K member fabrication, start over with tubular or add??? Chassis Fabricators step in! - Hot Rod Forum : Hotrodders Bulletin Board
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Old 03-14-2011, 07:17 PM
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K member fabrication, start over with tubular or add??? Chassis Fabricators step in!

Ok so i had thought i finished my frame over last summer, after my first test drive i realized it wasn't going to be good enough. The chassis twisted coming out of the driveway, and figured it wasn't good enough for my 300rwhp + nitrous motor. Well i got a new motor, 500rwhp LS stroker, so now i need to beef things up. I decided to buy a tube bender since it should be the strongest.

Here is a picture of the K or X member i currently have. First pic is the body test fit with tranny, next two were once it was finished and painted. Looks screwy in the second picture because of the angle, but its not. Also the only connection between the two center pieces is a bolt in tranny crossmember. The holes are to run the exhaust tubing.





Now should i add additional support below that? and some across from engine mount to mount?

OR start over, i have the motor and tranny out while i have the stroker assembled. With the body still on i can jack up the frame, make sure its square. The floor is removable once i pull the pedal assembly and seats out, so i have enough access to cut out the center and start over.

As of now i think im going to start over [while typing this i made up my mind i guess] These pics are not mine, if they are yours i will take them down, but its a reference of what i consider some good work. Flattery by imitation kind of thing!




In the next pic i would make the tranny mount removable. Down the line i need to have it rebuilt for my hp, its going to be crying with the new motor.



I also planned on something like the member under the pan, i don't plan to go a low, i prefer less of a curve for a little more strength.





I guess i know what im going to do, but would like some advice and pics of your own? Thanks guys.

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Old 03-14-2011, 07:23 PM
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Well that was confusing. So i guess yes. You should do everything you think you should.
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Old 03-14-2011, 07:38 PM
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yea im going to go back and edit that to make sense. I guess i talked myself through it
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Old 03-21-2011, 08:41 AM
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So never had a chance to go back and edit it, but here is what im planning to do more or less.





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Old 03-21-2011, 10:21 AM
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marcello
your on the right track, but maybe a little overkill.
your member is neither a 'K' nor 'X' and therein lies the problem.
an x-member should tie the frame together: top and bottom, side to side to minimize flexure.
your frame is open from the front member to the step up for the rearend.

below is a picture of my x-member and my reasons to build it this way.
trans mount is usually a good place for the X, my x-member ties the top, bottom and both sides of the frame together by brute force and resistance of the welded pieces. there is no actual X, but by nature of the amount of weld and thickness of the square tubing, everything is secure. the angle piece in the lower center has 4 bolts to keep it secure and allows me to remove it to drop the trans. the round tubing keeps the outboard body mounts from twisting and dropping the body.

behind my fabricated x-member is 2 stock K-members that have a box section across the frame and gussets to the bottom of the frame. they transfer load well and allow the drive shaft to move, good design so i left them alone.

i also boxed my frame front to rear as you have already done.







mine is not the only way, just mine and my reasons for doing so.

also my mustII x-member is also my motor mounts and yes you should add some structure there too.

you should start over; remove what you have and add half of what your drawing has and you should be good. anymore and your just adding weight.
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Old 03-21-2011, 10:48 AM
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So your saying i should focus less on the center, and more on adding support for the front cross member and rear step-up?

Im not 100% clear on what you mean. Here is what i got from it real quick:


Also i dont mind adding more weight, it very light as it is. I doubt i could get it to above 2500lbs even if i tried!
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Old 03-21-2011, 11:17 AM
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IMO that looks better, but...
straight pieces will flex less than curved pieces too.
straighten all those blue pieces.
also might want to add a little reinforcing where the frame steps up.
triangulate everything, triangles are very rigid.

this A,X,K is more rigid than U,S,O (look at the shape, not the letter)
that's why they have A-arms, K-members and X-members

also let someone else weigh in here, i'm an engineerd
i tend to over design by nature
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Old 03-21-2011, 11:39 AM
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Quote:
Originally Posted by ogre
IMO that looks better, but...
straight pieces will flex less than curved pieces too.
straighten all those blue pieces.
also might want to add a little reinforcing where the frame steps up.
triangulate everything, triangles are very rigid.

this A,X,K is more rigid than U,S,O (look at the shape, not the letter)
that's why they have A-arms, K-members and X-members

also let someone else weigh in here, i'm an engineerd
i tend to over design by nature

I don't blame you, im an engineer as well, i have my bs electrical and only been out of school for 2 years. So the frame stress isn't anything i've covered before. Although i learn very quick, I've been working for a year strait at my current company and i was promoted to run the final test department 6 months ago.

Now that i look over it again, i should have the bends right were the other strait pieces connect. Im sure a bend is much stronger than a welded corner.

I just got a new project, i need to have some power amplifiers made with parts from a new supplier and test durability. So SW drawing will have to wait till the end of the week i guess, i just started learning it last week so im still a little slow.
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Old 03-21-2011, 12:18 PM
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ahh an EE that explains it...
i am a CE, had 2 ME and 1 EE roommates, we never knew what theroretical bs the EE was working on

"Im sure a bend is much stronger than a welded corner."
nope. replace your blue pieces with a single straight piece



and don't build it like the red frame in your pics, unless you live in england (right hand drive)

Last edited by ogre; 03-21-2011 at 12:26 PM.
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Old 03-22-2011, 07:14 AM
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Quote:
Originally Posted by ogre
ahh an EE that explains it...
i am a CE, had 2 ME and 1 EE roommates, we never knew what theroretical bs the EE was working on

"Im sure a bend is much stronger than a welded corner."
nope. replace your blue pieces with a single straight piece



and don't build it like the red frame in your pics, unless you live in england (right hand drive)
The bent peice im referring to is the one that meets at the intersection.




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Old 03-22-2011, 07:22 AM
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Quote:
Originally Posted by marcello7x
The bent peice im referring to is the one that meets at the intersection.







Brian
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Old 03-22-2011, 08:49 AM
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Ok so i like to post alot of pictures i guess. It helps me display my ideas the best! So i was looking over the design and forgot i needed to route the exhaust piping through the frame. It won't clear very well underneath. I figured a 1/4 steal plate would be able to extend down and still give structual suppose for the rest of the frame.

Let me know if this will drastically reduce strength or not. The plate will be 7" tall. The side of the frame is 4" so it will hang down 3" below. I also added color to what isn't currently on the frame and is what i plan to add.





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Old 03-22-2011, 04:33 PM
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Skip the plate idea and just add some bends to the lower tubes to bring them back up to the bottom of the frame rails.

Straight tubes are optimal, but bends are still stronger then the plate idea

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Old 03-22-2011, 06:19 PM
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ok thats what i figured but wasn't sure. I can't weld to the bottom like that tho. That section of frame before the stepup is all chevy top hat, its then lined ontop and on the inner side with 2*4 tube cut to make a really large v bar.

I'll redraw it with the radius i can achieve with the bender and see.

I really want to get started with the actual fabrication, but i don't have the DOM yet. Also its a little difficult without the motor. I have the correct length driveshaft and will jack up the tranny to the correct location, but will hold off on the tranny mount untill i have the motor in and leveled.
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Old 03-22-2011, 10:32 PM
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This may give you some idea's..
Making A Willys Frame !!!!!!!!
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