Plasma - Lowrider v2 (questions about both)

mikedub · January 16, 2019, 3:32pm

Hi All,

I’m planning to build a plasma Lowrider V2 and have a few questions regarding picking the parts and the design of both.

The end goal is to keep to a very strict budget without cutting corners, so I’m trying to research the crap out of my design to ensure I get the best possible value out of everything (I’m a bit of a scrooge).

Firstly to get it out of the way, the question regarding plasma.

Plasma HF - RF Emissions

I’ve seen a couple of plasma builds on here and researched other plasma tables, and from this research it tells me that a HF plasma is bad. Mainly bad for RF emissions that will kill electronics? / Wifi.

I would like to end up using a system which can be remotely controlled, Ie. Octoprint / cnc.js, which I assume may use wifi (I do have the option to run ethernet to it though). In saying this though i may have other wifi devices in the futures which may be a few meters away which I won’t want tampered with.

Question: Is buying a Non-HF plasma essential, or can the emissions be appropriately controlled with a HF Pilot Arc?

I was thinking surrounding the plasma torch in copper / aluminium to help reduce emissions as one idea (Obviously there will need to be a sufficient gap between it and the workpiece so it doesn’t get torched itself.

A HF Pilot Arc machine is considerably cheaper than a non-HF Pilot Arc machine, hence my question.

Low Rider v2 Controller

I see that the mini-rambo is the preferred choice for the low rider v2 controller, however as I’m in Australia, by the time i buy this board and gets shipped here it gets more expensive than I’d like.

Is there any reason why I cannot use a RAMPS 1.4 controller? Is it purely size or something else I’m not considering?

(The RAMPS 1.4 systems I’ve seen are around 1/3 of the cost of the mini-rambo system to get it here, and the ramps I’m looking at come with drivers for 5 steppers.)

GT2 16Tooth Pulleys

Will changing to a 20T pulley be compatible? Will this make it slightly faster?

I noticed the idlers are 20T.

These are my main questions so far, As I get further through the parts ordering process and design process, more questions may arise.

I really appreciate your help in advance!

Table Surface

I’m looking at making a collapsible / expandable table, which likely will have some sort of hinge / folding mechanism.

Will a slight 1mm gap between the table surfaces where it expands from affect the roller wheels / operation of the machine?

vicious1 · January 16, 2019, 6:09pm

I am no expert on the other stuff but will give you what I know. Ramps right now are a pure gamble some here have got several in a row that were garbage out of the box, including myself. Pulleys, yes you can go faster but you lose power, as it is we can go up to 120mm/s, do you really need faster? Most cuts are at 10mm/s.

barry99705 · January 16, 2019, 6:12pm

I’m running both my mpcnc and lowrider on ramps boards. No issues there except finding quality parts. Try and keep that gap as small as possible. Doing through cuts probably won’t be an issue, but if you ever do and 3d carving with a router, it will make a line. No clue on the plasma part.

mikedub · January 16, 2019, 6:43pm

Thanks Guys.

I guess I was thinking that power wouldn’t be an issue with plasma as theres no contact with the material, the only thing that would matter would be how powerful the torch is.

However if the current 16T pulleys can support upto 120mm/s, that seems quite adequate, I was aiming for a 55-60amp plasma which should be able to carve quite quickly through most materials.

I would like to leave the door open for a conversion kit to a router when the need arises, so I might stick with the 16T pulley.

As for Ramps, the place where I would buy it from comes with a money back guarantee, so i might give it a shot first, but if your right and i do have an issue first go, i will probably cave to the mini-rambo.

jeffeb3 · January 16, 2019, 6:47pm

Switching to a 20T later is pretty trivial.

uthayne · January 16, 2019, 7:30pm

I’ll link my thread here first because there’s a bit of the same discussion that I’ve talked about before with lessons learned from my build. https://www.v1engineering.com/forum/topic/somd-lowrider-plasma-cnc/ Note: The OP is a little out of date, I’ve switched around the electronics and posted about it later on. I need to update my first post to reflect the current setup… as soon as I stop working on my table…

