Sanding and finishing for resin casting

Hi guys, Rob Mack here, I've been using the Shapeways service for many things, one of which is my latest move towards the designer toy industry.

I have worked with the parts printed by Shapeways with varying degrees of success and think it a good idea to post my findings here... Hopefully some of you will be able to avoid some of the mistakes I made.

Firstly, I just want to say that Industrial Steel Wool has changed the way I work here. It comes in varying grades and is perfect for sanding in fiddly corners and on broad surfaces. I still use wet and dry sandpaper but steel wool always play a part in the finishing process.

OK... Let's get down to business here...

WSF: I've found this material to be exceptionally sturdy and the grain of this material, particularly at the bottom curved surfaces can be quite persistent... I usually attack these areas where the grain is most evident with a 240 grade wet and dry until they appear a little smoother.

I then coat with spray paint. Any spray paint will do the job but of course, you get what you pay for. I use Mr Surfacer 500 Spray Primer here when only the best will do. This paint is really thick and grainy itself and great at filling in the grooves of the print. I usually give (over 24hrs) 3 coats of this paint to my model and then leave it for 24hrs.

That's when the steel wool comes into it's own. The surfacer primer is like matte plastic when it sets and allows the steel wool to sand away the groove impressions in the layers of paint to leave a fairly smooth surface. basically what I aim for at this point is to have the grooves or grain of the print filled with primer and the primer sanded back almost down to the bare print. I may repeat this process if necessary, particularly on very small models.

From there, once happy with the overall smoothness I go to Tamiya fine spray surface primer. This stuff is also expensive but awesome!.. I've been working with paints for over 20 yrs and have great respect for a good quality paint. This paint is just what it says, a fine finishing primer. it goes on silky and sands to perfection. By now I am down to my finest grade of wool and just coat, return a couple of hours later, sand it back, coat again, sand etc until it's perfect.. Sometimes, depending on the level of detail I'm after, this stage can take up to a week.

Now I tout the good paint because of my experiences with hardware store paints... I purchased many models as protos for moulding and the process of making the mould creates a great deal of heat (here comes the tears) Cheap paint likes to do all sorts of things under heated conditions and I've had my beautiful weeks work of sanding come off my protos 'in mould' basically rendering my proto, and the mould, useless... I also have had some issues with cheap paint becoming sticky when sanding and 'balling up' basically ruining the surface I'm trying to create...

Detail Material: process here is same as for WSF but the softness of this material lends itself better to initial sanding before painting. It really takes to wet and dry sandpaper as well as steel wool so it's far better a choice for prototyping for moulding than WSF. The only disclaimer I'll offer with that statement is that detail material doesn't absorb paint as much as WSF and if using cheap paint you may experience some peeling under heat. No problems when using the other 2 more expensive paints above tho.

Will post some fotos soon

Hope that helps some of you who are interested in taking your prints to the next level

Cheers
Rob

Thats lots of useful info for us! Thanks a lot!

I was hoping that I could sand WSF with a 600 dry sandpaper to finish it but seems like I gotta get some more sandpapers and primer to get the job done. Waiting for you fotos, I´m very interested in how well you can smooth WSF!

Hi Lorddarthvik, glad the info was able to help a little... I literally started with the same idea of using 600 paper but found it too slow at the beginning and not fine enough for my needs at the end. I also made myself various odd shaped flexible sanding blocks from silicone leftovers but really, once steel wool entered the picture it dominated my workflow... Working on the fotos now

Got some happy snaps of my mess together, here they are...

First some of the not so successful I mentioned. This is an example of what can happen when using cheap paint under heated conditions




and an example of using (very) expensive paint... This guy has loads of primer as well as a shiny metallic coat of polycarbonate paint



Here's what a couple of coats with light sanding can do... I never intended this guy for molding



And here's a before and after in Black detail material



Shapeways has changed my life and given rise to opportunities that I never would have imagined would be available to me.. Guys, if you're reading this, the humblest of bows to you... I am truly in your debt

Cheers
Rob

Two questions, what mold material were you using that created enough heat to make the paint peel like that? Second, that metallic paint looks great. Polycarbonate you say? I've never heard of that. What brand is it? Does it hold up to handling and scratching a lot better than acrylic, enamel and "ultra hard lacquer" spray?

