Author Topic: CamBam seems to be scaling parts larger when outputting G-Code?  (Read 440 times)

Offline Poppas Workshop

  • Ewok
  • *
  • Posts: 6
    • View Profile
Hi there. I am a total newbie to this, so please forgive any errors/omissions.
My computer is running Windows 64-bit, and I have 16Gb of RAM.
My router is basically a home made/modified machine running through a GRBL controller.
I have just purchased CamBam1.0 and am real keen to get underway.
I've discovered that the final output on my router is larger than my drawing by approx 20%.
I am using the GRBL Post Processor, and have made no changes to any other settings.
Can anyone give me any idea what might be causing this.
Let me know if you need further info.
Many thanks
Steve

Offline dh42

  • Administrator
  • CNC Jedi
  • *****
  • Posts: 6491
    • View Profile
    • Cambam V1.0 French Doc
Re: CamBam seems to be scaling parts larger when outputting G-Code?
« Reply #1 on: June 13, 2021, 22:27:54 pm »
Hello

Probably your axes are not calibrated and you must change the "steps per" value to get the right scale.

steps per are parameter $100,101,102 for XYZ in GRBL

(pages 6 & 7) the formula is given in the PDF
http://www.barrel-organ-discovery.org/site/wiki/articles/Percage_GCode/PARAM%C3%88TRES%20DU%20GRBL_JPR_Freddy.pdf

++
David

Offline Poppas Workshop

  • Ewok
  • *
  • Posts: 6
    • View Profile
Re: CamBam seems to be scaling parts larger when outputting G-Code?
« Reply #2 on: June 15, 2021, 01:26:42 am »
Thanks for the info. Much appreciated.
I think I am going to have to do some serious study on the whole set-up, as most of what I am reading is like a foreign language.
I'll start with looking up some tutorials and take it from there.
Once again, many thanks.
Steve

Offline dh42

  • Administrator
  • CNC Jedi
  • *****
  • Posts: 6491
    • View Profile
    • Cambam V1.0 French Doc
Re: CamBam seems to be scaling parts larger when outputting G-Code?
« Reply #3 on: June 15, 2021, 01:55:58 am »
Hello

The "steps per" (units) corresponds to the number of steps (or µ-steps) that the motor must take for the axis to advance by 1 unit. (mm or inches)

To calculate it, for each axis you must know:

- the pitch of the screw
- the µ-step adjustment of the driver
- the reduction ratio between the motor and the screw (ex: if pulleys are using)

ex: if the driver is set to 1600 steps / rev (1/8 step), a screw with a 5mm pitch, and a 1:1 ratio between the motor and the screw (the motor is directly at the end of the screw) then:

steps per = 1600/5 = 320 steps / unit

++
David

Offline Poppas Workshop

  • Ewok
  • *
  • Posts: 6
    • View Profile
Re: CamBam seems to be scaling parts larger when outputting G-Code?
« Reply #4 on: June 15, 2021, 21:45:42 pm »
Hi David
On my machine, the X and Y axes are belt driven, so I'm not sure whether that formula applies.
The hardware details are as follows:
Belt = GT2 / 6mm wide
Motors = NEMA 17 (17HS4401)
Pulleys = GT2 / 16 tooth.
Is there a different formula for this type of setup?
Ta
Steve

Offline dh42

  • Administrator
  • CNC Jedi
  • *****
  • Posts: 6491
    • View Profile
    • Cambam V1.0 French Doc
Re: CamBam seems to be scaling parts larger when outputting G-Code?
« Reply #5 on: June 15, 2021, 22:05:05 pm »
Hello

Like a 3D printer ?

In this case the equivalent to a screw pitch = nb of tooth of the pulley * belt pitch ... If GT2 = 2mm tooth pitch (?), 16*2 = 32mm pitch (= 32mm of moving for one turn of the motor)

so with the same example of driver setting as 1600 step/rev, the "steps per" become 1600/32=50

++
David

Offline lloydsp

  • CNC Jedi
  • *****
  • Posts: 8452
    • View Profile
Re: CamBam seems to be scaling parts larger when outputting G-Code?
« Reply #6 on: June 15, 2021, 22:10:26 pm »
Don't forget that if the drive and driven pulleys don't have an equal number of teeth, you also need to account for the ratio between them!

