top of page

Working With 3D Printed Resin Parts

Updated: Nov 2

I've been getting a few questions about the resin parts, and 3D printed parts in particular, so here is my experience and tips on using these "parts-of-the-dark-arts".


Firstly, 3D Printed Parts have a lot in common with the regular resin cast parts we've been familiar with for many years, however there are a few distinct differences to take into account.


Note... I will be referring to a Silicone mould as a mould, NOT mold, Both are correct depending on which side of the ball you call home (I looked it up!), but for our purposes, mould and mold are interchangeable, and don't mean the nasty furry stuff on the left-overs hidden in the back of the fridge you said you were going to throw out last week!


To give an idea of these of the two resin types, it might be best to give a crash-course in how these parts are made - simplified version.


Traditional Cast Resin

  • A master part is made.

  • A Silicone mould is created around this master part.

  • Depending on the shape and complexity of the part, a 2 or 3 (or multi) part mould may be needed.

  • A ''sprue'' port needs to be created for pouring in the resin.

  • Vent holes may be required for the displacement of air.

  • Curing takes place - vacuum or pressure.

  • Curing varies greatly depending on the resin used and in some cases the application of the final part.

  • Silicone moulds are separated and the pouring sprue is removed.


How to identify a poured resin part

  • Will usually have signs of a relatively large ''scar'' where the sprue has been cut off.

  • If a multi-part mould is used you will see a parting line the same as you see on a regular plastic injection moulded kit.

  • You may see evidence of the smaller vent holes.

  • If not cast correctly, under pressure or vacuum, there may be small / tiny air bubbles present.


3D Printed Resin Parts

  • Design software is used to create the parts in 3D (either free-hand or reverse engineering an existing part and modifying, or 3D Scanning another part).


  • The part is then exported in a particular file format into the ''Slicing Software''.

    The Slicing Software allows for multiple pre-printing operations to be carried out.


  • Placing multiple designed parts on the build plate and orienting those for best results.


  • Adding the support structures to hold the part while it is being printed.


  • Other operations such as hollowing out solid structures etc.


  • Finally, the entire contents of the build place is ''Sliced''.


    The SLICING process is much like a medical CT Scan, where a ''slice'' of the part is made horizontally, at a thickness we determine. The finer the slices, the smoother the detail on the part, with the trade-off being increased printing times.


  • The sliced file is then exported in another specific format that suits the 3D printer.


  • This is then loaded into the printer, resin poured into the machine and the process started.


  • The parts are printed layer by layer (an LCD displays each layer of the sliced object in a silhouette). A high powered UV light source pushes light through this silhouette thus curing a very thin layer of resin to the build plate. This all happens in a matter of seconds. Once a single layer is created, the light source turns off, the next CT Scan is loaded up by the printer, the build plate raises up and down again, however is one layer higher than previous, giving space for the next layer of resin to be cured in place. Pretty cool when you think about it.


  • The printing process can take many hours (some larger prints taking up to 18 hours), but most of our parts will take between 2 and 5 hours to complete.


  • Once the printing process is complete, the parts are removed from the build plate and cleaned in various solutions (IPA / Methylated Spirits / rinsed in water etc).


  • After they have been cleaned and left to dry we remove the major printing supports and do a basic clean-up.


  • Final step is curing under a UV light. This finishes off the curing process so they are ready to be packed.


How To Identify A 3D Printed Resin Part

  • No parting lines.

  • No thick sprue scars or vent holes.

  • No flashing to remove.

  • You will see small (less than 1mm diameter) ''dots'' on the surface of most parts. This is where the support structures have been attached for printing and removed during clean up.

  • The complexity of the parts can be far greater than those achieved with traditional resin casting, especially where undercuts / overhangs are present.






A few points of note

Where a poured / cast resin part can usually only be made one at a time (unless a ''tree'' or runners are made to cast multiple parts in one pour), the 3D Printing process allows as many parts as you can fit onto the printer build plate to be printed at the same time.


