how to prevent resin bending

[Red Dog]

I sometimes have parts perfectly good out of the printer but some of them are sometimes bending over time. 

 

Here's an example:

 

Out of the printer with a coat of primer:

 

The same part 2 months after:

 

 

 

Any idea what might be the cause?
Resin? 
Temperature? 
Curing time? 

Any hint is welcome
Many thanks

Rd

 

[csavaglio]

I've found that dissimilar thicknesses or large flat pieces like those 50 or 70 layer test print cards will curl. I assume you post cured it after cleaning however long the resin maker says to. 

 

I'm not sure what causes it, but the resins I've printed and from some of the manufacturers(I've had a few slightly warped missiles), hot tap water works well and the resin holds its shape fine after cool water. You prob won't need stove heated or boiling water to make it malleable.

Edited May 5 by csavaglio

[Red Dog]

Thank you for your input

 

Are there tables of guidelines of curing time somewhere?

I never was able to make the hot tap water trick to work. I tried on this very piece and I snapped it off - you can see it's been glued back

I hardly have the impression the resin becomes any softer in hot water

 

 

[csavaglio]

Each resin manufacturer has recommended setting and post cure times. Sometimes on their bottles, sometimes on the website. It does take experimentation sometimes. 

 

What resin brand and type are you using?  Some are extremely brittle. If you over expose and/or over post cure, it'll get more brittle. Any UV exposure will add to that. 

 

If the hot water didn't work, try hotter... If it doesn't work, the part was no good anyway.

 

You might want to try a different brand resin too, but you'll have to calibrate your settings again

 

[Red Dog]

Thank you

 

I currently use standard rapid resin from elegoo in a saturn 3 which I expose 1.6s after doing the usual calibration tests

I cure usually 2 minutes un the Mercury plus curing station, the part don't see direct sunlight after that

 

 

[wunwinglow]

Curing at an elevated temperature helps. I have an industrial hot air oven rescued from employers 'reorganisation' and warm built parts to 50 C before curing with 405 nm UV light panels (Temu, I fepping hate your stupid games, mouse and offer nonsense, but SOME of your products are OK!) for 30 minutes or so, then letting the parts cool slowly in the oven for another hour or so. I leave the supports on until after they are cured, as the support to parts and allow an even exposure, at the same time. I have a motorised turntable, with a mirror on it, although I suspect the glass absorbs all the UV that falls on it! Warm parts, even exposure all around at the same time, let the parts cool over a while,  seems to work for me.   I suspect exposing one side, then flipping the parts over and exposing to other, is asking for trouble.  

 

 

[csavaglio]

I haven't used the elegoo resin, but those times sound reasonable. 

 

I can't add much to Wunwinglows advice. It's a mixed bag with the supports before and after final cure. They come off easier and leave less blemishes before, but like he said, curing can be an issue. 

 

Bottom line, I've got nothing

[Red Dog]

Well, big thanks to both of you. It's great to read advices and other's experience anyway. 

I am in the same boat with supports as well. I like to remove them before because I tend to add too many and that way they leave less traces. But sometimes it is not practical and it might be the cause here as I did multiple test parts and I remember removing supports before curing on some of the tests but I didn't document it; So now I don't know for sure if that's the cause here.

 

In any way, many thanks for your input gents

[Modelpig]

Red Dog,

The main cause of such warping is the mass of material distribution across the entire part. It appears to me the aft portion of the tail base is solid (as is the forward portion) and the more mass will "pull" on the smaller amount of material as it takes a bit longer to fully cure. One option is to hollow out the interior of the larger volume of material in the part design. Another option is to add an "I beam" shape of material along the full length of the support pad and allow longer than normal curing time prior to coating with primer. (even consider up to an hour in direct sunlight) The I beam will help influence the cure to more of a fixed straight line and avoid the banana effect. Hope this helps.

 

Patrick

 

P.S. Don't let the part in direct sunlight for multiple hours...it will eventually start to slowly and subtly shrink. Ask me how I know.

[Timmy!]

As Modelpig suggested hollow the part and add holes to get the uncured resin completely flushed out.  Are you using a curing station?  If so cure in a clear glass container underwater.  If you are sun curing then underwater is an absolute must.  Depending on the thickness I cure my parts for a minimum of 30-60 minutes in my curing station.  Thicker the part a longer cure is necessary to stabilize the part.  Since I’m no longer working with figure out yourself resin printers and resins, I cure as dictated by the manufacturer, although I always cure in water.

 

You are going to hear that a cure that long will make the resin brittle.  I feel that many of the flexible or break resistant resins are that way because they are under-cured.  It is a pick your poison situation, bent or brittle.
 

Timmy!

[Red Dog]

great tips and many thanks for the advices. I know what to try next. 
I'm grateful. Thank you

[SwissFighters]

On 5/14/2026 at 9:16 AM, Timmy! said:

As Modelpig suggested hollow the part and add holes to get the uncured resin completely flushed out.  Are you using a curing station?  If so cure in a clear glass container underwater.  If you are sun curing then underwater is an absolute must.  Depending on the thickness I cure my parts for a minimum of 30-60 minutes in my curing station.  Thicker the part a longer cure is necessary to stabilize the part.  Since I’m no longer working with figure out yourself resin printers and resins, I cure as dictated by the manufacturer, although I always cure in water.

 

You are going to hear that a cure that long will make the resin brittle.  I feel that many of the flexible or break resistant resins are that way because they are under-cured.  It is a pick your poison situation, bent or brittle.
 

Timmy!

I'm curious how curing under water helps?
Tony