Messages

681

General Mach Discussion / Re: High Speed Servo as Spindle - My Solution

« on: December 06, 2011, 07:03:30 AM »

Continued from last post . . .

I am prepping an old mill for sale and I am considering options for the head. Those options include: laser cutting head, 3d printing head, or just a more conventional high speed routing/engraving spindle (while maintaining the 4th axis capability), so I was researching VFDs and came across a new Hitachi model that accepts pulse train input, and has a rudimentary positioning capability. Not sure exactly how that all works at the moment, but it is definitely worth a look-see.

Comments on smoothstepper; This device does more than just generate a ver fast and clean pulse stream, it also adds I/O. Adding a 4th axis and second spindle (effectively) gobbles up I/O. I view smoothstepper not unlike a graphics card . . adding processing power for a specifc task, relieving the burden on the CPU. The smoothstepper objects to me using the esc key, it seems. It is annoying, but exiting the error seems graceful and non destructive, so it may just boil down to having to changing my own behavior. Like the old Vaudeville yarn PATIENT: "Doc, it hurts when I do this." DOC: "Then don't do that".
Also, I am using a BOB made by CNC4PC specifically for the smoothstepper. The smoothstepper allows LPT2 to be input or output, the BOB forces LPT2 to be inputs only with no option to change. This limits the usefulness of the board in our application (indexer plus two spindles), so I will be going back to directly plugging cables into the smoothstepper.

Lastly, in my case, the problem with using an AC servo drive for the main spindle is that the power is limited by availability of single phase 220V power. The largest Mistu that runs on single phase 220 is 750W (one HP), and I want considerably more that that amount.  

682

General Mach Discussion / Re: High Speed Servo as Spindle - My Solution

« on: December 06, 2011, 06:38:22 AM »

Damon, Thanks for the detailed reply. I have done some work with 4th axis with same goals as you are working toward. Obviously you have the knowledge and creativity to make the cat pretty nervous, so I was just curious about how you approached the problem.

It occurred to me in reading your posts that you had no way to run the 4th axis as a spindle and also run the main spindle simultaneously, but now I see that you have that on the list as well. My only comment on your method is to mention that if you are using a servo motor on an axis (S, A, whatever), there is no need for an index pulse to control speed. A single index pulse per rev, in my view, is pretty crude and also problematic in any case.

This is what I ended up doing . . .  again not saying this is *best*, just what I am running at the moment, and how I set up customer systems: Both the S and the A axis are dedicated to the 4th axis and I run the main spindle separately. M3,4, and 5 are editable macros 'out-of-thr-box' so relay on and off is no problem which only leaves speed. In my case, I have had speed under G-code control, and also manual and I much prefer manual, so my solution was an easy one. However, were I inclined to put the spindle speed back under Mach's control, I might spend some time noodling over the possibility of using the C or D axis somehow, but my thinking at this moment is that I would use one of the tiny 'PLC' like Arduino or PIC to generate the speed control for the spindle. Al ll you would need is to read the commanded speed out of Mach and send a command (pulse count would be easy) to the Arduino which in turn would adjust the spindle speed. Arduino/PIC could easily read an index pulse and provide a stable speed.

More comments in next post:

683

General Mach Discussion / Re: High Speed Servo as Spindle - My Solution

« on: December 03, 2011, 06:14:52 AM »

A couple of comments on the speed issue:

Some industrial AC servo drives allow you to have more than one multiplier and switch back and forth on command. This would resolve the multiple speed range issue. My Mitsubishi drives have that feature. Other industrial brands (Yaskawa, AB, etc) *probably* also have that feature as well.

A consideration on 'consumer' level drives is that not all behave well with software gearing active, and some only have a few preset ratios while others have separate numerator and denominator params which allow literally any ratio, and run smoothly with multipliers active.

One general FWIW:
Smoothstepper recently released new drivers and a new plug-in and now supports swapaxis. I have tested the new softwares and they seem to function to spec and are stable (so far). As a result, I have just completed switching over to the smoothstepper on my new (4 axis) mill. I am still using my hardware swapaxis board, but over time, if the smoothstepper performs in every other area, I will start experimenting more with the software swapaxis. Also note that Mach has functions where you can change many of the config params via macro. Before I get into trouble, let me just state that I am not pointing to any particular 'best' solution, only that there are a lot of ways to skin this cat.

And my original question:

What is the advantage of arranging a 'complete' swap axis to accommodate different A vs Spindle parameters over dedicating both MACH's A and spindle to 4th axis operation and running the mill spindle by another method?

You are going thru a lot of work to accomplish this so there must be some compelling reason. Just curious. I have some other questions to ask, but these are the fundamental ones.

684

General Mach Discussion / Re: High Speed Servo as Spindle - My Solution

« on: December 01, 2011, 06:31:08 PM »

What is the advantage of arranging a 'complete' swap axis to accommodate different A vs Spindle parameters over dedicating both MACH's A and spindle to 4th axis operation and running the mill spindle by another method?

You are going thru a lot of work to accomplish this so there must be some compelling reason. Just curious.

