Starting to design out my build, looking for critique

[AndyUK]

Cool, changes look to be in the right direction. Z axis will be much more stable - even more so if you can space those bearings apart a bit.

Add a mounting point for the Z-Axis NEMA 34 behind where the Y-Axis ballscrew currently connects to the Y-Axis sled.

Woowwww there cowboy! Hold up a second! A Nema 34 for the Z axis? That's a little overkill. Get a much lower inductance Nema 23, gain yourself some performance by not having a big inertia to overcome (and take the extra mass from the moving carriage), and give yourself more space up on the Z. Something like 2-3Nm - even that will be more than sufficient.

Substitute the Aluminium Profile for Steel Box section and weld it. The warping should be controllable in a machine this size, is what I am hearing.

Certainly do-able. I planned to do the same myself initially. But the welding will warp it, and mild steel box section is nowhere near flat to begin with, so either way you'll need to mill the faces you want to mount rails to. Or, you can epoxy them, but that won't be easy to get the two faces parallel. Then you have to consider how to attach the box section to the gantry end plates, which probably means capping them off and tapping them etc.

Rigidity? Look at my build thread. I simulated a steel L shape out of a box and a rectangle, then I simulated a slightly smaller Ali HD profile. Although the young's modulus of Ali vs Steel says you'll get more deflection from Ali, when you take the profile shape into account its really minimal. I think I went from 3um deflection in steel to 4um in Ali (but the real numbers are in the build log). Either way, its nothing to be concerned with.

Profile Ali is flat enough to mount straight to and just shim where and if needed. It also has nice ends which can be tapped in about 5mins and bolt directly onto your end plates.

Weight? Every extra kilo is lost acceleration!

Next question is cost - In my case, the aluminium was only marginally more expensive. Really not much in it - Approx £40 for steel, and £50 for Ali. The ease of Ali just won the day for me by a long margin.

Change the Y-Axis gantry to a design that has a Profile up top and one below with the ballscrew sandwiched in between. The rails would go to the front and both profiles would be held together at the sides, like they are now, and with an extra plate at the back. Alternatively manufacture this out of steel section.

So, two tubes with a large gap between? From memory of my deflection calculations that's a far less rigid structure. The L shape is good because it resists deflection both up and down, as well as twisting around it's own axis. I think that design would perform poorly in both situations.

[Chrono]

Wow, took me 4 weeks to finally find time and gradually work on those 4 items, huh... I really need to find more time for this :D

Anyways. I did get everything in order, and took your comments into account, so let's go over the changes.


Y-Axis Motor Mounting:


For a long time, the only place i saw to mount the motor without it interfering with anything was below the base. This would have been achieved by lengthening the side part below the linear bearings/ballscrew. Luckily, after taking a step back and looking at the model again, I found a much better place to do so, right next to the Ballscrew for the Y-Axis itself. The spot there is pretty much perfect, since it is below any part of the Z-Axis' top part, even if the Z-Axis motor is mounted on the back, but at the same time, it is above the lowest part of the Z-Axis, meaning it does not add any constraints for the workspace inside the machine. I would plan to get those mounting plates(the green ones) cut from steel sheets, since I can get that rather cheap.

Z-Axis Motor Mounting:


The second picture carries a lot of annotations, but I will go into the important parts again: I found two possible mounting spots for the Z-Axis motor, both are shown. Following your advice, I went for a NEMA 23 Motor on the Z-Axis, instead of a NEMA 34, like I am using for both the X- and Y-Axis. I now have the option of mounting the motor on the back, possibly compensating some of the torque the spindle places on the Y-Axis carriage. This, however, means that I need one more part to assemble the carriage, since I cannot just take two bent sheet metal parts. I would also need quite a significant amount more material, as you can see. The mounting on the back of the plate carrying the Z-Axis Bearings, would simply be using unused space that would already be there, and it would be relatively center on the axis, but possibly add to the torque of the spindle, since it is a bit forward. Using slots in the mounting bracket, I could easily change the height of the motor in that position to fit the mounting point needed, however.

I am unsure what spot to choose here. The top mounting position has quite a couple things going for it, but the back position does offer torque compensation at the price of significantly more complicated carriage assembly...

X-Axis Motor Mounting:


The X-Axis mounting was easy to do, since I already had a good talk with one of the mechanical engineers in my workplace about that one. It is a simple Omega Belt Drive structure, driving both ballscrews from the same motor, just as you advised me to do. The two pulleys on the movable arms are tensioned using springs, not only to tension the belt, but also to increase the contact area of belt on both the ballscrew- and motor-pulleys.

