When machine shops see an RFQ for a rectangular part that is 2.03″ thick x 2.1″ wide and volumes are high, eyes roll back in their heads. A top-shelf designer produces part designs with boundary conditions slightly under raw stock material sizes to save significant machine time/cost for production orders; start engineering with the raw material stock size in mind from the beginning.
If volumes are north of 100, 500, or over 1000? Potentially tens of thousands of dollars in savings can be achieved, and we do the right thing by not wasting material, energy, and resources.
Guideline for Boundary Conditions
Whether it is metric or imperial, ensure that the final part size is at least .030″ or .7mm less than boundary conditions presented in the table below. It ensures there will be enough material to clean up the final surface and not waste machine time on excess material. Use the table below as boundary conditions for your designs.
Round, Bar or Plate – inches
| Diameter | Thickness | Width | Length |
| 0.25 | 0.25 | 0.25 | 6 |
| 0.5 | 0.5 | 0.5 | 12 |
| 0.75 | 0.75 | 1 | 18 |
| 1 | 1 | 2 | 24 |
| 1.5 | 1.5 | 2.5 | 48 |
| 2 | 2 | 3 | 72 |
| 2.5 | 2.5 | 4 | |
| 3 | 3 | 6 | |
| 4 | 4 | 12 | |
| 5 | |||
| 6 |
Cost Savings Example
If your OHFC copper part design encompasses a boundary area of 6.03″ x 3.1″ x .51″, we would want to source 3.125″ wide bar that is .625″ thick and cut to length in efforts to minimize waste and machine time.
However, that combination of size and material type isn’t common for copper. So most likely it’s going to be 4″ wide x .75″ thick. If we have to buy larger material, it weighs more, so it costs more to ship and handle. Then we have to machine or cut away more material and we have more waste to manage. All of it is rolled into the price and lead time we can offer you.
What are the cost savings if this part was designed to 5.97″ x 2.95″ x .47″ in quantities of 100, 500, and 1000?
| Qty. 100 | Qty. 500 | Qty. 1000 |
| Save $5,046 | Save $25,230 | Save $50,461 |
The savings are incredibly high for such a fundamental and basic approach to design. Remember, we are machining material away as fast as possible to arrive at the boundary condition from the material’s raw stock material, and the larger the size of the part, the more potential for savings.
Imagine if you did this regularly, tracked the savings, and showed your boss how much money you saved the company come review time? If you are a manager, director, or VP, add this check to all your design reviews.
Plate Designs Are the Lowest Hanging Fruit
In general, a bar or plate is available in raw stock or tight tolerance thicknesses. If the footprint is large enough (greater than 6″ x 6″ ), it is usually more expensive to machine the plate to final tolerance than it is to buy it outright. Hence, if your part design requires tight thickness tolerances of +/-.002- .005 inches, we can buy the plate pre-machined (blanchard ground) to save time and money.
In this specific case fo larger footprints, you will have the most luck if you design exactly to any of the following thicknesses (inches): .1875, .25, .375, .5, .625, .75, 1, 1.25, 1.5, 1.75, 2
One of the easiest ways to research material size availability versus costs is to head over to the McMaster Carr Website and see what they offer. Pricing will be slightly higher than sourcing directly from the supplier, however, for the purpose of understanding costs versus boundary conditions, it’s easy breezy.
The Irony of Searching for Best Pricing
The irony is that every engineer and buyer is spending considerable time sending out quotes to multiple shops and negotiating for lower prices when design tactics like these are not employed.
Early in the design cycle, use this guideline, ensure your final part boundary is slightly under the values provided above, and track your savings.
If you have a plate design with parts mounted on top of it, but the bottom of the plate does not, call out a “raw stock” finish on the surface and save yourself more money by instructing us that the surface does not require machining.
Obviously, there are always a myriad of constraints that prevent a design’s boundary to fall just within nominal sizes, however, you would be surprised how easy it is to achieve if you add this to your design checklist as soon as you start modeling and even better, add it to your team’s design review checklist too.
Check out The #1 Killer to a Low Price CNC Machined Part for even more savings with your design.
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