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 Post subject: Round tube dimensions
PostPosted: February 17, 2020, 9:16 pm 
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Joined: February 16, 2020, 11:03 pm
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Working through a round tube book dimension chassis. Wondering if anyone has a cad drawing or pdf of their round tube car? The dims from the book and I’ve found online don’t quite translate.

I’ve gotten about this far and could use a reality check.

Thanks!


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PostPosted: February 17, 2020, 9:57 pm 
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If you're looking for "book chassis" dimensions as your basis, the drawings on sevenesque.com are more accurate than the book (I know that doesn't make sense, but such is life). What diameter and wall round tubing are you going to use?

The front piece is intriguing. If you get the bends (and other dimensions) right, I think you can get all the chassis hookup points in their original locations, without doing all that awkward multiplane cutting and welding that the front thingie calls for in square tubing. Good luck on this.

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PostPosted: February 17, 2020, 10:46 pm 
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I’m thinking either 1.25" .090 or 1" .090. I have a CNC bender at my shop. The fab is easy. The design is hard.


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PostPosted: February 18, 2020, 9:23 pm 
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Not sure yet if it’s close enough. But it’s done...


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PostPosted: February 18, 2020, 11:31 pm 
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You may find this of some help: viewtopic.php?f=39&t=8721

And look up "Aussie mods". It may help you fine tune the chassis design.

I'll be following this.

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PostPosted: February 19, 2020, 11:43 am 
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The 1.25 round tube is a lot stiffer than the 1" square for the same weight. The round tube if purchased as DOM is also often a better quality metal and process. It's typically either 1020 or 1025 and Drawing Over Mandrel work hardens the material a bit.

We typically use .065" tube, for decades and it has not been found too thin a wall. On my car I used .083" for some tubes because for a light car that was what was called out for roll cage tubing. So the upper rail, roll bar and door beams are .083".

If you use thicker tubes the strength is less, by a large margin, than a larger thin walled tube. Roll bars etc. are thicker to protect from impacts because the tube can become crushed.

Using the pointer from above the 1.25" round tube is %59 stiffer for the same weight compared to 1" square. That's just because the same metal was all pushed out as far from the center of the tube as possible, it's round!

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PostPosted: February 19, 2020, 11:54 am 
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It looks nice.
If I were going to change anything (with access to a CNC bender), I'd make the upper rear hoop (the top edge around the boot) and the rearmost diagonal brace to the bottom frame rail all one piece.
Up from bottom rail, bend toward boot area, 90 degree bend and run to far side, 90 degree bend back toward cockpit, bend down to bottom rail.

Then the upper rear bulkhead bar would be a straight tube.

I think the body panels would look nice with a bit of arch in that area.

Tommy's 2 cents. Your value may be higher or lower... :lol:

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PostPosted: February 19, 2020, 1:21 pm 
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The voice of reason
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In general tubes should join at reinforced junctions. In the picture above I think there is a missing diagonal from the back of the upper cockpit rail down to the floor at the bulkhead behind the driver.

Without this if you put weight in the car the upper rail will push against the side of the tube it is attached to and try to buckle it.

Another spot to look at is the way the bottom tubes on the side of the oil pan connect to the drive tunnel tubes. They are offset a bit and you may be able to adjust them or gusset a bit. At least be sure to weld the floor well there.

With careful bending you can make the top rails in one piece or at least do the bend at the front of the cockpit. I did that but haven't finished the car yet so not sure it worked but I think it's OK.

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PostPosted: February 19, 2020, 7:34 pm 
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Wow. A lot of great information here. Thank you so much.

I can adapt the model into virtually any tubing size as the drawing doesn’t care about the material. With that said, would you guys go down to a 1 inch, .090 or .065 wall? I don’t want to go smaller than that, as dies for my bender are very expensive and I won’t use it again.


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PostPosted: February 20, 2020, 1:55 pm 
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I'd use 1.25 if you have those dies.
.090 for roll hoops and crash structure, 065 for bracing members and diagonals.

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OOPS I did it again
http://www.locostusa.com/forums/viewtopic.php?f=35&t=17496

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http://www.locostusa.com/forums/viewtopic.php?f=35&t=15216


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