LARGE 5 X 10 STEEL ROUTER BUILD

[ramsey321]

Hello all, I need some advise on how to drive this beast. The gantry weighs about 800lbs and I would like to move it 1800 IPM using a rack and pinion system. What I am struggling with is should i use a planetary gearbox or can I get away with pulley reduction system. Also I want to use a nema 34 stepper setup. Attachment 361674Attachment 361674Any advise would be helpful. Thanks

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[Clackneil]

I am here to follow, please don't mind me.
Awaiting professional input lol

I really like you're table so far, by the way. Clean loomkng build especially for steel.

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[davy182]

Looks really well made. How much do you have in the steel at this point?

[ramsey321]

Looks really well made. How much do you have in the steel at this point?

Probably around $1000 for the steel right now. I still need to get the uprights and gantry machined to start the assembly process.

[ger21]

I think you really need to use AC servos, in the 750w-1kw range.

[davy182]

Nice, not bad on the price. What is shipping to florida for that? Ill take it.

[ramsey321]

Nice, not bad on the price. What is shipping to florida for that? Ill take it.

Shipping might be expensive! Lol...

[ramsey321]

I think you really need to use AC servos, in the 750w-1kw range.

Ger21 should I do a planetary gearbox or a belt and pulley reduction system?

[Clackneil]

I say geabox, but that's just me.

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[ger21]

That depends on whether you're using steppers or servos, and the size of the pinion you're using. If you can get away with 3:1 or 4:1 then a belt reduction is a LOT cheaper. If you need more reduction, than a gearbox is probably the best way to go. But make sure you get one with low backlash.

[ramsey321]

That depends on whether you're using steppers or servos, and the size of the pinion you're using. If you can get away with 3:1 or 4:1 then a belt reduction is a LOT cheaper. If you need more reduction, than a gearbox is probably the best way to go. But make sure you get one with low backlash.

Well I would like to use large stepper motors with a belt reduction system. What stepper motors would be a good fit with my setup? Also what is a good source for a well made belt reduction system that can handle the 800 lbs gantry weight?

[NIC 77]

Nice work so far!

It just so happens that I am doing some calculations for my own build. The build I'm working on will be ballscrew driven. I figure my gantry will be less than 600 lbs. 100lbs of that is spindle. I have some Nema 34 960 oz-in motors that I purchased from cncrouterparts.com. I plan to use those. I've been doing some calculations to figure out what pitch of ballscrew I need to use. Of course, I will not be going anywhere near 1800 IPM. I figure 500 IPM is good for me as a max speed. My travels are around 30" and 50".

cncrouterparts has posted a torque vs. speed graph using one of the drivers they sell. I think it's a 10x microstep driver. I've written to them to ask if the results should be the same when using a G201x driver from Gecko, and to ask if the driver they used was 10x microstepping. They have not responded as of yet....................very nice of them to make a graph using a microstepping driver, I admit. Something that is hard to find.

So the graph is here:

http://www.cncrouterparts.com/cdata/...rque_curve.pdf

And the equation I've used so far is from here:

Nook Industries

I've ignored backdriving torque and drag torque so far. I'm just using the basic equation:

Force = (Td x 2 x 3.14 x Efficiency) / (Ph (in mm/Rev) x 0.001)

Td = Driving Torque (Nm), Force is in Newtons, Ph is the lead in mm/Rev

I assume that this equation works roughly for rack and pinion also.

If you look at this rack and pinion setup:

Standard Rack and Pinion Drive, NEMA 34 | CNCRouterParts

It has a 2:1 reduction with a belt, and has 1.5708" of movement per motor revolution.

So we end up with this graph and tables that I made:



If I made any mistakes in the math, let me know. Obviously the available force is per motor, so x2 for 2 motors.

You can make your own similar graph in excel and change the parameters based on the torque vs speed graph of whatever you plan to use motor wise (servo, stepper, etc) and you can change the value of movement per rev (Ph) based on your gearing.

The real question is how much force do you need for acceleration and deceleration of your 800lb gantry at 1800 IPM where Force = Mass x Acceleration? I'm curious, what kind of acceleration are you planning for?

I hope this helps.

[ger21]

Yes, the real question, is "How fast do you want to accelerate?
1800ipm is useless if it takes the machine 2 feet to get to that speed.
You can use some pretty simple math to calculate rack and pinion force. Motors are rated in ounce-inch of torque. Say you have a 400 oz-in motor. This can apply 400oz of force, 1" from the center of the shaft. So if you have a pinion with a 1" radius (2" pitch diameter), you'll have 400oz of force. Reduce the diameter by half, and you have twice the force. Double the diameter, and you have half the force.
Similarly, a 2:1 reduction will double your force.

Calculating the force required all comes down to acceleration. Say you want to accelerate at 1G. To accelerate 800lbs at 1G, you need 800lbs of force. You also have to account for efficiency, and also allow for some headroom, so I'd aim for 1000 lbs of force. That's 16,000 oz of force.
If I wanted a machine to be able to move at 1800ipm, then I'd want at least 1/4G acceleration, which is roughly 100"/sec². That's going to require roughly 3500oz of force.

