New Machine Build- 96x48x22 plasma-router prototype build

[mcArch]

This is actually an upgrade . . . or actually a new table that will transfer the computer and electronics from the version 01.01.
X: 122"
Y: 49.5"
Z: 22.5"

A/C head: 380deg. ea - in the design but may have to be added a little later.

Porter Cable 1.5hp router
ESAB PCM1125 plasma
CandCNC MP1000C torch height controller & control electronics
Steppers from Probotix & HomeshopCNC
Gecko 203V drivers.
Rack & pinion on X & Y
Ball Screw from HomeshopCNC on Z.
3/8IDx1.125"x.375" bearings for slides on X,Y,Z.

Website log:
http://www.calvinodesign.com/90037/90037-01.02/

[mcArch]

Table Base & gantry initial assembly.
W6x16's used for rails.
Gantry is trussed made of 0.75"sch40 pipe, 1/2" round bar, 3/8" round bar diagonals, 1.25"sch40 for the main horizontals which have a 3/4x3/4x1/8 angle welded on for the track for the Y carriage.

Horizontal truss of gantry is bolted to the verticals to allow for fine adjustment, leveling, and for removal if required to move the machine.

Bearings are inexpensive route, 3/8idx1.125x3/8 bolted to plasma cut brackets & they ride on the bottom flange of the W6 (dust sweep should really be in order here, I figured the top flange should protect it somewhat, at least from direct contamination & then with a sweep & cover attached, it should do ok.)

The gantry is pretty stiff, deflecting about .029 under a direct 50# load on the spindle tip. It's a little more than I wanted, but in order to get it down much more, the gantry would have to get to heavy to drive it with the inexpensive steppers . . . I'm trying not to blow the budget here.

[mcArch]

A shot of the structural analysis model.

More gantry bearing plate detail photos. The adjustable plates will have internal tooth lock washers to keep them in place once they're tightened up to the best pre-load.

Got the Y carriage mounted on temporarily. The gear reduction/motor bracket is mounted initially here as well. The belt reduction is 3:1 (10 at motor, 30 at pinion) using a 20pitch, 20deg pressure angle, 20tooth pinion gear.

[tmbg]

just out of curiosity, why do you need so much Z travel?

I'm curious because I'm trying to work out how much Z travel to give my machine. It's going to be mostly a plasma cutter, so I don't think I need too much for that, but I'd like to be able to do some router duty as well. Even there I'm not seeing more than a couple of inches of travel as necessary. What are you gonna cut on that machine that can take advantage of 22.5" of travel?

[lukewarm]

Looks great what are the specs on your stepper motors and how much do you think your carriage weighs?

[mcArch]

Originally Posted by tmbg just out of curiosity, why do you need so much Z travel? I'm curious because I'm trying to work out how much Z travel to give my machine. It's going to be mostly a plasma cutter, so I don't think I need too much for that, but I'd like to be able to do some router duty as well. Even there I'm not seeing more than a couple of inches of travel as necessary. What are you gonna cut on that machine that can take advantage of 22.5" of travel?

Sometimes I'll have to throw a W-shape on the table & burn a series of holes in the flange or web. I also have some plans for making some 3d molds from foam (EPS most likely) in one milling to either pour concrete over, or lay up fiberglass - some custom roof structural/light monitor panels (these are still in design stage, but coming soon).

If you are just going to do flat stuff, then no, you don't need that much Z travel . . . most people don't. But I have an A/C axis head design for this as well that will enable faster milling of amorphic shapes like the skylight mold and will allow me to cut multiple angles on steel shapes for things like back-beveling for welding, or for pipe fitting.

I also sometimes will put a table top (old table saw top) with some short leveling legs on top of the plasma slats & it's like 3 or 4 inches high. This then requires me to raise the Z up above the leveling table plus whatever thickness of material I'm cutting. & it leaves open the possibility to cut/mill assemblies of material (like the top of a box for example) if needed.

To quote Edna Mode from "The Incredibles" . . . When asked "What on earth do you think he's going to be doing with this suit?" . . . she replied: "Well, I'm sure I don't know . . .!" what I'll be cutting with this thing, that's why I made it with as much Z travel as my roof would allow for now.

But, you're right, most will not need any more than like 6" or so.

Cheers!
-Mike

[mcArch]

Originally Posted by lukewarm Looks great what are the specs on your stepper motors and how much do you think your carriage weighs?

