3d printed roof vents crumble to dust, why?

[DCB]

I bought some proprietary 3d printed roof vents for an upgrade on some Graham Farish coaches.  Drilled the roofs and inserted some vents, but the heads crumbled on several just trying to pick them up.   Why?  Surely this is not normal.   Have they used the wrong material?

 

[njee20]

Hard to see from those photos, but yes, it sounds like it. A lot of printed materials can be brittle, and at that size it sounds like they’re just not strong enough. 
 

what are they printed from? Ie is it Shapeways or are they resin printed by someone?

[stevel]

If it is a resin print, I suspect they were over washed and or over cured, and as njee20 says many resins are very brittle.

A quick tip for photographing small objects, take wider shot from further away, and then crop the pic to what you want.

[DCB]

2 hours ago, njee20 said:

what are they printed from? Ie is it Shapeways or are they resin printed by someone?

 eBay seller, not from Shapeways... could be where I went wrong.

[MikeTrice]

Most resin 3D prints use UV light to cure. If left under UV light (daylight) they will continue to cure long after printing and will get brittle. You need to keep them under cover initially until a coat of paint can be applied which should protect them.

[njee20]

4 hours ago, DCB said:

 eBay seller, not from Shapeways... could be where I went wrong.

Not inherently. I think you get better results from home printers than from Shapeways. I would vote for over-cured then, as that means they’ve survived handling to get them out of the printer, removal of supports, washed and cured without breaking, but have now become brittle. 
 

Ask for some more!

[RedgateModels]

Matt Jarvis @noiseboy72 has some very nice black resin that is much more flexible than normal stuff, great for my 3D printed pan bases and APT half bogies 😁

Edited April 21, 2023 by RedgateModels

[njee20]

There are loads of flexible resins out there. RESIONE F80 is almost like rubber, you can print tyres with it and what not. Siraya Tenacious is great, particularly when mixed with other resins. 
 

They all tend to be expensive though and are harder to work with, so a lot of people will just stick to the normal resins, which can be great, of course, in the right application. 

[RedgateModels]

these came out great, bare black resin prints, connected to each other and an original Hornby half bogie

 

 

[noiseboy72]

On 21/04/2023 at 10:56, RedgateModels said:

these came out great, bare black resin prints, connected to each other and an original Hornby half bogie

 

 

Thanks Ian.

Yes, I use a variety of resins. This is an ABS like resin and I find it remains stable after printing. I've just made some signals for my garden railway, so time will tell how long it lasts. Hopefully it won't crumble. I use a modified Mars Pro, which uses high intensity light and a better screen to give very short exposure times, this seems to help with keeping things more flexible after printing. Post cure is limited to a few minutes, nothing more.

Edited April 22, 2023 by noiseboy72

[MikeTrice]

The point is if left in the sun unpainted they will continue to cure.