Question about duel X Axis drives

[Bobby783]

Hi All

I have finally taken the plunge and begun designing my first ever CNC router. I have bought a Chinese kit of Linier rails, ball screws, stepper motors, drivers and breakout board.

I plan on using Fusion 360 and Mach3 or 4.

I am hoping to drive the X Axis with 2 separate motors/ball screws.

My query is should each X axis motor have its own driver and be connected to the Z axis connectors on the breakout board or can I connect both motors to one driver?

Thanks in advance

[JAZZCNC]

My query is should each X axis motor have its own driver and be connected to the Z axis connectors on the breakout board or can I connect both motors to one driver?

You need a Drive for each motor. Don't let anyone tell you that it's ok to run 2 motors with one drive or two Drives with one Output Signal because while it can be done it will cause you problems that will frustrate the hell out of you.

The Slave axis is usually the B or C axis depending on how many axis your Breakout board provides. Ideally, you would use the B axis then it leaves the A-axis so it can be used as a Rotary Axis.

So in Mach3, you would go to Slave Axis Menu and then under X-axis select the axis you want to Slave with it.

Be careful when slaving axis and setting up because if one motor Stalls and the other doesn't your gantry will quickly get twisted up. Don't underestimate the power of steppers because they will bend a ball-screw in the blink of an eye.

My strong advice is to test the slaving on the bench or with the screws disconnected and make sure both motors are spinning in the same direction. Don't try to tune them on the bench or disconnected from screws because when connected to Gantry etc it will change the tuning and highly likely the motors will stall at a much lower velocity.

With Slaved motors Ideally you would use drives that offer Stall detection or if not one's that have a fault output in case of failure, which you then build into your emergency stop system to protect from high-speed stalls which can destroy ball-screws and mangle a gantry.!

If you don't have these things then you really need to leave a very large safety margin when tuning motors because as Stepper motor rpm increases the torque drops quickly so at a high velocity you have very little torque left and it's very easy for one motor to stall but other keep moving.!!!

To be honest my heart sinks when I see the posts like yours that say " I bought a Kit" because it's highly likely what you have bought won't suit using slaved setup. And if your lucky it just might suit a single screw setup at lower feeds. It's THE most common mistake made with new CNC builders.

Give me the details and I'll tell you exactly what you can expect.

[Bobby783]

JAZZCNC many thanks for tour reply. Having jumped the gun and bought a "kit" I quickly realised that that was a mistake. I intend to build my router as a test project and hopefully it will be sufficient to use to help build another one with better components. I will list what components have tomorrow and look forward to tour reply. I know I bought crap so please dont labour on it. Lol. The 6 axis parallel BoB that came with the kit never worked. I replaced it with a cheap USB 4 axis BoB and immediately got first motor running. So will get whole thing working on the bench at the weekend. More to follow later.
Thanks

[JAZZCNC]

I know I bought crap so please dont labour on it. Lol.

Don't worry I won't and please don't think I'm telling you this to put down what you bought. I see this thing all the time and it really pisses me off they get away with selling these kits. So anything I can do to highlight and hopefully discourage others the better while at the same time if I can help those who have bought them it becomes a bonus.

If you post me the details I can tell you what to expect in terms of performance which will save you chasing performance you'll never achieve and what to do to maybe increase this performance.

[Bobby783]

JAZZCNC

Last year when I decided I wanted to build a CNC Machine I knee jerked and went for the fasted option to get going, which to me at that time was a chinese kit which comprised the following

2pcs SBR16 - 350mm linear rail
2pcs SBR16 - 1000mm linear rail
2pcs SBR16 - 1500mm linear rail
12pcs SBR16UU block
1pc* SFU1605 - 350mm ballscrew with ball nut* *(BK12/BF12 end machined)
1pc* SFU1605 - 1000mm ballscrew with ball nut*(BK12/BF12 end machined)
2pcs SFU1605- 1500mm ballscrew with ball nut* (BK12/BF12 end machined)
4pcs BK/BF12 Support
4pcs 6.35*10mm coupling
4pcs Nut housing

4 Nema 23 motors
4 cheap Motor Drivers
1 Mach3 Break out Board (Parallel interface) this has now been replaced with a Chinese USB breakout board. The red one in the images attached.
So i still intend to build a ter with this kit to use as a learning tool but will want to build a more quality version in the near future whit bigger motors capable of cutting aluminium. High Speed cutting is not a priority for me

[JAZZCNC]

So i still intend to build a ter with this kit to use as a learning tool but will want to build a more quality version in the near future whit bigger motors capable of cutting aluminium. High Speed cutting is not a priority for me

Ok well first thing to clear up is cutting speed.? A common mistake made by new users is to think they can cut at any speed which suits them.! When In reality, to cut correctly so get a good finish and decent tool life the speed you cut at is determined by several parameters like the Material type, tool material #flutes dia & length, depth of cut.

This is where people go wrong and become disheartened because these kits won't allow the required feeds. I'm telling you this now so hopefully, you don't get pissed off and give up.

This kit just isn't suitable for a router, simple as that. The rails are ok but the rest will just cripple the machine.

I will need more details of the motors and drives and PSU to be 100% but I'm pretty sure looking at the pic that they are TB based drives and probably max out at 36V.
Worse still is the PSU looks like it's 24V which would fit because if you ran TB based drive at 36v you'll blow them up in minutes, so they leave a healthy safety margin.
Knowing these kits the motors will be High inductance motors which without getting too deep means they require more volts to get the same RPM as low inductance motors. Not good when you only have 24v to start with.
Steppers require volts to achieve higher RPM and still have any torque left. 24v will be crippling to all but small steppers. This leads on to the ball-screws.?

The 5mm pitch is too slow for a router which is compounded further by the low stepper RPM. For instance, a proper sized motor, drive, psu combo using 50V will safely allow around 1000rpm which connected to a 5mm pitchball-screw gives a max Rapid feed rate of 5000mm/min. To give some idea of proper feeds this is on the low sides for cutting even MDF correctly.
You also need to realize that at 5000mm/min the motors are close to the point of running out of torque so only really run at this speed for rapid positional moves not cutting underload. A safe Max cutting feed would be 4000mm/min which depending on MDF and cutter etc is likely to burn edges or give a poor finish.

The point to this is that your electronics and ball-screw combo if running at 24V will be lucky if let you run at half this speed so you'll be lucky if can cut at 2000mm/min.
Now here's where it really gets daft.!! . . . . . You won't be able to cut MDF or other soft materials that require speed but if you build it strong you will be able to cut Aluminium as you'll rarely cut much above 1500mm/min.

My advice is to sell the KIT and start again. OR Just sell the Electronics start with decent electrics and build a nice strong frame to give self half a chance then replace the ball-screws at later date with a higher pitch. You'll only need to replace the ball-screw as all the bearings etc can be reused.
If you take my advice you will save your self a lot of frustration and some money at the same time.

[Bobby783]

Thanks for all this advice which I am going to take. So if I keep the rails and screws for now and sell the rest can you give me a list of good components and where best to get them.

[JAZZCNC]

Thanks for all this advice which I am going to take. So if I keep the rails and screws for now and sell the rest can you give me a list of good components and where best to get them.

Yes, I'll knock up some suggestions for you. But before I do that just post some better pics of the drives, motors and PSU to see exactly what you have.

[Bobby783]