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Author Topic: Newbie with Mach 4 Lathe - again - Mach 4 and dial ind do not agree  (Read 739 times)

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Hi all,

Really confused here.

I Jog X -0.100. DRO on Mach goes from 3.893 to 3.693. Makes sense since I am in diameter mode. But my dial indicator only shows -0.050 movement.

Step belt pulleys are the cross slide are the same diameter. I cannot find a "scaling" parameter in the config.

Suggestions??? - send it back is not an option  ???

Confused,
Dale
Re: Newbie with Mach 4 Lathe - again - Mach 4 and dial ind do not agree
« Reply #1 on: October 05, 2019, 03:38:40 PM »
Dale Grice <dfgrice@gmail.com>
   
2:18 PM (1 hour ago)
   
to Joe, Ron
Adding on to my previous email.

I set the default to Radius mode. I move x -0.100, DRO goes to -0.100. Dial Indicator mores -0.049.

Next step; I found where the "scale factor" is under Control > motors > counts per unit. Mine was set to 10000. After a couple tries, 20,000 moves the dial indicator -0.095 when the DRO shows -0.100.

Next step; changed counts per unit to 21,000. Now the dial indicator moves -0.100.

I am going to check Z. Then go back to diameter mode.

Z is stranger. DRO says I moved 0.100. Dial Indicator says 0.058.

Count per unit now set to 16,500 on Z. Dial indicator moves 0.100.

Comments?

But another new anomaly. I am trying a turning cycle. It seems after each pass, the compound moves in the -Z direction. In other words, each pass, the compound does not return to Zi. It starts to the left on each successive pass. Any thoughts?
Re: Newbie with Mach 4 Lathe - again - Mach 4 and dial ind do not agree
« Reply #2 on: October 05, 2019, 08:24:43 PM »
Hi,
you should not have to guess what the steps per unit value is....you should calculate it precisely.

The variables required to calculate the correct step/unit value are:
1) The pitch of the lead screw. Note this must be accurate to be of any value. The common pitches are 4mm, 5mm, 6mm
and 10mm in metric screws and 0.2, 0.25 inch in imperial screws. Note that 0.2 inch is very close to 5mm (5.08mm to be
exact) and is easy to confuse the two. MEASURE PRECISELY or take up another hobby other than CNC.
2) The microstepping regime, common are fullstep, halfstep and 1/4 setp. These are simple but prone to midband resonance
and so 5, 8, 10 and 16 microsteps per fullstep are recommended and the norm. Microstepping beyond 16 microsteps per fullstep
gains you little or nothing.

For example if you have your stepper driver set to 8 microsteps and given that the basic two phase stepper has 200 steps per
revolution so with the micorstepping works out to 1600 pulse per revolution.

3) gear or belt reduction, this should be exact. It becomes less than exact if you are using Vee-belts as the diametrical pitch is not clear.

Idnentify those numbers and we can give you a hand to calculate the exact steps/unit. Any discrepancy between the calculated and
actual will teach your more about your machine than anything else.

Craig
My wife left with my best friend...
     and I miss him!
Re: Newbie with Mach 4 Lathe - again - Mach 4 and dial ind do not agree
« Reply #3 on: October 23, 2019, 06:08:08 PM »
Hi Craig,

Makes perfect sense. But my feeble mind had not thought of that.

Dale
Re: Newbie with Mach 4 Lathe - again - Mach 4 and dial ind do not agree
« Reply #4 on: October 23, 2019, 07:16:28 PM »
Hi Dale,
give us some numbers and we'll calculate the steps per unit and see how close you are.

Craig
My wife left with my best friend...
     and I miss him!
Re: Newbie with Mach 4 Lathe - again - Mach 4 and dial ind do not agree
« Reply #5 on: October 24, 2019, 06:46:27 PM »
Hi Craig,

Thanks for the help.

On my X, I put a dial indicator on it. I rotated the X axis one revolution using a level as my reference. I got 0.159. I have asked what the pitch of my X and Z leads are. They state they are metric. It is thought they are 5 mm. My measurements get 4 mm for X and 5 mm for Z. This is a mini lathe. Starting small.

My calculation for X comes up with 4.0386 mm. So I am assuming 4 mm pitch for X.

I looked up the Z stepper on the internet. I had to remove the end cap to get a part number, KL23H276-30-4AM. I am told my X and Z steppers are the same. Anyway, the spec sheet states 0.9 degrees per step, 2 phase.

Off to the stepper driver. I am told it is configured for 8 pulse per step. I need to open up the box and double check that. But my math puts steps per unit at 20320, with the assumption that unit in "counts per unit" under conifg > motors > X is inch. That is what I have set in Config > general.

20320 was close to 21,000 that I had set for X. I checked Z as well. 5 mm ball screw. I calculate 16256 which is close to what I had set.

Dale