I attended a modellers' weekend at Great Missenden and participated in the course given by Alan Buttler of Modelu covering CAD for 3D printing, etching and laser cutting and I reported on the course forum my initial trials and tribulations as below.
I thought a little update on what I have been doing since the course might be of some interest. My first attempt at 3D drawing has just gone off to the printers and I'm curious to see how it will turn out.
Typically for me I started at the end instead of the beginning (of Alan's course) and set out to draw a chimney for 3D printing. How soon I get round to drawing for etching and laser printing will depend on the result of the printing experiment.
I had all sorts of problems with Sketchup particularly with snapping and getting things lined up properly. Particularly irritating is its drawing of circles as polygons.
So I tried Autodesk Fusion 360 and found it to be extremely powerful but with an interface that is, to me, extremely odd. Negative aspects have included a terrible help system, creation in a drawing of "read only" items that could not be moved (or exported), non recognition of ctrl+a,c or v! Despite what it says, it will not import Sketchup files. I failed to understand how to use the lofting function. Still it has functions that make it particularly attractive for doing other things.
Things I found easy with Fusion include handling of dwg files, filleting and screw threads (the dome and safety valve should have threaded holes to aid mounting - regrettably the system did not seem to include BA threads so I used metric ones - I wonder how well they will turn out). I also had very positive experiences when asking for help on their community forum (I'll post separately about the help I got on making the flutes on the dome and safety valve cover).
So I drew the chimney in Sketchup but had problems lining up things as a result of the program not recognising quadrant points on a circle. When using the solid inspector on the final drawing there were errors that could not be fixed but the help system failed to indicate how to resolve the issues.
A change of tack led to work on the dome and safety valve in Fusion and after struggling with alignment (yet again) I managed to draw the basic shapes. But then I hit the problem of the flutes: I could create a flute on a flat object very easily (draw rectangle, push in, fillet internal corners) but this did not work on a curved surface.
Then on to the springs - dead easy to draw one, but impossible to mirror it to make a second. All I could do was to copy it rotate the copy and move it to the desired place. Then draw the second type of spring, insert it in the drawing and find it impossible to move. Does anyone have any ideas why this could be?
Before going any further I thought I'd try netfabb to check for errors - springs were OK but there were problems with the dome and safety valve. Netfabb fixed some but couldn't deal with them all and the error messages made no sense to me.
Thinking of odd problems with other programs (not CAD) sometimes errors vanish when shutting everything down and starting up again. And with my CAD drawings the same thing happened - netfabb coming back and reporting fewer errors (but still some unfixable ones). So onto the next tack - try exporting from one program and importing into another; often this does not work but sometimes it does.
A very positive finding - importing the problematic safety valve into 3D Builder (that came with Windows 10) resulted in all the errors being fixed! (That's the first really positive thing I can say about Windows 10!)
Further such playing around resulted in assembling all the components I wanted into a single Fusion file with them attached to a sprue as this is said to be the thing to do for companies like Shapeways. Now the fun really started - it was impossible to select everything for printing. Any one item (or group drawn at the same time) could be selected but not more than one! And exporting the file in any format resulted in bits being missed out.
A final thought was to try TurboCAD that I used to use for 2D drawing only (but I now prefer Draftsight). The only common denominator I could find was STL so I created STL files of each component separately and then imported these into TurboCAD. That went very easily except for the chimney: this managed to place itself so that the sprue ran right through the middle of it! However TurboCAD would not let me select only the chimney to realign it properly.
A check with netfabb showed to my surprise and delight no errors at all! So I decided that I could cut the sprue from the chimney and drill out the inside if this proved necessary and sent the file off to the printers.
The advice came back that the lips of the chimney and safety valve had thicknesses just below the normal minimum but I've decided to have them printed anyway. I had wondered before I began if these lips would actually be better in turned metal than in plastic - I'll have to decide on this when the print comes back.
To summarise my learning so far:
1. different programs have very different strengths and weaknesses - one may have to use more than one
2. transferring items from one file to another, especially if from different programs, can cause problems
3. aligning in 3D is not a simple extension of aligning in 2D (which it should be), one may have to adopt differnt drawing techniques to accomodate this. (Does anyone know of a guide on this?)
What I would like to learn is how to work with coordinates (eg draw a line from x1,y1,z1 to x2,y2,z2). Is this option available in Sketchup, Fusion or 3D Builder, but buried in the interface options?
I was very pleasantly surprised when the print came back from Shapeways, well packed and with a technical appraisal of what I had done.
1. I had made some sprues too small and some fractured.
2. The spring hangers were, as I expected them to be, much too fragile.
3. The hole in the base of the spring formed well - in future such a technique would really help subsequent assembly.
4. The "lamination" of the springs showed up well.
5. The fluting of the dome and safety valve worked very well.
6. The threaded holes in the dome and safety valve did not form well enough for a standard bolt to simply screw in. I didn't investigate further to see if the thread formed was different from my bolts or if running a tap into the hole would have solved the fit - I was in too much of a hurry to get the model finished enough to take to the AGM.
7. The lip of the chimney printed perfectly and was strong enough to handle. Unfortunately it is just too brittle to survive the loco being put upside down on the bench - little bits have chipped out of it. Solutions suggested have been to print in a tougher material or make the edge thicker - I don't think the latter would be acceptable.
This forum will not allow the uploading of STL files so I can't include it here: if you think that the file might be of use to you, let me know and I'll make it available by other means. You should note that the items were produced from the small diagram in an RCTS book - I failed to find any dimensions for the fluting of the E.B. Wilson boiler fittings so these were a real guess, and from photos of other Wilson locos I'm not 100% happy with the proportions.
