An idiot buys a CNC machine

I’ve owned a Mark II 30x30 LongMill for about a year now. I have little kids, a full time job, no woodworking experience, and no desire to make money with the CNC. Which I think makes me a strange user. I think most people in my situation would by a 3D printer, but I hate how cheap and plastic the results are. So instead I bought a really expensive and super huge CNC machine.

What I have learned:

  1. Work holding is SUPER challenging. I have destroyed so much wood from stuff moving. I usually clamp stuff down and use tabs…but sometimes the tabs aren’t big enough. Or I don’t clamp well enough. Still trying to figure this out. Plywood is extra challenging because using tabs is effective…but then cutting them out by hand tends to rip and shred the “show” layer…

  2. Fusion 360 is free and crazy complicated, but doesn’t limit you. I spent a lot of time watching Youtube videos. After a several months I’m sort of competent at designing stuff that can be machined. I live in fear that Autodesk will take away the free hobby accounts.

  3. I have had so many issues with gSender failing partway through complicated jobs. Where complicated is anything with curves. This isn’t just gSender, this seems to be a common issue with Fusion 360/grbl and the various grbl sender. Some stuff that helps:

  • Turn off the tool number (this at least usually fails right away)
  • var xyzFormat = createFormat({decimals:(unit == MM ? 5 : 5), forceDecimal:true});
  • editing the GRBL cps like the line above helps a lot
  • screwing with the tolerance setting in Fusion 360 may help…
  1. I naively thought I could do big jobs and just walk away and let the CNC do stuff. Not true. The CNC is just an unthinking computer and if it smashes into a clamp, pulls the dust hood into the router, and lights the wood on fire it will keep humming along until the job is done. You have to monitor the job. Otherwise you can literally burn your house down. I’m debating setting up an old iPad so I can monitor the CNC from not-my-garage but even then that is risky because out of sight is out of mind…

  2. REALLY important to have a some kind of checklist to avoid stupid stuff:

  • always run outline to make certain you haven’t swapped x/y axis or a clamp will rip off the dust attachment
  • holding holding holding are you holding well enough???
  • triple check your XYZ zero-ing
  • can you reach the red kill button???
  1. For long running or multi-step jobs it is crucial to design in some reference holes (at least two) so you can reset the workspace if you have to smash the red kill button or stop the job and turn off the computer

  2. This page is amazing and I love it: Feeds & Speeds ⏩ - LongMill MK2 CNC

  3. Dust collection. You need it otherwise EVERYTHING in the room will get coated. Also you might destroy your lungs.

  4. Eye protection, breathing protection, and hearing protection is crucial.

What I have made:

  1. Trash can holder.

  2. Double sided knife holder

  3. Wall hooks

  4. Stirrups

  5. Desk hooks

  6. Boot tray

  7. Garage corner shelves

  8. Coffee maker base

1 Like

@dmcg Welcome to the group, David. You sure make a strong first impression. :grinning:

Thank you much for your detailed description of what you’ve gone through to get to where you are now. Work holding is not something that comes up here often, and you are spot on in emphasizing it. When work slips, at best you have a ruined piece. At worst, you have a fire, as evidenced by at least one Youtube video showing a work piece slipping along with the router, so that the bit was really staying in one spot. Scary stuff.

Finally, congrats on all the projects you have completed. It’s good to see someone making practical things on their Mill. Keep up the excellent work and keep posting.

Practical things…nice!! We are very very similar, including having what appears to be the same trashcan. I’ve been doing CNC stuff for over a year now and have pretty much converged on your exact points 1-9.

Adding to point 5… I have developed a habit of checking v-wheel tension and looking for any backlash in all axes prior to any job (having started my CNC journey on a relatively weak Foxalien was the best thing I could have done).

Oddly enough the LongMill is the least of my concerns. I haven’t used it enough to run into any wear issues. I think I overtightened (if anything) all of my V wheels and they still seem about the same. I did spend HUGE amounts of time calibrating the X Y (as it is challenging for some jobs to have 500mm be 501.2 mm). But for quite a while now the LongMill just runs.

That trash can base was shockingly hard to design. As you likely know, the bottom of it is not a simple shape. So I hand traced it, turned that into a SVG, spent many hours cursing at Fusion 360 to turn it into a shape, extruded it, cut a test base with a piece of scrap plywood, cursed some more as the test base was like 1% too small, and then cut the real one.

I’m learning a bit of zen as virtually everything I make has some issues. The trash can base is oddly wavy in a few spots (that’s a Fusion 360 problem), anything with plywood has a few spots where the birch face is splintered/peeled, the boot tray was kind of destroyed after like 10 different successful cutting operations when I did the final honeycomb pattern with a new bit and forgot to reset the Z and it plunged WAY into the oak…

Ah, Fusion 360. I have a love/hate relationship with it. To date, most of my cnc work has been designed in Vcarve as my previous machine was smaller and I only have the desktop version. Fusion is a bear.