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Metric on an imperial machine , setting up question
« on: January 13, 2018, 10:55:27 AM »
Hello , a quick question .

I'm used to and would like to continue working in metric . So if I understand the manual correctly
I have to set the native units to mm .

My machine however  has  16tpi lead screws , coupled directly to the
steppers . Steppers are rotating nuts so I'm stuck with the 16 tpi and cannot change that . .

Setting to mm would mean I have 25.4/16 = 1.5875mm/rev .

Let's assume a 1/16 ustep driver and my steppers are std 200steps/rev .
That results in 2015.748031496063........ steps/unit .
Other ustep setting produce similar "impossible" figures .

I can't seem to find any setting of the ustep driver wich would produce an integer nr of steps / mm .


Not sure what to do here , suggestions appreciated .


Thx
Pat ( Belgium )

Offline Davek0974

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Re: Metric on an imperial machine , setting up question
« Reply #1 on: January 13, 2018, 01:29:44 PM »
I would get it close then use the auto-tune setting in Mach.
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Re: Metric on an imperial machine , setting up question
« Reply #2 on: January 13, 2018, 03:17:15 PM »
Hi,
can you not use inch units as 'native' but when operating the machine issue G21 which causes all the DROs and Gcode interpreter to be in metric?

Fairly simple matter to try it and see.

Craig
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Re: Metric on an imperial machine , setting up question
« Reply #3 on: January 14, 2018, 02:45:00 AM »
That would be awesome .

If I understand correctly  all I have to do is issue a g21 at the start of each session , and that will make
it read and work in mm until otherwise specified . 

Well worth trying .

thx

pat
Re: Metric on an imperial machine , setting up question
« Reply #4 on: January 14, 2018, 04:41:19 PM »
That results in 2015.748031496063........ steps/unit .

   Are you building parts for SpaceX or the shuttle?   Round it up to 2016 and cut some parts?
Retired Master Electrician, Commercial HVAC/R Service and lots of Hobbys.
Re: Metric on an imperial machine , setting up question
« Reply #5 on: January 15, 2018, 02:08:55 AM »
Yes I'm aware that I could round it , and that the error for a single mm will be so small
it can't even be measured .
And even if it could be measured , there  will be more error in my leadscrews then that .

But unlike the leadscrew error , the step error will repeat itself and accumulate for every unit of travel .
If I have 250mm of x-axis , that will be 0.25 step *250mm /2016 = 0.03mm .
And that can be measured , and for certain operations will be a problem .
Fi dowel pins .

Soi if there's a way around it I prefer to get the basics right .
I will make enough errors myself in operating it .
I don't need the machine to be wrong from the start  ;D


pat
Re: Metric on an imperial machine , setting up question
« Reply #6 on: January 15, 2018, 07:22:52 AM »
Why not enter the number as is and let Mach do the work in the background?

I would then measure the actual movement since the screw is most likely not perfect.

Mike
We never have the time or money to do it right the first time, but we somehow manage to do it twice and then spend the money to get it right.
Re: Metric on an imperial machine , setting up question
« Reply #7 on: January 15, 2018, 09:51:04 AM »
So is it not 1 mm the unit of measure 1 / 2015.748   vs  1 mm / 2016 ?    So maybe I am thinking wrong, but its .0004909 or .00049603?    I usually use a reamer if I want to install a dowel pin.
Retired Master Electrician, Commercial HVAC/R Service and lots of Hobbys.

Offline ger21

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Re: Metric on an imperial machine , setting up question
« Reply #8 on: January 15, 2018, 10:05:26 AM »
Quote
I can't seem to find any setting of the ustep driver which would produce an integer nr of steps / mm .

You don't need an integer number of steps. Even if it theoretically worked out to an integer, in reality it probably wouldn't be, due to the tolerances of the screws.

Do the math, enter the number, measure the distance traveled, adjust to suit.
Gerry

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Offline Davek0974

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Re: Metric on an imperial machine , setting up question
« Reply #9 on: January 15, 2018, 10:52:51 AM »
Hmm, as i said in 1st reply - set it near, run auto-set feature, enter exact value and forget - its that simple ;)
Bridgeport Mill, Mach3 V062, CSMIO-IP/A controller, AC Servo Drives.
Plasma table, Mach3 V062, Step motors, C&CNC THC.