A proper conductive polymer mix?

In which your narrator begins to test a new conductive polymer mix.

Do you want to read more?

One of the long term grails of the reprap project is to be able to print circuitry. Currently, Rhys Jones, a PhD candidate working for Adrian Bowyer at the University of Bath, is devoting a lot of his time to addressing this issue.

Heretofore, we've looked at very low temperature eutectic alloys like Rose's and Wood's metal and confected methods of extruding it into preprinted channels.  More recently, Rhys has demonstrated that ordinary solder can be successfully printed onto ABS.

We've looked at various concoctions of carbon, silver and other conductive materials with polymers at arm's length.  Always, though, the conductivity of these mixes has been too low for them to be useful in printed circuits.  Rhys, however, has looked at a two step process which may get us by that.

The main problem with printing PCBs with a reprap machine is that PCBs are not that hard or expensive to have made using conventional, proved materials.  This makes coming up with a method of printing them a bit tricky because it not only has to work, but it also has to yield a product that is not all that much difficult to use than conventional boards.

Recently, I ran across a high-tech company, Integral Technologies, located in Bellingham, Washington.  They've come up with a different approach to creating a conductive polymer mix which uses conductive fibers mixed with conventional polymers.  Probably the most exciting is their mix of very fine stainless steel fibres mixed with a blend of polycarbonate and ABS.

The volume resistivity for this material on the data sheet runs to 0.06 Ohm-meter.  This is far too high for a useful conductive plastic.  I rather shrugged the material off until I got a look at a few non-technical demonstrations of the material.    This one shows two small bars of the material used to conduct 110 v current running an electric drill.

Interestingly, Bill quoted me a price range of between $9-45/lb depending on the composition. More interestingly, the PC/ABS mixes which resemble what we are already used to using in Repraps are at the cheap end of the price spectrum.

As well, they demonstrate measured resistance across an extruded plate of their material using an analog multimeter.

There was obviously a mismatch between what their data sheets said and what the non-tech demos indicated.  I explored this question with Bill Robinson at Integral.  It boils down to the "skinning effect" mentioned in the first clip.  Simply explained, it means that the metal fiber doesn't tend to show up at the surface of an extrusion.  This means that the material is partially insulated at the surface of an extruded surface.

That left the issue of how, in the second demo clip, ordinary multimeter probes registered effectively zero resistance when measuring resistance across a extruded plate of their plastic.

Bill sent me some demo plates of the material a few days ago.  I have a digital multimeter rather than the analog Radio Shack multimeter.

Multimeters are not particularly good at accurately measuring low resistances.  Anything reading below about 5 ohms for most multimeters is not something you want to bet your life on.

I tried duplicating the measurements in the clip and kept running into skinning effects.  In places I could get readings less than 1 ohm, but others I would be in the mega ohm range.  I made a cut across one end of one of the samples.  You could barely see the fiber ends.  Integral is using VERY fine fibres.

I then drilled 1.5 mm holes through the plaques and put the probes through those.  I was able the get more consistent and lower resistance measurements.  Mechanical contact between the probes and the fibre ends is how good conductivity is achieved.

The best I was able to get consistently was 0.6-0.8 ohms over about 100 mm of the material.

Bill at Integral suggested that if we used a 0.5 - 1.0 mm extrusion nozzle we out to be able to avoid jamming of our extrusion nozzle with the stainless steel fibres.  Making strip extrusion as we can with a Reprap printer should tend to align the fibres much better than a simple injection moulding would do.  The problem as I see it will be making a conductive connection between two traces and making a connection between a trace and a component.

The question now is whether what we know about this material now justifies having a sample turned into fibre for further testing.

Getting into threading...

When I bought my Sherline lathe, I went for the loaded option.  As I am finding out, it was a very good decision.  I don't think I'd have been able to use at all it without the digital readout box.  I understand how people in times pass could have used a micrometer to do measurements between cuts.  I doubt that I could have had the patience, though.


