Browsing posts in: CNC

Candle lantern design thoughts…

I’ve been spending some time doing a design in Fusion 360 for a laser-cuttable lantern, and I’ve discovered a few things. I’m recording them here to help others and to remind myself when I come back to this in a few months/years.

I started with a simple outline drawing of a tree that I wanted to use as the inset for the side panels:

Alder

I need to get that into Fusion in a way that works. Here’s what I came up with

From 2d to 3d

There are a couple of different approaches to doing this. If you have something that is simple, I recommend the “trace it yourself method”. In this, you insert the picture into Fusion as a Canvas (Insert->Attached Canvas), and then draw an outline in a sketch using it as a guide. I used splines and did a reindeer and rabbit outline pretty quickly, and then nice part is that manipulating the splines after that is simple and quick.

That was going to be a ton of work with the branches and I was both lazy and worried that it would be too complex to work well. So I took the alternate approach:

  1. Load the image into Inkscape and save it as an SVG.
  2. Use SVGtostl.com, upload the svg, and specify how thick you want it to be. You will be able to change this later though it’s a pain, so try to get close.
  3. In Fusion, in a new design, choose Insert->Insert Mesh, and choose the file.
  4. Switch from model mode to mesh mode.
  5. In the browser tree, right-click on the mesh and choose “properties”. My trees end up with 13000 facets, which is about 3 times as many facets as I wanted.
  6. Use the modify->remesh and modify->reduce options to get down the count that you want. You will probably have to experiment a bit to get it to work right. Start with Remesh, and preserve sharp edges and boundaries. You now have a mesh.
  7. Switch from mesh mode to patch mode
  8. Select the mesh in the browser
  9. Modify->mesh to brep. This is changing from the mesh representation – which you can’t really modify in Fusion – to the brep representation, which you can. This may take a while. At this point, you have both a mesh and brep version of the object in the tree. Delete the mesh version as it’s just taking up memory.
  10. If you look at the brep version, it has a ton of faces on it. This will slow things down, so it’s nice to clean up the faces. Modify->merge, choose “select chain”, and then click on one of the front faces. That should select all the faces.
  11. Click “ok. That’s going to sit and spit for quite a while, but eventually it should finish and you should just see one common face. Or maybe Fusion will hang and you’ll have to restart it.
  12. Convert the resulting body to a component, and save it.

Using the resulting design

The resulting design is very complex and will likely kill Fusion. It tried to use it to create panels for all four sides of the lantern, and that was a full failure; it would take a full 30 seconds to render.

What I ended up instead was doing the full design in Fusion without the complex branches. It looks something like this:

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I designed one side of the lantern and then used pattern on path to duplicate it around 4 sides to make sure everything worked, and then used it to cut the top and bottom for the tab holes.

Then, I took the original side that I designed, converted it to a component, and did the compositing of the side and the branches in a design that only had those parts. That worked well from a performance standpoint and since all four sides are identical, I can just cut the single one four times.

To get this to work I had to move the components so they were okay left/right, use align to move the frame so the front is coplanar to the front of the branches, and then extrude a couple tools to cut off the branches where they were too wide for the frame.

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Cutting on 2.7mm plywood (was supposed to be 3mm….) took about 5 minutes for each side, and a couple of minutes for the top and bottom.

Here’s a totally uncleaned/unsanded version. It would also look nicer if I taped the wood to protect it:

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Bespoke bicycle Holder

My nice bicycle currently hangs on two old shelf standards that are screwed into the wall, with some foam on them to protect the frame.

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It works, but the foam has seen better days and if we got a quake, it could easily shake off the ends.

It’s time to build something a bit nicer, so I dug out some leftover hardwood plywood I have (maple, I think) and spent a little time with Fusion 360, and came up with the following design:

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This is a render in oak. The holes are 16” apart so they can screw directly to the studs, and the hangers are a bit closer together so it’s easier to hang the bike with batteries on it. The arms that hold the bike have two hefty tenons that stick all the way through the back piece.

