Hi,
I’m looking into the LowRider to cut cardboard. I would like to mount a vibrating knife (mounted power tool on a rotating axis, not a real tool head) and I would need the software to calculate the knife direction for tangential cutting.
I’ve look on the forum, it doesn’t seem that this kind of project already exist.
Is it a crazy project or it’s totally doable ?
I’m ok in electronics and fairly good at coding (C++/Arduino/PlatformIO).
Regards !
Not sure if this helps but there are some people on the forum that made needle cutters to cut foam. They may have some ideas. Welcome aboard!
You’ll need to find or write a post-processor for your CAM program of choice, but the FluidNC kinematics will certainly support it.
edit: On second read, it looks like the FluidNC kinematics (in an experimental branch of the software) will ‘just do it’ for a tangential knife. It’s a drag knife that you would have to do some path manipulating gymnastics for.
Welcome Samuel (@sbarabe ), there have been a couple forum members playing with this over the years. Here’s one that seemed to be going in the right direction.
Make sure to start a build thread so we can follow along. Best of luck!
I have found this StepCraft OTK-3 tangential knife, I will look on how I could fit it on a LowRider. It’s cheaper then the industrial type, but still a lot cheaper in time for R&D for knife development.
I’ve also found this light industrial head with mounting plate. It’s about 3kg. Is it too heavy for the gantry ?
It would be a wonderful tool, expensive but wonderful !
Looks like OTK-3 has 2 open loop steppers, am not seeing any load sensors for precise pressure control. Maybe has a limit switch to home knife angle, but not seeing inbuilt way to home oscillator stepper? Guessing the manual adjustment wheels attached to the dual shaft steppers are used to manually fine tune pressure when oscillator is not being used for cuts. From OTK-3 manual…
From section 6.2 pintout, it does seem like there is a home switch for blade orientation. There is also a speed signal and a job status signal (pause/resume oscillation I guess).
There is no pressure adjustment, both knobs are for manuel positioning of blade…
Are you looking to drive the angle of the knife as an extra axis - or more of a traditional drag knife where it’s just free to rotate and there’s an offset to the blade to allow it to do so?
I made one of the 2nd style for my original MPCNC years ago. I remixed an existing design to add the mount I was using on my machine at the time: HicWic dragknife by jhitesma | Download free STL model | Printables.com
It functioned well, but I never came up with a software toolchain I was happy with for generating the moves needed to deal with corners.
Donek who make a commercial drag knife have a spreadsheet they share which is supposed to be able to add the corner moves to existing gcode: Free cnc router software downloads for our Drag Knife But I don’t have excell and couldn’t get it to work correctly in google sheets or open office.
dxf2gcode is also supposed to be able to do it - but I never got it to successfully process gcode from estlcam - it either crashed or just created garbage.
A quick search and I see a new python option has come up but I haven’t tried it: GitHub - psol/drag_knife: G-code post processor for drag knife (such as Donek) on a CNC.
I did do a few test cuts in cardboard just without sharp corners - but with just a standard utility blade my old original (considerably larger than recommended) MPCNC really struggled with the forces. My main use of my machine was for cutting foam board (which was why I made it as large as I did) and again while the drag knife could cut it I wasn’t really happy with the cut quality and found my needle cutter to cut faster and cleaner with much easier gcode creation.
I did experiment with using the needle cutter on cardboard after some people asked. And…while I was able to cut most cardboard with it I can’t say it was something I would recommend as it was really putting a lot of stress on the needle cutter compared to cutting the foam it was designed for.
The link shared by @Bigchepin above is an older thread from around that time where someone was developing a driven tangential knife which I do believe they had success with.
I also experimented with cutting vinyl with a standard vinyl cutter head - but again had the same issues with post-processing the offsets for corners that I struggled with on my drag knife. I’m sure it’s a solvable problem - I just didn’t have enough interest in solving it since my needle cutter worked well for my needs so I didn’t put much effort into finding a solution.
Hi Jason,
Thanks for all the reference for the draging knife !
I was looking for no particular solution but the tangential cutting with axis rotation and an oscillating/vibrating blade seems the best way to cut cardboard.
I was looking to design and make furniture based on recycled cardboard and not being shapes limited by the cutting tool.
I’m still looking for all possible solutions, I’m not settle yet.
Have you considered a diode laser?
Yes, even CO2 laser. But I’ll have to manage all the smoke over that big table and I’m not sure I like the burn cut effect.
Co2 is a lot more work with mirrors and chillers. Engraving causes a lot more smoke than cutting does in my expereice but yeah it’d need managed if you’re cutting all day every day.
Fair point about the soot - I think with tweaking it can be minimised there’ll always be some.
I’m really happy with the versatility of my diode laser - I just used it to mark some of the kids things for school next year, pencils, lunchboxes, anodised water bottles.
Lasers are cool. 
You can cut trough corrugated cardboard with diode laser ?
Very tempting solution !
Nice, how about speed ?
Could you use saw dust like caption, like with the router) for smoke ?
What kind of diode laser are you using ?
Use a dust extractor for smoke you mean? I don’t see why that wouldn’t work.
I haven’t done any material tests so that was a guess at settings
1000mm/m with air assist in 7mm cardboard.
As far as I know you can use lower power and multiple passes to reduce soot.
using a 30w laser LASER TREE K30 30W Optical Power Laser Module
(i got it for less than $300 - still, it ain’t cheap). I can cut a lot with it though - even 8mm MDF with patience and even very thick wood (this was in 2 passes, one from either side.
Ok what else do I need with the laser head ? Air pump ?
And the working surface is a kind of metal mesh ?
What about the bottom of that working surface, can it be wood or it will burn ?
Sorry lot of questions…
Thanks !
Metal mesh is good, free floating might also work. In my experience, laying the material on wood is not good for cutting through as you get very thick smears of soot around the cut line, at least on my much weaker diode laser
No, no problem, it was my hijack so only fair.
Air - cheap aquarium pump like thing. You can use a compressor if you have one but this works for me.
You can use a honeycomb mesh, some big co2 bed lasers the bed is upturned L profile in rows like ^^^^^^^^^^^^^^^^^^^^^^^^^^^^ it’s something to keep the underside of the material in space so it doesn’t char. If you had wood underneath if would probably burn yes BUT the easiest way round that would be a layer of aluminium kitchen foil which the laser can’t penetrate.
Remember you also need safety googles. You only get 2 chances if you get a beam bouncing off something!