After my last attempt at doing a deep drilling and cutting down a piece of aluminum bar stock, the next thing I wanted to do was use the threading attachment.  Between Joe Martin's Sherline book, Tabletop machining and the Sherline Accessories Shop Guide I was able to puzzle out how to re-rig the lathe for threading.  My motive in getting a threading attachment was to have the possibility to cut my own lead screws and thrust collars.  The studding used in the Rapman and Mendel 3D printers, not to put too fine a point on it, suck the middle out of canned Vienna sausages.  When you buy studding it is rarely, if ever, straight.  When you try using it as a z-axis lead screw, it does not very pleasant things to your print quality.


As well, I am quite fond of the polymer pump design on the Rapman.  My primary reason for wanting to do my own threads was to be able to make the threaded drive shafts for those, too.


The biggest shock for me in this adventure happened when the instructions book told me to demount the lathe motor.  It turns out that you cut threads on the Sherline lathe with a hand-powered handle.  Using it reminds me of my grandmother's old foot pedal powered Singer sewing machine that I learned to use when I was about four.  It has a very similar, 19th century feel to it.

By and large the threading system design is quite good.  The real pain in the tail, however, is that little black lever that you see below the spindle in the above picture.  Getting that to work right had me taking the whole lathe apart about three times.  Sherline needs to rethink that part of the design.  It really sucks.


Other than that, the threading attachment was quite easy to use.  It is set up to do standard and metric 60 degree threads.  The carbide cutting tool did that quite easily.  


For a first try I did a really coarse metric thread, 2 mm.  

I figured that that deep a thread would require the most muscle.  It was a bit tiring but not at all impossible.


For lead screws, the Sherline will handle about 15 inches of threading.  If the diameter of the stock is less that about 9 mm, a longer unthreaded piece of stock can be snaked through the spindle.  Given that manufactured lead screws about cost $1/cm and thrust collars typically cost $30-35, this capability will save me some money over the mid-term.  

First lathe experiments

I finally got a few days off, so this morning I began to do things with my new lathe.

My initial motive in getting the lathe was to have the capacity to make my own extruder hot ends.  Given my total lack of experience with lathes, I decided to see if I could try sinking an 1/8 bore in a piece of aluminum round stock using a fixed drill bit in a chuck inserted into the tailstock.  An idea of what I did can be seen here.

After a considerable time, I was able to sink a 50 mm hole into the centre of the round stock.  The steady rest that you see supporting the end of the aluminum round stock nearest the drill bit reduces vibration and misalignment.

When I worked with Tommelise 1.0, I used a 5/32 inch braised copper tube (1/8 inch ID) hot end several inches long with its top only heated using nichrome wire.  I was able to get well past the whole issue of having filament melt in the PTFE thermal break with that approach.  These days, I hope to do something similar using aluminum.

Here you see the drilled round stock after I've trimmed it down to 12 mm outside diameter and trued up the end.  It takes a nice finish.

Arrived

The Sherline lathe arrived on Thursday. I was working that night but stayed up extra late and more or less got it assembled. It went together without a lot of drama. The digital readout box makes whether you bought the lathe with American or SI verniers irrelevant since you can select metric or "Imperial" on the digital readout box.

The readout box also includes an optical tachometer to keep track of the rpm rate of the lathe. The DC controller knob will give you stable rotational rates down to about 200-250 rpm.

This morning, I mounted the lathe on a piece of chipboard for stability.

I bought a couple of pieces of aluminum round bar, a piece of stainless round bar and 3 feet of hot rolled steel round bar to practice on.  You can see one of the aluminum round bars mounted in the lathe.

Taking a different direction

A few months ago, I had planned on acquiring another BfB Rapman with two print heads this time so that I could explore the use of PLA as a support material for ABS prints.

With the sale of BfB to 3D Systems, continuing troubles with BfB firmware and the catastrophic failure of my expensive Rapman hot end and the discovery that BfB isn't warranting such failures, I've decided to build my own second printer.

To that end, I've just purchased a Sherline 4410 metric lathe.

It will be arriving Thursday.

Annoyances and changes

UPDATE: I let my anger run away with me in this blog post. I've just spent time with Ulf Lindhe at Netfabb. Ulf has sorted out the problem I was having with the boolean operations and got me upgraded to version 4.6 at no charge.

