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Drive onto the lumberyard of Cerro Pacific in Redwood Valley, CA, and you will see stacks and stacks of redwood boards. A whiteboard in plant manager Roberto Carillo’s office is filled with notes for various orders for 2x4s, 2x6s, etc., and the inventory to fill those orders. Forklifts whiz around, loading orders on trucks.
One facet of Cerro Pacific’s business is to produce stair treads from pre-cut redwood boards. Cerro Pacific’s business model does not include custom design but works to make a profit by doing the same thing over and over in the most efficient manner possible (economy of scale). All stair treads have the same rise and run, only differing in the number of steps (3, 4, or 5).
Prior to the purchase of their first ShopBot CNC machine, the stair treads were created by two employees working at 30-year-old industrial band saws. One employee takes a pre-cut 2x12 and places it in a sliding jig, then slices the board at a 45-degree angle. Her co-worker then uses the second band saw, set at 90 degrees, to finish the tread. Waste pieces are thrown onto a conveyor belt that carries the waste away. Finished treads are stacked in bundles and banded, ready for shipment.
Why change a working technique? Their bandsaws are aging out and difficult to repair, and the blades need to be replaced frequently, often daily. Even if they were available, replacing the band saws themselves would be as expensive as a full-size ShopBot gantry tool. More importantly, there is a chance that an employee could be injured while working with a band saw. With that in mind, owner Lee Burgess was looking for an alternative solution.
Lee and Roberto researched CNC options and decided to purchase a 4’x8’ ShopBot PRSalpha with a 5HP spindle as a test to see if it could replace the band saw method.
During Sallye Coyle’s first visit to Cerro Pacific in February of 2021, her goal was to correct some of the technical issues with the ShopBot set up, and then to work with Roberto to see if it was feasible to use a ShopBot to cut the stair treads. With a standard support board and sacrificial board on the table, she created a CAD file in VCarve Pro that included all the stair treads in their respective blank sizes.
Then, it was time to play with the CAM side, testing bits, feed rate/spindle speeds, and pass depth. Redwood is relatively soft, and trials showed that the 1.5” blanks could be cut through with a 3/8” bit in two passes. That pass depth of two times the diameter of the bit (.375 x 2 = .75”) is pushing the manufacturer’s recommendation of 1.5 times the diameter of the bit. That being the case, Sallye added a ramp in at the beginning of each pass to reduce the stress on the bit and spindle.
For more details about the software settings and adjustments see page 2 of this PDF.
The next step was to figure out technique to position and hold down multiple blanks. Using 2x4s, Sallye and Roberto set up a series of jigs to hold 3 blanks at a time. Screwing down the blanks was not the most efficient technique for hold down, but it was what was available. The CAD file was set up to move from one blank to the next. Sawdust flew, and a few bits got broken if they hit a screw, but the ShopBot could cut a tread in about the same amount of time as two employees on two bandsaws.
Lee Burgess takes the long-term view and was satisfied that the ShopBot could do what it had been asked to do. So, Sallye made her way back to Portland while Lee and Roberto worked on solutions to hold down the blanks and rid the table of the waste material.
To be continued…
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