JB's 3D CAD & Printing bench

During Summer using Anycubic resin I managed a 60sec bottom exposure but for Winter reverted back to 90secs.

 

Having increased the bottom exposure time and beefed up the top section of the supports a bit, everything printed pretty well. Here are the prints of the renders in my previous post - pretty much straight off the printer with minimal cleaning up.

Talk about cruel closeups....The layer lines on the smokebox door are barely visible with the naked eye. I'm going to try a couple of things. Firstly just paint it and see if the paint smooths the steps, and secondly reduce the layer height from 5 microns to 3 microns. May not be necessary, particularly as these will eventually be cast, but we'll see. For scale, this is just under 2cm wide.

The springs need a bit of remodelling in Fusion to make the join between each leaf a little more distinct.

Coupling hook - perhaps half a mill of so too long, but printed really well

Blowdown valve - needs a dusting but at 2.8mm long (including the spigot at the top) this is the smallest thing I've tried printing. My poor photography equipment (skills?) doesn't do the detail justice.

The buffer body and heads printed well. These are 2 separate components, which once cast will have a self contained spring - the wire, which prevents the buffer head from falling out will be trimmed back, soldered in and filed smooth. I need to alter the 3D model a bit though as it's a bit of a tight fit at the moment.

 

I had a couple of smokebox doors printed for me a couple of years ago. The first ones were printed flat and came out like yours with contour lines. Reprinting with the doors supported at an angle of about 45 degrees eliminated the contour lines.

 

I printed mine at about 20 degrees, do when I print it next time I'll tilt it a bit more

 

Anti aliasing might help.

 

Slowly getting there with the iClass - etches are almost done which I'll share a preview of before they head to the etchers. In the meantime I have been designing the inside motion. I was hoping Laurie Griffin might have something that would fit, but this loco is so tiny that I needed to start from scratch. Here are the slide bars - the rest of the components to follow. I'm hoping to learn how to animate all this in Fusion if time allows.

 

Here's the rest of the crank motion - the benefits of 3D modelling this first is that I can check everything fits! And it seems to work so far. Valve gear next.

 

Here are the first test prints for the inside motion for the Old Class i. For those of you familiar with resin 3D printing, you'll understand how critical getting settings and supports for the prints exactly correct for them to print correctly (or at all). I prefer to print in standard grey ABS-like resin first, as it tends to be the cheapest, meaning failure are less costly. The next phase in their development is to print it in a 'tough' resin (made by e-Sun). I've never used this before, so there will be a lot of experimenting with settings. I'll be interested to see how 'tough' it is, and whether it could be used as a final material for the model, or whether they will need to be cast (which is where I originally envisaged it going). Time will tell.



Slide Bars




Connecting Rods - the eagle eyed amongst you will notice that the big end needs to be in 2 parts to allow it to be fitted to the crankshaft......doh .


Cranks


Crosshead


Eccentric Sheaves


Eccentric straps (2 printed fine, but the other 2 I tried printing in a different orientation, and didn't work). They are a bit bent - this resin isn't really strong enough to stand up to handing/sanding, as the rod is only about 1.5m thick.


Expansion Links


Balance weights


One half of the motion mocked up for a picci

 

Progress has been a little slow recently.... not really anything to report on the inside motion, other than it doesn't look likely the tough resin will be up to the job of moving parts. It's strong enough for most parts, but the thin eccentric rods, which are only a millimetre or so thick, are still a bit too flexible.

In the mean time, I have been teaching myself how to use Blender. This is another 3D modelling program, which I think a lot of gaming, jewellery and 'minis' creators use as it's really good for sculpting. I'm currently putting sprues together for the castings, which will be printed in a castable resin before being sent off to the casters. Fusion is brilliant for modelling the parts, but I find Blender much easier to arrange and place items on a sprue. Just one of the sprues below and I'll post some images of the others once they are done. Then I'll attempt to print them (just in grey standard resin first) to see if I can work out how to support them before moving onto the expensive castable resin.

