4th axis on my probotix cnc

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4th axis on my probotix cnc

Postby clintontull » Sun Oct 11, 2015 3:33 pm

I am still in the means of learning the methods on my cnc. I have the 4th axis on my probotix cnc. Listed here.
http://www.probotix.com/CNC-ROUTERS/METEOR-CNC-ROUTER

How can I do a guitar neck using the 4th axis and wrapping? I want to be able to mass produce the necks.
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Re: 4th axis on my probotix cnc

Postby 4DThinker » Mon Oct 12, 2015 1:16 am

Your CNC should be able to cut necks on the 4th Axis, but it will depend on whether you can build the needed 3D model in some CAD program, then know how to import it, unwrap it, tool path it, then use the right post processor to make an .NGC file your LinuxCNC controller will know what to do with. Once you get ONE to cut you can use the same file over and over and over again.

What I've learned so far... X values changed to A values are considered degree per minute rather than inches per minute. So if you have ordinary 200 +/- ipm feed speed set for any tool cutting around the rotating object it will cut VERY slow. You need to edit any tool used to cut around in the A direction to use a very high feed speed. A value that would be comparable to 200ipm on a 4" cylinder would be 4" x pi = 12.57" in 360 degrees. 200/12.57 = 15.91 revolutions per minute. 15.91 X 360 = 5728, the IPM feed speed you'll need to give X moves that become A moves around your rotary axis so they'll seem like 200ipm cuts. There is a simple formula in there you could create to use block diameter, desired feed speed, and a multiplying value. My mind is not up to coming up with it tonight though.

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Re: 4th axis on my probotix cnc

Postby IslaWW » Mon Oct 12, 2015 1:39 pm

Clinton...
The simple formula for rotary feedrate is 115 * (XY Feedrate) / Wrap diameter. Actually 114.5916, but close enough.

So for Mike's example 115 * 200 / 4 = 5750 degrees per minute (in round numbers) A large number, but is only around 15 rpm, which is not fast at all for rotary work.

In WinCNC and ShopBot control software this formula has been added to the rotary post processors so that the user selected XY feed will be automatically applied to the rotary axis. I am fairly sure that it could be added to most other controls that allow math in the code.

That said, most of the successful high quality guitar neck cutting that I have witnessed was done in robust jigs, not on the rotary axis. The length and density of the part often requires additional support beyond what most rotary axes provide. Especially of you are looking for mass produced high quality components.
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Re: 4th axis on my probotix cnc (speed rate?)

Postby tgauthier » Tue Jun 13, 2017 4:00 pm

IslaWW wrote:Clinton...
The simple formula for rotary feedrate is 115 * (XY Feedrate) / Wrap diameter. Actually 114.5916, but close enough.

So for Mike's example 115 * 200 / 4 = 5750 degrees per minute (in round numbers) A large number, but is only around 15 rpm, which is not fast at all for rotary work.

In WinCNC and ShopBot control software this formula has been added to the rotary post processors so that the user selected XY feed will be automatically applied to the rotary axis. I am fairly sure that it could be added to most other controls that allow math in the code.

That said, most of the successful high quality guitar neck cutting that I have witnessed was done in robust jigs, not on the rotary axis. The length and density of the part often requires additional support beyond what most rotary axes provide. Especially of you are looking for mass produced high quality components.


I just installed a rotary on my CNC Router Parts Pro4848 and trying to practice with the rounding "wrapping gaget". I set the .25EM tool speed at 100ipm but the A axis rotary is painfully slow. It looks like from the comments above that I need to change the X feed but I am not sure where to do this in the settings. I am using VCarve Pro 8.5 and Mach3. Any help with this would be so grateful.
Thanks, Ted Gauthier Pontiac, Michigan
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Re: 4th axis on my probotix cnc

Postby TReischl » Tue Jun 13, 2017 4:31 pm

About speed on the rotary:

It depends a lot on your control software. For instance, Mach3 can be set so there is no issue of having to adjust for the A axis moves. None. Mine is set up that way.

