Stainless Steel Tolerance

Hello all,

I am currently designing a model train Ho scale. I would like to print one of the part in stainless steel to get sufficient weight but I have a question on the tolerance of Stainless Steel printing.

The design rules page says: "Parts are accurate within 2 mm of the design. Depending on how much binder is deposited, parts may shrink or grow slightly during the printing process. Binder deposits should vary depending on the geometry of the Shape in a build. Since Shapeways prints a variety of shapes in one batch, some parts might come out inaccurate."

- Does this mean that the tolerance is +- 2mm? In other words, my part can be up to 2 mm longer or shorter (imagining a rectangular part) This is a lot!

- Can this +-2mm can be in any dimension of the piece? +2mm in one direction, -2mm in another dimension?

- Do I also understand that this tolerance depends on the printing, meaning that if I reprint a part, the second one could be up to 4mm different in size from the first part? (making spare parts impossible!)

Also, I attached a step file of the part I would like to print. I guess the small rectangular holes (for attachment of the model bogies) are too small to be printed in steel? And if it could be printed but with a +-2mm tolerance, it would be unusable.

Thanks in advance for your answers.

A tolerance of +/- 2mm is in any dimension. I wasn't able to open your step file, but I would recommend using a material with higher detail and better tolerance. For weight leave pockets for lead or tungsten weights.

Hello bvanout,

I have purchased several parts using the shapeways SS process and have characterized them mechanically and compared them to my CAD models. For small parts (<2" x 2" x 2") I believe that you will find that you will get much better tolerances than +-2 mm. More like +- 0.2 mm.

This tolerances comes from the manufacturing process. I'm not going to go into great detail here, but part of the process involves burning out a binder material and sintering of the part. This causes the part to shrink. Shapeways attempts to compensate for this shrinkage, but due to the variation in the amount of binder deposited it cannot be exactly accounted for in the manufacturing process. This results in all SS parts either being slightly smaller in size (like you shrunk the whole thing by like 0.25% for example) or slightly larger. Additionally, this shrinkage or over correction to avoid the shrinkage varies depending on the geometry of the part.

Now, what this means for you from a practical standpoint is that your model dimensions will be accurate relative to one another but the whole thing might be shrunk or expanded slightly. As an example, let's pretend you make a 10 mm cube of material and have it printed. If the part shrinks, all three edge dimensions may turn out to be 9.95 mm x 9.95 mm x 9.95 mm or 10.05 mm x 10.05 mm x 10.05 mm depending on how much binder/correction factor was used. From my experience and understanding of the manufacturing process, you generally wouldn't receive a cube that is 10.05 x 9.95 x 9.95 mm. It will all either be shrunk or expanded.

Hope this is helpful.

Thanks both for you answers. This is what I was looking for !