Arvid's first CNC machine!

[arvidb]

I'm beginning to think I've gotten far enough on the planning to actually start building!

However, I think it is really ugly! Or perhaps it's only because my CAD program doesn't do perspective transforms properly? Or something? *LOL*

So please comment the overall design, it'll soon be too late to change.

Arvid

[arvidb]

From the front with the Z axis lowered:

[arvidb]

Close-up on the Z axis with the front plate removed. Not much space left here! Maybe I should have chosen smaller components (THK/ballscrews) to make things less clumsy?

Arvid

[Hobbiest]

I think it looks really good Arvid. Don't hink the horizontal parts of the table frame need to be so tall, but then that may be from your software like you said. Start building it!

[arvidb]

Hobbiest,

Thanks for the encouragement!

But what do you think about this alternate design? (Idea from Pistachio's machine, http://www.cnczone.com/showthread.php?threadid=3211).

Arvid

[Hobbiest]

One thing that I liked about your origional design, was that the carriage actually moves past the edge of the uprights. This is handy, in that it keeps the table size closer to the width of most of the machine. That is one thing that I think makes Cranky's designs look even smaller. I also like the stiffeners on the gantry uprights. I like the table height better on the second design. Overall it does look cleaner. I would rather build something that looks like a Sherman though, instead of a Miata, if that means that the tank will be better engineered. The extra mass, etc. all makes the product nicer.

[arvidb]

Hobbiest,

thanks for the really good input! I'm happy you identified my thoughts with the first design (less floor space and rigidity).

But since I first came up with the original design, after reading lots of the threads here, I have realised two drawbacks:

1) Dust. It would end up everywhere. In the second design it has a natural "sand box" to fill first.

2) Enclosure. It would be a lot easier to build a sound dampening enclosure for the second design.

It wouldn't be very difficult at all to add stiffeners to the gantry uprights on the second design, either. I could even cut them on the machine!

I'll have to think some more about this, but right now I'm leaning towards the second design. Strange, just a few hours ago I was convinced I would build according to my first idea. See what happens when you spend too much time here at CNCzone

Arvid

[Hobbiest]

Is a "natural sand box" really something desireable? Seems to me that any dust would best be kept away from the machine.

[arvidb]

*aahrg* I just paid $395 for 3 servo drivers for my nice 3-ph servos. They are very professional and all, and doesn't even require a power supply (they are just hooked up to the mains)...

BUT I'm not completely sure they'll work with my motors! And I don't have a clue where to get the correct motors for them if the ones I've got doesn't work

So I'm really nervous here. Hopefully they'll be here in a week or so...


Hobbiest,

I've thought about the "sand box" (chip box?) issue, and I think I would prefer to have the chips stay in the box below the machine, than going everywhere. I have very limited space and it won't be a dedicated machining room. I will have to make sure to clean it between uses though...


Arvid

[mhackney]

arvidb and hobbiest - the sandbox idea is fine if you hook up a vacuum system to remove the collected dust/chips. That is one of the first steps in outfitting a woodworking tool like a table saw for dust collection - enclose the cutting area and provide a "trap" (aka sandbox) for the dust chips to accumulate and be sucked out.

[Graham S]

What made you go for 3 phase servos? Given the cost of geckdrives and DC servos and the fact that you don't have to buy expensive motion control cards or develope your own control system it seems a difficult way to do things. I hope you can get it working, it will be awesome when it does!

Graham

[balsaman]

If you think your design is ugly one thing that can be done is to taper the 4 upright supports towards the top (half as wide at the top and just a little wider at the bottom?), and maybe even eliminate the ones at the back... I think that will change the look a bit and it will still be rigid. Try it and have a look.

Eric

[arvidb]

Originally posted by Graham S
What made you go for 3 phase servos? Given the cost of geckdrives and DC servos and the fact that you don't have to buy expensive motion control cards or develope your own control system it seems a difficult way to do things. I hope you can get it working, it will be awesome when it does!

Graham

Heh, maybe I just like to make things difficult for myself?

Actually, I think when I started looking around for servos (that was before I found this excellent board), most of the info I found was about industry servo systems (I searched google). I didn't know about the geckos, xylotex or rutex drivers.

And when I found a guy that was actually selling these nice used motors and drivers at a very reasonable price ($40 for the motors and $80 for the drives) there was really no question about it.