For example, if we place ONE part (like our 1/8 Revell Jaguar Battery) on the build plate, the printing will take around 3.5 hours. If we can fit 10 of the exact same battery kit on the build plate, it will still only take 3.5 hours as the machine is building / printing the parts horizontally, regardless of how many parts are on the plate any one time.

Below is a pic of the parts just as the printing process has completed. You will note the parts printing inverted, so the need for the support structures. The grey ''stuff'' you see in the vat is the liquid resin (we use grey but could be any number of colours).




This image below shows the same build plate removed from the printer. The amount of time it took to print this is only as long as the tallest part. In this case, the tallest part is the main carburettor body for the Pocher Rolls Royce. In theory you could ''pause'' the printing process and remove the items that are shorter and completed mid print, but this is highly inadvisable as the printing process relies on the plate moving up and down with 100% accuracy, and if you upset this process you will have misaligned prints at best, complete failures at worst. The trick is to group parts of similar heights to print at the same time thereby getting better value for time.


You will also note the support structures on the parts (have a closer look at the inlet runners for the Pocher Rolls Royce). All the ''scaffolding'' will be removed. This removal is what leaves the small round ''dots'' mentioned earlier.

We personally take a lot of time and do a few test prints to try and place all these support structures on areas of the model part that either won't be seen on the model once installed, or on areas easily accessible for filing, sanding, filling and painting.


Those of you who have the Rolls Royce Carb kit will see those support dots on the inlet manifold, but will know they are on the underside that really won't be seen once assembled...making for a neater display with much less prep by you... you're welcome.


This now bring us to the point of this blog.


Working With 3D Printed Resin Parts

Essentially working with the printed parts is just the same as cast parts, or injection moulded plastic parts.

Preparation

  • To remove the scars left by the supports, your usual files, sanding sticks / sanding pads will do just fine. Remember though this will create resin dust which is never good to inhale, so the usual warning will apply here. While the resin used in 3D printing isn't toxic per se when printed, it is best to use suitable gloves when handling and filing.


  • When sanding / filing, make sure to remove ALL of the support dots. In a lot of cases the parts are designed to be a very close fit. Leaving any of these little resin bits behind can mean a part doesn't sit flat and flush,


    Clean files out after using on resin though as the dust will clog up the surface of the file - get yourself a few of those brass bristle cleaning ''tooth-brushes'' from the auto parts stores to clean off your files.


  • If you accidentally gouge the part during preparation, still do a test fit as if this gouging occurred while removing the support dots, in most cases it won't be seen once assembled, however, you can fill with regular fillers, or the quicker way is a drop or two of superglue. Let it dry, then sand and file.


  • Resin parts are very strong when cured correctly, so can be drilled and tapped if screws are required to hold the part in place. If drilling, use the same action as you would when drilling wood. A mm or 2 at a time, remove the drill, brush off the resin dust, then drill again until the required depth is reached.


  • If you receive a part that is slightly warped (ie: some larger flatter items), use gentle heat from a hair dryer on the part as this can soften the resin just enough to bend back in to shape. You don't have a lot of flexibility with this but may mean the difference between fitting or not.


  • After prepping and dry fitting the parts, and all filing / sanding etc is completed, wash the parts in warm soapy water. Dishwashing detergent is fine but only use a couple of drops as you don't want to leave any residue on the parts. Once washed, rinse in clean water then set aside to air-dry.


  • Cyanoacrylate (superglue) is about the best adhesive to use. In all its forms (liquid, gel etc). Keep in mind the liquid version does bond the resin parts almost instantly so if you need a little time for ''wiggle room'', the slower acting Gel versions would be better. Regular model adhesive is largely ineffective with the resin. It will work, but does take quite a long time to attain any great strength and I can't attest to how it holds up over time.


  • If you get the part glued in the wrong place, learn to live with it!! Not kidding, the chances of you separating resin parts bonded with superglue is pretty much non-existent so dry fit as many times as you need to make sure where it ends up, is where you want it.


