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Project Anatomy

Project Anatomy

We are going to follow the steps involving the CNC router as the five-compartment bowl is made.

 

QuadTray

We assume that the design, the tool paths and the resulting G-code files have been completed.

Step1-BottomMounted

Here we mounted the glued-up stock for the bottom layer on the router. The board is roughly 18 inches square leaving plenty of leeway as we cut the 16 inch diameter tray.

The brown board underneath the stock is a “spoil board” that has been surfaced such that it is truly parallel to the router’s travel.

A recent addition is a LED light that illuminates the cutting location.

Step2-ZeroingXY

A cross hair was drawn in the center of the stock. The tools was then jogged over the cross hair and the X and Y axis were zeroed in the Mach 3 software. The tool path patterns were set with the origin at X and Y zero.

Note how the light comes in handy for this step.

 

Step3-BottomPockets

The router is in full swing as it carves out the shallow pockets in the bottom layer. About a tenth of an inch is left both at the bottom and perimeter to be removed later by the bowl pattern bit.

You may be able to see two small holes near the outside corners of the pocket. These are registration holes where pins will help aligning the layers as they are glued together.

After the five pockets are cut, the outside perimeter of the bowl shape is scored with a smaller router bit about 2/3 through the board (not shown here). This will serve as the guide when the outside scrap is removed with the band saw.

There is not much more to say about this step. It is just brute force chip making. The next step is much more interesting.

 

Step5-MiddleLayerOnRouterl

This picture shows the middle layer (Walnut in our example) of the tray after it was completely routed with a 1/4” bit.

The final shape will have very little wood left. Therefore, it may distort easily as the registration holes are duplicated.

Note how the raw stock was laid out such that flaws in the wood fall either outside the round shape or are positioned on the interior cut outs.

 

Step4-MiddleLayer

The router bit cuts all the way through the stock except for so-called holding tabs. Small triangular pieces are left tying all parts together. This preserves the integrity of the shape.

 

Step4-MiddleLayerDetail

Here is a close-up of the holding tabs as viewed from the bottom.

 

Step6-MiddleLayerCutoutl

Here is the middle layer after the interior pieces were cut out. The residue from the holding tabs are clearly visible.

As was the case with the bottom layer, the routed shape leaves about a tenth of an inch on all sides (see below).

 

Step7-MiddleonBottom

We tested how the middle layer fits onto the bottom layer. The registration holes are pocket holes in the bottom layer and through holes in the middle layer.

The middle layer was used as a template to drill pocket holes on the underside of the top layer (not shown here).

The step visible on the bottom layer will be replaced by a cove shape with the bowl cutter bit.

 

Step8-ThreeLayers

“Dry” assembly of all three layers.

The dimensions of the top layer conform to the exact design. The shape of the top layer will be used as the template for the bowl cutter bit as it is lowered in several steps until the final depth of the pockets is reached.

The scrap seen here on the bottom layer was removed with band saw before the final shaping.

Step-BowlCutter

The final shape of the bowl’s pockets and perimeter is obtained with a bowl cutter bit, lowering it in several steps.

A router bit extension is used for the deeper cuts.

The router base was extended with a 1/4” thick piece of Polycarbonate (Lexan) such that the router rides on all surfaces of the bowl.

All edges of the pockets and the perimeter were rounded over with the appropriate bit using the same large router base.

QuadTrayCherryWalnut

OK, the bowl has reached its final shape. The finishing still requires many hours of sanding even between applying Polyurethane. Some of this work can be done with electric tools such as random orbit sander, oscillating finishing sander and sanding pads attached to a flexible shaft. However, the interior surfaces must be sanded by hand until the fingers are sore.

The picture at the very top of this page shows a version of the bowl with only two layers (Maple and Cherry).

 

 

I thought this bowl’s use included placing veggies into the quadrants and a dip into the center bowl (using a ramekin or other food bowl).

But then, there is my 9-year old grandson. He loaded the bowl with a glass of orange juice, a cup of cereal, a mug of coffee and some flowers from the yard and carried the whole thing upstairs to serve breakfast in bed to his mother. Sweet, isn’t it?

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