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  #1  
Old Tue 26 January 2010, 09:14
ScottGus1
Just call me: Gus
 
North Plainfield, NJ
United States of America
Does Mach3 have "read-ahead travel optimziation"?

I don't know exactly what it is really called, but let me explain:

My boss just got majorly depressed, because the adjustable-angle aggregate he got for his 3-axis Biesse Rover is too big for the Z-axis height on his machine, despite what Biesse said. So he is looking into getting a 5-axis machine for his shop. He is put off by the for-now-prohibitive cost of such a machine, so I said, why not build one? I know that at least Shopbot and Mach3 will sell controllers and motors, all we need is a pile of thick metal to make a table and gantry...

I have a Shopbot in my garage (PRTalpha 96x60x12) and am familiar with the operation of the machine. I read up on Mach3 (including the SB vs M3 thread on this forum) and I now have a question for the Mach3 users, as well as anyone who have used both SB and M3:

Looking between the two systems, I see that Shopbot has 5-axis control, and this thing that I am calling "read-ahead travel optimziation"(see below), but no G41/42-style tool compensation (I know SB can read G-code through various means). Mach3 has 6-axis control and G41/42 tool comp, but I have read that it has a bit of a problem with "read-ahead."

By "read-ahead travel optimziation" I mean that when the controller sees a series of cut movements in the code that could be strung together in one smooth movement without slowing down (much), the controller moves the head in that smooth flow through the cuts, instead of interpreting each movement on its own, and as a result moving rheumatically through the cut. I know Shopbot has this because I have seen it work on my machine. But I have read that Mach3 may have a bit of a problem with this.

I like the 6 axes and tool comp in Mach3. But I believe that smoothness of movement is of higher importance. (BTW, I have read of chatter in the SB cuts, and it is my opinion that the chatter is from the style of rack & pinion that is used on the SB, not any inherent controller problem - I have noticed that the chatter marks are spaced the same as the rack teeth, and our Biesse, which also drives the X axis with rack & pinion, has angled teeth and no chatter.)

So, the question: Does Mach3 have this "read-ahead travel optimziation" or does it have a problem flowing through the cuts it ought to be able to flow through?
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  #2  
Old Tue 26 January 2010, 09:20
Gerald D
Just call me: Gerald (retired)
 
Cape Town
South Africa
See the context of this post, and the forum/post it links to. A while back I believed that ShopBot's "lookahead" was better than Mach's. Havn't compared them recently.
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  #3  
Old Tue 26 January 2010, 10:13
riesvantwisk
Just call me: Ries #46
 
Quito
Ecuador
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Gus,

I don't have a direct answer to your question, but EMC2 does do read ahead optimization with G41/G42 tool compensation on (highly likely). I cannot compare quality of it between systems since I don't have that level of experience.

Since you have the experience in comparing the system and identifying the problems, you might want to give EMC2 a try and see what it can do for you. If you are going to, I am curious to know about your findings.

Ries
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  #4  
Old Tue 26 January 2010, 10:17
sailfl
Just call me: Nils #12
 
Winter Park, FL
United States of America
Gus,

You say that you notice that the chatter marks are spaced the same as the rack. Do see chatter marks in all directions of your cutting. Are they there when you cut X only, Y only, X and Y only?
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  #5  
Old Tue 26 January 2010, 11:13
ScottGus1
Just call me: Gus
 
North Plainfield, NJ
United States of America
Gerald: Thanks for those links, I dodn't notice them in my search. It got a little hot in there, didn't it? Have you noticed any improvement in Mach3's "read-ahead"? in the last couple years, or has it stayed the same? (BTW I remember you from the Shopbot forums a few years ago, along with Mike Richards, whose posts I saw in that thread, too.)

Ries: I have looked at EMC2 as well. Leaning to Mach3 or Shopbot because the motors/drivers come with the software. But I am curious, Do you have a working EMC2 setup, and if so, where did you get the drivers/motors?

