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PostPosted: September 18, 2017, 7:54 pm 
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Joined: June 28, 2016, 9:21 pm
Posts: 21
Hi all,

I am ready to buy some material to build a frame. The book says to use 1in x 1in16 swg square tubing. 16 swg is 0.064" (1.63mm) wall thickness. A few questions pop up in my head.


1. Wall thickness
Is 0.064" wall thickness strong enough? Is 1in tubing strong enough, if my estimated horsepower of the final build is around 250 to 300HP. Should I use thicker wall thickness like 0.085"? Or even bigger tubes like 1.25"? Well, I guess I can always add gussets at corners to reinforce the frame.

2. Hot roll VS Cold roll
I read online that cold roll provides better dimension integrity. However I doubt locost frame will need that kind of tight tolerance as you are always measuring as you weld and suspension are adjustable to compensate error or distortion. Strength wise, Hot roll and cold roll should be the same, correct?

3. Material
Some steel places don't tell you the what kind of steel are the tube made of. They only say it's cold roll or hot roll, or they just say it's mild steel. How would I know the Yield Strength if I don't know the material? Will it be fine if I use some "Hot roll mild steel" tubing to construct my frame?

4. Where to buy
Currently I am looking at MetalSuperMarket, as they provide the lowest bulk price, based on my initial research. I am wondering is there any better sources? Maybe try some local steel companies? Looks like the material for the book frame is going to cost around $300 excluding shipping. Is it too much or just normal?


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PostPosted: September 18, 2017, 8:14 pm 
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Joined: January 10, 2008, 4:47 pm
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Location: Massachusetts
Hi Yuta,

The wall thickness is sufficient. It may make sense to use 1.25" for the main rails. That provides a reasonable bump in strength and stiffness, it's about twice as stiff as 1" tubing. Diameter makes it stronger much quicker than wall thickness does.

It is not advisable to just use any tubing. You would like 1020 alloy. I bought mine from OnlineMetals.com, they will give you a copy of the MTR ( Material Test Report ) for that batch of tubing and it will state the yield point. They sell it as hot rolled although the tubing I bought and another builder's looked like cold rolled when it arrived. Cold rolled has a much nicer finish because it does not have mill scale, the hard black stuff that covers hot rolled material. It is also stiffer because it does not have work hardening from being formed.

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SketchUp collection for LocostUSA: "Dream it, Build it, Drive it!"
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PostPosted: September 18, 2017, 10:06 pm 
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Joined: January 31, 2012, 12:49 pm
Posts: 1431
Location: Louisville KY
Metal Supermarket has been a nice surprise here in Louisville.

https://www.metalsupermarkets.com/

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Louisville, KY
Hayes front, S10 +2 rear, Lalo body.
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PostPosted: September 18, 2017, 11:47 pm 
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Joined: October 24, 2008, 2:13 pm
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Location: Carlsbad, California, USA
Echoing what Marcus (horizenjob) said, the hard mill scale on hot rolled must be removed before welding. It is often a real bitch to get it off. I used some hot rolled plate in some areas and it was a lot of extra work. Use cold rolled. You'll save in time all that you spend on the material itself.

I went 1x1-1/2 on the main rails, which is over-built. However, I didn't have any good analysis tools (like FEA) at the time, I'm an amateur welder, and I have a high-torque V6, equal to a Chevy 305 or Rover V8, as a power plant, which I plan to take to the 300 HP area. The extra size and weight weight of the tubes seemed like an good insurance policy to me. If you did an analysis, 1-1/4 square would likely be fine too. There's a couple of V8 powered Locosts that have used 1-1/4 square tubing for the main rails and the owners seem fine with the result.

Cheers,

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PostPosted: September 18, 2017, 11:51 pm 
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Joined: January 31, 2012, 12:49 pm
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Location: Louisville KY
part of the question is "strong enough for WHAT?" If you're running race slicks (wrinkle walls) and a high torque motor, well, that used to twist full-size frames plenty.

I'd guess that for most of us, we're not gonna drag race, and by the time that the frame is bending dangerously the rear tires are breaking loose?

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PostPosted: September 19, 2017, 6:02 am 
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Joined: May 22, 2017, 7:36 am
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If there is a industrial steel supplier close by I would lean towards that, I found metal supermarket to be good for aluminum and remnants but almost 3 times the price for 16ga 1" square. I can get 10ft sticks of 16ga 1" square for $7.77 currently from my local steel supplier. Plus there is no minimum purchase from my guys which is really nice.


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PostPosted: September 19, 2017, 4:41 pm 
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Joined: July 4, 2006, 5:40 pm
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I also used Online Metals, and agree their 'hot roll' looks better than a lot of cold roll. It's 1018, I believe, with a yield strength of 36K psi, which doesn't sound like a lot but after 40K miles of hard driving on a lot of rough roads, my standard book frame Locost still feels like it was carved from a single hunk of steel.


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