I've got a pair of 1280ozin.'s on the X, & they're geared 3:1 for the 20pitch, 20tooth pinion gear, that means I'm going to get 1.0472 (Pi/3) inches of travel per revolution. In theory I should be able to push the gantry with it but I suppose I'll have to see. I have a 400ozin on the Y and the Z. The Y is geared with same rack & pinion as the X, & the Z uses a 5turns/inch, 5/8"dia. ball screw. The whole gantry with Y & Z together, by initial calcs weighs somewhere between 200 - 250#. The Z carriage without the router or plasma torch weighs about 15, maybe 20# . . . the small PC router is 8#. The tricky thing is when I put the A/C head on it, that's going to add like 25 or 30# right there & I may need to go to a higher gearing ratio, or bigger steppers all around, or both. It's a work in progress!

I'm really no expert with this & I've just tried to do as much research as I can, calculate things when I can, & try it . . . this gantry is a little lighter than my current/first one and the bearing system is way smoother, so I'm hoping it will work much better . . . the original has worked fine for me for more than a year, it's just not as accurate as I want & it uses lead screws with brass nuts for the drive system on X & Y & this is really bad news especially with plasma dust because the brass just wears away & you get some pretty bad backlash pretty quickly. Rack & pinion is the way to go.

Cheers!

[tmbg]

you may find the 1280's to be monstrously overkill. I have a pair of 205oz-in steppers driving my gantry at the same gearing (3:1 driving a 1" pinion for pi/3 inches per rev of travel) and I was getting 600ipm rapids with 200in/s^2 accel without breaking a sweat on 24v power. I just got my G540 and 48v supply in last night, and I think that I can run it even faster.

Now granted, my gantry is probably lighter than yours, but 1280oz seems like entirely too big a motor. Remember that you trade speed for torque, so you may well end up with much slower travel than you'd want!

[mcArch]

Hmm, thanks Ian, that's sounds promising, I have those 1280's running my current machine at 24V (they're limited to about 1190ozin by the gecko's only allowing 7 amps wide open), with the lead screws, it travels at 2 revs/inch and I get only about 200ipm on the X & the G203V's show the orange light - meaning they are operating at full capacity if I understand it right.

This old machine doesn't have the greatest slide bearing system, so the new one should be much better. But I'm glad to hear that your thoughts are that they will be plenty of power. I hope you're right. I'm thinking I'll get about 400ipm with them, that would be plenty for me on X & Y. Thanks!
-Mike

[mcArch]

Ian, what are you running for your linear slides?

[tmbg]

You'd be amazed how much force these motors can make through the type of gearing we're using. If you go too big, you just end up slow. I don't have torque curves for your motor, but here's a keling torque curve:

1200oz-in nema34:
http://www.kelinginc.net/KL34H2120-42-8AT.pdf

So, at the 4000 pulse per second data point, we're turning 600rpm (4000 pulses per sec / 2 half-steps per pulse / 200 steps per rev * 60 sec per min = 600rev/min) and making 2Nm of torque. You have two motors, so that's 4Nm torque acting on the gantry. 3:1 belt reduction makes it 200rpm and 12Nm torque. That torque turns the pinion, acting on a lever arm equal to half the pitch diameter, which is 1". So your arm is 1/2", 12.7mm. 12000Nmm / 12.7mm = 945N force. F=ma, and a Newton is a kg accelerated at one meter per second per second, or N = kgm/s^2. Gravity is 9.8m/s^2, so 945N can accelerate 96.4kg at 1G, which is equal to 384 inches per second per second accel.

Now, just plucking another motor off the keling site:
Nema23 185oz-in. MUCH smaller than you're running
http://www.kelinginc.net/KL23H256-21-8BT.pdf

at the same 4000pps half-step, we'd be turning the same speed. The little motors make 0.6Nm each for 1.2Nm total, through 3:1 gearing gives us 3.6Nm. 3600Nmm/12.7mm = 283N force, or 29kg at 1G. So we can run a 64lb gantry at the same snappy 1G accel.


Sorry, I got off on a tangent, but the point is if your motors are too big, you have torque that's not actually doing anything useful for you, since there's only so fast you need to accelerate the gantry. However, you'll severely limit your top speed with the bigger motors. For plasma, you are gonna want a max cut speed of around 400ipm.

Do you know how much your gantry will weigh?

[tmbg]

Originally Posted by mcArch Ian, what are you running for your linear slides?

THK SSR25 rail for Y, THK HSR12 rail for X (along gantry), and HiWin MGR9 rail for Z and floating head.