Thursday, October 29, 2009

 

Another Child Darwin



In the hopes of increasing my printing speed, and to confirm that it is actually possible to make a RepRap with RepRapped parts, I've printed out and assembled a child Darwin. It's mechanically complete, and the axis all run quite nicely - at least 3000 mm/min so far on the X and Y. I have yet to get a firmware that will run the stepper based pinchwheel extruder, so no minimug yet, but I thought I'd post my results so far. I'd love to hear from anyone who has a stepper driven extruder running with any of the Arduino/Sanguino/Extruder controller firmwares. Also, a big thank you to Barry, who soldered up and donated the stepper drivers and opto endstops!

Also, while I've been assembling the 2nd Darwin, I continued printing out parts, and am now just a few parts away from completing a third set of printed Darwin parts. They're going to some students from UBC, more about that later. Interestingly, the parts fit on the bed when you dump them out of a bucket onto the bed, but unfortunately, the Darwin isn't able to utilize the entire bed space for printing. :)

Here's the parent machine:

A little worn down, but still printing!

Wade

Wednesday, October 28, 2009

 

Lazy Susans and filament



Three millimeter filament generally comes packed in two formats, first as ...



coils as seen with the four 5 lb lots of PLA at the seen on top of a standard shipping spool of ABS seen carrying 20 lbs and capable of carrying 40 lbs which is the second format.

While several solutions have been confected to deal with coiled filament, I wanted to use ABS directly off the spool. Having lived and worked in Guangdong in China for several years I became happily acquainted with the lazy susan tables which enabled hungry Cantonese dinner parties to load their rice bowls at dim sum restaurants with a minimum of fuss.

The ball bearing race mechanisms for such tables are readily available in larger US hardware stores for about $10.



I also bought a pair of precut plywood rounds at the same store. Once I locked the race down, I lubricated with a light oil spray.

What you wind up with is a mounting table for quite a heavy spool of ABS which uncoils with about an ounce of force.



I suspect that one could knock together a much smaller spool for coiled filament and use the lazy susan arrangement for those as well. Given that most extruders exert kilograms of force to push filament into the extruder barrel this arrangement shouldn't cause feed problems. I'll keep you posted on how it works out.

 

Colour Printing - the next step



To follow on from the basic twin extruder test in the last blog, here we have the results of my first test using support material

The machine is loaded with two colours of ABS, mainly for convenience at this stage, Black for the object and Yellow for the support material.

The file chosen is a bearing cap, printed from the bearing axis up, this has a semi-circular void that runs front to rear of the part. Actually this file prints very well without support material but it is a small part suitable for testing the head change.

Small it may be, but it still contains a fair number of layers and therefore lots of head swapping!

The first test was done with a hand edited file, I added several new lines of G_Code to manage an orderly change over from one head to the other. On more complex parts, it would not be practical, the new codes need to be added by Skienforge.

Skienforge already deals with support material by issuing a temperature change to flag the start and end, I need several other codes inserting at this point. To do this I have made a simple modification to Skienforge to pick out the support material, then insert my new codes as required.



The image shows the first complete part made by running the file from Skienforge.
Finish on the part is crude as the G_Code has been generated with 0.4mm layer thickness, this ensures a relatively quick build and gives a manageable file size.



The print is far from perfect, but I have to say I am encouraged by the results.

Tuesday, October 20, 2009

 

Cutting Spur Gears with Meccano

An item of interest I found when worrying the web about gears.

Meccano Gear Cutting Machine

It is a machine made from meccano that can cut more meccano compatible gears using a Threading Tap. It uses an existing Meccano spur gear as a template for the one to be cut.

A novel way to make gears without a lathe.

Interestingly enough it should be only a small set of modifications to make the machine able to cut worm gears by hand also without the need for a lathe.

I don't have any Meccano but thought this would be useful enough to cover here for those who might.

Sunday, October 18, 2009

 

Just about done



I finally sorted out the last parts of the extruder on my Rapman and should be able to start printing after I get acquainted with the operations manual.