Finally: The Back bearing mounting plates:


These are basically the same as on the front and just simple metal pieces to hold the bearings of the ballscrews. The problem I currently have with them, however, is this: They are three-dimensional 20mm plates with pockets milled out of them. A better idea I had, to make them easier to manufacture, was to instead buy some longer Ali extrusion in the X-Direction, to bring the front and back edge of the machine more in line with the front face of the ballscrew-mounting-blocks, both in the front and back. Then I could use simple flat sheets of metal with some shimming underneath to equalize any tolerances. This would make those mounting brackets easier to manufacture, but add some "dead-length", when it comes to the ali extrusion, where it becomes longer, but the rails or axis are not. Still, I think that would be a better approach.


To-Do:
Normally I would now lay-out what was on my mind, when it comes to next steps, but I cannot come up with anything concerning the CAD model, it looks pretty much done to me. What I need to now look into, however, is the electronics side of things: Find out what I still need in terms of controllers, motors, Power delivery, etc. and get some rough pricing, as well as model it into the CAD as needed. Where would be a good way to start here? For the gantry and machine design there were some helpful collection threads on here, comparing different gantry designs, for example. Is there also something like this when it comes to the electronics?

As always, thanks for any help!
-Chrono

[AndyUK]

Normally I would now lay-out what was on my mind, when it comes to next steps, but I cannot come up with anything concerning the CAD model, it looks pretty much done to me. What I need to now look into, however, is the electronics side of things: Find out what I still need in terms of controllers, motors, Power delivery, etc. and get some rough pricing, as well as model it into the CAD as needed. Where would be a good way to start here? For the gantry and machine design there were some helpful collection threads on here, comparing different gantry designs, for example. Is there also something like this when it comes to the electronics?

Suggest you start here:

http://www.mycncuk.com/threads/1524-...otor-do-I-need

Once you're up to speed with the description, open the spreadsheet and customise to your needs (its setup for a smaller machine). Find reasonable values for your cutting forces and repeat for each axis in turn (increasing the moving weight as you go - ie. Z has a small moving load, Y has slightly more, X even more). I rebuilt the sheet from scratch to show all axis at once with individual inputs which helped.

Next is the leadscrew calcs - lookup typical efficiencies of the system you're using, and what each of the measurements mean. This will give you screw inertia and critical speeds. From your screw pitch, you then have your maximum permissible speed on that axis. Tailor the ballscrew configuration until you're happy with the maximum speed.

Now you have to decide what max cutting speeds and rapid speeds you want. I aimed for 5m/min rapids - some people here can get 7.5m/min. Cutting speed depends on the material (as does the cutting force).

Then you can start plugging motors into the spreadsheet. Find a few example motors online, look at their specs, and put them in the sheet taking best guesses where needed. Then play with your power supply settings, and the sheet will tell you if the motor is up to the job or not. This is how I came to the conclusion that NEMA23s on each axis were more than suitable for my application.

The motor drivers are then somewhat dictated by the current required, and the PSU is calculated by summing the maximum currents on all axes, then multiplying by a stepper usage factor (I think its 2/3rds? but you'll find this in the Power Supply threads). The voltage for the PSU is dictated by the inductance of your motors - the sheet will tell you an ideal voltage, and the drivers will have a maximum voltage - aim somewhere between those two allowing for variations in mains supplies.

Rest of the electronics are essentially personal preference. Many ways to skin a cat...

[Chrono]

I have been dabbling in the motor sheet, and found motors that would work, but i hit a couple road blocks...

The weirdest one was not finding german stores that sell steppers. I could only find one real store, that sells for okay prices, but even that one only sells to companies. The general electronics sites here, only sell steppers for horrendous prices, and only around about 10 different models max.

Another issue I was having with the sheet was the cutting forces and speeds. Is there a good summary of what to aim for, a collection thread of sorts? As it stands I am kind of lost here.

What that post also left open, is what the different types of support (like supported-supported) actually are. What would a ballscrew with its two bearing blocks count as? Supported-Supported?

On the upside, I could find motors that work for the X and Y axis (At the store that only sells to companies). This one in fact: Link. Using the weights I calculated, those motors would manage to get me 7.5m/s rapids as long as the axis is 1.5m long at max, as well as 2.5m/s cutting with 50N of force, a value that i chose at random judging from the values mentioned in the post.
I did not yet look at a NEMA 23 for the Z-Axis, because of the aforementioned problems I was having with the spreadsheet.