If your intent is to do a lot of plasma cutting, there are some corners which you definitely don’t want to cut. First one starts with the plasma cutter itself. You’re correct that a HF cutter is not what you want for CNC. At best, it disturbs stepper signals and you will lose positioning, maybe reset the PC/controller. At worst it fries your electronics. You will drive yourself crazy trying to shield and ground everything from the RF noise. Spend the extra and get something that is A) Pilot Arc start and B) Demonstrated to work well with CNC systems. I used the Lotos LTP5000D for a few months with decent success. I recently bit the bullet and bought a Hypertherm 45XP (not saying you need to start here, but it’s what the big boys all use) Take a look at plasma cutters that have integrated CNC ports that can give you access to torch on/off, divided voltage signals of the arc and an arc-ok signal. These can all be tapped off of a cheapie plasma cutter like the Lotos, but it takes a little more work to do so.

Regardless of the plasma system you buy, the environment will be noisy, especially with the cheap offshore types. WiFi was knocked out as soon as I turned on my Lotos, and even with my Hypertherm it can go in and out. Don’t plan on controlling over WiFi while using the plasma. To add a bit for safety, obviously don’t run the machine remotely. Routers can and will start a fire, and I’m sure you can guess what plasma cutters are capable of doing.

I used the RAMPS 1.4 setup for a bit with my plasma cutter and it seemed to work fine. I agree with Ryan that its a gamble with those boards. Idk if I lucked out with my cutter or not, but I didn’t have to shield everything. I ran 22/4 alarm cable (shielded) for all of the motors and limit switches and never had a problem. If you go with this, you’ll be able to control the torch via solid state relay and it would work.

Finally, a torch height controller is essentially mandatory to getting anything to cut on thinner gauge (<12ga). As the torch cuts, it puts a lot of heat into the metal and warps it. If your Z height is fixed, you won’t be able to stay ~0.060" from the surface which provides good cut quality. You’ll find yourself either running into the metal or it moving away from the torch and no longer cutting. I’ve detailed in my thread my setup, but there are other options out there for THC.

Take a look at plasmaspider forum. Tons of great information there for plasma cnc systems.

120 mm/s (~283 ipm) is plenty fast. The Lotos I had was only capable of cutting 16ga at ~150 ipm. I rapid at 310 ipm and the Hypertherm book says to cut 16ga at 250 ipm. Since there are no cutting forces, you don’t have to worry about missing steps at the higher feed rates.

mikedub · January 16, 2019, 7:46pm

Thanks Bryan,

Yes your thread was one of the ones I was talking about when reading up on plasma, its been a huge help, thank you.

The remote control part will mainly be for monitoring progress etc.

I will have to physically go down and open up my shed to turn the power on for the system, its not something I would tend to run in a closed environment without having the ability to physically stop it, unless i installed safety shutdowns coming out my wazhoo!

I was originally hoping to keep my build under $800AU, but with a non-HF plasma, that will prob shoot upto $1100-1200… IF the one I’m enquiring about will work with an AU Plug.

On another note, what size cable chain did you use Bryan?

uthayne · January 17, 2019, 11:22am

WiFi has been a huge plus for me in my setup. I run Linux on my LowRider controller, so I can transfer files from my main computer via an ftp. Saves the hassle of using flashdrives back and forth. If I need to transfer something, I just turn the plasma cutter off momentarily.

I’ll have to check on the size tonight for the cable chain.

Edit: Cable chain I used for the X and Y axis is roughly 1.5"x1". Got a good deal on Igus cable chain on eBay.

forcerouge · January 17, 2019, 7:03pm

Here are my 2 cents on plasma cutting:

You can use any kind of plasma cutter you want, any of them can work in the end… BUT… choosing a good one without HF starting will help tremendously because you’ll have less shielding work to do. Many people had success with very minimal tweaking using the hypertherm cutters so I suggest you to look into these.

I believe you already had a look at my thread too if you did some research on plasma and MPCNC, but in case you haven’t here you go: https://www.v1engineering.com/forum/topic/my-mpcnc-made-in-china/page/6/

I had a rough time trying to make this thing work with a very cheap plasma cutter, but in the end it did work.

