This instructable describes a low-cost CNC pen-lift that:
- accepts different diameter pens,
- supports different pen angles,
- is precise,
- and extremely sturdy.
Only two 3mm bolts are required to attach it to the plotter described in https://www.instructables.com/id/CoreXY-CNC-Plotte...
Photo 1 shows a fibre-tipped pen attached vertically by means of two small "tool clips"
Photo 2 shows a self-inking water-color brush attached at an angle by means of a large "tool clip".
Step 1: Design
The simple pen-lift shown in photo 1 has five disadvantages:
- each pen diameter requires a new custom fitted bracket.
- the pens are prone to wobble as they won't drop if there is friction.
- a new pen-lift collar is required for each pen size
- different pen angles are not supported.
- pencil traces are faint.
Solution to problem 1
What we need is something that automatically adjusts to the pen diameter.
Believe it or not such a device exists in the form of spring-metal "tool clips". These clips come in a range of overlapping sizes:
- 10mm tool clips are suitable for pencils.
- 13mm tool clips are suitable for sharpies and watercolor brushes.
Solution to problem 2
Eliminate the source of wobble by attaching the pen to a friction-less sliding plate.
This is achieved by attaching a tool clip to one side of a metal plate and four V-groove pulleys to the other. The pulleys allow the plate to move up and down a vertical Z-rail attached to the plotter.
Solution to problem 3
Eliminate the need for different size pen collars by bending the top of the plate ... one size now fits all.
Solution to problem 4
The tool clips are held in place by means of a single nut and bolt ... simply angle the center tool clip.
Solution to problem 5
This problem solved itself ... the extra weight from the tool-clip(s), metal plate, and V-groove pulleys ensures that all pencil lines are clearly visible.
Step 2: Parts List
The following parts are required:
- 4 only V624ZZ V-groove pulleys 
- 1 only 80mm x 40mm piece of 18 gauge aluminium sheet 
- 1 only 10mm x 3mm x 60mm length of aluminium extrusion 
- 6 only 3mm bolts
- 2 only 3mm nuts
- 2 only 9mm threaded nylon spacers
- 2 only 10mm tool clips 
The V-groove pulleys are available from https://aliexpress.com in packets of 20. You should have 4 pulleys left over if you built the plotter described in https://www.instructables.com/id/CoreXY-CNC-Plotte.... The remaining parts may be obtained from a hobby shop or hardware store.
Instructable https://www.instructables.com/id/How-to-Cut-Fold-S... describes how to cut and fold aluminium sheet.
18 gauge aluminium sheet is less rigid but may work as a substitute.
Large pens may require 13mm tool clips.
Step 3: Construction ... the Z-rail
Two 3mm holes were drilled through a 60mm length of 3mm x 10mm aluminium bar using the drawing template shown in photo1 .
Two 3mm holes were then drilled into the pen-carriage assembly using the holes in the above bar as a template.
9mm threaded nylon spacers were then attached to the pen-carriage assembly using 3mm bolts.
The Z-rail was then bolted to the spacers as shown in photos 2 and 3.
Step 4: Construction ... the Slider
Cut an 80mm x 40mm strip of aluminium sheet using the the method described in instructable https://www.instructables.com/id/How-to-Cut-Fold-S...
Drill and fold the aluminium as per the template shown in photo 1.
Mount four V-groove pulleys as shown in photo 3. If necessary elongate the 4mm holes on one side of the Z-rail to obtain a perfect fit.
Bolt a tool clip to the center hole and attach your pen. The extra tool clip shown in the opening photo isn't really required but ensures that the pen doesn't move when doing complex plots.
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