LowRider v3 CNC - Tool-less KINEMATIC Accessory Holder for LowRider 3 CNC 4.0

Here’s the video I made about this!

Ok, as discussed over here, here is a link to where I posted the new KINEMATIC tool mount, tool-less quick change accessory holder.

Download: Printables

This is an adaptation of a Maxwell Kinematic coupling. You can read about that here: Kinematic coupling - Wikipedia

Original motivation was a nudge from Jamie K on the V1 Engineering forum.

Speaking of which, Jamie has now remixed this in a way that requires no acorn nuts, no screws for troughs, only one magnet on one side, no need for drilling any magnets for additional countersinking, and no need for prying any magnets out for flipping them. Check out his remix here. His remix avoids acorn nuts and avoids troughs made from screws, all by having both “mounds” and “valleys” made from 3D printed plastic. Here’s a photo of Jamie’s remix:

Additional inspiration for my work here came from Workshop Feedback channel’s posting of his custom CoreXY printer and it’s electromagnetic tool-changer. My design is a freshly created thing from the ground up, and I don’t at this point utilize his concept of having flexible printed mounts for the magnets, but I drew heavily on his excellent work on his tool changer.

Summary of Kinematic coupling: “fixtures designed to exactly constrain the part in question, providing precision and certainty of location.… consists of three radial v-grooves in one part that mate with three hemispheres in another part. Each hemisphere has two contact points for a total of six contact points, enough to constrain all six of the part’s degrees of freedom.”

In this case, I’m combining use of disk magnets for the coupling force, common M3 x 16mm screws arranged in a 3D-printed “mobile base” to form the “three radial v-grooves”, and common ¼"-20 acorn nuts (aka cap nuts) arranged in an opposing 3D-printed “fixed base” to serve as the “three hemispheres” and thus is achieved an easy, affordable Maxwell Kinematic coupling.

Note: I will link to separate Printables listings for various specific tool holders, intended to serve for attachments. I’ve already created for this: a NEJE diode laser module holder, a drag knife holder, and two pen holders, which are remixes of prior remixes (with the most recent being an “inverted” one by Jamie, @ jamiek on the V1 Engineering forum, which served for my first tool holder for this new accessory quick-change mount system).

This system affords a one-to-many relationship between a “fixed” side (you need one set of it) and as many “mobile” side sets as you want, interchangeable.

  • The “fixed” side is comprised of two parts:
    • new Main Mount that is merely a new iteration of my previous pen-mount / tool-changer designs, which gets attached to a LowRider v3 using two (2) M5 x 45mm screws), and
    • new Fixed Base that gets attached to the Main Mount using at least three (3) M3 x 16mm screws. The Fixed Base has one of two disk magnets.
  • The “mobile” side is comprised of two other parts:
    • new Mobile Base that gets a specific tool holder attachment on one side, and which has the second of two disk magnets in it on the other side, allowing it to be magnetically bonded to the Fixed Base, for what we hope is a suitably strong hold for using add-on tools.
    • A specific add-on tool holder, for items such as pens for plotting/drawing, drag knives for cutting vinyl signage, and diode lasers, while other possibilities include a depth finder I’ve been pondering conjuring for a while that would be a bit like a BLTouch, except for LowRider CNC work.

Aside from the two M5 x 45 screws, and two tapered head M4 x 10mm screws and nuts (or M4 x 12mm, depending on your situation), so far pretty much everywhere else I’m using M3 x 16 mm screws (and nuts), and M3 x 12mm screws (and nuts). The M4 screws are serving to hold the magnets in the bases, and thus are optional as you could opt for epoxy glue instead.

The magnetic force of attraction is adjustable, and ranges from adequate to overkill. When the length of an attached toolholder / tool comes into play, then that adds leverage, which helps with the task of separating the coupling halves, when desired.

Note: since acorn nuts can vary from brand to brand, not all 1/4"-20 acorn nuts are the same height. This can be accounted for by measuring, editing a parameter in Fusion 360, and reprinting the Fixed Base as needed.

I have two brands of acorn nut that are vastly different. One has its “dome” approximately 2.7mm taller than the other brand. This added height makes a huge difference. Unless compensated for, the magnets are too far apart to be effective. The workaround is to edit the “Fixed Base” component and deepen the capture wells that hold the acorn nuts. In this way you can tailor your Fixed Base to the acorn nuts you have available. I have uploaded both a Fusion 360 file and a STEP file to make it easier to remix/tailor to your needs. To edit this depth, in Fusion 360, in Design mode, click Modify > Change Parameters, and then edit the value of the “Depth_of_acorn_well” parameter. After editing, you can right-click on any affected components, in this case “Part B, Nut Side as Fixed Base” and choose “Save As Mesh.”


