Making molds of a part or 2

Kidd said
Thats awesome to see ! Lots of work there.How much over size do you make the parts to adjust for the shrinkage? I never took that into account, untill I asked a buddy about doing a 3D model of a slant 6 head, so I could shop around for a foundry.Shows how I dont know the field very well.
Great stuff, might look at some kick panals whan you get your extra sets.Keep up the great progress!
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Thanks I have fun doing it.

here's a list I use.
COMPARATIVE MOLD SHRINKAGE VALUES
----------Material -------------------------Type-------------------- Shrinkage/in/in

  • Polypropylene-- -------Semi-Crystalline---------- 0.010 – 0.025
  • Polyethylene----- ------Semi-Crystalline---------- 0.015 – 0.040
  • Nylon (6-6)----- ----------Semi-Crystalline ----------0.007 – 0.018
  • Acetal---------------------- Semi-Crystalline -----------0.018 – 0.025
  • ABS -------------------------Amorphous-------------------- 0.004 – 0.009
  • Polycarbonate--------- Amorphous -------------------0.005 – 0.007
  • Polystyrene -------------Amorphous------------------- 0.004 – 0.007
  • PPO------------------------- Amorphous-------------------- 0.005 – 0.008




on a formed part that will curve around parts it's about 1% overage. that's 3 solid coats if hi build primer and sanding smooth . or 1 coats of slick sand and 1 or 2 coats of hi build.. I do have to spray thinned epoxy glue over top to lock things down solid after that. on flatter pieces (like the splash shields and kick panels) it's a little easier I shoot for 2% oversize and let them stay big to trim. there's a BIG tolerance on these parts I'm making. darn near 1/4 difference from 4 or 5 different sources(different original parts checked to verify).

ABS and styrene have a large shrinkage amount , comparatively speaking that is:D (acetal .025 and nylon .018 was the worst of the easily available and moldable stuff) polypropyline(late model gas tanks and red gas cans ect...) and the others ones that shrink bad take more equipment than I care to make. (injection molding and molds $$$$$$ not an easy task) I can make em but I just don't have that kind of money 10's of thousands(for a good DIY injection machine and a grand or better for each mold, no screwups allowed) and instead of just a grand or 2 for each of my machines. and LOTS a bondo and primer!:cheers:


for an exact to the thousandth replica It's a crapshoot. you just add or subtract layers until the part comes out right. using the above list as a reference you can come pretty close on the first try but to be exact you have to make mistakes and correct them.

heck I'm learning all sorts of stuff since I started my restoration project on the dart. am I a pro? NOPE , ask me about windshields,sidelights(side windows in a car) and back lights (DUH right) and running a NC machine, printing using a silk screening process to lay out 90% pure silver onto glass or robots that need programming to move and manipulate glass products and I can give ya a good response. With the stuff I'm learning as I go with a little experience from years gone by when I had a small 2'X2' one for my R/C hobby. The internet is your friend in this case!