Thursday, 31 March 2011

Building the Prusa Mendel

I acquired more m8 rod and all the other required vitamins and it was time to build

First some Frame triangles



Then the entire frame

Add some steppers  and the Y Axis


And all the rest and move the electronics from the repstrap


And finally with head added, a print test.


It works!!!

First 'real' print
This little guy I found on thingiverse  I had to shrink him by 50% he took just over an hour to print. He is just big enough to hold my iPhone (oh the irony)

Test 40x40x20mm cubes now take only 6 minutes to print, a vast improvement on over an hour.

This is where I'm up to so far.


But I am far from finished, there are still niggles to address. The Z axis threads are not as parallel to the Z bearings as they should be, consequently they kept breaking the coupler and require a lot more force than they should to move, for now I am using an aluminum couplers till I work out which part needs moved where and why etc.... 
Also one day soon I intend making a heated build platform to once and for all kill any remaining warping.

My repstrap tuning, and Prusa Mendel parts printing

The first thing I had to do is setup a machine profile. This defines how many steps are required to move 1mm in each of the 3 axis. In This case 320 steps moved things 1mm and was the same on all axis.
  
The next thing to work out is the extrusion rates. I calculated the speed the machine moves at 3.33 mm/sec.

NB this is incredibly slow! This is because it takes 320 steps per mm, the final machine the axis are driven by belts and one step move approximately 1mm

So I moved the Z axis to it a high point and set it to extrude for 10 seconds. The aim being to get as close as I can to extruding 33.3mm of filament.

The following is a picture of some of the extrusion speed testing. Pick a extrusion rate, extrude for 10 seconds, measure the length, to long and shorten the rate and try again and if its to short increase the extrude rate and try again. 


Once your happy set this rate into Skeinforge speed settings.

You also need to set your temperature settings, these are different for ABS and PLA. The temperature information can be found on the pages I have linked to.


NB ABS sticks like mad to acrylic, I was using a chisel to remove parts from it.


I started with ABS as it was all I could get in a hurry.  I have since switched to PLA, why? mostly because the fumes given off by ABS are not fun, and it is a oil based plastic.  PLA is much nicer and is corn starch based and is biodegradable.


The next step in tuning is to try and get a test cube to come out like a cube.
this can be found here,


My test cube came out brilliant! But did take over an hour... So I skipped the rest of the tests as I wanted to try something else more fun.

I had a look on thingiverse.com and found the Stanford Bunny

He was huge, so I scaled him down a lot and hit print.
To my surprise I got the following (after a little bit of clean up)


I did a little more tweaking and learning to use the software and began to print Prusa medel parts

The large piece took 6 hours to print! This was followed in time by the following parts

Here I ran into a problem, dispute the ABS sicking like mad to the acrylic, it still started to lift up in the corners badly on large prints.

After lots of trial and error, I switched to PLA which doesnt curl up anything like as much.
I also switched to a new build surface, 3M Blue masking tape. This enabled me to print the larger parts (a heated build platform will also get around this issue)


This is one of the last medal pieces, it took 16 hours to print!!

I now have a full set to Prusa Mendel printed parts, though some of them are in ABS and some are in PLA.

Repstrap software

Firstly what does the software do?, obviously it allows you to control your reprap, but it is so much more. This is the smarts that takes a 3D model and cuts it up into layers to be printed.

Most people seem to be under the impression there is only the official reprap software and you must use that.  This is not the case.

After talking with another reprapper I have decided to run the replicat.org software and firmware.

The reasons in short are:
Nicer GUI
Less buggy (this is just my impression)
The system parameters are in configuration files vs. in the firmware
The firmware also support using the SD card
The GUI lets you pass the generated G-CODE threw Skeinforge from within the GUI
You can also select which version of Skeinforge you want to run.

Once again I struck a snag, the standard firmware does not directly support a stepper driven extruder

Luckily you can compile it in, full details here.
NB you need to run Skienforge 3.5 so you can run the RPMFY plugin to change the motor gcode commands into stepper gcode commands. 


Tuning the reprap is also a time consuming but the following link helps a lot.


