Speed and feed Computer

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Speed and feed Computer

This topic has 3 replies, 3 voices, and was last updated 10 August 2020 at 10:16 by SillyOldDuffer.

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9 August 2020 at 09:48 #489772
Mike Poole
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@mikepoole82104
I have been considering using a stepper motor to provide power feed on my mill. Not being an every day machinist I always end up calculating the speeds and feeds from first principles or using an online calculator. We now have many programmable devices that can readily calculate the speed and feed if we know the material and cutter data. With feedback of the spindle speed we could vary the feed rate to compensate automatically if we adjust the speed for any reason. I am imagining a display and simple buttons to input parameters and directly interfacing to the stepper controller, an analog output could even set the spindle speed if you have a VFD or other speed controller.

Mike
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9 August 2020 at 09:48 #32122
Mike Poole
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@mikepoole82104
9 August 2020 at 10:03 #489777
John Haine
Participant
@johnhaine32865
Mike, that sounds eminently doable. I've posted some photos of my power feed using a stepper.

The controller (on the left) uses an Arduino running GRBL with a Bluetooth link to my Smartphone, which runs "GRBL Controller". GRBL just needs simple text strings via a serial port, which could be generated by a program such as you describe. It can also set spindle speed and turn on/off with the right external interfaces. I run GRBL on a Uno which only just has enough grunt so needs a separate computer to host the user interface, but you can also run GRBL on a Raspberry Pi which might allow you to host the MMI and your feed computation on the same computer. It even has Wi-Fi so you could conceivably get the information off one of the online sites such as **LINK**!
10 August 2020 at 10:16 #489925
SillyOldDuffer
Moderator
@sillyoldduffer
Being real CNC GRBL may be overkill. How about something like this for power assisted manual machines:

A, B and C are cheap rotary encoders with press buttons.

Turning 'A' selects materials: Steel, Aluminium, Brass, Cast Iron, Bronze etc. Pressing A could switch to a nested menu, giving access to different Steels, EN1A, EN8 etc, but I think this is unnecessary complexity.

Turning 'B' sets cutter diameter. Pressing B selects single point, or 2,3 or 4 flutes.

Button 'D' toggles between Carbide and HSS.

Based on A, B and D, the computer suggests Depth of Cut, RPM, and feed rate. DoC & rpm are set manually by the operator, the feed rate will be fed to the table motor when C is pressed to start the motor. (Pressing C also stops the motor) However, the suggested feed rate can be overridden at any time by turning C.

The override means it's not necessary for material and other details to be entered before the table can be used. The operator can set any speed he likes. However, the controller's calculator mode lets it recommend cutting parameters, which the operator can apply or not. I think operator control is important – my hobby mill must be driven within it's limitations, and it would be unwise to allow an automatic calculator to thrash it with an industrial work rate.

My description is pure metric, but the controller/calculator could just as easily be Imperial. Or both (another button would be needed) The display needs thought. 4 line by 20 character LCD displays are cheap, but my 3rd line starting DOC= is too long. Needs trimming!

Dave
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