Cut Rifling Machine Help

Hi All

Looking for some help and advice with linuxcnc and basically to confirm what we're trying to do can be done with this software.

Bit of back ground, I work for a British company that makes rifled barrel blanks for precision firearms, mainly using the single point cutter method. We are currently using very old Pratt&Whitney sine bar machines, which are great and still produce very accurate barrels but we're struggling to keep up with demand and decided we need more cut rifling machines. To find more Pratt&Whitney machines is unlikely in the UK so we went down the route of looking into making our own CNC version of one. (There are some commercially available ones on the market but the're expensive and have little support for them in the UK if it went down and needed repair.) 

We have got to the point now where we have finished all the hardware tasks; such as building a bench top prototype machine, sorted the control box, wired it all in, installed linuxcnc and made some stepper motors move. To be honest these were our strong points so we took the easy route first and are now trying to sort the software side of it out. Looking back we really should of sorted this part out first before we committed the resources to the physical side of it.

 Basically really need help with a few points about linuxcnc that we've naively assumed can be done but actually might not be possible. These's are probably really stupid questions to people more experienced but we are complete novices.    

1) Can you make a complete custom GUI with ini and hal files to suit for a machine that doesn't behave anything like a mill or lathe in linuxCNC. (No current template like axis or Gmoccappy would really suit a rifling machine). Is it a task that realistically needs a very experienced user to do and is not feasible for novices to achieve in a reasonable time frame.

I know linuxcnc is installed with Glade to help develop GUI's but is it capable of developing something from the ground up?  

We need to have 3 set up screens and one job monitoring/status screens. The machine has 3 axis's of sorts, hence the need for 3 set up screens. First screen is for setting linear movements along the barrel. Second screen is for tool rotation as the linear axis moves it along the barrel. This will set the rifling twist and no of grooves to be cut. And the last one is to raise the rifling cutter hook in the tool after a set of grooves has been cut.

And all of this will need connecting up to the hardware side of things through, i'm guessing, the .hal and .ini files. 

2) If part one is possible with linuxcnc, can anyone recommend any reading/learning material to help us. Or any videos of similar projects to point us in the right direction.   Any help or advice much appreciated.

James  
 

SPC89 wrote:

H1) Can you make a complete custom GUI with ini and hal files to suit for a machine that doesn't behave anything like a mill or lathe in linuxCNC.

Yes. One example is my gear hobber screen, It's a good example of something that was thrown together quickly (and it shows): wiki.linuxcnc.org/cgi-bin/wiki.pl?Hobbing

We need to have 3 set up screens and one job monitoring/status screens. The machine has 3 axis's of sorts, hence the need for 3 set up screens. First screen is for setting linear movements along the barrel. Second screen is for tool rotation as the linear axis moves it along the barrel. This will set the rifling twist and no of grooves to be cut. And the last one is to raise the rifling cutter hook in the tool after a set of grooves has been cut.

You might want to consider a GUI that sends parameters to a G-code subroutine. It sounds to me like you need coordinated movements of a rotary and linear axis. You can do this in two ways, either by moving one axis and calculating the required position of the other axis (as is done in hobbing) or by moving both axes simultaneously with G-code. I think that the latter approach would be best in this case.
(The hobbing config that I linked to earlier actually does both of these things, the coordination of the hobbing cutter and work spindles is dobe by calculation, whereas the feed cycles are G-code routines that use parameters from the GUI.

2) If part one is possible with linuxcnc, can anyone recommend any reading/learning material to help us. Or any videos of similar projects to point us in the right direction.   Any help or advice much appreciated.

Firstly you might want to decide which GUI designer you want to use. There are three main options, GladeVCP, QTVCP and QTPyVCP.

I think that they all work, but for future-proofing I would suggest starting with the development version of LinuxCNC which has made the transition to Python3. You can get this from the buildbot once you have made a stamdard installation of LinuxCNC.

I would suggest skimming the docs for each and choosing one. QTPyVCP isn't (currently) part of LinuxCNC and is documented on its own web site.

linuxcnc.org/docs/2.8/html/gui/gladevcp.html
linuxcnc.org/docs/2.8/html/gui/qtvcp.html
www.qtpyvcp.com

Gscreen might be a good starting point, it is a working GUI designed for customisation.
linuxcnc.org/docs/2.8/html/gui/gscreen.html

Thanks for the pointers and links. Got some reading and understanding to do but it does look like we can achieve what we want with Linuxcnc. This is all a bit alien to us but will give it a try and hope we get somewhere. Otherwise its probably going to be outsourced to someone who does know what there doing.   

Yes....the movements between the linear and rotational axis's are critical, they must be co-ordinated and repeatable otherwise very bad things happen. We have used closed loop steppers for those axis's to help with this.

Once again thanks for replying  

James

   



 

SPC89 wrote:

Thanks for the pointers and links. Got some reading and understanding to do but it does look like we can achieve what we want with Linuxcnc. This is all a bit alien to us but will give it a try and hope we get somewhere. Otherwise its probably going to be outsourced to someone who does know what there doing.   
 

You can rely on getting plenty of support here. FWIW I am also in the UK and used to shoot competitively. (but only at paper) 

If you can design your GUI then connecting it all up should be relatively simple. 

Have you considered progressive rifling? That would be pretty simple now you are CNC. 
 

Yes it seems a friendly community on here with lots of help. The problem I've got is the steep learning curve with this software and my lack of technical knowledge on the subject. I was brought up on manual machines and have had some experience on 2 axis CNC lathes for profiling the blanks but building a machine from scratch is a different game.       

That's interesting you used to target shoot. Might of used one of our barrels maybe? We come under Sassen Engineering now but used to be called Border Barrels based in Scotland. If your ever in the area of Birmingham and fancy seeing how we make our rifle blanks drop us a message.

Progressive rifling was one of the reasons why we wanted to build this machine. Its impossible to do on our Pratt&Whitneys sine bars and we've heard good things about it across the pond. Apparently slight gain, for example, 1in8 at chamber to 1in7.8 at muzzle really helps accuracy in certain calibers. CNC will also help with us switching over the number of grooves to be cut, every time we go from 4 to 5 to 6 its a 1 hour job needing two people really. Hopefully on a CNC machine it will be as simple as typing a number into a box.

James  
  

SPC89 wrote:

Yes it seems a friendly community on here with lots of help. The problem I've got is the steep learning curve with this software and my lack of technical knowledge on the subject. I was brought up on manual machines and have had some experience on 2 axis CNC lathes for profiling the blanks but building a machine from scratch is a different game.

It probably makes sense to draw out possible GUIs on paper first. I don't think that there is enough complexity to need more than one screen, but I could be wrong.

Though the best place to start is probably with a simple config to get the machine moving under G-code control. That is likely to be the most satisfying place to spend your efforts next.

For the initial config just pretend that it is a lathe, you can change the axes to a rotary and linear (probably A and X) later.      

That's interesting you used to target shoot. Might of used one of our barrels maybe?

It's unlikely, I was shooting in the mid 1980s as a student, and using old rifles owned by the club. My preferred one was an immensely heavy Martini-action '22. Nobody else liked it, but I found the stability helpful. It didn't occur to me at the time, but it could have been very old.

Apparently slight gain, for example, 1in8 at chamber to 1in7.8 at muzzle really helps accuracy in certain calibers.

That's a surprise, I would have expected to start at 0 and move logarithmically to 7 or 8.
Given knowledge of the projectile speed at each point in the barrel you could arrange for absolutely constant angular acceleration. As a physicist that has an appeal to me.
(I don't know if projectile speeds are easily measured, but you could infer it from chamber pressure)