Never become complacent! After a long spell of trouble-free printing, I started to encounter problems a couple of weeks ago. First off, the old problem of lack of adhesion to the printer bed returned. I had become lazy about replacing the blue masking tape and the surface had become worn. After replacement and re-levelling, all seemed well again ... until the heat wave struck. The next problem was uneven printing. It was too hot for me in my work room, so I left it alone while I got on with designing components for the Armstrong Goods on my laptop.
When I ventured back to the ‘hot room’, I noticed that the printing filament seemed to have become hard and brittle. Some reading on the web confirmed that this is a symptom of water absorption in high humidity. I unwound the outer layer and it seemed better underneath. I must take care to keep my filament reels in desiccated containers, as recommended. Next, I tried a test print of one of my outside frame overlays and found that filament was ‘stringing’ between the rivet heads, so that they merged into raised lines. Earlier prints of frames for my Gooch tender had been very good, so I had yet another problem to investigate.
Poor-quality 3D Print
From more reading on the web, the principal suspect was filament temperature. I realised that, with my work room almost 10°C warmer than usual, the filament exuding from the print head was cooling less rapidly, so I lowered the print-head temperature by 10°C to try and compensate. Results improved considerably, although still not as crisp as I had on my earlier tender. I shall have to wait until the room temperature drops, to see if the previous performance is restored.
While trying to solve the problems, I made several test-prints of the side frames, which profligacy was fortunately not too serious, since the cost, calculated by the ‘Cura’ software, was only £0.02 per frame In addition, each print only took 10 minutes to complete, so I was able to assess the effects of changing parameters quite rapidly. This is an important advantage, gained by assembling a model from small individual components.
I needed to print four main components to add flesh to the brass skeleton, plus a set of wheels from ‘Alan Gibson’. The quickest to print were the outside frames at 10 minutes per print, followed by the smokebox at 19 mins., then the footplate and splasher fronts at 40 mins., with the boiler and firebox taking the longest, at 57 mins. None of these times was sufficient to present a deterrent to making trial prints for testing clearances and fit during assembly.
I printed the boiler vertically from the firebox end. Unfortunately, this precluded adding boiler fittings, such as the dome, as they would require additional support which might be difficult to remove without damaging the surface finish. I decided to print these fittings separately.
3D printed cladding on brass boiler tube
After the other printed components were complete, I glued the outside frame overlays onto the sides of the brass chassis assembly. To check the clearances around the wheels, my method is to thread the wheels onto long M3 machine screws and then add nuts to hold the wheels at an appropriate back-to-back spacing between the frames. I have used this method for my broad gauge models as well and find it a convenient way of checking the overall alignment before committing to fixing the wheels onto their axles. The component parts are shown below:
3D-printed parts added to the brass components, with temporary wheel fittings
My checks showed that the clearances for the footplate and splashers were appropriate, so I could now assemble the parts to make the main body of my Armstrong Goods engine. With its strong brass skeleton, my model has a good ‘solid’ feel.
Components loosely assembled on chassis
I tried 3D printing a dome and, while the main shape printed well, the flange to the boiler did not. I shall need to give more thought as to how to support this part of the structure during printing.
I did include the dome when I pasted a photograph of my model over the illustration of prototype No. 661. I am very pleased with the results so far, although there is still quite a lot to do in order to complete this model. My next steps will be to print the smokebox front and the backplate.
My Model (brown) superimposed over Engine No.661
EDIT - On looking at the photos, it was clear that the hind splashers were incorrectly positioned. Re-measurement of the computer drawing showed I had placed them 1 mm forward from their correct position. I have no idea what happened except that "to err is human". I have re-positioned them and will re-print. this component