Overly Complicated Pen Holder

[MadHatter]

A few months ago I posted that I was a little irritated at how difficult it was to swap pen colors when I was making multi-colored yard sale signs, and how I had planned on designing a new pen holder that would hopefully eliminate the need for having to precisely locate the pen tip height every time you needed to swap out the pen.

Well, here it is - at least the design. I have the models ready to print, but my printers are printing other things at the moment, so I am a bit early to be posting pics, but I am going to do it anyway.

The idea is that if you are using a Sharpie (or similar designed felt tip marker) with the little lip on it, they should index on the shoulder of the pen in the green pen holder. The reality though, is that all of the pens have a slightly different distance from that shoulder to the pen tip. So, there will also be an indexing stand that should be used to set the pen tip distance to standardize all of the pens / pencils you will be using.

I plan on printing multiple pen holders so that I can easily remove one and drop in another one and continue on. The pen holder will be held in place with both the keystone tapered mounting boss, and Neodymium magnets, so theoretically, the swap over should be quick and painless.

The yellow slider is for setting the bottom of travel for your pen, because there will be a lot of variation in mounting location, spindle height, stock height. . . so being able to set the lower limit of travel will be nice, if you need it.

Other holders can be designed to accommodate other sized pens / pencils, or a sleeve set can be designed for smaller diameter pens / pencils to be held properly centered in the holder. Whichever seems to make sense. Maybe a little bit of both? Let me know.

[HeuristicBishop (Tyler Sowers)]

You should make yourself a tool length setter that seats your pen carrier and has a hard stop for setting each pen to the same stickout.

Here is a crudely drawn example.
Lets you ensure all pens have the same effective length without having to mount on your machine.

[MadHatter]

Well, for the most part, things went pretty well. A couple of small changes to be made, but nothing drastic.

Usually, my 3D prints tend to be just a bit oversized by 0.01" or so. Oversized, but in the “drawing outside of the lines” manner. Like, 1" cube may measure 1.01" on sides, but 0.5" hole in the cube measures 0.49", so I usually just add or subtract that 0.01" as needed to the dimensions to get that fit I am going for.

Well, this time, that didn’t work out so well for whatever reason.

This is the gap I had set up for the keystone boss for the pen holder. 0.01" gap on each side. I figured it’d be a good fit.

Sad Trombone Noise

It was not a good fit. Oh well, the good news is, I can modify the small part and reprint it in about an hour. Also, being that it is tapered, I can slightly undersize it this time and if it does not seat all the way at the bottom, that is fine, as long as it is 85-90% down, that should be good enough.

Also, the holes for the linear rail line up nicely, but again, due to the 0.01" over/undersize, they are a bit too small for the thread forming tap to do its thing. It just gums up and rips the plastic out instead of forming it.

And I have to reprint it anyway, because I made a rookie mistake and forgot to tell the slicer to not put supports in the curved channels, so they are clogged with support with no way to get it all out.

Overall, not bad for a first go. A few small changes and I’ll be printing a new iteration shortly.

[MadHatter]

Well, believe it or not, I actually worked on this over the holiday break. I adjusted the dimensions for the interface between the pen holder and the receiver that mounts to the linear bearing block.

I also designed a small Sharpie cap since the regular one will not fit when the pen is in the holder. I tried the fit on 11 different Sharpies I found around the house, and it fits them all with varying amounts of tension, but nothing too tight or loose.

The interfaces look like because there is some play even when they are supposed to be locked together tight. I tried sanding down the surfaces / magnets to get a better fit, but it’s just not going to happen.

I think I will switch to a vertical V notch interface with a screw to pull them together. I’ll hopefully have something mocked up by tomorrow afternoon.

Anyway, overall, the design is functional, and probably more rigid than what I was /am currently using, but I want what I want, and I want more rigidity, so I am going to keep fiddling with it.

[Redlander (Tim Jones)]

@MadHatter

Pretty cool design there!

[HeuristicBishop (Tyler Sowers)]

Could you use a magnetic pin or ball bearing to more positively lock the holder in place? I’m thinking something like a v groove wherein the magnets in the interface pull a ball and seat it just under the diameter of the ball bearing.

Think something like a ball detent or kinematic constraint. It should automatically provide positive locking while still being “breakable” when going to remove the pen. (Maybe an integrated flexture in the 3d print you could press to break the magnetic hold on the ball )

Tool less changeover is convenient enough to warrant a lot of additional experimentation in my opinion

Looking good so far though, I’ll be ordering the linear rail today.

[MadHatter]

I was able to get the new mounting interface designed today. I switched out the heat-set inserts for #10-24 stainless steel square nuts, since those are cheaper and easier for most people to use. No soldering iron needed, but you have to pause your print and drop them in, so a little more work than hitting print and walking away.

The pen holder will end up being more rigid with the panel running most of the way down the side, and I also swapped out the thumb studs for 3D printed thumb collars that can have #10-24 SHCS epoxied in to make them. I prefer stainless, but whatever you choose would work.

