Resizing a 400x400 honeycomb bed to 400x300

Resizing a 400x400 honeycomb bed to 400x300

I got my Full Spectrum Laser hobby laser used, and unfortunately, it did not include its honeycomb laser bed.

I ordered a small one initially, because it was on sale, even though it was small.  Overall, it measured 295 mm x 295mm, though it had markings in the middle that range 0 to 250.

The enclosure of my laser allowed for a honeycomb about 400mm wide (X axis).  Depth (Y axis) could fit quite a bit, but the gantry takes up a lot of it.  And using the too-small bed as an example, it seemed reasonable to target about 300mm depth for the new bed.

It's surprisingly difficult to find a 400mm x 300mm honeycomb bed these days.  Most, it seems, are geared towards diode lasers, which are 400mm x 400mm.

Prices are coming down quite a bit, too.  I saw one person wanting to sell her used, cruddy honeycomb for $80, but I could buy one new on Amazon for $18.99 (with "free" shipping).

I bought one of those 400x400 beds, and got it in a few days.

 

The bed I got did not have measurement markings on it, like the 295x295 did.  But overall, it was constructed in a similar manner.  There were four edge pieces, which appeared to be extruded aluminum.  Those were connected somehow using rivets, two on each corner.  The honeycomb itself appeared to be strips of corrugated steel, and there were rods going through them.

Naming, labeling, analyzing

 

I named the frame pieces Top (1), Left (2), Right(3), and Bottom(4).  The corrugated strips run parallel to Top and Bottom.  The internal rods run up and down, parallel to the Left and Right frame pieces.

Remove six of the rivets

My first investigative task was to drill out a few of the rivets.   I just used a hand-held power drill and a strong-looking bit.  After some amount of chipping out, the last thin ring of metal breaks off with a satisfying click.  I ended up removing the two rivets for each of the Top, Left and Right frame pieces.

A look under the covers

Once I had the rivets off, I could wiggle the top frame edge off.  This then revealed what was going on under the covers.

 

As it turns out, the honeycomb is quite simply and somewhat accurately built.

The four frame edge pieces are indeed extruded aluminum.  In my case, it appears they're anodized, so they are black on the outside.  They're like square tube, missing one side.

The frame edges are cut at a 45 degree angle at each corner.

The edges are joined using steel L corner brackets.  They're strenghtened by a little crimp to keep them from bending under force.  The rivets held the L brackets and frame pieces tightly.  This is one of the corner brackets taken from a top corner, and before I'd removed the rivet backing.

The width of the corner brackets, and the width of each corrugated steel strip, are quite close in size to the width of each frame piece channel.

Remove the frame side pieces

This picture shows the side and top removed.  Note the rod at the top.

Under the top frame piece, welded across all four vertical 4mm rods, there is a 3mm rod.  While this was butted up against the topmost corrugated strip, it wasn't attached to the strips.  It was just holding the vertical rods in place, and kept a little pressure on the corrugated strips.

Having the top and bottom bars welded like this would keep the whole assembly from twisting, too.  And I suppose it would make the top more rigid.  But really, I think that having tight tolerances in the strip widths and the corner bracket width, with respect to the frame channels, keeeps things from moving too much anyway.  So, I didn't see there to be a great need to re-weld the rods later.

Check for square

At some point, I held the Top, Left, and Right pieces up to each other, and was really surprised to find that they were not all the same length!  I think that was a manufacturing flaw originally, and I just didn't notice it.  (For the picture below, the bottom edges of all three frame pieces are resting on flat ground.)

 

Detach the top rod

I used a Dremel with a cutting wheel and cut down through the existing weld.  Remember to use proper eye and breathing protection when cutting!  Once in far enough, I could use a flathead screwdriver to break the rods apart without too much effort. 

Clean up the weld points on the top rod

I had taken off the top rod in order to remove excess corrugated strips.

I used the Dremel again, this time to grinding away the remaining weld on each vertical rod.  Remember to use proper eye and breathing protection when cutting!  

This left some material on the rod.  I tried to slide strips up and off, but they would get hung up on remaining weld material.

To get things round and smooth again, I stuck a little piece of sandpaper inside my handheld drill, and spun the sandpaper around the weld point until smooth.  I'd then tighten the collet and repeat until satisfied. 

Remove the strips

 

I lifted many of the corrugated strips up along the four rods, and off.  (If the rod weld points aren't clean enough, you'll know when you try to do this step.)

