First Build 5 x 12 Steel Frame CNC router

[Scott Damman]

BST automation is the usual choice for Chinese stuff and linear rails, so its a well known and recommended seller. Price wise, packing, support and warranty.

Do you have a cable chain? If not i highly recommend the Russian ARKO 22x80 R60 which is cheaper and better than the similar Chinese

Awesome, those are good prices, I need to see how much shipping is going to be but that was good timing cause I have not purchased chain yet.

Jazz, thanks for the video exactly what I was looking for in a review. Time to order some motors and drives... I emailed to see if I could get a price for motor/drive and 7m cable set.

So the resolver feedback into Mach is awesome, shows how new I am to this I didnt even know that was possible. Anyone know if the smooth stepper from warp9 can do this? It shows resolver connections on the board but does it send back to mach? Also looking at the CS lab boards as well since Jazz has a good review on them. Im thinking I might go for a servo for Z as well since that can give me position feedback into Mach rather cool feature.

Gerry, I had started a build log over at CNC Zone but after finding the great information here I decided to put my build log here instead. Also for me the cnc zone website is painfully slow!

Currently using the rotating ballscrew design to design one that I can build with the machines I have. Might be a little crude, also sending out designs to some local cnc metal shops for quotes on parts. One question, (of many im sure) do you guys find you need to grease the ballnut more since it is sometimes spinning rather fast?

Thanks for all the help, I will post some design ideas shortly for the rotating ballnut.

[JAZZCNC]

Anyone know if the smooth stepper from warp9 can do this? It shows resolver connections on the board but does it send back to mach? Also looking at the CS lab boards as well since Jazz has a good review on them. Im thinking I might go for a servo for Z as well since that can give me position feedback into Mach rather cool feature.

Yes and No. The ESS can send the encoder signals back to Mach but only for display purposes and to different set of Encoder DRO's on separate screen. (or can add to Custom screen if you like) Mach will not know anything about positional error and the Main Work DRO's will not update if position moves.

To work like you see in my Video the Controller deals with the Encoders and informs Mach of position directly. The Closed loop between motor and drive is then extended to the controller which keeps track of position and updates Mach's Main DRO's. The ESS cannot do this.

Very Few Step and Dir Controllers do this. Even the CSlabs IP-S which uses STEP & DIR cannot do this. Only the Analog IP-A Version does this.

[Ger21]

One question, (of many im sure) do you guys find you need to grease the ballnut more since it is sometimes spinning rather fast?

On our Morbidelli, it's recommended to grease the spinning nut every 40 hours of run time. linear bearings and non spinning nuts get greased every 3 hours of run time with an auto lube system.

But a lot more grease goes into the spinning nut, as it's much larger.

[Scott Damman]

So Im looking into and learning more about long ballscrews and how to run them. Obviously spinning the ball nut is a way to go but each unit gets to be pretty costly by the time you are said and done.

Another thing I found was supports along the ballscrew which effectively push the critical speed to a higher rpm. Has anyone ever looked into this type of design?
http://www.linearmotiontips.com/achi...d-ball-screws/

Thermwood does this on the long axis of some of their CNC machines. It looks like the support flips as the ballnut passes and then supports the ballscrew again on the other side of the ballnut.


I assume these are just nylon but cant find any further details on this type of support. I wonder if it could be considerably less expensive to incorporate this, provided the same performance is achieved in the end. Thoughts?

So still learning about the CSLabs IP-A and trying to decide if the extra money is worth it. With all ballscrews, I dont know that there will ever be a time that the system could move while the drives are disabled? I.e. I would have to manually turn the ballscrew or the motor to put it out of position. However, if Mach knows absolute position does that mean that the system needs to be "homed" less often? Between cuts etc. Are there other benefits to having Mach know the absolute position from the resolver? I hope to make a decision here soon on a motion control card... If anyone has any further thoughts I greatly appreciate it.

