Posts Tagged ‘ inventables

## New CNC Cut : HexBeam

Continuing to play more with MASH in Autodesk Maya, I came up with this experiment:  I used a ramp node with a wave to mask where the hexagons are placed, then randomized their scale.  Applied a dark stain on the uncut top, and a natural stain on all the hexagons.  Material is a reclaimed redwood beam.

About half an hour of modeling in Maya, and 1h45min on the X-Carve CNC with a 1/8″ 1-flute upcut endmill.  Probably another half hour of sanding.

## New Commission: Denali

Was recently commissioned to make another Denali cut on my X-Carve.  This time I swapped out the 1/4″ ballnose used for the rough cut for a 1/8″ ballnose on the finish cut:  Really helped the mountain detail pop.

I had split the rough and finish cuts into two files:  Only downside was that using Chilipeppr, it started to choke on the 4.8meg finish pass file. It would cut for 8 seconds, then pause for 4, etc, repeat… making it take waaay longer than it should (3.5 hour finish pass). Talking on the GoogleGroup, I guess this is a known problem, and the SPJS grbl code needs a port from tinyG. Next time I’m going to give UGS a shot…

I’ll give another shoutout to Terrain2STL, the great app I used to generate the terrain data.

## New cut: Lake Tahoe

Have been trying to get cutting faster: My Denali cut took around 4.5 hours.
I got “Lake Tahoe” down to 1hr 42min : Rough cut was 17 min, finish 1:25. This piece is smaller by 4.5″ (6″x7.5″) based on the aspect ratio of the map, and not as deep of a cut, but I increased my roughcut stepover from 50% to 75%, and increased the final pass speed from 90 to 120″ a min to help with the time. Machine had no issues at these speeds, so I’ll just keep pushing it up…

# Overview

I’ve been using removable glass build plates for years on both my Makerbot Replicator 1, and my custom C-Bot:  I get double-thick glass cut at my local hardware store (Orchard Supply Hardware has had a great price on this), always thinking it was ‘totally flat’.  But is it really?  My C-Bot has a 12×12″ heated build platform.  When I go to level it with the glass, I get each of the four corners dialed in perfectly.  But the middle always sags slightly… even though it’s glass.  Double-thick glass.  But glass is actually somewhat plastic, and this sag has always bugged me.

Back in December I assembled my 1000mm X-Carve CNC, and it’s been so much fun cutting wood.  I knew it could do aluminum as well, but needed  a project.  And that’s what this post is all about:  Using my X-Carve to machine a new removable build plate out of .25″ mic6 aluminum for my 3d printer.  I am so happy with the results.

# Sourcing the material

Before I started this, I had no idea what ‘mic6’ aluminum was.  It’s also referred to as ‘cast aluminum tooling plate’ or ‘ATP’, since mic6 appears to be a trademarked brand name.  Simplistically, it’s a standard for (among other things) a very flat aluminum plate, to .001″.  After reading a plethora of forms, and researching my local options, I settled on Midwest Steel And Aluminum’s “Cast Aluminum Tool & Jig Plate“, .25″ thick, 12×12”, which came to about $20, and the ground shipping another$20.  I could have bought it locally for \$45 + tax (ugh).

A note on the order:  The plate was packaged in one layer of cardboard, that was it.  It appeared to have been dropped several times in-transit, 3 of the 4 corners were blunted, and there was an small indentation in the middle of plate itself.  If I was using this for something really precision I would have returned it.  Just a note to tell them to ship it better if you go this route.

Once it showed up, time to make some cuts!

# Initial cuts

When I first got the plate I knew I had to notch a section out of each corner, since the heads of the bolts that hold the MakerFarm heated build platform stick up about 1/8″ish from it:  I didn’t want the plate resting on the bolt-heads, so I need to make little pockets for each.  Before I even considered my X-Carve CNC, I figured I could use my drill-press to pocket these.  Long story short:  It did not work well, and made a mess of the corners.  Based on that frustration I went down the ‘how about I use that dormant CNC right next to the drill press…” road.

For all below cuts, I used the same 1/8″ 2-flue upcut carbide endmill.

