Design issue question

[Mountaincraft]

Okay.. I'm about to cut a couple parts for the vacuum system, but I see a potential problem, and I'd like to get some input on how to deal with it, as this is going to be something that crops up continually as I design projects...

There is a technique where interlocking cutouts are made in two pieces, so that they can be slid together perpendicular to each other and create a rather strong joint..

The joint I'm talking about is the kind used to make the dinosaur models in that great thread above, or when creating furniture that can be assembled without glue or fasteners of any kind..

You know, where you cut a rectangular cutout in one piece, that is half the depth of the overlap, and then an equal but opposite cutout in the mating piece that is also have the distance of the desired overlap, so that when one is slid into the other, it appears both pieces are passing through each other...

If there is a name for this technique, please tell me, as it would be nice to not have to type out such long descriptions...

Anyways, the issue I forsee, is that when doing an 'inside profile' cut, the corners are not sharp, but radius'd the same as the cutting bit... And this occurs on both mating cutouts... The result, is a gap the same amount as the diameter of the router bit between both mating pieces..

How do you guys account for this or deal with it... I want the pieces to mate together as I need this to be a strong glue joint?... And I'd rather not manually saw them out if possible..

I have an 'idea' of how to deal with this (small rabbit joints on each side of each piece), but I'm hoping there is some simple and elegant solution to this..

Thanks,
Mark

[ger21]

Either route a notch, like I show in the bottom corner, or drill a hole, like I show in the top corner, for clearance.

You can upgrade to V Carve Pro, which handles this automatically. From their website:

Bone Filleting corner filleting options are available that help ensure parts cut from sheet materials will slot together after cutting.

The 'Dog-Bone' and 'T-Bone' fillets allow toolpaths to ‘notch’ the inside corners of slots and grooves, allowing mating parts to fit flush against the true base of the pocket. This technique allows the radius of the cutter to be removed from the bottom of slots.

These filleting tools are perfect for designing and machining furniture, cabinets and model aircraft components etc. where precision fit is needed.

[Mountaincraft]

Thanks Gerry...

Man, they just give you enough to 'tease' you in Cut 2D, don't they? LOL

[louieatienza]

Crap.... I forget what the joint is called... in guitarmaking, when doing the x-brace, we call it a saddle joint. I believe it may also be called a halved notch joint, not sure?

The easiest workaround if you don't have the "dog bone" option is what ger suggested, draw circles at the center of every inside corner and use a drill path to clear the corners out before doing your slot cuts.

A long time ago, I worked for an old-school carpenter. When he cut stringers out, he'd drill the inside corners before cutting the tread and riser cuts. His theory is that it relieved pressure at that corner. I never doubted him, though I always finished the corners with a jigsaw or handsaw...

[Mountaincraft]

Crap.... I forget what the joint is called... in guitarmaking, when doing the x-brace, we call it a saddle joint. I believe it may also be called a halved notch joint, not sure?

The easiest workaround if you don't have the "dog bone" option is what ger suggested, draw circles at the center of every inside corner and use a drill path to clear the corners out before doing your slot cuts.

A long time ago, I worked for an old-school carpenter. When he cut stringers out, he'd drill the inside corners before cutting the tread and riser cuts. His theory is that it relieved pressure at that corner. I never doubted him, though I always finished the corners with a jigsaw or handsaw...

That's how you stop crack in other materials as well.. ie concrete, plastic, etc...

What I did was just edit in a little square pocket up and down (1/8"H x 1/4"W) and had the machine cut them as part of the profile... Worked perfect... as the result was exactly what Gerry illustrated, a half round at the top and bottom of the fillet....

[mlabruyere]

I use the method Gerry states, since I have VCarve Pro....very nice program, for cuts that will not be visible or visible and don't really care about the look.

For parts that I want to have that nice crisp look I use the smallest endmill I have to finish the inside corners then use a file to finish them off (lots of work blech).