So it begins... Cnc plasma table buid

[GoodB0Y]

I truly appreciate your input but I'm so confused with this stepper motor thing lol.. And I might also be using the incorrect terms or description lol.

I've read a ton and it seems like what I need to do is figure out the physics of my table... Calculate the inertia... Divide by pi or something and...Ya that's a bit much so I'm trying to cheat!

Now I'm not cheap and but I don't want to spend dollars on things that aren't matched. And my thoughts were over sized motors just add weight.. Not good so...

But... Idk...Grrr lol

Anyway! I did buy the plans for the jd garage buid. Because it peaked my interest and was cheap. I quickly realized that the plans weren't for me and a gantry style with linear rails was the way to go for me.

So... Saying all that.

Is a nema 17 at 1.7 amps and related holding power sufficient for the z axis, torch holder/lifter?

Iis a nema 23 in the 3amp and 300oz power range adequate to drive my what I think is the x axis or the part that traverses the gantry?

And seeing as my gantry is light would two 300oz 3 amp steppers drive my under 30# gantry?

I'm not looking for a " buy this" but maybe a " your getting in the ballpark" kinda help

Any pointers are really appreciated!

[adbuch]

I used Nema 23 stepper motors for all 3 axes of my diy build. This is a small table, but made mostly from steel - not aluminum extrusions.

Z axis - Stepper Motor, NEMA 23 280 oz-in torque Dbl. Shaft part# KL23H276-28-4B
X axis - Stepper Motor, NEMA 23 269 oz-in torque Single Shaft
Y axis - Stepper Motor, NEMA 23 269 oz-in torque Single Shaft

Nema 17 would be undersized, and not worth messing around with.
Nema 34 would be overkill for a small light weight table.

You can see some of the specs and photos of my diy build that I designed and built back in 2018 here.
https://www.desert-hybrids.com/id57.html
http://deserthybridscom.ipage.com/deser ... index.html

David

[adbuch]

I'm not looking for a " buy this" but maybe a " your getting in the ballpark" kinda help

My suggestion for you is to look at other existing designs that you like (and know work) and find out what size motors they use. If you are building something lighter and you feel that the motors they are using in their existing designs would be overkill (or possibly too costly) for your particular diy design/build - then delve into the actual calculations and theory/formulas used for correctly sizing a motor/driver to a particular physical situation.

David

https://www.cnccookbook.com/step-and-se ... e-for-cnc/

stepper motor calculator.jpg

[acourtjester]

With the stepper motor types the weight related to power stays fairly the same, some lower power may be half length of the others. I went with 425 for Y and Z axis and 34 for the X. My table are all steel except for Z axis parts. Now I use a axis layout like Milling machines, so my X and Y and different, see attached diagram. I don't think you are saving much weight with using either and 300 or 400 Nema 23. And pricing seems to about the same. The drivers are the same and the current is adjustable with switches. If you go to small and then want to expand to larger table later you will need to buy again.

axis direction.jpg

2 tables 4x4 and new 4x8.JPG

[GoodB0Y]

Ok thanks for the replies... Going to think about this

I know what the jd garage table uses for steppers... But it also uses roller skate bearings running on steel tubes... And apparently they run hot. Just watching it perform I would bet money that it isn't going to be as freely moving as mine. Add to that if I use similar motors I'll have two rather than the one for the y axis.

Think I've talked myself into a decision lol.

The hgr20 rails come tomorrow... And I'll purchase the x beam here soon. I am going to try a large nema 17 for the z axis... I've seen it work on a couple of builds so I'll give it a try.

A notes for anyone else who is interested in building a cnc plasma table. Imho using sbr rails is more of a pita then the money saved. I did sbr on my x axis and now wish I went with hgr. Two sbr rails (one on top one on the side) work just fine and are a bit more forgiving in alignment maybe... Idk... But ya just my opinion from a guy who hasn't yet finished his table lol



I truly appreciate everyone's help!

[acourtjester]

I would like to point out the similarity between the SRB and HGR types of linear Bearings. They both are ball bearing arranged in a path in a leaner fashion, with rubber seals on both ends. This is for a linear movement rather then a rotational movement.
DIY means you build what you want. A plaque I love which shows the great thing about DIY. My comments are from my experiences not that I am an expert, IMHO Just remember your table will be a great addition to your shop, so have fun with the build.