Thanks to Fred over at BST for working with me, I have ordered motors, 2 for X, 1 for Y, and 1 for Z. I decided to go with servo on Z as it seemed silly for the price difference to have that axis be a stepper.

Next up is HTD timing gears/belts just need to figure out speeds and gear ratio. Thanks Boyan for posting the 20t:30t Starting point and after putting it on paper sure makes sense to me.

So some math just to make sure I have things right
Lets say 20000mm/min travel
Ballnut is 5mm per revolution

(20000mm/min ) / (5mm/rev) = Ballscrew rpm => 4000rpm

Gear ratio 20t:30t = 0.666

4000rpm * gear ratio => Motor Speed => 2666rpm.

The motors I purchased from Fred are 3000rpm so this looks reasonable to me.

[Ger21]

Figure out what you want your max velocity to be, and gear it so it reaches that at 80% of the servos rated speed.

[Boyan Silyavski]

ball nut is 10mm per revolution. Only z is 5mm

[Scott Damman]

ball nut is 10mm per revolution. Only z is 5mm

Figure out what you want your max velocity to be, and gear it so it reaches that at 80% of the servos rated speed.

Gerry thats just the problem, dont know what I want or need my max velocity to be...

Boyan, so you are taking the gear ratio the other way then? i.e. screw speed (or ballnut speed) * 1.5 to give motor speed. If I take the same equation from before your 20,000 mm/min with a 10mm/rev screw gives a motor speed of 3000rpm?

What would be the disadvantage to doing a 5mm screw? I know the torque issue with gearing the motors the other way. However I ended up ordering 1.8kw 6Nm 3000rpm motors since they ended up being cheaper than the 1kw motors so I think I can sacrifice some torque to a gear ratio. Are there other issues with 5mm? I havent ordered the long screws so I can go either way just asking the question.

I am thinking about implementing brake resistors, I do this on my VFD's (to run 3 phase woodworking equipment) for quick motor braking. Im just trying to decide if the inertia of the gantry being so high warrants braking resistors or not. Has anyone needed to add them to their setup?

My motor order was as follows (in case anyone is interested)
Qty: 3 - 6Nm 1.8kW 3000 rpm servo motors - these will be for 2 for X axis and 1 for Y axis
http://www.aliexpress.com/store/prod...761095604.html

Qty:1 - 2.4Nm 0.75kW 3000 rpm servo motor - this one is for the Z axis
http://www.aliexpress.com/store/prod...760999511.html

[Boyan Silyavski]

i was trying to say / but as i was busy at workshop/ people typically use for woodworking machines xx10 screws on all axis and xx05 on Z, as this more or less gives compromise between speed, precision and step count/pulse train needed to generate movement


So say you have a servo motor that will spin to 3000rpm. From look of the servo it says 2500PPR/ pulses per revolution/ if i am not wrong. And ball screw moves 10mm per revolution.
Then ball screw needs 1/10 rev to move 1mm. If no geared then 3000/max rpm/x10=30 000mm/min max speed , like Gerry says thats your max velocity in Mach3. So from above it seems then you will need 250pulses per mm , so 1mm/250pulses=0.004mm resolution.

There is something important that Gerry told you but you missed his point. The servos should not be greatly OTT as you may think, they must be closed mutch to what effort they will do, otherwise youwill run in other problems. read literature about servo sizing. Its not a good thing to be much bigger than job they are meant to do.

Then read carefully page 14 from my build thread where Johnatan explained me very well how to calculate details and especially about snappiness.

And by the way i was suggesting 20t at the motor and 30t at the rotating ball nut, not vice versa. So you finish with slightly geared up machine, 0.7-1kw servos, and very fast acceleration. But just do your self the calc. My gantry is moved by 2x 400w servos, not 2x1.5kw ha ha

[Clive S]

Scott Damman

Did you remember you needed longer cables !! that listing say 3mtrs