At Kelso High School in Kelso Washington, an innovative approach was taken to solve two fixturing requirements when machining Hepplewhite style furniture legs.
Requirement 1. The first requirement was to be able to quickly swap student project fixture plates onto the CNC machine without requiring re-alignment of the student fixture every time.
Solution. A melamine laminated board was mounted permanently on the CNC machine and made into a vacuum fixture using a 1/8th inch diameter closed-cell foam cord to act as the vacuum seal. The foam cord is held in place on the board by a few pieces of double-sided adhesive tape. This method of holding the foam cord allows flexibility to accommodate other fixture sizes for future student projects. To locate the incoming student’s project fixtures accurately, two locating dowels and a stop dowel were added to the vacuum fixture in alignment with the axes of the CNC machine.
The vacuum fixture with locating dowels and mounted on the CNC machine
Requirement 2. The second requirement was to quickly machine four sides of four Hepplewhite style furniture legs in a single setup.
Solution. A second piece of the fixture, the student project fixture, was designed to hold four blanks of wood, the furniture legs, in a custom clamp or vise assembly (bolts and parallels). After one side of the four furniture legs was machined, the clamp was loosened, the legs were rotated to the next side, re-clamped, and that second side machined complete. This was repeated two more times until all four sides of the legs were machined.
Vacuum fixture and student project fixture together on the CNC machine
The total fixture design worked very well to satisfy both requirements. The students could more rapidly move their projects on and off of the machine and could achieve great results.
These Hepplewhite style legs were surface modeled in McNeel’s Rhino CAD and the tool paths were then directly created on the model using MecSoft’s integrated RhinoCAM. According to Pete Sorenson of McNeel Corporation, “the teacher of the school is quite fond of the way RhinoCAM is inside of Rhino and the ease this makes changes both in part size and tool path options.”
Our thanks to Pete Sorenson at McNeel for the insight into this ‘real experience’ school project. Pete designed and built this fixture system for the Kelso school. By the way, Pete has an article published in the Fall 2014 issue of Digital Machinist Magazine about vacuum fixtures and using bridges in machining. Check it out for a good read.