From Manual to CNC - Sherlines

[zeeprogrammer]

Well well. Success of sorts. Failure of sorts.

Now there are many many things wrong with this picture...

1) Yes, the stock is sticking way too far out. This is only a test. 
2) Depth of cut is too deep.
3) Part got pushed into the chuck. (Too deep a cut.)
4) Pulled the cutter out of its holder (see how it's angled?).
5) X at 0 was set along the X axis but it looks like it thinks it was nearly a half inch away.
6) Related to '5', it seems it thinks the raw stock had a greater diameter. Many cuts in air before it met metal. That is, the number of passes in Z seemed much more in Mach3 than in CamBam.

While running I heard a horrible high pitched scream. Happened only once while rapid moving back to home. No idea what that is but may be related to the motor tuning I did. I have no idea what the proper settings should be. It's supposed to be trial and error but I don't have a good idea of what I'm shooting for. At times I changed settings but it didn't seem to change operation.

Prior to this run, the X axis had gotten loose from the stepper motor. A preload nut is used to attach the lead screw to the motor's coupler. The nut was supposed to screw onto the lead screw but didn't. I found one in the mill CNC kit that fit. (Which means I need a replacement before I convert the mill.) A 4-40 goes through the coupler into the lead screw. I don't have a lot of confidence in that setup.

In any case, nothing broke, nothing caught fire, and I didn't hurt myself.

I call it success.

[crueby]

Sure that scream wasn't a shop elf caught in the works? 

[zeeprogrammer]

Sure that scream wasn't a shop elf caught in the works? 

Wishful thinking.

[Dave Otto]

Hi Zee

The scream was probably one of your motors stalling, did you notice either one of the axis stop moving when this happened?
Have you checked that your step value is correct? if you command 1" of travel is that what you get?

Not sure how you set your x tool offset, on our lathe at work you manually (with the jog) take a fuzz off the OD of the stock and with out moving the tool in X, you mic the part and enter the value into the control. I have never done this in  MACH but some how the control needs to know where the tool is.

Might be a good idea to set up an indicator and issue some commands in MDI and make sure that it repeats back to 0 in both X and Z (checking for missed steps) assuming that your step values are correct?

Dave

[kvom]

Dave has it correct!   Once the diameter is read and set in the DRO, both CAM and Mach need to use diameter mode.  I think in Mach3 it's a Pots&Pins setting.

[zeeprogrammer]

The scream was probably one of your motors stalling, did you notice either one of the axis stop moving when this happened?
That's what I had thought too. It was a long scream but I didn't notice anything being off position as the process continued.
Have you checked that your step value is correct? if you command 1" of travel is that what you get?
Yes. I checked both X and Y. I do need to revisit that but I was within a few thou.

Not sure how you set your x tool offset, on our lathe at work you manually (with the jog) take a fuzz off the OD of the stock and with out moving the tool in X, you mic the part and enter the value into the control. I have never done this in  MACH but some how the control needs to know where the tool is.
I used the jog function to face the stock. Then I jogged to its center and zeroed home. I was probably off a bit in X but not enough to be a problem. I'm sure Z was right but my placement of X home needs looking at.

Might be a good idea to set up an indicator and issue some commands in MDI and make sure that it repeats back to 0 in both X and Z (checking for missed steps) assuming that your step values are correct?
Did. But I should certainly do more checking.

I need to review the g-code again and verify the various movements. My suspicion is I probably didn't set (or I incorrectly set) some parameters.

Thanks Dave.

Feeling too good right now to pursue further until tomorrow. My celebratory drink(ing) means the machines stay shut down tonight.

Just saw your post Kirk. I do need to look into that. I'm not sure how 'diameter mode' changes things. My thought was g-code is g-code. If I say move G0 X1.0 Y1.0...it will move to position 1.0,1.0 from home. Are the positions given in the g-code modified by such parameters?

[kvom]

 Yes, the X words are just numbers that can indicate distance from centerline (radius mode) or twice that (diameter mode).

So CAM and control need to be in agreement.

My advice to you is to cut air for a while until you think it looks correct.

[Mike R]

The scream happening during a rapid is a sign of the motor stalling - likely due to
1) being asked to accelerate too quickly.
2) overall top speed is to high and the motor runs out of chooch at the top speed due to way and screw friction.


My bet would be on a combination of both, mostly 1 and a little of 2.  They can be hard to separate as the machine is only so long so if you have a really gradual acceleration you may not achieve the top speed - run out of runway so to speak.
A few different ways to tackle. 


1) try adjusting the acceleration only - bring it down 20% and rapid the z back and forth. You can setup an indicator,  set it to 0 and slowly move away (G1 Z something positive and reasonable feedrate F) and then Rapid back same amount (i.e. G0 Z0). Note that I have rapid only one way.  A lot less likely to smash your indicator this way - if it looses steps it will fall short, where as rapiding both ways can result in random loss of steps and could loose more steps moving away than back (experience here...).  Should always return to 0 regardless of any other scalling if you go out and back the same amount.  Be sure to set the indicator to 0 just like when running a manual lathe - i.e. account for backlash - were only working one issue at a time here!   Repeat with more or less acceleration so that you know what its capable of before stalling, then reduce by a good amount (my rule of thumb is 30%) to account for cutting loads etc. Do the same for X as you didn't mention which one screamed.
2) with the same setup above try adjusting the top speed until it stalls or is not repeatable.


Top speed and accelerations are not important to hobby machines so you can really dial both back and be much happier with a reliable, but slightly slower machine than one that will also be reliable,  but only at quickly making scrap pieces and making you scream.


Mike

[Dave Otto]

Hi Zee

I wasn't sure how much setup and verification you had done, sounds like you are close.

Dave

[zeeprogrammer]

 

Changed the feed rates, the roughing clearance plane, and depth of cut and then used a simplified part drawing.
Verified both CamBam and Mach3 were in 'radius' mode.

Still many many questions but I think I have a 'Hello World' system.

[Dave Otto]

Hey Zee

That looks like pretty good progress!

Dave

[crueby]

... I think I have a 'Hello World' system.

Your software background is showing!  Still got your copy of K&R?

Glad its starting to come together!

[kvom]

Now shorten the tool holder stickout.

[zeeprogrammer]

Your software background is showing!  Still got your copy of K&R?

Left it at work for the next poor soul.  Nearly memorized anyway.

Now shorten the tool holder stickout.

Hee hee. I was waiting for someone to notice. But yeah.

[crueby]

Your software background is showing!  Still got your copy of K&R?

Left it at work for the next poor soul.  Nearly memorized anyway.

Now shorten the tool holder stickout.

Hee hee. I was waiting for someone to notice. But yeah.

I wound up keeping my copy - had it since college, couldn't bear to leave it behind. Though I have not opened it since!

Now shorten the tool holder stickout.

Good point - though on Sherline scale, its only out an inch!  Question - other than keeping it in tight for rigidity, is there a rule of thumb for how far the tool point is out from the toolpost is okay?