  • A VERY important point here is to make sure you STUDY the assembly instructions where necessary to follow the relevant steps. I will tell you how I know this is important.


    While test building our Pocher Rolls Royce Carburettor set, there is a specific build sequence that the body of the carb has that MUST to be followed.


    ''I designed this thing, I know what I'm doing'' soon turned in to ''I designed this thing and can't follow my own instructions''!


    I had glued the other minor assemblies to the main carb body before I attached a toothed cap / disc that sat a bit lower on the assembly. As a result, I wasn't able to attach the toothed cap to the assembly as there was no longer clearance to get it in place, and, because I had used superglue on the other parts, even though minor and small in size, (the whole thing only needing a mm to slide into place there was absolutely no way it was coming apart for me to correct the sequence. To add a little more embarrassment, at this point I had already created the kit assembly notes and just didn't follow my own steps.


    End result, I scrapped the entire assembly and printed another one to test build.


    The moral of the story - if it can happen to me, it can happen to you... like a twist on the old carpenter rule... MEASURE TWICE, GLUE ONCE.


    Painting

    This is perhaps the simplest process when using resin parts.


    Paint these as you would any other model kit parts. Lay down a primer coat. Go through the usual steps of sanding, levelling etc as required, then on to your colour of choice.


    Told you it was simple. Nothing really difficult or special when painting these, though the usual warnings again apply (spray in a ventilated area, away from flame etc).


    In some cases you may be painting the parts / sub-assemblies prior to final fitting. If this is the case, double check the mating areas / surfaces of the resin parts to others around it. Remove any built up paint in these areas as the paint thickness could cause the part to not fit correctly.


    No real specific requirement for types of paint either. If using lacquers, build up the base coats slowly, with a break between each coat so they have a chance to cure / outgas before subsequent coats.


    IMPORTANT NOTE

    This is important for any larger ''hollow'' type resin parts. Although we don't print parts that are hollowed out, I feel this should be mentioned.


    In some larger parts (especially figures), the designer may hollow these models (basically like an Easter-egg with a matrix of supports internally). You as the builder won't see these structures but they are crucial in making sure the model doesn't collapse in on itself. as they allow for much less resin to be used with a wall thickness of only a couple of mm.


    Before printing (during the slicing phase), the designer may add some small drain holes to allow less suction / vacuum to be put on the model during printing. This also allows drainage of the liquid resin once complete.


    The hollow model body, in combination with the internal support matrix, is a great place for uncured resin to hide out, and can sometimes still be present even after the cleaning and curing


    IF you receive a 3D Printed Resin model and notice a liquid coming from any drain holes, please put it aside and contact the person you purchased the model from.


    IF you get the resin on your hands or arms or anywhere else, try to avoid direct sunlight as this resin is UV Light curing, and ABSOLUTELY DO NOT touch your eyes. This stuff will cause a great deal of discomfort if exposed to sunlight or other UV light, if it's on your skin or in your eyes.


    Use some Isopropyl Alcohol or Methylated Spirits to clean off from your skin and wash thoroughly with soap and water. You may need to do this several times.


    If it gets in your eyes, stay out of the sun, and thoroughly rinse your eyes with clean running water. You may require a number of good flushes to get rid of it.


    The usual warnings and precautions apply here too, so if you are concerned or cannot flush the area completely, seek medical advice / attention.


    That's about it. I hope this has been useful. If there are any points in this you would like me to clarify just let me know.


    Overall, simply take the usual precautions, use the same tools you would for prepping regular plastic parts.


    In a lot of cases I also provide a few extra parts and spares in each kit so you can experiment with those before committing to a particular process.


    Take care,

    Leadfoot Models

42 views1 comment

Recent Posts

See All

Our First Blog - Welcome!!

G'day, and welcome to our first blog! Thanks for stopping by. As this is our first blog we thought it might be a good opportunity to give...

1 comentário


Chris Craddock
Chris Craddock
01 de nov.

That’s fantastic!

Curtir
bottom of page