Allowance offset

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Allowance offset

Postby kstrauss » Thu Jun 14, 2018 1:52 am

I want to use my CNC to grind the outside of a hardened part. To do this I need to make multiple passes around the part while moving a grinding stone a tiny amount closer on each pass. I can get the desired effect by duplicating the same toolpath multiple times and minutely reducing the allowance offset for each pass. Since I need to use dozens of passes having to manually adjust each toolpath is tedious. Is there any way to make the task easier?
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Re: Allowance offset

Postby dhellew2 » Thu Jun 14, 2018 4:46 am

I'm not certain what type of cut you are making.
Is the cut around the outside of the part or on top?
What type of cut are you using ie profile, pocket, etc.
A bit more information and/or a picture would be helpful.
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Re: Allowance offset

Postby AlanAndrews » Thu Jun 14, 2018 9:00 am

As mentioned already, it always helps to see the design of what you are seeking to machine.

Is this a 2D/2.5D shape or 3D shape?

What type of toolpath/finish are you looking to achieve?

How much of an incremental move are you needing with each pass?

What type of bit are you using and dimensions of the bit?

If you are able to share your VCarve model, then this will help enormously.
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Re: Allowance offset

Postby kstrauss » Thu Jun 14, 2018 2:45 pm

My desire is to cut an outside profile tool path. The "cutting tool" is actually a small grinding point mounted on a 1/4-inch shank and spun in my mill spindle. I have attached a sample of the shape that I wish to grind; the feeds and tool RPM in the sample are not ideal. The desire is to form a HSS form tool that will be eventually be used with my lathe. I want to be able is secure a blank of HSS to the CNC mill table and make multiple passes around the outside (starting with just grazing the edges of the blank) until the final shape is ground. I can get the desired result by setting the allowance offset to, say, 0.1 inches, duplicating the toolpath and reducing the offset by 0.001 until the offset is zero. Doing this manually is extremely tedious!

Hopefully this will make things clearer but ask and I'll try again.
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NeckToolDemo.crv
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Re: Allowance offset

Postby Adrian » Thu Jun 14, 2018 3:55 pm

It might be easier to create multiple offset vectors (offset tool with select new checked) and create one toolpath against them so the allowance is actually part of the vector. If you use the order tab in the toolpath you can make sure they're machined in the right order.
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Re: Allowance offset

Postby FixitMike » Thu Jun 14, 2018 4:58 pm

Adrian: Just for the heck of it I tried the profile toolpath with multiple offset rectangle vectors selected for an outside cut. It cut only one of the vectors. Then I rotated one of them and moved the corner of the inside one. The cut path got weird--It acted like i had used the weld tool.

Your offset suggestion works well to make the multiple vectors, but to me, it looks like Alan will have to make an separate toolpath for each pass.
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Last edited by FixitMike on Thu Jun 14, 2018 5:08 pm, edited 1 time in total.
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Re: Allowance offset

Postby Adrian » Thu Jun 14, 2018 5:05 pm

It won't work with closed vectors but Alan's example had open vectors which was why I suggested it.
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Re: Allowance offset

Postby FixitMike » Thu Jun 14, 2018 5:11 pm

Adrian wrote:It won't work with closed vectors but Alan's example had open vectors which was why I suggested it.


Interesting.
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Re: Allowance offset

Postby FixitMike » Thu Jun 14, 2018 5:26 pm

Duh! The profile toolpath is designed to handle interior pockets, similar to the way the pocket toolpath does.

Another thing I noted: When a rectangle is offset multiple times, the start node moves to different corners on different copies.

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