I stacked the strips as I was going.  It's best if you flip every other one so that all the lengths match and the holes line up. 

I didn't know how many I would be removing, so I just kept going until I had about 11.75" remaining (measured from outer bottom frame edge to top strip).

The following picture shows the honeycomb with many strips removed, and long rods accessible.

 

Measure, mark, and cut the four vertical rods

(Prior to this step, if you want to practice using a die to thread the rod, you can.)

This part was tricky.  If you don't take the whole thing apart -- that is, if you leave the bottom rod welded -- then it's hard to measure and make all four rods the same length.  I took a "close enough" approach here.  

The 4mm rods were spaced about 95mm apart.  I had a 1/2" plywood board with holes in it already, so I could press that down each rod to the point where the honeycomb strips were tensioned, and then draw marks.  To get this right, I took off more strips (to account for the 1/2" of plywood) and then put those back later.

 

When done, I eyeball-checked the alignment of the four marks (one on each rod).  In the picture above, I had marks in Sharpie that were incorrect.  The right target is the scratched point closer to the honeycomb.

For cutting the rods, it was easiest to start by using bolt cutters to cut close to the real cut point.  That left room for the Dremel to get closer.

I used the Dremel cutting wheel again to get through most of the way, and then cut with flush cutters at the very end.  Remember to use proper eye and breathing protection when cutting! 

After cutting, I used the Dremel again.  This time, I was trying to chamfer the top, cut edge of each rod.  This would make it safer and also it would make it easier to die-cut threads onto the rod ends.

Use a die to make screw threads at the top of the vertical rods

This was a handheld operation, but it worked pretty well.  (I practiced on the longer rods before step 5).  I wasn't sure what thread to use, but just tried different dies until one fit.  As it turned out to be a #10-24, I felt comfortable using it.  I cut the thread about 1/2" down on each rod.

For this step, I removed more strips temporarily.

One problem I faced was that my tap/die set has a die with arms that are pretty long.  They provide leverage, but in this project they would hit the neighboring rod on each half turn.  I ended up starting each thread with the leverage arms in place, and then removed the arms and continued cutting as I got further down.  

This picture shows the rods now with threads.  Extra strips have been removed so that I could have room to work.

Then I put the temporarily removed strips back.

Use a nut to hold the strips in place, rather than welding a top rod.

I didn't have #10-24 nuts immediately available, so I drew some up in Autodesk Fusion, complete with modeled threads.  I printed those in PETG and they worked straight away.  Each rod got one.

Chop the left and right side pieces to the new length

I put the top frame piece back on, kind of as a dry fit.  This allowed me to get a rough measurement for cutting the Left and Right side pieces down.

I also tested the springiness of the assembly, and I figured I had a 1/2"  of travel, so I could afford to be a little imprecise in my measurement.  The main thing was to ensure that the Left and Right sides (A) had near-perfect 45 degree cuts, and (B) were exactly the same length with respect to each other.

To do that, I lined up both pieces, and stuck them together with blue tape.

I used my chop saw to do the actual cutting.  I used its bevel mechanism, tipping the whole blade over to 45 degrees, and used a separate measuring tool to ensure it was really close to 45 degrees.  Then, I did a first test cut, partly to make sure the blade was up to the task, and partly to get a feel for the cut.  Finally, I marked the cut points, and cut the pieces.

Nobody was injured.  The pieces looked really good.  At this point, I also used some sandpaper to smooth out any sharp edges resulting from the cuts.

Tap the L brackets

The L bracket holes were slightly under 4mm, and so it seemed doable to use #10-24 threads for them now.  I realized around this point that I really had to drill out the Bottom piece rivets, and at least loosen the Bottom piece in order to remove the bottom two L brackets.

I then cleaned off all the remaining rivet material from all L brackets.  This was best done by using a flush cutter to chop off the small, outward protrusion.  Then, I used pliers to pull out the large, inner piece at each hole.

Once that was all done, I used a #10-24 tap on a non-powered drill press to thread the holes.  By this point, I had spent $1.48 for a packet containing ten #10-24 x 1/2" pan-head screws.  Each came with a nut.  I tested each threaded hole as I went, using a #10-24 screw, to make sure I wouldn't be surprised during assembly.

