That looks like an EPM?

Hi mate, what does EPM actually stand for? I understand you mean the circle on hilt that has remained after the saber was removed from the sprue, but I am curious what the initials stand for.

Whilst trying to find out about EPM, I did a search on the TIG forum and found a good thread from Scott and Stefan on the Pop-up sabres. I posted a link below incase anyone has not seen it yet.

R2D2 Pop Sabre Variants

Actually the thread that Bryan showed me in another post, has details for this...

Full thread here: New Weapon guide

Scroll down to see Marco's (Dr Dengar) little write up! Nice Marco!

Dr Dengar wrote:

wbobafett wrote:

Hey feelars,
We have to keep in mind that EPMs are not a sign of a unique mold/Coo family because weapons were produced one spure trees! Of course this cannot be said generally....but some weapons have "reversed" EPMs but also belong to the same batch! Let us just think of the lettered lightsabers....then we have a vague opinion of how many weapons can be on one spure or can be from the same production.

I tried to understand this a bit better, and just did some digging on the internet.

Sprue Tree


Source: http://imoldmaking.com/mold-making-2/mold-design/runner-and-gate/injection-mold-sprue-and-runner/


Source: http://en.wikipedia.org/wiki/Injection_molding

• Sprue: A sprue is a channel through which a molten plastic material is being injected from the nozzle of the injection machine into the mold. It has a smooth, round, tapered wall to allow smooth material flow.
  
• Runner System: Runners are channels where material flows from the sprue to the cavities.
  
• EPM (Ejector Pin Mark): Mark the spot where the newly injected plastic product is pushed out of the mould by ejector pins.
  

Ejector Pins

Source: http://www.bridgat.com/mold_components_ejector_pin_punch_guide_pin-o266889.html


Well it seems that ejector pins can't just be drilled through steel, so there need to be holes in the steel mould for these pins to be able to reach the central plastic injection cavity to be able to push the freshly cast sprue trees out. Right?

That means that that the existence of EPMs on products is a characteristic of the steel mould used to produce the corresponding sprue trees.


It can be imagined that every product (weapon, belt, etc.) within a sprue tree is directly ejected by pins during the process.
For some accessories - the Ledy cane comes to mind - this seems to be the case. Every Ledy cane has an EPM.

Just a few pins connected to 1) the runner or 2) just to a few of total actual products can also be enough to eject the complete sprue out of the mould. In that case 1) none or 2) only a small number of products have the EPMs.
On a very side note: that would be an explanation for the rubbery Meccano/POTF cane with EPM, whereas these canes normally lack EPMs.  




Now with respect to the placement of the EPMs (top or bottom):

It seems logical that the pins approach the sprue tree from one side. Pushing the sprue from two opposite sides with two sets of ejector pins just seems not very effective. In case the products (guns, weapons,..) are facing the same side towards an imaginary set of ejector pins coming from above or below the plane of the sprue tree, you would expect all EPMs to be placed on the same side of the product.


Source: Source: http://bloodofkittens.com/wargaminghub/2013/10/08/alternative-heavy-weapons-battery-new-uk-plastics-company-pdc-gaming/

When you look at the sprue above, all the guns are having the same orientation towards an imaginary set of ejector pins. In case the pins would come from above (below) all would have an EPM at the right (left) side

Now take the second sprue and focus on the four guns at the top left. The first and third gun are rotated 180 degrees towards the other two guns. Still all four guns face the same side towards an imaginary set of ejector pins.
In case the pins would come from above (below) all rifles would have a EPM at the right (left) side.


Source: http://bitzbarn.com/oscommerce/catalog/popup_image.php?pID=8789


From these examples it is clear that products having EPMs on opposite sides, must be orientated differently inside the sprue (and not just rotated).

Now it would be interesting to dig up some pictures of vintage SW sprue trees, and see how the different weapons are orientated.


BTW: This is not my field of expertise, just did some searches on the internet and wrote down what seems logical. Would be really good to have some input from someone who has a professional knowledge on industrial plastic injection.