8x4 Build based on plans by Joescnc Hybrid R&P

[GrahamWhite]

So I'm looking at motor/driver choices and yes while i'm after advice can I ask that you switch off the 'best possible solution 'head and use the 'I expect that will be suitable' head!
This is a kit for nema 23 4Nm with 48 psu instead of the 36v they offer with other kits.
https://www.cnc4you.co.uk/CNC-Kits/P...4-Axis-Nema-23
I know I will need screened cables as well but is there anything glaringly obvious missing?
Sorry if it seems like i'm doing it all wrong but I'm loving my build so far as it's starting to take some shape :)

[driftspin]

So I'm looking at motor/driver choices and yes while i'm after advice can I ask that you switch off the 'best possible solution 'head and use the 'I expect that will be suitable' head!
This is a kit for nema 23 4Nm with 48 psu instead of the 36v they offer with other kits.
https://www.cnc4you.co.uk/CNC-Kits/P...4-Axis-Nema-23
I know I will need screened cables as well but is there anything glaringly obvious missing?
Sorry if it seems like i'm doing it all wrong but I'm loving my build so far as it's starting to take some shape :)

Hi

Graham White

People here like to go for 68v diy psu and 80volt digital drivers.

And you can too, for about the same price.


Grtz Bert.

Verstuurd vanaf mijn SM-A320FL met Tapatalk

[JAZZCNC]

Sorry if it seems like i'm doing it all wrong but I'm loving my build so far as it's starting to take some shape :)

Your loving it now but you won't be if you keep ignoring advise cutting corners trying to save a few extra pounds. It's very easy to spoil a machine when just few £100 more would make a great machine and unfortunatly you only realise this after the money is spent.!

I won't give Bum advise so I'm not giving you a "just good enough" solution but will give you solution that is what's required for good machine.

Because your using R&P which is only 50-60% efficient compared to ball screws which are 90-95% couple this with linear rail system that's is even less efficient then you'll need extra power to deal with lower efficiency. Also because you'll be using ratio 3:1 then you'll want motors which spin little faster but still have torque higher up the RPM range and 50V drives with 48Vdc won't provide enough power. (Also 48V is too close to the Drives 50Vdc max so you risk blowing drives up)

Ideally, with R&P setup, esp one that isn't very efficient then you'd run Nema 34 motors with Mains voltage or higher Dc voltages around 100Vdc.
So if you must use Nema 23 motors then you want to be running them around 70Vdc with 80Vdc drives.
Also you want Unregulated PSU not Regulated Switch mode supply. Reason for this is that under de-acceleration the motors become dynamo's and dump the power back to the drives which then dump this back to the PSU (Back EMF) and if the PSU as protections built into it then will shut down which is bad news.
On Small slower machine with light gantrys then can sometimes get away with this but on large machines with heavy gantry traveling at higher feeds whcih routers tend to do then it will become a problem.
The PSU you want is Unregulated toroidal PSU which use capacitors that store energy and absorb any Back EMF. These are actually very easy to make and will work out cheaper than buying a large PSU, it also means you can tailor Voltage and Amps to your exact needs.

So the setup I suggest with nema 23 motors is this.
4Nm motors
80Vdc Digital drives running motors at 68-70Vdc.
Toroidal PSU transformer spec'd to output 68-70Vdc

With Nema 34 Motors:
4.5Nm Nema34
80Vac (100Vdc) Drives
Toroidal PSU transformer spec'd to output required.

Stay away from kits they are always compromised in some way.

[GrahamWhite]

Appreciate the info:)
I can understand all you have said and will take it on board and not order the kit :)
so the steppers are fine ,will have to go with the 4Nm 23's as the mounting holes are already drilled.
An 80vdc board
https://www.cnc4you.co.uk/Microstepp...r-60VAC-CWD872
I have no clue on building a toroidal PSU!! lol so would need a touch of help there!

[Clive S]

I have no clue on building a toroidal PSU!! lol so would need a touch of help there!

Look at these two vids.

https://www.youtube.com/watch?v=4OoQ...zD30sZjtp_VyqY

Rapidonline https://www.rapidonline.com/ is a quick and simple place to buy the bits.

[JAZZCNC]

Appreciate the info:)
I can understand all you have said and will take it on board and not order the kit :)
so the steppers are fine ,will have to go with the 4Nm 23's as the mounting holes are already drilled.
An 80vdc board
https://www.cnc4you.co.uk/Microstepp...r-60VAC-CWD872
I have no clue on building a toroidal PSU!! lol so would need a touch of help there!

Yes, I had a feeling you were stuck with 23's hence why didn't push 34's which would be the better option.

Regards the Drives and PSU then those you linked can use AC so all you would need is Transformer the drives will do the AC/DC conversion so don't need Caps and Bridge rectifier. However I prefer to use DC supply as I feel it takes some of the stress off the drives and can have little bit more smoothing.
This will work for you either way. Just add Caps and Bridge rectifier if want to go with DC.

https://www.rapidonline.com/vigortro...-x-25v-88-0012

[GrahamWhite]

So this is the progress so far

The Y axis to X are not finished yet, still have more support for the gantry to be fitted.
The plans called for ACME lead screw on the Z but after hunting for the elusive 1/2"-8 2 start bar across the planet, I gave up and bought a ball screw 16mm 05 lead off of ebay with the mounts and coupler.
I'm hoping they are similar - the acme was a 1/4" lead per turn where as the ball screw is 5mm - not sure how that will affect the Z performance at all?
I will be running the 4Nm 23 motors at 68-70vdc as Jazzcnc suggested so there should be enough extra oomph I hope to compensate for the Z?
Now onto a redesign of my Z to allow for the ball screw mounts

[Clive S]

I'm hoping they are similar - the acme was a 1/4" lead per turn where as the ball screw is 5mm - not sure how that will affect the Z performance at all?

The ball screw is far superior than the acme. With the ball screw I would go with nema 23 3.1Nm

[JAZZCNC]

The difference in screw pitch will mean very little performance difference. The difference in efficiency, however, will be a lot better.

Now your not going to like this next bit but it's in your interest it's said.!
The Z axis is THE most important part of the machine so whether Acme or Ballscrew won't make a jot of difference because of the weak nature of this Z-axis design. Those V bearings are simply not good enough for Z axis and this design will be massive weak link. It would be wise choice if you changed the design and invested in some profiled linear bearings.

[GrahamWhite]

Yes I have to agree with you:( lol
although it's not so much of a problem now that I have to modify it for the ballscrew anyway.
I'll probably do a quick fix for the vee bearings to make sure on clearances and then the first decent mod. i'll redo the Z.
Would supported round rail be an option over the vee bearings?
-------------
I've gone for SBR16 rail- looking at a few z axis they seem to be built with the idea I have in mind
Also got the 84mm long bearings so plenty of stability I hope
All mounted on 19mmx 90mm 6062 ali plate with 6" piece crossways for the spindle mount
This option works with the X axis as I have bearings studs through the front face so hopefully I can make it work