4x4 Homebuilt Motor Size Question

leggman · Post by **leggman** » Mon Mar 21, 2016 2:21 pm

I am in the process of building a 4 foot x 4 foot cnc plasma table and I have a question as to what size stepper motors to buy? At first I was thinking of the nema 34 1600 oZ. kits from longs but since it is a plasma table and therefore only moving a torch head around could smaller (cheaper) stepper motors work.
How about a nema 34 for the Y axis and a nema 23 for the x axis with a nema 17 for the z axis.
I plan on using a dual shaft nema 34 for the y axis mounted on one side with a shaft running to the other side and a dual chain/sprocket drive system. Please help, I am ready to order a kit and I just thought a four axis nema 34 kit would be overkill. Thanks

Simko · Post by **Simko** » Mon Mar 21, 2016 6:48 pm

How heavy is your gantry going to be?

CandCNC (a well known company recommends the following)
300 oz-in for up to 50 lbs
620 oz-in for up to 100 lbs
980 oz-in for up to 200 lbs

All of those assume a reduction so that one motor rev = one linear inch of travel

I would look closer into doing two separate motors on the y-axis instead of a cross shaft / chain / sprocket.

leggman · Post by **leggman** » Mon Mar 21, 2016 7:13 pm

Still considering that option , just thought the 1600 oz stepper would push it fine. Gantry will be as light as I can make it.

Post by **acourtjester** » Mon Mar 21, 2016 9:23 pm

I use the single motor and cross shaft on the table I build and it works great. I use one 1600 (34) and two 425 (23) motors with the correct power supplies for them. Chain drive for the long axis and rack and gear for the other axis with lead screw 10 turn per inch for the Z direct connect.

Simko · Post by **Simko** » Mon Mar 21, 2016 9:39 pm

leggman wrote:Still considering that option , just thought the 1600 oz stepper would push it fine. Gantry will be as light as I can make it.

They most likely would push it no problem. It's not a matter of power as to why I recommended two motors, it's a matter of being able to accurately position both sides of the gantry. When you have two separate motors, you can home each side so the gantry is always square to the table.

Chains stretch, sprockets wear...

Four 1600 oz-in steppers would be crazy overkill especially for the X and Z axis. I just finished the mechanical build on my table and used (2) NEMA 34 980 oz-in steppers (3:1 reduction) on the y-axis, (1) NEMA 34 980 oz-in stepper (3:1 reduction) on the X-axis, and a NEMA 23 620 oz-in direct coupled for the Z axis.

Another thing that I have read (but only know enough to be dangerous with) is that some steppers that you can buy with super high torque ratings, will not actually have that torque available during use due to poor design of these motors (impedance, inductance, whatever

) just something to look out for and maybe do a little more reading on.

leggman · Post by **leggman** » Tue Mar 22, 2016 3:53 pm

I found a kit on ebay and ordered it today, Item # 281533490183
It is a 1600 0z-inch nema 34, and two nema 23. That should work just fine. I am going to try to find a couple of gears to do a reduction on the y axis.

Post by **acourtjester** » Tue Mar 22, 2016 7:22 pm

I use the cross shaft with one motor and I have never needed to re-square my table. One motor never gets out of sync with itself

Here is the same kit cheaper 301706118110. I would advise you to buy another BOB as that one is not for plasma no torch relay.
171124049182 check around you may find a better price on the same BOB.
This is the one I used until I want with CandCNC DTHC-IV 3100 kit.

Post by **acourtjester** » Wed Mar 23, 2016 7:58 am

Legman PM me and I will give the info for the gearing and steps using the stepper and drivers you bought.

leggman · Post by **leggman** » Wed Mar 23, 2016 5:30 pm

I just purchased the 5 axis bob you suggested. Thanks

leggman · Post by **leggman** » Wed Mar 23, 2016 10:06 pm

One of the things I just can't get my head around is how do you program/adjust the system to know where it is?, I know I just lack experience but I am curious as to if the cutter moves a inch how does the computer know it moved a inch. Am I making any sense or just babbling?

Post by **acourtjester** » Wed Mar 23, 2016 11:19 pm

there is a setup to calibrate the movement of each stepper for axis positions, The g-code will instruct the program how to move each stepper.
When running the table you can start from the axis home positions ( called zero X, zero Y, and Zero Z) or from a position anywhere on the table by setting that position to zero (there are buttons to set each axis to zero) and then start the operation. It is like GPS the program knows where it is and then is told where to go.

leggman · Post by **leggman** » Thu Mar 24, 2016 1:18 am

I understand the zero or home thing. I was just curious as to how to calibrate it so when the g code says cut 2 inches it actually knows when it reaches that distance? I have a lot to learn

sphurley · Post by **sphurley** » Thu Mar 24, 2016 7:27 am

Using stepper motors, you enter into the machine configuration file the number of steps it takes to move the machine one inch (or mm)
The machine then 'knows' it takes X amount of steps to equal one inch. There is no feedback on 99% of stepper systems.
If you install servos then that is a different story as the don't step they 'move' and require a feedback system to provide location.