I also attached the spreadsheet with my values, as well as another spreadsheet I used to calc the masses, so that it becomes more transparent.

Another question concerns the other electronics. At this point i am wondering what I need in total. As far as I understood, the following is needed (mostly going off of Joe Harris' Build http://www.mycncuk.com/threads/4513-...0655#post90655):

• A PSU
• A Controller
• A driver per stepper
• A VFD
• A Water Pump
• A Spindle

Am I missing something here? Also, again, is there some kind of collection post of different options for this?


Now, for a bit of a curveball... The problem I am currently running into, is that I am not going to be at the company I am currently at for much longer. They do allow me to use their hardware, however, which would come in really handy, building the machine. I am wondering now, if it would be okay to start ordering parts and building the frame/gantry now, while I still have access to the tools and the mechanical engineers willing to help, in parallel to getting the electronics planned out, or would should i wait to be done with that?

I also want to take a quick second here, and really thank you for all the help you have been providing me. I don't think I could have been here without all of the assistance you provided. Thank you a lot!

[AndyUK]

Will reply with a more detailed look at your spreadsheets when I get time, but to quickly answer a couple of points:

The weirdest one was not finding german stores that sell steppers. I could only find one real store, that sells for okay prices, but even that one only sells to companies. The general electronics sites here, only sell steppers for horrendous prices, and only around about 10 different models max.

As you're in the EU, pretty much any EU store is an option. CNC4YOU.co.uk is where I got mine, Zapp Automation also seem pretty good.

What that post also left open, is what the different types of support (like supported-supported) actually are. What would a ballscrew with its two bearing blocks count as? Supported-Supported?

So here you may need to read up on ballscrews and their mountings. Free means no support (an end which is floating in mid air), Supported means on a bearing but with no axial constraint (like a BF mount), and Fixed means a bearing that can take axial force (like a BK mount). Typical configuration is Fixed-Supported, with a BK at the motor end and a BF at the other. You'll need to know this when ordering your screws, as they need to be machined appropriately.

Another question concerns the other electronics. At this point i am wondering what I need in total. As far as I understood, the following is needed (mostly going off of Joe Harris' Build http://www.mycncuk.com/threads/4513-...0655#post90655):

• A PSU
• A Controller
• A driver per stepper
• A VFD
• A Water Pump
• A Spindle

Am I missing something here? Also, again, is there some kind of collection post of different options for this?

Oh wow. Theres like a billion different options. Finding a path is tricky! Ultimately, you need some way to turn GCode into motion.

That often starts with a PC sending the Gcode to a parallel port - but PC's aren't great at realtime and they're not often made with parallel ports these days, so some kind of motion controller is often used to simulate a parallel port and deal with the realtime aspect. Recommend ethernet variety. Then you may or may not need a breakout board depending on which controller you use - a UC300eth for example just gives you five headers with lots of pins, its nicer to have a board like the UB1 attached to output all those pins nicely and deal with a few other things like relays.

Next, the controller sends off pulses to the drivers. Depends on the motors you choose, but the Leadshine AM882/EM806s are popular around here. Nice to have a decent current range and voltage range that are applicable to your motors, and missed step protection is nice. As you point out, one driver per stepper.

PSU to power the drivers. Calculate the right voltage and current, then size appropriately. Some folks like Joe build their own, its not too hard. Other PSUs will be needed for the sensors and auxiliary components, you'll have to draw up a diagram to figure out what you need. Typically a 24/12/5V, or maybe even multiples.

Spindles and VFDs often bought together from China. Recommend ER20 or ER25 for the larger tooling. Water cooled will be a lot quieter. Some even come with a pump - to be honest, it doesn't seem like the cooling requirements are massive, an aquarium pump will probably do.

Other electronics - Circuit Breakers, Contactors, Switches, Relays, loads of wire, Limit switches, Home switches, fans.... the list is endless. Don't forget software, and somewhere to keep all these expensive electronicals.

Now, for a bit of a curveball... The problem I am currently running into, is that I am not going to be at the company I am currently at for much longer. They do allow me to use their hardware, however, which would come in really handy, building the machine. I am wondering now, if it would be okay to start ordering parts and building the frame/gantry now, while I still have access to the tools and the mechanical engineers willing to help, in parallel to getting the electronics planned out, or would should i wait to be done with that?

