Saturday, February 17, 2007


First print for Tommelise

I've got the xy move command and the Mk 2.1 extruder command module combined on the PIC 18F4610 after a fashion and working. It's not nice, but it's a start.

I'm running it on manual line-by-line commands and playing with the flow rate. I started on the left and then got a bit better on the right. When you get the flow too low the extrusion trace doesn't stick to the cardboard and when you get to the corner you drag the unattached trace around a bit, thus that weird diagonal in the left box.

The blobs on the corners happened because I had to type in a new move xy command while the extruder was still pumping. I'm a fairly fast typist, but not that fast. The splay on the top side of the right box happened because I did a typo in coordinates. Positioning looks pretty good. I need to find a flatter piece of corrugated cardboard though.

The trace on the far right is my best effort. The flow was running a bit fast making the HDPE trace 1.25 mm wide. For scale the box is 30.5 mm on a side.

One thing, I crossed extrusion traces several times and it appears that HDPE will make strong joins between extrusion traces.

Hey, I'm up to date again! ;)

So that looks promising. Is it hard to find cardboard that is flat enough? I would think it would often have a slight compound curve to it... I notice it can be sensitive to fluctuations in humidity. If it is left on a non-porous surface it will sometimes curve after a few hours!
LOL! I have no doubt that I can find a flat surface to extrude on. Cardboard was what I had at the moment. The piece I used I hacked off of a shipping box lying around. Very informal.
No no, not finding something other than cardboard! That's easy! If cardboard is good, because it's cheap and easy to pop parts off, can you find nice flat bits easily or do they have enough of a curve in them to spoil things?
This one piece I have isn't too nice. I also tried printing onto typing paper and that might be better except that the firmware that coordinates plastic flow from the extruder with the xy movement isn't quite doing what I want it to do just this minute. I have an idea what's wrong but I'm getting too tired to try out the code fix. I'm giving up for tonight and will go at it again in the morning.
Here's a funny idea. If one could smear a big blob of silicon onto a stable flat substrate using something like a ruler to create a flat smooth plane, would that be of any use for extruding onto?

I did a few tests, and molten plastic should stick just fine to the silicon, but once it cools and hardens, it should pop right off!

This would also provide a smooth finish on the backside of the extruded object...
Silicon? Blob? Do you really mean silicone?
Ah, yes, I'm glad you reminded me of the missing "e"! It happens a lot around here. ;)

In any case, I took a moment to smear a blob of white silicone onto a scrap piece of plywood. I used two straight metal rods from a printer as guides on each side, and a disposable knife blade as a spreader. I should have only swept the blob once, the other passes just introduced ondulations and defects as the silicone -very- quickly forms a thin film and disturbing it messes things up.

I now have a little area of 10 by 7 cm or so, about 5mm thick. I'll try stuff with it tomorrow once it has cured.
You have an extruder running?
How did you determine the cap/resistor/length of nicor wire to use?

I'm trying to order the parts for my extruder controller board, and am at a loss for figuring out what i need, and what length of nicor wire to use...

I posted a message on the other forum, but no one's come along and responded!
Well, the #32 nichrome 80 wire I bought has 10.32 ohms/foot of resistance. I also have 12.34 volt supply to heat it.

Using the old high school physics formula


and shifting terms

R = V/I

to get 2 amps of heating you need...

R= 12.34/2 = 6.17 ohms

That means that you need

(6.17 ohms)/(10.32 ohms/ft) = 0.6 feet or 7.2 inches of nichrome 80

It's important to remember that this 7.2 inches of nichrome includes the leads away from the the heating coil you make of it and that nichrome is near impossible to solder to anything else, or itself for that matter so you'll need a compression connector like a screw terminal to connect it to copper supply lines. Because it gets hot you'll also need a screw terminal that can handle heat.
Speaking of nichrome and heat, I spotted a can of spray paint today touting its ability to withstand 1600°F or 815°C iirc. It was at a Canadian Tire store, and was about 50% more expensive than the other more common paint. The brand name seems to be VHT.

Could be handy! :)
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