Toolpaths in simulation v.s. on machine

[kwertmanX3F6N]

So I am struggling with an issue that I cant seem to grasp. First of all I am using a pro light cnc lathe made by intellitek. I am a tech ed teacher and am trying to get this machine operating again after sitting for approximately 10 years. I think I am very close to making this thing functional but I have hit a quirk or something that I am asking some help on. 

The part: I am attempting to machine a chess pawn with the typical rounded top. 

Issue 1 : The tool path when the part is profiling works great until I get to the I and K lines in the G code. I think these are arc vectors. Whenever the line of code is to run the I and K arc vectors it changes everything in the feedrate and depth of cutting. This is fine when machining wax but in aluminum it looks like a crash and stalls the machine. The part has v shaped notches cut in it and its uses the arc vectors to plunge in to machine those out. I have everything set super conservatively in fusion toolpath wise but these lines of code seem to ignore all of those parameters. 

Issue 2: So through trial and error I have learned that if I have a radius on the end of the chess pawn the tool crashes right into the end of the part and then performs some off task circular toolpath cuts in the location that the tool has just removed from the part. In fusion 360 this does not happen in simulation. I feel the arc vectors are the issue here but I dont know what a possible solution would be. Just to try something today I eliminated all radius from the end of the part and it machines it fine. What gives here? Is it the machine that is not capable of machining a spherical shape on the end of a part or is it the post? I am using the generic turning post from the autodesk site. I know very little about these I and K and didnt know what they were until I did some probing on google. I am an entry level player here so any assistance would be appreciated.

 I feel I am setting all offsets, tooling, and part measurements correctly since it machines the rest of the part fine and it machines fine without a radius.   

[Steinwerks]

Can you export your file as a .F3D and attach it here? It's difficult to diagnose without the file in this case.

[kwertmanX3F6N]

The actual part file I was machining is at work but this one is the same idea. I will post process it and put the G code on here too. I hope its something simple that I am not understanding. Like I said I am a beginner trying to get this thing running. 

[kwertmanX3F6N]

And of course I dont see any of the arc vector I and K lines in this code anywhere. I will see if it comes up in the CNC motion software for the lathe. 

[kwertmanX3F6N]

So in this code its giving me an R which I assume is radius. I wont be around the machine until Monday to do more troubleshooting but I must have selected something to create that mess. I just wish I knew what it was so i'm not guessing. I'm not sure why I cant access the drawing I did at school today from the cloud but its not there. One thing all this trouble shooting has done is helped me with fusion 360 and the machine software through repetition! Have to see the positive in everything.  

[Steinwerks]

Alright so before we dig into the feed issues from your initial post, what post processor are you using? In most of the posts in the dialogue that comes up there is a useRadius property in which you can choose to use an R value for the radius, or I and J. Often times R is more compact but is not always available on all machines, and either option can produce problems in some controls (IE one works and the other creates odd arc behavior or program failure).

[kwertmanX3F6N]

I am using the following post: 

pro light turning (4).cps- Generic pro Light Turning 

I have my cutting depths set way light which is creating a lot of code for such a simple part. I question that a bit but I would like to have kids turn aluminum stock and this machine would not run the .040 default depth used in fusion. I dont know if the massive amounts of code could be a factor or not. Thank you for taking the time to look at this. 

[Steinwerks]

Well I couldn't find anything in the program that would be making radical changes to the way the machine operates without knowing more about the machine itself. I also realize that this is a very small lathe generally suited to training (as you're using it), and very small work, so my best guess is that something may not be defined correctly on the machine itself, such as the stock being slightly offset from the front causing the machine to dig in when it starts the front radius more aggressively than when it is taking straight passes. One solution is to program a few facing passes first so any excess stock is removed before your profile roughing operations begin.

Actually as I was typing this I realized that 40 IPM is REALLY HEAVY. At 500 RPM (if that's what the workpiece is turning at) that's .100" per revolution, a massive pass on any machine. Drop that down to 2-4 IPM for a reasonable chipload (.004"-.008"/revolution) on such a little machine.

One reason for excessive code is your Groove operation is creating a lot of point moves and I would suspect that is a larger issue for the machine than arcs. Turn on Smoothing on the Passes tab and the code gets dramatically smaller - less than a third of the original size. You also have the Part operation pecking at .005" with a .001" retract which is making over 300 lines for a single toolpath and I'd definitely recommend increasing the peck depth to something more like .025"-.05".

[kwertmanX3F6N]

I will give these a shot. The lathe isnt capable of the feed per revolution so if I forget to uncheck that the code shows errors so those heavy cuts have never made it to the machine. I will definitely use smoothing from now on and adjust that pecking depth. I guess it would be very helpful if someone who runs production on these operations in fusion and made up a list of what gets the job done that may be helpful. Its a bit overwhelming looking at all the options and I have found checking one box can completely change the job. Ive watched you tube videos to get me to the point I am at now and I learn something new every day. I just need to build more confidence and gain more experience to keep students from crashing this machine. Thanks for the help. I will give it another shot tomorrow and see what happens.    

[kwertmanX3F6N]

So i noticed today that the code is running g3 rather than g2. My curiosity has me wondering if my issue is in this. What parameters impact clockwise or ccw arc movement. I tried allowing it to machine in both directions and ended up plowing right into the end of the part as it did before. The shape of the curve would require a ccw cutting path but it is in fact trying to cut the curve in the opposite direction. I feel im so close to chasing this down.


Kurt Wertman
Technology & Engineering Education Teacher
Montgomery Area High School
TSA Advisor



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