Up to you. If that was my situation I'd probably be making a start while I've got the opportunity to utilise the expertise, but be prepared to backpedal slightly more than if you've got a plan sorted from the start.

[Chrono]

More progress, at least in the design department!

I did decide to design out the Z-axis a bit and plan on how to build it up, especially since one of my coworkers asked me the fateful question of: "Well it is technically possible to manufacture, but are you sure, that you can actually put it together like that, when it is in front of you?". With the earlier draft, I have no idea if that would be possible to actually assemble without a huge hassle, so I thought about it and came up with a better design, using screws and bent steel plates. The pink plate I will probably be changing out for a thicker aluminium one. Also something of note is that the bends and such are not accurate. I simply don't have enough time in Fusion's Sheet metal work-space, so I just went with the default settings for convenience's sake. After taking another look at your machine, since I was asking myself how to get more length out of the Z-Axis, I will probably also switch the rails to be on the sled and the bearing blocks to be on the gantry, like you did.



I also changed the size of the machine in my Fusion design to reflect my "updated" plans for size. This broke a couple things that I did not yet get around to fixing, like the floating plates and angles, as well as those two Z-Axis bearings floating in the middle of nowhere. The original size was guesstimated around 1m x 0.8m x 0.2m while I was still messing around with the base design. The "new" size I plan on having is: X: 2m, Y: 1m to 1.2m, Z: ~0.3m to a max of 0.5m. I am not quite sure about what a good measurement for the Z-Axis would be, so if there are any values that have generally found agreement in what not to exceed, let me hear it :D



For the linear motion setup, I am planning to use Chinese 1610 Ballscrews and HIWIN-style rails (note: not original HIWINs). The reason for that is that I started pricing out the build to where I now have a pretty "final" (well, as final as it can be at this stage) price for it, bar the uncertainty of import tax and the like. All in all this puts me at around a 3k € to maybe 3.5k € total, if taxes end up really high, and of course, planning in a cushion in case something goes wrong. The difference of the Chinese rails to the original ones is quite significant in that, however, with the bundle of ballscrews, ballnuts, BK and BF blocks, linear rails and slides, being 50% more expensive, when using original rails, with all other things being constant. But I still have to ask: Are those rails okay to get, or are there any known problems with them, accuracy-wise or otherwise?

I have also checked these lengths in the motor calc spreadsheet, and with the 2m axis, I would now be down to 5.2m/s rapids from 7.5m/s. Should I reduce this to get back up, or should I be keeping it? My reasoning for going as big as possible, is to get the "best value", so to speak. I don't want to be caught standing there with my pants down, when a project requires me to have big machine. Alternatively I could also go with 2010 ballscrews and up-size my stepper on the X? I might need to properly calculate the increase in price for that out.

Another thing that caught me off guard is just how much the motion controller, and especially that breakout board cost! 300€ for a control board and its breakout sound properly astronomical to me :D But alas, I also know not to skimp on the important bits.

With the leadshine drivers, and a spindle, that should nearly do it for electronics. Speaking of spindles, however, I was looking at this 2.2kW one. Is 2.2kW a good amount of power for my uses (wood, plastics, some aluminium, PCBs)? They also do carry a 3kW model.

Regarding Sensors, so far I have only been able to think of Endstops and homing switches. What else would I be needing? Another question that was on my mind, is why I need homing switches? Does the "home" need to be different from {0,0,0}, or am I missing something here?

You also mentioned software in your post. I know of Mach 3 and I also saw that they now make Mach 4. Are there any others out there, or are these ones the ones to get?


Now, on a completely new note: I have finally taken into account that I still need a table. I have chosen to keep this one on the back burner for a bit, until I got a preliminary pricing done for the machine itself, and I am now considering how to do this. Most machines I have seen so far, are using a steel table, that even reaches above towards the Y-Axis, where I have those big plates. Since I am using aluminium profiles already, I was thinking that I could just buy some more and make the table out of that. This would also allow me to slightly redesign my machine and allow for a similar design like yours, for example, with the raised sides. I am guessing that would be a huge plus in terms of rigidity, compared to my steel plates approach? I would, of course, loose some access and some space on the sides, accounting for the width of the extrusion, but with how wide the Y-Axis sled is, that should not be a problem in terms of actual cutting width loss, if executed correctly.

[Clive S]

I have also checked these lengths in the motor calc spreadsheet, and with the 2m axis, I would now be down to 5.2m/s rapids from 7.5m/s

You could also think of using rotating ball nuts 2Mtr is a long way with 16mm screws