DSCN0493.JPG

[GoodB0Y]

I would like to point out the similarity between the SRB and HGR types of linear Bearings. They both are ball bearing arranged in a path in a leaner fashion, with rubber seals on both ends. This is for a linear movement rather then a rotational movement.
DIY means you build what you want. A plaque I love which shows the great thing about DIY. My comments are from my experiences not that I am an expert, IMHO Just remember your table will be a great addition to your shop, so have fun with the build.
DSCN0493.JPG

Well said!

And thank you I'm really excited!

[GoodB0Y]

So quit work early cuz there wasn't much going on... Made a stop at the metal supplier...

Picked me up some metal

You know bigger is always a good thing in life... That includes shop equipment!

So when I ordered my y axis hgr rails I bought them knowing that I wanted to have a cutting area of 33 inches x 48 inches. So dumb me knew that the table would have to be longer than that to achieve that... So I ordered 1.5 meters of rail that's 11 inches more than I need! Now that I think about it if you space the carts equal to the gantry thickness including the torch location you don't need more rail!

So ya... My table is growing

I just picked up 66 inches of 2x3 sharp edge aluminum tubing. Along with my 59 inches of rails I'm pretty sure I'll be way over my original design lol

I know their are some belts out there now that can span longer distances... Going to have to research that haha

[GoodB0Y]

Quick question or 2...

Im planning out my limit switchs... Can I use any contact switch?

And I'm still struggling with the water depth... My y axis long side beam is 2x3. This does give me the ability to have 3 inches of water but dam that's alot of water lol.

I can design it 2 ways. One where the slats and water is even with the side beam or slightly lower. But My head keeps going towards the cutting surface lower than the sides to idk keep water and sparks off the top of the beam and further away from the linear rails that are mounted on the outside... It will limit my cutting area by the thickness of my torch and holder... Grrr decisions lol

Thoughts?

[adbuch]

Yes - you can use "contact switches". The choices would be normally closed or normally open. For most circumstances - the normally closed versions are preferable due to reduced noise interference and reliability issues.

David

"For a CNC plasma table, it is generally recommended to use normally closed (NC) limit switches as they provide a safer fail-safe mechanism, meaning if a wire breaks or the switch malfunctions, the circuit will open and the machine will be alerted to a potential problem before causing damage; whereas a normally open (NO) switch might not signal an issue until significant damage occurs.
Key points about normally open vs. normally closed limit switches:

Normally Open (NO):
When not activated, the switch contacts are open, meaning no current flows through the circuit until the switch is pressed.

Normally Closed (NC):
When not activated, the switch contacts are closed, and the circuit is interrupted when the switch is pressed.

Why NC is preferred for CNC plasma tables:

Safety:
If a wire breaks on a NC switch, the circuit immediately opens, alerting the controller to a potential issue.

Error detection:
A broken wire on a NO switch might not be detected until significant damage is done as the circuit would remain open even when the switch is not activated.
Fail-safe mechanism:
In most safety-critical applications, a NC switch is preferred as it automatically disengages the system in case of a malfunction. "

[adbuch]

And I'm still struggling with the water depth... My y axis long side beam is 2x3. This does give me the ability to have 3 inches of water but dam that's alot of water lol.

I'm personally not a big fan of water trays where the water level is located such that the end of the torch is either submerged in the water (water level even with material being cut) or the water level is such that water is blown onto the torch and consumables. Jim Colt concurs.

I know that others do have their water level right up to the material being cut and they seem to have no problems.

My water level is well below the bottom of the cutting grates, but I use a combination of water tray/draft system (exhaust system) and this combination has worked very well for me over the last 8 years.

My table is 4x4 , my water tray is 4x4 with a depth of 4".

David

[acourtjester]

When using limit/home switches if you use a NC setup you can run them in series and only use one input pin for the circuit. I used a roller type switch as seen in the first video I attached above. I use one switch per axis as both home and limit, the software for many controllers looks at what the table is doing and will act to that. Meaning if moving to a home a switch trip will stop and reverse away from it. If not a homing action and it hits a switch it is a safety and stops motions. You can also hook the floating head switch in this circuit as the G28 command is a homing action. Here is a diagram of how I wired the switches.

switches.JPG

[TJS]

My water tray holds about 80 plus gallons of water. If you make you own water tray, do not do what I did. I used steel. I made a picture frame out of angle, then welded sheet to it. It warped like crazy no mater how much I moved around. I had to make custom stud clamps tacked to the underside of the sheet and pull it down to the crossmembers. I am, I think 9 years into my machine and now my table is leaking. I have not investigated where it is leaking but need to get to it.
So........with that being said. Have a shop bend up a one piece tray for you out of stainless. I know I know, stainless is expensive but do it one and done and just weld up the corners.