Lloyd
"Pyro for Fun and Profit for More Than Fifty Years"

Offline dh42

  • Administrator
  • CNC Jedi
  • *****
  • Posts: 6491
    • View Profile
    • Cambam V1.0 French Doc
Re: CamBam seems to be scaling parts larger when outputting G-Code?
« Reply #7 on: June 15, 2021, 22:20:56 pm »
Hello Lloyd

If I well understand, it is like a 3D printer, not like a motor pulley and a screw pulley, the calculation is as for a rack-and-pinion drive. (and of course the 2 pulleys have the same # of tooth)



++
David

Offline lloydsp

  • CNC Jedi
  • *****
  • Posts: 8452
    • View Profile
Re: CamBam seems to be scaling parts larger when outputting G-Code?
« Reply #8 on: June 15, 2021, 22:43:30 pm »
Ah...  May be.  I was suspecting a belt and two pulleys, leading to a screw.  You're probably right!

L
"Pyro for Fun and Profit for More Than Fifty Years"

Offline Poppas Workshop

  • Ewok
  • *
  • Posts: 6
    • View Profile
Re: CamBam seems to be scaling parts larger when outputting G-Code?
« Reply #9 on: June 16, 2021, 02:41:06 am »
You guys are amazing!!
I've done a bit of further reasearch, and have come up with the following.
The belt pitch is definitely 2mm.
The specs for the 17HS4401 stepper motor state that each step = 1.8 degrees.
Therefore, there would be a total of 200 steps to make a full 360 degree rotation.
If I'm thinking correctly, your formula would become 200 steps/rev divide by 32 gives me a "steps per" of 6.25.
Does that sound right?
Steve

Offline dave benson

  • CNC Jedi
  • *****
  • Posts: 1470
    • View Profile
Re: CamBam seems to be scaling parts larger when outputting G-Code?
« Reply #10 on: June 16, 2021, 05:31:30 am »
HI Steve

No you forgot the micro-stepping value, multiply 6.25 by 8 to give 50 steps per.
out of the box GRBL Ver 1.1 is set for 40 steps per because the majority of
machines use 20 tooth pulleys, as you have 16 teeth pulleys you need to
change the default value from 40 to 50 this is where your 20% larger error comes from.

Dave

Offline Poppas Workshop

  • Ewok
  • *
  • Posts: 6
    • View Profile
Re: CamBam seems to be scaling parts larger when outputting G-Code?
« Reply #11 on: June 16, 2021, 21:59:27 pm »
Hi Dave
Thanks for that. It certainly worked OK.
Where did the micro-step value of 8 come from?
Just trying to get a good handle on how to work things out properly.
Regards
Steve

Offline dave benson

  • CNC Jedi
  • *****
  • Posts: 1470
    • View Profile
Re: CamBam seems to be scaling parts larger when outputting G-Code?
« Reply #12 on: June 17, 2021, 01:12:24 am »
Hi Steve

The micro-step settings for most common GRBL compatible boards like the one in the picture
are set by adding or removing jumper pins, which are usually underneath the stepper motor drivers.

As a general rule micro-stepping goes like this:
Higher micro-stepping rates = smoother running and more resolution but less torque at the motors
and if the micro-stepping is to high (perhaps X16 or X32) then you lose torque and high end speed.
For you 1\8 micro-stepping is the best compromise.

With the motors you have, you could expect to be able to engrave with a V bit, and drill smallish holes and mill plastics, wood ect.
Milling aluminium and steel not so much. The rigidity of the machine comes into play here.
If you making circuit boards, or driving a 3D printer\Laser then your good to go.

Dave

Offline Poppas Workshop

  • Ewok
  • *
  • Posts: 6
    • View Profile
Re: CamBam seems to be scaling parts larger when outputting G-Code?
« Reply #13 on: June 17, 2021, 04:04:39 am »
Hi to all
Great information everybody, and much appreciated.
I feel I can now move on with some confidence.
Steve