Completed the working printer today with the final assembly of the frame and the assembly of the X-axis and extruder carriage. I still have to wire up the motors and add the limit switches and controller but a few followers have been asking for the frame files so they can start making one for themselves so I have uploaded them all to Thingverse here: http://www.thingiverse.com/thing:33946

To finish the printer I have used Kuhling’s excellent X-ends for the Mendel-Max 1.5 and use 10mm Z-rods so were a perfect fit for my printer. I have also use my X-carriage and quick-fit extruder developed earlier this year.

For this printer I have used GT2-3 belts and pulleys but it will work just as well with XL/T5 or T2.5 belts so belt clamps for all these common size belts will be added eventually along with a range of printable pulleys.

It’s hard to keep the project flowing sometimes when you know something isn’t right. I wasn’t happy with the lack of belt tensioner on the y-carriage and although it is easy enough to pre-load the belt to negate the need for a tensioner, I really wanted to make it easy to adjust later on. So a short update today as I also have a day job that pays the bills on my growing list of hobbies.

Of course version 1 had a few minor flaws so the pretty red unit you see here is actually version 2. It uses the reprap favourite, the 608 bearing mounted with a couple of washers and on a short section of 8mm linear rod I salvaged from a photocopier. It is designed with 10mm deep recesses for 9mm diameter springs either side of the bearing shaft. The springs I have used have sufficient tension to not need the machine screws as well but I know a lot of people like to rack their belts up so tight you can play C flat on them so for them it also has provision for 4mm machine screws through the middle of the springs as well.

After the second attempt I got the carriage to work with the belt, motor and frame clearance.  Version 1 had the aluminium plate clearing the end bars but once I added the aluminium plate height adjusters they fouled on the frame so I had to sacrifice another 5mm to z-axis build height.

Fortunately the y-carriage design is made up of the four bearing holders and the central frame so at least redesigns only need to replace parts and not the whole. As well as the print bed crashing into the frame the belt connectors were slightly high so needed to be lowered as well so that the belt would clear the frame. I ended up using some GT2-3 belt I had so I had to make the y-axis motor pulley fit this belt profile as well as be large enough to clear the frame cross-beam.

The basic y-carriage design is an aluminium plate suspended on three or four corners (I have opted for four) on springs under compression. The springs provide a bit of give if the hot end accidentally plunges into the print deck plus it makes bed leveling a lot easier. To level the bed there is a thumb wheel adjuster with a captive 3mm nut in the underside so turning this nut raises or lowers the bed for fine adjustment.

The frame is still just tacked together at the moment as there are a lot of machine screws to take out every time you want to make a change. I can’t see any more changes needed but I will still need to add mounts for the electronics as well as wiring clamps and some sort of spool feeder for the filament.

Next up is the assembly of the x-axis carriage so I might get onto that tomorrow, then again we are having a great spring/summer here and I hope to go blokarting (land-yachting) tomorrow so it might have to wait for another day.

For the last couple of days I have been concentrating on the y-axis. The basic arrangement is the same as a lot of reprap printers with a carriage running on linear rods and driven by a stepper motor via a belt. I was hoping to fit it all in the perimeter of the frame but I have already abandoned that idea in favour of mounting the motor and idler outside the end frames. First up I made the idler using a 608 bearing and a short length of 8mm linear rod held in a PLA printed bracket. The idler sits along the lower rail and the belt feeds either side of the rail and this works fine because the 19mm diameter 608 pulley is larger than the 15mm extrusion. At the motor end this means that the motor pulley needs to be similar size so I have made a T5 belt pulley with 15 teeth which measures about 20mm in diameter using Droftarts parametric SCAD file on thingiverse here: http://www.thingiverse.com/thing:16627.
So next up was the motor end. I have seen a few designs for y-axis motors that fail through being too thin and from being printed the wrong way around. The 3D printing process builds up three dimensional shapes layer by layer and these layers form a grain much like timber.

The weakest direction of any print is along this grain which is why a lot of bearing holders crack when you tighten them up. (and is why the LM8UU bearing holders I am using for the x and y carriage are are all printed vertically to avoid this). So the y-axis motor has a thickened front plate and is reinforced in two planes. The face that the motor is mounted to and the face that bolts it to the frame are in the correct orientation to avoid the laminar separation. Plus I made it look like the z-axis mounts I had made earlier to keep some design continuity going. So next up is the y-axis carriage which will ride on four of my proven LM8UU bearing holders from here: http://www.thingiverse.com/thing:30365.

Over the last couple of days my main printer has had some serious print quality issues which I eventually tracked down to a clogged hot end. Of course I first tried new gears, new hobbed bolt and changing my usual settings on Slic3r before I realised where the problem was. But it is printing better than ever now and non-stop catching up with my design changes over the same period. 

First up as I mentioned in the last post I have reverted to top mounted cross bars as the gain in height by spreading them to allow the x-carriage to pass between them has proved to be of minor gain for the added build complexity and loss of overall rigidity.

I have also added two more rails front and back to take the load of the motor and idler for the y-axis carriage that will be coming soon. The 15mm extrusions are very strong and would take the load but it is less stress on the frame corners to add the extra rail and I had spare extrusion from the 5 metres I have cut up for this printer so no additional cost and a stronger and easier build.

Along with these changes I made some minor changes to the z-axis motor mounts so all in all I have remade every part of the machine this week – no wonder my faithful V2 Prusa had a breakdown.

For the last couple of days I have been reworking the top vertices moving the top rails and rethinking the position of them to maximise the printable height. My original idea of lowering the top rails to be able to pass the x-axis carriage between them and thus gain more build height has been proven incorrect. No matter where the top rails are the x-axis rails hit the side angled extrusions before or at the same time as the top of the extruder hits the top rails so there is no advantage in relocating them. In fact it is more complex to mount them lower and produces a less-rigid structure.

So I am now designing top vertices with the top cross-members at the top My first two attempts were to include everything in the one part however it has proved weaker and more troublesome to print than separate parts for the vertex and the z-axis guides so I am now printing out discrete parts for them. My V2 Prusa has been printing non-stop for several weeks now and tonight decided to have some extruder issues, first the extruder gears got so worn that they were skipping and slipping, then the replacement small gear broke after a few minutes of printing so I am now crossing my fingers hoping the last set of gears I have  will go long enough for me to finish these parts. I guess I should print out a spare set tomorrow before I get too far down the track. My reject parts pile for this project is starting to get  to be a small pile.

Spent most of today designing, printing and redesigning this part and version 4 is currently printing so hopefully that will be the final version. The z-axis is the up-down one and controls the layers that are printed. To print in three dimensions you first use a program called a “slicer” to convert the 3D shape into a series of two-dimensional slices which when stacked on top of one another make up the 3D object.

The z-axis height is managed by using a lead-screw driven by two stepper motors – one for each side of the printer. In early printers these were placed on the top of the printer but most newer printers place them on the bottom to improve the stability of the printer frame. My motors hang from the Open Beam side rails and to save extrusion I have opted for only one side rail so I am also using a the z-motor mounts as extra feet. This should make the whole platform more stable and rigid but just in case I am also using heavier 10mm z-axis guide rails which will add to the overall frame strength as well as improving the print quality by reducing z-wobble.

For now I am using existing off-the-shelf type x-axis ends so I have set up my motors, lead screws and guide rails to match common spacings used on other printers but eventually I am planning on redesigning the x-ends as well to better distribute weight as well as make it more compact.