Last week I was asked by a customer if it was possible to remove or strip acrylic paint from a 3D printed model.  Knowing that some 3D printed plastics can be sensitive to chemicals this was not something that I had attempted but decided it was time I found out.  In this post I will share with you what works.

You may be wondering why you would want to strip the paint?  Well, there are several reasons but two of the most common are splattering caused by blockages in an air brush and paint being too thickly applied.  Both can ruin the finish of a model.

With injection molded parts the paint can be removed with 91% alcohol or certain paint thinners.  However even some of the stronger ones can remove detail from plastic parts.  With 3D printed parts, particularly stuff printed in Shapeways’ Frosted Detail materials, these chemicals can have a disastrous effect as they react with the material causing it to melt or break up.

After doing some research I found a product called Dettol here in the UK which can safely be used to strip acrylic paint.  Dettol, as pictured below, is a low price cleaner and disinfectant which can be watered down for cleaning tiled floors and work surfaces as well as cleaning minor cuts.

The primary chemical is chloroxylenol (C₈H₉ClO); the rest is pine oil, isopropanol, castor oil, soap and water.

In order to test this product I need something 3D printed which had been painted, and something that I would not be upset about if it turned in to a blob of plastic and paint.  For over a year I have had one of my Yosemite Valley Railroad Log Cars sat on the work bench in a half-painted state.  This car had been dropped and some of the detail parts had broken off so it was not high on my priority list.  As you can see below it had received a total covering of the primary paint.  The paint was an acrylic made by Revell.

As this is only a small model I found a small jar, filled it with Dettol and popped the car in.

Having read all sorts of suggestions about how long to leave the model in the Dettol I decided to be on the cautious side and only left it for two hours.  I removed the car and already the paint was coming off on my fingers.  I ran the model under the tap and gently rubbed the flat areas with my fingers and they almost went back to white.

For the underside with all the lumps and bumps I used a tooth-brush to gently scrub and this worked a treat.

At this point I stopped. I could have removed every last bit but I was simply trying to find a method that works.  There is a drawback to doing this.  The Dettol does have a temporary effect on the 3D printed parts.  The car went very soft and pliable; it was very similar to when I heated this material with hot water to remove a bow. You can read more about that here.  This softening did not last and once the part had dried it began to stiffen again.  I don’t believe that it will remove any of the detail from the parts but if handled roughly in this pliable state the parts can easily be broken or torn if they are particularly thin.  I left the car overnight and the next day it was back to being a hard model and was ready to receive paint, although there was a smell that took me back to falling over in the playground!

So if you reach the stage with your 3D printed model that there is nothing you can do to cover a bad paint job all is not lost and you don’t have to order a new shell.  However I would still advise caution before dipping all your models in baths of Dettol; make sure you have a set down area ready for when the parts come out to reduce the risk of damage and avoid keeping the parts submerged any longer than necessary.

On another note should you wish to buy another 3D printed model, or even order your first 3D printed model, Shapeways are offering free shipping on any order untill the 12th of July 2015. Simply add your items to the cart and the free shipping discount is applied.

This week’s post will be a short one as my wife has got us tickets to see the new Hobbit movie, so I am off to the cinema, but I promise I won’t give any spoilers!  Last week I shared with you my new 3D printed O Scale UP water tenders for the excursion train, you can find the post here.  So this week I will share some of the work I am doing on the tenders, starting with cleaning them up.

The tenders have been printed in Shapeways’ Frosted Detail material. Models printed FD or FUD (Frosted Ultra Detail) have a waxy residue and need to be soaked in Bestine, Goo Gone or somthing similar. This leaves a powder on the surface which is the dried up wax residue.  I have also found that models in FD have more powder than models in FUD.  To remove the powder on my N Scale models I normally use a soft toothbrush and gently scrub the model.  This does not always remove it all, particularly from the difficult-to-reach areas.  To get over this I have a soft brush that fits onto my mini drill, similar to a Dremel tool. With the large surface area of the O scale tenders this made the job much faster and helped me get into all the tricky areas such as around the grab-rail posts.  These can be delicate and the toothbrush has an increased possibility of knocking them off.

With all the loose powder removed any areas showing evidence of the printing process become clear.  On these particular models it was on the curved ends.  You can see in the picture below that there are ‘veins’ running down the end of the tender.

These are actually plastic and attached to the model.  To remove these I use my mini drill again with a small sanding stone bit; because it is tapered it allows me to get the flat surface across the face of the model.  The trick here is a little bit at a time, if you go at too hard it is very easy to remove too much.

Once the area is ground flat, I use the soft brush bit again to remove any new dust.  In the picture below you can see the finished surface.  It is smooth to the touch.  You can still see the marks where the ‘veins’ were but these will disappear when the model is painted.

Painting the tenders will be the next step and I will share that with you in a later post.

Now the prints have arrived it’s time to clean them up and get them ready for painting. Actually I’ve had 3 versions of the log car printed so far with each being an improvement on the last.  The first was very short on detail, due to some modeling errors which have now all been fixed.  The second came out very well although I was unhappy with the deck planks all being exactly the same length; this caused the plank detail to disappear and the model looked too square and a little unrealistic.  The third and current version looks fantastic, although when I opened the box from Shapeways I could see there was a problem.  There was a bow in the main deck of the car.  I have had this before with other prints and it has resolved itself during the cleaning process. (please see my FAQs for more information on the cleaning process).

All the parts where put into a jar containing Goo Gone to remove the wax residue as normal.  I was hoping this might help soften the FUD material and fix the problem but unfortunately this time it increased it.  Here is the car after the cleaning process was complete.

So why does this happen?  Well the FUD material is printed along with a wax that supports the delicate parts as the print is developed layer by layer.  Once the print run is complete the parts are put into an oven to melt away the wax.  When the parts are removed and left to cool, one side will cool quicker than the other, and because this car is long and thin it will cause it to curl, very similar to the effect caused by heating and cooling a Bimetallic strip.

Although the Goo Gone softened the FUD material it was not enough to undo this effect, and leaving it to dry again caused the bow to increase.  However this can be removed from the model by using hot water.  Water at 150F (66°) will bring the model back to the temperature of the oven and the bend can be reshaped and as it cools it will hold the new shape.  For this log car, after making a cup of tea and letting the water in the kettle cool for a few minutes, I poured a small amount of the hot water over the middle of the car.  Almost at once it became softer and flexible, the bend straightened without any effort and I held the car in my fingers as it cooled and became ridged again.  In the photo below, the lower car is the one that had the bow in it.

I had to be careful as it cooled not to let the effect make the car bow the other way, if this did happen I could simply pour on a bit more hot water.  I will now leave the car to totally dry overnight, checking that the bow does not come back.

In the next post we will look at painting and decaling the car.