Curves vs. Bezier Curves

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Mikehell
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Curves vs. Bezier Curves

Post by Mikehell »

Noticed something the other day that I haven't noticed before

A Bezier curve gets broken up into many sections by the post processor, but if you right click / convert to curves, the post processor converts it to arcs. This may make little difference to most people, but when you're limited by file size it's a big deal.

We're currently on an older version of V-Carve. Would later versions handle Bezier curves differently?

tomgardiner
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Re: Curves vs. Bezier Curves

Post by tomgardiner »

In my experience, Bezier curves produce fewer nodes than arcs which is way better than what's often imported. I also found that it is important to convert to curves once you have done any transformations. You can preview any conversions and see which will give the least number of nodes.

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Adrian
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Re: Curves vs. Bezier Curves

Post by Adrian »

There is no g-code command for a bezier curve whereas there is for an arc so the output would be smaller if the job was suitable to have arcs rather than beziers and the post processor/control software supports arcs. Most modern control software will interpret the multi smaller moves into the "correct larger" move as far as I'm aware.

Mikehell
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Re: Curves vs. Bezier Curves

Post by Mikehell »

tomgardiner wrote:In my experience, Bezier curves produce fewer nodes than arcs which is way better than what's often imported. I also found that it is important to convert to curves once you have done any transformations. You can preview any conversions and see which will give the least number of nodes.
But, that's the odd part. A curve made with a Bezier may have fewer nodes. However, when output to GCode, the post processor converts it to many segments because it doesn't understand a Bezier curve, where the same curve without the Bezier gets output as an arc. I always assumed that Bezier curves got converted to arcs surfing GCode creation, but that doesn't seem to be the case.

Had a file with 20 curved parts on it, two curves per part, so 40 curves (these were Bezier curves). Output was over 300k. I think 380 something k. Converted to curves, the file ended up being well below 100k..

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Re: Curves vs. Bezier Curves

Post by Mikehell »

[quote="Adrian"]There is no g-code command for a bezier curve whereas there is for an arc so the output would be smaller if the job was suitable to have arcs rather than beziers and the post processor/control software supports arcs. Most modern control software will interpret the multi smaller moves into the "correct larger" move as far as I'm aware.[/quote]

Modern control software. I laugh. I'm on a Gerber machine that's using pretty old technology. Has a proprietary controller (not a PC) that you can send GCode to via good old hyperterminal over a serial port at 9600baud. As far as I can tell, the memory is limited to 256k. At least that's what I have figured out so far. Gerber support sucks, they won't even talk to you before you shovel a bunch of money to them. Machine is built like a tank, but the controller is wack

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Re: Curves vs. Bezier Curves

Post by Adrian »

Mikehell wrote: But, that's the odd part. A curve made with a Bezier may have fewer nodes. However, when output to GCode, the post processor converts it to many segments because it doesn't understand a Bezier curve, where the same curve without the Bezier gets output as an arc. I always assumed that Bezier curves got converted to arcs surfing GCode creation, but that doesn't seem to be the case.
An arc can always be replaced by a bezier but a bezier can't always be replaced by an arc. That's not a CNC thing.

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Re: Curves vs. Bezier Curves

Post by TReischl »

Mikehell wrote:But, that's the odd part. A curve made with a Bezier may have fewer nodes. However, when output to GCode, the post processor converts it to many segments because it doesn't understand a Bezier curve, where the same curve without the Bezier gets output as an arc. I always assumed that Bezier curves got converted to arcs surfing GCode creation, but that doesn't seem to be the case.

Had a file with 20 curved parts on it, two curves per part, so 40 curves (these were Bezier curves). Output was over 300k. I think 380 something k. Converted to curves, the file ended up being well below 100k..
That is incorrect, the post processor "understands" bezier curves just fine. Most CNC controls do not. What the pp understands is that most cnc controls do not read bezier curves at all. As a result it converts the bezier to small moves so the control can follow the curve. Circles, true arcs and bezier curves are completely different things. The underlying mathematics for circles/arcs and bezier curves are completely different. A fast google will explain it.

