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

[JAZZCNC]

Suggest you don't use the Relay on BOB and save for something else. Instead, use the Relay built into the VFD.
Reason to not use it is to keep potential Noise away from the BOB where it's more vulnerable to interference.

[GrahamWhite]

I spoke to cnc4you today and they suggested for rack and pinion instead of running nema23's 4Nm with 3:1 reduction I could have just gone with 34's at 8.7Nm and run them direct or fit a larger pinion for slower speed??? would that be the same?

[JAZZCNC]

I spoke to cnc4you today and they suggested for rack and pinion instead of running nema23's 4Nm with 3:1 reduction I could have just gone with 34's at 8.7Nm and run them direct or fit a larger pinion for slower speed??? would that be the same?

Bad advise for several reasons and just shows how little experience CNC4YOU have.!
#1 The resonance directly on the motors will play havoc with the drives causing rough running. It will also Kill the motor bearings quick time.
#2 Bigger pinion will make go faster not slower.
#3 Bigger pinion will reduce resolution.

The reason for the ratio is two-fold.
#1 To increase resolution. Even a small pinion of say 15T (Mod1) will have a pitch of 47mm which is too high and will give a low resolution. It will go like the clappers but resolution or in simpler terms Smoothness will be rubbish and this shows in the cut. You want to aim for pitch between 10mm-20mm Max.
The CnC-router parts pinion I believe is 1" or if Mod 1 will be 25T which will give pitch of roughly 78.5mm with 3:1 ratio this brings down to 26mm which is still little high for me if want to do very detailed work.

#2 It increases the motor torque which is required to overcome the inefficiency of R&P.

Also, the belts help lower Resonance which affects motor/drive performance. DONT under estimate Resonance because it will and DOES cripple machines performance. This is why you'll often see recommend Digital drives because they handle Res so much better, but still they have limits and Direct driving R&P off the motor would challenge them and your abilty to tune the resonance out.

Edit: Just to go little further on why direct drive is bad idea and pinion sizes etc.
When using a machine it's important that you spec your components so that you have best performance while cutting. One important consideration with stepper based machine is that you aim to be cutting in the motors RPM range which gives best performace while cutting.

So if you have direct drive with big pinion and say your feed is low becasue say doing 3D work, then your problems start to multiply because now your motors are hardly turning. This scenario puts the motors/drives in place which isn't always good.!
Yes torque will be higher but do really need it while going slow.? However motor smoothness will suffer and this will often show in the finished cut which very much matters on say 3D work. OR affect the drives thru resonance causing rough running and others problems.

Hope this helps.

[GrahamWhite]

Ok Thanks ,so I have gone the sort of correct ish route!

[GrahamWhite]

I'm finally looking at the motors and drivers and found this place -omc-stepperonline.com
in particular this driver
https://www.omc-stepperonline.com/st...or-dm860t.html
is that pretty much the same as the cnc4you one?
https://www.cnc4you.co.uk/Stepper-Mo...r-60VAC-CWD872
The stepperonline place don't do the 4Nm stepper though but they do have a 3Nm that pulls 4.2a as well as a 3Nm pulling 3.2a
They have nema 24 @4Nm would they fit my pinion plates ?
---
read more so the 24's will fit ,they have the same mount hole spacing within .1mm
Agghhh - I know I need a Bob as well-one full of connectors or just a basic one, I have ordered a UC300eth for connecting to my pc so need 5v to power that- it that then an extra psu I need or can I pickup 5v from somewhere!

[JAZZCNC]

I'm finally looking at the motors and drivers and found this place -omc-stepperonline.com
in particular this driver
https://www.omc-stepperonline.com/st...or-dm860t.html
is that pretty much the same as the cnc4you one?

Yep pretty much and will work fine for your needs.

The stepperonline place don't do the 4Nm stepper though but they do have a 3Nm that pulls 4.2a as well as a 3Nm pulling 3.2a
They have nema 24 @4Nm would they fit my pinion plates ?

read more so the 24's will fit ,they have the same mount hole spacing within .1mm

When comes to motors whats more important is the inductance which is rated in mH. Lower the better and when wired Bi-polar parallel you want to be looking for around 2.5-3.5mH for best performance.

Be careful when comes to Nema sizes because some companys state Nema 23 which should = 56mm but the frame size is actually Nema 24 which =60mm. Prime example is that exact Cnc4you motor you linked to. The data sheet gives Dims of 60mm but they sell it as Nema 23.!!

Agghhh - I know I need a Bob as well-one full of connectors or just a basic one, I have ordered a UC300eth for connecting to my pc so need 5v to power that- it that then an extra psu I need or can I pickup 5v from somewhere!

Don't try to pick up 5V from else where like PC or USB. You need a stable 5V supply and ideally to lower risk of noise affecting controller you want it separate to any other devices.

Ideally you want to be getting away from 5V for things like E-stop, Limits etc because it's very susceptible to electrical noise which gives all sorts of weird and wonderful hair pulling mysterys.

Re- Bob's then you won't want to go the route I'd recommend because of price. Which would be UB1.
So in which case I'd say go with cheap Bob and just make sure it uses isolated Inputs. Most Simple Bob's don't have isolation so stay clear of those.

Highly recommend you draw up schematic and use 24Vdc safety circuit using relays. This will allow you to use 24Vdc to run thru E-stop and limit wires on the machine lowering any chance of false e-stops etc thru noise. The 5V signals you need for the Controller/BOB can then be kept to short wire runs and inside the control box which lowers chance of noise affecting machine.

Machine just relying on 5V for everything is very open to electrical Noise. Crazy things can occur.? ie: Mr's turns on hairdrier machine E-stops, Boiler fires up machine E-stops, Kettle on, Door bell etc etc.!!. . . think you get the picture. Anyone who's been affected by noise will tell you it's pain in the arse and only beat by resonance to which pulls the most hair.!