UniversalPenTouchProbe

Universal Pen Holder and Touch Probe Tool Head

Table of Contents

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Introduction

Having read and been inspired by Homebrew Touch Probe, The "One Penny" Touch Probe, the work done by Greenarrow and ongoing discussion re PCB Prototyping on the Rep Rap Forum. I was looking for a way to combine as much of this as possible into a useful, simple and most importantly cost effective Tool Head.

I wanted to make a tool head that could take a number of different pens, one at a time. That would tell me when the pen tip was dragging or touching on the surface of the work piece and where the pen "touched down" destructively I wanted the tool head to give a little so as to avoid damage to the pen tip.

Recovering from a "touch down" the pen should ideally return as close to it's centered position as possible.

In achieving all of the above using the techniques used by touch probes it is a minor step forward to make a pen insert that was actually a probe and could be used to touch digitize (although very slowly) a three dimensional object.

Again a minor step forward is to use the touch tool head to check the Z Axis Bed alignment and it's degree of parallelism with respect to the carriage assembly.

Making the Tool Head

Pen Holder

The Pen holder is made from the following parts :-

1. One plastic 20mm Conduit Male Adapter
2. One plastic 20mm Conduit Coupling
3. One piece of plastic 20mm Conduit 70mm Long
4. Three M3 Pan Head Machine Screws with nuts and washers
5. A light Spring of minimum ID 28mm
6. A spring retaining disk ID 20mm by OD 30mm (Make the disk OD greater than your spring OD or it won't work)
7. A Jubilee or Hose Clip which will wind down to at least 18mm and open up as much as 25mm

If like me you had problems finding a spring you can wind one using springy wire. I used a 20mm Conduit coupling for the former. The OD of these is approx 24mm. A 1.5mm stainless steel welding rod was used for the wire. Stainless Steel being what it is does not like being tightly wound around the former and expands to a useful ID of approx 28mm when you let go.

Refinements

The electrical contacts in this case were made using Bright Zinc Plated M3 Pan Head Machine Screws.

Logical improvements are:-

• Replace the bolts with a material that can be gold plated and electroplate them to ensure a longer contact life.
• Screw an internally threaded tube over the M3 contact pins that has again been gold plated to improve the contact surface.
• Add an LED to the tool head so the bed alignment can be checked without realy needing the drive electronics to be present.

Uses for the Tool Head

• CNC Etch a Sketch
• Pen Plotting
• Checking the Cartesian Bot's Z Axis Alignment.
• Digitising your own hand made components for printing.
• Photoplotting (You need to add a light pen, light source and shutter or switch to do this)
• Simple PCB prototyping through direct application of etch or photo resists.

Acknowledgments

-- Main.AndyKirby - 29 Aug 2008