Cannot change axis speed

[Ollie78]

Hi

I have been running UCCNC for a few years now on a 300eth controller and I mainly use vcarve pro.

Lately it has come to my attention that to get the correct chip load when cutting plywoods, MDF and solid woods I really need to increase my X and Y axis cutting speed.
I have had the x and y axis speeds set up to run at 3000mm/min really since I initially set up the machine, it does produce good work at this speed but for a single flute compression bit the recommended speed is 5000mm/min plus, and more for multi flute cutters en at slow spindle speeds (18000 is recomended for the single flute compression).

So when I go to change the speed in the configuration/axis setup menu in the velocity units box from 3000 to 5000 it just cancels the field back to 3000 again and I can`t work out why. Do I need to check or uncheck another setting or something ?
It`s been so long since I configured the machine I think I must have forgotten something.

As far as I can tell this setting is the maximum allowable speed so even if I have set the tool in Vcarve pro to 5000mm/min it will still only go 3000mm/min, is this assumtion correct ?

Thanks

Ollie

[ger21]

Use the MDI and type S5000.

[dezsoe]

Gerry, it was the axis speed not the spindle.

Ollie, don't forget to press enter when you type in a new value. If it still reverts to a lower speed than 5000 then maybe your steps/unit and kernel frequency settings limit the maximum axis speed. The max. frequency depends on your motor driver. You may have to lower the resolution (microsteps) on the motor driver and change the steps/unit in the same ratio.

[Ollie78]

Thanks @deszoe.
I can imagine it could be as simple as not pressing return after the value, that would be typical !! If it is not that simple explanation and it is limited by the steps/ unit or kernal frequency how would I be able to tell which is limiting it ?

I will be in the workshop tomorrow so I will have a look at it then. If the first solution fails I will note the settings and report back.

Ollie

[dezsoe]

To get the maximum velocity here is a formula:

Code: Select all

MaxVelocity = fKernelkHz * 1000 / StepsPerUnit * 60 * 0,95

where
- MaxVelocity is the maximum speed that you can set,
- fKernelkHz is the kernel frequency in kHz,
- StepsPerUnit is the set steps/unit.

The fKernelkHz is multiplied by 1000 to get the cycles per second, you have to multiply the result by 60 to get the units/minute from units/second and the maximum speed is limited to 95% to be safe.

E.g.: if you have 100 kHz kernel frequency and 250 steps/units set then the maximum velocity is 100 * 1000 / 250 * 60 * 0.95 = 22800 units/minute.

The kernel frequency is limited by the motor drivers. Professional drivers can handle higher frequency, however, most of the cheap drivers which write 200 kHz in their manuals cannot handle 200 kHz.

[Ollie78]

Ok, so I am an idiot, it turns out I was not pressing return before saving the setting !!!

Many thanks dezsoe, your information about the maximum velocity is useful and may yet come in handy. I am finding that I need to run at a faster mm/min in order to get the correct chip loading.
I have never investigated this thoroughly before and have been getting decent results slower but I am getting better chips and cleaner cuts in the wood rather than dust.

I am unsure how slow I can run my spindle been running at 18000 mostly, its a 24000rpm water cooled 2.2 kw spindle. If I could run as low as 14k or maybe 12k then I would not have to run the mm/min so fast.

anyway thanks

Ollie

[formantjim]

Seeing the formula for the first time MaxVelocity = fKernelkHz * 1000 / StepsPerUnit * 60 * 0,95 prompts me to ask a question.

I have been using UCCNC + ETH300 for a few years now together with Clearpath enhanced servo's and my Steps per unit is 32000. My main purpose is to make circuit boards typically SMD devices so fine lines and accuracy is a must. However when doing other jobs machining plastics etc when cutting large circles 20" diameter or above I find the machine will faulter but will still continue to cut the part accurately it does not lose steps at all. This is with the Feedrate at about 40"/min higher than this then I experience the faultering. Am I running into the Max velocity limit of the ETH300 or is it the little Windows stick PC that is causing this? I know this is a slightly different topic but it got me to question things once I saw this formula.