I am not familiar with the LinuxCNC control software, so someone else will have to chime in. If it is not capable of doing the calculations internally I would be very surprised.

TGauthier: Do some digging in this forum section and you will find the settings for Mach3 so you do not have to edit the A axis moves. One thing for sure is that you have to adjust your Config file in the Motor Tuning for that A, the numbers on mine are quite high, a LOT higher than you would set for the other linear axis. Here is another thread about this subject:http://forum.vectric.com/viewtopic.php?f=38&t=23640



In other words, if you are using Mach3 I can definitely tell you that you do NOT need to edit feedrates once you set up Mach3 correctly.

Here is a typical program generated by the rotary post, notice there is no "adjustment" for A axis moves. The tool setting was for a 30 IPM plunge, 150 IPM feed:

(Toolpaths used in this file:)
(Profile 1)
(Tools used in this file: )
(1 = End Mill {0.25 inch})
N130 G00G20G17G90G40G49G80
N140 G70G91.1
N150 T1M06
N160 G00G43Z4.1695H1
N170 S12000M03
N180(Toolpath:- Profile 1)
N190()
N200 G94
N210 A0.0000 X0.0000 Z4.1695 F150.0
N220 G00 X-4.0549 A-146.9250 Z2.2400
N230 G00 X-4.0549 A-146.9250 Z1.9900
N240 G1 X-4.0549 A-146.9250 Z1.7400 F30.0
N250 G1 X-2.4372 A-146.9250 Z1.7400 F150.0
N260 G1 X-2.4372 A-280.5750 Z1.7400
N270 G1 X-4.0549 A-280.5750 Z1.7400
N280 G1 X-4.0549 A-146.9250 Z1.7400
N290 G1 X-4.0549 A-146.9250 Z1.4900 F30.0
N300 G1 X-2.4372 A-146.9250 Z1.4900 F150.0
N310 G1 X-2.4372 A-280.5750 Z1.4900
N320 G1 X-4.0549 A-280.5750 Z1.4900
N330 G1 X-4.0549 A-146.9250 Z1.4900
N340 G1 X-4.0549 A-146.9250 Z1.2400 F30.0
N350 G1 X-2.4372 A-146.9250 Z1.2400 F150.0
N360 G1 X-2.4372 A-280.5750 Z1.2400
N370 G1 X-4.0549 A-280.5750 Z1.2400
N380 G1 X-4.0549 A-146.9250 Z1.2400
N390 G00 X-4.0549 A-146.9250 Z2.2400
N400 G00 Z4.1695
N410 G00 A0.0000 X0.0000
N420 M09
N430 M30
%

Edit: Another hint about using an A axis. Negative A moves keep a chuck from loosening up on the spindle. At first I was wondering about why it output -A moves as a rule, then it dawned on me.
Last edited by TReischl on Tue Jun 13, 2017 4:43 pm, edited 1 time in total.
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Re: 4th axis on my probotix cnc

Postby TReischl » Tue Jun 13, 2017 4:40 pm

BTW, it is best if the controller does the feed calculations for rotary moves. This is because as the diameter decreases the feed rate must increase to maintain the correct surface feet per minute.

Or, a mosquito standing on the edge of an LP recording is going a lot faster than one standing on the label. (If you do not know what an LP is, then you are too young to be doing rotary work 8) )
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Re: 4th axis on my probotix cnc

Postby IslaWW » Tue Jun 13, 2017 4:49 pm

Ted...
Something to consider...
The rotary axis moves negative because it performs like moving table. Moving the material negative while the bit remains fixed. To achieve proper wrapped axis positive action, the rotary must move negative


The chuck thread direction, which in many cases ae not required, are coincidental
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Re: 4th axis on my probotix cnc

Postby TReischl » Tue Jun 13, 2017 9:14 pm

IslaWW wrote:Ted...
Something to consider...
The rotary axis moves negative because it performs like moving table. Moving the material negative while the bit remains fixed. To achieve proper wrapped axis positive action, the rotary must move negative


The chuck thread direction, which in many cases ae not required, are coincidental


Mr Isla, I wrote rotary software for cnc lasers. There is no requirement to use negative values in the program because the table on a flat bed machine moves in the negative direction when a positive move is programmed.

