Hi, new here, & electric sprue cutter prototype

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Hi, new here, & electric sprue cutter prototype

Postby nev » Sat Feb 18, 2017 5:21 am

Hi there guys! I just joined youse! Hehe. My first post here. Great to see an ossie site! Electronics is my main hobby, with military modelling a close second. I have incorporated a bit of led lighting & sequencing into models in the past. Usually though, there's not much 'cross over' between the 2 hobbies. Until now. More on that very shortly!

The other day I couldn't resist, & I just HAD to buy the 1/35 miniart armoured dozer after reading up about it. I bought the nice Eduard PE set to go with it as well. Whoa! About a thousand parts in a little wee tractor that's not much more than 4 inches long. 250 parts per inch! Yup!

I love all the detail, especially the little petrol engine & its gearbox that were used to start the main diesel. Twin fuels. So much detail
there. Injector hoses. Injectors even.

Too nice, so my dozer won hisself a brand new bluprinted engine, epspecially built & tuned by an ex race driver back in the late 50's or
60's, I've heard. The D7's owner was owed a huge favour by this fella, who took on the job. So naturally, this guy painted the rebuilt donk
in titanium gold like was the norm for F1 racing engines & gearboxes back then.

So that's what happened. That's my/the dozer's story & I'm/we're stickin to it!

Actually, it's my excuse to paint the engine a nice bright metallic colour, rather than lose so much of the intricate details & gubbins in the dark
olive drab colour. Even after weathering & oil leaks etc, the nice detail should still be mostly visible with the lighter colour. I'l do the rest of it
in the old army colour though. I'm also considering whether to not include the armoured cab, as I have a lovely driver figure from L.Z. models to go in it, & a mechanic figure too. Not sure about the cab yet though.

Further research though warned me of the number of attachment points many of the fairly brittle parts have - like some the hoses & pipes - to
the sprues. Removing parts like that - I now knew - was going to be a problem. Even my little electronic cutters that I have used on those leadless 'surface mounted components', which are pretty small, would still impart that sideways 'jerk', that breaks the end off that small piece!

For another project I am slowly gathering the bits together to build a variable temperature hot wire cutter, so I was thinking about using heat to cut through the attachment points on my models perhaps?

So I bought an inexpensive 25 watt soldering iron from Jaycar electronics. I removed its plated copper tip & carefully hacksawed lengthwise down it's tip with a small hacksaw, down to where it goes into the barrel. With the tip split in half I fitted a scalpel blade there & clamped it
with a 2mm nut, bolt & washer. The 2mm bolt fits through the hole in the scalpel blade.

I was hoping enough heat from the soldering iron's element would get through to the scalpel blade to just sort of melt it's way through as it's
sharp edge moved through the plastic. Hopefully, without smoking the place out & melting the whole thing.

Well it seems to work! It will cut pretty cleanly through a 3 or 4mm sprue in a couple of seconds, with just gentle pressure - in only 1 direction!
I haven't busted any dag gum bits yet or flung them into another dimension, never to be seen again! - touch wood.

It has worked on the smallest of parts so far too, & if I use it to cut the last attachment point of a particular small part, the part will stick to
the hot blade, where I quickly remove it from the sprue, & lift the part off the blade quick smart! So the 'flick/jerk' action is avoided, & in fact
the part stays put.

The other handy thing is that the attachment points are not flexed or distorted, & the structure of the plastic is not changed. Like when
polystyrene turns white when distorted. These points are less of a mess now, especially along the seams. Blessed seams ay! - Not my favourite part of modelling at all - especially gun barrels.

There's not enough heat in the scalpel to melt adjacent parts nearby from it's radiant heat, which is a relief. I must remember though that just 1 touch of that hot scalpel - on an adjacent part - is likely to melt some kind of mark into it! D'oh!

As for the relatively small (usually) attachment points, the 'smodelling iron' just goes them easily. I use stainless steel wool to clean it every
now & again. It makes a lot less smoke than someone smoking a cigarette next to you, for example. Way less.

I haven't tried it but it may be useful in cutting out hatches & doors, or in place of a hacksaw at times.

It's a 25 watt iron though, & the wattage is the important spec here. A 30 watt iron might still be ok but a 10 watt probly won't get hot enough,
& a 50 watter may start to overheat other parts & generate too much smoke!

I should mention that a large enough fire from burning polystyrene plastic can kill you with the toxic smoke.

But we're just melting it so there will be way less of that. A small fan maybe just to blow the fumes away from you as you use it may be all you


I'm going to grind off 5mm from the blunt end of the scalpel to bring it closer to the heat.

I'm going to add another nut, bolt & washer & have 2 clamping points on the scalpel blade.

One day when I get down to the hobby shop & remember, I'm gonna get some copper sheet, or shim, to pack out the slot in the tip, & give a more snug fit for the blade.

Not only will these mods alllow the blade to get a little hotter, but get to that working temperature quicker.

Well, that's what I'm hoping anyway. Oh & I forgot too that having a second nut & bolt will stop the blade from spinning in the tip, obviously.

I hope this helps, or someone else finds it useful. It may have already been done, but anyway. I still keep hearin bout busted parts!

I'll try to post a coupla pics. Cheers & thanks.
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Re: Hi, new here, & electric sprue cutter prototype

Postby bell209 » Sat Feb 18, 2017 8:37 am

Great idea! I'm likely to move it sideways and melt the part, though. :-(

On the bench:

1/48 Airfix Hawker Hurricane Mk.I
1/48 Classic Airframes de Havilland Vampire Mk.35
1/48 Revell SNJ Texan
1/537 AMT USS Enterprise A (repair/refurbish)
1/72 Hasegawa SP-2H Neptune
1/72 Hasegawa AP-3C ELINT (rebuild)
Posts: 1880
Joined: Tue May 15, 2012 6:23 pm
Location: Sunshine Coast, QLD