Sturdy and Fast all Steel CNC , my first build

[HipoPapi]

Beautiful build, and a lot of great info. Congrats on the final outcome. Must have been hard to part with it :).
Thanks again for sharing.

[HipoPapi]

Hi Silyavski,

I see you have used HTD pulleys and belts on your machine. Did you get those from Zapp?
Also I see they do key cutting which makes it easy to mount the pulley to the servo but how did you mount the pulleys on to the ballscrew. I know its a newbie question but that is what I am. I am thinking to use 3 to 1 reduction and trying to figure it out. Also do you need any special machining for the ballscrews when using pulleys? HTD belts are a good option for me as they are rated to -25 Celsius.

Thanks,
Vass

[Boyan Silyavski]

Hi,
All pulleys and belts are from beltingonline.com
Nothing special, ball screws machined normally. 2 grub screws on pulley. A drop of instant glue on the shaft. If I was doing it for myself i would file or drill the shaft where the grub screws are. Now it's more forgiving for mistakes

On the big machine I am building now for myself I use only aluminum pulleys as it would be geared 20:30 t and the rotating nut is heavy so I don't want to have too high inertia. These I bought from China as here prices are prohibitive. Aliexpress.

Normally you don't need any special machining given that the motor plate is not thicker than 10mm.
On the Z however is good idea not to make it too strong especially if geared for some reason. Cause hitting the bed can do some damage especially with strong motor.

[HipoPapi]

Hi,

Thanks for the info. I am thinking 3 to 1 on X and Y and 2 to 1 on Z as my Spindle will be large about 15 kg. I see they offer grub screw and key cutting service as well so will have key cutting on the servo side and grub screws on the ballscrew.
I understand from your info given ( 20:30) that you calculate the gearing ratio by the tooth count?

I see you are using on your new machine the west systems 105+209 wich I know is ideal for this application the only problem beeing that here in the uk the weather isn't ideal :) Do you think I will be ok with the 105+207 or 206?

Thanks again,
Vass

[Boyan Silyavski]

Hi,

I understand from your info given ( 20:30) that you calculate the gearing ratio by the tooth count?
Vass

Yes, cause 1:2 , 1:3 or whatever seems not to reflect reality , misleads the mind. The reality is that 16t is the smallest one and geared 1:3 means 48t for the second one which is in fact 75.25mm in diameter and at 100mm separated center from center they have only 6t in mesh. So imagine the inertia if from steel. Even from aluminum.

I assume you will be using servos. So the encoder count + ballscrew pitch will dictate your gearing, as it will determine resolution, max speed of the machine.

I see you are using on your new machine the west systems 105+209 which I know is ideal for this application the only problem being that here in the uk the weather isn't ideal :) Do you think I will be ok with the 105+207 or 206?

Thanks again,

No, it will be a problem. Its not only the time, the faster it cures the more heat generates, the more it distorts. Whats the problem with the weather in UK? humidity is not a problem if its not raining directly on it. And where i live its much more humid.

[HipoPapi]

Hi,

I am planning to use 2x 750w servos on the X, 1x 750w servo on the Y and a 400w servo on Z.
The shaft on the 750w servo is 19mm dia and 31mm long so in fact that is what determines my smallest pulley.
I am planning to use 25mm HTD belts as my gantry will be close to 200 kg plus the belts are rated for -25 degrees Celsius.

In the Case of a 5 pitch pulley for 25 mm belts F= 30.5 which means that that is my whole 31mm shaft. So if I would want to use the whole L which is 38 I would have 7mm of the pulley hanging of the servo shaft. If I want to use grub screw I would be limited by Dm and an even larger Dm if I want to use key. So I have decided to cut of F from L and use just F and key cutting therefore I can use a smaller pulley and I am limited only by (De) and have nothing hanging of the shaft.
So basically 24 t pulley on the servo where Dp=38.20 and 72 t pulley on ballscrew where Dp = 114.59 giving me
a ballscrew rpm of 1000.09 on the ballscrew with 3000 rpm on the servo side so essentially 3:1.
With a 2010 ballscrew my critical speed is 1128 so would be able to get 10m/m rapids or I can go with 2020 ballscrew and get 20m/m.

With the resin my worry is that here in the uk we are getting around 21-25 degrees Celsius during day time and it goes down to 15 during the night. But I did not look into it so deeply yet and maybe that isn't a problem with the 105+209. If By any chance you already know it please let me know.

Thanks,
Vass

[JAZZCNC]

Vass you cannot just rely on the Key you will need Grub screws as well to stop the pulleys coming off the shaft. You can buy pulleys with larger Boss so can get more screws in but also not uncommon to put the screws thru the teeth and provided they are below the teeth and deburred correctly it's not a problem.

Regards the servo's the rated Continous speed will probably be 3000rpm which is the Max speed they will provide continous rated torque but in practice they often will reach higher speeds at lower torque 4 or 5K is not uncommon.
Really thou you don't want to go past the rated speed/torque esp with a heavy gantry so your calcs are correct but with 3:1 ratio and 750W servos's you'll have much more torque than you need so won't be a problem within reason.
To be honest you could go lower on the ratio and increase the speed and lower inertia slightly at same time. Like I said in emails the critical speed isn't critical and you can run above it without any issues so 2010 run at 2:1 would give 1500rpm and 15mtr/min rapids which is more than enough. You won't be running above critical speed all the time and infact rarely will be for more than 2-3s at a time so it never becomes an issue. My own machine as been running 2005 screws with 1:2 ratio so double speed and well above the critical speed for 6-7yrs without any issues.
I would only use 2020 screws if the screw length was long and needed to lower screw speed to resist whip. In this case I'd go with 3:1 ratio to increase torque and make up for lower mechanical advantage from larger pitch.