 

Wednesday, 30 March 2011

repstrapping the cartesian bot

The next stage was to add the parts required to turn the Cartesian bot into a repstrap.

For this I needed an extruder, this basically feeds the plastic into the hot end.
There are a few options for extruders, I went for a Wades geared extruder as there where readily available on e-bay.


This also requires a hobbed bolt, I also got this on ebay





Add one stepper motor and assemble and you end up with something like this.

Now my gear is actually on upside down, this is due to two reasons, one the hobbed bold seems to have the hobbing in the wrong place, and secondly the gear would catch on the stepper motor bolts. It works fine this way.



Next I needed a way to melt the plastic, this consists of two parts, the heat core and the hot end.
Due to time constraints, I wanted this before x-mas, I got a local engineering firm to make me the equivalent of a mendel parts v5 hot end  The peek and the PTFE came from DOTMAR, the brass the engineer has in his scrap bin.


For the heatcore I ordered one from makergear The instructions where very complete, even a near sighted monkey could make these.


I tested the heat core and hot end just by pushing plastic into the back of it, and got a nice 0.5 stream of plastic.

I joined the Extruder to the hotend with wood screws to a block of wood. The block of wood has a hole threw it for the 3mm plastic


Next I needed real reprap electronics so the software would be able to control things.

Once again I went to ebay.com and found that Gen3 electronics where readily available


These came pre flashed with the reprap firmware and boot loaders.

I wired everything together for testing and found I had an issue, the stepper motors I have wouldn't work on the extruder controller.


these are Lin Engineering steppers from alltronics 

Attaching the stepper to the extruder is a bit of a hack, they use standard motor controllers to drive the stepper motors. It apparently works really well, unless, you guessed it, you have Lin Engineering steppers.

But all was not lost, I just needed a real stepper controller, I found that a local supplier robokits.co.nz is New Zealands distributor of Pololu products including their very nice stepper controller so I orded one.

I made a simple break out board for the Pololu

 
The connectors are now compatible with a standard reprap stepper board.

After more testing I was happy that all the electronics works as it should, I attached it to the Cartesian bot




And a repstrap was born.

In the next installment software...
.

Tuesday, 29 March 2011

Back at the start

At the start of September 2010 I decided I wanted to build a reprap.

At the time I had been watching the project for years, but had not started anything towards it.
Looking at the various options I decided building a repstrap and printing my own parts for a Mendel was probably going to be the beast way to go, since being in New Zealand is somewhat isolated getting printed parts was going to be expensive, especially when you convert to NZ dollars and there is also that nasty additional cost of shipping.

I decided on building a McWire Cartesian Bot 1 2

Although this project is now marked "Death March: Do not build!!!" It wasn't when I started, I also like the idea of having a general purpose Cartesian bot around.

I started gathering parts...

Then the 04 September Quake hit,

So for a month or so after this no one really did anything as we where all somewhat quake shocked.

After a time things began to get back to normal, and I continued to get parts.
I managed to get most parts locally, the hardest was the U channel aluminum, I eventually got this threw Element14, but they warned me this was the last of the stock and there wouldn't be any more.

One of the first things to turn up where the NEMA 23 stepper motors




I tested these with a controller I got from morestuff.biz


The next step was to build a frame, Unfortunately I could not find anyone to supply me with bits of pipe, not for a price I could afford. So I had to find a substitute. I found burnings had aluminum and joiners, so I built the frame from that.


I also had some difficulty finding acrylic, eventually I found a guy on trademe.co.nz who would sell me what I wanted, even cut to the correct sizes.

After much cutting and gathering of parts I had enough pieces to assemble the Cartesian bot
Here it is, just placed together



As you can see, no fancy laser cuts parts here.

After much drilling and gnashing of teeth and screwing and bolting, I had a Cartesian bot.


Since I had to modify the stand, I found that the Z axis moved to much, so I had to add braces


The next step was to turn this into a repstrap...

This is going to be a log of my Reprap experiences

I made the decision today to move my reprap info out of facebook and into a more public forum.