Saturday, July 17, 2010
Mendel & multiple materials
It has always been the intention to fit a head changer to Mendel, I've had a go myself on several occasions but always ran into the same problem i.e. I haven't been able to do so without substantial modifications to the core frame of the machine unless there is a substantial loss of build volume (...I once had a design that ended up having a maximum build height of 2cm.very practical:D). Moreover, it’s more difficult to have a head changer for extruders whose designs are still in the early stages (such as the paste extruder). The main problem I suffered with is that regular designs of extruders are just too bulky without increasing the overall size of the machine, which incidentally I think is the perfect size as it is. Any bigger, and I would find it too big to find houseroom for!
Thankfully, eD had the idea of bowden extruders some time ago, which quite a few people seem have gotten work. Thus I think way forward for the time being is to implement a carriage for multiple bowden style extruders. Although this is almost certainly going to reduce build quality slightly. Some have already designed multiple bowden extruder carriages; here is my take on it:
The main differences are:
1. Support for three extruders, either bowden or paste. (limited syringe size of 10cc).
2. All the multiple head machines I've seen rely on the extruders being exactly the same height in order to get the bed clearance just right to produce good builds. I've always found getting adjusting bed clearance is tricky enough just for one extruder, and I think it's likely that there will always be a build up of tolerances that extruder heights will always change by significant magnitudes. Even still, with warping and so on in the carriage, it may still be difficult even if the extruders were identical. Thus, the carriage treats each extruder clearance like pretty much everything else on Mendel, by allowing for adjustment. All extruders are attached to a mounting plate, of which on the underside are of series three captive nuts for each extruder arranged in an equilateral triangle. Three compression springs are then placed between the plate and the extruders, and cap screws are used to adjust the compression of each spring independently. (In the picture above I’ve only used the springs on the left hand extruder, it makes sense to fix the main extruder and adjust the other two to match it)
3. In the same style as the mini carriage, the bearings are all located within the carriage itself. Having the bearings located on the outside surfaces of the carriage( like the standard Mendel design) ensures that the walls of the carriage must lie between the bearings and any extruders, eating into the working volume. However this does result in quite a wide carriage.
4. I needed to make some compromises, neither of which I'm particularly happy with, so that I don’t have to redesign the whole x-axis. Firstly the belt travels through the carriage itself on the 360 side, and secondly the belt is clamped from the inside out.
5. Finally its NOT makerbotable (its about 115 x 95mm), but it should be a fairly easy redesign to allow for only two extruders. . Even still, if you have a RepRap I'd recommend printing in PLA or using a heated bed or you'll probably run into trouble
Anyway, I’ve heavily modified the Paste Extruder, and used it in parallel with a bowden extruder I designed that based on Erik’s design but using a worm gear to do the driving (Designs to be on the SVN/thingiverse shortly). Gerrit Wyen (an intern at the RepRap Lab @ Bath Uni) created a simple script to take account of the offsets between the extruders and modify the GCode accordingly. Also Adrian has done so much I’ve forgotten exactly what he’s done, but its a lot:D. Here is a video one of the first prints; it’s a cube using PLA for the outline and top and bottom layers, and silicone sealant for the interior infill:
Whilst I did reverse the extruder to prevent ooze, and this is sufficient during a "normal build", its sat there for such a long time doing nothing whilst the paste extruder is working it still oozes horribly. For this reason I built little barrier to collect the ooze from hitting the part, but I think we may need to lower the extruder temperature a little when not in use. Anyway, here is the final part, which came out surprisingly well:
There are some more photos of the test setup and some other less successful prints here.
Labels: Bowden Extruder, extruder, multiple materials, paste extruder, x carriage
Sunday, January 06, 2008
Paste Extruder water tests.
Adrian has also made some beta firmware that we hope to get out there soon, using the PIC16F648A CPU. I've stuck it in my Darwin and seem to be able to make things extrude.
Darwin now has a snug carry-case, and I hope to test it out on a trip to Wellington in the near future.
Vik :v)
Labels: paste extruder, reprap, squirt, water
Friday, June 29, 2007
Filling in the cracks
As promised here is the paste extruder working with Polyfilla wall-crack filler paste. As with the silicone yesterday, the flow rate is still a little high (next: try a smaller diameter nozzle), but it works smoothly.
The principle of the device is proved. Now what needs to be done is to improve the design: it's a bit difficult to refill, and that needs to be made better. Also, at its heart, is a turned brass part that I think can be replaced by a rapid prototyped one. The nozzle is a slightly modified version of the one on the polymer extruder, but there is no reason for the two not to be identical.
Labels: paste extruder, polyfilla
Thursday, June 28, 2007
Silicone enhanced RepRap
I have got the paste extruder working on RepRap. It consists of a 500 ml fizzy drink bottle containing a balloon that in turn contains the paste. You pressurize the bottle using a bicycle pump, and the flow is controlled by a latching solenoid that clamps onto a soft silicone tube on the way to the nozzle. The clamp is the red rectangular piece hovering over the tube in the picture below (the solenoid is behind the green support). When the red bit moves backwards the flow is shut off.
Here is a close-up of it laying down a test square. The material is PolyDiMethylSiloxane (PDMS - silicone bathroom sealant). I had the flow set too high and the movement speed too slow, so it's flooding a bit. But that should be easy to fix.
The controller electronics are really simple - just the standard RepRap controller with slightly modified firmware (which I have just posted in the software repository as extruder_1).
The silicone doesn't set if you leave it in the device overnight, except for the bit actually in the silicone tube that forms the valve. I suspect that this is caused by the fact that the materials are the same, and so a little of the catalyst that caused the tube to polymerise when it was originally made is leeching out and setting the working material as well. If I am right, to fix this we just need a soft tube of another material.
When the valve closes, it deposits a splodge of goo as it displaces some material. The tube I used for the valve is 3mm internal diameter, which it doesn't need to be. I'll try and find some of 1mm I.D. That should cut down the closure volume, and hence the problem, dramatically.
This means that we should be able to work with just about any material that is a paste at room temperature. Tomorrow I'll use up another balloon (no expense spared) and try Polyfilla wall-crack filler paste.
Labels: materials, paste extruder