I decided to add a locking lug on the left side of the pen mount as well, to help reduce any deflection. We’ll see how well it works. I will probably have to play with the dimensions to get things to lock together tightly, but I should be able to do it with the screws instead of the magnets. Also, the layer lines are now parallel to the mating direction. The previous design had the mating direction perpendicular to the layer lines, which caused binding instead of being able to seat tightly.

[MadHatter]

Well, I finally got around to printing and assembling the pen holder, and it is pretty solid.

The interface between the block and pen holder has no play whatsoever. The captured square nut in the mounting block can take a lot of force, so the holder can really be cinched up tight.

I may have gone a bit overboard and printed a few of the holders.

Here is a video of how easy it is to remove and replace the pen holder.

The flex you saw in the video was from me actually putting a lot more force on it than it would ever see in normal use, and a lot of the flex was at the linear rail, not the pen holder.

I’ll post a video of it actually in use in the next couple of weeks, since we will be having a yard sale soon, and as the yard sale gets closer, the “clean my CNC surface” moves up the priority list.

I have a pen height setter tool designed, but for now it will set everything at one height. I will probably modify it to be adjustable, but for now I am just going to make it set the height at the same height as the Sharpie markers.

I need to print different sized reducing collars to allow smaller diameter writing instruments to fit inside it and be clamped down and centered properly, so there will be a hole in one side for the screw, and it will have some sort of indexing mechanism, so you won’t have to play the “hunt for the hole” game when you try to tighten the clamping screw on the writing instrument through the reducing collar.

[MadHatter]

Well, it works just fine. I’m saying fine because it works, and it’s pretty solid, but at 200in/min there is a bit of wobble in the line when it is making rapid and short line segments. It’s not too noticeable at a distance, which is my current need, but I’ll probably be redesigning the holder and linear rail bracket to move the bearing block closer to the pen tip.

[Julien]

Just stumbled upon this thread, great project!
I miss the days when many people here spent unreasonable amounts of time to design custom add-ons for their Shapeokos, so this is refreshing

Not that I don’t enjoy seeing all the nice things people do with their Shapeokos these days, but it was fun when folks where doing things TO their Shapeokos

[HeuristicBishop (Tyler Sowers)]

I could draw that by hand in half the time and 1/20th the quality

It really did turn out great, I always see pen plotters and such using specific pens. So it’s a pleasant surprise to see such a great result from a regular ol sharpie. Awesome work.

@Julien I tend to agree, not a whole lot of mods these days. That said, get a Shapeoko in my garage and I’ll do things to it you wouldn’t want to see
(Like, why isn’t the table off the Shapeoko also a good stand in for a table saw? In my shop I don’t have the footprint for both so maybe the answer is a good integration…just pop the saw up right through the table )

[Julien]

@HeuristicBishop

why isn’t the table off the Shapeoko also a good stand in for a table saw?

Well at some point I had a lathe in/on/inside my Shapeoko. Marginally less dangerous though

[MadHatter]

@HeuristicBishop

I could draw that by hand in half the time and 1/20th the quality

Oh, same here. That’s why I take my “natural artistic talent” and put it in the corner where it belongs, and then design crap on the computer and have it do the drawing for me.

[MadHatter]

Decided to avoid yard work this morning and re-designed the pen holder to try to make it more rigid. I discovered that I need to get below the spindle shaft somehow, and it’s either going to be on the mounted side or the pen holder side.

I tried the pen holder side, and it was okay, but by moving the offset to the mounted spindle side I can beef it up a bit more without adding mass to the bearing block. I put three castellated holes through the extended part and I plan on using epoxy and some carbon fiber tube segments and try to make it more rigid than the PLA alone.

I was also able to move the pen 0.050" closer to the bearing block. It’s not much, but every bit counts. I can’t go much closer or there won’t be much PLA for the SHCS to press against to hold the reddish block to the bearing block.

[CullenS (Cullen Simpson)]

I will sometimes put a slight offset on the letters and do a contour on the line pass with a black marker on those vectors to make the letters pop. It really helps in the case of a lighter color.

[MadHatter]

Thanks for the tip. I’ll have to try that, maybe with a fine tip.

[CullenS (Cullen Simpson)]

A fine tip is a good idea if it looks ok. That would reduce the chances of bleed with the colors.

[MadHatter]

Well, I received the longer linear rail and was finally able to assemble the new version of the pen holder, and I was a bit surprised to find that the oscillations in the pen tip appeared to be pretty much the same. In some places, the oscillations are higher frequency, but the amplitude appears to be about the same.

New, shorter pen holder with longer linear rail part attached to spindle.

First pen holder, with longer pen holder and shorter linear rail part attached to spindle.

Here’s the new pen holder assembly. After this test, I’m just going to stick with the original one, since with the new one, you have to remove it if you want to cut things since it protrudes down so far.

I think about the only thing I can think of to change is make the pen cap smaller. Apparently, I am so smart, I made the pen cap large enough that it can’t pass through the pen holder, so you have to remove it to insert / remove a pen from the holder.