Later, when it turned out the drivers he sold were actually not dismantled from the same machines as the motors, and did not work with the motors ($80 + $30 shipping down the drain - or maybe not completely, he might compensate me somehow)... well, it was only after that I began to wonder if I had made the right decision. 'Cause by then I had found this place and learnt about the availability of DC servos.

But I don't know... even if it turns out these new drivers won't work, I'm still reluctant to switch to DC servos. I think I'm a bit of a perfectionist when it comes to ... I don't know; sleekness and simplicity, beauty of physical systems. The 3-ph servos are simply a so much better mechanical device than the DC servo, and it would bug me to change them out.

Have you compared the construction and specs of 3-ph and DC servos? 3-ph servos have the windings in the stator, and suddenly you don't have to rely on air flow (which is *very* inefficient compared to conduction through metal) though the motor to cool them. The motor can be sealed; no need for air holes that let dust and chips in. There's also no windings in the rotor, so lower moment of inertia and a smaller motor too. No brushes, which means no brush wear, and an electrically much more quiet motor.

It would be a very fun project to DIY a 3-ph servo driver. But it's a big project, and I already have too many unfinished projects running... two of them actually needing the router for their completion . But perhaps I'd go that way, instead of chosing DC servos. I'm a very stubborn person .

Arvid

[arvidb]

Originally posted by balsaman
If you think your design is ugly one thing that can be done is to taper the 4 upright supports towards the top (half as wide at the top and just a little wider at the bottom?), and maybe even eliminate the ones at the back... I think that will change the look a bit and it will still be rigid. Try it and have a look.

Eric

Ok, I tried it, and it did make the machine look better, especially removing the supports at the back (tapering while retaining the back supports made it look *really* weird ). There's not much space available for tapering though, and I will have to figure out a new way to mount the Y axis motor if I don't have the back supports.

I'm still leaning towards the "new" design since it allows me to easily enclose the machine and collect (at least some of) the dust.

Arvid

[Hobbiest]

Will you have to build a phase converter for you industrial strength servos?

[arvidb]

Hobbiest,

I'm not sure what a phase converter is?

The motors are 3-ph, and to drive them the 1-ph 50 Hz mains will have to be "converted" into 3 variable frequency and current controlled phases. This is done with a servo driver (like a Gecko, but for 3-ph motors). Is this what you mean by a phase converter?

I have bought three servo drivers (or Servopacks as the manufacturer Yaskawa calls them). They are on the way, but delivery seems to have been delayed now over the easter holiday :-/ I hope to get them within a few days.

Arvid

[arvidb]

*long sigh of relief...*

the Servopacks seems to work just fine with my motor, even though they are different type (200W motor and 400W drive). I'll just have to limit the current accordingly... I hope. Still not sure they won't fault out once I put a load on the motor, but why be pessimistic?

If this actually turns out OK, I think it's really great:

$330 + $65 S/H for 3 servo drivers, including built-in power supply
$120 + $100 S/H for 3 servo motors with 2048 pulses/rev differential encoders

= $615 for a complete 3-axis 200W servo system with analogue speed input (+/-10V) and scalable (1-4096 counts/rev settable in driver) quadrature output.

I will need hardware for the position loop (to convert parallell port step/dir to +/-10V speed signals), but I think I can build that myself. It would be lots of fun!

*whew* - it's been a nightmare laying out all that money without knowing if it would work though. But worth it now

Arvid

[Hobbiest]

I was being funny about the phase converter. A phase converter is used to run 3 phase equipment (lathe, mill, etc.) with a single phase circuit.

[arvidb]

Okay, maybe it's time for an explanation... I'm aware that I don't *need* all these fancy things... like 3 ph servos, THK linear guides etc. I will never be able to build a machine that comes close to their tolerances anyway.

I put down all this effort simply because I think it's fun. I like these nice components, and they will make me happier just by the way they look and the fact that they could have been sitting in a $50,000 machine. Even if they don't make my machine better than it had been with DC servos and skate bearings on supported shaft.

And all that math is also because I'm fascinated by it; this is a perfect opportunity to actually test how well all that one has learnt in school actually fit in the real world - and I believe it's a useful tool that answers a lot of questions.

I'm not trying to show off here (well, not more than anybody else ). We all think CNC machines are cool, right?


Arvid

[arvidb]

... and to more directly answer your phase converter question: they may be industrial quality, but they are not very large. The mains 230V @ 10A should be plenty for 3 axes (axises? )

Arvid