That said, on further thought, I don't think I was correct either. If they were worried about spinning a chuck off the spindle, it would not help one bit when the cut had to go in the opposite direction.

So, I think we are both wrong!!!!! Maybe it has something to do with getting the cutter on the correct side of the line, but since I don't write software anymore.....I am not going to worry about it.

Think about it, what they have done is map negative degree values, those could have just as easily been positive degree values. Hard to verbalize, but if you think about the coordinate system, you can specify it in units like inch/inch or inch/degrees. At first I thought I always got negative values because my system is normally set to spec zero at the top of the part. (that is because I use a vise a whole lot and it is a good idea to set zero against the fixed jaw) but when I moved zero to the bottom edge, no change.
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Re: 4th axis on my probotix cnc

Postby tgauthier » Wed Jun 14, 2017 2:50 pm

Hi Guys, Thanks for your input. Your thoughts are really appreciated. From your posted replies and reading the attached links it looks like I need to change some settings in my Mach3. I need to convert the Feed rate to radial Rate? and maybe adjust the A axis motor tuning? Not sure where to find the settings to adjust feed rate to radial rate. I do know how to make changes to the A axis motor tuning but not sure on the settings. I will take a longer/harder look at the settings in the evening and hope to locate them in an attempt to speed up my A axis. Am I missing something or just confused.

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Re: 4th axis on my probotix cnc

Postby TReischl » Wed Jun 14, 2017 3:06 pm

Hello Ted,

The settings pages you are looking for are buried pretty far back in this section of the forum.

When you set this up keep in mind that you will need two profiles for your machine.

The first one is the one you are using now. When you start Mach3 you will select it and all will be normal.

The second one will be for the rotary axis. Obviously you will pick that one when doing rotary work.

What that means is that once you have the rotary configured it is just a matter of selecting which profile you want to run the machine with.

I took some time and found this:
http://forum.vectric.com/viewtopic.php?f=38&t=7283

That should get you started if not get you all set up. Like I said earlier in this thread, when you set the motor tuning for the A axis it is a very high number so do not be too shy.

One other thing, you might want to remap which keys cause the A to rotate. I set mine so that Home and End cause it to rotate from the keyboard. It has been a while since I configured it so I am not sure why I did that, but since I am basically lazy there must have been a reason for doing it.

One other thing you want to think about. For doing rotary work it is usually best to set the zero at the centerline, not on the surface. In fact, IIRC, you have to do that or Mach won't be able to figure out the feedrates for A axis. Could be wrong about that.

I put a touch off plate on my tailstock so that it is easy to set Z zero. Without doing that, there is no easy way to figure out where the centerline is. You might want to check into Ger21's excellent screen set for Mach 3. It is called Screenset 2010, you can google it or contact him here, he is a member. It has some nice features that make some of this a lot easier. Like the touch off plates. I think he still charges about $20 for it and it is worth every penny. I like Mach, but I never liked their weird screens, messy at best.

BTW, Ger21 is right in your neck of the woods. You might want to drop him a private message. Gerry is a wealth of knowledge when it comes to CNC stuff.
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Re: 4th axis on my probotix cnc

Postby tgauthier » Wed Jun 14, 2017 7:14 pm

Thanks TReischl..... for taking the time to respond. Yes, I have set my Zero to the center of the stock. I never gave it any thought about having a second profile for rotary but that make sense. I currently use 2010 screen set for flat work and love it. Now that I am trying to learn rotary, I have been switching back and forth to Mach3 only because I know that in Mach3, I can hit the Tab button on the keyboard and then I have access to the A axis control buttons and I just did not know how to do that in the 2010 Screen Set. Yes, Gerry is very helpful and I was planning on trying to reach out to him tonight. I will send him an email.
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