In my opinion, the thing you should absolutely plan in advance is how will you make a cutting height adjustment system. At some point your machine will work fine, but you’ll run into issues with warping of the material during the cuts and this is, in my opinion, the biggest problem. But some solutions exist so you should be able to overcome it, just spend some time right now to plan in advance.

As for using a raspberry to monitor the thing, just forget the idea. A plasma cutter is probably one of the most dangerous thing that can legally exist in a homeshop, pulling out more than 18 000 degree C, it can burn through anything and start a gigantic fire anytime. You absolutely need to monitor the thing yourself directly, it’s not like a job will last very long anyway, plasma cutting is extremely fast. Let’s say that you monitor using the Rpi and a camera: you have blazing hot metal particles flying all over the place. If one of these ignites something outside of the view angle of your cam, then you’re done. So again, forget it, use the SD card and go there yourself to monitor it directly.

Regarding ramps and Arduino, it will work fine as long as you get the whole thing in a grounded metal box, including the screen (at least with a HF start cutter). I suggest you to use a ramps and arduino because there is a good chance you’ll fry a couple of those before getting the setup right, it will be way cheaper to burn one of these versus burning a Rambo (but rambo are supposedly much more resilient).

To increase the speed, you can do the following things:

-Larger pulleys, since you don’t really need a lot of torque (you only need it for acceleration and jerk, there is no effort applied on the torch itself)

-Lower microstepping: I think you can go up to 1/4, 1/2 or even maybe full step (depending on your pulleys diameter). A plasma cutter is not the most accurate tool in the shop so I guess the plasma will be limiting your accuracy far before the steppers themselves. By doing this you’ll gain a lot of speed as well as a lot of torque, at the expense of higher noise (which isn’t a problem since the plasma cutter will be far louder) and possibly at the expense of vibrations (which may or may not be an issue, you’ll have to experiment).

For the table surface, I strongly suggest you to make a water table. Plasma cutters make a real mess, there is molten metal flying in all directions, it will ruin your floor and possibly start fires in unexpected places. Plus a water table helps to limit warping, because it keeps the metal temperature more uniform across all its surface.

Good luck with your build and keep us posted!

mikedub · January 27, 2019, 3:45am

Hi all,

Another question regarding low rider capabilities.

I’m exploring an idea to make the slats on my plasma table adjustable.

Can this support a 4th control axis and would it need to be programmed differently for my implementation?

The idea is to make the slats on the part of material lower where it is burning, so the slats don’t get burnt.

To implement this with the least amount of steppers, I’ve put together a alternating crank pattern that might do the job.

Each side requires 2 cranks to ensure that the material is always supported at the same height and does not drop while working.

This would need a stepper per crank, so potentially 4-6 steppers (extra 2 for midline support).

Here is a link to the proof of concept video: https://www.youtube.com/watch?v=eerAwXxAJw4&feature=youtu.be

Additionally, is there anyway I can calculate the size of stepper motor required for the job?

I’ve calculated that each stepper would probably only be lifting about 15kg at a time MAX.

Thanks for your help and insight

jeffeb3 · January 27, 2019, 6:10am

Steppers are rated in torque, so if you have them straight on those crankshafts, you divide the torque by the radius to get the force. If they are geared down you can multiply the torque by the ratio.

A couple of points though:

The height will change overall. When some slats are high, they will be higher than when they are all even.
How will you attach the workpiece to the slats?
Slats are designed this way to be cost effective, right? They should last a really long time and they are not precious metals.
As far as the controlof those motors go, they should be aligned with one axis. So if the slats span the Y axis, these would move with the X. The easiest way to do this is to carefully construct the mechanics to move in lockstep with X and wire additional steppers drivers in parallel. The next easiest is to have an additional arduino reading step and dir from te X driver and driving these stepper drivers.

mikedub · January 27, 2019, 6:12pm

Thanks Jeffeb3, I appreciate your feedback.

