30"+ work space low cost diy CNC router parts kits?

[ger21]

I'm trying to understand how those motors differ to the ones sold on eBay or the OpenBuilds store for my purposes

As Andrew said, you want motors with a lower inductance. Lower inductance motors will have more torque at higher speeds, giving you more speed.

Those motors are the same price as the Openbuilds motors.
http://www.automationtechnologiesinc...23h2100-35-4a/

[Goemon]

As Andrew said, you want motors with a lower inductance. Lower inductance motors will have more torque at higher speeds, giving you more speed.

Those motors are the same price as the Openbuilds motors.
http://www.automationtechnologiesinc...23h2100-35-4a/

I think I am going to buy a set so I can complete my linear actuators.

[Goemon]

What are people doing with these 4-axis kits that come with 4 Nema 23 motors? I assumed you needed a geared motor with a lathe chuck attachment to build a 4-axis machine.

Are people buying the chuck attachment separately or are they creating a different style of 4th axis (like table rotation) that doesn't require a chuck? I couldn't see any Nema 23 to lathe chuck adapters for sale anywhere....

Also, I noticed that the kits with 4 motors come with a 12a psu instead of 7.5a. Is the 12.5a psu necessary for running 4 motors or could you run 4 with a 7.5a psu?

[ger21]

What are people doing with these 4-axis kits that come with 4 Nema 23 motors?

Building gantry machines that use two motors to move the gantry.

7.5a is borderline for 4 motors. It would probably work most of the time, but could cause issues.

[Goemon]

Building gantry machines that use two motors to move the gantry.

7.5a is borderline for 4 motors. It would probably work most of the time, but could cause issues.

What is the thinking behind using 2 motors for one axis? It sounds like a potential source of minor alignment issues (through one motor moving slightly faster or slower than the other)? The chances of any two of those cheap Chinese steppers being exactly in spec and identical is somewhere between zero and nothing....


if you use two motors for the X-axis, do you then give up the opportunity to add a fourth axis or do you wire two motors into the same connector on the Gecko board?

if two motors are wired to the same driver connection, does that mean you get identical emails speed and torque from each?

This word "gantry" is new to me. Am I correct in thinking that it refers to a design where the X-axis motors move the spindle instead of moving the table?

Openbuilds refers to all of their slide plates as "gantry plates" regardless of what they are used for which is why I want to make sure I understand what we are talking about....

[awerby]

What is the thinking behind using 2 motors for one axis? It sounds like a potential source of minor alignment issues (through one motor moving slightly faster or slower than the other)? The chances of any two of those cheap Chinese steppers being exactly in spec and identical is somewhere between zero and nothing....

[It's to avoid jamming when the rectangular table rotates slightly. Think of opening a wide bureau drawer; what's going to work best, 2 handles, one on either side, or a single handle in the middle? While the motors might not be exactly identical, they can have the same number of steps per revolution (usually 200) so it's not too hard to keep them in sync. Control programs also usually have squaring routines to keep them adjusted correctly in relation to the limit switches.]


if you use two motors for the X-axis, do you then give up the opportunity to add a fourth axis or do you wire two motors into the same connector on the Gecko board?

[If you did that, using the G-540, then you'd need a separate driver for the 4th axis, with connectors of its own.]

if two motors are wired to the same driver connection, does that mean you get identical emails speed and torque from each?

[Each needs a driver of its own.]

This word "gantry" is new to me. Am I correct in thinking that it refers to a design where the X-axis motors move the spindle instead of moving the table?

Openbuilds refers to all of their slide plates as "gantry plates" regardless of what they are used for which is why I want to make sure I understand what we are talking about....

A gantry is a moving crane; in the CNC world it denotes a Y/Z assembly that rides along the X axis. The other type of machine commonly built uses a fixed "bridge" with the Y and Z axes running on it and a moving table for X.

[ger21]

This word "gantry" is new to me. Am I correct in thinking that it refers to a design where the X-axis motors move the spindle instead of moving the table?

The gantry is the beam above the table. You can have either a moving gantry, or a moving table (and sometimes both).
Most moving gantry machines use two motors, as a single motor will usually allow the gantry to rack when there are larger forces at the ends of the gantry.
A quick glance at the Openbuilds website shows mostly moving gantry machines, driven with two motors.

It sounds like a potential source of minor alignment issues (through one motor moving slightly faster or slower than the other)? The chances of any two of those cheap Chinese steppers being exactly in spec and identical is somewhere between zero and nothing....

Actually, the chances of them not being in alignment is closer to zero. The controller sends both motors the same number of steps, at the same time. So they are always in sync. If you have a motor that's losing steps (and position), then you pretty much have a useless machine, whether it's using one motor or two.

if you use two motors for the X-axis, do you then give up the opportunity to add a fourth axis or do you wire two motors into the same connector on the Gecko board?

