# Not able to reduce the cost

Discussion in 'Design and Modeling' started by yiomultimedia, Jun 15, 2014.

1. yiomultimedia New Member
Hi!
I reduced the volume from 45 to 32 cm3 and the cost remains the same (EDITED: well, not the same, but this item does not qualify for a discount, see below)

(in) 2.524w x 3.396d x 2.772h
(cm) 6.412w x 8.626d x 7.042h
Volume 32.3288cm3
Density 8.30%

The model is this Doghouse 01 Large - 1:12 scale

I guess this has to do with the relation between bounding box, density and cost as it says in https://www.shapeways.com/materials/strong-and-flexible-plas tic

"... Details on pricing / Density discount
We also offer a volume and density discount on Strong & Flexible materials. For models that have greater than 10% density (material volume divided by bounding box volume), volume above the first 20cm3 is calculated with a 50% discount.
Bounding box pricing on big low density products
Large, extremely low density models printed in White Strong & Flexible are priced based on bounding box volume rather than material volume. For models with a bounding box over 10,000cm3 and a density less than or equal to 2.6%, the price is \$.0385 per bounding box cm3 plus a base price of \$1.50. See our blog post to learn more..."

According to this, since my model has a density less than 10% there is no discount.

Is there any way to reduce the cost?

I thought: Should I make the walls thicker? But with Volume = 56.9690cm3 and Density = 14.63% is worst

Last edited: Jun 16, 2014
2. mkroeker Well-Known Member
You could try to optimize your wall thickness for 10.1% density - or put a (loose) dog or some other small item that you wanted to print anyway in there.

3. yiomultimedia New Member
I added a pet bowl in another model.

Anyway, the fact is simple: in this case the price is calculated based on volume but increasing density doesn't make the model eligible for a discount (I dont now why) so I just made the walls thinner. (right now they are too thin, oops, I still have to tweak them a little in order to pass the tests)

Last edited: Jun 16, 2014
4. mkroeker Well-Known Member
Note that the discount is applied to the fraction of your model above 20ccm only, so you will pay the same for more than half of your model regardless. A quick "back of the envelope" calculation further seems to show that the maximum savings are in the order of four dollars, and it is quite easy to overdo it so that the cost of the added material outweighs the money saved through the discount:
Current model according to your post : 32.3 ccm @ \$1.40 = \$45.22 and density 32.3ccm/385ccm = 8.3%
"Ideal" model: 39ccm (as 39/385=10.1%) cost 20ccm@\$1.40 + 19ccm @ 0.70 = \$41.30
Same price despite discount: happens at 44.6ccm (which corresponds to a density of 11.6%) : 20ccm @ 1.40 + 24.6ccm @ 0.70 = \$45.22
(Now this is not a rip-off, as the difference would be both more pronounced and in your favor if you needed a higher density model - at around 14% density or 55ccm of material, the discount would save you \$25, or a third of the non-discounted price)

5. yiomultimedia New Member
IÂ´ve got it.
I will tweak my model in pursuit of that 10.1% density.
Thanks for the calculations

6. yiomultimedia New Member
The discount is working ok
I tried several models:

White Strong & Flexible Plastic \$1.50 handling fee / \$1.40 per cm3

A model that has thin walls issues:
(cm) 6.412w x 8.626d x 7.042h
Volume 29.3365cm3
Density 7.53%
\$42.57 (1.50 + 1.40 x 29.33 = 42,562)

A model ok:
(cm) 6.412w x 8.626d x 7.042h
Volume 39.3385cm3
Density 10.10%
\$43.04 (1.50 + 1.40 x 20 + 1.40 x 19.3385 / 2 = \$43,03695) vs (1.50 + 1.40 x 39.3385 = \$56,5739)

Last edited: Jun 17, 2014