Starting to design out my build, looking for critique

[Chrono]

That cleared things up a lot, thanks! I gotta admit, for a second there I thought the aluminium profile construction was "out of the question" entirely, so to speak, so I am relieved on that end

I also thought about putting in some more support pillars, so I will do that. They are so short anyways, that they don't cost enough to not put in. regarding a crossbar, I could easily put one in in the back, without even impeding X travel, since the gantry's body will sit on top of it, and it will run out of rails before the spindle would even get a chance of touching it.

You also put in angles in the middle pillars. I definitely see their point, but I am looking at them protruding into the machining area, so I might try and make them removable, with accessible screws, so I can put them there for smaller projects, and take them off, when I need the space. That way I get the best of both worlds, so to speak.

Also, regarding the distance between the bearing blocks on the X: That is one of the parameters I can just change on-the-fly, so changing that is easy-as-can-be :D I am mostly leaving it as a kind of place-holder while I am working on getting everything into place. Afterwards I just need to open the variables panel, and go to town dialing everything in.

Finally, on the topic of the thin plate, and the associated double-stack of rails, with one opposite linear rod bearing: It is not that much about building tolerances (I mean I am not perfect, so there will be those), but also things like thermal expansion, and so on. I am going off of the one lecture in mechanical engineering I got in my electrical engineering course, but with the linear rails on both sides, you would enter statically-overconstrained territory, which is exactly the reason for me to go for the steel rod and linear bearings, exactly because they cannot take on torque. however, if this ends up not panning out, changing the lower rail over, would be quite easy, since all i would have to do is cut down the gantry extrusions by 7mm (which the linear bearings are higher by, compared to the rails and bearing blocks), or shim it with another plate, and swap in one of the rails, not a big hassle.

And I found a picture of the Zeiss machine I was talking about:

As you can see, it has a similar design, with rails on existing on the right, while the left either rolls on the table or hovers on it, I cannot remember if the hovering was another machine, though, and a quick search did not throw up any info. Either way, looking at the YZ-Plane, one end is fixed, while the other is allowed to expand/move. Of course, that does not mean that it works the same for me, but I thought I would post that for illustratory purposes :)

I also plan to add some slits in the plates themselves, serving as holes for potential cross-supports, should it turn out that they are, indeed, too bendy. I will attach a picture hereafter, looking at the right plate, with such a support in vibrant pink. I am afraid that picture can explain this much faster than I could in words. Those plates should serve to add further rigidity, in the same sense as the bends all around the Z-Axis do, and if I find I need them, I can put them in, weld them in place, and go from there.



(also seen in the picture, in the front left of the machine, the WIP of new angle plates. The right is not in yet, because I still need to move the right ballscrew vertically in between the two rails)

What do you think of those measures to address these problems? Is there anything else I should be doing to increase the rigidity?

[MartinS]

You're planning to beef up the side rails, add the bed whilst you're at it.

Much advice has already been given to you and there is sooo much more on this site from some VERY talented, knowledgeable and experienced people :

http://www.mycncuk.com/forums/253-DIY-Router-Build-Logs

Don't get too hung up on the design of CMM's.

Time you put a new blade in your hacksaw!

[Chrono]

You're planning to beef up the side rails, add the bed whilst you're at it.

Much advice has already been given to you and there is sooo much more on this site from some VERY talented, knowledgeable and experienced people :

http://www.mycncuk.com/forums/253-DIY-Router-Build-Logs

Don't get too hung up on the design of CMM's.

Time you put a new blade in your hacksaw!

I have to completely agree, without all the advice from the people here I would not even have remotely come this far!

Currently I am reading through some of those build logs to hopefully find a good one about the PSU section of the build. All the electronics are pretty clear to me, but the interface between machine voltage and net voltage. I see that a lot of people build their own transformers, which is definitely an option, but I am still looking into that. Most of what I am still missing on the machine side mostly related to the spindles and which I want to have in hand, before commiting there.

If all goes to plan, I thus want to sort out the electronics over the next two weeks and then move on to buying parts. That is when I want to make a final pass and move on to the next step, if there is not a flaw that needs sorting out. Once I do move on to buying, I will probably make a proper build-log post as well.

