Gauging frame strength - opinions requested

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Re: Gauging frame strength - opinions requested

Postby saltydawg » Mon Nov 08, 2021 10:11 am

mnswamp wrote: Timbren strongly recommends .125 as a minimum... I could probably mickey mouse doubler plates over the attachment, under the attachment, and squish tubes inside the tubes, but at this point I think it's back to 2x2x.125 for the frame.

~marsh


Its easy to add thickness where you want it, the added weight of going thicker and with more flex I dont like. Do the side frame rails out of 2x3 .120 if you the extra thickness, no need to do the whole thing with with it.

But personally I would just weld on some plates where the axles goes.
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Re: Gauging frame strength - opinions requested

Postby KCStudly » Mon Nov 08, 2021 10:37 am

If you do decide to do the double (or "scab") plates, consider making them with tapered ends (i.e. diamond shaped). If you just scab on rectangles the edges can form stress risers, concentrating fatigue.

See halfway down this page under the heading "fatigue".
https://www.steelconstruction.info/Desi ... uction#top
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Re: Gauging frame strength - opinions requested

Postby mnswamp » Mon Nov 08, 2021 2:58 pm

Heh. Talk about 'over-engineering'... It's an interesting technical read, well above my pay grade. What I did glean is that they are talking about kNewtons of force on a bridge deck. I suspect that to build to the same specs, a TD would have to weigh 20T or more!

All kidding aside, it's a very valid point. The best way to avoid stress risers in anything is to avoid sharp points, especially in stressed areas. An arched surface is almost always better, be it on a welded gusset, a bridge or the fillet on a 3D print.

At the end of the day, I will apply the KISS principle with a few extra do-dads. Axles are in, lights are in, steel is on order. Next up, measure, measure, cut, deburr and wash.

BTW, jackstands on Craigslist are the way to go. Typ $20/pair around here for the better ones.

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Re: Gauging frame strength - opinions requested

Postby KCStudly » Tue Nov 09, 2021 6:43 pm

No need to read or understand the engineering, just use the taper outline ratios shown in the picture. The little wedge bevel at the tip of the diamond probably isn't needed. More better than a blunt transition. The theory of flexure absolutely applies to our little trailers, even if not the same magnitude as rail cars.
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