I don´t know what brand of paint he used, but I used Pactra and Tamiya a lot. They are both pretty good paints. I used those to paint my R/C cars´ lexan ( polycarbonate ) bodies. You can buy it in model/hobby shops usualy in spray-cans.
Applying it to the surface is the same as with any other simple spray paint, just point and shoot on the cleaned surface.

I can´t realy tell about how well it holds to handling, as lexan bodies have to be painted from the inside. As far as I can tell they hold onto the surface very well, I only had some pealing when I painted in cold-foggy weather and used too much paint. And the pealing only happened after hitting a wall with my R/C car at 60km/h speed
Also once I tried to scrape off some of Tamiya metallic red paint I used, and no matter how much I forced it with my nails it didn´t matter, there was no visible scratch. It felt like if the paint molded together with the lexan.

Those are some realy great models and photos, thanks for the post!

bvicarious, I'm testing a couple of different types of silicone for moulding and each of them generates a fair amount of heat 'in mold'. the heat becomes very concentrated inside and makes cheap paint react (and steam come out of my ears). The polycarbonate is a tamiya paint. They have a PS ans TS range. The PS of course is the polycarbonate and yes it sets rock hard after a week or so. much more stable than any other paint I've worked with in 20yrs... THat's why I pay the premium for it

lorddarthvik, thanks mate, glad you like my mess and yep, most of the paint I'm using is Tamiya

Tamiya. Got it. Can't wait to try it out. Strange thing about the silicone creating heat. Is it RTV (room temperature vulcanization) silicone? I've only used OOMOO, smoothSil, dragonskin, and platsil silicones and none of them generate heat - I've even used them to create molds of wax figures.

Great input. Thanks a lot ...

woody64

bvicarious.. Most of the silicons I'm using are rtv but one of them was much harsher on the paintwork. It definitely generated heat and possibly one of the chemicals softened the paint. The silicon that I've decided to keep using is addition cure, non toxic beautiful stuff called Pinkysil It's perfect for my needs

woody64.. Glad if it can help bro, I've worked on some pretty small parts too but probably not as small as yr hats. I suggest an airbrush maybe and a sandblasting kit

I use mainly Smooth-on's Mold Max for my molds, and it doesn't produce enough heat to damage any paintjob.
And i've made molds of very thin objects (30x30x0.5mm)completely engulfed in the Silicone rubber without it damaging tamyia paint, or gunze or alcad, auto-air colors etc.
It's pretty safe to use that stuff.
You just have to be careful to use phosphor free plasticine if you make 2 part molds since that usualy is the cullprit in these heat issues.

Here are a pair of pics taken during the workflow, preparing some WFS parts for the mold.

The steps are:

1) washing the parts with water&soap, brushing with a toothbrush (not the one i actually use for my teeth).

2) sanding with 320 wet sand paper, then wash again.

3) 2 layers of Tamiya Grey Primer (at least 12h from each other) then wait for 12 hours.

4) steel wool refining (with 4/0 steel wool).

repeat steps 3 & 4 until satisfied.

It's quite the same workflow explained by Daddymack (kudos!!!) and it's the same i use with sculpey figures. Now i'm waiting for a couple of Mr. Surfacer 500 cans from Japan to give them a try!

After 2 primer layers and some steel wool refinishing:




After the washing and the first primer layer:



More pics: http://www.flickr.com/photos/alessino/sets/72157616003228817 /

thanks for the finishing info. perhaps you could help me out with my problem, as i am having trouble finding info. i need to cast some small parts for an electronics enclosure. some of it must be glass clear. it also must be strong, and thin as 3mm in places. i tried easy cast clear casting epoxy. it sucks. even a 5mm slug, fully cured, is easily bendable at room temp, and really soft if heated even slightly. also, the alumalite rtv silicone i used imparts a nasty yellow color to the epoxy. i have some better silicone on order now. what should i try for a better resin? should i just go to poly resin? any input would be greatly appreciated. i hate wasting money and time on junk that won't work. thanks.

Try Smooth-on.com for casting and molding supplies. They have a huge selection of products for all types of applications.