help needed - separating thin parts from sprue

[mikasa]

How do you get a thin cast part off a sprue without breaking it, or bending it irreparably? I have had trouble with masts and yesterday with arms on a Japanese gun director. So far I've been able to bend them back with the help of a little cement to soften the joint at the bend even further, but I have to think there's a better way to get the parts off without damaging them.

Thanks
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[Timmy C]

Try to make cuts farther away from the part - right on the main sprue "backbone", if you have to. This distributes the stress through a larger portion of the tree, with less bending at part connection point itself.

Try to make your first cuts at points that are less likely to see heavy resistance by the tree frame. End points of a mast are better to start with than in the middle, as the end points can flex more easily than the middle, which has multiple connection points that resist flexing.

[reigels]

Masts can be tricky - sometimes it helps to free the skinny ends first, and save the center attachment (if any) for last. I find that if I cut the center first while still attached elsewhere and it can kink.

Also helpful in some cases to cut the runner itself somewhere to release pressure on the part when separating it with your knife or snipers.

95% of my cutoffs are a rough cut to separate at a safe distance and a second finish cut to clean up.

[hawkeye3d]

I try to cut the attaching sprue completely off the major sprue. That way my cutter can be maneuvered with more easily and precision. Sometimes I find its helpful to just not use the sprue cutter and "chop" the small fragile part off with an exacto blade similar to what you would do with PE. Most damage can be repaired with a little glue but with these infinitesimally small and fragile parts there is a great risk of feeding the carpet monster.

Bob

[drasticplastic]

Most sprue cutters (Xuron type) push the plastic apart as the blades cut through. This put pressure on the thinner plastic of the part and can bend or break it, depending on the flexability of the styrene. That's why, as stated above, it's better to cut leaving a lot of sprue connected to the part, and trim later.

[Kometa]

Another alternative:

Use Hot Knife Cutter.

[drasticplastic]

Another alternative:

Use Hot Knife Cutter.

Well, that's a good way of totally destroying the plastic part!

[PetrOs]

I use a ultrafine razor saw, like this


P.S.
Apply no pressure when sawing, and do not saw exactly where needed - keep 1-2 mm distance. After the part is off the tree, use diamond files and a classic razor blade (in same handle as the saw, freehand is way too dangerous) to sand off the stub.

[Kometa]

Another alternative:

Use Hot Knife Cutter.

Well, that's a good way of totally destroying the plastic part!

Oh, no.
Absolutely not. There are two models. One simple and one more expensive. I have tried the first in many models without any problem.

[drasticplastic]

Now we're getting into expensive hardware for a simple job. How about a laser cutter for precision?

[PetrOs]

Well, if you have tools for other purposes, you can use them for hobby too. If I use my SMD soldering station to provide hot air for tensioning the stretched sprue rigging, its not using a microscope for hammering the nails - its use of existing tooling. If someone has a precision laser cutting device, why not In fact, I consider to get one selfmade CNC laser cutter for plastics or plywood for my shop - to make some model railroading modules for my layout

[Kometa]

Hello again.

I agree with PetrOs. I am seriously considering this tool. Red for metal and blue for plastic.

[drasticplastic]

Is that a Jedi light saber??