LowRider v3 CNC - Tool-less Quick-Change Accessory Holder / Tool Holder - for laser, drag knife, pen, etc (v3.0)

DougJoseph · May 19, 2023, 2:31am

Tool-less Kinematic Accessory Holder for LowRider 3 CNC 4.0 (BETA)

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

It’s in beta. Testing needed! Help requested.

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

Inspiration 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: this project is in BETA. Testers needed. I will link to separate Printables listings for various specific tool holders, intended to serve for testing attachments. I’ve already created a pen holder for this, which is a “remix of a remix of a remix of a remix” (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.

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). 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 seems possibly adequate — if I try to manually pull apart the Fixed Base and the Mobile Base, it takes a good bit of force to separate them. However, when the length of an attached toolholder / tool comes into play, then that add leverage, which means, honestly, I’m not sure the magnets are strong enough, and testing is needed to see if the magnet approach is viable. I’m trying to get to the process of both designing additional tool holders as well as testing what I already have. Help is welcome.

PRINT INFO:

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.

BUILD STEPS & NOTES:

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.
Install the disk magnets into the Fixed Base and Mobile Base.
- NOTE: The two disk magnets have to face in a way that attracts. This means either that one of them has to be “chamfer up” while the other is “chamfer down” or else it means you have to pry out one of the magnets from its metal cup, and flip it over and reinstall it. If you choose to flip one as “chamfer up” then either it has to be glued in, or else the screw hole will need a counterbore area opened up 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 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 dan’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 16mm. 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.
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!

Q&A:

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

BOM:

Filament of your choice (I’m using PLA)
These disk magnets: https://amzn.to/43slRo7
Three (3) of these ¼"-20 acorn nuts: https://www.lowes.com/pd/Hillman-3-Count-1-4-in-Nickel-Standard-SAE-Cap-Nuts/3035978 (or if you want to have a stash: Amazon.com)
Two M5 x 45 mm screws (from my stash but like these): https://amzn.to/3Wgltqa
Two M4 x 10mm / 12mm screws & nuts from this assortment: https://amzn.to/43c0wie
12 or more M3 x 16mm screws & nuts from this assortment: Amazon.com