You add another driver for the additional axis.
It's not recommended to run two motors from one drive, as it doesn't work well as rpm's increase.

[Goemon]

The gantry is the beam above the table. You can have either a moving gantry, or a moving table (and sometimes both).
Most moving gantry machines use two motors, as a single motor will usually allow the gantry to rack when there are larger forces at the ends of the gantry.
A quick glance at the Openbuilds website shows mostly moving gantry machines, driven with two motors.



Actually, the chances of them not being in alignment is closer to zero. The controller sends both motors the same number of steps, at the same time. So they are always in sync. If you have a motor that's losing steps (and position), then you pretty much have a useless machine, whether it's using one motor or two.




You add another driver for the additional axis.
It's not recommended to run two motors from one drive, as it doesn't work well as rpm's increase.

I'm glad I asked. You guys have saved me from making a design error there. I was going to move the gantry on two rails with one motor and one 1/2" lead screw. It sounds like that is not the way to do it right so I need to order an additional lead screw, motor and associated hardware. It will add an additional $130 but I need this machine to work right.


Out of interest, what is the advantage (if any) in moving the table instead of the gantry? I could understand if the X-axis used some type of conveyor belt instead of rails to allow infinite cutting length but that's not what we are talking about here. I assume there is another reason?

If all 4 motor connectors on the Gecko G540 are taken up with the X, Y and Z axis, where would the additional driver for the 4th axis attach to? Would it plug straight into the computer via a second parallel port card or USB etc?

Future upgradability for a 4th axis is important to me so I want to make sure I understand what needs to be done.

[awerby]

Moving the table rather than the gantry makes for a more rigid machine, since the Z and Y axes can run on a heavy bridge that doesn't need to move. The sides of a moving gantry make it less stable the higher it is, while a table is always rather low. And the weight of the gantry needs to be kept low, since otherwise you run into problems with inertia. The disadvantage of the moving-table fixed-bridge design is that it has a larger footprint; you need more space in the shop for a machine like that.

[wizard]

I'm glad I asked. You guys have saved me from making a design error there. I was going to move the gantry on two rails with one motor and one 1/2" lead screw. It sounds like that is not the way to do it right so I need to order an additional lead screw, motor and associated hardware. It will add an additional $130 but I need this machine to work right.

If you are doing a moving gantry design, dual screws generally become a must have. It comes down to how much space you can afford to waste spreading the linear bearings apart but eventually dual ball screws are the only sensible solution. In other words the wider the machine the more likely dual ball screws are required.

Out of interest, what is the advantage (if any) in moving the table instead of the gantry?

Well personally I think the design is easier to build and maybe more importantly easier to square up and keep the machine squared up.

Mechanically you will have a much stiffer machine for a given amount of materials.

I could understand if the X-axis used some type of conveyor belt instead of rails to allow infinite cutting length but that's not what we are talking about here. I assume there is another reason?

Well stiffness and simplicity are the big ones. As with any machine there are advantages and disadvantages to an arrangement. If you follow the hobby of 3D printers you will find dozens of designs floating about the net each with advantages and disadvantages. The same thing happens with routers, The alternative designs aren't ""wrong"" they jus support a specific purpose.

If you look a the design of a moving table machine you will find that you can create any amount of stiffness, in the gantry and table frame coupling, you budget permits. This is because the frame the table sits upon, the gantry uprights and the gantry beam itself don't move. This means there is no limit on how strong you can make the parts nor how you join them together. This makes these machines very useful to people that intend to machine metals as stiffness can dramatically improve results.

If all 4 motor connectors on the Gecko G540 are taken up with the X, Y and Z axis, where would the additional driver for the 4th axis attach to? Would it plug straight into the computer via a second parallel port card or USB etc?

That depends upon the software and hardware. Frankly I don't have a G540 at the moment. Personally I would prefer to mount individual drives and go with a breakout board.

Future upgradability for a 4th axis is important to me so I want to make sure I understand what needs to be done.

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I wouldn't get too excited about your electrics until after you nail down the mechanical design.

[ger21]

I would say that a moving table makes it easier to build a more rigid machine, but it doesn't guarantee it. And, a moving table can require nearly double the length, as the entire table needs to move it's entire length.

If all 4 motor connectors on the Gecko G540 are taken up with the X, Y and Z axis, where would the additional driver for the 4th axis attach to? Would it plug straight into the computer via a second parallel port card or USB etc?

If you're using the parallel port, then yes, you can add another one. Or, you can use an ethernet or usb motion controller with multiple ports. You'll generally want to use a breakout board on the second port, to make it easier to connect an additional drive and other things you may want to add.