So if the radius that the crank shaft turns is 20cm (the turn is only 90 degrees), what talk would i apply with it? If I looked at applying a 59Ncm stepper, how does that equate to what it can lift / turn?
I'm not sure what you mean about the height changing overall, as I designed it specifically so it doesn't do this. Side view Video: https://www.youtube.com/watch?v=YkamFfXKeNc&feature=youtu.be The crank curves out and then comes back in line with the center shaft, it doesn't extend out the other side, and they only move 90 degrees back and forth, both of these were required to achieve this.
Most work pieces will be heavy enough to not need any bracing, still working on how to accommodate smaller pieces.
I've just seen some slats that have been burnt through, so I think at the start I will begin with vanilla slats, then if they are getting torched, cut out the crank shafts with the plasma and install them.
So the slats would span the X axis, so yeah i would plan to move them with the Y axis, I dont see a way to mechanise this with the roller assembly, so i think a separate arduino might be the go.

If I've missed something please let me know. Thanks for you help :)

jeffeb3 · January 27, 2019, 7:16pm

20cm is pretty big. Are you sure? Of that’s right, then (59Ncm)/(20cm)=3N. 1kg is about 10N here in earth. And that doesn’t account for any torque sucking friction. So you’ll need quite a few gears and when you start getting into the 100:1 stuff, you should probably find a mechanical engineer (I am a software engineer and physicist).
Ah, so there are actually two crankshafts for each side and they don’t move continuously?
So you can play with counting the pulses and reading the direction and enable pins from a driver circuit. That should give you the step count that Marlin is thinking. Then you’d have to use that to decide where you want your crankshaft and control a separate (couple of) drivers.

mikedub · January 27, 2019, 7:37pm

Ah oops, I meant 20mm (2cm)

Yes I’m also a software engineer, but I like dabbling in creating other stuff as a hobby!

So according to that formula, (59Ncm)/(2cm) = 29.5N.

And if 10N = 1kg, then the NEMA 17 could lift 2.95kg?

So to lift 15kg, I think i would need something like a 3Nm NEMA 23

This would equate to (300)/(2) = 150 / 10 = 15KG

However those motors are at least about $60 a pop, + about the same for a motor driver, might get expensive very quickly.

Yes there are 2 shafts each side, one that controls the even slats and one that controls the odd slats. each one only moves the opposite direction one at a time at max 90 degrees.

jeffeb3 · January 27, 2019, 7:40pm

Easier would be to have gears to increase the torque, I would think. Speed won’t be a problem for a while.

forcerouge · January 28, 2019, 2:00am

I think you’re complicating the whole thing way too much for making a marginal economy of a few bucks for a few slats a few times a year.

I suggest you to actually build the whole thing, make it work and then only maybe decide on such improvements if you ever feel like it is necessary. You’ll have plenty enough challenges ahead to make this thing cut already, no need to add more!

Those kind of things might be justified for factories who cut thousand of plates per month, I really don’t think it is worth it for the homegamer.

But anyway, I think 2 big steppers should be enough, just use one at each end. Each stepper could be connected with the crancks on both sides through a timing chain or a belt, who could be used for driving both at the same time while also providing demultiplication.

I’m pretty sure it is even doable with only one stepper with some clever gearing/cams.

mikedub · January 28, 2019, 2:09am

Yep, I think this will be kept on the shelf for when i get upto level 500 Thanks for the feedback!

mikedub · February 11, 2019, 4:20am

Well after a couple of weeks I’ve been working on a design that best suits my needs.

Here’s a preview of what it’s going to look like, hope to have it finalized soon

mikedub · February 11, 2019, 4:22am

2nd pic

kd2018 · April 8, 2019, 12:31pm

What are y’all using for your plate material? Are there any issues with plasma burning up the wooden, plastic, and rubber parts on the lowrider?

I could make them out of steel I suppose but that leads to other questions. How thick/heavy can the plates be? Or rather, how thick would it need to be? Would a steel/metal plate eventually warp riding over that torch all day long? how warped is too warped for the lowrider?