how to driving a solenoid needle valve on wax printing head

I am building a wax printing head to enable me to print jewellery for lost wax printing. I have tried to make the solenoid valve open and close using the stepper driver for the plastic feed on the extruder. I am running ramp4. Not being an electronics engineer I am at a loss how to drive the needle valve that will open and close the nozzle. I have also got compressed air connected to the print headto spray the wax out. It is a system that I have used before in mechanical engineering to spray wax onto sheet metal and am trying to adapt the consept to spray/build up wax models. I am connecting the stepper driver using one paired set of wires from the ramps .

You could use the direction pin of the stepper driver to control a relais or MOSFET.
The solenoid will need a spring to close the valve when powered off.

For fast on/off moves you better use the MOSFet.
-Olaf

Thanks for that, have picked up a mosfet and will try it tomorrow.

If the direction pin logic is inverted you can invert the extruder stepper in firmware.

Make sure you have set retraction to a very low threshold in the slicer to make sure the direction pin changes at the end of a track.
-Olaf

Do you already have a valve that you are trying to mechanize (pics are always nice)? If so hooking a stepper up to it with an endstop for it home like x y and z would be logical. You could also peek into other kinds of drivers systems, like what normally would work the valve?

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Master Tinkerer

I have built the valve myself and have fitted a solenoid to the end of the needle valve to enable the solenoid to open the print aperture. I have fitted a compressed air inlet to the side of the print head to spray the wax out of the print nozzle to print rather than let it dribble out. I am trying to use the signal to the stepper drive ( no stepper fitted ) to open the solenoid. this would enable me to print jewellery in wax that could then be lost wax cast. I have no pictures of the print head but will take some and post them. I am hoping to print layers approx. 0.08mm thick x .25mm wide, i know this is very thin etc but most jewellery is small but intricate.

Would a servo motor be strong enough to drive the valve? How much do you need it to move? A stepper motor would be perfect, however the only problem, and one that I can see being a very big one, is that the needle valve would need to be treated like a normal axis (with an endstop). This means that some custom code would be necessary to home the extruder (to fully open or closed). A servo my recommendation if possible, maybe one that turns 3 or 4 times around on full throw if you can find one. You can connect servos to a ramps board to stuff like auto-leveling probes, but again I think that some customized code will be necessary.

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Master Tinkerer

The firmware for the Duet electronics has a gcode configuration option that would probably work for this. It's meant for paste extrusion, and it drives the FAN0 mosfet with a configurable PWM signal whenever extrusion is taking place. You could connect the solenoid to the FAN0 output, and add a flyback diode across it.

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Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

Sorry, but i'm a bit of a noob..
What's a flyback diode? I've heard of flyback transformers in CRT displays, but that's it.

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Master Tinkerer

A flyback diode is for suppressing the induced voltage when you remove power to an inductive load, such as a solenoid or motor. Most power mosfets can handle a certain amount of energy from slightly inductive loads (see the repetitive avalanche energy rating in the datasheet), but a solenoid would typically exceed this energy. Hence the flyback diode to dissipate it harmlessly (actually, most of the energy is dissipated in the resistance of the solenoid when a flyback diode is present).

In a CRT display, the flyback energy when the current in the horizontal deflection coils is turned off is used to generate the high anode voltage needed by the CRT. In this case, the driver transistor is a special high voltage type, and the capacitance of the coils (along with any added capacitance) limits the voltage to a value that the transistor can handle.

Edited 2 time(s). Last edit at 09/01/2015 02:42PM by dc42.

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Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

Dialman, is the needle valve a push/pullable valve, or a screw needle valve?

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Master Tinkerer

the needle valve is a pull to open with a return spring on the solenoid ( weak one ) and a stonger return spring that I have fitted to the needle valve.