Saturday, 30 November 2013

Gunbot Broken

I've had my custom 250mm x 150mm 3D printer 'gunbot' for about 2 years now...and I've broke it. It uses the extruder controller that nophead developed some time ago and I went and plugged the extruder stepper motor where the hot end and thermistor should be connected. This connected 12V to the input of a 3.3V micro, and it is no more.....

The micro in this design is a 28 pin TSSOP package and this is a bit hard to remove without resorting to scalpels.

But my mate Dave has access to 22,000UKP worth of SMD rework station.
It's a nice piece of kit that heats the PCB from underneath and when near the re-flow temp, activates an infra red source to heat the targeted chip to the melting point of the solder. Here the IR beam can be seen targeting the faulty chip:

After the faulty chip is removed, a CCTV camera with a zoom lens is used to accurately apply solder paste to the pads:

The SMD rework machine has a CCTV camera and a prism to allow the chip and the PCB pads to be aligned. A light source can be faded upwards or downwards to illuminate the PCB or the underside of the chip to be placed. By fading between the chip and the PCB pads the chip can be accurately aligned. A vacuum holds the chip on a manipulator, and the chip is lowered onto the pads, and the vacuum released to free the chip.

Here is the PCB with the replaced MPU:

Saturday, 23 November 2013


Now I have found the best source of ABS pellets, I decided to try colouring the ABS with masterbatch. The recommended mix ratio is 1:100. I found it hard to believe that this would be sufficient, but this mix:

Produces this output:

Plastic, Plastic, Plastic

My earlier revelation that I had solved the extruder jams I was experiencing with filament produced by my Filastruder were premature.

I have had all my subsequent prints fail:

Here the extruder jammed.

And here it jammed, after putting down several poor quality layers first.

I was getting a bit disheartened by this stage. Then I realised that I had been extruding filament from some random ABS pellets I bought from ebay. I had got 5Kg from CraigRK on emaker some weeks before, so I decided to try these pellets instead.

What a difference it made. The filament produced was much smoother and did not feel as brittle. And the first print I did came out as good as any I have made with commercially produced filament. Success!

Wednesday, 20 November 2013

Further Filastruder Fun

I've been doing some empirical tests with my Filastruder in an attempt to optimise the Filament produced from the ABS pellets I bought. I decided to extrude 1m of Filament at a range of temperatures, and measure the diameter at 6 positions along each length.
This allows me to calculate an average diameter and a max-min deviation.
I extruded at temps. from 190C to 205C in 5C steps. With the following results:

I'm aiming for 0.1cm deviation with an average diameter of just under 3mm. The inlet manifold of my reprap extruder is 3.2mm and so I want to stay comfortably far away from this with a minimum deviation.

Looking at this rather small data set, it seems that 200C is the best temperature for the ABS pellets I have. Temperature less than this start to make the die swell a significant factor, increasing the filament diameter to over 3.0mm.

I also noticed that as the temperature increases, the surface of the produced filament become rougher.
I took some x10 magnification shots of filament with my trusty old stereo microscope:

First, 3mm ABS filament purchased from Reprapsource

Nice and smooth.

Second, Filatruder made 3mm ABS filament extruded at 190C:

Not bad, considering it is home made. Next, 3mm ABS filament extruded at 210C:

Noticably rougher. In the prints I have done, I do not see this as being an issue as the extruder hobbed bolt will average out the 'roughness'. So long as the filament is a reasonably consistent diameter, all should be well.

However, I found an unusual problem when using Filastruder filament, but in a wierd Z axis kinda way....

I've had great results with a couple of my Milestag Lasertag gun handgrips.

I decided to try a more complex print, this one is of my infra red focus tubes:

The print failed around Z=30mm, but seemed to recover at about Z=35mm. A second print of the same gcode failed in the same way. This is gcode I have been printing with reprapsource filament without issue for 2 years.

This image shows the failure on one of the tubes at approx. Z=30mm

A print of another of my Milestag gun parts failed twice, also around the 30mm mark:

I decided to try a simple 20mm square tube print to a height of 40mm, this also failed around the Z=30mm mark:

The only common factor here is Z. All the prints have massively varying X and Y deviations. Z is the only common factor.
Which is when I realised that some months ago I was having a problem with skipping on the X axis. Some prints would fail due to a loss of x motor steps as the layer changed to the new layer. It turned out to be a lack of current on the X axis stepper, but prior to this I changed the software to raise the extruder by 10mm at the start of a new layer.
The thought behind this was that the extruder was jammming on the previous layer as it homed to the start of the next one.
My 'gunbot' is in a heated chamber, with the ABS filament entering from the top:

Through a small hole:

My theory was that the roughness of the 210C extruded filament was catching on the walls of the heated chamber when the extruder raised itself by 10mm at the start of each new layer. This caused it to bend inside the chamber, and exert pressure on the extruder. This slight increase in pressure was enough to clog up the extruder after about 30mm of Z printing.

Here is the same breech part successfully printed on the left hand side with Z retraction removed, compared with its failed peer, which has the 10mm Z retraction:

Saturday, 16 November 2013

Further Filastruder results

After flushing my Filastruder out I've finally got some excellent results from the filament. Be prepared to use all the sample ABS supplied with the kit on the flushing process...and maybe more. Here is one of my lasertag gun grips printed from the filament spool I made here.

Here is the spool above the printer:

Sunday, 10 November 2013

Filastruder Progress

I've been playing some more with my Filastruder this week, and I've made some discoveries.

First, the things it does not tell you in the manual, and some that are:

1) The manual states that you should clean the nipple (AKA tube) well before fitting to clear out any swarf. I blew mine out with a 110psi airline before fitting, but even that was not sufficient. I started finding bits of metal in the extruded filament:

This sort of thing will obviously choke an extruder. It is not a design fault of the Filastruder, just my failure to ensure the nipple was clean. Bear in mind you may need to flush some plastic through the unit to clear out any crap.

2) It is not made clear that the unit needs to be operated with a significant overhang. As the filament is extruded, if it snags on anything it affects the output quality. The radius of the filament as it coils from a height of approx. 1.3m is 1m. So the end of the Filastruder nozzle needs to be about 1.3m from any wall that could foul the filament as it falls. I also had an issue with the unit design. As the filament is extruded, it tends to fold underneath the machine as it coils on the floor. The problem I had was that it fouled on the wooden block that mounts the fan:

This caused the filament to back up at the extruder, resulting in a fatal kink:

After leaving the unit unattended on another occasion I came back to this:

I decided to design a new filament guide which would allow the filament to fold underneath the unit as it coiled. I came up with this:

It has an outreach of about 110mm, an inbuilt fan mount that allows the fan to be raised/lowered and moved forwards and backwards as needed. It also has multiple mounting holes to allow the distance between the extruder nozzle and the support bar to be adjusted. The support bar has been turned from some delrin bar I had lying around. It could easily be made from a length of copper pipe supported between screws.

Here it is fitted:

It clearly allows the filament to 'bend backwards' without fouling:

If anyone is interested, I'll upload it to Thingiverse. I now have a bounty of filament:

BTW Creating filament for 6 hours in the kitchen does not make you the most popular person in the house.