Thursday, April 16, 2009

Nice housing

To make all the electronics studentproof I dicided that it needed a housing. And wouldn't it be nice if it matches the Fabber? So I designed a PMMA housing in Inventor (my 3D program) in the same way the Fabber was build. The only problem is that it isn't possible to make this with a mill because it has some sharp internal corners to make the slots for the nuts.

Last week I went to a Fabtable at the fablab in The Hague ( were the labmanager offered me to use the machines at the lab. One of wich is a lasercutter! So I asked if I could make the housing on this wonderfull piece of equipment and he said yes.

With some PMMA sheets and the CAD drawings I went to the Fablab and this is what happened:

With a thickness of 6mm the 35W laser was just strong enough to cut trough the material at a rate of 3mm/sec. The panel on the picture took aprox. 15 minutes to cut.

Ofcourse I hadn't brought enough material to cover the first f*ckups but a quick trip to the workshop got me a new sheet. In the end all 6 panels came out very good and all the components fit perfectly.
Front: 2 temperature controllers and the switch for the heater. In between the controllers there is a hole for a switch to control a solenoid. The solenoid can raise or lower one of the extruders.
The main circuitboard is the one from the computer power suply. The board on the right (with the blue connectors) hold the resistors for the permanent load and the FET's for the heater.

The back panel is almost the same as it was in the computer. Only the DIN connectors are added to connect the extruders. The wiring will be for the thermalcouple, the heatercoil and the solenoid.

And yes, I know the tag on the fan is upside down...

Lots of thanx to the men at Fablab for letting me use the lasercutter.
Wasn't there someone who tried to install a laser on a RepRap?

Tuesday, April 7, 2009

Temperature controller

Yesterday I decided to stop trying to build a budget heater. For good thermal control I need temperature controllers that measure the actual temperature take action acoording to this and the set value. The way in wich the Reprap does this works good, at least that's what I understand from the stories I read from other users. For this project it would be too much work because the Fab@Home uses a totally different language and I'm not good at all with software. I hope to keep it this way...
For a mechanical engineer I still had to dig in deep in to electronics to find out how to control the temperature. In the end I found a very nice controller. The controller will work with the most common temp sensors like thermalcouples, ptc, ntc, pt100 and some. The ouput varies from a relay to some electronic signals. 
I also managed to make a power suply for a desktop computer suitable as a power suply for the heater. This involved some resistors and a switch because the suply won't work without load. Also it needs to be turned on, same as you turn on your computer. The package is completed by a MosFET between the heater and the powersuply to regulate the powerinput to the heater.
This is no rocketscience elektronics but for a mechanical engineer it's a bit of topic...

Wednesday, April 1, 2009

F***ing powersuply

I tried to spot weld the heatingcoil with four different powersuply's, the first one gave the best result: at 10 amp (max current) the wire welded together but they didn't fuse as much as I wanted.
Another powersuply (22 Amp) had a shortcut saffety so no current at all. With the third I was able to set the current, but when I switched it on it started smoking, without any load connected. Some internal shortcircuit or something, the suply probably hasn't been used for a couple of years so no one knows...
The last attempt was a self build suply. I found an old transformer (240 V -55 V) with coils made of thick wires. This one should be able to give me the current I need. A variac on the primairy coil should give me the ability to regulate the welding current. Unfortunately I blew the fuse...

So, I tried soldering with silver. It was tricky not to overheat the wire with the gastorch but I managed. Unfortunatley this connection broke after some fiddeling.
In other words: I walked a lot of kilometers today to get all the stuff together for nothing. Good thing the sun is shining!

Monday, March 30, 2009

Lots of sparks

The feedwire from my heatingcoil broke today. It's a double wire of the same kind as the coil itself, it's more like a thin strip. The end of the coil is folded between the feedwire and fused together. An attempt to fuse them again with the spotwelder that we have here resulted in a rain of sparks and evaporated wires...
Now I've build a spotwelder in the lathe. One elektrode in the chuck and one in the tail stock. The elektrode in the tailstock slides in a PVC bush for the insulation, a spring behind the elektrode presses it towards the chuck-elektrode. A powersuply will provide the current to weld, I hope 10 amps will do the trick. Pictures of the welding will folow.

