Lathe not cutting the correct pitch

ecs

ECS
My lathe isn't cutting the correct pitch. I've tried a 2mm pitch and a 1.5mm pitch and both are out.

Attached are picture of the pitches as well as the encoder setup.

I have all my axis dialed in so i'm not sure what could cause such a big error.

When i'm threading the machine just sits there for 30 or more second before it starts and on one of the threads it stopped half way through and sat for another 30 seconds mid threading cycle.
 

Attachments

  • encoder.jpg
    encoder.jpg
    3 MB · Views: 17
  • 1.5mm.jpg
    1.5mm.jpg
    2.9 MB · Views: 12
  • 2mm.jpg
    2mm.jpg
    2.8 MB · Views: 14

evermech

evermech
What's the max feed speed in settings for z axis?

Might try a slower rpm and thus feed speed just to see if it improves. I'm not sure how fast the Masso can read the pulses from the spindle indicator

Guy
 

evermech

evermech
Hey I'm running out of ideas on this one, maybe double check encoder calibration, not sure if it matters is the spindle actually going the rpm asked for. Maybe try 200 rpm and see if the amount that the threads are out seems to get better or worse.

Guy
 

ecs

ECS
@evermech - i have checked it twice now and can't see any problems. I'm going to print the wheel again to make sure there is nothing wrong with the first print. I ran one at 200 RPM and it still didn't fix it. But it might be slightly better than the other ones i've tried. Its really hard to tell. I think the masso is struggling to read the encoder pulses. At 200 RPM it instantly starts cutting where as when the RPM is 1000 it takes 30 seconds to engage.
 

machinedude

machinedude
maybe the lead into the thread is not long enough? you need to have enough run way to let your motor ramp up to full speed. if the acceleration is slow then the pitch is not going to be correct. this is just a thought as to what might be going on here. the faster the rpm you run at would require more time to get up to the proper speed before you start cutting.
 

evermech

evermech
Is the sensor engaging the black and white disc pattern properly? Does it see that black spot that must be the zero point for the spindle
 

ecs

ECS
I have it starting 5mm before the part. Maybe it should be longer?

I have turned the spindle over slowly by hand and every black and white spot the little leds light up. So i dont think thats the problem.
 

machinedude

machinedude
i would at least start the tool back further to see if it improves the problem or not so it can be ruled out or looked at closer if it was me.
 

machinedude

machinedude
Quote from evermech on August 23, 2019, 5:02 am

@machinedude

i recall reading somewhere that using the length of thread for the lead in is a good rule of thumb

Guy

well you have to look at it this way it's like physics class all over again with time to accelerate a distance traveled. these home built systems have to be learned as what the motor controller combo is able to do. your feed rate and RPM are what makes the pitch correct or not so having enough distance to reach you needed speed makes sense as a problem point for bad pitch on a thread. so i am thinking you either need to improve the acceleration or give it more space to get up to speed before cutting.
 

breezy

Arie
Staff member
Quote from machinedude on August 23, 2019, 5:13 am

your feed rate and RPM are what makes the pitch correct or not so having enough distance to reach you needed speed makes sense as a problem point for bad pitch on a thread. so i am thinking you either need to improve the acceleration or give it more space to get up to speed before cutting.

Also you need to take into account is the deceleration at the end of the cut.

Regards,

Arie.
 

ecs

ECS
So i've printed a new encoder wheel on 1200 DPI and glued that over the existing one. Then increased the acc & decel to 1000. I started the thread 25mm before the part. I have the RPM at 500. All of which have done nothing. Its the exact same error.
 

machinedude

machinedude
well you can always indicate the Z axis to check if it moves what you tell it to move but how have you checked the spindle speeds? one other thing you could check would be to take a very small cut in one pass just so you scratch the surface enough to see your mark so you can check to see if it is a thread tracking issue. i'm not a metric guy but if i were to check my settings i would check if i had the right amount of threads in a inch of travel over on this side of the pond :)
 

evermech

evermech
Is your spindle running at the programmed speed continuously while the threading routine is happening? It's not stopping and starting at the beginning and end of every pass is it? If it's continuously running we can eliminate motor start up time and accel and decel issues and look somewhere else.

Maybe a screen shot of the encoder setup will help.

when you program an rpm in Masso and run the spindle, does the vfd indicate the same rpm? Should be able to view on vfd panel while running if you poke the right buttons, might have to refer to the manual.

It appears that the pitch is too close together from the pics? You could always add to the screw pitch until the threads line up with your gauge? Say 1.55mm or something. This may get you through your job until the problem is solved. Also it may indicate how many percent off the problem is which could lead to an answer possibly.

just some ideas. Guy
 

ecs

ECS
@machinedude & @evermech - I've gone away and done some checking and videoing.

Everything seems to be in order from what i can see. Have i missed something?

I did some testing regarding changing the thread pitch to get the 1.5 to cut correctly and it ends up at 1.57. Its still not 100% i think it would be 1.575 or 1.58. At the 1.57 i'm able to get a nut to thread onto the end with a great fitment. I'm actually pretty impressed at how it came out straight of the tool!

@masso-support - does anything stick out been wrong?
 

Attachments

  • M10X1.5.jpg
    M10X1.5.jpg
    1.9 MB · Views: 16

evermech

evermech
Unfortunately I am not able to view the videos but interestingly enough 1.575 is exactly 5% off of 1.5. What are your encoder settings in spindle set up. How many pulses per rev?

If you added 5% to the 2mm thread would it be correct. That would be a 2.1mm thread?

Guy
 
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