Starting to design out my build, looking for critique

[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

[Chrono]

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

How would I mount the rotating nuts? I guess I would need the motors on the gantry then? Would that also mean that I would either need an elaborate timing belt setup spanning the gantry, or use two motors?

I can also just use 2010 or 2510 ballscrews and get a stronger motor for the X, which is something I am actively thinking about. According to the motor calc sheet, the Y and Z are perfectly fine as is, at 7.5m/s rapids, using 1610 ballscrews.


On another note: After thinking more about the changes I talked about and talking them, and other things, over with my colleagues, I am remaking the CAD file from scratch. While doing that I am also reworking everything to be 100% parametric, which is taking a while, but is paying off massively. Basically fixing mistakes made the first time around.

Current progress is the following: The table and X axis are done, except for the X axis ballscrews. The Gantry and Y axis are complete. What is yet missing, is everything concerning the Z-Axis, pending a complete revision, Motors and timing belts, and E-chains, that I want to account for. All in all, it is progressing nicely.

[Chrono]

Hey everyone! More progress on the redesign. I sat down and actually worked on it everyday this week, and got some real progress done, finally. I am much more satisfied with how that one turned out, compared to the old one. Here is a side-by-side:


It is probably obvious, but the old one to the left, the new one to the right. This will be the convention for pictures for the rest of the post as well. (On a side note: The blue extrusions are going to be changed from 45x90 ones to 45x45 ones, to save money. I just have not gotten around to fixing them in CAD, since they were pretty low on the list in terms of priority)
While being at it, I also changed a whole couple of things: Like the Z-Axis

New:

The Z-Axis got completely changed. Where it was a complex part before, it is now a rather simple bent sheet steel piece. The motor is now also affixed to the Z-Axis itself, and is moving with it. This is to keep the Gantry-side Y-Axis sled small. It also theoretically means, that I don't need to change anything but the Z-Plate, the rails and the Gantry sideplates to add more Z-space later on, if I ever decide on it. All in all, I like the design change of putting the bearing blocks on the Gantry sides, and the rails on the Z. Allows the parts to shrink a bit. That is one design change I picked up from AndyUK's build. The Ballscrew is also mounted on the moving Z-Axis, with the Ballnut being fixed on the Gantry Sled. One question that I still have, however, is how the cutting spindles actually get mounted to the Z-Axis. I understand that the spindle itself is mounted in the red aluminium ring, but how is that ring mounted? None of the pictures I could see in the offers showed any mounting holes. Are you meant to drill those yourself?

The Gantry itself got a revision as well!

New:

The obvious thing is probably the size and shape change. I went from an L-Assembly to a C-Assembly. This is so that I could move the rails up front, which should not only give me more rigidity overall, but also allowed the massive simplification in assembly for the Z-Axis and Y-Axis Sled. This is one change I really took a liking to.

Something that was not quite obvious from the last post, but was already in it, is that one of the side plates fixing the gantry beam to the X-Axis is much thinner than the other one, in this case the left one is thinner (3mm of steel) than the right one(10mm of steel). This is to give the machine a way to have a bit of play, should something not be fully aligned, and off by a tiny bit. Another measure to the same effect has been brought up by my colleagues multiple times now: To only put linear rails and bearing blocks on one side, and have the other only constrained against translation/force, not torque, and we finally came up with a workable example, I want to discuss here:



Let me explain. The plan would be to put the second linear rail on the lower extrusion on the right (looking from the front of the machine), and have both of them on the same side. Then, instead of a rail, have a supported smooth steel rod, and a cylindrical type round linear bearing on the left side, to replace the rail. That way, the linear bearing still constrains the movement on the translational axes and takes on the forces, but it would permit torque, which would fix the problem with it being statically overdefined. What do you guys think of that? None of the Logs and posts I have read here, so far, have reported any real problems with any of this, but one of my colleagues who has had contact with similarly built machines, with a different purpose (cannot exactly remember) is bringing it up as the thing they and their competitors did, to avoid problems in the same vein. And looking at the budget, one rail with linear bearings should not be the point that bankrupts me here :D

