Benefits of roughing before finishing in 3D

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Re: Benefits of roughing before finishing in 3D

Postby Adrian » Thu Jan 24, 2019 8:59 pm

wmgeorge wrote: So if the so calling Finishing takes two or more passes because You programed the Depth of Cut to be not more than .01 why would that not work??


It won't though. The finishing pass is only ever one pass. That's the way it works. It will never be two or more passes.

If you're calling the roughing cut you're doing the finishing pass then that's a different matter but a true finishing pass is one pass and one pass only regardless of what the pass depth is in the tool database.
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Re: Benefits of roughing before finishing in 3D

Postby wmgeorge » Thu Jan 24, 2019 10:10 pm

Leo wrote:Nice thing is - you can always do whatever you want to do.

Using the .125 ball nose with a roughing pass and 0 material is certainly one way to skin a cat.

Maybe this came across the wrong way, but it seemed to me at least that you were asking for advice about using the roughing pass vs not using it.

Not everyone uses a roughing pass, depending on the project. Sometimes just a finishing pass. What you are proposing is certainly doable, yes. Will take longer - yes. But it is certainly doable.


Yes Leo and thanks, I was just checking to see If it would work... before I screw up the project even more. I warmed the shop up this morning and mixed up some walnut sawdust with some glue in the hopes I can patch up the gouge. To be honest I have been using VCP since 2008 and I can count on one hand the screw ups I had to used for firewood. Its going to be - 11 below F tonight so I do need some firewood :D but not walnut! Thanks again.
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Re: Benefits of roughing before finishing in 3D

Postby Xxray » Fri Jan 25, 2019 4:33 am

I used to be a stickler for roughing just about everything, now gaining experience I have a good sense of when its needed and when its not so I use it as necessary. If you need to hog out alot of material, for sure use it. Its simply a software tool/option designed to save you from breaking/dulling expensive finish bits - Endmills are designed for rough grunt work, finishing tools are not.
Don't let mdf fool you, it is very abrasive and tough on cutting tools.
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Re: Benefits of roughing before finishing in 3D

Postby Tailmaker » Fri Jan 25, 2019 7:54 am

rscrawford wrote:.......Its usually just the first deep pass that is hard, because you are cutting a full 1/2" width in my case....

In that case I do only a roughing cut in depth steps with a very narrow boundary vector (basically a slot with the width of the finish bit) to get started. That goes very quickly.
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Re: Benefits of roughing before finishing in 3D

Postby martin54 » Fri Jan 25, 2019 1:45 pm

wmgeorge what you want to do will certainly work but may take for ever for a couple of reasons, firstly the project is going to cut from the surface in very small steps so may (don't know the model thickness) take hours cutting air untill it gets to your remaining material, as well as the long time cutting because of the small DOC it is also going to take a long time because of the small step over value you need with a finishing pass. If I were doing your job I would simply run the roughing pass again BUT leave a smaller material allowance for the finish tool. I still don't understand though why your 0.125 ball nose is having problems with 0.04 of material if you have the finish pass set up to cut in the right direction grain wise & have a small step over then it is cutting almost nothing with each pass :lol: :lol:
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Re: Benefits of roughing before finishing in 3D

Postby wmgeorge » Fri Jan 25, 2019 3:10 pm

Yes your right Martin, when it warms up I will head out to try what your suggested, after I heat up the shop.

Its -8 F this morning but my Border Collie is not a wimp (53 lbs) went out this morning and did her patrol duties. Can't allow those squirrels and rabbits to take over the yard!
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Re: Benefits of roughing before finishing in 3D

Postby martin54 » Fri Jan 25, 2019 8:28 pm

what stepover are you using for the finish pass ? I tend to use between 6 - 8 % for most of the 3D jobs I do & with most wood types I cut with the grain but always worth a quick test because sometimes cutting across the grain works better :lol: :lol: On small detailed projects I might use a smaller stepover, it's really all about trying to save myself as much clean up as possible after the machine has finished ( not a fan of sanding lol).
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Re: Benefits of roughing before finishing in 3D

Postby LittleGreyMan » Sat Jan 26, 2019 12:55 pm

A lot of good answers here. I think Doug summarised the topic in his last post.

If you're not comfortable with the various toolpaths, all their options and the way they work, always use a roughing toolpath then a finishing toolpath.

You will quickly understand when you can skip the roughing step or use workarounds.

Roughing means roughing and finishing means finishing. That's not a bad pun, it's just that she roughing strategy is designed to get quickly rid of the unused part of the material and the finishing strategy to remove the remaining "skin".

That's how all CAM system work, and there is a reason: it just makes sense. Think of sculpting manually your 3D model. How would you proceed?
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Re: Benefits of roughing before finishing in 3D

Postby redwood » Sat Jan 26, 2019 7:16 pm

LittleGreyMan wrote:. Think of sculpting manually your 3D model. How would you proceed?



Very good analogy there. A carver is going to rough out his project before getting to his detail work.
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Re: Benefits of roughing before finishing in 3D

Postby Leo » Sat Jan 26, 2019 10:24 pm

I would use roughing for a couple of reasons, and I don't always use a roughing pass.

1) I will set my stepover to 50%-60% foe a say 1/4 inch ball nose cutter.
2) I can leave a small amount of material for the finishing tool.
3) I can use a faster feedrate
4) There are a couple of strategies depending what I want for a final result

I would not use it for the entire 3D because I want a really fine finishing at the end. Whatever I want for the final result like minimal stepover, really small ball nose cutter, will need to be programmed into the entire process.

My finishing pass may be with a 1/16 ball nose with a .002 stepover. To go through a full process using a roughing only tool path could take several days of a week or more.

It is possible, but in my opinion - impracticable.

On something really tiny, maybe, but then maybe just a finish pass is all that is needed.
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Re: Benefits of roughing before finishing in 3D

Postby Xxray » Sat Jan 26, 2019 10:36 pm

1 trick of getting away with a finish only toolpath when perhaps roughing should also be used, start the toolpath with an angle, say 90. Then the finish bit will start nibbling away in a corner, very gradually working its way into full passes, instead of starting out with 1 long, screaming pass the width/length of the entire work piece with 0 angle. This 1st pass is the most critical as 100% of the tool is biting through material, in all subsequent passes until the end, it is 50%, thus being far less stressful on material and bit.

I do this occasionally, usually with plexi or corian, if there is a large amount of wood or mdf to be hogged out I just cut through the chase and use a roughing pass, not worth the time trying to figure out a workaround and not worth the risk of snapping a $50 bit. One thing I do is set Z a hair above the work piece, that way the 1st pass is a little less harsh and also, you ensure you will not be biting down too deep into finish territory.
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