Miscellaneous Tips - reshaping resin

[miscmini]

A few folks have asked me to provide some tips, steps, and answers about how I do things. This seems like a good week to start. I'm setting up a camera by the workbench and will try to capture things I think are interesting. If there's anything special that anyone wants to discuss, please let me know.

The first subject I'll go into is reshaping warped resin. Unfortunately, sometimes minis will end up getting warped as they come out of the mold, during shipping, or during storage. It's a little frustrating when I'm set to get to work on a project only to discover the resin mini is warped. It's usually a relatively easy fix to correct the problem. The steps are to warm the resin so that it's relatively flexible, reshape the mini, and cool the mini. Sometimes the steps need to be done a couple of times to make sure everything is where you want it.

Here's a resin mini that I had in a storage drawer. The wings and stabilizers are a bit warped.



I've gotten everything I need for the process, hot water, the warped mini, cold water, and a tool to get the mini out of the hot water. I've a reference picture off camera that I'll use to check the mini against.



Here are some minis sitting in very hot water. The water has previously boiled and has cooled slightly. I'll leave the minis in the water until the affected areas are flexible. I generally start by letting the minis sit in the hot water for about a minute. Thin parts warm faster, thick parts take longer.



I'll fish the mini out of the hot water with the fork once the parts are warmed. Sometimes the parts will revert to their originally shape, sometimes I'll have to help them back into shape with a little pressure. The resin will start to cool, if it cools before I get everything where I want it I'll put the mini back in the hot water.

Once the mini is back in shape I stick it in ice water and let it cool.



And here's the result.

[gully_raker]

Nice "How to" Kevin & the pics add to it.

[Flying Officer Kyte]

A very succinct little "How to" Kevin.
I'm sure that will be of help to several members.
Thanks, and please keep them coming.
Rob.

[Blackronin]

Thanks for the tip, Kevin!

[Flying Helmut]

Thanks a lot - very helpful!

[miscmini]

Thanks all. I've been taking pictures as I work and hope to have a couple of more threads later this week. Kevin

[ReducedAirFact]

I know the original topic was aimed at Resin, but you end up doing a similar thing to "straighten out" warped Shapeways models too.

If you do this procedure with Shapeways models, be aware that "Strong & Flexible plastics are heatproof to 80℃ / 176℉ degrees. Higher temperatures may significantly change material properties." Frosted Detail Plastic I'm seeing mixed messages; one says 80C, another "55 ºC – 65 ºC (131 ºF – 149 ºF)". A candy thermometer can be handy in getting the right temperature. Erring on the low side is better than the high side. :-)

[Flying Helmut]

I know the original topic was aimed at Resin, but you end up doing a similar thing to "straighten out" warped Shapeways models too.

If you do this procedure with Shapeways models, be aware that "Strong & Flexible plastics are heatproof to 80℃ / 176℉ degrees. Higher temperatures may significantly change material properties." Frosted Detail Plastic I'm seeing mixed messages; one says 80C, another "55 ºC – 65 ºC (131 ºF – 149 ºF)". A candy thermometer can be handy in getting the right temperature. Erring on the low side is better than the high side. :-)

That's good to know.
I have a number of WSF planes with bent undercarriage struts which need straightening, and also a few birds with "wing droop".
Thanks for the tip!

[grumpybear]

Great tip thanks

[Ragnar200]

I heartily second Daryl's caveats about using heat to reshape 3D-printed models. The filament materials like ABS are monomers, and normally have a "memory" similar to the styrenes and epoxoids and urethanes. The concern when reshaping is the adhesion between the fused layers of filament.

The usual casting resins have a really remarkable capability to restore their original shapes when heated. I typically use boiling water (100C/212F). Others take a page from the optician and use heated sand to achieve gentle overall heating. It is fascinating to watch warped models actually move back to their previous shape whilst being dunked. The trick is to get the model to retain that shape as it cools.

It would be wise to proceed cautiously with any resins. The solid urethanes like Castmaster go plastic quite easily and the filled resins at higher temperatures. Be aware also that some casters use high temperature steel or aluminium filled epoxy resins that may require heating in an oven. My personal worst case experience was in trying to straighten some badly warped FM Schultz models from Berlin. Fredy's day job was manufacturing solid urethane food display items like sausages, so he used a fairly soft, inexpensive material that sagged quite readily. For thin sections like airplane wings and tails, Fredy made his castings with reinforcements like bits of window screen. Unfortunately Fredy occasionally also used some kind of spring steel strips, which I discovered only after carefully straightening a model and then watching it rewarp before my very eyes. The only option, in that case, was to cut through the reinforcement with a motor tool, correct the droop, and then fill the excavations with steel-filled epoxy.

I'm waiting for someone to ask how a steel-reinforced casting can warp. There is, of course, only one possible explanation. The models were warped when the resin cured, probably from being removed from the moulds while the material was still plastic.

Ron

[Flying Officer Kyte]

Very enlightening Ron.
I have only worked with simple Monomer plastics, and had no real knowledge about the printed materials. They were only just becoming easily obtainable when I retired, so that fills in another gap for me.
Rob.