On another note, I can of course ask the casters, but if anyone knows where best to place the 'feeders' then let me know. Never having done it before, I've just gone with my best guess.

 

John,

I found a nice list of 10 rules for casting 10 rules for good casting that may be useful to get a general idea. Some of the rules are not really applicable for the small parts we want, but it may give you an idea what to do and do not.
I have learned the theory of at university, but never had to use it practically, so I am certainly no expert. I think your approach looks pretty good. As an example, all cylindrical parts should be fed in their axis.

Michael

 

Thanks for the link - that will be tonight's bedtime reading

 

I know this isn't 3D/CAD related, but I don't want to start a separate thread for this (see the build story here: Manning Wardle L Class 0-6-0, Bamburgh), but here's a different Manning Wardle, an L Class, I have just completed (an Agenoria kit, not one of my own).

 

A couple of updates.....

Having fiddled and fettled the 3D CAD work on Fusion for the Old Class i, I have got them to a point where I was happy with them. I then printed them in a castable resin. I used PowerResin Zero (mainly because it was on sale!) which has produced my best quality prints yet. Incredibly sharp and detailed, just by using the recommended settings - almost unheard of!

Just a few examples.... difficult to see the level of detail because it's black, but you get the idea. As the eagle-eyed will spot, I haven't sanded down the pips from the supports, and I did snap a couple of parts by not being careful enough.



















These have now been sent to the casters, so I should find out in a few days how well they will turn out.
I have also been playing with making my own wheels. I'm currently experimenting with a high tensile resin to see if it will be durable enough. I have printed a wheel centre to be a tight push fit into a steel tyre that I've had machined up by a helpful & local retired engineer. I then either file or drill a 'key' into the resin and the tyre, and fill with 2 ton epoxy. So far this method seems to keep the wheel concentric to the axel, but time will tell if the union between the wheel and the axel will be strong enough with the resin alone.

My next hurdle was the crankpin - even when tapping slaters wheels for a 10BA screw, I've never had much success tapping them perfectly perpendicular to the face. So to perhaps the most over-engineered solution ever. I used the .stl from the wheel centre to create an inverted 'imprint' of the wheel into a lower 'base', and corresponding top half with a correctly sized hole to hold the tap vertical. The wheel is put in upside down in the base, and the lid put on top, preventing it from moving. This allows the hole to be tapped nice and straight. You'll all be laughing at me now as you'll use one of many ways to ensure your holes are straight, but this one seems to work for me!! The resin was a translucent water washable job, which needs using up as I don't really use it for anything.


Ignore the screw in the back - this was just staged for the photo with a wheel I'd already made. It wouldn't normally be there at this stage.





You can just about see the key at the bottom of the wheel here:

 

And here are the castings literally fresh from the postie this morning. No cleaning up, and pips left on the prints from the supports still very much there. Generally very good quality and happy with them, although not without blemish - I'd set myself up thinking that they would come out as perfect as the prints, which was probably a bit unrealistic to say the least. The detail on the smaller parts is excellent, and all of the castings are better than some I've come across before - it’s the bigger parts where the most noticeable imperfections are. All being well, they will put the finishing touches to the model quite nicely. Now they are all here (apart from the one sprue I seem to have forgotten to print and therefore not cast - it had the expansion links and the top ends of the connecting rod to fix them to the crank shaft), I can start work on construction the model itself. I have designed the frets which are back from the etchers, so I'm all good to go! I'll start a separate thread for this though
Apologies for the number of photos that follow - but we all love photos! Also bear in mind they are VERY cruel close-ups!

 

I've started a new thread to follow the build of the Manning Wardle Old Class i - you can follow it here if you like

7mm - Manning Wardle Old Class i: a self-designed 'kit'

 

Impressive work

 

The photos intrigue me. The infilled letters look like the casters have made rubber moulds from your prints and the rubber has torn out around the letters while removing the print from the mould before squirting wax into the moulds. I could be wrong but I would expect the lettering to be better formed if they had poured the investment plaster around the prints and burnt out the resin. Could the casters have been worried about contamination, or not realised the resin is made to burn out with no ash? There would usually be a significant difference in price, especially for one offs. Just curious to know how the ‘defects’ came about. The parts you need look good.

