Finishing techniques for SLA prototypes

Is there a way to achieve a very smooth finish for SLA models that is relatively quick and easy? So far, I have been sanding models through a range of grits, starting at 220 and working my way up to 600 for wet sanding. I have gotten decent results, but it thas taken me quite a long time. I have also tried some priming, but I’m not absolutely thrilled with the results the primer has given me. Any suggestions?

No. Unfortunately, there is no quick fix. SLA parts are not known for thier cosmetic qualities.

What kind of primer are you using? Check with your local DuPont paint supplier and see if they sell a primer that offers a heavy build up. You may need a spray gun. They will also likely sell a product caslled “guide coat”(I forget the brand). Its essentially an ink based spray paint that you lightly mist the primed parts as you near your 600 grit. As you wet sand the parts the black specks will highlight the low spots. It may take a second coat of primer and bondo if the parts are real bad.

you could spend 20-50% more to get the modelshop who made it to finish it…

We used to try to save some money for one client by trying to fix up unfinished “quickproof” models on our own. It took forever and never looked as good as the ways the pros finish them. In my opinion, not worth trying

Thanks guys!! much appreciated.

We get all of our prototypes made in China for a fraction of the price of US prototypes. They prefer to CNC (vs. SLA) their models because they can make them faster and require about the same amount of finish work. There are a few SLA machines in China, but they are expensive to maintain and service - so the models cost more.

Their transparent prototypes look better than molded off-tool parts (impossible with SLA)!! I was worried when we first started using China, but now I’m a believer and have started using them for freelance projects also.

Before you send any requests for names - they only speak Chinese, so you need a friend in China to help with the logistics.

After sanding the models (or beadblasting) I use a standard Krylon Clearcoat spray paint and it give the models a very smooth surface. It also helps to clarify the SLA parts, they never become clear like acrylic, but the do look much much better.

rather then sanding using sand paper, use a sharp single edge razor blade and scrape the part, this will remove the magority of the steps on flat surfaces and some round surfaces as well. also, if you have access to one, glass bead the part and this will leave a nice consistant surface finish.

A few things that may help.

If you’re not sanding through the primer coats then you shouldn’t have too much of a problem with the final finish, however SLA models absorb a lot of moisture, even from the atmosphere. I’ve seen SLA parts only 3 months old completely bulge and distort to the point where they are useless. If you need the model in the long term I would strongly suggest casting a silicon mould to capture the geometry while it is still reasonably accurate. You can create urethane parts from the silicon mould which are much more stable and have better strength charecteristics than the SLA resin. Depending on the urethane, you will probably find it easier to get a better finish than the SLA part too.

Yep, a mist coat is always helpful to show low spots and straighten rads, etc. No need to buy a specialised product , just get black acrylic paint in a can and spray the paint so it only lightly ‘falls’ on the surface. The idea is to leave speckles as pdog said, it’s also known as a dust coat fo robvious reasons.

It’s also important to tell whoever is making your SLA models, which surfaces you require to be the best quality. Beacause the models are ‘laminated’ (for lack of a better word) surfaces that are on slight inclines relative to their orientation in the machine will have deeper (longer) steps which will require more clean up.

Personally I would go to an 800 grit finish, but it all depends on the paint you are using. Steel wool can be helpful for polishing hard to reach places too.

Hope this helps some

This is a very informative discussion, especially for those interested in printing their designs. Lighting design is something where rapid Prototyping seems to be making some headway. However, the problem of dust retention , warping and yellowing seem to be major problems. Any advise in overcoming these issues ?