It's taken a few days, but I can now print at about the same quality with a 0.5 mm extruder as I was able to print with my now ruined 0.3 mm extruder. I've gone back to work on the active telepresence project and the present task is to create linear servos to as the muscles to operate the hand and fingers.  I'm building my own from gearmotors rather than buying after some bad experiences trying to adapt servos designed to operate the flaps and rudders on model airplanes and sailboats to operate hands.  Andreas Maryanto was good at this, but I am definitely not.

Doing this, I am leveraging the herringbone rack and pinion scripts that I wrote.  While Nophead's advice to simply not fiddle with my 0.3 mm hot end settings got me 95% of the way to where I wanted to be, that last 5% took a little tweaking.  I'm quite happy with the final results.

The pinions peeled off of the rafts with a minimum of trouble and only took a touch on the belt sander before they were usable.

That was relatively easy.  When I started working on the rack, however, I quickly ran up against the limits of Art of Illusion.  While it is easy to assemble a set of solids to represent what I want to print in AoI...

Doing the Boolean opeations to make them into one solid is quite beyond AoI's boolean ops capabilities.  Bogdan told me repeatedly that I could do this sort of thing in Netfabb Professional, so I read up on the method and set about to use my now copy and discovered that the Netfabb people had somehow disabled this feature in my copy.  I had a email from them about version 4.6 {I have 4.4} but no clear idea if I was going to get a free upgrade or have to pay them even more to do something that I am already supposed to be able to do.


The more I think about that the more pissed off I get.  If I don't hear from them in the morning, I am going to build boolean ops into Slice and Dice and give it away for free.  The way I feel just now I might just do that anyway.    I am getting sick and tired of getting ripped off.

Getting to the bottom of the Rapman hot end failure

In which your narrator gets to the bottom of why it was that his 0.3 mm Rapman hot end failed and perhaps even why it started causing resets prior to the failure.


The hot end failure that I experienced on 14 October is a relatively rare event. The only other person with a Rapman who reports the sort of ABS leakage that I experienced was Klazlo.


Once I had my Rapman repaired and usefully printing again, I turned my attention to doing forensics on the failed hot end. Once I took a hard look at the hot end and the pictures that I took immediately after the failure hints of the means and mode of the failure began to recommend themselves.


Taking a look at one of the forensic pics that I took on the 14th two items jump out at you. I've circled them in red.

If you look closely at the top red ellipse you will notice that one of the three bolts which secures the spacer on the hot end ensemble was either not tightened adequately at the factory or, more likely, worked its way loose via hundreds of heating and cooling cycles while in operation.  This threw the alignment of the hot end out opening a route for hot ABS to escape between the PEEK sleeve and the aluminum extruder barrel sleeve that fits around it.  You can clearly see the billowing flow of ABS in the picture.  ABS was only leaking on the side of the PEEK barrel where the spacer bolt was loose.  That part is straightforward.


The vertical ellipse on the right hand side of the hot end is much more ominous.  If you look closely, you can see that one of the thermistor leads has exposed above the sleeve leading down to the extruder tip where the extruder is housed.  A bit over 4 mm of exposed thermistor lead is open to the air.  You can see that happening a bit more clearly with this picture.

The larger red circle encloses the exposed lead.  The smaller one shows the recession of the purple plastic insulation on the lead that occurred once the ABS began to boil out of the gap between the PEEK and the aluminum and contacted the lead.


At first I thought that the hot ABS had actually caused the gap in the insulation.  Closer inspection, however, revealed that the lead had most likely been stripped too liberally and originally was only just barely covered by the yellow silicone sleeve.  The heat of the billowing ABS almost certainly caused the shrinking of the insulation from just being covered by the silicone sleeve to its present situation.  It's easy to see the shrinkage in the second circle.


I then removed the PEEK cylinder from the aluminum extruder head.  Originally, I had thought that the PEEK sleeve in contact with the aluminum might have shrunk.  It measured 10.09 mm outside of the aluminum sleeve and 9.9 mm inside.  That could have been either because of heat shrinkage of the PEEK over time or some sanding of the PEEK tube at the factor to get a clean fit.  Unless the parts had been measured before the hot end was put into service, it would be impossible to tell for certain.


