Who takes care of shrinkage allowances in the precious metal material.?

The precious metal material option provides a very cost effective strategy for one off production of Model engineering items.

However it would be good to know who is responsible for applying the shrinkage allowance normally anticipated in the investment casting process.
The allowance can vary as a function of material and volumetric geometry

I do not have a problem adding an allowance to the model before the STL is created, but would like guidance from Shapeways on what allowance would be anticipated before the model is uploaded for final costing and production.

Can the Shapeways team advise please

Hey 3Dcompanions,


Thanks a good question, the designer is responsible for making the design according to the guidelines. You can find them by visiting the materials page on the website.

For cast metals there is an accuracy of ± 0.125 mm. This includes any variation caused by printing, shrinkage, polishing etc.

I hope that helps!

Best,
Andrew

Andrew, you've given a tolerance on printing, without giving the OP any guidance whatsoever on the shrinkage to expect. You didn't answer the question at all.

Shrinkage rates and tolerances are two very different things.

In other words, you've said allowing for shrinkage is the designer's responsibility. But how the heck can they do that if you don't give a percentage to expect in shrinkage? Any foundry can quote those figures easily, and SW needs to as well- the shrinkage allowance needs to be right in the material guidelines page.

I'm very interested in making some brass parts, but without very specific shrinkage rate guidelines I won't be wasting my time and money. Give me the shrinkage rate AS WELL AS the tolerance, and I can make intelligent choices in my 3D model.

Not everybody is making decorative things that have a great forgiveness for size.

Thanks,

Steve Hunter

I believe the closest we ever got to an answer was in this thread.

@mkroeker, I think you are right.

I do not understand why SW does not take the Materials pages seriously.

A big mistake, imo.

Typical lost wax shrinkage from other foundries tends to run about 1-3% in brass- ASSuming a properly sized wax print is used (different in other metals). For lost wax brass casting where cast wax masters are used rather than printed ones, it is typically 5-6% as there is wax shrinkage + brass shrinkage involved

I would really like to see this in writing on SW's materials page, as the present system places a ridiculous amount of risk on the customer.

I can't access my copy of Machinery's Handbook right now, so I'll include a couple of links for reference- note the doubled-up shrinkage due to two-stage casting...

http://www.shelmetcastings.com/shrinkage-allowance-for-metal -casting.html

http://benchpeg.com/toolkit/the-jewellers-toolkit-factsheet- 06-lost-wax-casting.pdf

Lost wax casting isn't a black art. With the amount of work done by SW, it should be very easy to confirm the shrinkage rates we can expect in each cast metal, and put it in the material specs. Remember, not all customers are engineering types who know to ask these things!

Steve Hunter

Hey Steven,

The accuracy listed in the material sheet is is what we can guarantee. We don't specifically mention variable for casting because, in the end result there are other factors, including printing and polishing.

If thats insufficient I'm happy to talk to my team about it, but please note that Shapeways isn't explicitly offering materials for engineering purposes. We can only guarantee what we print is fit for decorative purposes and that what is printed accurately represents the 3D file its based on within the limits of the manufacturing process. Those limits we share via the material guidelines. For more information you can take a look at our terms

For any other information you're welcome to ask our community as you're doing here, or feel free to test the material yourself.

Best,
Andrew

Hi, Andrew:

The thing is, if people know what shrinkage can be typically expected, your accuracy (tolerance) performance can't help getting better- it gives you even more breathing room on what constitutes a good print, while giving a far better chance of nailing the desired dimensions.

Of course, we have yet to hear WHO needs to apply the shrinkage, the designer or the SW employee who prints the wax model.

I'm not trying to be difficult, and not whining about your tolerances, which are fine, but this really is important to know and could greatly increase the number of individuals who would order cast parts.

Steve Hunter

I'm not sure why you're still worried. The answer is right there in the second post of this thread

The way I interpret that is that if you find a measurement out by more than that, you can ask for a re-print.

If memory serves, I read somewhere that Shapeways scales the model to account for shrinkage in the lost wax process. (I've also seen in a video somewhere that this doesn't happen for stainless steel prints, so I guess it's not true across the board.)

If SW does this, why are they unwilling to come out and say so?

+/- .125 mm may be insignificant in most applications, but it can be a show-stopper in many others. I am unwilling to undertake a rather expensive experiment based on hopes and conjecture.

So, SW, do you scale the models to account for shrinkage, or can we help things along by scaling in advance?

Steve Hunter

There has been between 0.3 and 3% shrinkage on all things I've ever ordered in brass. I now scale up a little to allow for this.

"There has been between 0.3 and 3% shrinkage on all things I've ever ordered in brass. I now scale up a little to allow for this. "

Thank you, Alan. This is precisely what I was hoping to hear from SW.

It is greatly appreciated and will help bring parts much closer to nominal! Have you noticed any tendency toward the low, or high end of the curve, or would 1.35% be close to where you would go?

It's pretty odd that SW couldn't just state a range of shrinkage like this instead of hiding their head in the sand and repeating their stated tolerances.

Maybe I can bring a few brass projects off the back burner now!

Steve Hunter