 

I was wondering this too. I’m away on holiday at the moment - the castings arrived the day before I left. I’ll be getting touch with them when I get back home - not to complain, because the castings themselves are mainly fine - more out of interest. I don’t think they made a mould - at least I hope not - as I made it quite clear this was not required. They certainly did not charge me for a mould. My only guesses are that, a) air became trapped between the letters ,although in theory this shouldn’t be the reason as a I’m sure they vacuum the investment before it sets; or b) they didn’t follow the burnout cycle for the resin and ash was left. Possibly neither - I’ll let you know once I’ve contacted them.

 

I think an explanation of a couple of aspects of casting might help you.

Two things the caster needs to avoid are insufficient filling and porosity, small holes or sponge like areas in the casting. Porosity comes from a couple of sources, one being shrinkage of the metal as it cools, the other being gases trapped within the metal if it is kept molten too long after being cast. Ideally when being cast the metal should go from molten to solid almost as soon as the plaster mould is filled.

The problem is that a thin casting such as a thin smoke box door or some of the levers on your sprues will cool much faster than something like a dome.

Most casters control these things by adjusting the temperature of the flask (the tube that holds the investment, the plaster,) when the metal is being thrown into it. For castings that are fairly thin the kiln temperature might be set at 750 degrees C* so the flask the metal is cast into will be at that temperature. The high temperature ensures the mould fills but the thinness of the items mean they will still go from molten to solid quickly and so will cast well.

If a heavier item such as a dome is cast at that temperature it will maintain it's molten state for longer and you will get some porosity. For something like this you might set the kiln to soak the flask for a while at 650 degree C so you're casting into a cooler flask and the metal will still go from molten to solid quickly.

To put it simply if you put heavy items on the same sprue as fine items you'll almost certainly get some poor quality heavier items or you'll get good heavy stuff and fine items that haven't filled. Of course you could get everything wrong with some not filled and some porous! The thing is that you don't want to be mixing heavy and fine items on the same sprue.

The second issue here is the sprues. As you know metal shrinks as it cools, the problem being that this can lead to porosity caused by the shrinkage pulling different parts of a component or sprue system in different directions and leaving holes between them as they pull apart.

This is avoided by structuring the sprue system so that the fine components that cool first can draw molten metal from the sprue as they shrink. There's a link here that shows a sprue ready for investing. You'll see there are fine components that are attached to a thicker sprue that are attached to an even thicker central sprue. As the fine components cool they can draw metal from the small sprue that will cool just after the component and that way the component should be free of porosity. This isn't too critical but you don't want to be casting through too thin a sprue or you can get porosity where the component joins the sprue as the two things pull apart on cooling.

It also helps to have everything set up so the metal flows smoothly in one direction into the flask, sprue system and components, not always possible or critical but just do the best you can.

A suggestion for domes would be to have them hollow, easily done with Fusion 360. They don't have to be thin, just not a solid lump.

My knowledge comes from several years of practical experience of lost wax casting but I'd be interested to hear any comments (or corrections) on the subject from any of the proper engineers out there.

Hope that helps.

*Temperatures are just examples, they'll vary with the equipment used.

 

We use vacuum investment casting at work, from plaster flask to final pour, casting a variety of sizes and types of objects ranging from organic material to 3D printed parts (Form3 FYI). The latter is very much a constant learning process, and the adoption of new castable materials always involves a fair amount of testing.
Overseer, I see what you are suggesting but highly unlikely. This happens with porosity as Graham states, but also changes to the investment plaster around these finer details during casting. There are quite a few variables at work here so won’t bore, but the flow of gasses does interesting things to finer details next to a larger molten body.
John, it would be good to know your caster’s equipment and process.
We have trialed a variety of steps, from burnout programmes to different spruing strategies as Graham has indicated to try to ensure consistent casting with very fine detail.
They are great parts, and it is really positive to see for first attempts. Look forward to seeing them evolve.