I then removed the silicone tube from the inside of the PEEK sleeve as you can see here.

This is the most revealing forensic evidence in the whole exercise.  At first, it appears that the silicone tube has shrunk on the hot end.  While that is true to an extent, the reason for the shrinkage is actually because the inside diameter of the PEEK sleeve has shrunk because the PEEK has expanded within the confines of the aluminum sleeve.


It was fortunate that I bought several unassembled hot end kits before BfB began making premade ones because I had some disassembled PEEK and silicone tubes.  The unused PEEK sleeves had an outside diameter of 10.0-10.1 mm and a consistent inside diameter of  6.36-6.40 mm.


When I measured the failed PEEK sleeve the cold end inside diameter was 6.40 mm but the hot end had been reduced to 5.88-5.92 mm.  The silicone tube outside diameter on the hot end was more or less the same as the inside diameter of the PEEK sleeve.


What was revealing, though, was that the hot end of the silicone tube was virtually entirely closed.  It was impossible to slide a 2.9 mm ABS filament through it.  I was able to blow tiny bubbles through the silicone tube into a glass of water.  What that says is that the ABS filament was being melted in the silicone tube and squirted into the aluminum extruder barrel rather than being melted in the extruder barrel.


I don't think that that was how the hot end design was intended to work.


Getting back to that exposed thermistor lead, it is well known that blowing hot air past plastic surfaces will create a static charge.  Not only was that exposed lead within millimeters of billowing hot ABS it was also touching the bottom acrylic plate of the x-axis carriage {part 10034}.  Periodic static discharges off of this heated acrylic surface were most likely at least deranging the temperature measurements off of the thermistor and also causing the MCU board to reset.  During last winter, I walked in socks across the floor and picked up sufficient charge to where when I touched the MCU board the system reset.  


Conclusions:


The failure of the hot end had two aspects.  

• The loosening of the spacer bolt, most likely from repeated heating and cooling cycles of the hot end allowed for a hot end misalignment that created a path for leakage of hot ABS out one side of the hot end between the aluminum extruder sleeve and the PEEK sleeve for the silicone tube.
• The swelling of the PEEK sleeve over time reduced it's inside diameter almost entirely closing the silicone tube and causing the ABS to have to melt in the silicone tube rather than in the aluminum hot end.  This was certainly not the intent of the hot end designers.

It seems quite obvious that the combination of a PEEK sleeve enclosing a silicone sleeve for the plastic filament need to be rethought.

The placing of an MDF plate and an acrylic plate at the top of the hot end spacers through which the securing bolt has to pass also needs some careful.  Replacing the MDF with a PEEK plate with the bolts secured by lock washers to the PEEK plate and recessed through the acrylic with the acrylic and PEEK secured by a separate trio of short bolts might be more successful.  An aluminum plate as a replacement for the MDF might also be considered.

Chylld is a parts design genius

As I mentioned earlier I replaced to destroyed 0.3 mm hot end with one of my spare 0.5 mm hot ends and began to get used to using the larger nozzle size.  After some frustrating tries at adjusting flow rates Nophead suggested that I stop fiddling with things and just use the settings that I'd used before.  He was right, of course.

A quick print of some of the bones of the hand yielded good results, so I decided to have a try at one of Chylld's corner replacements for Rapman cut acrylic.

So far there's been no sign of the wall-to-wall resets I was getting with my Rapman in the hours before the 0.3 mm hot end finally failed.

The corner block printed in 2:15 and  mounted with a minimum of drama.

There was a minimum of post print part processing required.  the x-axis bar was a little tight, but a brushing out of the hole cured that.  All bars had a tight, friction fit and the tightening screws were largely cosmetic except when the printer wanted moving.

Chylld is a parts design genius.  I've never seen anything work quite this easily.

Operational again at 0.5 mm.

Okay, I got one of the spare 0.5 mm extruder heads mounted. I measured the output and discovered that I was getting swell to about 0.66 mm. That works out to 0.34 mm^2 cross sectional area.

