3D Printing - General Thread

[eTraxx]

Zooming in .. note the part that I have highlighted. This sharp edge .. call it a knife edge .. failed on the checks. Remember .. I posted the minimum wall thickness for WSF. That is .7mm .. and the software sees that 'knife edge' .. the sharp bit .. as being under that .7mm minimum. You would think that the software might be smart enough just to round that bit off .. but .. shrug .. not so.

[eTraxx]

To get around that 'sharp edge' error .. I simply raised a .8mm ledge at that point. At the 1:48 scale model it only makes a small bump .. no biggie .. and it passed the checks first time

[Bill Gill]

Ed, Thanks, Excellent! Reference information combined with your experience.

[eTraxx]

Since the plan is to scale the chute up to 1:24 I made a change .. I flattened that sharp edge. Note that I made it .8mm wide .. not the .7mm minimum. I have to repeat .. the minimums cause a lot of pain. I think it has to do with and .. and I mean .. ANY ... rounding of the minimum .. will cause the software to take a dump. By adding that small .1mm to the minimum eliminates that problem.

looking at the chute with a sectional view shows that I made the walls .8mm .. everywhere as the minimum. In O scale .. that .8mm works out to about 1-1/2" full-size.  Note also that there are two sizes of holes printed. The ones on the flange sides are .762mm/0.030" .. to match the .030" shank on Tichy nbw. Honestly .. there was no reason to put the holes in the flange there as they will be covered with the gate assembly. I suppose it is just one more instance of my OCD. I did it because I could! The holes across the top I made 1mm/.040" after the test printing as I ended up drilling out the original .030" holes with a .036" drill bit.

The small 6.35mm box? That will allow me to scale the model .. later.

[eTraxx]

Ed, Thanks, Excellent! Reference information combined with your experience.

Thanks Bill. That is what am trying to do here .. show how I screwed up .. and how I fixed that screw up.

[eTraxx]

Ok. Enough of that. Let's scale the darn thing. So. Since the model is in Pmm (Pseudo mm) the model is in .. call it .. virtual mm. In O scale 1ft = 0.250" or 6.35mm. I simply created a cube 6.35mm on a side (yeah .. could have made a simple square .. but the cube is prettier). Various dimensions indicated for the 'fun' of it. Note the ... " ... since I am actually modeling in Decimal Inches .. but ignore that. Pretend you are modeling in mm

Scaling is as simple as using the Tape Measure tool .. clicking the 6.35 length of the box .. typing in 1.270 (in 1:24 1ft - .5" or 1.27mm) .. and hitting enter. Ah ha. Instant scaled model. Oh .. since the ... " ... (units format) may confuse people I unchecked it so just the numerals show. Hooray .. we are modeling in mm (well .. Pmm)

Take note if you wish of the dimensions but we will look closer at them in a bit.

[eTraxx]

Let's look at some of the numbers ..

• nbw holes are now 2mm dia. Full-size that would be 1.89 in.
• The boss has a 3.124mm dia. Full-size that would be 3 in. dia.
• The boss height is .6mm. Full-size that would be .57 in.
• The flange is 1.6mm thick. Full-size that would be 1.5 in. thick.
• The chute walls are 2mm thick - Full-size 1.89 in.

So .. this starts some questions ..

• the nbw holes. I used Tichy #8035 nbw. These represent a 3" washer with a 1.5" sq. bolt in O scale. The shank is .030"/1mm. In 1:24 you could for example use Tichy #8273 which would be a 3.75" washer and 2" sq. bolt.  This nbw has a .050"1.3mm shank.
  In any case .. the nbw used .. will dictate the dia of the hole.
• Again .. the boss dia will depend on the washer dia of the nbw used. If the Tichy #8273 were used I would suggest a 4" dia boss - 4.5mm dia perhaps. Again .. depends on which nbw is used. Just pointing out that selecting the nbw dictates the design.
• The .6mm boss height is fine .. minimum embossed height in WSF being .2mm
• Flange and chute wall thicknesses seem about right .. but that is the sort of thing that needs looking at early on in the design.

[Ray Dunakin]

Thanks for taking the time and effort to post all this!

[eTraxx]

Heck .. fun times Ray. 

at this point the important thing is the shank size for the flange nbw. The other question is the thickness of the flanges and such. Note that the chute itself is now 2mm .. which calculates to 1.89 in. full size. That seems a bit .. excessive . IMO! I would push it back to the 1mm thickness that I used for the 1:48 model. The flange thickness not such a big thing

[eTraxx]

Think it might be helpful/interesting to show how I stumble though re-working the rescaled chute. Calling this V1 for the purposes of this discussion. It isn't really but 'good nuff' for showing off the changes. I reduced the flange widths to .8mm .. which in 1:24 is approximately a 3/4" flange. I left everything else along for the moment .. I like to save each major change under a 'version' because you can guarantee I will screw up something at some point.

[eTraxx]

Here's a better look at the chute at this point .. I removed the chamfering as trying to reduce flange thicknesses would be a pain otherwise. I tried adding larger bosses to fit the Tichy #8273. Looked ok .. pretty much .. but afterwards I decided that I really didn't need them since the #8273 nbw has those large washers. There was also the problem with trying to add a chamfer which possibly could interfere with the bosses.

[Bill Gill]

Ed, Among the many things you do that I really like is strike an elegant balance between prototypical fidelity, modeling necessity and artistic expression. Good stuff!!!

[eTraxx]

V3 - removed the bosses. Added centerlines for the nbw holes. This is where you really need to keep this copy before proceeding .. with ANOTHER copy

In the next two steps I punch holes for specific Tichy nbw .. but this is a good starting point if we need to drop back and punt with another brand/style of nbw for example .. or even move/re-arrange the position of said nbw

[eTraxx]

V4 - punched 1.36mm holes through the flanges. This is an *assumption* (with all the dangers that term presents - with why you always work from a copy) .. assumption that we are using #8273 nbw with a 0.050" shank. That translates to a 1.27mm shank. Therefore making the hole .1mm larger works pretty well.

Just for the fun of it I have put a couple of Tichy #8273 nbw in place for visual 'fun'.

[eTraxx]

Finally with V5 - I added .4mm chamfers to the V4 chute.