forum.cncdrive.com

I've been trying for a long time now to figure out how to get smoother toolpaths. The vast majority of my work is in complex 3d mold surfaces so I rarely am able to use G2/G3 circular interpolation, therefore when running finish routines with close tolerances the toolpath will consist of large amounts of small point to point motions. See attached photo:



For reference this is a toroidal shape with an approximate 1.4" radius at the top edge. At the top edge the toolpath consists of roughly 30 blocks at 48ipm to complete the radius. Notice the faceting--it's evident in the finished surface and it can be felt in the machine as a subtle 'stuttering' at each block. I've made numerous attempts at modifying the CV parameters, going from one extreme to the other on every available setting, but nothing has ever made a difference so my thinking is that this must have nothing to do with CV. I have seen in other threads suggestions that acceleration plays a part and the usual suggestion is to increase the acceleration. I normally have it set to about 30 in./s^2, as I increase it the problem generally gets a little worse. When I slow it down to 10 or less the problem gets better, but having slow numbers like that causes other undesirable issues.

Could this just be a limitation of UCCNC? I've seen mention on occasion of a new trajectory planner being worked on, will it address this issue at all? Incidentally I have 2 identical mills with one using closed loop steppers and the other fitted with servo motors, and both machines exhibit the same behavior, so it doesn't appear to be a motor/hardware issue.

Profile attached.

Thanks,
Dan

I don't have any experience machining metal, but have spent a fair bit of time researching CAD / CAM and in my view is that your problem is more likely to be the toolpath configuration than UCCNC.

Which CAD/CAM software are you using? Are you cutting the profile you have shown in a single pass or using a roughing pass followed by a finishing pass?

If you are using Fusion 360, you could look at the tolerance and smoothing options, along with feed rate optimisation, but again I'm no expert on metals and there are more experience people who I'm sure will provide advice as well. I'm interested to hear what others think about this.,

Hi Roby--

I've been a professional programmer for almost 30 years and a moldmaker for 45 years so I have a lot of experience under my belt. I use Mastercam for programming and have programmed and operated numerous industrial machines. I don't see this issue with the industrial machines, which is not to be construed as a criticism of UCCNC. I'm very impressed with it and it's a great value for the money, but it's not in the same league as what I've used professionally for many years. This issue is really my biggest disappointment with it, and if it truly is a limitation I'm okay with that, but if there's a solution for it I'd really like to know.

Just as a reference, one of the shops I help out does mold and pattern work and UCCNC did the same thing and we worked with setting for about 6 months changing everything possible before we found a solution to the problem.

(;-) TP

Vmax549 wrote:Just as a reference, one of the shops I help out does mold and pattern work and UCCNC did the same thing and we worked with setting for about 6 months changing everything possible before we found a solution to the problem.

(;-) TP

And what was the solution ?

Unfortunately it was to change controllers We were never able to get UCCNC to run the 3d code smoothly enough to NOT have to manually smooth up the molds and patterns and THAT did not fit their work profile to have to spend so much time hand finishing.

IT did work ok for basic router type basic profiling but not mold work.

Just a thought (;-)TP

Not the answer I was hoping for but it is an answer, so I guess I can stop looking for a solution. I did a search on 'planner' to see if there were any updates on the newer trajectory planner and found this:

http://forum.cncdrive.com/viewtopic.php ... +max+G2+G3

I remember running into this a while back but forgot about it. It's been well over 3 years since that thread ended so it would be nice to get some kind of update from CNCDrive about the planner status. Funny to me that the conclusion was pretty much the opposite of my experience, i.e. increase acceleration rather than reduce it. Maybe I just never got it high enough to work. I was able to get up to 40 in./s^2 before I started getting unhealthy sounding mechanical banging on the axes. Still wasn't enough to smooth out the toolpath.

There is no problem with the motion planner, just some people does not understand how it works and how to properly configure it.
Try to set the CV planner tolerances low to see if it resolves the problem. If it is not then it is not even motion planner problem, but probably mechanical issue.