"Core-Shift" [?] of Older Kits' "Tooling" ?

[1972coronet]

I was ready to start on the MPC 1974 Road Runner (latest reissue) when I stopped due to a misaligned body & bowed A-pillars. 

Now, I've straightened bowed A-pillars before -- it's no big deal; an easy fix. 

However, I'd noticed that the right (passenger) side of the body has "core-shift". The base of the right A-pillar is off markedly, being +/- a one-sixteenth of an inch from where it should 'terminate' at the cowl. 

Furthermore; the front fascia is likewise off , though not as 'much' as the A-pillar; maybe one-thirty-second of an inch.

I was hoping to do a simple OOB build of this kit, but that A-pillar made me put the kit away until I can figure a way to fix its position -- which is where I'm stuck for now... like, Where should i make some 'pie' or 'wedge' slices in the roof to bring that pillar back to its proper position?

Has anyone else noticed this artifact-of-old-tooling on their copy of this kit? If so, did you fix it, or just go about building it as-is? 

[1972coronet]

I believe that I've got the issue addressed. I separated the lower-junction of the right (passenger) side A pillar at the cowl-fender-door, moved it inboard slightly, then glued it in its new position with Plasti-Struct [sp?]. I'll reinforce it after the adhesive cures.

I realise that this seems like I'm "picking fly s__t from pepper"; however, it was significant enough to compel me to fix this exponential "shift" of the body.

Still begs the question: has anyone recognised marked "core-shift" results of the tooling of these 45+ years old kits? 

 

 

[Mark]

I'd check the body against earlier issues of the same kit.  I've thought of "core shift" more as a misalignment between outer and inner halves of a mold.  Something like that would result in an interior bucket or body being paper thin on one side, and overly thick on the other.  A 1:1 engine block with core shift might have cylinder walls that are thinner than desired in critical areas.

[Ace-Garageguy]

Injection molding dies are typically pinned or otherwise positively indexed to each other, theoretically making repeatable precise alignment between the die cavities.

However...if an indexing pin (or whatever indexing means is employed) wears or falls out of an old tool, and the QC wizard whose job it is to pay attention to things like that happens to be texting or looking at panda videos instead, you get what you get.

I understand there's a pretty horrible misalignment on the nose of some of the Foose Ford pickup cabs, by the way.

EDIT: see below (photo by Nacho Z in his Foose Ford FD-100 in Splash Paint thread)

 

Edited March 3, 2022 by Ace-Garageguy

[1972coronet]

16 hours ago, Ace-Garageguy said:

Injection molding dies are typically pinned or otherwise positively indexed to each other, theoretically making repeatable precise alignment between the die cavities.

However...if an indexing pin (or whatever indexing means is employed) wears or falls out of an old tool, and the QC wizard whose job it is to pay attention to things like that happens to be texting or looking at panda videos instead, you get what you get.

Thanks for the correct terminology -- I used the term "core-shift" in the sense of misaligned die cavities. 

I don't remember what the prior Racing Chumps release (the one with the 1975 dashboard and chassis) body is like, as I haven't touched one since I did a commissioned build some 20 years ago. At that time, I didn't recognise any outstanding A pillar misalignment -- just the slightly-bowed pillars, which was an easy fix. 

Thus far, I believe that I've remedied the right-side pillar issue. I knocked-down/eliminated the parting lines before I attempted to repair the pillar junction. Next step is reinforcing the repaired area, then it's on to primer.

Thanks for your input .

[NOBLNG]

On 3/2/2022 at 2:53 PM, Mark said:

I'd check the body against earlier issues of the same kit.  I've thought of "core shift" more as a misalignment between outer and inner halves of a mold.  Something like that would result in an interior bucket or body being paper thin on one side, and overly thick on the other.  A 1:1 engine block with core shift might have cylinder walls that are thinner than desired in critical areas.

Like the interior bucket on the AMT ‘36 ford!

[Ace-Garageguy]

1 hour ago, 1972coronet said:

Thanks for the correct terminology -- I used the term "core-shift" in the sense of misaligned die cavities...

Thanks for your input .

You obviously understand the concept. Core shift means pretty much the same thing, as the "cores" in a sand-cast operation are almost always keyed to the outer molds to maintain alignment of cavities and material thickness, just as in any molding operation...be it pot-metal, cast iron or steel, zinc alloy, aluminum, magnesium, bronze, plastic (either thermoplastic or thermoset), open or closed molds for composite materials, etc.

If you're not in or close to the business, you're not expected to have all the terminology.  

EDIT: The "keys" between typical sand-casting molds are the little fingerlike projections on either side of the actual mold cavities and inserts, and are identical in function to what you'd find in injection-molding dies.

Edited March 3, 2022 by Ace-Garageguy

[Mark]

That is exactly the part I was thinking of.  I have a couple of earlier issue kits, should check those to see if that was there from the start...

[1972coronet]

56 minutes ago, Mark said:

That is exactly the part I was thinking of.  I have a couple of earlier issue kits, should check those to see if that was there from the start...

It's similar to the MPC 1971-1976 Duster-Demon-Dart Sport annuals and subsequent reissues (most recently, the '1976 Dart Sport'): every issue of that kit --well, at least from 1972-onward-- has an offset front wheelbase. Initially I'd believed that to be a result of eliminating the torsion bars (1973 & later kits), but that's not the case: my unbuilt 1972 Duster 340 annual has the same offset front wheelbase. Certainly, the offset has become exaggerated with time and ad infinitum reissues; yet, it's gone 'unnoticed' by the Q.C. folks.

While there are other issues with the otherwise nice MPC Dart Sport et al. kits (manual trans, but automatic shifter & console, and no brake master cylinder), at least the offset front wheels are an easy fix.