When I was working with the 0.3 mm extruder head I was getting a swell to about 0.42 mm which works out to about 0.14 mm^2 or about 40% as much.

I tried printing a test raft using the old extruder set points and noticed that the base print roads for the raft, which had been well separated before, are overlapping now. In the morning I'll lop 60% off of the extruder's stepper speed and see what happens.

Repairing a catastrophic failure of the Rapman 3.0

Little did I know when I was upgrading Slice and Dice to do prints of laser-cut Rapman parts that I would soon be confronting the problem of replacing such parts without having a 3D printer to print the parts. That is an ENTIRELY different problem.

I had upgraded Slice and Dice to do a better job of printing my sample laser-cut part from last time and was doing trial prints when I noticed that I was getting an enormous number of resets. This was odd because ordinarily I only get one or two resets per month since I uploaded firmware version 4.0.2. I checked the humidity and it was a bit dry, so I fired up the hot mist humidifier and drove the relative humidity up to 52%. No joy.

The next morning I undertook a new print and noticed a mushroom of ABS had formed under the extruder.

When I attempted to remove the extruder, the mushroom of ABS proved to be too big to easily get out of the mounting hole.  I then began to disassemble the x-axis carriage that holds the extruder only to discover that the top plate was being held together by the grace of God and nothing else.  It crumbled into two major pieces and half a hundred small fragments when I began to remove the bolts.

As well, one of the tiny little bars that hold the x-axis belt had also broken in half as is readily visible in the previous picture.

As you might imagine, this all made me very cranky.  A quick calculation revealed that I had historically been spending considerably more on preassembled BfB hot ends that I was on the filament that goes through them.  I run a lot of filament, too.

I spent several hours chatting with both Iain and Andy at BfB.  They were attempting to be as helpful as they could, but somehow I came away with the same feeling that I get when I take my car into the garage and they say recursively, "It MIGHT be X.  We could work on that and see what happens."  I began to steam up a bit when they started talking about my not using "BfB gcode".  They'd latched on to that fact that I'd written my own STL processing software that produces gcode right out of their manual and tagging this as a possible problem.  They then started talking about the fact that I was using very short line segments {0.1-0.1414 mm} and that was possibly touching off heretofore unsuspected bugs in the firmware.  I pointed out that the Rapman is supposed to have 0.1 mm resolution and you can't print objects at that level of resolution unless the firmware can handle that short a line segment.

I finally decided that I had to stop talking before I said things I'd regret later {I do that a lot}, and have a good think.

Here's what it came down to...

• I needed a new top plate for the x-carriage and a new hot end.
• I was going to have to pay for these and it was going to take a week to get them
• It was entirely possible that the hot end had been destroyed by a firmware bug
• There was nothing to say that the new top plate would last any longer than the last one, viz, ten months.

No matter how I looked at that equation it just didn't seem to balance.  A big bone in my throat was the fact that BfB wanted me to pay to replace a hot end that it was very possible that their firmware had broken.  A bigger bone was that there was no guarantee that if I put the new hot end that I bought into the system that the firmware wouldn't ruin it, too, in short order.

It seemed to me that the most reasonable course was to see if the problem was with the firmware.  I typically print with a 0.3 mm hot end.  I like what that kind of resolution does for my prints.  Before I settled on 0.3 mm, however, I bought two, preassembled 0.5 mm hot ends, so I had those in stock.

I also had Bogdan's experience that replacing the top plate on the x-carriage and grounding the hot end to it would stop the resets.  This from the observation that resets were most often caused by a static charge building up on the plastic of the x-axis carriage and extruder and then discharging, causing a reset.  BfB which is apparently located in a damp environment had never encountered this issue.  I noted that resets tended to get quite common when the relative humidity in the room holding the printer dropped  below about 42%.  I'd sorted out resets, except for the ones I encountered most recently which have led to the hot end failure, I think, by using a hot vapour humidifier.  After seeing how the top plate had crumbled, however, the notion of replacing the acrylic one with an aluminum one began to sound very attractive.

