

Maybe....MEK will effectively weld the styrene into a single unit; epoxy will just join everything together but you could use extra along the joint to add strength.  I dislike MEK due to the smell and flammability, but my supply of DCM has just about dried up.

I'd consider just using a length of stiff heavier gauge steel piano wire; at least 1 switch on my layout is actuated this way.

I always use solvent cement with styrene. Tenax was my go to brand but they closed up shop. I had it analyzed at work and verified its was mostly Methylene Chloride, now not available to the public.  Micro Mark started selling “Same Stuff” thats supposed to be the same as Tenax. Not sure it still is but it seems to work almost as good. Also Plastruct makes a couple of solvent cements that work if not as fast a MC.

Epoxy would be a second choice, not the best.

Pete

If you are going to use an adhesive, MEK is definitely better in this applicable than epoxy. As noted above, you want to weld/melt the pieces together so that they cannot come apart. Hobby stores also sell "safer" solvent alternatives which are better for you than MEK. Glue it together, let it cure properly, and it will be fine.

We did a test of this recently at about 22 inches.   We used .047 Piano wire in a 1/8 brass tube running nearly the entire length.   The tube needs to be stabilized,  so we mounted the motor on a 1/8 plate that also ran the full length,  then put a cover of 1/8 board over the tube to keep it from moving.   It works,  plenty of tension on the point rails,  but thankfully in the end we didn't need this set up.

Dave

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