RepRap: Blog

Looks like we have a failure mode for PLA corner brackets. This picture shows a relatively recent bracket torn apart by the forces of fitting an 8mm rod into it and over-tightening one of the grub screws.

As you can see, the break is hardly a neat delamination, and the line of separation is at the apex of a teardrop-shaped hole. The corners also have little plastic in them, even after being squared off so they parted easily too.

As a temporary solution I am putting bolts through empty holes to hold things together. We'll see how it goes, but I think we may need to remove some of the unwanted honeycombing from the design and beef it up a little. I'm also installing the next one upside-down, so the apex of the teardrop is at the bottom of the bracket.

Vik :v)

Labels: corner bracket, failure, pla, reprap

I've got a 30kg test batch of PLA filament ordered up in New Zealand, which I'll distribute at cost. So if you'd like a 100m roll or two, shout up. I'll dispatch overseas, but do check the swingeing NZ Post overseas rates first. A roll is 420mm diameter and about 30mm thick, weighing approx 800g. If you want larger quantities, I'll put another order in for you no problemo.

Also, PMB Electronics of New Zealand now have the L298N and L297 stepper driver chips in stock at reasonable prices and low volumes. Tell 'em Vik sent ya. No, I'm not on commission. I've asked them to consider stocking Arduinos too, but mentioning it again wouldn't hurt :)

Vik :v)

Labels: pla, pmb

It took me 3 goes. One cable pulled, and a stuck filament roll; but I got it printed in the end. Thanks to Steve for helping with the STL file. The object took 5.8 hours to print in PLA using Darwin hardware and Adrian's latest fixes. It has really picked up steam now and the quality has improved as the nozzle moves faster - as predicted.

No hint of curling on this part either.

If you look inside the holes on the left, you can see some stringing, but it is now more like annoying cobwebs than a barrier that needs drilling out with a cordless drill. Just as well - I did stick an 8mm drill bit in my hand last time.



Here's the view from above, with a clearer view of the stringing. The thick stuff is caused by a plotting error we're looking into, and the fine, spider-web stuff is what the more persistent stringing issue now looks like.

I've tried to bend the part, and it doesn't break despite the plastic flow being a little low, so we should be good to give it a go in a real Darwin.

Vik :v)

Labels: bed, corner, darwin, pla, reprap

Just for kicks, I printed out a couple of belt clamps and a pulley. Oh, and about 95% of an X-axis restraint (software crash, blue-tinged air etc.) but it looks like we're on our way to starting an X-axis here.

I've switched to a 0.78mm nozzle now, and the new shape is an improvement in preventing strings - or at least shedding them quickly - but not much so. Also having a few problems with PLA not adhering to my new machine bed so well. Hopefully a good wipe-down with acetone and a scrape with a wire brush (for the Reprap, not me) will improve things.

Vik :v)

Labels: pla, x-axis

OK, here's the tidied up version. I had to ream out the vertical holes by hand, the horizontal holes were fine and just needed de-stringing. I have seen how threads of molten plastic climb up the curved surface of an acorn nut nozzle and I'm modifying one to see if I can reduce the stringing. The holes in general were smeared somewhat, mostly due to a soon-to-be-fixed software bug which resulted in the extruder not being turned off at appropriate moments.

In the previous post, you can see the part starting to curl like a king-size mattress being stuffed into a queen-size fitted sheet. The curl is not very pronounced, but did distort the 8mm holes making the insertion of an 8mm rod very tight indeed - you can see shavings on the end closest to the camera. The nuts fitted into the rectangular slots at the top without a problem. The other holes were a little tight and required gentle persuasion to drive the nuts home - a bolt and very large washer was used to winch them in.

What didn't fit was the nut down the channel in the 8mm hole. My reaming didn't clean that out enough and I had to resort to a dremmel tool.

It near enough works and I'll be building it into a Reprap as soon as I can.

I'm extruding in 0.55mm layers, 1.62mm outline size and 0.73mm infill size from a 0.86mm nozzle. Max x-y movement speed is set to 238. This gives fat outlines, but because of the jerky movement between points by the head, curved lines are fatter than straight lines and the slow speed minimises the difference in width.

A very respectable 0.5mm width wall was printed by mistake during a buggy phase of this printout when the nozzle moved without being turned off, but this is good as it shows what the hardware is actually capable of - even with a 0.86mm nozzle.

Vik :v)

Labels: bracket, idler, pla, x-axis

I've run off a couple of PCB clips and a couple of brackets from PLA. You can see the stringing on the X constraint bracket - it looks like it as been enveloped by a spider. The thread can easily be picked off with a sharp point, fortunately.





The blob on top of the constraint bracket is where the software crashed. Fortunately it waited for the last layer...

Vik :v)

Labels: darwin, pla

By raising the extrusion temperature to 165C I've managed to get PLA going through without blowing up the extruder motor - earlier attempts tightened the clamp too much and overloaded the poor little motor (may it rest in peace). PLA strings more than CAPA, but is significantly more rigid. Here is a Darwin bed clamp that I printed off on Zaphod last night:




The holes have since been cleared of stringing with a penknife. I'll try some more complex Darwin parts later, but there are some modifications needed to the code to conserve memory for large or complex builds.

I've also got to fit the modified extruder drive - the one with a flexible shaft. Hopefully this will let the rigid PLA filament feed more freely still.

Vik :v)

Labels: bed, clamp, pla, zaphod

Back at the start of the year, plastics suppliers Claraint were kind enough to donate 10kg of polylactic acid (PLA) granules to the RepRap Project. Alan from Imagin Plastics - a welding rod and extrusion specialist in Henderson, New Zealand - then ran these granules through an extruder to produce 800m of 3mm diameter filament which I picked up on Friday. It was dried overnight at 60C and then extruded using a 180C die and 170C feed. Here's there wondrous extrusion machine:




And here's the batch of filament I picked up. It's actually quite transparent.




By running an unmodified Mk2 extruder at 155C and increasing the pressure on the filament - it's much harder than CAPA - I managed to run it well enough to produce this shotglass:




This material definitiely has some artistic possibilities.

Further experimentation is needed, but it does look like it will be possible to make watertight containers with a reasonable degree of strength from PLA in a Darwin. A straight-through extruder would probably have an easier time feeding filament, as the stuff is rather stiff.

Vik :v)

Labels: clariant, extrusion, filament, henderson, imagin plastics, pla, polylactic acid, reprap, zaphod