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spindle rpm readout



i am thinking of masso for a milling machine conversion to cnc.

i have some things to figure out yet and i would appreciate any help.

please forgive my silly questions but i am not having any experience with that kind of machinery.

the milling machine is a Optimum bf20L equivalent to Grizzly 604 or 704 i am not sure.. the machine has a dc motor installed with a potensiometer and a speed readout from a sensor on the spindle.

1)is there a way to connect the masso to that sensor so i will have an rpm indicator?how you guys do that?

2) is there a way to control the motor speed within the masso?

for the momment i would like to keep the stock motor and the two speed gearbox.the max speed in this momment is 1250rpm in speed1 and 2500rpm in speed2. i am not thinking to swap the motor yet and i will stay with the 2500rpms until i am up and running.

plan B is to change the motor and use a vfd. same problem here. Yes masso can control the vfd  but still have somehow to connect the spindle sensor to the masso. how?




Speed readout - would need to know some details about the actual sensor that picks up the speed signal. May be more cost effective to add Masso's speed sensor on.

Potentiometer conversion - Have a read of my Sherline motor conversion issues (ignore the bit where Breezy asks about homing switches). I have 5 empty PCBs (the company that made them for me sent me 6) and a spare linear opto-isolator. I suspect changing to a VFD is going to be the cleanest option (looking at it myself for high speed work - basically a spindle speed over 2800 RPM).

VFD motors have (more or less) constant torque over the entire speed range as torque is proportional to winding current, therefore the delivered power is proportional to speed. If you have a 1200W VFD that runs at 24,000 RPM it will only deliver 12W at 240 RPM. What material are you intending to cut with and what diameter end mills?

DC motors torque curve decreases with speed which is useful for milling (it is almost an automatic gearbox).

EDIT - Another option would be to replace the DC motor speed controller with one that supports an isolated 0-10V signal (KB Electronics has a cost effective controller for 90-100V DC motors).

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it seems that for start the new dc speed controler is quickest solution . so for now lets say problem with masoo controling the speed is solved.

massos speed sensor? is there any for mill machines? (remember my max speed is about 2500rpms). i found one at masso site but it says lathe setup only.

i will take a look at your conversion.

also from what i understand from your writings, the best for mill that has about 2500-3500rpms are dc motors and not vfds?

i will cut aluminums, steel and parhaps inox , so i need small speeds and high torque.(high torque is one reason i would like to keep the stock gearbox. only concern is a single plastic gear. i do not know how long this gear wil last if vuts are made with 2500 maxed rpms) what is your suggestions about that.? parhaps an upgrade to dc motor and controler?  what power?

Im i correct?




Using the LittleMachineShop "Speed and Feeds" page as a reference:

  • Aluminium sort of falls between DC motor and VFD. Apparently you can run a 6mm carbide end mill at nearly 14,000 RPM. Some people have issues with the chips melting/welding together using a VFD spindle.
  • Cutting low carbon steel is more in the range of a DC motor. Using a 6mm carbide end mill the calculated speed is 5,000 RPM. When using a 6mm HSS end mill the calculated speed is 1,380 RPM.
  • Stainless steel (inox) requires half the speed of low carbon steel - again a DC motor is more appropriate.

As for the motor power rating - the Sherline DC motor is rated at 60W continuous and 160W for a 25% duty cycle (5 min on, 15 min off).  The power rating of the BF20L is 850W (downloaded the manual from Hare & Forbes) - which sounds more than sufficient.

I think the motor and controller look good as it stands. Have a look at the CNC4PC C41 breakout board. for connecting your CNC controller to the motor speed controller in place of the speed control pot.

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from the the CNC4PC C41 breakout board. "This card lets you control your spindle with PWM and direction signals, as if it was an axis motor. It converts the step signal into and an analog (0-10VDC)."

so this card takes a PWM signal and outputs a 1-10v?

from the masso documantationt i get : "MASSO provides 0~10v and PWM control signals to control a variety of VFD and DC spindle drives."

so is it possible to use masso directly?

also , all pots use 1-10v?




Yes - the card takes a Pulse Width Modulated (PWM) signal and outputs a 0-10V signal (the output voltage range is tunable). The reason for using a PWM signal is opto-couplers / opto-isolators can only do on/off signal transfer reliably. The PWM signal is averaged using a low pass filter to provide a voltage signal.

Masso can support PWM speed control, it is part of the Spindle configuration in the F1 screen. I believe you use the FWD terminal for the PWM output.

Most speed controllers usually have an internal 12V supply (the speed controller for the Optimum has a 12V supply). Having an internal supply voltage higher than 12V will require components to be rated for a higher voltage such as capacitors, this adds additional cost and size to the circuit board. Typically a couple of volts are not usable due to circuit bias voltages (varies between 0.6V to 1.2V) as a result the control voltage range will be up to 10V.

Additional note: There are opto-couplers that can transfer voltage however the cost is about x20 that of a PWM => Voltage convertor.

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1)from the spindle control documentation by masso i get :   pin1 1-10v dc output ----> type :Analogue

can i use that? it is analogue NOT optoisolated ?,  this is the reason why you suggest the card with the Pulse Width Modulated (PWM) signal?

if yes , is it so important to use an optoisolated signal instead of the massos analogue?

the masso controler will be about 2 meters in distanse from the machine and the 1-10 existing controler inside it. is this important? will be the 1-10v signal from masso analogue to the controller reliable?


2)what about servo motors? i saw in youtube that many conversions of that kind of machinery uses a ac servo about 1kw motor.

is this reasonable upgrade?i assume that if i go that way i will have to convert also to belt drive. But if i do that the new question is if the ac servo motor will be equivalelnt it torque with the 1gear speed of the dc motor.

do you have any suggestions about that? parhaps use a larger 2kw ac servo?are those servo motors eqivalent in torque with the dc?

also, can Masso drive the ac servo spindle? how ? with the pwm signal or as a stepper?


2)i am searching the Masso documentation and i cannot find any pinout. is there any?





Question 1) Is analogue NOT optoisolated ?

Pin 1 of the Spindle terminal connections is not isolated as it uses the same ground connection as the Masso power supply.

Question 2) What about servo motors?

Servo motors are outside my area of experience.

My understanding is a servo motor is a motor with an encoder. A servo motor can be run in either velocity mode (speed control) or position mode (like a stepper motor).

The "A" / "B" / "C" axis are rotation around the "X" / "Y" / "Z" axis. A spindle servo motor would be a C axis motor and the Masso controller only supports 5 axis, not 6 axis.

Question 3) Searching the Masso documentation and i cannot find any pinout. is there any?

The Masso documentation search is not good. I use google and add "" to my search term.

The Spindle-Control page has the terminal details for the Spindle Control terminals.


My advice would be to get the mill running using the original motor with the speed manually controlled. Add functionality or upgrade the motor some other time.


Guessing from the time of your messages and phrases used that you are in France.

No i am in Greece.

Thanks zombieengineer .you helped me a lot!!


HI @achilles

my first little milling machine had a gear box with a plastic gear for the spindle. Although it is ok for very light duty work it's not really suitable for heavy machining. You will probably end up taking light cuts and lots of passes.

You will find that most of the feed and speed numbers recommended for cutting are not likely to be too realistic as they are perfect case scenario.High rpm is great in aluminum but doesn't usually work to well in any kind of steel.

I use servos and I like them better than steppers because of the closed loop feedback. I would think 750 watt motors with 1/2 gear reduction woul be plenty powerful enough but still leave some good travel speeds

could you post a photo of the machine