Rectangular stock for a rotary job

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SRiddle68
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Rectangular stock for a rotary job

Post by SRiddle68 »

I am running Vcarve Desktop V9.510 and I am using Mach 3 with an A rotary axis. My question is how can I reduce wasted cutting time? I model a 3D part, something like a hatchet handle, in Onshape, and then import it in and 3D rough and finish cut it on my rotary axis. It works just fine. The question I have is how could I start with a rectangular piece of stock instead of a round one? My part is basically an ellipse. When it goes to rough out the ellipse shape out of a round, and I am using a rectangular stock piece(real part on the CNC), I cut a lot of air where the rectangle is smaller than the starting round shape in software. I would like to either be able to specify a rectangular stock part or take the specified round part and make a first cut to make it rectangular and then from the rectangular shape I would do my rough and finish cuts to make the part I want. I would then just ignore the first cut, to make the round stock rectangular and then do my actual rough and finish cuts.
I am open to any other ideas or if my second idea would work can you help me with how I would fake it out to make a rectangular part from a round and then continue on with my shape. I don't know how to sketch a rectangle on the end of the part to make the part a rectangle but in a 2D view of the unwrapped rotary part.
I am assuming that Vectric is not looking to change the initial stock shape for a rotary job but I can hope.

Thanks for any help you can provide.
Scott

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Rcnewcomb
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Re: Rectangular stock for a rotary job

Post by Rcnewcomb »

Skip the roughing. If you need to reduce material to avoid breaking a bit then don one finish pass with a large diameter bit and a larger stepover. Finish passes are always at full depth. Roughing passing will always attempt to remove stock it believes is there,
- Randall Newcomb
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SRiddle68
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Re: Rectangular stock for a rotary job

Post by SRiddle68 »

My spindle is not super rigid and I have it pretty much maxed out feed rate and depth wise now, so how I do the cutting doesn't matter. But regardless of the strategy I use to cut it, it wastes a ton of time cutting air.
See the attached picture for a better understanding of what I mean. 2/3 of the time to cut this part will be just cutting air, not wood.

Thanks
Scott
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AIR CUT STOCK.jpg

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Rcnewcomb
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Re: Rectangular stock for a rotary job

Post by Rcnewcomb »

It will not air cut if you just use finishing passes. You can run more than one finishing pass if needed.
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SRiddle68
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Re: Rectangular stock for a rotary job

Post by SRiddle68 »

The problem is that I cant go full depth to the final part size. In the attached picture, the final part is in green. You can see the corners would be almost a .50" deep cut if it went full depth. I can only do about a .125 deep cut with a 50% step over on a .25 dia ball nose carbide router bit.
I appreciate your help on this. It helps me a ton to get other thoughts and ideas.

Scott

AIR CUT STOCK 3.jpg

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Re: Rectangular stock for a rotary job

Post by mtylerfl »

Perhaps this job is better suited for two-sided machining?
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Re: Rectangular stock for a rotary job

Post by rscrawford »

Why can't you cut more than 1/2" depth for your finish tool path?

I just finished a 3D cut, and I was making 2.5" deep cuts with a 1/2" ball nose. It is really not much of a cut, because I was only taking off 7% per pass, or 0.035" per cut.

With a 1/4" ball nose, you should easily cut 3/4" depth as long as you keep your stepover under 10%. Use a raster, so you start at one end and work your way up the 4th axis.
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Re: Rectangular stock for a rotary job

Post by 4DThinker »

I'm with Michael. This looks like a great excuse for 2-sided carving. I'd start with a block 7/4 thick, a couple inches longer than you need the finished part. Clamp or screw down the ends parallel to one axis of your CNC. The moulding toolpath could be used to cut the top side. Flip the blank over end for end, screw down again and use the same toolpath for the bottom side (now on top).

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Re: Rectangular stock for a rotary job

Post by SRiddle68 »

Russell's idea would work if my CNC had the rigidity for that heavy of a cut. I can only do about a 1/8 deep with 50% stepover and 40 FPM. If I go more it chatters like crazy and I end up losing steps on the motor. This is a light machine, not a large industrial one. I am working on a lathe that will be able to take very heavy cuts with live tooling but that is months off.
I like the 2 sided idea and just use X,Y,Z moves than flip and repeat. The next wrinkle I have is I project a cross-hatch pattern of lines on the surface of the ellipse. I then use a 60 deg v-carve bit to trace the lines. The bit is always perpendicular to the surface when rotating the part. If I do a 2 sided operation and go to v-carve the cross hatch lines projected onto the ellipse the bit would not be perpendicular to the curved surface always. I probably could make it as 2 separate Vcarve projects. The first would be 2 sided in flat mode and then just do the cross-hatching v-carve work as a rotary project.

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Re: Rectangular stock for a rotary job

Post by martin54 »

Have you tried reducing the stepover? Russell said to take a deeper cut but at a smaller stepover :lol: :lol:
Worth spending a bit of time experimenting with the software to see how it affects carving time :lol: :lol:

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