[jpvonoy]

Goemon, these are the steppers I used:
http://www.automationtechnologiesinc...lat-381-oz-in/

They are almost identical to the ones linked to earlier in this thread, except they are 200 steps per revolution rather than 400. To understand what this means, you have to know the lead or threads per inch of your screws. You can then calculate how much linear motion you will get per step of the motor. With 400 steps per rev, it allows more precision, but with the 10x microstepping on the G540 it may be overkill. It was in my case since I have 10mm lead ball screws. 10 mm / (200 steps x 10 microsteps) = 0.005 mm or 5 microns. The 400 step motors would give me 2.5 microns. I have at least a factor of 10 more error introduced from other components, so this difference would be insignificant.

Also I would think you may end up limiting the machines speed by having to perform a lot more step commands for a given distance and the computers latency can only support so many steps per second? Maybe someone can confirm that last bit.

The other difference is the motors I bought have two shafts, one on each end. This is not necessary...I did it in case I wanted to instrument the motors to monitor actual distance vs commanded distance. You could go with a single shaft model, but I don't see that version on their website currently.

Sent from my Nexus 6P using Tapatalk

[ger21]

That's my mistake. I didn't mean to link to 0.9° motors, and didn't notice. You really want 1.8° steppers.
However, don't assume that you'll be able to achieve the microstepping accuracy.

[Goemon]

If you are doing a moving gantry design, dual screws generally become a must have. It comes down to how much space you can afford to waste spreading the linear bearings apart but eventually dual ball screws are the only sensible solution. In other words the wider the machine the more likely dual ball screws are required.

Well personally I think the design is easier to build and maybe more importantly easier to square up and keep the machine squared up.

Mechanically you will have a much stiffer machine for a given amount of materials.

Well stiffness and simplicity are the big ones. As with any machine there are advantages and disadvantages to an arrangement. If you follow the hobby of 3D printers you will find dozens of designs floating about the net each with advantages and disadvantages. The same thing happens with routers, The alternative designs aren't ""wrong"" they jus support a specific purpose.

If you look a the design of a moving table machine you will find that you can create any amount of stiffness, in the gantry and table frame coupling, you budget permits. This is because the frame the table sits upon, the gantry uprights and the gantry beam itself don't move. This means there is no limit on how strong you can make the parts nor how you join them together. This makes these machines very useful to people that intend to machine metals as stiffness can dramatically improve results.

That depends upon the software and hardware. Frankly I don't have a G540 at the moment. Personally I would prefer to mount individual drives and go with a breakout board.



I wouldn't get too excited about your electrics until after you nail down the mechanical design.

You mentioned something I was going to ask about. It was suggested to me (by someone on another forum) that I might not need two lead screws and motors on my X because I am building a fairly narrow machine. My cutting needs are 30" by 8".

Realistically, with the part I have bought, I will end up with around 30" x 12" of cutting space which makes my machine a little narrower than is normal (for it's length). Does this change anything in terms of what you guys recommend or are two lead screws needed regardless of the width?

My gantry will be made out of carbon fiber (with a few aluminum screw mounting plates cooked in) so I am not expecting it to be particularly heavy. I do however have a desire to build the stiffest machine I am able to.

Does building a fixed gantry design effect my ability to add a 4th axis later on? I am talking about the lathe chuck kind, not the indexing table kind. I guess the other axis could stop moving while the part rotates.

[ger21]

If the travel along your gantry is only 12" or so, then if it's well built, you can probably get away with a single screw.

My gantry will be made out of carbon fiber (with a few aluminum screw mounting plates cooked in) so I am not expecting it to be particularly heavy.

It has nothing to do with weight. The issue is when you have cutting forces and one end of the gantry, that side will want to "fall behind".
And it doesn't really matter what materials you use. It's more about the design, and how you use them. You can build a poor quality steel machine, or a high quality wooden machine.

[wizard]

If the travel along your gantry is only 12" or so, then if it's well built, you can probably get away with a single screw.




It has nothing to do with weight. The issue is when you have cutting forces and one end of the gantry, that side will want to "fall behind".
And it doesn't really matter what materials you use. It's more about the design, and how you use them. You can build a poor quality steel machine, or a high quality wooden machine.

This is so true. You could design a 20 foot long cantilevered gantry type machine with enough engineering effort but the question becomes is it practical to build.

It is in effect the simple machine we all learned in high school, the lever arm. The longer the cantilever the greater the torque that gets applied to the bearings that the gantry rides on. Designing a machine to resist this load becomes non trivial. The two lead screw approach is a simple and very effective way to deal with the issue of torque, twisting the beam.