I decided to acquire the means to cut both acrylic and aluminum.  Harbour Freight in Salinas had a very nice scroll saw on sale for $69 which would reputedly do the trick.  

I bought that, a sheet of 0.22 inch (5 mm) acrylic and a billet of 3.35 mm aluminum plate.  I decided to cut an aluminum top plate first.  I began the process by simply tracing the bottom plate, which was identical to the top plate onto the aluminum with a fine tip marker.

I did the rough cut with the scroll saw and dressed it with a grinding wheel and a half round ring file after having set the plate in a small vise.

I then remarked two holes at diagonal corners of the plate, drilled 1/16th inch guide holes and widened them to 13/64th inch {as close as I could get to the 5.2 mm holes as I measured them on the original piece.   I did this with a hand drill after securing the plate in a vise. 

This done I then bolted the acrylic bottom plate to the developing aluminum one and drilled the guide holes for the rest of the holes using my Dremel drill press.

I then removed the acrylic bottom plate, secured the aluminum plate in the vise again and drilled out the rest of the holes.  

Afterwards I cleaned up the finished plate with a wire wheel and checked it for fit on the x-axis.

At this point my dyslexia set in.  The plate is not symmetrical and I'd got it flipped and completely reassembled and tested the carriage this way.  I didn't notice the problem till I tried to fit the extruder into the top plate assembly and discovered the symmetry problem.  The next pic is from the original, incorrect assembly.

The new top plate works smoothly.  Now I've got to swap out my ruined, 0.3 mm extruder with one of my spare 0.5 mm ones.  I will be able to see if I have a serious firmware problem or whether I just have a design fault with the hot end.  It could be either, or both.

I'm entering a big of a crisis with respect to 3D printing.  I bought into BfB's Rapman because I wanted to do some printing instead of screwing around with printer design and problems all the time.  At the time, a year ago, it was a good move.  Rapman was a bit pricy, but it was solid and the components of it were affordable. The 32bit MCU board was a delight after all of the Linux/Arduino/Sanguino/Bullshitino nonsense.  Some months ago there was talk of extending the Rapman MCU to where you could parameterise the firmware setpoints to deal with different machines and extruders, like the Mendel, for example, or even machines you'd designed yourself.  As it stands, it's not clear that BfB can design reliable firmware for their own machine, much less a parametric firmware app that would make it applicable to a wider range of machines.  

On top of that, they've recently jumped the price rather dramatically.

As it stands, BfB's Rapman has two Achille's heels; their firmware and their hot end.  Neither are reliable and the hot end is very difficult to repair.  I'm told that BfB is working on successors to the hot end, but that does me no good at all.  I'd like to shift over to something like Nophead's power resistor driven hot end.  The problem with that, however, is that I'll have to design a MCU to drive it and the printer both.  By the time I've done that,  BfB is out of the picture, since the those two components are what is defensible as corporate worth in the BfB.

I don't know quite what to do.

Replicating laser-cut parts

In which your narrator confects his own idiosyncratic method of replicating laser cut parts.

The recent acquisition of the UK manufacturer of the reliable Rapman printer, BitsfromBytes {BfB}, by the American firm 3D Systems has exacerbated a long standing problem that the Rapman's users' community has had, vis, getting drawings of the laser cut acrylic parts that make up the system. While BfB uploaded drawing files of one of their early Rapman designs into the Reprap website, they have neglected to do so with version 3.0 and later models to the best of my knowledge.

That wouldn't be such a problem save for the fact that the acrylic parts in higher stress parts of the Rapman tend to develop shear cracks and spalls after hundreds of hours of operation. Rapman owners are then left to either request replacement parts from BfB or print their own spares. Interestingly, there is a healthy spares design effort underway for the Rapman, part of which is hosted on the BfB website itself.

Here the printed white ABS grips for the x-axis linear bearings replace the lower plate for the extruder carriage in a much stronger configuration that the original.  Indeed, at this moment, there is a very exciting redesign of its printable parts underway by an Australian newcomer that greatly reduces the print time required for what were finicky corner blocks.

