Shapeways, Prusa and Interesting Things

Wow I’ve been looking for elbows, flanges, valves, fittings, ect. ect. You have so many pieces I need…..but i need everything in 1:24-1:25 scale. Gets me to my question, do you up scale any of your pieces? Let me know and I’ll be in touch again soon.
Thank you, (name redacted)

This was posted to my Shapeways 3d Printing Forum a few days ago and since my reply may be useful to more than just (name redacted) I’m going to answer here.

I have used Shapeways since that long ago time when they existed only in the Netherlands and that they might have a printing facility in the US was only a dim glimmer in a Dutch eye. Prior to this I used a service called Print-A-Part. In those far distant days and even after they opened that facility in New York they provided a service to modelers that was reasonable and dare I say .. affordable. Over the last few years though it seems to me that bean counters have taken over the company and it no longer for me is affordable. That was part of the reason I purchased a Prusa SL1 resin printer so I could – “Roll my own”.

This has caused some difficulty as the CAD file that is uploaded to Shapeways is not the same as what I send to my Prusa printer. Shapeways uses a multitude of different printers but the one that I mostly have used is the prints from their Multi-Jet printers. This used to be called FUD (Frosted Ultra Detail) and FXD (Frosted Extreme Detail) but now Smooth Detailed Plastic and Smoothest Detailed Plastic. This irritated me as such unneeded changes in naming to me show a severe Bureaucrat influence.

The Multi-Jet printer can be thought of as a fancy ink jet printer with multiple heads that prints with a liquid plastic rather than ink. The model is printed in layers (something lie 26 microns and 16 microns for the ‘smooth and smoothest’ detail plastic respectively. Where it doesn’t print the slice of the model it prints wax which acts as a support. In contrast my Prusa SLA printer like other resin printers uses supports – like scaffolding around a building under construction as supports. This requires a difference somewhat in the design of the model. There are differences in how the models are laid out for printing – if you need 20 pipe fittings printed you will be charged by Shapeways for material in the model, support material, the machine space taken up by the height, width and length of the 20 models, and a charge PER part. This means in order to save money it makes sense to put the parts on a sprue – which adds to the material, support material and volume of everything taken up for the print. My resin printer mainly adds the additional cost of resin for the supports and for the most part does not require a sprue unless we are trying to print something very small.

The above was a quick overview to give at least a minimum of an overview of having a model printed at Shapeways or on a resin printer. Those 20 pipe parts .. let’s suppose they are 1:24 elbows if printed at Shapeways are arranged on sprues. Those same 20 elbows printed on my Prusa SL1 are 20 individual elbows with each sitting on the scaffolding/supports (during printing they actually HANG from this scaffolding – while called supports they are probably better described as hangers). What this boils down to is that when designing to print at Shapeways I am very careful to hollow out the model to save on material cost. This is not nearly as important when printing on my Prusa.

The important thing to understand is that if I design something for 1:48 scale and re-size it to 1:24 the wall thickness would be reduced by half. If my original design was designed with minimum wall thickness at 1:48 then simply scaling to 1:24 will mean those wall thicknesses will be 1/2 minimum wall thickness (around .3 mm).

Designing for 1:25 means that then it has to be done ‘on purpose’ for the most part. Simply scaling up a 1:48 model that is hollow with minimum thickness walls will not work as the walls will be too thin. Scaling up from a solid model works .. physically at least but then you get into design issues with pipe diameter itself.

To the left was a 1:25 scale model I did for a Fire Engine for a customer. The Elbows, Tee and Valves were created with wall thickness appropriate to the scale (this means that I scaled up a Valve for example by first removing the interior walls to make a solid model followed by using a CAD program to then hollow the scaled up model so the walls were about .4 mm thickness). This was by the way a pain in the rear to do. The elbows not so much as they were created from scratch so wall thickness was just part of the CAD work.

These were in fact uploaded to Shapeways and the customer purchased the spruced parts from my Shapeways store.

With all of that out of the way the final problems with scaling pipe fittings is the following:

Nominal Pipe Dimensions (US Standard)

  • For NPS ⅛ to 12, the NPS and OD values are different. For example, the OD of an NPS 12 pipe is actually 12.75 inches (324 mm). To find the actual OD for each NPS value, refer to the tables. (Note that for tubing, the size indicates actual dimensions, not nominal.)
  • For NPS 14 and up, the NPS and OD values are equal. In other words, an NPS 14 pipe is actually 14 inches (360 mm) OD.

Evergreen Scale Models Rod and Tube
It makes sense to me to design scale pipe fittings to fit readily available items. Evergreen plastic rod and tube are readily available with even a small selection found at Hobby Lobby. Larger sizes of tubing can be found at Plastruct. Since I design my elbows, tees and valves with a stud to fit the ID of tubing – normally Evergreen and occasionally Pastruct this limits these designs to those particular dimensions. Rod is not so useful to me in the smaller scales since the rod slides into a fitting which then needs to have minimum wall thickness – about .4 mm/.015″. It makes much more sense in smaller scales to use tubing.