Off to the garage to use the Shaper Origin…

Cutting

The cutting mostly went pretty well, but it took longer than I expected and I worked past a point of being too tired and therefore had a couple of issues. I’m using a piece of maple plywood that I had lying around that is unfortunately not very wide, so I had to put some auxiliary pieces off to the side with shaper tape on them so that it could figure out where it was. This mostly worked, until I got to the last cut on the last piece, and partway through I bumped my setup and that piece – which was partly clamped but not correctly clamped – moved.

That is *bad*; the shaper throws up a big banner that says “the markers have moved and you are SOL”, or words to that effect. I tried a cut after that, and they were right, so I finished cutting through with an abrasive disk on my dremel and cleaned up with a little sanding drum.

A little sanding, and it was time for gluing and clamping. The nice part of the holes and tabs approach is that there is a ton of surface area, so lots of material for the glue to grab onto. It’s probably strong enough with the glue because of the way the geometry works; the arms that hold the bike can only pull straight out, and even that is difficult. So, no fasteners required, but a lot of clamps.

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Give it 4 hours for the glue to set, and we are left with this. The dark coloration looks like a burn but is really just the plywood.

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Overall, it came out mostly okay; in some places the fit isn’t as tight as I’d like – which I attribute to some wiggling because of how I did the cutting – but it’s more than functional.

Four 3” screws to mount it – yes, that’s overkill, but it’s so easy with an impact driver…

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and we’re done. I’m hoping the sunscreen shelf will help remind me to use it before I leave. I used some short pieces of the foam from the old holder to pad the new one.

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Draft: Compound miter saw table…

I have a decent DeWalt compound meter saw next to my garage; it lives next to my table saw on a stand like this:

Image result for dewalt dwx723

The stand is nice a rigid and easy to take places, which is nice. It does have a few issues:

  • The legs stick out towards the car that is parked next to it, taking up space.
  • There’s no good place to stack stock; it will fall off of the rail.
  • The lack of support between the saw table and the extensions is annoying.
  • The table is about 1” higher than my table saw, which means you have to move the saw table to do even a small cut on the table saw.
  • It lives right where a small outfeed table would be nice.

I’ve been playing with some ideas on how I might build something in my second shaper origin project, and here’s what I have so far.

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It’s drawn to use 18mm baltic birch plywood. The drawing is pretty rough; no connection tabs, no holes, just a bunch of rectangular solids so far.


A few cutting remarks–USB charging station part 3

In our previous episode, we had just finished cutting the hub portion of the station.

Now, it’s time to cut the remaining parts. I started by cutting the biggest part – the base. It’s about 8″ x 10″, and it has 17 slots in it and 4 holes, and each of those need to be cut in two passes. I decided to cut all the interior holes first in two passes, and then cut the outline. So, I started at the bottom and cut about 13 slots, and then I found that there were four slots missing.

When somebody added shelves to the design, he forgot to do the cut operation with the new shelves, so there were no holes there. Which means that the design needs to be redone, and since shaper doesn’t support an “update my design” operation, I had to abandon that section, though I did manage to cut a shelve out of it so it wasn’t a total loss.

The rest of the cutting was pretty repetitive. The shaper mostly worked okay, though it crashed a number of times and hung a few times as well. The back has 7 holes and a bunch of tabs and the shaper crashed on the last cut. Then I rebooted and found that both the workspace and the placement information is stored in non-volatile memory, so as long as the crash doesn’t damage your workpiece, you can continue.

Eventually, I finished cutting all the pieces, and started cleaning them up:

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The shaper uses an upcut spiral bit so that it can easily pull the sawdust out; that cuts well, but leaves a fuzzy edge to the cut. I tried an offset technique where you do the initial cut a bit to the outside of the final line and the second cut right on the line, but the results weren’t any better. I’m going to explore whether a nicer bit would give a better result, but the result here is really worse than it looks. A couple of minutes with some 220 grit sandpaper and it cleans up nicely.

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A bit more time for cleanup, and I had a bit pile of parts:

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So, is this going to actually work, or was all that effort for naught?

Well, guess what?

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The fit of the tabs was very nice and it looks pretty good even without any glue to hold the parts together. Success!

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Next up is to look at all the joints and do a bit more tuning on the fit, especially on the hub holder in the left of the last picture.