Re-starting a file

[ljdm]

I did a search, most posts were re-starting after z-dive, lost position,etc..... In my case, I paused the cut for the night. Murphy's Law - power failure during the night. I like to bring the x against the stops to ensure no out of square from power off. I did write down the line number and x,y,z positions. What is the procedure to use in this case. Yes, I know it has been discussed before, wondering if the procedure is any different in this case. Running Sb2.38. I assume I use "FG", never used it before, so bear with me. Newbie - yeah, but I'm learning.

[ljdm]

Never mind - figured it out. Worked out pretty good, was off by a few thousandths on the x-axis, just have to sand a ridge across the relief. Next time I'll have to clamp the y and x rails together overnight to prevent wander until I tighten up/reinforce things. Must have got racked good enough where it doesn't want to keep in shape when the motors are powered off. All part of the 1500 mile journey in the back of a truck. Gives me a chance to learn the machine a little more.

[knight_toolworks]

even pausing it for a time and throw it off. tried it with a lithophane for a hour and the z was off. sometimes it is easier to just start over.

[mrdovey]

At the risk of sounding crassly commercial, accurately (re)zeroing all three axes relative to a fixture, workpiece, or reference mark is the problem I solved with my Super-Zero plate.

If you missed the discussion, you can catch up at
Let's Talk ShopBot >> ShopBot Accessories >> Super-Zero Fixture.

...Morris

[paco]

I think the FG command need improvement. It's too tricky to use... I know how to use it but it's been complex to solve at first (broke some bit and destroyed almost finished part).

I do have "some background" and I can tell I wouldn't like it if I was new at this. Most other CNC tool I used before had this feature more friendly user. Whatever happen, one could move around and resume the cut from a single touch.

That's a weak point of SB3. I'm not loudly complaining but more talking this opportunity to point something that need some work...

[mrdovey]

Paco...

There are two solution strategies that can be applied:

[1] The 'Bot could be built with absolute position encoders so that the hardware always knows the absolute (x,y,z) coordinates - and the most recently commanded (x,y,z) location - and remembers the last z-zero offset.

[2] Provide some means of re-zeroing all three axes relative to some workpiece reference point.

The first approach would likely be fairly expensive in that it would (I think) require significant modifications to both controller hardware and control software.

The second approach is less automatic but is offers three clear advantages: It's less expensive, it works for existing 'Bots, and it corrects for workpiece axial (but not rotational) "creep" during the time the 'Bot is down.

...Morris

[paco]

Hi Morris!

I think there might be confusion within this discussion between (re)-zeroing axes (all) and resuming a cut (FG) command.

I think that with a good set of proximity switches, one can re-zero all axis and be back with in 0.005-0.01". At least it's my case. Before I installed my proximity switches system some months ago, I was using a fixed aluminum block with a drill rod as the TBC reference. It was very accurate but more steps to re-calibrate the tool and since I was having numerous connection issue with my tool, it was actually a pain. With the prox. switches, it take a few seconds.

Resuming a cut after a pause, tool breakage or a crash is different. One may want/have to start over but what if there's a power failure during a 8 hours 3D carving at about 75% of the work done? One would like to resume rather than start over right?
Right now, the resuming of a cut with FG command is no fun (read tedious) and has pitfalls. To ease the process, the control software has to record the location of the stop, record the current line of the file and enable manual mode until the user want to resume. I think the FG command, as it is now, is more suited is the tool jump off track, power failure, control malfunction... where one have to re-zero all axis anyway. But what if I just pause for a tool change of to see if I'm cutting through or if it look good enough to continue?
I did have an idea for a routine for this purpose but I haven't had the time to toy with it yet...

Resuming a cut face two situations; having to recalibrate the tool (severe condition) and just pausing (no major failure). It may be necessary to address each differently...

I hope I'm making sense...?

[mrdovey]

Paco...

You're making good sense.


There are really three problems:

[1] Determining where you were in the program when you stopped (for whatever reason).

[2] Re-establishing the coordinate system relative to the workpiece before resuming.

[3] Resuming execution of the part program where you left off (which might require repositioning the bit).

I use the proximity switches to locate the table (0,0) position, but if I'm using a pallet or fixture, I zero all three axes to a reference point on the fixture.

I did something similar to what you were doing with the aluminum block - which was a pain in the neck - until I did a little machining on the block and wrote a little SBP program that allowed zeroing all three axes using my movable block and my XYZ_ZERO.SBP program. Most of the time I do the zeroing with the bit I'm going to be cutting with.

What this does is allow me to restart with the same workpiece coordinate system I started with.

Another technique I've used is to add code to record (in a file) checkpoints for re-starting. I normally only do this for long runs, but it lets me look at the file to see where in the program to I want to resume. Any tool motion between the checkpoint and where I left off will be repeated, but it does allow executing initialization commands and then doing a GOTO to avoid repeating all the code before the checkpoint.

This allows me to stop the program partway through and shut the machine off, then come back and turn the machine on, re-zero the axes to the workpiece, and resume cutting from the last checkpoint with a worst case error of 1 step.