Post by **acourtjester** » Thu Mar 24, 2016 9:26 am

When you set you table up there is a procedure in Mach 3 that you run, simple stated you say move 5" and you then measure how far it did move. then you answer that question (box provided) and mach will calculate the amount to correct it's signal so it will move the 5". you repeat this about 3 time to refine the calculations for each axis and it is done. end of calibrations

leggman · Post by **leggman** » Thu Mar 24, 2016 9:50 am

Thank you very much. I knew it had to be something simple.

leggman · Post by **leggman** » Sun Mar 27, 2016 9:43 pm

OK, I have been watching videos on youtube and been trying to get acquainted with sheetcam and inkscape. been doing ok until I get to the point where I need a post processor????? The video I have been watching just kind of skips over this part of the process.
Am I right that the post processor converts the image to g code?
Please help and thanks. Dave

sphurley · Post by **sphurley** » Sun Mar 27, 2016 10:00 pm

Yes the post processor creates the G-code. There are some that are custom to use extra features with some machines.
There are some basic Mach 3 processors included in sheetcam when you purchase it.

Post by **acourtjester** » Mon Mar 28, 2016 10:10 am

When you look at picking a post processor you will see that there is a list to choose from. These are set up for different tables and or options on the table. For basic work when starting your table setup you can use Mach3 plasma it is a generic type. Later you could change to a more advanced type that was developed to work with other electronics. Many here use CandCNC's electronics and they have some post processors that have be setup for that.

mach 3.jpg

Bigdogbro1 · Post by **Bigdogbro1** » Tue Mar 29, 2016 8:50 am

leggman,

I designed a 4x4 table and tried the single motor approach and found that the slave end of the y-axis gantry would juggle just a bit at higher speeds because the 3/8" hardened aluminum driveshaft had torsional twisting. I designed in the ability to add a slave motor with another 3:1 gear reduction for the slave side. This method on my 45 pound gantry proved to be a better solution at higher cut speeds on the thinner material (16ga).

I used the C&CNC Bladerunner (NEMA 23) 320 Ethercut system but bought an extra 620 stepper motor for the single drive motor design. I then added an unused spare 320 motor from the kit to the Y slave drive side for the upgrade. Since the extra motor was added I now have the gantry locking on both ends with great results. The driveshaft is still installed and connects both Y axis sides. I left the shaft installed because it was a large teardown to remove it and I didn't think it would hurt to keep it in.

A table walk around video.
https://www.youtube.com/watch?v=D-mfRaXM3Og

Table cutting video.
https://www.youtube.com/watch?v=DCGO1P2gQUY

Capstone · Post by **Capstone** » Tue Mar 29, 2016 1:30 pm

Bigdogbro1 wrote:leggman,

Table cutting video.
https://www.youtube.com/watch?v=DCGO1P2gQUY

It's always cool to see other folks using one of my designs. (no sarcasm, I'm really happy) Is it a good seller for ya?

leggman · Post by **leggman** » Tue Mar 29, 2016 8:27 pm

Do the mach3 post processors come with the trial version? How do I find them?

Post by **acourtjester** » Tue Mar 29, 2016 10:39 pm

In SheetCam click on options at the top then machine on the drop down menu then post processor. You should see a list of the post processors,click on the down arrow by the post processor name and and the list will display.

leggman · Post by **leggman** » Tue Mar 29, 2016 10:49 pm

Thank you sir.

leggman · Post by **leggman** » Tue Mar 29, 2016 10:52 pm

I received my electronics kit today from China. Just had enough time to unbox before I had to come to work. I WILL be playing with my new toys tomorrow.

Brand X · Post by **Brand X** » Wed Mar 30, 2016 11:07 am

I had driveshaft setup.. Made of 4140 steel. No flex, and worked well for years. I decided with my upgrade, adding a another 620 oz motor and gecko drive to me Y axis was about time.. I only have one switch to home that axis.. I could add another one, but just use hard stops to sq the table when I first start it up. Really never gets out of SQ., unless I am yanking the gantry around (Unlocked)even then stays on the same tooth for both sides.. The hard stops never change, and is accurate.

4x4 Homebuilt Motor Size Question

4x4 Homebuilt Motor Size Question

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