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Old 02-25-2014, 01:20 PM   #1
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Default DIY Tubular Subframe Discussion and Builds

So counting myself there are about 5 of us that want/need a tubular front subframe. I've been studying pictures and it looks like you could build these for about $200 a piece. I have about 30hrs of MIG experience so I think I can tackle this project. I planned on getting a 99 subframe, rack, and arms to make the jig out of. Looking for ideas on using DOM tubing, pipe, or square bar? How thick of a wall? Diameter size? How thick for the plates. Best way to make the alignment tabs for the eccentric bolts? I don't want to over build this as its tied into the unibody and supports a light 4cyl engine. I found a few threads for diy Miata subframes, but if you have or are in the process of this post up. I will probably be starting this next month, just in the design idea faze now. I have access to decent welder, water jet, and cheap pipe bender.

Home built subframe
MiataV8 Conversion: Tubular Subframe with Ford 302
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Old 02-25-2014, 01:42 PM   #2
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no suggestions really, other than you should make a thread and document this when you start!

Otherwise, DOM tubing would make the most sense I Think.
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Old 02-25-2014, 01:44 PM   #3
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For sure, I will list all measurements, dimensions, material. Once you notice that you can buy a Mustang K member for $300 it starts to make sense to build your own if you have the means. I wonder if I should use 1.5x.095 wall or 1.375x.125 wall, which is lighter? I'm also thinking 1/8" plate is enough for the suspension pickups and mounts to unibody. It needs to be light but also withstand a T-Rex attack.
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Old 02-25-2014, 07:01 PM   #4
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Pipe bender you're using for this DOM tubing?
I've personally had bad luck with a cheap bender and DOM.

Also, you'll need some type of notcher. I don't see why the kind that hooks to a drill press wouldn't work.
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Old 02-25-2014, 07:16 PM   #5
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I seriously considered building my own subframe, but in the end, I just bought one from V8 Roadsters. After looking at the one I purchased, it has given me some confidence that I could possibly pull off building a rear tubular subframe for the win.


I think to really pull it off, you need to build a jig around your factory subframe to get it perfectly straight, and so everything aligns properly. That will take more time and more materials.
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Old 02-25-2014, 07:21 PM   #6
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Quote:
Originally Posted by miata2fast View Post
I think to really pull it off, you need to build a jig around your factory subframe to get it perfectly straight, and so everything aligns properly. That will take more time and more materials.
There is no other way to do it than this way.
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Old 02-25-2014, 07:51 PM   #7
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Wasn't sure the OP realized that or not.
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Old 02-25-2014, 07:54 PM   #8
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Quote:
Originally Posted by jacob300zx View Post
bla bla... I planned on getting a 99 subframe, rack, and arms to make the jig out of...blabla...[/url]
Yes I realize a jig is a must. Keep the conversation going though.

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Pipe bender you're using for this DOM tubing?
I've personally had bad luck with a cheap bender and DOM.

Also, you'll need some type of notcher. I don't see why the kind that hooks to a drill press wouldn't work.
I'm looking at the JD2 Version 3 bender, I have used something similar to build rollbars, racks, and bumpers before.

https://www.jd2.com/p-32-model-3-bender.aspx

Or this

http://www.pirate4x4.com/forum/shop-...ng-bender.html

I'll probably grab a used miller off of craigslist and my family owns a fab shop in south Texas for the water jet plates.

Past project I did summer of 2012, 2x6 slider rocker replacement, aluminum rack, and front bumper. Ignore the wiring, we did it last minute so we could meet up with some buddies out at P.I.N.S at mile marker 35, last minute after it went dark.



I did the 4x6 rocker at home with a $100 HF MIG, the rack was with a aluminum spool gun, and the front bumper was with a nice Miller.

Last edited by jacob300zx; 02-25-2014 at 08:27 PM.
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Old 02-25-2014, 08:02 PM   #9
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God damn it. Once again my skimming habit gets me in trouble.


Onward.
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Old 10-24-2014, 06:14 AM   #10
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I've been heavily considering fabing my own subframe in hopeful preparation of a future J series swap. Looking at things I started to wonder if I could also fix some geometry issues from lowering too much, as in the a-arm angles and bump steer angle. Moving their mount locations UP would help even everything back out.

The easiest way I pictured doing this would be to first make a jig off the original subframe (obviously)
Then before fabbing the subframe, 1 inch spacers would mount the the frames body mount locations, and motor mount locations if using the stock engine. The jig would have to be made with this in mind so that bolting on spacers would actually move the mount location straight DOWN.
From there, fab as normal.

Once bolted to the car, the a-arm and rack mounts would be moved up from their stock locations, but the motor would stay put.
Now is there enough room to move the mounts up an inch? I can't say.
The main clearance issues would be the steering rack to oil pan, upper arms to the body's frame rail, and possibly the rear mount of the lower arm.
Raising those points any amount should help a car that isn't factory height though, it doesn't necessarily have to be as much as an inch.

Just something to think about when fabbing your own subframe.
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Old 11-02-2014, 02:16 AM   #11
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J swap sounds cool.
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Old 07-04-2016, 12:45 AM   #12
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I really wish this thread didn't die, anyone on here build one?
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Old 07-04-2016, 10:11 AM   #13
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Buying the mountless subframe from v8r is just too easy to **** about with making your own jig and getting a tube bender. Rough math puts return on investment of setting yourself up to make your own somewhere around 20 subframes, not including your time making them.
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Old 10-20-2016, 01:43 PM   #14
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What I would REALLY like to see is someone take a oem subframe and move all the control arm mounting points up an inch.

As well as the steering rack of course...
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Old 10-20-2016, 02:10 PM   #15
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Quote:
Originally Posted by d k View Post
What I would REALLY like to see is someone take a oem subframe and move all the control arm mounting points up an inch.

[...]
With that the RUCA would pretty much bind on the body right away, wouldn't it?
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Old 10-20-2016, 02:40 PM   #16
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That's why I said it WOULD be nice.....

Maybe cut holes in the body?


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With that the RUCA would pretty much bind on the body right away, wouldn't it?
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Old 10-20-2016, 08:32 PM   #17
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Wouldn't that = drop spindle?
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Old 10-20-2016, 08:34 PM   #18
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Similar yes.

Both correct roll center and bump steer.




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Wouldn't that = drop spindle?
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Old 02-22-2017, 09:05 AM   #19
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Hey guys i wanted to shed some light on this subject, I am a mechanical engineering student at Cleveland state and have 5+ years of experience of machining and about 3+ years of welding and fabrication experience. I designed a K-member that is similar to the v8R kit in solidworks using a factory 95 miata k-member. I already bent up all the tubes and made all of the tabs I just have to put them in the jig that I made and start welding. if you guys have any questions let me know as I may be able to help, ill post updated photos as I go along. i do not yet have the rack and pinion mounts braced in my solidworks design but I plan to come up with a good solution then add that to the model.


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Old 02-22-2017, 04:57 PM   #20
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I think you might want to mimic the NB subframe suspension points and rack mounting.

Nice work, BTW
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