Parent Category: Big Blue Saw Blog
Created: Tuesday, 10 March 2015 13:00
Written by Simon Arthur
"Nesting" refers to packing multiple shapes together.
As many of you know, you can get a much better per-part price if you put multiple parts of the same design in to a single file to upload to our instant quoting system.
I'm often asked by customers looking to order multiple parts in a single file how to correctly arrange the files together in order to get the best possible price. In the majority of cases, the answer is "don't bother". Sometimes it does make sense, though. We'll take a closer look at when you might want to pack your parts closely together and when you shouldn't worry about it.
Note that this information is current as of the date of this article, and we may update or improve our instant quotes in the future.
When nesting doesn't matter at all
Let's first take a look at a case where it does not matter how you nest the parts.
In this design, four rectangles are spread out over an area about 31.4 inches by 15 inches. If we pick one of Big Blue Saw's most expensive stock materials, Stainless Steel 304 at 0.75 inches thick, we get a single set price of $247.90.
So we pack them closer together. Now the rectangles are squished into 18x7.1 inches. The single set price with the same material as above is now... $247.90.
Finally, we'll really pack them in and get rid of almost all the space between parts so that they're now 17.5x7.1 inches. The price then becomes... $247.90 yet again. So for all of our effort to get a good nesting on these parts, we've saved no money.
When nesting matters a little
But nesting DOES matter in some cases. Take a look at these two parts within a single file. They are approxmately 11x17 inches and 1.4x8.4 inches. When you get a quote for these with aluminum 6061 in 0.125 inch thickness (one of our most popular materials), you get a price of $97.60 for quantity 1 set or $23.34 each set in quantity 10.
Now let's fit the two pieces together as shown here. The price comes down to $96.80 for each set of 2 or $22.49 in quantity 10. So you'd be saving 80 cents off of your total price in quanitity 1 or $8.50 in quantity 10.
Why did this nesting change the price when we saw earlier that packing the shapes closer together didn't affect the price? The online quoting system looks the rectangles measured horizontally and vertically which enclose the parts and uses those to calculate the amount of material needed to make your parts. If the rectangles don't overlap, you have the case we saw earlier, where the nesting did not affect the price. However, if the bounding rectangles overlap, we can probably use less material to make your parts, and thus you will save money.
Note that if nesting two parts together gives an enclosing rectangle with an area larger than the area used by the parts separately, the quoting system will add the two bounding rectangles together in order to give you a lower price.
When nesting matters a lot
With that in mind, let's take a look at an extreme example. In this case, the parts are 10.9 x 17 and 12 x 8.6 inches. When we choose an expensive stock, like 0.75 inch thick stainless steel 304, the price for 1 set is $479.10 for the separate pieces and $366.80 when the pieces are closely nested. Here, the difference is between two enclosing rectangles 10.9 x 17 and 12 x 8.6 inches or 288.5 square inches vs. a single enclosing rectangle 11.5 x 17 inches or 195.5 square inches.
Here's another case where how you position the parts in your design can have an impact on your final quote. The pieces on the left and right have the same dimensions, but the one on the right has been tilted almost 45 degrees. The piece on the left has a measurement of 0.9 inches X 15.9 inches. On the right, it measures 12.5 inches horizontally by 11.1 inches vertically. When made with stainless steel 304 0.75 inches thick, the price goes from $96.90 for the piece on the left to $250.10 for the piece on the right. This is because the enclosing rectangle for the tilted piece is significantly larger, so the quoting system thinks that it will take a lot more material to make the part.
Making things easy for us
We often get e-mails from customers wanting to change their nesting in order to "make things easy" when the parts are cut, wanting to fit into a whole sheet, and the like. This usually doesn't make sense, as we cut most of our parts from very large sheets and charge you strictly for the material used. Often, the sheets we're using have already had a few previous parts cut from them, so your nesting may not fit into the stock we have available.
If you happen to make the parts too close together on an order with stock material, this isn't a problem for us, as we typically end up re-nesting anyway.
The one case where having a nesting from a customer may make a difference is if we are cutting a custom material supplied by that customer. When you're ordering this way, should know the dimensions of the material you're providing. Keep in mind that for waterjet cutting, we need a 0.25 inch margin around all edges and a 0.125 inch space between each part. For laser cutting, we need an 0.25 inch margin, and 0.03 inch spacing between each part.
For designs with a mostly rectangular outline, changing the nesting won't change the price at all.
If you can fit one part inside another, it may help the price, especially on more expensive stock materials.
Rotate your parts to minimize the enclosing rectangle.
After you order, when it's time for us to cut your parts, we often re-nest parts on stock materials.