Another question I am having is regarding the long ballscrews on the X-Axis and the motor calc sheet. As discussed way earlier in this thread, I want to stay with a single stepper for the X axis, even though I have two ballscrews, linking them with timing belt. Now my question is, in the Calc sheet, don't I need to input a "times two" into the calc of the torque needed to spin the ballscrews, since the stepper needs to drive both of them at the same time? Since I want to go to 2010 or even 2510 ballscrews, that is one hefty variable to think about. From my initial messing around, I can either go less fast with a 2010 ballscrew (Around 6.3m/s rapids) with a weaker stepper, or find a much stronger one to drive the 2510 ballscrew at the full 7.5m/s rapids. Of course, cutting is another thing entirely, and I am still not quite sure what speeds to aim for here, but for reference, I have managed to get around 2.5m/s with 50N of cutting force, in my testing. Another way would be to stay with 1610 ballscrews and scale the X down from 2m to 1.7m, but that is something that I only want to be doing as a last ditch effort, so to speak.

And another on the ballscrews: Would I just mount normal timing belt pulleys to them, to connect them to the motors, or would I need special machining or parts here?



Regarding the Electronics: other than the Steppers, I have also been looking at all the other electronics. And I think I have it down to the following:

• X-Axis Stepper: Still looking
• Y-Axis Stepper: ST8918S4508-A
• Z-Axis Stepper: ST5909M2008-A
• Stepper Controllers: Either Leadshine AM882s or EM806s times three, after AndyUK's recommendation, still trying to figure out the exact differences there.
• Controllers: Either the UC400ETH or the Smoothstepper ESS, although I am still dabbling about the electronics section of the forum. I don't think that I will be getting breakout boards, since I can easily deal with electronics, and just soldering the proper cableing sound much more reasonable to be, instead of buying a 130 pound breakout
• The VFD will likely be a YL620-A packaged with a chinese 2.2kW watercooled spindle, alongside a water pump
• And finally: six microswitches for end stops. A thought here: would there be any profit had from using proximity switches?

Regarding the choice of controllers: I had a quick dabble with the Mark 4 demo, and as I understand, it is pretty much indifferent to the exact board I choose, and the board itself does also not really need to be wired up in any special way, since I set all the necessary port/pin assignments in Mach 4 itself (granted that I match input pin to input, output to output, etc.)?

When it comes to schematics: I just installed AutoCAD today to get something done, and thankfully I have got some people with a background in high-power electrical installations to help me with the cabinet and all the safety measures needed. After I have everything in there, I can think about all the PSUs needed.


All in all, I am really satisfied with the progress had in a week's time, and I am constantly working to finally get to the point where I am comfortable with the end result. If anyone spots anything that seems off with the revision, however, I would be very glad for any criticism on it. Ultimately, the more eyes and voices are involved, the less likely that mistakes fall through the cracks. And to that effect, here is the link to the web interface of Fusion, where you can take a look around the newest, up-to-date version of the 3D CAD Model yourself, and take a closer look.

On the note of getting a lot of feedback, however, I am noticing that other post here get a lot more traction, when it comes to user response. Don't get me wrong, I am by no means meaning do downplay the contributions made my AndyUK, CliveS and Washout(Who literally brought me here), you guys are the reason I have comes this far, and I cannot thank you guys enough , but at the same time, I am wondering if my post broke etiquette, or if I did something else, that made people not want to engage here? Because if that is the case, I would like to work on fixing that.

Anyways, I am already staying up way too late to finish up this post, so I am just gonna end it here and head to sleep.
Thanks,
Chrono

[Washout]

Hi Chrono

No broken etiquette as far as I know. You're probably doing a great job and nobody has much more to add ;)

A few comments I would have from your last set of design drawings are:
- whilst 4 rails looks like a good idea, you will have a devil of a time aligning them I expect. Maybe 2 rails of a larger size might be better?
- Also consider the CS-Labs kit for the controller - many on here use them, including the venerable JazzCNC (which is always a good sign imho)
- Proximity switches if they are the type in a threaded housing, will give a nice amount of adjustment for the trigger point - you can do the same with micro-switches, but they then need a plate with slots to mount them to to achieve that

Keep going and I expect interest will pick up once you start building

[AndyUK]

I'm still aware I haven't gone through your calcs yet... Finding time is hard! Sounds like with the design changes though I may wait a little longer :)

I second Washout's comments about the CS labs stuff, looks brilliant. The thing that put me off was that the base model is only 4-axis, and it doesn't handle slave axis homing native-ly (although there are decent workarounds posted on here). Anything more than the base model is horrendously expensive, and I wanted future expand-ability to add a 4th axis which is gone if you use the 4th for a slave - but you avoid both of those issues by having a connecting belt and single motor.