Lets use five sizes of Evergreen tubing as an examples and see how they can be used in 1:48 and 1:24 scales.

  • #223 – 0.093″/2,4mm OD and .039″/0,99mm ID
  • #224 – .125″/3,2mm OD and .069″/1,8mm ID
  • #226 – .187″/4,8mm OD and .131″/3,3mm ID
  • #228 – .250″/6,3mm OD and .194″/4,9mm ID
  • #236 – .500″/12,7mm OD and .444″/11,3mm ID

Now let’s see what these dimensions would be in both 1:48 and 1:24. I will show the size each tube scale to in 1:48 and 1:24 and then what nominal pipe size that is nearest to (referring to Nominal Pipe Size on Wikipedia). I am ignoring the pipe inside diameter.

  • #223
    • 1:48 – 4.464″ OD : 4″ pipe has a Nominal 4.5″ OD. Using #223 tubing then means it is 0.036″ undersized full-scale. In 1:48 that is absolutely “Good Nuff”.
    • 1:24 – 2.232″ OD : 2″ pipe has a Nominal 2.375″ OD. Using #223 tubing then means it is 0.143″ undersized full-scale. In 1:24 this is only 0.006″. Perfect IMO or so close it makes no difference.
  • #224
    • 1:48 – 6″ OD : 6″ pipe has a Nominal 6.625″ OD. Using #224 tubing then means it is .625″ undersized full-scale. In 1:48 this is 0.013″ undersized. While someone with OCD might get ‘itchy’ for me it is .. “Good Nuff”.
    • 1:24 – 3″ OD : 3″ pipe has a Nominal 3.5″ OD. Using #224 tubing then means it is .5″ undersized full-scale. In 1:24 that is about 0.021″ .. At which point my own OCD might start to itch
  • #226
    • 1:48 – 8.976″ OD : 8″ pipe has a Nominal 8.625″ OD. Using #226 tubing means it is 0.351″ oversized full-scale. In 1:48 that is only about 0.007″.
    • 1:24 – 4.488″ OD : 4″ pipe has a Nominal. 4.5″ OD. Using #226 tubing means it is 0.012″ undersized. For me .. “Good Nuff”
  • #228
    • 1:48 – 12″ OD : 12″ pipe has a Nominal 12.75″ OD. Using #228 tubing means it is .75″ undersized full-scale. In 1:48 this is about 0.016″. Honestly .. for me .. “Good Nuff”
    • 1:24 – 6″ OD : 6″ pipe has a Nominal 6.625″ OD. Using #228 tubing means it is .625″ undersized full-scale. In 1:24 this is about 0.026″.
  • #236
    • 1:48 – 24″ OD : 24″ pipe is 24″ OD. Using #236 tubing means it is exactly the size needed.
    • 1:24 – 12″ OD : 12″ pipe has a Nominal 12.75″ OD. Using #236 tubing means it is .75″ undersized full-scale. In 1:24 this is about 0.031″.

I trust that using the linked Nominal Pipe Size Wikipedia page, Evergreen tubing sizes and a calculator you can run the numbers for the rest of the Evergreen tubing.

    Flanges and Bolts
    This finally brings us to Flange thickness, Flange Diameter, Bolt size, number and bolt circle diameter. Generally speaking the larger the pipe, the larger the flange and number of bolts. This means that while you can physically use say a 6″ Flanged Elbow made for 1:48 scale for a 1:24 scene it will fail in the number of bolts (ignoring the flange dimensions) – probably. To compound even more the flange diameter and thickness, bolt circle diameter, number and size of bolts changes depending on the class of the flange – Class 150, Class 300, Class 400, Class 600, Class 900, Class 1200 and Class 2500 – Diameters and bolt circles for standard ASME B16.5 flanges – 1/4 to 24 inches – Class 150 to 2500 … examples:

    • 3″ pipe: For Class 150, a 3″ pipe flange is 7-12″ dia with 4 3/4″ bolts while for Class 2500, a 3″ pipe flange is 12″ dia with 8 1-1/4″ bolts.
    • 12″ pipe: For Class 150, a 12″ pipe flange is 19: dia with 12 1-1/8″ bolts while for Class 2500, a 12″ pipe flange is 30″ dia with 12 2-3/4″ bolts

    Personally .. I am more than happy to keep everything at Class 150 (Pressure classes are defined as the hydrostatic water working pressure of the pipe in psi. The thicknesses of pipe are adequate for the rated hydrostatic working pressure plus a surge allowance of 100 psi with a safety factor of 2.0 for that sum.)

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Alan Rogers

Thank you for your website, fine article and willingness to mentor others.
I am emerging from a very high-tech industry in healthcare, but am a luddite when it comes to CAD files, 3D printing and laser engravng. I am on a BIG learning curve right now!!!