Why is this happening?

[FoothillFurniture]

This chair back was designed in other software and imported into vCarve Pro. Everything works great, except that on the top side finish toolpath with a ballnose bit, the tool path plunges the bit all the way down into a 3inch thick blank, instead of ramping down? I can't figure out why? I have included a screencap of the toolpath. I have tried zipping the file, but it's still too large to attach.

Can anyone tell me why this happens?

Thanks, David

[ohiolyons]

You are going to have to post the file, if not copyright issues.

Dropbox or google drive or something similar.

[adze_cnc]

Does it look similar in VCarve's preview? (This appears to be your control software's preview.)

You'll eventually, probably, maybe, need to adjust the "Boundary Offset" to prevent the path from rolling over the edge.
 

[sharkcutup]

You would be better off doing this in 2D using the various tools available in V-Carve Pro.

This sample is from a High Chair Rocker that I have carved many moons ago!!!

Sharkcutup

[FoothillFurniture]

DropBox link to file: https://www.dropbox.com/s/c054rfjucid1k ... k.crv?dl=0


@Sharkcutup - I don't know VCarve well enough to do that? What tools did you use for this?

[adze_cnc]

sharkcutup: Note that the ends of the object are not straight up and down but slope. So, an extra fluting or moulding toolpath would be needed to effect that.

[ohiolyons]

I didn't see what you are talking about in the preview.

BUT

On your Front roughing cut you are going down 2.4", Does your bit have a 2.4" cutting length?
Unless you lower the sides with a pocket there will be an issue when you actually cut it.

Same issue with the finishing bit.

[sharkcutup]

True, I agree!

After looking at the ops file I stand by what I posted earlier.

Fluting toolpath and Swept Profile would work

Sharkcutup

[ohiolyons]

Boundary offset on finishing toolpath is .25 on a .25 bit.
That is why it is going completely over

[adze_cnc]

As a 3D project you could do the following. Because the sides are vertical this lends itself to having the curves cut with roughing and finishing toolpaths and having the final form cut out with a profile toolpath.

You should change both finishing toolpaths' "Boundary Offset" from 0.25 to something like 0.03125 (just enough to roll over the edge but not plunge).
 

Create a boundary vector on the back side by selecting the chair back and clicking on the yellow circled tool

 

This is what you'll get

 

Create a profile toolpath on the back side and add tabs at the centre of your 3D modelled tabs

 

Note the thickness of the tab. This is to make sure that it is somewhere in the side of the vertical wall. 3D tabs won't work here.

 

[TReischl]

......
Can anyone tell me why this happens?

Thanks, David

Capture.PNG

As others have mentioned, it happens because there is nothing to stop it. I know, that sounds strange, but it is what happens.

I run into this all the time because I work in "other software". And no, I am not interested in fiddling around with fluting paths, etc. I just want to 3D cut the piece. Yea, I know, fluting, etc will cut faster, but that does not suit the way I like to do things. So what do I do? Create a surface in the model that controls how much the tool will go "over the edge". Like this:

I do this a lot and it works well. And it will work with pretty much any model. What is essentially being created is what is known as a "parting line".

Edit: I generally put X0 Y0 in the center of the material when using this technique for obvious reasons.

[FoothillFurniture]

Thanks everyone. Changing the Boundary offset worked very well to stop it from plunging. As far as the tool depth, I just cut out the extra with a bandsaw to keep the tool from hitting the workpiece. I cut out from the top and then when I turned it over I cut off what I needed from the bottom. Not the perfect solution, but it works well and it's fast.

I did use the moulding method for the seat and it was very simple and fast, but I still can't figure out how to do the seat Back this way?

[adze_cnc]

One way (no attempt was made to make it look pretty) is attached. Certainly, some of the real moulding experts will have a better method.