Edit. You can see my water try in my build in my signature.

[SegoMan DeSigns]

Here's my Nickles worth today:
I use a small micro N/C switch on Z for home/float options.
I use N/C PNP proximity style on X/Y as they don't get damaged when you come into the L.Z. Hot..
I used metal for both my water tray and tank. The tank got blasted/etched/3 coats of epoxy primer and 2 coats of raptor bed lining. The tray I left bare and use laundry soda for rust inhibitor. The 2x2 table is 8 yrs in service and the metal still shines when buffed.
Rails I mounted below the slats for ease of material loading / unloading.

[GoodB0Y]

Thanks for the tips and help!

I managed to get what I think is my z axis started. I had no idea how to do it. Lots of people seem to have 3d printers and print alot of it. Others use extruded aluminum with wheels. Here's my take.

This was really difficult. I have calipers and rulers, scribes and center punches, and I had a hell of a time doin this! I'm not totally happy but I need to move forward with the buid. Pretty can come later.

Have to get the stepper mounted. It'll b on a 2x2x3/16 angle bolted to the plate.

Then the torch mount but that can be done later. It was important to get this portion done as alot of the z axis and gantry effects everything else... And I didn't know if I could do it lmao

Then look into limit switches and connecting the floating head to the torch lifter thingy haha. Limit switches will be done in a manner that they won't be broken or smashed.

Overall I'm pretty happy. Everything is going to work...

[adbuch]

That looks great! Very similar to what I did with my little diy cnc table.
David

diy z.jpg

[acourtjester]

One thing I would recommend is to use flat head machine screws, it make attaching another plate on top easier.

DSCN2496.JPG

When you want to shorten the shafts they are hardened so a cut off wheel in an angle grinder works great.

[GoodB0Y]

Thanks for the tips! The machine screw idea makes sense... I might not have to go that route but if I do that's a good solution!

I've been watching alot of videos and reading but have a question on limit switch placement and operation.

When a limit switch is triggered is there any travel past the point of the switch being triggered? Will the machine stop exactly at the point where the switch is activated? I've been watching some vídeos and it looks like there is a tiny bit of travel past the point of the switch being triggered. If that's the case I'll add a bit of room past but I'd like to keep as much usable travel as possible

[weldguy]

Without encoders on your motors there can be some over travel depending on how the system was designed, but it will be very minimal. Some systems will slow the ramp speed down when it gets within a certain distance of where it thinks the switchs are and the slower speed will assist in softer stop and more accurate positioning. Your build looks awesome so far and looks like a lot of fun.

[GoodB0Y]

Ok great thanks!

I think I'll design it so there is some adjustability if I can... Maybe add an 1/8th before the hard stop.

And just thought I'd share a tip that I came up with.

I have a vinyl cutter... A cricut. I use it mostly for my powder coating projects like stencils and masking. It's great to make circles or exact shapes for masking. But what it's really good at it designs with.01 mm accuracy! This allowed me to take the engineering drawings and measurements I took to make drill guides for bearing blocks! With the sticker perfectly square and at the dimensions I designed... Along with 2mm holes at the proper spacing it helped a lot in drilling holes on my drill press for the mounting plates.

If you have a vinyl cutter it can also be a drill guide

[weldguy]

Thats a great idea. My daughter has a Cricut and i was always impressed with how detailed it could cut.

[GoodB0Y]

Cricuts aren't just for girls

[weldguy]

I guess not

[acourtjester]

I used a similar setup for the hole marking for the linear bearing mounting. I used a CAD program for the hole positioning and a marking tool plan in SheetCam and marked the pattern for the holes on paper, then for center pinching on the aluminum plate I mounted the bearings to.

bearing holes.JPG

[adbuch]

One thing I would recommend is to use flat head machine screws, it make attaching another plate on top easier.
DSCN2496.JPG
When you want to shorten the shafts they are hardened so a cut off wheel in an angle grinder works great.

Tom - that is a great idea for instances where the heads need to be flush to accommodate an overlapping plate. Otherwise - I only use flat head machine screws when I absolutely have to - as it is often a pain to do the countersinks and have them all at the same depth and centered on the hole. A Bridgeport or drill press can make this easier to do than "free hand" using a hand drill.

Yes - I like using an abrasive cutoff wheel in a die grinder for cutting off the motor shafts. Then you can dress the ends to make them square with no burrs.

David