• From: SF Bay Area
  • Registered: 2012-01-06
  • Posts: 721

Topic: Plinth On Top of a Spreader Plate

So, has anyone welded a plinth to the top of a spreader plate and passed tech?
If so, what kind of area did it have?

  • I have a emails into TEO, without response, yet.

  • Of course they'll be of appropriate thickness.

  • Yes, I read the "How To Not Fail Tech" manual.

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  • Registered: 2011-10-14
  • Posts: 4,167

Re: Plinth On Top of a Spreader Plate

In our case they were the full 24 sq in.

  • From: Tustin, CA
  • Registered: 2010-12-30
  • Posts: 3,275

Re: Plinth On Top of a Spreader Plate

Short answer, yes.  The Imp has plinth boxes on top of spreader plates.  TEO quite likes that cage and Spank's work on it.  Just about all of Spank's cages were built with plinth boxes on spreader plates.  Making the boxes is fiddly though.

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  • From: Scottsbluff, NE
  • Registered: 2013-12-01
  • Posts: 60

Re: Plinth On Top of a Spreader Plate

Yes, we had to build plinth boxes around the base of our main hoop floor connectors.   It was there to make up for the splice we had to do at the base because our Rhodes roll cage kit was too short for our seat.    I will post pics when I get a chance.

  • Spank
  • Utter Madman
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  • From: Escondido, CA
  • Registered: 2009-06-10
  • Posts: 5,864

Re: Plinth On Top of a Spreader Plate

I use a plinth when it allows me to essentially build up a platform that allows me to  put a larger spreader plate on top of a sill or box section of the unibody. I do put a spreader under the plinth as well. But just because I've done it doesn't mean it's right.

In the case of the below pics, TEO said the plinth is done well and/but/so the spreader plate on the flat part of the floor pan doesn't do squat (which I interpreted as it wasn't needed). I put it there, though, to tie in to the next body channeled section under the center of the floor pan mostly so that I can use it as an attachment point for seat mount rails in the future.

http://hubgarage.s3.amazonaws.com/photos/6166071/IMG_2941_detail.jpg
http://hubgarage.s3.amazonaws.com/photos/6166079/IMG_2943_detail.jpg

If you tie it in to the sill or a vertical component of the car, I don't see a problem with just going ahead so long as it is a reasonable size. If you're using it in place of a 4" piece of tube and it's just an isolated pillar in the middle of the floor pan, you definitely need a ruling ahead of time.

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  • From: SF Bay Area
  • Registered: 2012-01-06
  • Posts: 721

Re: Plinth On Top of a Spreader Plate

My main hoop is about an inch shorter than I'd like it.
My thinking was to raise it on a plinth.
I have more than 24"sq on my spreader with vertical attachment as well.
So, I think a 4"x6" plinth where the rect. tube is now,  tied into the vertical on the outside
should work.
http://i42.photobucket.com/albums/e346/GGolsan/Main%20Hoop%20Plinth_zpsmjflfxor.jpg

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  • From: Merrick, NY
  • Registered: 2009-05-13
  • Posts: 2,155

Re: Plinth On Top of a Spreader Plate

All of our plinth's are on spreader plates, we had a bit of rot on the floors so the spreader plates (which in some cases are fairly large )were used to fix the floor and then mount the plinth boxes to.

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  • From: Hayward, CA
  • Registered: 2010-03-23
  • Posts: 1,762

Re: Plinth On Top of a Spreader Plate

DelinquentRacer wrote:

My main hoop is about an inch shorter than I'd like it.
My thinking was to raise it on a plinth.
I have more than 24"sq on my spreader with vertical attachment as well.
So, I think a 4"x6" plinth where the rect. tube is now,  tied into the vertical on the outside
should work.
http://i42.photobucket.com/albums/e346/GGolsan/Main%20Hoop%20Plinth_zpsmjflfxor.jpg

In my opinion this should be great, assuming two things. The cross sectional area of the Plinth plates is bigger than the cross section of the tube, and you box it and weld all around.

The whole idea of the "spreader plate" is to spread the load from the tube end (assume another car falls on top of your car), so that the small cross section tube does not tear through the thin floor pan.  In this discussion I calculate that the 24 sq in spreader plate has ~48 times the area of the tube cross section, thus reducing the load (lets say a 5000 lbs car lands on one tube, so 5000/48 = 104 lbs applied to each square inch of the spreader plate, instead of 1000 psi (5000/0.5 sq in).

Welding all around will keep that tube from collapsing under weird direction loads.

A better thing to do is copy Spanks design and have the upper plate rest on the sill, then box it in down to the spreader plate. This puts some of the load on the (stronger) sill and some on the spreader plate, with greater cross sectional area than just the tube.

Here is a discussion about what I consider to be a bad design of the a plinth or mounting box.
http://forums.24hoursoflemons.com/viewt … p?id=27034

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