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A-frame Design & Construction Thread 
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Hello All,

This thread is for everyone to share their ideas, experiences, tips, designs, and above all, pics/vids! All are welcome, including admiring and/or disgusted comments.

In case you don't know what an A-frame is, here's a picture for your viewing pleasure:

Image

Fred.

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Tue Feb 17, 2015 8:41 am
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Motivations:

Ute is far from legal and driving it on the street is risky at best with extreme consequences possible.
A track day with rare parameters is 2 weeks out, and rather than FreeEMS the Volvo for the road trip, the majority have asked that I take the ute to it.

Thus I need to build an A-frame. Thus I need to design it first.

I immediately acquired a tow coupling for it for 39 NZD: https://twitter.com/FredCookeNZ/status/ ... 3077147648
And here are my detailed measurements to which I'll be referring shortly: https://twitter.com/FredCookeNZ/status/ ... 3006559234

Which might display here, if I'm lucky:

Image



Design: TBC...

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Tue Feb 17, 2015 8:46 am
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delet4ed by LPGo


Wed Feb 18, 2015 7:20 pm
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This was finished ages ago, and put to use towing the truck/#2 to Hampton Downs race track for a day of FreeEMS abuse and fun :-)

I uploaded some pics of it ages ago, but didn't link here. Let me try to find them...

Image



And a few more that I just uploaded:

https://twitter.com/FredCookeNZ/status/ ... 4638144512
https://twitter.com/FredCookeNZ/status/ ... 2944914432
https://twitter.com/FredCookeNZ/status/ ... 1677112321

The one I was looking for never got uploaded because it had a plate in it. May edit and post that soonish.



And just as a reminder, you're a coward and a poor engineer, to boot:

LPGo wrote:
delet4ed by LPGo

Glad you're gone, boy.

Fred.

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Sun Jul 05, 2015 11:47 am
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Cross references to alternate uses of this thing:

1) Towable precision work bench/table: viewtopic.php?f=15&t=2541
2) Volvo 940 Caravan project: viewtopic.php?f=15&t=2634

Currently it's stuck behind the hotel in the corner. That has to change soon, though, as the caravan must make way for a new toy in about a week. So the A-frame will be coming out of storage and being put to some good use! :-D

Fred.

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Sat Feb 06, 2016 8:23 am
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I missed out a few critical details, so will try to reproduce them from reverse engineering:

  • Two mounting holes to the chassis of the ute
  • Spacing appears to be 35mm centres, though a bit wider could work, I think
  • Fasteners that hold the hinge brackets to the ute are M12x1.5 with 17mm and 18mm heads.
  • Hinge bolts have OD 15.5mm
  • Hanger brackets come with holes 15.0mm
  • Drilled out to 16.0mm, probably using a 15mm drill bit and some enthusiasm

Back to the caravan thread for a wee update.

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Mon Mar 28, 2016 9:46 am
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More missing details:

  • Dimensions of hitch plate are 130Lx170Wx5mm
  • Length of the 50x50x3 box pieces is 1900mm each
  • The steel used for hinge points on the A-frame is 40x16mm bar
  • Overall length from tip to tip including hitch is 2202mm (~150 past the end of the box @ front, ~170 past the end of the box @ back)
  • Overall length from tip to tip excluding hitch is 2087mm (hitch sticks out 115 past flat plate)
  • Overall length from hinge centre to ball centre is 2142mm (~40 back from tip of hitch, 20 forward of tip of hinge)
  • Centre to centre of box at hitch end is ~120mm
  • Centre to centre of box at hinge end is ~640mm
  • Outside to outside of hinge bars is 703
  • Inside to inside of hinge bars is 672 (32 less than above, hopefully, one is wrong by 1mm...)

Math to gain three LOA numbers:

Triangles 1900 diagonal, 320 minus 60 equals 260 small end, final side: 1900^2 = 260^2 + ?^2, 1900^2 - 260^2 = ?^2, 3542400 = ?^2, ? = 1882mm

  • Overall overall = 1882 + 150 + 170 = 2202mm
  • Minus hitch = 2202 - 115 = 2087mm
  • Hinge distance = 2202 - (20 + 40) = 2142mm

Hanger brackets are made of 6mm steel folded into a U shape with a gap of ~46.5mm in between and an overall width of ~58.6mm, they are 76mm long, and 51mm high to the tip of the D.

