I am going to build a CNC machine, What do I buy?

[northwest]

I have spent a good few hours now looking at all the options and permutations. It appears to me that the Leadshine EM542S drivers appear to be the ones for me to go for. The only snag, as always is the £65 each cost as I need four of them! So another £260. Deffo starting to add up, if anyone can find these for less than £65 I would be grateful.

From everything I have read including @m_c comments regarding digital drivers this seems to be the best option. The other option of a toroidal transformer, bridge rectifier and capacitor I am not sure about, though it would probably work out £200+ cheaper. Maybe if someone could tell me exactly what I need I could maybe try that first?

 

[Hood]

I had a toroidal for sale here a while back but it never sold, can't recall if I still have it or not but will look. The voltage may not be suitable as I had it for an 80v supply but that would be in series so possibly it would be suitable in parallel for 40v, will look in a bit.
Oh I may also have a suitable capacitor, again I will look but not promising I still have them.

 

[northwest]

@Hood very kind of you and just have a look when you get a chance. I am going to go get myself a cabinet now though(tomorrow) as I know where there is a garage full:-)

 

[Hood]

Afraid I don't seem to have the toroidal, have a funny feeling some monkey down in snack beard land got it from me, maybe @eSCHEn can confirm.

I do have a couple of caps but I think only one would be suitable as the other is, looking at the code, just 25v where the other is 50v.

 

[northwest]

That's handy, I already have a bridge rectifier which is suitable (I think) so two thirds the way there. Going to need some connectors a distributor blocks for Din rail next but I think I might have a lead on some of those bits very local to me.

 

[m_c]

EM drives are good. Just make sure to source them from a reputable supplier, as fakes do exist :/
The differential inputs will work well the IP/M.

For a 25V transformer, RS part no 671-9148 is 21.39+vat for a 120VA, or a 160V can be had for 27.72+ and part no is 671-9025.
Airlink transformers have them slightly cheaper, but cheapest overall will depend on postage (if you have an account with RS, you get free delivery).

With EM542 drives, you could possibly get away with a 30VAC secondary, but you'd have to build it and check how high the DC voltage is. Theoretically it would give you about 41-42VDC, but by the time you factor in mains voltage fluctuations (you need to add about 9% for the upper UK voltage limit above the rated 230V), and load regulation of the transformer it may be closer to 50V than you'd like. To give a number RS list 32.57VAC off load for their 160VA 30V, which works out at 46VDC, but add 9% and you're at 50.2V. You can take off a volt or so to allow for voltage drop over the bridge rectifier, but you're still too close to 50V for comfort.

For connecting the stepper drivers, use the capacitor terminals as a star point to connect them to individually.
You don't fuse stepper drivers. Due to the switching nature of steppers, they dump power back into the supply during deceleration, so if they become disconnected, they're likely to go overvoltage on their power side and self destruct. You want as few connections as possible between them and the capacitor, and you don't daisy chain between drivers. Wire it up so you only ever switch the primary/230V side of the transformer.
You just want to ensure the transformer is protected with a suitably sized time delay/anti-surge fuse (toroidals have a big switch on surge).

 

[MCKDAVID]

@Hood very kind of you and just have a look when you get a chance. I am going to go get myself a cabinet now though(tomorrow) as I know where there is a garage full:-)

do tell..... always good to know of such aladins caves.... I'm looking for another 600x 600 (or thereabouts) if you happen to find one too many hahahha..

 

[eSCHEn]

Afraid I don't seem to have the toroidal, have a funny feeling some monkey down in snack beard land got it from me, maybe @eSCHEn can confirm.

Not me moon pie, I did take your old 3~ inverter and two dead servos to strip if that's what you're thinking of? The only toroidal I have here is a 5 x 12V or something so not going to be much cop due to the low output.

 

[Hood]

Ok, thought maybe in with the ballscrews. So unless it went to @MCKDAVID with the breakout bards etc then I must still have it. Will look again tonight.

 

[MCKDAVID]

sorry mate, didn't come with the boards, that's for sure....

 

[Hood]

No probs, must still have it somewhere then.

 

[MCKDAVID]

go look for something else, it'll fall off the shelf then.... at least that's how I find things here......

 

[Hood]

go look for something else, it'll fall off the shelf then.... at least that's how I find things here......

Shelf? What is this shelf you talk about? Is it similar to the floor?

 

[northwest]

Right, this is the Z axis servo, it was as originally fitted to the lathe. What I would like to know is, should I replace it for something a bit more "modern"?



If so, what? the hole centres are 70mm

So, having looked at the different specs this is NEMA 34 size. Would it make a difference playing Mix N Match? Handy the extra power on the Z though.

 

[eSCHEn]

Hole centres of 70mm should make it NEMA34 IIRC.

 

[northwest]

Hole centres of 70mm should make it NEMA34 IIRC.

Yes you are right. Might pay me to put a modern good quality NEMA34 motor in there. Probably need a single bigger driver though, which isn't the end of the world. But then I might be overthinking the whole project.

 

[m_c]

A more modern stepper would give a bit better performance, but the issue with Nema34, is you really need high voltage drives to make the most of them.
However on the Z, unless you're planning on plunging lots of drills through material, lower speeds aren't going to be as noticeable as slow X/Y axes.

Unless you really want to swap it out now, I'd run it as is and see how you get on with it.

 

[northwest]

Unless you really want to swap it out now, I'd run it as is and see how you get on with it.

You are right of course, i am overthinking it.

 

[MCKDAVID]

........Unless you really want to swap it out now, I'd run it as is and see how you get on with it.

exactly, agree entirely see how it works first, then upgrade later, one less thing to think about / pay for at the beginning....

 

[northwest]

Well, the controller breakout board magic thingy has arrived.Paid for Monday, arrived this afternoon. From Poland:



Very nicely packaged and presented.
All I need to do now is work out which drivers to buy, still not decided.