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

Cool!

Remember, once a tool holder and tool are attached, they have length and it gives you leverage. That would also grant leverage to any lateral forces acting on the tool, such as drag (literally!) on a drag knife or pen. Also remember that for the kinematic coupling to succeed, the magnets must not touch before the nuts get fully seated into the trenches between the screws. So ideally, the magnets are almost touching, but not quite. It’s working quite well for me. Video soon.

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Based on how the magnetic field is flowing in the strong magnets I sourced, the magnets seem to not be attracting unless one of the two is turned backwards, with its metal cup facing the other magnet. This seems to reduce attraction some. The main killer on the attraction is too much distance between the magnets, once the kinematic coupling has been achieved.

When placing a single magnet on my refrigerator, I’m seeing a huge difference between front and back.
I think this means that the cup is redirecting the field lines to be more effective on the front.

In this diagram the green section is the magnet and the red section is the cup. The left side shows field lines if it were a regular magnet in free space without the cup, effectively symmetrical on front and back, whereas the right side shows what might be happening if the cup allows a “short circuit” path for the magnetic field to get back to the opposite pole.

image

I don’t know for a fact this is happening. I am guessing based on what I know of magnetic fields and the large asymmetry observed in these magnets-with-cups.

This could explain why flipping the magnet in the cup vs. flipping the assembly is significantly different.

One thing I’m curious about is how sensitive the force is to the distance. For a desired force minimum and maximum, how large is the range of distance? It could produce inconsistencies, where even if people are getting successful kinematic coupling, variations in the acorn nuts could mean unusually high or low pulling force if the force is excessively sensitive to distance.

I think I can test this with a fish scale and some shims to get a rough sense of distance vs. force for one magnet against my well-calibrated refrigerator.

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@jamiek — sounds awesome. It would make sense to me.

Now that I have made available a parametric fusion 360 file that has an editable user perimeter for the depth of the well for the acorn nut, it is easy to edit and produce a printable file that accommodates different heights of acorn nuts. I still need to add precise measurements of the overall height of the Hillman brand acorn nut that the original was based on, which led to a well depth of 5.1 mm, and the overall height of the ones I got from Amazon that required the significant offset adjustment (2.7mm deeper well).

I currently have two “fixed base” parts made. One of them has the metal cup facing out, and the other has the magnet flipped with the metal cup facing in. My sense is that I could designate one of them as “moderate grip,” and the other one as “strong grip.” I may yet find use for both of them at different times, so I am not disassembling the one that is not going to be in primary use. I have not yet had a chance to actually install the one with the strong grip to verify that it is, indeed, more effective at holding a tool in place, but I will update on that once I try it out.

That is correct. The cup/shunt amplifies the strength on the front side.

K&J has a calculator you can use to get better estimates on strength vs distance.

I’ve used this 2D magnet simulation tool on a few work projects. I use it mainly for directional design guidance and not for specific numeric values but it’s pretty useful if you’re doing that kind of project.

Now things get really crazy when you start using multiple magnets in different orientations. The Halbach Array is one that is very interesting.

Some clothing theft prevention tag removal tools use a similar array to release the tag’s latch. But this is now going off into the weeds a bit.

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Those are exactly the weeds I want to explore though!

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@Bigchepin cool! Thanks for the info! Amazing stuff!

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Great work Doug!
I am watching this as i want a laser for the LR3, and love the idea of the pogo pins for that.

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You are too old for shoplifting, all those security guards are faster… :stuck_out_tongue:

I seriously woke up in the middle of the night with an overwhelming feeling something was wrong after dreaming I was chasing some bad guys on foot. Then I realised what it was - in my dream my knees weren’t hurting!! :rofl: :rofl: :rofl:

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Latest new tool holder added for this:

LowRider 3 CNC - Add-on - KINEMATIC Pen Holder v4.0 - generic design for pens on LR3 Dust Shoe (v4.0)

Printables

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).

OTHER COMPATIBLE TOOL HOLDERS INCLUDE:

  • Pen Holder Inverted, remix of Jamie’s inverted pen holder: Printables
  • Laser mount for NEJE A40640 Diode Laser: Printables

This is a remix of:

https://www.printables.com/model/420517-lowrider-v3-cnc-tool-less-quick-change-accessory-h

…but modified to be compatible with the new kinematic tool-less quick-change accessory holder linked above.

Print notes:

  • Print as oriented
  • Prints with no supports required.

Assembly and use:

Print this, then attach it to a spare Mobile Base printed from the above linked kinematic tool holder, using two M3 x 16mm screws. Attach a pen of your choice using two zip ties. Then attach this and its Mobile Base to the Fixed Base on the LowRider v3 (this happens by a magnetic click), and then draw/plot something. Please post your make here, and post your results in the comments here.

