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Cutting ramps into Plywood

2K views 5 replies 4 participants last post by  Arbee 
#1 ·
Hi All:

Envision a piece of plywood, say 3/8” in thickness.

Now, envision that a tiny box is cut out of one side of the plywood, some distance from its edges, say 1/8” deep, by 1/2” wide. Envision that the piece of plywood is, say, 3/8” in thickness.

Now envision that this tiny box is cut out of one side the plywood, some distance from its edges, say 1/8” deep, by 1/2” wide, by 1 1/4” long. It happens to be the plywood's underside, but orienting the plywood with either side closest to the sky for the task of making the cut is fine.

That's nothing my router couldn't handle with a 1/2” bit set to 1/8” depth, right? Drag it 1 1/4” at the right starting point and call it a day: easy peasy.

I need though to make a variation on this that adds complexity.

The cutout is in the same position on the plywood, and has the same width and length, but looking down on the hole from above, from right to left, it slopes down into the wood, starting out flush with the plywood, until it reaches this 1/8” depth, making a ramp of sorts.

The same happens when the cutout is examined from left to right, although the slope needs to be steeper.

So, for argument sake let's suppose both of these cuts meet about 1/2” from the left side of the cutout and 3/4” from the right side of the cutout. These measurements aren't precise yet. It's just conceptual at this point.

What tool and jig might you use to do this. Maybe a router whose bit angle relative to the piece can be adjusted and locked into place with a jig? Maybe a drill with a jig that can angle the bit and lock it into place? Maybe a pocket hole jig?

Looking directly down on the cutout it might look like this:

Drawing Text Sketch Design Diagram


The line in the rectangular cutout is the deepest point. From a side view it might look like this:

Text Font Paper Paper product Drawing


The cutout appears dashed because we are looking through the plywood to see it. The cutout, as mentioned, is distanced from all sides.

/\/\/\/\/\/\/\/\/\/\/\


People on the board seem to like the background story and pictures. While it's not relevant to the story, perhaps showing it will cause someone to come up with a better idea, or grab some interest.

This below is, as I've posted here prior, the Grand Central Coffee Table.

Furniture White Table Chair Stool


The double entendre, or play of words in its name being similar to a train schedule or table, like that found in NYC's Grand Central Terminal, is not lost on its designers' inspiration from a circular paper map they picked up there, which folded up into something that looks like a baseball home plate, only with the normally flat part of the plate closest to the baseball pitcher being arced. The designers decided to make this into a collapsible coffee table, 2 of whose 4 legs fold down next to two adjacent ones, to sit under the collapsed baseball plate when the table isn't being used in its open configuration, that opens to form an “X” with the legs when the table unfolds to a disk shape.

The table's 14 pieces, which together form a disk, are held together by its exoskeleton on each side. It was no easy task finding material resistant to expansion for the dual sided exoskeleton, that wouldn't suffer from fatigue when folded, to glue to the table top's dual sides. But roofing underlayment, which I painted afterwards with Flexseal TM rubberized painr, proved an excellent choice.

So here's the thing. As sturdy as this table is for its design (read: less study that a table made of 1 whole piece of wood rather than 14) in the open configuration, the space between two table legs on the table top is most susceptible to weakness. The table doesn't fall apart, it just bends there a bit more than elsewhere.

So I got the idea of adding some supports there that could be removed when the table is closed up.

Conceptually it looks something like this:


Furniture Table Chair Design Material property



Four pieces of wood, say 1/2” thick, each of whose ends would be cut at an angle, would, at one end, sit on the floor and be supported by the existing open four table legs. The other end of a support would be positioned into the aforementioned angled slots on the underside of the table that I hope to cut. The 4 angle cuts in the underside of the table would each be halfway of the arc between two adjacent table legs, and about 75% of the way to the open table's radius edge. The nature of the angled cut into the underside of the plywood table top, would match the cut of the 1/2" wide support wood support, keeping that support positioned into the cutout from slipping out. There would be 4 supports around the table, 1/2 way in arc between eatch table leg.

If you have other ideas on how to add supports, remember, nothing can come out of the plywood on either side or the table won't likely be able to fold flat and provide a flat surface in either its circular or baseball home plate shaped smaller configuration. Since I've tried other methods, ideas on how to effect my angle cut in the plywood would be appreciated most.

Thanks.
 
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#3 ·
Envision that your router is not sitting flat on the plywood.

Envision that it is actually on a pair of wedges. The top, or start of the wedge has the router bit just out of contact with the plywood, but as you slide it down the "wedges" it enters the plywood, you continue until you have reached the desired depth of 1/8". Not difficult at all...

Is english a second language for you?
 
#5 ·
English is my primary language. What about my description would make you think that it wasn't? Do people less than familiar with a language usually make double entendres in it?

That said I considered your idea but was concerned, as in my cross section diagram, that coming it at such a gentle angle from the right to left, with the wedges you described to create the angle furthering the distance of the router bit to the piece, that the bit might not be long enough.
 
#4 · (Edited)
I think its is a double ramped recess......

One ramp is a steeper angle, the other is more gradual. The issue of using a router is that the depth needs to taper from zero to 1/8" ... apparently?
Routers don't like to make tapered depth cuts since the base rides on the surface of the material. So a jig would be necessary to make the inclined recess. If it were me, I'd sharpen my 1/2" wide chisel, make a ramp for the chisel to ride on and start paring away. Do the same for the other ramp, stopping at the desired depth/intersection. This seems to be a issue where no power tool is exactly the correct solution. :sad2:


Now, another approach would be the "additive" rather than the subtractive one, described above. Make your ramped section on a separate rectangular piece using the bandsaw. Remove a rectangular section of the plywood such that you can insert and glue in your ramped section. Maybe not as strong, who knows?


:surprise2:
 
#6 ·
Thank you for your replies. I realized there is a better way to solve this problem that lies in how I cut each end of the supports.

Here's a cross section of one:

View attachment 390275

It's new design at top allows me to create a box shape cutout on the underside of the plywood that requires no "ramping" in the cutout as described above, and thus no angle on a router blade.
 

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