new to linuxcnc and building a plasma table

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13 Feb 2020 14:20 #157288 by tommylight

jay1st wrote:
Yeha i've been watching those, and i see you're in direct drive on the gantry, is it fast enough ?

Most of them can do over 48M/M, so way to fast for any needs. The fastest i could successfully cut was 7.8M/M cutting 3mm plate with 80A set on a hypetherm 3070 plasma source.

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13 Feb 2020 15:45 #157295 by jay1st
Ok so a direct drive is more than enough with enough resolution i guess.
Tnx mate

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13 Feb 2020 17:17 #157297 by tommylight
16 tooth GT2 pulley will give you 32mm of movement per revolution, a bit over the ideal, but still usable. About 20 to 25 would be better, so if you can do some reduction it would be ideal.

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13 Feb 2020 21:02 #157322 by rodw

jay1st wrote: Quick question, i've read the entire LinuxCNC plasma primer, and for the table my side it recommends using a belt drive, but any DIY plasma table i see over inter net has rack and pinion drive............;

Great to know people are referring to the primer I wrote with input from a lot of others.
I don't remember writing about drive methods. Can you tell me the heading number?

jay1st wrote: Is it that bad to use belts ? As i already have them, 20mm wide, on the laser ssystem i was given, it even has a belt driven reducter 5not sure about the proper term to use).


I don't think there is any right or wrong way subject to the usual considerations regarding backlash. Just on stepper motors you need to heed the advice under heading 22 for best results.
linuxcnc.org/docs/devel/html/plasma/plas...per_motor_revolution
A direct drive belt system's distance per rev is determined by the size of the pulley on the motor.

But if you have table, I would just use it as it is

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14 Feb 2020 08:47 - 14 Feb 2020 08:47 #157337 by jay1st

rodw wrote:

jay1st wrote: Quick question, i've read the entire LinuxCNC plasma primer, and for the table my side it recommends using a belt drive, but any DIY plasma table i see over inter net has rack and pinion drive............;

Great to know people are referring to the primer I wrote with input from a lot of others.
I don't remember writing about drive methods. Can you tell me the heading number?

jay1st wrote: Is it that bad to use belts ? As i already have them, 20mm wide, on the laser ssystem i was given, it even has a belt driven reducter 5not sure about the proper term to use).


I don't think there is any right or wrong way subject to the usual considerations regarding backlash. Just on stepper motors you need to heed the advice under heading 22 for best results.
linuxcnc.org/docs/devel/html/plasma/plas...per_motor_revolution
A direct drive belt system's distance per rev is determined by the size of the pulley on the motor.

But if you have table, I would just use it as it is




Rodw, the plasma primer is very interesting and usefull, glad you made it.
But for the belt reference i mixed up with the guide from Tommylight wich is based on your publication.
found here : forum.linuxcnc.org/plasma-laser/35349-op...ea-and-a-lot-of-info

This afternoon i'm going to have a look at the reducers fitted to the frame, and count the teeth or diemeter of the pulleys.
It has only 1 drive for each axis, gantry is moving with a single drive connected by a shaft to the belt drive on the other side, and the head is moving with belt an a reducer as well, i might remove it and put it on the other side to have 2 independent drives for moving the gantry so i'll be able to auto square it.
And end up with a direct drive for the head, as for Z i have a 30cm ball screw availible.

BTW what is the standard for axis naming ? i know Z is the vertical for the head, but Y and Z could be inverted or do we refer to the longest axis ?
My gantry is 1.5m long and the shortest axis has 1.2m rails bolted on the frame. Well my explanations might not be very clear is guess, need more vocabulary.......
Last edit: 14 Feb 2020 08:47 by jay1st.

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14 Feb 2020 09:39 - 14 Feb 2020 09:40 #157339 by rodw
Just following up on Tommy's post, my machine travel is about 32mm per rev and I am happy with the cut quality so I would not get too stressed if you are close but not perfect. This thread might also be useful and really marked the beginning of my plasma build so long ago. (And forced me to rework my Z axis.)

forum.linuxcnc.org/30-cnc-machines/31509...pinion-drive?start=0

As far as axes direction goes, you really can pick any corner to be the origin (x0,y0) but the geometry is all based around the X,Y cartesian geometry you might have been taught at school. So if you are facing the front of your machine, X0,Y0 is the closest corner on your left. I've had mine set up a couple of different ways but the most natural way for me was to have the gantry running across my chest when standing at the front of the machine. So in that position, the gantry running across the table becomes X and and the axes the gantry travels along the Y axis.

A plasma table does not really have a Z axis and you may hear the term lifter used instead. IN a CNC world like Linuxcnc, the there is generally a Z axis which measures the height off the table so Z axis = lifter...

EDIT: and don't worry about the dual motors on your gantry ends, one stepper is probably fine the way you have described it. it cant realy get out of square..
Last edit: 14 Feb 2020 09:40 by rodw.

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17 Feb 2020 08:54 #157572 by jay1st
Tnx rodw, i'll have to good reading i guess :)
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19 Feb 2020 18:21 #157882 by jay1st
So i got my electronics from Mesa yesterday, so happy about it


7i96 and a THCAD10


As for the frame, here is the twin laser cutter i'll be using


With the stock motors, i'll change the rails as those are all rusty, and a bigger gantry to hold the Z, going with a 1.5M long 60x120 extruded aluminium profile.


The laser heads and mirrors are still there with the tubes, 150w and 80w, all the electronics will be replaced but i'mkeeping the power supply for the motors and add a 3rd driver for the Z (THC)


By curiosity i'll check if it's the 150w tube or it's supply which is faulty and my be keep or sell them or make a smaller laser CNC.....
Attachments:

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19 Feb 2020 19:14 - 19 Feb 2020 19:16 #157889 by Clive S
Very nice.

If this is of any use my congis for the 7i96 + thc-10

File Attachment:

File Name: plasma_mac...2-19.ini
File Size:9 KB

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File Name: io_2020-02-19.hal
File Size:1 KB

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File Name: plasma_mac...2-19.hal
File Size:2 KB

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File Name: plasma_mac...2-19.hal
File Size:7 KB

File Attachment:

File Name: Mesa7i96Pl...xlsx.txt
File Size:18 KB


remove the .txt off the excel file
Attachments:
Last edit: 19 Feb 2020 19:16 by Clive S.
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19 Feb 2020 19:42 #157891 by tommylight
If there was a short torch that would fit inside with the lid closed, that would be nice !
Then again, plasma uses a thick copper cable and that might prove a bit much for the existing mechanics.
You might want to strap a torch there and move it around to check that it holds.
Torch with bent cable form 5 to 20 KG of pressure on all sides.
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