I need to put that spool of ABS on some sort of bearing loaded rack so that the ABS will feed into the printer smoothly.

 

Colour Printing



First attempt at two colour printing, not the most astonishing object but you can see the potential.
The print has been done on a BfB V3 machine fitted with twin extruders. The two single colour objects were printed together from one file, the two colour object by swapping heads through the build, changes triggered by G_Code.
You can see the potential for running support material along with the main print, swapping seamlessly back and fourth between the two.

The wall is single filament thickness so alignment has to be reasonably good between the heads. The object is far from perfect as its only the third print of a new machine fitted out with the twin head.
More to follow on this.

Tuesday, October 13, 2009

 

Open-Source to the rescue!

To build anything in a RepRap, you need to have a 3-D design, save it as a STL or triangle mesh file, and load it into the RepRap host software (or skeinforge).

To create these designs, RepRappers use different programs - Either an adapted 3-d modelling programs, originally used for animation (like Blender and Art of Illusion), or freeware versions of CAD software (like CoCreate). These solutions work, and work well, but each program has seperate advantages. I've been looking out for a 'better fit' - a CAD-style program, that supports building meshes and solids.

Make magazine today furnished me with a link to FreeCAD.

It's pretty slick - either I'm quite lucky, or it works quite well. Within a few minutes I was able to load it up, get started, create a small cube model, export it to an STL file and import it successfully into the RepRap Host software (not always an easy thing!).

OK, lets give it a real test...

Let's load up some data from a complex file: a human head.
To really test it, I created a large sphere, stuck it on top, and did a 'union' (Join).
This is not nice: most complex geometries cause all sorts of bent and broken and backwards triangles. Lucky there is an analysis tool to point all this out:
From FreeCAD

Pressing some of the 'repair' buttons sorted all this out.
From FreeCAD

This exported easily to an STL file: and then loaded straight into the host software.

From FreeCAD


It started to slice and print to gcode : it got to 55 layers through before I got bored and turned it off.

FreeCAD is currently alpha software so far, but certainly one to watch!

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Sunday, October 11, 2009

 

Sorry for the off topic post

Hi,

I'm building a reprap, but I'm way over the alloted schedule I made for myself (big surprise, when is anything done on time... :( ). So I've had to make a choice between continuing to work on my reprap or to do other things that I scheduled for this time.

I put my reprap on hold for now. I'm working on a designed based on a robotic arm and using FPGA's. If you want to know anything about it or would like to continue working on something similar, I'll email you what I got.

I'm taking a trip around the globe. I'm riding my bike from San Diego to San Francisco for three weeks in November. Then spending December with my family in Michigan and South Carolina. Then I'll spend six months circumnavigating the globe. The current travel plan is Hawaii, New Zealand, Australia, Japan, Philippines, Indonesia, China, Malaysia, India, Russia, most of the countries in Europe, Iceland, Greenland, Canada, then home. If you live along my route and wouldn't mind letting me sleep on your floor or couch for a day or two, drop me a line. :)

You can also follow my progress on:

http://thebikepacker.wordpress.com/

Again, sorry for the spam, but technically I am a reprap builder and this is a blog for builders.

Cheers!

-Brian

Saturday, October 10, 2009

 

One step forwards

G'day all.

I've been quiet recently - I had packed everything away into the garage as we were planning to move. Plans change, we're now not moving so I unpacked the RepRap and fired it up.
From ResistorHeater

First problem : blocked nozzle, due to a broken thermistor - overheated - and set the ABS solid.
Cleared down and drilled it out.

I replaced the thermistor with a spare 100k makerbot one - my last spare.

Interestingly enough, I soldered in a 100k thermistor from Maplins into a spare circuit, connected it up, and the temp read about 20C at room temp, and 34C while holding it - pretty good without any change in configuration. It might be a suitable replacement for the 'official' ones.

Replacement thermistor in, I warmed up the heater and 'let rip'
From ResistorHeater


It works! Extrusion is pretty slow (232mm/minute) and wide (nearly 1mm diameter through a 0.8mm nozzle) but it comes out reliably and pretty consistently. Temp was about 225C and power (screw thread/servo) at 180/255.