All this aside, there are many pieces in a laser-cut printer that simply need to be printed as-is in ABS rather than redesigned.  Heretofore, I found myself carefully tracing the parts out on paper and using calipers to get the dimensions.  While that approach works well with many parts some, like the extruder z-depth stop plate are much more problematical.

This particular plate is the antithesis of rectilinear and locating the holes and pockets is tedious to put it mildly.  I'd thought that it ought to be possible to use an ordinary 2D scanner to capture this sort of information.  Today, I gave it a try and discovered that it was not as straightforward an operation as I'd imagined.  


I had an extra copy of this part that I'd bought still in the protective blue film, so I threw it in my Epson Perfection V500 Photo scanner, a very cheap and extremely high resolution machine.  Even with the blue film the image captured didn't have a lot of colour information that would let you think that you could separate the part from its background.

I pulled that one into Slice and Dice and tried to separate out the image with RGB manipulations to no avail.  I then tried putting a intense red background behind the piece figuring that the blue would override the red and tried playing with the colour mixes in both Slice and Dice and Photoshop, again to no avail.

Two things were killing me; the transparency of the part and it's depth, which you can see very clearly in this scan.  When I tried to just capture the edges by going high contrast, the depth of the object spoiled everything.

It occurred to me that I could paint the part on one side with tempra paint, which can be wiped off of slick surfaces.  Rather than drive into town and given that the part was already protected with a blue film I simply spray painted it with red enamel.  I then put it back in the scanner with a piece of dead black HDPE sheet behind it and instantly got the colour separation I needed. 


Popping the scan into Slice and Dice and filling the black with green, I had an image I could work with.  As you can see, it was a little nasty, largely due to the messy laser cutting on some features and a bit of flare here and there.

A few moments in Paint cleared that up.

Now that I had crisp colour separation, defining the part boundary in Slice and Dice was trivial.

While I was in paint I took the pixel counts across the diameter of the outer circular feature boundary and measured the same feature on the part with calipers.  I then adjusted the size of the image in Paint.


With a bit of pushing and shoving in Slice and Dice, I processed the part and created a print file.  Here you can see the print roads for the part.

With a print file, I did a trial print to check the dimensions.  The acrylic part lay precisely over the printed part.

I photographed it again with the original part slightly ajar so that you can see the holes in the print.

If you look closely at the several layers of part print that I ran before aborting it you can see that I need to increase the print flow a touch.  More importantly, with a part of this size and complexity, however, I am going to have to write a routine that makes a better job of reducing transition distance between print roads.  Transitioning was taking far too much of the machine time.  That's on my "to do" list now.


What I've demonstrated here is not a smooth operation on Slice and Dice just yet.  I was mostly trying to prove the concept.  That was a huge success.  What this means is that owners of laser cut reprap machines can readily exchange parts information with nothing more complicated than an ordinary 2D scanner and a set of calipers.  This should give us considerably more flexibility than we have at the moment.


I am certain as I finish this blog entry that someone is going to show me a simpler, faster way to do this in a few hours.  That's certainly happened before.  If not, though, we have this approach.  :-D

When ego takes charge

Nordom recently printed a brilliantly executed M30x70 bolt, nut and washer ensemble.

I was, of course, quite jealous of his accomplishment and still am.  It is just a beautiful thing.

That got me to wondering, though, just how small a bolt one could print?  As usual, I was too impatient to wait till Nordom got permission to distribute the STLs for his bolt and finally found something similar in Thingiverse.

I hate recessed head bolts so I replaced it with a regular hex head and scaled it down to a M10x20.  After several tries I had something useful.

I've put it beside a similar metric bolt on the Rapman for scale.

Although the metric scale threads work in ABS, it seems obvious to me that something cut a bit deeper would be more useful.

Now that I've got that out of my system, I'll be going back to working on my carpal assembly.

An interesting stringing behaviour

The ability to reverse the extruder on my Rapman printer during transitions between print roads has reduced stringing to an enormous extent. What stringing I do get tends to be very thin and feathery.

I've noticed an interesting stringing behaviour since the release of firmware version 4.0.2, though. You can see it here.