Hinge pin bolts are M16x2 with a shank diameter of 15.75mm and 24mm heads, nuts are also 24mm.

If I want to lock the hinge end hard I'll need 30mm of spacer at a suitably low diameter to clear the M12 fasteners that'll be holding it on.

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Wed Mar 30, 2016 11:19 am
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Probably should have read up on this before I designed and built this, but I think all is not lost despite not having been prepared. Galvanising.

Three areas of concern in this thing:

  • Seal welded overlapping surface in the hinge bars, though this is well under the 10,000 sq mm min for venting
  • Sealed cross member section 35x35 box
  • Area around welded in hinge bars, definitely has some hollow areas, but probably all drain very well naturally
  • Two seal welded overlapping surfaces between box and hitch mounting plate, see next post (EDIT)

For the former, I just measured and this is the result: 40x40x16 bar with a trapezoid with 85mm sides, which would worst case be 85x85=7225 sq mm, but is much less. Thanks to wikipedia, I know that it's 40x85=3400 sq mm, a third of the threshold for venting. https://en.wikipedia.org/wiki/Rhombus#Area

The sealed box needs to be unsealed 4x or more. 35x35 = diagnoal of 49.5mm, drain holes must be minimum of 1/4 of that, so drain holes must be 12.5mm or greater. I have a 15mm bit that exceeds that. Vent holes must be 10mm or greater. I'll talk to the galvanisers first and see what they have to say. 10mm will be my preference, but I'll accept larger if they want it.

For the latter, I'll need to show them and discuss.

Reference for all of this stuff, page 35 of http://www.galvanizing.org.nz/docs/Desi ... nizing.pdf among others.

Hopefully it's not impossible to have galvanised! I'd even be up for replacing the box cross member with angle cross member to achieve this if required.

Anyway, as soon as the caravan is road legal, I'll take it somewhere, park it, put it on a block or two, and remove the A-frame from it to fix it up and get it treated.

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Fri Apr 22, 2016 9:37 am
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I might do a little cosmetic/weight saving/shin saving work on this this weekend, too, ie, cut the corners each side of the coupling at 45* and cut the box section end underneath at 45*, and maybe drill another shackle hole into the other side of the plate, too.

Actually, those are seal welded overlapping surfaces, too. /me goes down to measure... < 100x50, probably 98x50-5x60 or something like that, eg ~4600 sq mm, under half of their threshold, so should be OK.

It could also probably do with another cross brace near the jockey wheel location, as the jockey wheel has a bit of spring to it right now. Which BTW, is this A-frame's new castor wheel for more convenient A-framing :-D Pics, copy/pasted from caravan thread:

Pre weld prep: https://twitter.com/FredCookeNZ/status/ ... 2490689536
Tacked on: https://twitter.com/FredCookeNZ/status/ ... 4055508993
Welded back: https://twitter.com/FredCookeNZ/status/ ... 6249746433
Welded front: https://twitter.com/FredCookeNZ/status/ ... 3510515713
On three wheels: https://twitter.com/FredCookeNZ/status/ ... 0985916416
On three wheels: https://twitter.com/FredCookeNZ/status/ ... 8094340096
On three wheels: https://twitter.com/FredCookeNZ/status/ ... 0671699968

Thinking just now... having the castor wheel on the front will make hitching up to the tow vehicle a trival task. Simply wind the A-frame up to the right height and drive it on using the towed vehicle. Once aligned, hop out and lower onto the ball! :-D

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FreeEMS dev diary and its comments thread and my turbo truck!
n00bs, do NOT PM or email tech questions! Use the forum!
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Fri Apr 22, 2016 9:50 am
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Did a bit of the above today:

Drilled drainage and extra chain hole: https://twitter.com/FredCookeNZ/status/ ... 5838799872
Diced corners off at 45 degrees: https://twitter.com/FredCookeNZ/status/ ... 4543846400 (and gave it a bit of a wire brush)
Reattached coating everything in a thin layer of waterproof synth grease as anti-rust: https://twitter.com/FredCookeNZ/status/ ... 4201198593

Totally forgot about beveling the box ends, however that'd be better done with the A-frame not bolted to the caravan.

_________________
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FreeEMS.org - the open source engine management system
FreeEMS dev diary and its comments thread and my turbo truck!
n00bs, do NOT PM or email tech questions! Use the forum!
The ever growing list of FreeEMS success stories!


Tue May 24, 2016 2:11 am
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