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Post Processing to Remove Rafts?

PostPosted: Tue Sep 01, 2015 4:57 pm
by 3DPrinter
Hi. I've been able to make several prints on my ibox nano so far. I have looked into post-processing for resin prints, so I know about the isopropyl alchohol + uv curing in water process which has worked pretty well at it's intended purpose to remove small bits of resin and finish the curing of the print. However, my issue is with the rafts. I have been printing 10 layer rectangular rafts with holes in them, and I'm having difficulty removing them from the bottom of prints. Most of the raft tears off easily, but the part on the bottom of the print does not. Is there a way to remove this part of the raft? What would be the best settings for rafts so they are either easy to remove or unnoticeable while also insuring the resin will be able to adhere to the print bed? I'm trying the 'model footprint' one right now for the gears. Should I be using that one for everything instead? And if so what settings should I use for it (eg layers)?

I've attached a picture showing the raft on one side of a dice print I made.

Re: Post Processing to Remove Rafts?

PostPosted: Wed Sep 02, 2015 10:50 pm
by ron.kundla
It is virtually impossible to remove a foundation from a print because of the way the resin cures. The only surefire way is through abrasives like sandpaper or files. If you have detail on the bottom of the item (like the pips on your die) then you will probably have a defect in surface quality or lost detail.

The best way to deal with that is to use supports. However, many of us who have tried to use supports have been disappointed with the results. The thin supports will be malformed due to the resolution of the LCD film and they usually cannot resist the peel forces, so the item being printed gets torn away from the supports and stuck to the vat.

You might want to try setting the over-exposure of the first 10 layers to try to get the print to bond better to the plate, but the success rate is highly dependent on the footprint and the remainder of the print. If it is top-heavy, there is a high probability of separation.

I swapped the FEP tape for Qsil PDMS coating and it has resulted in a more gentle peel which allows me to print without a foundation, but it does still on occasion allow the print to break loose from the plate based on the geometry of the item being printed.

Re: Post Processing to Remove Rafts?

PostPosted: Thu Sep 03, 2015 10:35 pm
by 3DPrinter
Thanks for your quick response!

Ah, sounds like it's just going to be a challenge to find a good compromise between getting a good bond to the print bed and rafts that don't obscure surface features then. I've found that the model footprint raft seems to work well for the gears, so I might see what else I can get it to work with. So if I set it to overexpose the first x layers, will it do that even if I set the number of raft layers to zero?

Re: Post Processing to Remove Rafts?

PostPosted: Fri Sep 04, 2015 11:38 am
by ron.kundla
Yes, the overexposure settings are independent of the foundation settings.