Widen the holes in the frame pieces

Because I was using #10-24 screws, the existing holes in frame pieces had to be widened.  I used a #13 drill but could have gone a little wider.  The idea here is that you don't want the screw to be threading into the frame hole.  Ideally, the screw should slide freely through the frame hole, and catch on the L bracket thread.  In practice, the #13 hole size still was a bit too small, but it ended up being something I could force.

To do this, I finally gave in and removed the Bottom frame piece.

Partially reassemble Top and Bottom

I reattached the L brackets to the holes of the Top and Bottom frame pieces.  That's easiest to do when they're removed from the honeycomb.  Then, I slid each Top/Bottom frame assembly back in place.

The Top and Bottom pieces slide pretty easily back over the corrugated strips at top and bottom.  The side reassembly is harder, just because of how the corrugated strip ends can get offset, and even the slightest change in them can cause the edges to catch on the frame piece.

(In this picture, you also can see the pile of strips that were removed prior to this point.)

Make new holes in the chopped-down side pieces

At this point, the Left and Right pieces were chopped down, leaving the bottom section with its original hole, and the top section of each missing its hole.

I had two chopped-off ends, though, and they served as guides/jigs for determining placement of the new holes.  I lined up the chopped-off piece with each Left or Right piece, stuck them together with blue tape.

 

I went to the drill press and drilled a #13 hole exactly where a hole would have been.  

Assemble and align

Now I had the Right and Left frame pieces chopped and drilled, so all that was left to do was reassembly.  Or so I thought.

Getting the Left and Right frame pieces back over the full set of corrugate strip ends is difficult, but there is a technique that can be used to make it easier.  It involves hooking the Frame edge piece over one side of all the strips, and then  having an extra straightedge that aligns the strip edges. 

After each of Right/Left frame piece was back in place, I simply connected the #10-24 screws through the frame to the L bracket at each end.

At this step, it helps sometimes to loosen the L bracket's other screw, and then tighten them judiciously.  Overtightening one side can cause the ends to become misaligned, resulting in a bad corner and an exposed, sharp edge.

This is one corner with screws in place.

At this point, the whole honeycomb was back together again!

 At this point, I also zip-tied together all the extra strips.  Only one was kind of scuffed up -- the topmost one, due to how I broke the top rod welds -- but the rest are in good shape.  It looks like I ended up removing 25 of them to bring the honeycomb size down by about 100mm.

 

Measuring them, I'm getting about .33mm thickness, both measuring individually and averaged over a compressed stack.  They're nearly exactly 20mm wide.  Similar in flat, not yet crinkled, appears to be available online, e.g., this link on aliexpress (1000mm 301 stainless for $4.46?  That would be prohibitively expensive for this kind of build!).

Installation - fail

As a final step, I tried putting the new honeycomb into the FSL hobby laser, only to find that it wouldn't fit!  That's because the pan heads of my #10-24 screws were standing proud of the frame piece, much moreso than the original rivet heads did.

Flattened screw heads

I got out my bench grinder and ground much of each screw head away.  I didn't do this with any particular precision in mind.  I just wanted some of the material to go away.

This is what a ground-down screw head ended up looking like.  This is one of the better looking ones.  Other ones were quite unevenly ground.  They might be harder to undo at this point, but I suppose there shouldn't really be a need to undo these very often, if at all.

With that, the new honeycomb could fit in the laser bed.

 Conclusion

It's totally doable to take a cheap laser honeycomb bed and cut it down to size.  For me the material cost was about

$20 for the 400mm x 400mm bed

$1.48 for the #10-24 screws and nuts

Some nominal filament cost for the 3d-printed #10-24 "nuts" that I made. 

One crappy #10-24 tap that was made from some metal that wasn't as strong as the L bracket metal. :(

It took me quite a bit of time to do this project, but in part that was due to nervousness, never having done it before.  Having done it once, I could probably do one of these in a few hours.

Things to do better next time

I think I would have a better design for my 3d-printed nuts.

I might consider unwelding the bottom rod.  Since there's so much excess rod material, I could chop off the ends of the rods rather than clean the welding material off.  And, having all four of the 4mm rods free would allow me to (A) make sure they're of uniform length, and (B) die-cut threads on their ends more easily.

In retrospect, I could have laser-etched measurement markings on the frame pieces.  That would have happened prior to any reassembly.  I suppose I could still do that.  One of the beautiful things about this project is that I can disassemble and reassemble the honeycomb now.