I am also scouring the posts for something related to cutting forces and speeds, to be able to dimension the steppers. As far as I could gather from various posts here, I would pretty much always like to use the steppers in bipolar parallel connection, and using that, getting all the info and all the steppers I can find, I have not found a single one, so far, capable of driving two 2510 ballscrews at 7.5mm/s rapids... who would have thought? :D So I am thinking about moving to a one-stepper-per-screw setup. With that, however, I am still looking at one of AndyUK's first pieces of advice to me and hesitating. So I am thinking about putting a timing belt between the two motors to synchronize them as well, but I don't know if that is a good idea or if it even works. Looking at the motor calc sheet, however, there is a motor that would permit me to get 6.1m/s rapids with only a single motor, as well as letting me cut at 2.1m/s with 50N of cutting forces. But then again, I am still searching for posts on speeds to look out for.

[Chrono]

Long time no post, was busy these last couple weeks, but I am finalizing the build. Pretty much everything is done, except for the timing belts and the electronics layout.

I solved my motor problem by simply shrinking the machine to a tiny 1.8m on the X-axis. This allows the use of the smaller 2010 ballscrews, and, in turn, a single motor.

Other than that, I have been verifying dimensions and hole placements and been putting in manufacturer CAD files for all the rails and screws. I have been putting together some angles for the inside (the yellow one in the left side of the machine in the picture) that I can remove if I need the width and otherwise keep in. Since the CAD file already takes ages to change anything in, I only put in one, to keep the computation time down a bit, but the plan is to have two per column.

I guess I only have 4 questions left:
1. I have seen that people usually use transformers for their steppers, and I understand that that is because regulated PSUs may have problems with the current spikes (at least according to the app notes). I could not find a proper post on how to do it on here though, so If anyone has a good source on that, that would be perfect.
2. How do people usually tension their belts? I am still trying to figure out where to place my tensioners.
3. Where do you even get belt long enough for something like this, and what type of Belt? Using a manufacturerer's tools, I have been able to calculate that my belt would be approximately 4.8m long, for the X-Axis. I have not found closed-loop belt in that size yet.
4. Is there anything you would still change in the design? When I say finalizing, I mean that I am compiling prices and sources for my parts, and ready to pull the trigger whenever I am done and move this over to the build-log section, so this is the "final chance" to change anything, so to speak.


As always, here is a web browser accessible version of the model if you want a more detailed look.

[AndyUK]

1. I have seen that people usually use transformers for their steppers, and I understand that that is because regulated PSUs may have problems with the current spikes (at least according to the app notes). I could not find a proper post on how to do it on here though, so If anyone has a good source on that, that would be perfect.

My build thread, post number 30 has an outline of the process I followed, but I emplore you to find multiple independent sources of information and fully understand and verify before playing with a mains level PSU - this is the scary bit of the project to me, because one slip can potentially kill. Always ensure the caps discharge and never work near the PSU whilst alone in the room. I've have given the wife very clear instructions on how to isolate the supplies if it goes wrong. ALWAYS have a bleed resistor - it's not something I mentioned in my thread, but it's a must.

Scary bit over, it's not that hard or expensive. You just need to stay safe.

As for information, I didn't find a definite thread here, probably for good reasons. You're going to have to go research the theory of unregulated PSUs. Joe's videos are also quite good at explaining, and so are ThisOldTony's CNC build videos.



Sent from my SM-G950F using Tapatalk

[Kitwn]

There's a nice guide to designing linear power suplies here http://www.skillbank.co.uk/psu/

Whilst it's true a linear supply of a given rating can deliver significantly higher current peaks than a switch-mode supply of the same rating, you should look at the relative cost of a linear design and a suitably rated switching supply or possibly two separate supplies, one for, say, two motors on X and one for the single motors on each of Y and Z.

I can't see the point of spending a lot of time and money on building an unregulated power supply which can, even briefly, deliver far more current than is required to saturate the motors. The available current in case of a fault would also be much higher.

Kit

[Clive S]

Have you seen Joe Harris build log here is a link to his youtube channel on power supplies https://www.youtube.com/watch?v=4OoQ...Y&index=2&t=0s