With steppers, this gets tricky. You'll need that 3500oz of force from a standstill, all the way up to the 1800ipm. So you need to calculate what rpm the motor will be spinning at at 1800ipm, and you have to choose a motor that will have enough torque at that rpm to give you the required force. Since steppers lost torque as rpm's increase, you're going to have a problem getting enough torque out of a stepper. One thing you can do, is use less reduction, which keeps the motor spinning slower, where it has more torque.
Which brings you to another issue with steppers. Because they have a limited usable rpm range, and a fixed resolution, you typically need to trade resolution for speed. The CNC Router Parts link explains that a little. They use a 2:1 reduction to get more speed, but a 3:1 reduction to get more power. So their faster system has 50% less resolution.

As I stated before, imo, 1800ipm, and 800lbs, is well out of stepper capability. And if you can't reach full speed in 6-12 inches, you're better off with more accel and a lower top speed, as acceleration has more of an affect on cutting performance than max speed.

[NIC 77]

If I wanted a machine to be able to move at 1800ipm, then I'd want at least 1/4G acceleration, which is roughly 100"/sec². That's going to require roughly 3500oz of force.

3500oz = 218.75 lbs

According to the graph and charts I made and posted previously, using the CNCRP 960 oz-in 2:1 scenario, you could run your machine at approximately 570 IPM and have 1/4G acceleration.

At 1800ipm you'd have approximately 34x2 = 68lb of force (2 motors) available for acceleration.

Playing with the numbers for the lead value (or distance traveled per rotation of the stepper) in my Excel spreadsheet, there's no way to get to even close 1/4G acceleration at 1800ipm with these motors for an 800lb gantry regardless of what reduction is used. So you'd need some different motors for certain!

And my math probably leaves out a few factors that don't work in your favor.

As I stated before, imo, 1800ipm, and 800lbs, is well out of stepper capability. And if you can't reach full speed in 6-12 inches, you're better off with more accel and a lower top speed, as acceleration has more of an affect on cutting performance than max speed.

Ger, It looks that way to me as well. I was doing some reading today, and I came across someone who said that an 8 wire stepper motor can be wired in such a way as to give better performance at higher speeds. I wonder if this could be applicable here?

Ramsey, Gecko makes a servo drive. Not sure if its applicable to what you want to do. You know, after you've priced out all the stuff, perhaps find a few deals on EBay, it might cost around the same price at the end of the day to go with servos as it would with high end steppers?

[ramsey321]

Thanks everyone. We'll after those comments I could back down the rapid to say 800 to 1000 IPM rapid. This should be slow enough to allow for a proper sized steppers I believe. Also I will be cutting aluminum so the cutting force will be a little bit more than if I was cutting wood. So I definitely want the torque to do some heavy aluminum cutting. Of course cost is always on my mind as well.

[louieatienza]

You can wire an 8-wire stepper bipolar parallel, which would approximately double the speed of your available torque, but you'll have to run the stepper at double the current rating of the bipolar series wiring.

Marriss at GeckoDrives has a formula for rough estimating power needed to move a load, which is the Weight (in pounds) * Speed (IPM) / 531. In your case, (1800IPM, 800lb gantry) you'd need 2.71kW of power, or about 3.6HP! So as Gerry pointed out, a 1kW servo would work (rated at 5000rpm peak and about a 3:1 final drive ratio) which would something like a 7:1 planetary gearhead and a pinion with a 1" diameter.

[NIC 77]

I had a look at a few more things for you.

Sources:

https://www.amci.com/plc-automation-...tepper-motors/

https://cdn.automationdirect.com/sta...oselection.pdf

The amci steppers I found appear to have much better torque characteristics at speed. Also more $$. I assume you'd need to use their drivers to get that performance, I don't know what the microstepping capabilities are, so you'd have to calculate resolution.

I threw in a 750W servo for comparison, the source graph can be found in the link above. There are two lines, one for continuous duty and one for intermittent.





Using the AMCI stepper you can have 118 lbs of force per motor at 1800 IPM and 1.57 inches of movement per rev.
X2 = 236lbs. That should get 1/4 G.

Using the AMCI stepper you can have 126lbs of force per motor at 1800 IPM and 0.785 inches of movement per rev.
X2 = 252lbs. That should get 1/4 G also.

Using the 750W servo with 0.785 inches of moment per rev:

Continuous duty: 142lbs x 2 = 284 lbs. That would get 1/4G
Intermittent duty: 445lbs x 2 = 890 lbs. That would get 1 G

Of course, that's only if I haven't made any mathematical errors.

If you haven't built the thing yet, I have to think you can figure a way to trim the weight by 100 or 200 lbs. Good luck on your build, I would like to follow your progress. I'm also curious on what you have for a spindle.

[ramsey321]

I talked to this gentleman and this is what he said about his setup. His gantry is simalar in size as mine and he was using 2500oz stepper motors to get about 1100 IPM RAPID. see below....

A logitrol system is great and have had now problems with it at all. Plenty of power using the stepper motors even with the gantry weighing in at around 400kg. We can jog at up to 30m a minute but we limit it to 20m a minute.
The timing belt gear reduction on the x and y is 4:1
We used a ball screw on the Z axis with a 20mm pitch.

[ger21]

Have you priced 2500oz steppers and drives? You can get DMM 1.8Kw AC servos for about $600 per axis (plus cables). These would blow away 2500oz steppers.

Also I will be cutting aluminum so the cutting force will be a little bit more than if I was cutting wood. So I definitely want the torque to do some heavy aluminum cutting.

The cutting forces will be a fraction of what you need to accelerate 800lbs.

[ramsey321]

Ok great. So I could do the DMM servos with a belt reduction system? Do you know where I might be able to find a well made belt reduction system?