What the heck is an undercut?

[supervike]

It's a term that is bandied around quite a bit in regards to sculpting and casting. I've never truly grasped what it means.

Can anyone explain it to me in terms my feeble mind can comprehend?

Pictures would be nice!

 

[CreganTur]

An undercut is the void area beneath any kind of sharp overhang. They are areas where air pockets are most likely to form in the casting and/or molding process.

 

[cassar]

as above imagine if you will a ledge say on a bunker window the undercut is "under" the ledge, or insde some intricate detailing you have to be careful of undercuts as they can place a lot of strain on your moulds when extracting the product. it also means you have to think about the position you mould the piece in

 

[Einion]

Imagine a jello mould. You know how all the shapes basically face upwards? That's something with no undercuts, where you could basically pull it straight from a rigid mould and nothing would get left behind.

And undercut is basically anything that would prevent this kind of straight lifting out - even just under a pocket flap; basically anything where the master is narrower underneath something wider like under a nose, a visor or helmet rim, the hem of a jacket and so on.

Where there are undercuts either the mould needs to flex to let the casting go or for rigid moulds it would need to be segmented so each piece of the mould can be lifted off at the right angle so as not to catch (and rip off) any area with an undercut. This is how toilet bowls are cast for example.

Einion

 

[Wyrmypops]

I guess this is why cleap plastic mini's (SpaceHulk) are such a bugger for detail? They get that solid plastic running back into the mini on areas that on a metal/resin mini would just be an undercut. Metal molds, lack of flexibility without that segmented lark.

 

[Talion]

Here is a diagram explaining.

 

[BPI]

It's been particularly noticeable to me of late with painting both metal & plastic GW LotR Orcs. I'm gaming tonight but will try to take some useful pics later in the week

As above though, plastic has a rigid mold, metal/resin a flexible one. Thinking the production process through from there should help you to examine your own minis & spot the practical limitations of plastic (have you never painted a plastic & found that weird blank blob under an arm that doesn't really look like anything so you just leave it dark & hope it vanishes into the background? It's not lazy sculpting, just a limitation of the process).

Cheers, B.

 

[supervike]

Here is a diagram explaining.

Can I use my Flowbie for this type?


Thanks for the answers folks! I feel like I learnt sumthin'.

 

[BPI]

I seem to have missed a bit off my last post.

Unlike the plastics the metals have those dips & recesses rather than the blank fill. I only learnt this fairly recently though with reading on forums like this one. I've spent many years thinking that there was just some sort of magic going on, because I couldn't envision how they were made I still get muddled by this business of shrinking a sculpt 3x without it being done on a computer though.

Cheers, B.

 

[BPI]

Hi Supervike, is the term undercut making enough sense now or should I still try to take some pics to demonstrate? I confess I'm trying to get out of it but having said that I would, I will if it'll help

Cheers, B.

 

[supervike]

Hi Supervike, is the term undercut making enough sense now or should I still try to take some pics to demonstrate? I confess I'm trying to get out of it but having said that I would, I will if it'll help

Cheers, B.

Much appreciated, but I think I now have a working knowledge....

So, you are excused from photo taking duty (at least until I forget about this in a few months)