Project Metal Selection - How to decide?

[sarge338]

Merry Christmas, Everyone!

I have a question that I am sure is not a simple one, but I needed to see if I could get some feedback from people with more experience than me.

When you are starting a new project (not a repair), how do you determine what metal to use? I am looking for physical characteristics more than obvious cost considerations. Anytime I am repairing something, I try to match the metal on the part being repaired. But if I am going to build something from scratch, how do I determine when to use square tubing vs angle, as an example? Would 1/4" thick, 2"x2" angle provide the same support as 1/8" thick 2"x2" square tubing? If I wanted to use aluminum to save on weight, what thickness of aluminum is needed to reach the same strength as a similar peice of steel? Is there some kind of chart, formula, etc. that I can use to determine these things? I am obviously a newbie when it comes to this kind of thing, and I have been accused (rightly) of over-engineering things. I would like to use metals more appropriate for the purpose, rather than ending up with a part/project that weighs 3x more than it needs to.

Thanks in advance!

[ryanjones2150]

I’m an “over-engineerer” so not the guy for an opinion on what size of what to use. It just depends. Does it move? Does it stay put? Etc.

However, when it comes to the alloy, most of your metal suppliers have info such as what steel is good for axles or shafts, etc.

[MMW]

On the job experience. I'm sure if you had an engineering degree of some sorts you could figure out loads, etc but most people I know just use their experience of what works and what doesn't. Not much help for your situation though.
As far as determining angle vs tube vs pipe vs flat bar it mainly depends on the direction of load it will receive. For instance i-beams are strong in one direction, weaker in the other and terrible against twisting forces. Read all you can on the internet about strength and loads of different shapes to gain a better understanding. There are charts I am sure on specific capacities of materials and shapes. No easy answer.

[MAC702]

Walk through the backyard and grab the first thing that looks like it will work.

[Burnt hands]

If you like math or have trouble going to sleep, try these sites.
First one has formulas for square and round beams.

http://www.engineering.com/calculators/beams.htm

http://www-classes.usc.edu/engr/ce/457/moment_table.pdf

https://www.awc.org/pdf/codes-standa...ations/design-
aids/AWC-DA6-BeamFormulas-0710.pdf

https://mechanicalc.com/reference/beam-analysis

https://www.egr.msu.edu/~harichan/cl...e405/chap2.pdf

https://www.linsgroup.com/MECHANICAL...am_formula.htm

[walker]

Some of it is looking at what is readily available, or has already been done. Some of it is prior experience. A lot of it comes down to what you want it to look like and budget. For example. I build a fair amount of gates. Plenty of gates built out of 1” square .065” tubing, and they seem to hold up fine. Most of the gates I build for my clients use 2x2” or 2x3 tubing in .120 wall. You get much better feel out of a bigger, heavier gate.

[sarge338]

I appreciate all of the feedback. I’ll review some of those links to see if I can make sense of them.

The project in question is going to be essentially a replacement for my Miller dual running gear cart for my Multimatic 255. I don’t like the running gear at all! Feels like the wheels are gonna fall off of it every time I move it. Also, because the bottom drops where the bottles sit, it won’t clear the threshold of my shop door. So, I want to build a sturdier cart with larger wheels to move the 255 onto.

[manac]

Go make it! You know what you want and have a good starting point with known weaknesses and known good points. Don’t go crazy and beef everything up, you can always more material/bracing later.

[ryanjones2150]

A welding machine cart is one of those things you build with whatever scrap and junk you have laying around.

[sarge338]

ryanjones2150 That is the problem. Being a newbie hobbyist, I don't have much stuff laying around. I usually grab what I want to use from the scrap yard on the other side of the county. I just wanted to see if anyone had any good advice that would push me one way or the other regarding steel vs aluminum and/or angle vs tube. Of course, with it being a scrap yard, I am at the mercy of whatever they have at any given time.

Regardless, I'll head out there tomorrow and see what they have available. I'll go from there. Thanks for the input.

[ryanjones2150]

Some fab shops will cut and sell you bits and pieces too. It might take a while to find all the places around that you can do business with, but it’ll be worth it. Other than that, the steel yards generally have what you need, but around here at least, you have to buy a whole stick even if all you need is a couple feet. That’s where the fab shops can help. I also order a lot of my specific alloy metals for machine work, such as 1144, 4140 or 1045 steel, from McMaster-Carr in 3’ to 6’ sections. There are some online metal suppliers, but honestly, I’ve had hit and miss luck with their service, especially having what they say they have in stock.

[Aeronca41]

It may help you if you would post whatever you think your first project might be and get suggestions as to what materials to use. More likely to get a helpful answer if folks can see what you're building.

[MMW]

https://www.millerwelds.com/accessor...le-rack-301481

Why not just beef up what you have? Whatever diameter axle the rear wheels accept just put one solid pc. under the tray from side to side, this will stiffen and raise the back end. Then make a tubing spacer for the front casters of appropriate size to level it.

[Oldgrandad]

Here are 2 carts one modified to suit us the other from scratch made from whatever, 1" square, 1/2" square solid, a little diamond plate, some 1/4 x 2 flat bar. 1/2" bolts for axels. It will get some left over 4" casters for the front end. I'll post a pic of it when it's done.

[Aeronca41]

It may help you if you would post whatever you think your first project might be and get suggestions as to what materials to use. More likely to get a helpful answer if folks can see what you're building.

Well, don't I fell dumb! Sorry I missed the part of your post where you already did this!