Nils: I get chatter marks only on diagonal and curved cuts. (1:1 motors on my SB) I do not get chatter on the Biesse at work even though the X axis is driven by angled-tooth rack & pinion. Theory: the supposedly circular movement of a straight-across-tooth pinion on a fixed rack is really not exactly circular but has tiny pulses of difference in angular momentum because of the teeth interfacing with each other? And an angled-tooth system such as on the Biesse fights the momentum differences by having more than one set of teeth biting at any one time? (Probably slaughtering the scientific terms here and I have no way to test it, but the Shopbot has chatter, the Biesse doesn't. Hmmm...)
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  #6  
Old Tue 26 January 2010, 11:19
Gerald D
Just call me: Gerald (retired)
 
Cape Town
South Africa
Gus, your Biesse doesn't have 1:1 motors - that's where the major difference lies.

(Havn't bothered looking at the lookahead again)
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  #7  
Old Tue 26 January 2010, 12:28
riesvantwisk
Just call me: Ries #46
 
Quito
Ecuador
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Gus,

I do have a working setup with EMC2, the motors are from motion king and the drivers are from Gecko (V203)

I have seen occasions where Autocad files didn't do circles and ovals very well and they are all created with tiny little lines.

If anybody has a AutoCAD (DXF) file where a circle or nurbcurve made up of lines and the same DXF file where the circle is a geometrical circle and the nurb curve is the nurb-curve. I could run a test and see if there is a difference between each cut. I only have Q-Cad here and I am not beable to explode a circle into line segments...

Ries
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  #8  
Old Tue 26 January 2010, 12:37
ScottGus1
Just call me: Gus
 
North Plainfield, NJ
United States of America
Gerald, You're probably right on the Biesse's motors. I don't see anything that bears resemblance to a gearbox myself, but it could very well be in there. The next time you power up your baby, could you please indulge me with a multi-multi-segment straight or slightly curved air-cut line and tell me how it feels? Thanks...

Ries, Even our Biesse, surprisingly, doesn't do well with long runs of little lines. I've been fighting that for a while and am shocked that Shopbot at $15k does so much better than Biesse at $150k. (Of course the Biesse cuts WAY faster than the SB, so I'm not complaining much.) How hard was it to interface your controllers to your EMC2 PC? Any custom-made circuits, or just plug them into a port?
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  #9  
Old Tue 26 January 2010, 13:03
riesvantwisk
Just call me: Ries #46
 
Quito
Ecuador
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Gus,

since I use a parallel port on the PMDX 122 the setup is as straight forward as using Mach3 and the same hardware, no change there. Unfortunately, I don't know much about shopbot or your Biesse Rover and interfacing that to EMC2, I doubt is plug and play.... The EMC2 forum or IRC channel is the right place to ask.

However, since you mention you have problems with read ahead and lots of small little lines, there are CAM tools that can solve this issue by changing the little lines to longer line, circles or nurbs (depends on your controller if it can handle nurbs) within a tolerance, would this not be a better solution for you?

I do believe it's possible to convert any machine to beable to interface with EMC, but that would be my very very very last resort.

Within the EMC world they seem to call this 'Constant Velocity?' Constant Velocityl

Ries

PS: nurb curves in EMC2 is currently in a experimental stage.
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  #10  
Old Tue 26 January 2010, 13:19
ScottGus1
Just call me: Gus
 
North Plainfield, NJ
United States of America
Thanks, Ries, I was hunting around a little and just found that PMDX board, too. Looks like it makes assembly a lot simpler. I do notice that the Biesse runs smoother when the arcs are G-code circles instead of lots of lines. No plans to convert Biesse or Shopbot. We're considering custom-brewing our own 5-axis monster.

Will be looking into that board for our new project. Thanks.
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  #11  
Old Tue 26 January 2010, 13:25
riesvantwisk
Just call me: Ries #46
 
Quito
Ecuador
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Gus,

if your Biesse runs smoother with the circles, then I think your current best solution is to get a CAM program that can combine the little lines from your CAD into longer lines/circles with a good proximity to your desired lines and curves.

Gus, are you going to create a blog/thread on cnczone of the 5axis monster? People would be curious I think about that built...

Ries
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  #12  
Old Tue 26 January 2010, 13:29
ScottGus1
Just call me: Gus
 
North Plainfield, NJ
United States of America
It might be intersting to do that. Right now the monster is very much in the earliest pre-embryonic stage, ie, still in my head. But If I can give my boss good answers we might press ahead, and who knows? A blog could be fun! I'll keep it in mind.
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