Tapered Sides with a Moulding Toolpath for Butterfly Keys

I've not been successful getting a VCarve moulding toolpath to cut a 1-degree slope down a butterfly key. The response from Vectric follows. Has anyone ever tried doing this with or without a tapered EM tool? I've already succeeded in cutting the butterfly keys and the mating mortises with straight shoulders, but I'd like to eliminate the glue line (the closest I've gotten so far is .002 on each side while still being able to drive the key into the mortise, and that leaves a visible glue line).

The reason you are seeing the moulding strategy toolpath this far over is due to a combination of the boundary offset and the
tool dimensions. You can limit this by just adding a vertical 'leg span' to the bottom of the profile, choosing not to boundary
offset and selecting a much smaller stepover as shown in the following video - https://www.screencast.com/t/dS6JIonP
It is possible to achieve this Jeff using either the moulding or Chamfer strategies, but really we wouldn't recommend doing
this as it's not an efficient way of cutting this if you are requiring many parts. The most straightforward way of doing this would
be to source a tapered EM tool of the angle required and applying a straight profile toolpath to a vector representing the
base of the butterfly key ( so that it tapers from bottom to top ).

Jeff, I actually agree with Vectric on this. Very steep slopes along an edge are difficult to cut like that because of the relationship between stepover on the passes and the very quick change it depth. I don't normally taper any butterfly keys I create, but I do own some Amana tooling that has very slight angles that could conceivably used to do the cutout like you want. (larger finished face down) I'm not sure any of them are as tight as 1º, however. I think that 3º is the tightest I have.

Blacktail Studio has sanding dust available while doing the actual gluing of the keys and rubs it into the joint before wiping away excess glue. That combined with cutting your allowance for a fairly tight fit should eliminate the glue line. Use PVA, not epoxy, too. Epoxy can sometimes tend to produce a more visible glue line.

Jim, thanks for the reply. I’m stubborn so I’m going to try a tapered bit. 1.5 degrees is what I found so far. At a .5” thick key, 1.5 degrees is .013 at the bottom, which is marginal for PVA but at half the distance, it’s .0065 — that’s fine. Plus, the bottom is flooded with glue so I’m not concerned 1.5 degrees will result in a weakened joint. The mortises are easy to cut with an end mill, and only a little chisel clean up. I’ll update this thread after a few experiments. If I’m pleased with the results, this will be the cat’s meow for butterfly keys — at least for most of what I use them for.

Just pay attention to your passes if it's got a narrow tip like mine do. They are designed more for 3D carving with some reach after one or more roughing passes. For cutout purposes, you need to work your way through the material and not stress them. Now if it's a beefier piece of tooling that just happens to have a slight taper, you can be less concerned, although you still have to "follow the rules" for speeds/feeds to not break your tool as well as have adequate chip load to take away heat.

I'll be using a square bottom, tapered bit -- likely 3/16" diameter. I always ease up on feed and plunge rates, and pass depth when I build the tool paths. The defaults that manufacturers offer, in my mind, are very aggressive. A fine example; the Amana tool database has the 3/8" ballnose feedrate at 100 inches/min and the plunge rate at 50 inches/min. Ahhhhhh, no. I would rather it take longer than break bits or tear up material. I found a 1-degree tapered bit; that's really what I want. Thanks, and I'll update this thread as I get further.

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Originally Posted by Jeff Ramsey

I'll be using a square bottom, tapered bit -- likely 3/16" diameter. I always ease up on feed and plunge rates, and pass depth when I build the tool paths. The defaults that manufacturers offer, in my mind, are very aggressive. A fine example; the Amana tool database has the 3/8" ballnose feedrate at 100 inches/min and the plunge rate at 50 inches/min. Ahhhhhh, no. I would rather it take longer than break bits or tear up material. I found a 1-degree tapered bit; that's really what I want. Thanks, and I'll update this thread as I get further.

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I'd be running that .375" ball nose at twice that speed on my machine, but not likely with a cut depth per pass of more than between .25" and .375", depending on the material. It's all relative and there's nothing wrong with being conservative with speed and pass depth as long as it's moving at a speed combined with RPM that produces a chip load that can take away the heat of cutting. Heat is a big enemy, too, not just pressure on the tool from lateral movement.

I don't understand why you'd use a straight bit for the mortise. If you use a tapered bit for both the sides will mate perfectly and the keys will be low, flush, or proud, depending upon what offset you use.

John

The challenge for the mortise cavity is that the taper will cut the butterfly plug from the bottom down (upside down), where the mortise cavity would have to be cut from the top down. The angle would have to be reversed on the mortise cavity. Here's the VCarve drive rail at 1-degree over .5". Consider the plug being cut from the bottom (upside down) so the narrowest portion of the taper is at the bottom, then the mortise cavity would have to be cut in the reverse. That's not possible with the tapered end mill, unless the mortise cavity was a through mortise and the piece was flipped over, which would affect the split arresting strength of the butterflies (my only intent for the butterflies).

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