Also, on the four rails idea, I think you'll definitely end up spending a few days becoming best mates with your dial gauge - but it could pay off in the end?

First impressions on the redesign; I think your CAD is coming along nicely, really shows. I do have a few concerns though:

• I question the Z axis travel length and why the plate is so large - Don't forget you'll have a bit attached to the end of your spindle, and its going to have to be quite a long bit to make use of your Z travel. I've got 18cm, and honestly, its probably far too much, most of the time you're really only needing to cut say 18mm plywood! The distance between the bed and the gantry looks huge - All that Z extension reduces the rigidity of the machine. Have a think about what you really need - can it be acomplished in other ways, such as an adjustable height bed or overhang section which keeps everything stiff for the majority of the time, but when you need to use the router on something large you can?
• How are you going to assemble the Z axis? Look through the design, building it up step by step, and imaging when you will or won't have access to each screw and what that implies. I've got my ballscrew and motor on the fixed bit because I can easily get to the four screws holding the ballnut onto the Z plate, undo them, then slide off the rails. Your design looks a little harder to physically assemble.
• The C beam - how are you going to attach those profiles to each other? Any weakness here will be quite problematic and you've got two joints which need to be constrained.
• 10mm of steel looks quite beefy for a side plate, but 3mm seems quite weak in my head. I realise its intentional, I'm just not convinced!

[Chrono]

A few comments I would have from your last set of design drawings are:
- whilst 4 rails looks like a good idea, you will have a devil of a time aligning them I expect. Maybe 2 rails of a larger size might be better?

Also, on the four rails idea, I think you'll definitely end up spending a few days becoming best mates with your dial gauge - but it could pay off in the end?

It seems I have messed up my explanation here. I do not plan on using four rails, but instead three. Two linear HIWIN-style rails on one side, mounted atop each other. The other side only has one rail, and a different type, namely the cylindrical Igus-Style rails that you also often find in 3D printers, like the Prusa MK3. That will still take some work aligning, I get that, but it should technically work to help let the machine compensate. I know, technically is a nice word, but practically often takes precedent :D I have added another picture, with the HIWIN rails in their place, to hopefully make that more clear.

[*] 10mm of steel looks quite beefy for a side plate, but 3mm seems quite weak in my head. I realise its intentional, I'm just not convinced!

This one's along the same vein, and it honestly also seems off in my head, but the math should check out there. Ultimately, the sideplates don't cost much to make, especially not the smaller one on the left, so if it turns out to be a problem, I can change it around without much of a problem.

First impressions on the redesign; I think your CAD is coming along nicely, really shows. I do have a few concerns though:
[LIST][*] I question the Z axis travel length and why the plate is so large - Don't forget you'll have a bit attached to the end of your spindle, and its going to have to be quite a long bit to make use of your Z travel. I've got 18cm, and honestly, its probably far too much, most of the time you're really only needing to cut say 18mm plywood! The distance between the bed and the gantry looks huge - All that Z extension reduces the rigidity of the machine. Have a think about what you really need - can it be acomplished in other ways, such as an adjustable height bed or overhang section which keeps everything stiff for the majority of the time, but when you need to use the router on something large you can?

Something like that came up when talking to my colleagues as well, today. We came up with inserting angles to hold up the sides, which could be removed if needed, but when there, would make it a bit stiffer. I really quickly added one in the picture above, highlighted in pink. Imagine four of those in the corners.
Could you maybe elaborate on how an adjustable Height bed and that "overhang" would work? I have a hard time imagining those two.

[*] How are you going to assemble the Z axis? Look through the design, building it up step by step, and imaging when you will or won't have access to each screw and what that implies. I've got my ballscrew and motor on the fixed bit because I can easily get to the four screws holding the ballnut onto the Z plate, undo them, then slide off the rails. Your design looks a little harder to physically assemble.

