Oswestry Works

Locomotive works diorama in 4mm

Category: Experiments

Pushing the envelope with a B9 resin mix

GWR 9000 Class Top Feed test print

After what was in retrospect disappointing results with Spot HT – through my own ineptitude I must add, I went back to the tried and tested  1:1 mix of B9 Creator Red and Cherry resin.  This isn’t to say one is any better than the other, but with little life left in the layer of PDMS silicone before it needs replacement I didn’t have the leeway to experiment further with Spot HT.

This last batch of prints has been more experimentation with what level of detail is possible.  Second time round I reduced the size of the whistles and the steam heating cock to be a more prototypical size, even more challenging for the printer.  After quite a few false starts (left the projector lens cap on, build table not calibrated properly, not enough resin, ultrasonic died), I finally got a successful batch of prints of the highest detail so far.

This feels like uncharted territory because I’ve not wanted to let myself believe that it was capable of this kind of detail, until I’d seen it with my own eyes, coming out of my own printer.  I firstly revisited the design of the top feed for the Dukedog, the previous version not having a recess for the pipework.  This was designed to fit 20 swg copper wire, but the printed hole is slightly tight. It was a good exercise to see how well the resin could be worked with and the small hole could be opened up easily twiddling with a small drill bit.  This top feed will end up on 9014.

The whistles came out almost perfectly, considering that some of the detail in the design was under 0.25mm it would be impossible to see with out a macro lens or magnification.  Once cured these fine parts are quite robust, they aren’t indestructible but they did handle tweezers and finger tips, positioning them and trimming away traces of Tacky Wax under a magnifying glass!  It’s the detail presented on these that has really left me speechless.

GWR Standard whistles and mounting bracket test print

GWR Standard whistles and mounting bracket 30 micron xyz print

The beauty of this resin is it’s use to complement traditional materials, in this case matching up the whistles and mount with a Comet whistle shield etch and two strands of 36 swg copper wire to represent the whistle pipework.  The whistle print stood up to the finicky task of glueing everything together well, with impatient tweezer nibs looming, third hands full, trying not to drown the details out in glue.  This is the kind of detail I was hoping to attain after a few abortive attempts last year.

So with that done I think I’m out of excuses as to why 5726 can’t be finally painted and have its correct numbers fitted!

5726 with new whistle assembly

Comet Whistle Shield Etch, 36 SWG copper wire and 3D printed whistle and bracket assembly

5726 with new whistle assembly

5726 with new whistle assembly

Experiments with Spot-HT Resin

Other B9 Creator users have had some impressive results usingSpot-HT resin, in particular for small highly detailed components.  The main difference with this resin to the proprietary B9 resins is that you cannot use it for casting, it is also much less viscous which should mean that it settles quicker.

I’d just about enough life left in the layer of PDMS for another print, so today I tested printing some detailing components using Spot-HT.   The test parts I’ve roughly drawn up in Sketchup, some will need a little more work depending on the results of the print.  The test pieces were:

  • 4x Pannier tank rear steps
  • 1x Top feed for 74xx
  • 12x GWR Whistles pairs and mounting bracket
  • 14x Steam heating hose cocks

Spot-HT Test Print components

First up, the steps have come out really well, with a thickness of 0.5mm they look just right.  The rivet detail has come out nicely but I will probably increase the size next time round.  There is some flash to remove from the edges of the steps, due to the positioning on the build table.  Another thing for next time is printing these small components on a sprue. They were a devil to get off the build table without damaging! That said, this material is pretty tough even before curing under UV light.

The whistles have lost quite a lot of their detail but I think this is down to the clouding of the PDMS.  However, the small nut on top of the whistles has printed really well, considering its 0.25mm wide its pretty amazing!   The steam heating hose cocks also look pretty good, with the addition of a turned brass pipe and handle made from 0.4mm handrail wire.  However both these items are slightly overscale, I’ll have to get the micrometer out next time and make them more accurate!

Spot-HT test prints

5726 with 3D printed steam heating hose cock

For now that’s it for printing.  I’m waiting on my spare vat to return from the USA as its being fitted with a replacement for PDMS called Nuvat, developed by Evert on the B9 Creator forum (details here).  This new material should last a lot longer than PDMS.