Since these cuts were so simple, I used Inventable’s Easel: I designed a circle with a diameter of .4″ across, .175″ deep, and used that to pocket each of the four corners already mangled by my drill press.  I used the default ‘aluminum’ Easel setting (5 ipm, .003″ doc, DeWalt on speed 1) with the first pocket (which took about 20 minutes), then started cranking it up: By the final pocket I had it running at 20 ipm at .01″ doc, with the DeWalt on speed 2, taking about 5 minutes..  It did great, and the bit was cool to the touch after the cuts.  When all four pockets were complete, it fit right on the bed with no collision with the bolt-heads:

All the rough stuff to the right of the bolt-head was the abuse by the drill-press.

I have four bulldog clips that hold the plate on, one on the middle of each side.  The issue is even though I’ve bent them down to move them out of the way, parts of them still stick up slightly, and on a large print the nozzle could collide with them.  So going back to Easel, I designed a new rectangular pocket that would keep the bulldogs out of the way of the toolhead.  These were 2.25″ x .3″, cut .075″ deep.  I positioned them in the center of the left\right sides of the build plate, but had to offset them on the front\back based on my leadscrew config.

An in-process cut:

And all four final cuts:

Installed on the printer:  No more clearance problems with the bulldogs!

# Prepping the plate

I use a highly secret (50% wood-glue, 50% water) slurry on my build plate to get PLA to stick.  But the mic6 is so smooth, I first scoured it with steel wool for several minutes to give the glue something to bite into.

Note for the future:  First, use something like lacquer thinner\acetone\mineral spirits to clean the plate of any oils:  Quite to my surprise, after many minutes of scrubbing, I could clearly see my handprint on it.  The oils deposited from my hand actually protected it from the steel wool.  So I went back and liberally scrubbed it with lacquer-thinner soaked rag, then went back to the steel-wool treatment again:  No more handprint.  Be sure to wipe it down with lacquer thinner after the steel wool too:  The wool actually leaves quite a bit of itself deposited into the aluminum.

After the plate was scrubbed, cleaned, and glue-slurry applied, I did some test prints.  And while the flatness was super awesome, I realized something very quickly:  The slicer said the bed heated up waaaay faster than it actually did:  For big prints in PLA, I’ll heat the bed up to 60c.

It dawned on me that the thermistor that does the temp reading is taped to the bottom of the MakerFarm heated build platform, while the thing being printed is sitting above it on .25″ of aluminum… that is taking much longer to heat up.

After brainstorming, I came up with the idea of cutting a groove into the bottom of the plate, that I could tape the thermistor into:  It should then be reading the temp from the removable plate itself, providing a much more accurate temperature.  This means I’ll also need to snip the leads running to the thermistor and install a barrel-jack into the mix to allow for the plate to be removed, since there’s now a sensor taped to it.

# Secondary cut

Going back to Easel, I designed a .5″ wide groove cut .0312″ deep that I could recess the tape into, then another smaller groove .2″ across and .1″ deep to run the wires to the thermistor.

Here it is mid-cut:

Cut gotchas:

• Easel has (based on what I’ve experienced) no idea of conventional cuts (bit spinning in the direction of travel) and climb cuts (bit spinning opposite direction of travel).  From what I’ve read, climb cuts can provide better finish, but only on ‘professional\beefy’ machines:  not the X-Carve.  Conventional cuts fare much better on the X-Carve.  This (as I found out) can cause dangerous problems.
• When the top cut started, it was all conventional cuts, and cut fine.  But when the next layer started, and for every layer down, it was climb cuts.  Because of that, I noticed a lot of bit defection, chattering, and even gouging.  To avoid catastrophe, I had to manually monitor the cut, and really crank up the spindle speed as needed to compensate.
• Note that MeshCAM gives you the option in the rough-cut to do either conventional or climb cut:  For future aluminum projects I’ll be using it for sure.

To help with heat transfer (that is only a theory of mine) and to prevent any sort of plate-slip (which is legit), I shoot the bottom of the plate with rubberized undercoating.  I then snipped my thermistor line, soldered barrel-jacks onto either side of it, then taped it into the groove on the bottom of the plate:

Putting it back onto the HPB, I reconnected the barrel-jacks:

# Final thoughts

It works, great.