Elephant’s Foot Warning:

This tool, when mounted, can be thrown off kilter by Elephant’s Foot (when the bottom one or more layers of a print are squished too much during printing). To try to prevent this, I’ve added some chamfers on the face that lays on the print bed. If your tool should be pointed crooked when mounted, check that face, which aligns against the Mobile Base, for any excessive Elephant’s Foot, and cut / sand it off.

Change log:

  • May 23, 2023 — initial release.

My PayPal tip jar: https://paypal.me/design8studio

Various LowRider 3 CNC remixes:

View all my models and remixes on Printables:

*Amazon product links are affiliate links.

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Another new tool holder added for this:

LowRider 3 CNC - Add-on - KINEMATIC Drag Knife Holder v4.0 - 1.0mm spring leaf (for drag knife such as sold by V1 Engineering)

Printables

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).

OTHER COMPATIBLE TOOL HOLDERS INCLUDE:

  • Laser mount for NEJE A40640 Diode Laser: Printables
  • Pen Holder Inverted, remix of Jamie’s inverted pen holder: Printables
  • Pen Holder, not inverted, v4.0 - generic design for pens on LR3 Dust Shoe, made for this v4.0 kinematic system: Printables

This is a remix of:

https://www.printables.com/model/420517-lowrider-v3-cnc-tool-less-quick-change-accessory-h

…but modified to be compatible with the new kinematic tool-less quick-change accessory holder linked above.

Print notes:

  • Print as oriented
  • Prints with no supports required.

Assembly and use:

Print this, then attach it to a spare Mobile Base printed from the above linked kinematic tool holder, using two M3 x 16mm screws. Attach the drag knife using zip ties. Then attach this and its Mobile Base to the Fixed Base on the LowRider v3 (this happens by a magnetic click), and then slice some vinyl to create something. Please post your make here, and post your results in the comments here.

Elephant’s Foot Warning:

This tool, when mounted, can be thrown off kilter by Elephant’s Foot (when the bottom one or more layers of a print are squished too much during printing). To try to prevent this, I’ve added some chamfers on the face that lays on the print bed. If your tool should be pointed crooked when mounted, check that face, which aligns against the Mobile Base, for any excessive Elephant’s Foot, and cut / sand it off.

Change log:

  • May 24, 2023 — initial release.

My PayPal tip jar: https://paypal.me/design8studio

Various LowRider 3 CNC remixes:

View all my models and remixes on Printables:

*Amazon product links are affiliate links.

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OK, so quick confirmation… regarding the above, I had previously mentioned:

I did finally get time to swap the “moderate grip” Fixed Base out and replace it with the “strong grip” Fixed Base. I do indeed feel stronger grip on it. I also can confirm that while its grip is so strong that without leverage I cannot pry them apart with my hands (when the two sides are connected away from the Main Mount and with no tool-holder added on) I am indeed able to remove the Mobile Base from the Fixed Base when the former has a tool-holder attached and the latter is attached to the Main Base. The grip is so firm that trying to move or dislodge the Mobile Base with a strong pressure can actually cause a visible bit of flexing in the whole system, but then pulling even more firmly on the tool-holder can get the coupling to separate. I like the extra gripping power, and will probably leave this Fixed Base on the Main Mount (i.e. the one with the magnet flipped so it faces out instead of the metal cup facing out).

So using my calibrated refrigerator, I measured the pulling force to be something like this:

I used varying layers of index cards and with each setup I measured how much force it took to pull the magnet off the refrigerator. The side of the refrigerator is about 50% higher than these numbers, which were on the front of the refrigerator. Maybe the metal is thicker on the sides, or a different composition.

When I try to gauge the force with my hand, it feels like this:
image

That made me nervous that the force would be super high or too low unless extremely tight tolerances were achieved, but I am glad to be wrong about that.

A tolerance of 0.5 mm and a pulling force of 1 kg for a pen is very reasonable.

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LOL :joy:

LOL again! :joy:

My “medium strength” Fixed Base with the metal cup facing out, would likely have been just fine for use with pen and diode laser, although I was a little nervous about it with drag knife, which I don’t even own, and may not ever get. However, my “high strength“ Fixed Base with the magnet flipped so the metal cup is facing in… is gripping tremendously, and I would feel very confident using it with pretty much any tool that could be attached. Its strength of grip is such that the whole setup, including the main mount, all has to flex a bit in order for the coupling to be separated.

DW660 for LR3 (left) and DW660 for Primo (right).

Printing these now, and I’ll post them if they work.

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@jamiek Cool!