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 Post subject: Datums
PostPosted: Wed Feb 14, 2018 10:58 am 
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Joined: Mon Apr 05, 2004 11:23 am
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Location: Eastern Melbourne
Before you get to excited that’s Datums not Datsuns. I’m looking to place centrelines and datum points on the body to allow quick accurate referencing. So step 1 would be engage Ausmini collective experience and step 2, follow as directed. :roll:

Let me know what to do for step 1 and why.


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 Post subject: Re: Datums
PostPosted: Wed Feb 14, 2018 12:27 pm 
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Location: near Baulkham Hills, NSW
People not robots spot welded Mini shells together, I doubt any 2 are identical.;)

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 Post subject: Re: Datums
PostPosted: Wed Feb 14, 2018 12:35 pm 
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Location: Wollongong, NSW
You can find the alignment diagrams in the Body section here, page R.11 to R.13
http://www.ausmini.com/manuals/Mini%20W ... 20Body.pdf

Remainder of the documents here:
http://www.ausmini.com/manuals/Mini%20W ... 0-%201967/

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 Post subject: Re: Datums
PostPosted: Thu Feb 15, 2018 7:54 am 
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Joined: Sat Mar 24, 2012 1:39 pm
Posts: 494
Location: qld
besser , using the vertical alignment check diagram on page 11 of timmy's link, i have always used approximations of F and H.. ( I say approximations because i find it a bit nebulous that the datum line isn't exactly defined in reference to the ground... and i say always, as in i have struggled to get my head around this a number of times)( I understand tyre pressures etc make a difference , but for me on a standard ride height car i would look to measure A and Measure O being 35 mm different.
Given different hi los, etc etc, even for a road car , i would suggest getting a corner weighting first at about 63 percent front 37 rear ( or thereabouts.. these come from a historic race car with roll cage but weight optimised otherwise) and then taking the sill measurement differences ( F and H or make your own repeatable spots), and then adjust ride height keeping the relative differences.
Would love to hear others opinions on this also.

I think i like the DATSUN question better Besser..... Cheers darryl


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 Post subject: Re: Datums
PostPosted: Thu Feb 15, 2018 2:32 pm 
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Joined: Fri Apr 01, 2011 8:33 pm
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I think people are tarting from there wrong end of the stick... A datum is a post you measure from rather than to...

So your horizontal datum is the flat level garage floor. Depending on what you are trying to do, flatish and levelish will be fine.

Create points to measure to by marking various points on the subframe and shell using a white engineering marker.

As explained in the Black Book use a plumb bob to drop vertical lines from the reference points onto the floor and mark these points with a marker. You can then use these floor marks to draw centrelines and check the alignment of your various reference points.

IF I was going to the trouble of doing this, I think I would get several pieces of high quality (stiff and stable) ply to form a false floor under the car. I think it would be almost impossible to get the car accurately back on top of the floor markings once you moved it. Whereas, the ply could be moved around to align it exactly in the same place under the car should it be moved.

However, unless you're trying to reassemble various pieces of a shell I can't really see why you would want to do this.

Cheers, Ian


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 Post subject: Re: Datums
PostPosted: Thu Feb 15, 2018 4:24 pm 
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You have vertical and horizontal datum's. It will take too long to explain how to use them. Remember most points on a mini are symmetrical opposite eg lengths are the same both sides. Panel fit is usually the way I check the body ,the front subframe in a lot of cases has a small twist. Easy to fix tie one side down and jack up the other .If you are fitting new guards and front panel you need to know what you are doing as the Heritage panels will need modifications in various areas. Most unitized bodies like a Mini are usually ok if the panels fit, if they don't you will need a Caroliner or Auto Robot to rectify the body. P7676


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 Post subject: Re: Datums
PostPosted: Fri Feb 16, 2018 11:17 am 
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1071 S,

Hi Ian

I totally agree about datum s being measured from. BUT my interpretation from the diagram referenced above, is that the datum line is NOT the ground and thus the silly need to go about things backward. More of a brain teaser for me, as i think for 99 percent of people, the fingers between tyre and wheel arch measures are close enough, but as with besser i am interested in other ideas. Cheers Darryl


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 Post subject: Re: Datums
PostPosted: Fri Feb 16, 2018 5:35 pm 
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FNQ wrote:
1071 S,

Hi Ian

I totally agree about datum s being measured from. BUT my interpretation from the diagram referenced above, is that the datum line is NOT the ground and thus the silly need to go about things backward. More of a brain teaser for me, as i think for 99 percent of people, the fingers between tyre and wheel arch measures are close enough, but as with besser i am interested in other ideas. Cheers Darryl


That's my interpretation of the diagrams... but it doesn't really matter. As I asked before ..as Mr Bridger might ask "for why?". Reading the measurement methodology ("Raise the vehicle and support it parallel to a level floor using the comparative measurements..... ") suggests that these measurements are not intended in any way to set ride height but to determine body shape/alignment.

If you're only interested in setting the height then the best way is to choose a wheel clearance at a front corner (horizontal drive shaft is a good place to start) then corner weight all 4 wheels... Bob Holden used to advocate jacking the back end up more than most people would accept to improve handling....

Cheers, Ian


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