I hope I'm making sense.


...Morris

[paco]

quote:Paco...

You're making good sense.
Ouff...

quote:I use the proximity switches to locate the table (0,0) position, but if I'm using a pallet or fixture, I zero all three axes to a reference point on the fixture.
I hit C5 to write, on file, the working offset. From there it's easy to recover my working (JIG, fixture) location. This is something I highly recommend to learn to do and use on a regular basis. In fact, I should have put this in my CAM posts since I use it all the time.

quote:Another technique I've used is to add code to record (in a file) checkpoints for re-starting. I normally only do this for long runs, but it lets me look at the file to see where in the program to I want to resume. Any tool motion between the checkpoint and where I left off will be repeated, but it does allow executing initialization commands and then doing a GOTO to avoid repeating all the code before the checkpoint.

This allows me to stop the program partway through and shut the machine off, then come back and turn the machine on, re-zero the axes to the workpiece, and resume cutting from the last checkpoint with a worst case error of 1 step.
Sound good, is that only SB code?


I think we're talking about the same thing.


Still, I'd like to see something new about the FG command...

[mrdovey]

Paco...

Yes, it's all SBP code - but it does require manually entering the label for the GOTO.

I gave up on FG because using it created more difficulties for me than not using it - and one of those difficulties was spoiled work.

I'll be quiet and make room for someone else to talk about the FG command.

...Morris

[Brady Watson]

Morris,
The FG command could use a little tweaking, that's for sure. The trick is to write down the X,Y,Z where the machine was stopped, and insert a jog command just above it, with the same coordinates, and the Z set up at 1" or so. Then run the FG command and tell the machine to goto the line # where you put the new J3 command. From there, it will run over to the spot, and gracefully plunge into the work and resume cutting. One KEY factor here boys and girls is to remember to set your move speed in SB3 BEFORE you run the FG command. Since the program will not begin executing until the line number you specify, it is very likely that the machine will run at an undesireable speed, UNLESS you have coded a MS command after the starting line of the FG. If you don't start the FG command at a jog command line, then I can pretty much gaurantee that your router is going to move on an XZ or YZ plane and screw up your part. Perhaps a good suggestion for a future version of FG would be to take the line to start & behind the scenes, insert a J3 command and prompt the user for an appropriate safe Z height. This would eliminate the ramp of destruction moves...

When I used to run SB2, I was always losing steps (since I was just learning) and had to figure out how to get my 0,0 back in case of catastrophic failure. I never ran proxy switches on my machine, so everything is done by eye. If for some reason the machine craps out, zero the tool where it sits (Z2)...then in keyboard mode, move the tool back to your original 0,0 point or a known location. Sometimes I will bore a small hole into the spoilboard with the cutting tool at a known location from 0,0 and write it's location (EG - 12,12) on the spoilboard next to it in pencil. (This technique is for people without proximity switches by the way)...After you have moved the tool to your original 0,0 point, write down the X & Y position shown in the red DRO in SB2 or SB3. It will most likely be 2 negative numbers: -24, -12 etc. Then zero out the tool (Z2). Then FE to look at your file and scroll down until the code reads close to the location you wrote down, but in positive: M3,24.125,11.98,-.25 etc - Observe what is going on in the code, and see if that is where you need to be. Sometimes it is easier to create a new part file (using FE) and copy & paste up to a certain line & run in preview mode. SEE if it looks like the location where you left off. If it does, then go back to that area of the code (original file) and copy the line where you want to start. Hit enter for a blank line & paste it right above the line you want to start cutting. Change the M3 command to a J3, and any negative Z value to a positive. EG - M3,24,12,-.25 should be changed to: J3,24,12,1 - JUST ABOVE this line, enter in an appropriate speed, something like: MS,2,1. Then write down this line number (shown on bottom bar of SB Edit). Now run the FG command, enter in the line number where your NEW MS command is sitting, and click on 'Go'. It will cycle thru your code until it gets to the line you entered. It will highlight the line in SB3 where it will start. If this is the correct line, then click on 'Run From Here' and your back in biz. Don't forget to do a C2 if you think you lost Z position, before running the FG command...and, as with anything else, you should run the FG command in preview mode if you are not certain how it will work.

Hope I didn't make understanding the FG command even more difficult...


-B

[john_r]

Just experienced the same problem this morning on a beautiful figured piece of cherry. Re-started the cut and the Z cut down almost a 1/16 deeper. Sucks! had to start all over.
Theres got to be a better system, rather than starting all over.

I've kinda got used to cutting everything in cheap foam before I cut expensive materials like this.

[Brady Watson]

John - Read my litany above. You can use the FG command rather than starting all over...You just need to understand how it works, and try it in Preview mode before doing it on a live tool.

-B

[john_r]

I'll give it a try Brady. I may have spoke too soon...


Thanks,
John

[mrdovey]

John...

If you need to re-start, it's a really good idea to ensure that you're using the same coordinate system as before.

Re-zero your machine!
4886

...Morris