When the HPB heats up, and it finally gets to temp…. it really feels like the top\bottom are the same temp.  And I can level each of the four corners, and the middle is the exact same distance as the rest of them from the toolhead.

Super rewarding project with one machine improving another.

## Visual comparison of ballnose stepover values on the X-Carve

I built my X-Carve back in December:  It’s been a great new tool to learn.  I’m still very new to the world of CNC, and like to visually grasp the concepts.  So I decided to do a series of tests to understand how ‘stepover’ values effect the finish-pass quality of the surface both on X, and on the XY axes.

The MeshCAM blog does a great job of describing the fundamentals of stepover here.

Here are the stats for the cuts:

• Hardware:  Inventables 1000mm X-Carve.
• 1/4″ ballnose bit, 2-flute upcut.
• Feedrate 60ipm, DeWalt set 1 to 2.
• Wood type:  Unknown (came from an old bookshelf bottom), but if I had to take a guess, I’d say pine.
• 3d Design Software: Autodesk Maya
• CAM: MeshCAM
• Sender: Chilipeppr

The specifics from MeshCAM below. All values for all cuts were the same except of the stepover, and either “Cut along X”, or “Cut X then Y”.

I wanted really extreme examples, so I set the following stepover percentages for my test: 100% (1/4″), 75%, 50%, 25%, 10%, 5% (only done on X, not XY).

I started by designing a model in Maya that incorporates a variety of surface angles.  The inside volume is just over 2×2″, by about 1/4″ deep.

(that’s a flattened sphere in the middle)

I then made multiple different gcode (nc) via MeshCAM, and started cutting them.

The whole piece for the X-cut:

And the whole piece for the XY cut:

(note, no 5% test here)

Individual close-ups below.  X pass on the left, XY on the right.

Note the rough-cut for all pieces took just about exactly 2 minutes.  All the times listed below are for the X & XY-Axis Finish pass in min:sec.  So to get the total cut time, just add two minutes to the below values.

• 100% stepover, .25″ : This is obviously super rough.  I honestly expected the segment to be closer together.
• X Finish Pass Time:  0:47
• XY Finish Pass Time : 1:34

• 75% stepover, .1875″ : Not too much different than 100 really.
• X Finish Pass time : 1:03
• XY Finish Pass time : 2:03

• 50% stepover, .125″ : Still really rough, but arguably could do something artistic with the ridges at this point.
• X Finish Pass time: 1:30
• XY Finish Pass time : 3:00

• 25% stepover, .0625″ : Carry on, nothing to see here.  Even with the XY pass, it’s still pretty rough.
• X Finish Pass time: 2:50
• XY Finish Pass time : 6:40

• 10 % stepover, .025″ : Now we’re getting somewhere: Ridges are still visible, but small.  Pretty smooth to the touch, but you can still make them out.  Sanding could take care of this.
• X Finish Pass time: 7:10
• XY Finish Pass time : 14:00

• 5% stepover, .0125″ : Done.  Finished.  Can’t make out the ridges with the naked eye.  Very smooth to the touch.  No sanding needed really.
• X Finish Pass time: 14:20
• No XY pass done.  Not much point considering the quality already achieved.

Final thoughts:

• Notice on all X-cuts that the lower-left section of the hemisphere is rough.  Must have to do with the direction of the toolhead (left<>right on X) and the spinning of the bit (clockwise).  The XY cuts removed these issues.
• If you are ok with sanding, 10%/.025 stepover is ok.  If you want to avoid sanding entirely, go with the 5%/.0125″ stepover.
• Even though the 5% X-only stepover and  10% XY stepover took the same amount of time, the X-only has a far better surface quality.  You’d still need to sand the 10% XY one.
• What do I take away the XY Finish pass?  The XY Finish Pass times are generally 2x the X-only times, but don’t really increase the quality.  Not much point unless you’re looking for ‘that look’ in the cuts.
• I feel like the speeds could be greatly increased on the finish pass:  I was only running the router on speed 1 to 2.  The smaller the stepover, the smaller the amount of material you’re removing, so arguably the faster the toolhead could move to compensate for this under load:  There’s a lot of speed left in the router…. sounds like another good test to try.