Now I have something working, I can refine the nozzle size ( I should be able to get some 0.6mm B&Q nozzles) and the original BfB 0.4mm nozzle, plus I have some small drills.

I now need to get my settings and speeds right in the host software - my current version is months old, maybe I should update. I've been thinking about upgrading to version 3 electronics, too, but with the excellent Mendel design out with a much smaller footprint, I quite fancy that. It might be time to build a Mendel using my Darwin....
:-)

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Wednesday, October 07, 2009

 

Working with Cotronics 907

I let the first application of Cotronics 907 on the Rapman extruder barrel air dry overnight. The material was quite hard. The next morning I used some fine grit sandpaper to smooth it down so that the mounting flange could slide over it. It took some time to smooth it out sufficiently, but you can see that it dressed dowquite nicely.




I was also able to dress the PEEK thermal break so that it fit into the extruder barrel socket firmly without jamming.






Unfortunately, I read the oven curing instructions incorrectly and encountered a problem that the Cotronics people were very open about with this product. If you don't cure it properly and heat it too hot and too fast, it tends to form blisters which separate the ceramic slip from what you are putting it on. Thus my careful sanding and dressing of the flange joint was for naught. It is worth noting that once I saw the bubbles I was able to remove the 907 with the wire wheel on my bench grinder relatively easily while it was still warm.

From there I applied a second coat, this time with the flange in place so that I wouldn't have to do any sanding. Doing it that way I was able to put the basic underlayer for the nichrome heating coil, the flange fillet joint and the flange pad all on at one go.

After four hours of air drying, two hours curing in my fan oven at 90 C, another hour of post curing at 120 C and a final post curing hour at 200 C, I was able to secure the nichrome heating coil as per BitsFromBytes instructions on yet again.



On that I put a slip coat of 907 and after it had air dried was able to put a coat 907 to secure the leads for the heater as per BitsFromBytes instructions. I was also able to place the thermistor in its socket as you can see from the following picture.




Using the "helping hands" electronics jig, I was able to secure the thermistor leads and the extruder assembly. This was very handy because it let me monitor the assembly for shorts in both the heater coil and the thermistor while I was applying the 907 ceramic adhesive.




I will be letting it air dry till morning after which I will do the 8 hour curing and post-curing in the fan oven. Hopefully, I didn't overdo the ceramic application and the curing will be successful.



Tuesday, October 06, 2009

 

Getting away from fire cement...

I'm currently finishing building a Rapman variation on Darwin. The construction has gone remarkably smoothly until recently when I began to build up the extruder's heater barrel. I had the whole thing finished with the nichrome and thermistor properly embedded in fire cement which encased the aluminum barrel.

When I tried to insert the PEEK thermal break, however, things went wrong. The PEEK cylinder jammed in the extruder barrel's sleeve and in trying to get it back out again I managed to apply a bit of torque to the barrel. This shattered the fire cement.

I was able to recover both the thermistor and the nichrome heater wire, largely because the fire cement, even oven cured, has the consistency and tensile strength of dry silt mud. I cleaned the barrel with a small screwdriver and electrical pliers with zero trouble. You can see the results here.




I had used ceramic coatings before with nichrome and called Danny at Cotronics in Brooklyn. He recommended their 907 formulation which is, if I've read the data sheet correctly, a mica-based ceramic adhesive formulation with considerable compressive and tensile strength. Better still, I was able to order it through a retailer, McMaster-Carr, here in California in Long Beach. I was able to get it ordered, shipped and delivered overnight using a local courier service for about $5.

You apply 907 with a brush. The adhesive in liquid form is a bit like very wet clay mud getting an even coat on the aluminum barrel was quite difficult. Once dried, however, it developed a very hard, glassy surface as you can see here.






Right now I am trying to decide whether I should sand it down before or after I heat cure it. If I'd been smart I would have painted it on after I installed the heater barrel flange, then having to slide the flange over the ceramic adhesive wouldn't have been an issue.

It adheres very tightly to the aluminum.

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