What you will get is a thin string between two objects being printed being propagated and then the string acting as a brush on th extruder orifice at intervals between roads.  These brushed accretions build up into quite beautiful forms resembling frost.

When you get just a tiny bit of string hanging off of your print you will see the brushed accretion building up at 45 degree angles into something resembling fractal patterns.

This phenomena isn't a big issue for me.  The accretions are thin and fragile and brush off easily without sandpaper.

They are pretty, though, in my opinion at least.  :-)

Dealing with detaching rafts

In which your narrator seems to have come up with a way to prevent raft peel for ABS on an acrylic print table.

About two weeks ago, the rafts for my ABS prints started detaching from the right hand side of my print table.  I was losing one out of two to one out of three prints that way.  At first I decided that my acrylic print table had simply got too warped and I had too much variation in level on the acrylic.  I removed the acrylic print table and checked its flatness with a milled straight edge.

Indeed, it was a little warped so I used a belt sander on it till if was as flat as the milled straightedge.  That seemed to work for about an hour but I was soon back to where I began.  I then decided that the table was now adjusted properly and went to a great deal of trouble getting it so on my Rapman.  Same result.

In desperation I began to print on the left hand side of the print table and the problem went away.  It was still troubling, though.

On Tuesday, I finally caught on.  In the last weeks the weather had cooled to where the outside temperature was in the teens more often than not and dropped into the single digits {Celsius} in the early mornings when I began to work.  I looked at the printer table and noticed that the window I used to ventilate the work area was on the right hand side of the printer.  The next time that I had a raft detach I measured the acrylic work surface temperature with my IR thermometer and discovered that whereas it was about 25-26 C on the left hand side of the table the draft from the window dropped that to 22-23 C on the right hand side.  I was rather shocked that I got that wide a variation in surface temperature over a few centimeters distance, but I certainly did.

I closed the window and the peeling instantly stopped.

That remedy wasn't workable because of the ABS fumes, so I rigged a portable heat lamp onto my camera tripod to shine on the print table.

The radiant energy keeps the acrylic print table at 34-40 C with the window open.

I haven't had a raft detach since then.  I've done a few dozen prints, mind.

Second go at the carpal ensemble

Acid test

I decided to give the new non-loop road finder routine a tough workout to see how robust it is. For that I designed a 20 mm diameter herringbone pinion gear.

I did a solid print for strength.  As you can see, there were no problems.  The stl's processed without drama and the gcode is good.

Changes to Slice and Dice

Slice and Dice was fine as long as your parts were more or less continuous along the z-axis and not so complicated that you got a lot of clashing with print loops. When I got to working on the thumb joint on my telepresence hand, however, I started having a lot of trouble with both of those limitations.

A major strength of Slice and Dice is that if you have a dodgy STL file you can clean up little imperfections on the slice images. That's wonderful until you have a part that you want to print that has little in the way of commonality between slices. I found myself fixing faults on 30-40 slices in Paint. That was seriously not fun. The main problem, as it developed, lay in the implicit dependence of Slice and Dice on looped road descriptions. Once you get into complicated parts it becomes very difficult to meet the app's expectation of clean looped print roads.

This is the part that started causing me trouble.

Virtually every slice is unique.

I rewrote the road making routine to deal with non-looped roads this evening. This is the resulting test print of the part shown above.

A problem that the old Rapman firmware was that it expected minimum print road line segments to be about 0.6 mm long. When I finished the rewrite, I was not looking forward to fitting line segments to the non-loop print roads. I had the output, but it was all 0.1 mm print roads.

Andrew at BitsfromBytes has said that the updated firmware would handle 0.1 mm roads with no problem. I frankly didn't believe him because the older firmware would slow the print down to 6 mm/sec with 0.1 mm roads. I decided to give it a try with the 4.0.2 code, however, and it turned out that Andrew is absolutely correct. The Rapman firmware has no trouble print sequential 0.1 mm line segments at my chosen print speed of 16 mm/sec.

That made the print file for the two halves of the thumb joint some 8 meg long. Since I have a 1 gig SD card, however, that's no trouble at all.