So finally I’ve found great and easy way how to mount my PCB heatbed.

Problems is that PCBs aren’t flat. If you’ve got your PCB and it’s not flat, its not a big deal.
You always have to help it to be flat. Ideal stuff is glass sheet, since it’s cheap and pretty flat.

What we also want is quick swap of the print surface. Before I tried mounting whole heatbed on magnets, unfortunately, it was more PITA then good solution. The glass in this solution wins again.

Many people used the four holes in the corners to mount the bed on standoffs, which again wasn’t the most brilliant idea under the sun, since it wasn’t enough to keep the bed flat enough.

What you need:
PCB Heatbed
20x20cm glass sheets, 3mm or 2mm
Two part epoxy glue
4 bulldog clips

How to do it:
1) Place the heatbed on the wooden top plate on your Y axis and mark the corner holes and its outline on wood, remove heatbed and drill the holes with 3mm drill.
2) Place the bulldog clips on the marked contour of the heatbed and mark how deep it goes into wood. Then cut this pieces of wood away, it will allow you to freely hold the glass on bed with these bulldog clips.
3) Mount the pcb. Add three washers between the wood and PCB. It will allow the pcb to be more flexible = easier to make it flat with glass and also, air is better heat insulator then wood.

4) Use bulldog clips to hold the glass on the PCB.

5) Mount thermistor with some kapton tape on the glass. I place some wool and alu foil on that and then I tape it down again. There is also possibility to glue the thermistor on the bottom of PCB Heatbed with the epoxy, which will be more handy if the glass is changed frequently.
6) Put some kapton on the top of the glass or just clean it to print pla.

Electrical wiring:
I suggest to use my PCB heatbed with RAMPS 1.3 which has great support for heatbeds.Use some thick wires, the PCB will eat almost 11Amps.

There are two 0805 surface mounts LEDs. Idea is, to have each of the in different direction, so the PCB will shine if you connect it both ways.
You also need one 0805 SMD resistor, 1kohm should be fine for every led to dimly signal you the activity of heatbed.

So, if you are wondering whats new in Prusa printer development, I’ll answer some of your questions today. And maybe even bust some myths First I want to show you results!

(Darker blue is print from Dimension uPrint, Lighter blue is print from Prusa with felt bushings)

Most of the development is done lately in felt branchhttps://github.com/prusajr/PrusaMendel/tree/felt on my githubhttps://github.com/prusajr, which started as idea to remove need of the PLA bushings and replace them with easier to get stuff. After all it ended up much better then I thought.

New bushing look.

It’s printable directly on the carriage! No glueing needed, you just need to print all x-ends and x-carriage in same direction.

Another amazing thing is, that it can be used with more materials then just felt! Which I found pretty amazing!

In the same printed object you can use:
- felt (100bushings for $5 if you use best felt)
- brass tube (80bushings for $9)
- pla bushings (one prints in about 30seconds )
- igus bushings (as Shapercube use, its pretty expensive because of matching rods)
- sku bushings (steel with teflon inside. expensive because of rods $50full set incl rods)

All of this stuff remains snap in! So you can remove your carriage without disassembling half of printer.

During the big demand I will incorporate the possibility to use linear bearings too, but it will be few days after this release. And it’s not going to be the main stuff. Simply because it’s not better and sourcing is harder and pricier.
ETA to merging it to master branch is about two weeks. Catching last bugs out. And also, from this point, every commit will have its own ThingDOC documentation, which is under huge development during moving documentation to the files!

ThingDOC is now Ready for its prime time!

n this article I want to help you with SF40 calibration.

Main difference over older version is volumetric flowrate.

It basically means that SF counts how much of the plastic its should extrude for given layer height and width of trace (height*width*lenght = volume).

Most confusing on all this is to realize SF uses the length of filament which goes in instead of extruded thread which goes out. For that you need to set your e_steps_per_mm in your Firmware to count with filament instead of extruded thread. And I’ll show you how.

Tools you need:

1. Some permanent marker which can make visible marks on your filament
2. Calipers
3. Brain
4. My RepRap calculator http://calculator.josefprusa.cz/#ExtrusionSF40

So how to do it?!

1. Set your e_steps_per_mm to some nice value. Lets say 50. You can do that either by re-flashing FW or simply by sending “M92 E50″ G-code (Works only on tonokip based FWs = Tonokip, Klimentkip, Sprinter, …) (See note 1)
2. Heat up your nozzle to temp you normally use for the print. (Or you need to remove nozzle. But we are lazy, right? Or atleast I am )
3. Find the speed at which it can safely extruder without skipping steps. E.g. hit the extrude button in Repsnapper, if the filament extrudes, you are fine, if not, reduce speed.
4. Mark some length on the filament with the permanent marker and calipers. I use 3cm, but longer it’ll be more it will reduce our measurements error. Then mark another segment right after the 3cm one. Let it be 1cm, this will later be used for validation of our new settings.
5. Extrude just enough material to get the first mark on filament aligned with intake of extruder.
6. What we will do now is extruding of the marked 3cm. So hit extrude button as many times as it needs and count how many times you pressed the button. DON’T CHANGE THE EXTRUDED DISTANCE DURING THIS. (You actually can, see note 2)
7. Now we have all the info we needed to count our new e_teps_per_mm Which you can count ( (extrude button clicked times)*(extruded lenght per click in host)*(e_steps_per_mm we set [50]) ) / (marked length on filament in mm we have [30]) Or you can use interactive calculator athttp://calculator.josefprusa.cz/#ExtrusionSF40 Explanation: ( (extrude button clicked times)*(extruded lenght per click in host)*(e_steps_per_mm we set [50]) ) Counts how many steps we used to extrude our marked distance on filament. When you divide it by the distance in mm, you’ll get number of needed steps per mm.
8. We should test the new e_steps_per_mm. So send “M92 E???” to your printer, where ??? is the number you’ve got from calculator.
9. Now we want to move the filament for exactly 1cm (we marked it before) so do it in your host SW GUI. For example in Repsnapper set distance to 10mm, and speed somewhere around 60. If it’s exactly 1cm, you’ve won! “G1 E10 F60″
10. This still doesn’t have to be exactly right. You’ll need to tweak it sometimes a bit. If the lines aren’t fused in solid layers, just add 5% to the e_steps_per_mm It’s not rocket science  

    Setting up Skeinforge:

    1. In dimension tab, set precise filament diameter. Filament packing density leave at 1.
    2. In speed tab. Set same Flow rate as feedrate.

     

    There are few alternative ways how to do it. Best alternative is calibration script written by Nathan shipped with Kliment’s amazing Pronsole. Or araspitfire’s posthere.

    Note 1:

    You don’t have to change the e_steps_per_mm during the experiment at all, you just need to be sure what number you use now, and at the end use your number instead of 50.

    Note2: You can use multiple distances during the 3cm lenght. What you really need to know after this is the overall length you extruded. But interactive calculator wont allow you to do this, you’ll need to use your brain and  this formula ( (extruded distance in mm)*(e_steps_per_mm we set [50]) ) / (marked length on filament in mm we have [30])