256K? Really? Whoaaaa. A lot of what I run is over 1mb in size. IIRC the largest file I have ever run was right at 8.8mb. Since the iron is good maybe you should be looking into a retro fit of some sort?
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Re: Curves vs. Bezier Curves

Post by martin54 »

Modern control software. I laugh. I'm on a Gerber machine that's using pretty old technology. Has a proprietary controller (not a PC) that you can send GCode to via good old hyperterminal over a serial port at 9600baud. As far as I can tell, the memory is limited to 256k. At least that's what I have figured out so far. Gerber support sucks, they won't even talk to you before you shovel a bunch of money to them. Machine is built like a tank, but the controller is wack

As Ted has suggested a new control box with modern electronics would be the way I would go, in fact it is the way I went :lol: :lol: I bought my machine for basically scrap value, the signmaker who previously owned it had spent over £2000 trying to get it fixed, the Company who maintained & supplied Gerber machines here in the UK didn't seem to have a clue what to do, apparently they kept replacing parts hoping to fix the fault. The owner was losing money & work was piling up so he bit the bullet & bought a brand new machine from another Company.

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Re: Curves vs. Bezier Curves

Post by Mikehell »

256K? Really? Whoaaaa. A lot of what I run is over 1mb in size. IIRC the largest file I have ever run was right at 8.8mb. Since the iron is good maybe you should be looking into a retro fit of some sort?
I'm pretty sure the memory can hold more than 256k, the smallest reference I can find to memory on that machine is a 1meg. However, it crashes with a UART OVERRUN when I feed it more than 256k.

If it were my machine I'd tear off the controller and replace it with something more modern. I think I'll wait till I've been there a few months, and past my 90 day new employee status, before I start telling them that their machine is garbage and needs to be upgraded.

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Re: Curves vs. Bezier Curves

Post by TReischl »

Mikehell wrote:
256K? Really? Whoaaaa. A lot of what I run is over 1mb in size. IIRC the largest file I have ever run was right at 8.8mb. Since the iron is good maybe you should be looking into a retro fit of some sort?
I'm pretty sure the memory can hold more than 256k, the smallest reference I can find to memory on that machine is a 1meg. However, it crashes with a UART OVERRUN when I feed it more than 256k.

If it were my machine I'd tear off the controller and replace it with something more modern. I think I'll wait till I've been there a few months, and past my 90 day new employee status, before I start telling them that their machine is garbage and needs to be upgraded.
Ahhh, I see, not your machine. . . . you could mention that virtually all of the hobbyist guys you know have way, WAY better controllers, LOL.
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Mikehell
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Re: Curves vs. Bezier Curves

Post by Mikehell »

[
Ahhh, I see, not your machine. . . . you could mention that virtually all of the hobbyist guys you know have way, WAY better controllers, LOL.
We don't do anything complicated. The machine does what we need it to do. So asking for an upgrade will be a hard sell. In case it ever comes up, how much would it cost to retrofit this thing?

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Re: Curves vs. Bezier Curves

Post by jginvc »

Mikehell wrote:
256K? Really? Whoaaaa. A lot of what I run is over 1mb in size. IIRC the largest file I have ever run was right at 8.8mb. Since the iron is good maybe you should be looking into a retro fit of some sort?
I'm pretty sure the memory can hold more than 256k, the smallest reference I can find to memory on that machine is a 1meg. However, it crashes with a UART OVERRUN when I feed it more than 256k.

If it were my machine I'd tear off the controller and replace it with something more modern. I think I'll wait till I've been there a few months, and past my 90 day new employee status, before I start telling them that their machine is garbage and needs to be upgraded.
Sounds like a handshaking/flowcontrol problem....

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Re: Curves vs. Bezier Curves

Post by TReischl »

jginvc wrote:
Mikehell wrote:
256K? Really? Whoaaaa. A lot of what I run is over 1mb in size. IIRC the largest file I have ever run was right at 8.8mb. Since the iron is good maybe you should be looking into a retro fit of some sort?
I'm pretty sure the memory can hold more than 256k, the smallest reference I can find to memory on that machine is a 1meg. However, it crashes with a UART OVERRUN when I feed it more than 256k.

If it were my machine I'd tear off the controller and replace it with something more modern. I think I'll wait till I've been there a few months, and past my 90 day new employee status, before I start telling them that their machine is garbage and needs to be upgraded.
Sounds like a handshaking/flowcontrol problem....
Need to get Fred Flintstone and Barney Rubble to consult :shock: :D
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Re: Curves vs. Bezier Curves

Post by Rcnewcomb »

how much would it cost to retrofit this thing?
You can get a quote here: CENTROID CNC Quote/Information Request
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Re: Curves vs. Bezier Curves

Post by highpockets »

I'm rebuilding my Mach3 with the Centroid Acorn. Great system.
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