If I do this link right: https://www.google.com/url?sa=i&rct=...92552491492566 we should see a link to what looks like a planner mill with a cantilevered gantry (maybe arm in this case.) There is a significant amount of mass in that arm and support column and even so I would expect that the machine is light duty compared to a machine with a full set of columns. Hey it worked!.

So what is the reality here for the original poster? For a 12" span you could drive from one side if you address the issue of twist. One of the simple ways to address this twist would be to spread out the linear bearing cars on the driven side of the machine. As Ger21 points out it is an issue of design, if you want to go this route you will need to put in some engineering effort.

[Goemon]

This is so true. You could design a 20 foot long cantilevered gantry type machine with enough engineering effort but the question becomes is it practical to build.

It is in effect the simple machine we all learned in high school, the lever arm. The longer the cantilever the greater the torque that gets applied to the bearings that the gantry rides on. Designing a machine to resist this load becomes non trivial. The two lead screw approach is a simple and very effective way to deal with the issue of torque, twisting the beam.


If I do this link right: https://www.google.com/url?sa=i&rct=...92552491492566 we should see a link to what looks like a planner mill with a cantilevered gantry (maybe arm in this case.) There is a significant amount of mass in that arm and support column and even so I would expect that the machine is light duty compared to a machine with a full set of columns. Hey it worked!.

So what is the reality here for the original poster? For a 12" span you could drive from one side if you address the issue of twist. One of the simple ways to address this twist would be to spread out the linear bearing cars on the driven side of the machine. As Ger21 points out it is an issue of design, if you want to go this route you will need to put in some engineering effort.

Given my general lack of engineering knowledge, it sounds like I am better off ordering the extra ball screw and motor. Basically, 4 motor drivers like the Gecko G540 are 3 axis devices, not 4 as advertised, unless I switch to a fixed gantry design.

I still don't understand how one side of bearing blocks gets ahead of the other on the THK rails if they are connected with horizontal steel reinforced carbon fiber plates but maybe I don't need to fully understand every last bit if I want the machine to get built while I'm still alive.

[ger21]

I still don't understand how one side of bearing blocks gets ahead of the other on the THK rails if they are connected with horizontal steel reinforced carbon fiber plates

If built right, they won't.
But everything flexes to some degree. as long as you can keep the flex to an acceptable amount, then you'll be fine.

Have you ever sat in a car on an overpass, and feel the bridge beneath you bounce up and down? Everything flexes, no matter how strong and stiff it is.

[Goemon]

Goemon, these are the steppers I used:
http://www.automationtechnologiesinc...lat-381-oz-in/

They are almost identical to the ones linked to earlier in this thread, except they are 200 steps per revolution rather than 400. To understand what this means, you have to know the lead or threads per inch of your screws. You can then calculate how much linear motion you will get per step of the motor. With 400 steps per rev, it allows more precision, but with the 10x microstepping on the G540 it may be overkill. It was in my case since I have 10mm lead ball screws. 10 mm / (200 steps x 10 microsteps) = 0.005 mm or 5 microns. The 400 step motors would give me 2.5 microns. I have at least a factor of 10 more error introduced from other components, so this difference would be insignificant.

Also I would think you may end up limiting the machines speed by having to perform a lot more step commands for a given distance and the computers latency can only support so many steps per second? Maybe someone can confirm that last bit.

The other difference is the motors I bought have two shafts, one on each end. This is not necessary...I did it in case I wanted to instrument the motors to monitor actual distance vs commanded distance. You could go with a single shaft model, but I don't see that version on their website currently.

Sent from my Nexus 6P using Tapatalk

My lead screws are half inch 2 start for all three axis. I'm not sure if I should have gone for 5 - start but either way, it's done now and I don't care if the machine is slower. It's not a particularly large machine anyway. My main concern is achieving a quality finish, even if it's super slow.

I'm going with those 381ozlow inductance motors. In addition to asking here, I asked multiple CNC stores which ones they recommended for my needs and they all recommended the ones they sold.

The only thing nagging the back of my mind on those motors is that the CNC mill motors kits all seem to have 8x the amount of holding torque. I understand that those things are meant for cutting harder metals like steel but it indicates that more torque is better for harder materials. I would like to try making aluminum molds at some point so I am hoping that having 381oz motors doesn't become the thing that stops me.

Anyway....time to stop stressing about stepper motors and time to start stressing about my choice of spindle. On to the next sea of indistinguishable choices I don't fully understand!

[ger21]

With 2 start screws, you could get away with even smaller motors, actually. I'm running 250oz motors on 24V, with 1/2-8 2 start screws, and I can get about 190ipm. With more voltage, and better drives, I could probably get 300ipm or so.