When milling a part for a prototype piece of equipment, it is often useful to start with a piece of material that is not much bigger than the part that you are making. This is called a Blank. Using blanks, especially with Computer Numerical Control (CNC) systems, can reduce the amount of time needed to clear excess material during the milling process.
We describe a method for making plastic milling blanks for CNC milling operations and for making a "Jig" that helps place holes for conveniently mounting the blank onto the milling machine's table.
There are several ways to do this. We chose to make a vacuum-formed plastic sheet mold. We then poured two-part plastic resin into the vacuum formed mold in order to create the blank for milling.
Using this technique, it is possible to create complex blanks that may have very unique shapes. This makes it possible to decrease the amount of material that needs to be removed by the CNC milling process.
The platform that we use is a Home hobby vacuum forming unit that was easy to build and very inexpensive.
Try visiting the local dollar store, toy store, or even a grocery market and find something that is about the size that you need, comes packaged in a formed clear plastic shell and use that instead in order to pour your plastic blanks.
Top Left: Vacuum forming "Platen", Top middle: MDF wood models under vacuum formed plastic molds. Top right: Clear plastic vacuum formed molds for blanks. Bottom left and right: Cutting out molds to cast the blanks for CNC milling.
•Three 5 1/2" x 2" x 3/4"
Dividers and Side Supports
•Two 3/4" x 3/4"
•Two 5 1/2" x 2.0" x 3/4"
Standoffs for Top
•Carriage bolts 3" x 0.25"
All parts are pine or, if you prefer, MDF wood. Assemble as shown in the CAD model. Drill holes for bolts to slide through snugly. Place the holes to align with the corners of your unique mold for the blanks.
When prototyping parts for experimental scientific equipment, it is often useful to have custom plastic blanks that are suitable for use in CNC milling operations.
We have outlined several methods that can be used to create molds for making plastic blanks and a jig for placing fixation points for CNC milling operations.
In summary, MDF wood models are created to desired measurements of the milling blank. The wood model is then used to create a vacuum formed mold of the wood model. The mold is used to create the blanks from two part plastic resins. A vacuum degasser may be used to assure absence of bubbles or void spaces in the plastic milling blank.
Facility: RWJUHH Investigational Pathology Division and
Center for Parabiotics Research Section: Special Projects Application: CNC Milling - Preparing Plastic Blanks Technique: Rapid Prototyping in laboratory science Title: "Rapid Technique: Preparing Plastic CNC Milling "Blanks" for Parts Used in Prototyping Scientific Equipment" Project Team: R. Siderits and A. Maskey