Fitting two rings together

[wilkigr]

I am running VCarvePro 10.5 in Windows 10.

I am trying to cut two rings from two different pieces of material. The smaller of the two rings is to fit snugly inside the larger of the two. I am attaching the .crv file.

I am completely confused by the terminology, I guess. To cut the outer ring, I want to cut outside/right of the middle oval; that is, to cut between the middle line and the inner line. However, to do this, I seem to have to choose "inside/left". When I choose outside/right, which to me is where I want to cut, the preview shows it cutting on the left side of that line - that is, between that line and the outer line. Why is that?

The opposite holds true to the smaller ring. I replace the material with a different piece, since the kerf from the first cut means that I cannot use the offcut and have it fit snugly.

In this cut, I would think that I need to choose "inside/left" since I want to cut on the left side of this oval - between it and the outer ring. Instead, I need to choose outside/right to get it to cut there. Why is that?

I have added a .002 offset to each cut as I thought that would give me snug fit between the two pieces. It did not, the smaller piece is about .125" smaller all around.

I have done jigsaw puzzles successfully, so I can't figure out what I am doing wrong with this much more simple project.

Can someone please explain where I am going wrong?

Thank you

small_test.crv

(290.5 KiB) Downloaded 34 times

[adze_cnc]

You might be overthinking things. Think of each ring as if it was the only thing being cut. For each of them you want the bit to run on the ring's "outside" and on the "inside" of the ring's void.

When creating a toolpath for any object the has an "outside" and an "inside" set the toolpath to cut "outside/right". Also, get in the habit of using the vector selector to select vectors on their layers rather then try to select them manually.

See images for the inner and outer ring toolpaths. Set the settings as I have them and Bob's-your-uncle.

--

Inner ring toolpath

Outer ring toolpath

[wilkigr]

Thank you very much. I will try that. I am still confused by the end result, though. (Dense, I guess.)

When I look at the toolpath in the 2D view, with "solid" turned on, the outer ring cut looks fine. The cut is cutting on the waste side of the drawn oval and it is cutting a very small amount - .002" - over the line. In the case of the inner ring, it, too, looks fine. the cut is cutting on the waste side of the line common to the two rings, slightly over the line. So, to me, the gap between the two rings should be .004".

Aside from getting inside and outside straight in my mind - and your screen caps will do that after I read them a few more times, where am I going wrong on the gap issue?

Edit: I changed the settings to match your screen caps. Is it correct to say that they only work if I cut both perimeters of each ring at the same time? That is, load up one blank and cut both the inside of that ring and the outside. Then, load up another blank and do the same with the other ring.

[wilkigr]

I guess the ability to edit posts times out quite quickly.

I cut the two rings and your method worked like a charm. I need to play with the offset a bit, as the fit is too tight. I used a mallet to put them together. In the final version, they will be painted and I don't want want to be whaling away on a painted surface.

Thanks much again. I'm still going to review the process so that I can understand why it worked. But, for now, I can continue on with the project.

[adze_cnc]

My error (it's been that sort of day) I forgot about the wretched offset for a slip fit.

So let's re-think this. We're going to need a minimum of three toolpaths. The criteria for the two rings are:

• the outside of the outer ring does not need an offset
• the inside of the outer ring could be offset if the inner ring needs to be exactly the size it is drawn (otherwise no offset)
• the outside of the inner ring does not need an offset if its size is to be exactly as drawn (otherwise offset)
• the inside of the inner ring does not need an offset

In the attached file I presumed the size of the inner ring needs to be as drawn so the inside of the outer ring is offset. There are three toolpaths:

1. "outer ring outside" : only cuts outside the outer ring with no offset
2. "outer ring inside with slip offset" : only cuts the inside of the outer ring but applies the -0.002 offset
3. "inner ring inside and outside" : cuts inside and outside of the inner ring with no offset to either

It's left as an exercise for the reader to figure out the changes needed if the inside of the outer ring needs to be sized as drawn.

[wilkigr]

I'm very grateful adze. I'm going to play a bit with the offset to get a good, but tight, slip fit. The rings will be painted different colours, so the "seam" will be visible. I just don't want a gap. With this test, I put the inner ring on my belt sander and sanded a "chamfer" onto the outer edge. It slipped in and then wedged in with a bit of persuasion.

Thanks again. I hope nature is more friendly in Vancouver than it is in Ottawa right now.

[wilkigr]

I used your file, adze. The final offset was .003. I was like Goldilocks. .002 was too small; .004 was too big; .003 was just right.

Thanks again for your help.