685

Show"N"Tell ( Your Machines) / Re: Success! Mini Machining Center under Mach3 control - Video link

« on: November 22, 2011, 06:51:14 AM »

More videos:
Use 4th axis for sharpening
http://www.youtube.com/watch?v=Y3PIdnNwsAg

Internal shaving of keyways
http://www.youtube.com/watch?v=Nnfcc2fqeTA

Major bench mill upgrade phase 1 table
http://www.youtube.com/watch?v=HTQ7u3pcdYs

Major bench mill upgrade phase 2 column and head
http://www.youtube.com/watch?v=QsuJgCCPSl0

686

General Mach Discussion / Mach BUG in xx.50 skip line after sub is back.

« on: October 21, 2011, 05:49:03 PM »

Old bug has returned.

Also check the thread on Cutter comp for description of another bug in that function.

687

General Mach Discussion / Re: cutter comp

« on: October 20, 2011, 02:58:11 AM »

If you have an example of the comp code  switching sides I would love to see it. It would make a good test sample for future testing.

I ran these on my office computer which just got updated to XX.50 yesterday and it looks like there have been some fingers in the cookie jar. Comp is even more bizarre now! Now it is switching sides even on connected arcs. This example shows how MACH inserts tiny arcs . .  a bonus. Another new behavior is that there is no separation between the original and comp toolpaths, Note the tool diameter and also note the scales. First screen shot is with both axis at -1 scale. Second screen shot only one  axis at -1 . . BOOM!   That is opposite of what it was doing in the earlier version in the shop. The behavior in the earlier version is also different in that the comp arc started on one side and endied on the other side of one of the long arcs that make up the sides of this part. If I changed the scale from -1 to -.999, it still switched sides, but at a different location on the tool path where I could live with it, so I did that and got the parts cut. As I siad, I do not use comp much at all, but typically, I find that comp seems to work OK on simple unscaled toolpaths, especially closed paths, but if you go 'outside the box' . . . it can get  ugly.

I cannot release the G-code on this part. If this occurs on releasable code, I will be happy to provide the code. I understand it is difficult to debug without a repeatable example, sorry. I just came in to add some new video links to my 'mini machining center' thread and thought I'd poke around a bit and see if I could be useful, however I am unsubsribing now. I hope my comments were helpfull, but just do not have time to participate in-depth on forums.  

688

General Mach Discussion / Re: cutter comp

« on: October 19, 2011, 08:55:46 PM »

I use comp for just almost everything I cut, and have never seen it switch sides. But I have seen a  bug where the tool just takes off out into space, but it wasn't my part, and it was a profile made up of many short segments, which comp doesn't like.

I made the point in an earlier post that the erratic behavior occurs if one or more scales are set to -1 to mirror a part. The I commented again and genralized. Sorry for the confusion.

As to arcs, Mach itself puts arcs in the comped toolpath. And I seem to recall (although I wold not swear to it) that MAch has also put arcs at the beginning. Again, this behavior is not 'normal', but occurs if for example two arcs are not attached to each other and this would be imperceptible during a normal cut, but cutter comp calculates unpredictable results . . like sticking a tiny arc in between the end of one arc and the begining of the unattached arc . . and switching sides.

Never the less, I shal henceforth never use arc intentionally as lead-ins since it is apparently 'illegal' . . . that is on the rare occation that I woudl need to use cutter comp at all.


Good discussion.

689

General Mach Discussion / Re: cutter comp

« on: October 19, 2011, 08:46:27 PM »

SO IF I did a lead in away from the part instead of into the part Mach would get it wrong??  So far as I can tell Mach does not care about the direction of the leadin it just needs room to actually do the move. AND it some cases it WILL go out of its way to actually do the required move in order to get it correct, Arcs in general (bad form to use arcs as leadins).

I don't see how you would conclude that from anything that I said. It would not matter if your lead in was away from the part, in fact that would not even be unusual. By your logic, there would be no reason for both G41 and G42. Think of a simple square hole that you want cutter comp to enlarge by ,010. If you start off going up the left side of the square with G41 (comp to the left), then you will get a larger hole, however, if you start from the top and move down (i.e. a different DIRECTION), the comp will STILL be to the left and you will get a smaller hole. That's how it works.   A detailed description of how and why Mach accomplishes cutter comp is well detailed in MACH's own documentation. I suggest giving that a read.

690

General Mach Discussion / Re: cutter comp

« on: October 19, 2011, 03:31:19 PM »

Symantics at work here. G41/42 does not set direction, it chooses compensation on the right side or left side of the path. I suspect that is what you meant by 'direction'? Mach needs the lead in to determine direction so that it can determine left from right . . . because that is relative to the direction of travel  . . .   and it needs to know that before the first actual toolpath move so that the comp can be in place by then . . . . so the comp cannot be calculated until direction is established . . . by the lead-in  . . . . so that Mach knows which side to offset on  . . . . .  based on the choice dictated by G41 or 42  . . . . or at least so sayeth the Mach documentation.

The actual comp value is taken from the tool diam in the tool table of whatever tool is active or chosen by the 'D' parameter unless the other parameter (I think it's 'P') is used to over-ride the tool table entry. 

However, the length of the lead-in could be required for the reason you mentioned. You will get and error if the lead in is not long enough. The message seems to change depending of if the lead-in is a straight line, an arc, or if it is Thursday . . . .

I try not to use G41/42 in Mach if possible as it seems a little unpredictable . .  often switching sides in the middle of the toolpath . .  usually at long arcs . . . .  or if it is Tuesday.