Removing Parts From The Sprues

[Dances With Wolves]

Hi folks.

Seasoned campaigners will already have their preferences in this regard locked ‘n loaded, so this is for anyone new (or relatively so) to kit mutilation, as well as the incorrigibly curious (like me) who just like to see how others do things.

My five friends, from the back and left to right.

1. Sprue nippers. Capable of chopping through most sprue gates, their only real drawback is they may cause the plastic on the part to scar from time to time (ie – the act of closing the jaws tears a little plastic out of the part where it joins the gate), requiring a little filler to rectify. This is because they ‘cut and crush’ the gate (the part of the sprue frame that connects directly to the part itself), rather than ‘cut’ in the way a razor saw does for instance.
2. No.10a scalpel blade in a retractable handle. There are innumerable ways parts can be ‘mapped’ on to a sprue frame. Sometimes access to a small part is so confined, the 10a is the preferred choice. You can either draw the blade over the gate repeatedly, until through or cut a ‘v’ in it that you deepen before repeating underneath on the side of the gate opposite. Never fit a blade to a round handle. One day it’ll assume a tiny life of it’s own, roll off the bench and with a high pitched ‘Wheeeee!’ dive bomb your foot, point first. It’ll hurt. The flat retractable holder stays put and the blade only needs to come out when it’s needed.
3. Tweezer nippers. These are a step up in cutting power over the 10a and capable of accessing the same tight spaces. Again, they ‘cut and crush’ but to a significantly lower degree than full size sprue nippers.
4. JLC razor saw. This gets the most use by far and has fine and ultra fine teeth. I use the latter on most applications, the principle being to cut only on the draw stroke to keep the cut accurate and controlled.
5. Razor saw. A heavier version of the JLC, this is great for cutting gates ‘full width’, as you’ll see below in a subsequent image.

 

Here’s a 1/72 engine for the Autocar in Airfix’s US Bomber Re-supply set. The part is small and the four gates are in locations where the moulded detail can be easily damaged if removal is attempted by cutting right next to the part. The crushing action of sprue nippers would be transferred to the part, pushing it away from them and distorting the other gates, likely causing tear damage. Best avoided.

Access for removal is tight. Time to travel a more circuitous route to where we need to get to.

To avoid such damage, take a step back and a different approach. The heavier razor saw was used to cut the gates away from the sprue frame itself.

The result is to now have the part completely released from the sprue frame, with the gate stubs far more readily accessible.

Once the part is thus safeguarded, the JLC saw can be used with the ultra fine teeth to cut the gate stub free. Once again, cut on the draw stroke (as you pull the blade towards you). Don’t attempt to saw back and forth but cut on the draw, re-position the blade, cut on the draw again and repeat until the gate drops away. This helps ensure a straight cut. If you’re less confident about this, simply ease the saw slightly away from the part and then cut on the draw. The surplus gate left on the part can then be trimmed off with the 10a and tidied with 1500 grit abrasive paper.

Here are the tweezer nippers in action. cutting at their tips causes almost no part distortion and they can access all manner of awkward gate placements but are obviously limited to smaller gates, as they exert less pressure than full size sprue nippers.

The sprue nippers have a flat side to the blades. Orientate the flat side to the part for the cleanest cut. You can opt to cut a little further away from the part if you think the plastic may scar, then trim with the scalpel afterwards and tidy with a little 1500 grit abrasive paper as necessary.

So, that’s the end of this mini-tour of one of modelling’s basic tasks. Think twice, cut once. Plan parts removal and as you’ve seen, don’t rush it. Better by far to make multiple separation cuts to free up access to the gates ‘off sprue’. Obviously the number of gate combinations and parts access you will potentially encounter in your modelling life is huge but the principles here will go a long way to ensuring parts damage is either eliminated or kept to a minimum. That means ‘frustration avoided’ and helps ensure a happy plastic basher.

Have fun with that plastic! Beer and cider has the same effect too…

[Mick4350]

I find the Xuron brand of sprue cutters to be a good way of removing parts from the runners without causing much damage to the part. They are a bit more expensive to buy and I don't mind paying the extra amount for the quality of the tool.

[Stew Dapple]

+1 for the Xuron cutters, though these days I prefer to use the JLC saw for removing clear parts as clear plastic seems to be more brittle and prone to splinter/fracturing than 'normal' plastic.

 

Cheers,

 

Stew

[CedB]

Great post Steve, very useful.

+2 for the Xuron cutters but they do sometimes cause scars as you say.

I'd add RB Productions nano-saws to the list - like the JLC saw they're great for close work and they're also much smaller, making it easier to get into little gaps in the sprue and avoiding the inadvertent scratches that careless use (ahem) of the larger saw can cause.

Tweezer nippers added to the shopping list!

[malpaso]

Good advice about cutting the sprues back from the part.  The design of modern sprues with external perimeters often means cutting both sides of a part can stress when cutting the first. I sometimes cut the runner the parts gates come from (ie the one parallel to the part) so that there is no pressure on the piece.

 

My sprue cutters are 20+ year old tamiya ones, which cut with barely a need to clean up.  But the blades are quite thick so cutting away nearby sprues is often essential.

 

A tip for avoiding stress cracks when cutting transparencies from sprues is to to cut them with a hot scalpel.

 

Cheers Will 

[CedB]

p.s. I now desire some 'tweezer nippers' and have spent some time searching for them. A quick zoom on the picture shows that they're Micro-mark #82393 and they're pretty unique and only available (as far as I can see) from Micro-Mark in the U.S. $19.95 with $10.49 shipping... total $30.44. That said they get good reviews.

Anyone know where they can be had for less in the UK please?

[Grey Beema]

I have a small pair of side cutters I use (wire cutters).  

 

When I am cutting off the spruce I turn them so that the flat side is against the piece I want to cut (the angled side away to wards the runner).  Also, if you can, put the length of the cut into the jaws rather than across the jaws (if you see what I mean)..

[Grey Beema]

4 minutes ago, CedB said:

p.s. I now desire some 'tweezer nippers' and have spent some time searching for them. A quick zoom on the picture shows that they're Micro-mark #82393 and they're pretty unique and only available (as far as I can see) from Micro-Mark in the U.S. $19.95 with $10.49 shipping... total $30.44. That said they get good reviews.

Anyone know where they can be had for less in the UK please?

 

Did you look here @CedB?

 

http://www.squirestools.com/tools-and-materials.htm

[Zebra1922]

I normally use sprue cutters, but I like the look of those tweezer nippers.  I'm off to do a search for some....

[Black Knight]

I too use mainly side-cutter, but also a SM no.12 blade [a hooked shape] and in the case of delicate looking parts, especially canopies I cut the sprue near the part first with a hot knife blade so there is no force at all on or near the part.

[CedB]

2 hours ago, Grey Beema said:

Did you look here @CedB?

 

Thanks Grey - what a great supplier! They didn't have the specific tweezer nippers BUT pawing through the catalog was, er, expensive...