Friday, March 27, 2009

Too hot and rising...

I found a piece of insulation material after searching the entire building. It's glassfiber with a sheet of aluminiumfoil. After wrapping it around the barrel I was curious how hot the barrel could get.
So I turned up the amps to 2.2 A at 24 volts. At 380 degrees celsius it was still climbing but I thought that was hot enough because some smoke was coming out of it and I don't trust the Celeron at these high temperatures.
I started experimenting with extruding HDPE and ABS, it works. Now the tweaking starts to get an optimal flow of material.

The Celeron turns out to be a very good solution. It's very easy to work with, it handles a bit like wood. When you turn it on a lathe I do advice to keep a vacuumcleaner next to it to prevent the machine from getting covered in a layer of yellow dust.
The thermalcouple reeds a temperature around 160 degrees celsius IN the material, just under the surface where the heaterbarrel (260 C) is attached. So I would stop spending money on PEEK, Celeron is cheaper and stiffer. It is possible to cut a thread but with frequent loosening and fastening I would advise to use metal inserts.

Some more good luck came to me today in the discovery of a stack of various thermalcouples. The shipment is dated from 1983 but I don't really care as long as they work...! After that I found a 30V/3A powersuply that works better than the one I was using.
It turns out that when you know where to look (usually places where no one ever comes) you will find lots of 'forgotten' equipment, parts and tools that come in handy in some way.

Now my weekend starts...I can't wait till monday...


Yesterday I went with a group of students and teachers to the Solitaire. This is a ship from the company Allseas wich is specialised in laying pipes on the seabed. These pipes are upto 60 inch in diameter (!) and can be laid to a dept of 2700 m! The ship is in fact one big pipe welding factory wich welds sections of 12m into one big pipe that slides of the stern of the ship and is held by big tensioners wich can tow 3x300 metric tons. Quite an extruder in a way...

The pipe makes a S-shaped curve and lands on the seabed. It's as easy as that ;)

The ship was in a dok in the Rotterdam harbor for major maintenance and we had permission to fotograph anything we wanted during the tour trough the entire ship. Briljant! Underneeth a couple of shots to give an impression.

Start of the main firing line in the bow.

End of the main firing line in the stern with a view on the stinger

The main firing line goes over the length of the whole ship (300 m) and consists of a line-up station, 5 welding stations, 3 tensioners, a none destructive test station and a seeling station.

The stinger guides the pipe into the first S-bend and extends the ship with 150 m.

A 'small' pipe in an opened tensioner. The pipe is covered in concrete to make it sink and to protect it.

A view from the aftbridge. In the back you can see the stinger. The crane (one of two) on the right is used to hoist pipes on board. The ship is almost constantly resuplied wit new pipes while at sea. There are two bridges, one for normal sailing and one for pipelaying.

Wednesday, March 25, 2009

I like it hot...

Today I assembled my test heater. The goal of this heater is to try some different shaped heaterbarrels and nozzletips. The heater consists of a brass tube with the wire from the soldering iron wound around it. An aluminium nozzle and heater channel are placed in the tube and closed in by a bolt. In this way it's very easy to switch between different nozzles and barrels to see wich shape gives the best result.

As thermal insulator I used a piece of Celeron (aka Tufnol or hard linnen). I didn't expect to much of it but I just had to try because it was there. The specs say that it can resists temperatures upto 160 degrees celsius. Surprisingly it held out very well in my first test, the contact surfaces of the brass and stainless flanges became 200 degrees celsius.

The backside. It shows the stainless flange and the bolt that holds the inserts in place. The rod sticking out of the nozzle is a thermal couple connected to a display.

The frontside. You can see the coil from the soldering iron with the mica sheets between the coil and the brass.

The inserts. The nozzle has a 0,3 mm hole, the drill is next to it. Sweet isn't it? The hole trough the barrel inserts hasn't been drilled yet.

The connection of the heaterwire glows because of high resistance. Even without insullation, to keep the heat inside, the display of the thermal couple read 300 degrees celsius... As expected, the 50W from the soldering iron is a bit overkill. I'm planning to shorten the coil.

The testfacility. Unfortunately the ordered polymers didn't come in today so I haven't actualy been able to extrude yet...