Good shout! On the first look, I should be able to do a similar thing, but with removing the screws of the Z-Ballscrew Bearing Blocks instead, but I will definitely check that again.

[*] The C beam - how are you going to attach those profiles to each other? Any weakness here will be quite problematic and you've got two joints which need to be constrained.

I have enough space between the screw and the profiles, to be able to insert some angles to bolt them together (that is going to be some fun fiddling with angled hex drivers, however :D) and I can also bolt them together on the back side as well. With the sled in front, forming a closed frame and additional bolts in the side-plates, that should be enough then, right?

- Also consider the CS-Labs kit for the controller - many on here use them, including the venerable JazzCNC (which is always a good sign imho)

I second Washout's comments about the CS labs stuff, looks brilliant. The thing that put me off was that the base model is only 4-axis, and it doesn't handle slave axis homing native-ly (although there are decent workarounds posted on here). Anything more than the base model is horrendously expensive, and I wanted future expand-ability to add a 4th axis which is gone if you use the 4th for a slave - but you avoid both of those issues by having a connecting belt and single motor.

With that much of a recommendation, I will definitely take another look. But I must admit, the price of the units, especially compared to the other controllers is quite steep. I might just stick with one of the cheaper ones and maybe upgrade later on. I am managing to stick within my initially laid out budget for now, but I want to also reserve a buffer in that, so that a problem won't throw me off course completely.

- Proximity switches if they are the type in a threaded housing, will give a nice amount of adjustment for the trigger point - you can do the same with micro-switches, but they then need a plate with slots to mount them to to achieve that

Yeah, that was my thought. My 3D printer uses a proximity switch for leveling, and needs exactly that adjustment, which also means that it can be calibrated pretty finely.

I'm still aware I haven't gone through your calcs yet... Finding time is hard! Sounds like with the design changes though I may wait a little longer :)

Don't worry, no rush :D I am pretty sure I have suitable Y- and Z- Motors, but the X-Stepper is what I am still fiddling with the spreadsheet for. My main problem is how to calculate the thing driving two ballscrews at the same time. I just added a multiplication by 2 in the part of the equation that contains the Screw Inertia.

[Chrono]

While I am busy getting all the detail into the CAD and making sure all the dimensions are correct, a question came up, that I want to ask the collective of experience in this forum.

This question is, if I can use the chinese linear rails (like these), or if there are any known problems with their accuracy or surface finish that makes them bad alternatives? I am asking this, because of just how much cheaper they are to get. Same question goes for the ballscrews.

[MartinS]

Hi Chrono

It seems I have messed up my explanation here. I do not plan on using four rails, but instead three. Two linear HIWIN-style rails on one side, mounted atop each other. The other side only has one rail, and a different type, namely the cylindrical Igus-Style rails that you also often find in 3D printers, like the Prusa MK3. That will still take some work aligning, I get that, but it should technically work to help let the machine compensate. I know, technically is a nice word, but practically often takes precedent :D I have added another picture, with the HIWIN rails in their place, to hopefully make that more clear.

When I first saw this design, I couldn't help but think that was far, far too flimsy

Now with your explanation of the gantry driven from one side only (above)......it's getting worse!

Don't forget that to reduce cutter breakage, wear, chipping, improve accuracy and surface finish, the whole machine must be as rigid as possible and subject to as little resonance and vibration as possible. This is why machines traditionally are made in cast iron or synthetic granite (Granitan etc) that are "dead" materials, they don't "ring".

In the latest design, you are driving the gantry from one end only (and I still can't understand what the benefit is of the lower ballscrew). This goes against evrything that you will read on this forum, "ballance your forces", " place the cutter forces in between the bearings" etc. It is akin to digging a hole in the garden whilst standing on a diving springboard!

And the 6mm thick gantry sideplate.......

Compare yours



with this from Boyan.



Yup, Boyan's is built like a brick sh!thouse. Some may say that it's over the top, but I bet it does the job!

Or just taks a look at Andy's build

http://www.mycncuk.com/threads/11552...-2x1-0m-Gantry

Sorry if I seem somewhat hard on you but I don't want you to waste time and money unnecessarily.

Any other of you forum guys have a comment?

Good luck Chrono, you'll get there.

Martin