Small mod to make swapping pens easier

#1

I’ve been mildly annoyed by how fiddly it is to change pens on my plotter so I made a little mod to make it easier.

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I’ve replaced the pen holder with a piece of pvc pipe and an eyebolt. This allows me to change pens by hand loosening the eyebolt replacing the pen and hand tightening it again. I find this much easier than using a hex-driver and mini-spanner.

Since the bolt is a bit longer than the pen carriage was before I’ve also repurposed the pen holder parts to make sure the limit switch is tripped before the eye hits the frame.

Here’s a detail of the limit switch contacting part:

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The new pen holder is created by cutting a short length of pvc pipe, drilling 5 holes into it and flattening one side with a file.

Here’s the view from above:

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Take the pipe and select a drill bit that matches the width of your eyebolt. Drill a hole and screw the eyebolt into it. It should have a nice snug fit without any play.

Next drill two holes in either side for the entry and exit points of the zip ties.

The hardest part is flattening part pipe so it won’t rotate against the arm. I used a file to cut a groove into the pipe that was the same width as the arm then I used a chisel to make it flat. This was the hardest part. In retrospect I probably could have just made two cuts with a saw to form the walls of the flat and then drilled or chiseled out the valley.

Sorry that’s not too clear, here’s what I mean:

Note that the cuts on the side view are supposed to be the height of the pen arm apart so that it fits snugly on the arm,

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#2

Can you provide measurements and I’ll put up a model on Thingiverse if folks want to print your pen holder. Alternatively, if you can provide the diameter of the pens, I can create a model to accommodate them.

#3

This thing is just cobbled together from stuff I could find at the hardware store. It I had a 3D printer I’d have designed a much better one that didn’t require zip ties. I’m glad you’re interested but I’m sure you can do better than to copy this thing.

#4

Happy to do that and send you one, but I’d still need measurements for the pen diameters and hole placements. Also, if you’ll include the measurements for the mounting holes I’ll design the mounting bracket into the model. :slight_smile:

#5

OK then, awesome, thanks.

Here’s my measurements along with the part and ruler for sanity checking.

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Can I just add what I think is a non-obvious design goal: to minimize the distance between the pen and the arm. There’s a potential volume conflict with one of the smooth rods if the pen is too far from the arm. I also think a V shaped opening would be better than a circle for securing the pen. I have to ratchet the eyebolt pretty hard to be confident the pen won’t move because I’m pushing it against a smooth curve.

#6

What a magic mod! Thanks for sharing it.

#7

Simple yet briliant! Thanks a bunch!

#8

So maybe a V shaped slot has to be put inside the tube?

#9

Right, I think a little notch might even do the trick, just to stop the pen from slipping without excessive force.

#10

I’ve just created a small penholder which simply screws onto the arm (where the original one screwed into). Uses two small M4 screws (I had plenty of these left over!)

You can download it from http://www.thingiverse.com/thing:2050135

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#11

That’s awsome! So much better than my clunky household item solution.

#12

Thanks - it’s working well for me so far.

I’ve also ported mDraw over to the Mac (native app) and some arduino changes (speed and limit control fixes) but I’ll do another post on that once soon!

#13

Lovely job! I’d intended to do that for someone else in the forum but my time has been consumed with the robotics team I’m coaching.

#14