  • Print as oriented.
  • Prints with no supports needed.
  • Use the same number of perimeter walls and same infill as most of the LowRider 3 parts.



  • Pen Holder Inverted, remix of Jamie’s inverted pen holder: Printables
  • Laser mount for NEJE A40640 Diode Laser: Printables
  • Pen Holder, not inverted, v4.0 - generic design for pens on LR3 Dust Shoe, made for this v4.0 kinematic system: Printables
  • Drag Knife Holder v4.0 - 1.0mm spring leaf (for drag knife such as sold by V1 Engineering): Printables


  • Print all the parts.
  • Insert three (3) nuts, M3, into three of the nut capture slots on the back side of the Main Mount. I chose to use the holes at 12 o’clock, 6 o’clock, and 9 o’clock. I left other holes just to allow for future possibilities not even on the radar. The upward protrusion on the main mount signals which hole is 12 o’clock.
  • Use of pliers can help with squeezing the nuts into the capture slots. Optionally you can insert screws through from the front, and tighten them until the nuts get pulled into the slots. It’s important for the nuts to be properly oriented for a straight approach by the screws, later, when attaching the Fixed Base.
  • If you plan to use epoxy or some other glue to hold the disk magnets in the Fixed Base and Mobile Base, you can skip this step. Otherwise, for use of M4 screws to hold the magnets in place, insert two (2) nuts, M4, into the back sides of the Fixed Base and Mobile Base. Use an M4 screw, inserted from the front, to tighten until the nuts are in place. Remove the M4 screws for now.
  • Install the disk magnets into the Fixed Base and Mobile Base.
    • NOTE: The two disk magnets have to face in a way that attracts. Based on how the magnetic field is flowing in the strong magnets I sourced, this seems to always mean either that one of them has to be “fillet up” (metal cup facing out) while the other is “fillet down,” or else that you have to pry out one of the magnets from its metal cup, and flip it over and reinstall it (and counter bore its side now facing out). If you choose to flip one as “fillet up” then either it has to be glued in, or else the screw hole will need a counterbore area opened up in the metal cup so the M4 screw can be counter sunk. If you choose to pry out and flip, then be aware that neodymium magnets are brittle. It’s easy to break them. However, I broke some and still used them. They are squeezed in between the screw lip and the edge of the metal cup, and they stay in place. Also, their brittleness can become apparent if you screw them down too tightly, or if you use too much clamping force in pushing them into position. The metal of the magnet is both hard and brittle. I found that attempting to drill out a counterbore hole in the magnet itself, was a futile effort given my available tools.
    • NOTE: In order for the kinematic coupling to work, the spheres, in this case the caps of the acorn nuts, must all make firm contact with the M3 screw troughs before anything else touches. Also, in order for the magnets to provide enough coupling force, the magnets must be almost touching, aka practically touching, by the time the acorn nuts get seated into place against the M3 screws. This means the M4 screws need to be totally flush, not proud at all. You may need to pre-grind the top of a screw off, if it’s sitting proud.
  • Install three (3) acorn nuts (¼"-20) into the three capture slots on the “star points” of the Fixed Base. I found it easiest to hold them straight with pliers, with their hexagonal bottoms positioned for straight entry, and then press them into the opening. Once they are “started” in, they can be tapped in the rest of the way with a rubber mallet or dead blow hammer. Avoid use of a regular metal hammer, or you will flatten the tops of the acorn nuts.
    • OPTIONAL: use of glue can ensure they don’t come out, but if you have a tight fit, it may not be needed. If you later need to remove them, say to move them to a new print, you can force them out by inserting something slender, like an allen key tool, through the holes on the bottom of each star point, and tap with a hammer.
  • Install six (6) screws, M3 x 16mm, into the Mobile Base, two into each of the “star points.”
  • On your LowRider v3: Remove two M5 screws — one from the right side of the lower router mount, and one from the right side of the dust shoe mount.
  • Replace the above M5 screws with longer ones (recommend M5 x 45mm), inserting them though the Main Mount part, then back into their original locations. Tighten pretty snug.
  • Attach the Fixed Base to the Main Mount using three (3) screws, M3 x 12mm. This corresponds to the above mentioned nuts at 12 o’clock, 6 o’clock, and 9 o’clock.
  • Attach some specific printed tool holder of your choice to one of your prints of the Mobile Base, presumably with the tool. :slight_smile:
  • Magnetically click the Mobile Base onto the Fixed Base. Check alignment and grip. Test out use of the tool. Report back here in the comments! :slight_smile:


  • Q: What’s the purpose of the upward protrusion on the Main Mount?
  • A: It’s sole purpose is to aid with assembly, by offering a visual cue for alignment of the Fixed Base
  • Q: For making my own custom tool holder to be compatible with this, what do I need to know?
  • A: There is an included file named “Blank for remixing mount for your tool holder.stl” that can be used to help you. Also, you can make your own blank by creating a “clock face” that is 53 mm in diameter, as thick as you need, and which has 12 screw holes (M3 size) positioned like the hours of a clock face, and at 21.0 mm radius from the center. This sketch from the Fusion 360 file shows some key dimensions:


  • June 9, 2023 — Regarding “Part A, Main Mount - mounts to LR3 Core” part being updated to v4.1: This new revision has a deeper screw well on the lower M5 mounting screw hole, to fix an issue of collision with Part B, which was caught and reported by fellow V1E maker Kris (**@**KL2001 on the V1 Engineering forum). Kudos to Kris. Thanks for the heads up. Also, watch for more new updates soon that will simplify making this tool mount, and the BOM for it.
  • May 19, 2023 — added link for new tool holder, for NEJE A40640 Diode Laser
  • May 18, 2023 — Quite a few design/print/test prototype iterations preceded this beta release. Video forthcoming. If I can get one hand free.

Change log:

  • June 9, 2023 — updated the “Part A, Main Mount - mounts to LR3 Core” part to v4.1. See “Updates” above for details.
  • May 23, 2023 — uploaded a slightly tweaked version of Main Mount, to get more perfect alignment of screw holes between Main Mount and Fixed Base. Changes were so tiny as to be barely measurable. No need to reprint if you already printed the Main Mount, unless you are having issues with using it.
  • May 20, 2023 — rebuilt two components using Fusion 360 instead of SketchUp, both for precision as well as to make key aspects parametric, so users can tweak as needed. Uploaded these two new components as STL files, and provided both Fusion 360 archive and STEP file for easier editing/remixing.
  • May 18, 2023 — initial release, in beta.

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Various LowRider 3 CNC remixes:

View all my models and remixes on Printables:

*Amazon product links are affiliate links.


First tool holder for the above:

LowRider 3 CNC - Add-on - KINEMATIC Pen Holder / Drag Knife Holder - designed for LR3 Dust Shoe (v4.0)


Based on @jamiek 's posted here: LowRider v3 CNC - Tool-less Quick-Change Accessory Holder / Tool Holder - for laser, drag knife, pen, etc (v3.0) - #60 by jamiek


Hey Doug, looks really interesting. The drag knife mount is missing that little groove again though. :yum:

I just finished creating a NEJE A40640 Laser mount v4.0 for this. I have not gotten to the new drag knife mount. That’s next up I guess, but first I need to get the laser mount added to Printables.


I like it!

It looks like it can also support revisions to the fixed base and mobile base without having to re-do the main mount or tool-specific holders, which is a bonus.

It also looks like there is available space around the perimeter between the three balls and the print orientation means that the fixed base and mobile base can have extra arms in the future. This can add extra function in the future, like a mechanical clip or a hole for cotter pins or who knows.

I’ll be building this but first I have to chop the Main Mount and add it to the bottom-clamp-660-primo.stl, which is equivalent to the corresponding piece on the LR3 DW660 mount. I’ll have to work out the clearance so the router fits too.

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Cool! Yes, regarding making modifications to it, I just placed an order yesterday for some banks of (magnetic) pogo pins, and their opposing connector strip sides, that should enable running wiring to the fixed base, and being able to get power/signal functionality out to a “tool” that can be attached and detached without having to mess with wires or plugging every time you put it on or take it off. I’m pondering all manner of possibilities there, but primarily I am hopeful of designing and implementing a depth finder that can be used to home the CNC machine down to the material for creating a matrix of grid data points for purposes such as universal bed leveling, but for a CNC instead of for 3-D printer. It would be an ambitious project but perhaps doable.


Latest new tool holder added for this:

LowRider 3 CNC - Add-on - KINEMATIC Laser mount v4.0 - designed for NEJE A40640 on LR3 Dust Shoe (v4.0) (BETA)


This is made to go with the LowRider v3 CNC - KINEMATIC Tool-less Quick-Change Accessory Holder - supports laser, drag knife, pen, etc (v4.0).

NOTE: This is in beta. Testers needed. I don’t yet possess a diode laser module, so I’m dependent on those who do for testing the full functionality of this holder. :slight_smile:

Print notes:

  • Print as oriented
  • Prints with no supports required.
  • There is a one-layer-thick sacrifice layer in two places were large tool access holes transition down to smaller screw holes. After printing, either burn away the sacrifice layer with a soldering iron tip, or cut it out with a knife or a drill bit, to clear it and open the screw hole.

Assembly and use:

Print this, then attach your NEJE A40640 Laser Diode to the tool holder. There are access holes on the back of the holder so your tool can reach the screws for this. Then attach the tool holder to a spare Mobile Base print in the listing above, using three (3) screws and nuts, M3 x 16mm.

