Sovol SO-1 Pen Plotter Modifications- Mounting Brackets and Rolling Arm for Cantilevered X Axis

Using my Sovol SO-1 plotter, I noticed a couple of issue when I started to do my first plots.  First of all, when the drawing head was at the right end of the X axis, the uneven weight would cause the device to tend to tip over to the right.  I decided to try to firmly mount the plotter to a flat drawing surface to help this issue.  I have a piece of MDF that is 2 feet by 4 feet x 3/4 inch that I will use for this purpose.  I will design some 3D printed brackets to attach the plotter to the MDF to prevent the tipping issue.  

The second issue I noticed is that there is some difficulty getting the pen height to be even across the range of drawing positions.  If I set the height at the origin, the pen would be low enough to draw on the paper even when in the up position, at the right end of the X axis.  I noticed a gradient in the pen height on the Y axis also, but to a much smaller degree.  In other words, this could cause the pen tip to contact the paper at some positions even when in up setting and in other cases to not touch the paper when in the down position.

I have an inexpensive set of digital calipers, I used them to measure the height of the Y axis extrusion on both left and right sides at the origin and far end of the extrusion.  I measured the far end to be about 1mm higher than the at the origin.  I measure the left side to be 0.5mm higher than the right side of the Y extrusion. 

 I removed the cover from the base of the unit.  One of the screws to attach to the extrusion is accessible and the other is at an awkward position because of the proximity of the board.  Loosening the accessible screw with an Allen wrench, I was able to allow a small amount of rotation of the extrusion.  At the far end, the two screws on the vertical piece are easily accessed and could be loosened.  I then made a small tweak rotation in the axis of the Y extrusion and tightened the 2 far end screws and remeasured heights making a partial improvement in the problem.

 

Next, I took a piece of aluminum foil that I cut with scissors into strips that I folded back and forth to make some shims that I put under the feet of the device and remeasured at the four points, adjusting the shims until I was able to get the height difference to be no more than 0.1mm with my calipers along the length of the Y axis extrusion.

Now, I decided to work on the X axis.  Holding the control box and the other feet of the unit down with weights so it wouldn't tip, I measured the height along the X axis with the drawing arm either near the origin or at the far right.  I measured the height to be about 5mm lower at the far right compared to the origin end.

It occurred to me the reason that this is happening is because of the cantilevered design, the X axis free end will tend to sag under a load.  I thought about different ways to support the cantilevered end, and decided to have a simple rolling wheel support.  I have some extra wheels from my 3d printer lying around.  I designed the rolling wheel support in Fusion360 and 3d printed it.  It mounts to the underside of the X axis extrusion with two 16mm long 3mm diameter screws and hammer nuts.  The wheel is mounted with a 5mm screw that threads into the plastic (no nut) that allows the wheel to spin freely.  I ended up needing to slightly shim it with aluminum foil tape between the extrusion and 3d printed piece to get the height to be 0.1mm difference across the range of X axis movements of pen holder.

I created brackets to attach the plotter to the MDF.  Again, I used fusion360 to model these parts and 3d printed them with pla.  For the front bracket, I used 3mm screws and hammer nuts to attach to the Y axis extrusion and then 6mm screws to mount to MDF (I had these in my shop from an old project)...  

    

I marked center of holes on top of MDF then drilled pilot holes through.  I then used forstner bits on the back side to drill holes for T nuts that accept 6mm diameter screws (and larger forstner bit to allow lip of t nut to not stand proud of mdf).  I used a small drop of ca glue on the t nut then used the hex driver to install them.  

I then designed a bracket with fusion360 to hold down the other end of the Y axis.  If I tried to attach a bracket to the far end via the extrusion it would interfere with the range of plotter, so I decided to use the metal vertical to mount instead.  I tested vertical with a magnet and did not stick, so not steel, would probably be anodized aluminum and not too hard to drill.  This bracket uses 5mm diameter screws through the aluminum vertical and again 6mm diameter screws to mount into T nuts in the MDF.

Now I went back through the height measurements and adjusted my shims as needed to get the heights to be within ~0.1mm tolerance.

I put the 3 files for the 3D printed parts on my Google Drive:

Sovol SO-1 3D printed parts

Here is a side view of the plotter with brackets and wheeled cantilever arm support installed.

And a front view.

Now it doesn't tip at all across the range of movements and the pen height is maintained within a 

~0.1mm tolerance.  

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