Attach this and its Mobile Base to the Fixed Base on the LowRider v3 (this happens by a magnetic click), and then laser engrave or laser cut something. Please post your results in the comments here.

What program are you using for the 3D modeling by the way? I’m finding very tiny asymmetries which are too small to have any practical effect (e.g. about 0.01 or 0.02 mm), but in reverse-engineering the exact dimensions they show up as discrepancies.

Hmm. I am doing these in SketchUp, and my mesh-editing work is at a 1:1 ratio size wise, and I know SketchUp “fiddles” with things in tiny ways, most noticeable when doing 1:1 work. I think that’s why some folks set their model to either 100:1 or 1000:1 size, and then shrink the result for their final. Is it show-stopping issues?

Also, there is the chance that it’s human error.

If you get a chance to show me where the inconsistencies are, I can work to correct them.

Nowhere close to a show-stopper, mostly just curiosity. On the Fixed Base, the top hole for the acorn nut is not exactly centered relative to the center hole. It’s shifted to the right by about 0.02 mm, which would never matter in real use. That doesn’t seem like a human error and feels more like a tool artifact. Also a lot of dimensions are “odd” numbers like on the Fixed Base, the center to the end of the arms appears to be 39.534 mm and the total thickness is 11.1153 mm.

Generally this makes no difference at all, as long as the parts are coherent with each other. The exception would be for third party extensions, you might want to release a drawing spec that identifies the interfacing dimensions, which would be essentially just the 12 holes on the Mobile Base. I am showing those as having a center that’s 21.045 mm from the center, which is not a bad number per se, but why not just 21 mm. Or you could torment people with 21.0344 mm which is 53/64ths of an inch.

These are great suggestions. Thank you!!

So, I opened up the SketchUp model, and not only found the minor inaccuracies, but also confirmed they are “caused” by SketchUp — when I try to correct them, I find that they cannot be corrected while working at a 1:1 size ratio. Note: In SketchUp, I have the model’s level of precision maxed, at 0.000000mm, and I have “enable length snapping” turned off. Despite that, there is apparently some type of a “grid” or some low level of snapping, and no matter how hard I try to get the screw hole centered, it nudges it like around .1 or something to either the left or the right. I think this affected all three star points.

I’m currently working on rebuilding the thing in Fusion 360.

PS: this is SketchUp 2017, and due to some effort by the developers to balance for optimized performance, and some notion that fine precision does not matter, it is not the best tool for modeling this kind of thing, if precision is deemed important.

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I have gotten the “Part B, Nut Side as Fixed Base” component recreated in Fusion 360. I am working to recreate the “Part C, Screw Side as Mobile Base” and may also need to recreate the “Part A, Main Mount - mounts to LR3 Core” component as well.

None of the new work has been posted to the Printables listing yet.

Note: since acorn nuts can vary from brand to brand, not all 1/4"-20 acorn nuts are the same height. This is a wildcard in this project.

I have two brands of acorn nut that are vastly different. One has its “dome” approximately 2.7mm taller than the other. This added height makes the magnets too far apart. The workaround is to edit the “Fixed Base” part and deepen the capture wells that hold the acorn nuts. In this way you can tailor your Fixed Base to the acorn nuts you have available.

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Just watching this develop Doug. I have sketched something similar/not similar but won’t be doing anything until I have a machine - and by then it looks as though the work will have been done for me!

Thanks! :smiley:


I have now recreated both the “Part B, Nut Side as Fixed Base” and the “Part C, Screw Side as Mobile Base” components, and have exported both a Fusion 360 archive and a STEP file. I’ve not used STEP files before, and so I don’t know if it’s a problem, or not, that the two components occupy the same spacial area or not, when someone tries to use a STEP file containing both components. I’ve also exported mesh STL files from both components. I will be updating the Printables listing with these two components.

OK, the Printables listing has been updated with the new components rebuilt in Fusion 360, and STEP file and Fusion 360 file added to ease editing/remixing as needed.


I love it!

Amazon was fast with the magnets and I am ready:

But holy crap these have huge axial pull when two are stuck together. I don’t think I’ll be able to separate them! I think I will find some washers or perhaps make some steel discs. If a full-size steel disc is more than enough, then the pull strength could be fine tuned by reducing the size.

Or maybe like that Workshop Feedback video, a compliant mechanism can maintain tension. Then a plastic shim between the magnets can maintain some separation so the force to separate is not too high.

Or probably better is something simple like a little gap for a screwdriver to pry the parts apart, or an extra bolt and captive nut on the mobile base to push it away from the fixed base when dismounting.

I don’t know, just thinking out loud.

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Why not muck around with printed.spacers till you find a compromise that works?

I don’t want to hijack Doug’s thread but I’ve been doodling with a mag switch arrangement- it’s quite complicated to build at first glance but if I can get it to work you lot will be the first to know!