Monthly Archives: September 2014

DIY hobbed bolt for Gregs Wade Extruder

Several designs and modifications of Gregs Wade Extruder are floating around the internet. I went for Gregs Wade Extruder Reloaded by Jonas Kuehling. The parts printed out nicely and bla bla bla but I still needed  a hobbed bolt. They sell for ~5€ on eBay. Five Euros. That are 10 DM. Which is like 20 € which is like 40 DM !!!! Highway robbery !!!!

It’s a simple partly threaded M8x50 screw. Make one yourself is pretty easy. There are several tutorial on youtube using a drill press and a M4 tap. This one I liked best.

There is even a are even several 3d printable jigs on thingiverse which use a rotary tool with a cutting disc to cut the teeth into the screw.

Still I did something wrong because the tap suffered really hard from drilling into the bolt.

It looks like the threads got abraded a lot. Applying cutting oil is really mendatory to maintain the lifetime of your tap.

Here is my result. Okay…a little bit off but it works.


Rostock Diagonal Rod Lenght and How to remove Epoxy glue

One of the most critical parts on a Rostock style printer are the diagonal rods. All rods must have the same exact length.

I asked the experts over at the reprap forums and got some fast and informative answers. You can read the whole discussion here. The short answer is given by Wildcard:

It is extremely critical. If they are not exact, the machine will suffer from mechanical effects. My first build had this problem and if you moved the effector/platform near the tower of the arms that were shorter, you would see the effector start to tilt up. If you moved it away, it would tilt downwards. So it effects how flat the printer will print and with changing angles like that, the prints will suffer from incorrect measurements and other print issues that will be unable to fix in the firmware unless corrected.

Too bad I expoy-glued the rods to the Traxxas u-joints before I sought advice on forum. Now epoxy can withstand forces of up to 1900Nm/cm² (that is a lot I guess) but the glue becomes brittle if you heat it up to 120-150 °C. So I removed the rods from the printer and put them in the oven at 150°C for 20-30 minutes. It turned out that this actually works really well and with a plier I could easily remove the u-joints.

Well, on my first try on connecting the rods with the u-joints I already did build a jig to aid the process of getting the u-joints in parallel to each other. This really work out well but as you can see from the picture it has one major drawback. You cannot reliably set the distance of the two u-joints. Every time you glue a pair together it has a different length.

Rostock Mini diagonal rods glueing rig that failed its purpose

Rostock Mini diagonal rods glueing rig that failed its purpose

Also the epoxy glue I used is a fast hardening  2 component  glue. The processing time is only 5 minutes which means you must be very quick and certain on trimming the length of the rods.

So I bought an epoxy glue with a processing time of 90 minutes. Plenty of time to mess around with. I made a new jig using 2 M3 bolts, 2 nuts and 2 washers. The pictures below should explain it.

The washers on top have a big enough surface to help to get the two u-joints in parallel.

That’s it. Perfectly aligned and all six rods with the same length.

Rostock Mini frame parts

The Rostock Mini frames have arrived from Formulor. They were packaged really nice and clean and came undamaged.

I immediately started to assembly them to my Rostock as one little detail struck me like thunder. There were some holes missing. Rushing to the Formulor site, which saves your uploaded designs, I checked what I did upload there. And it seemed that in the process of  arranging the frames in Inkscape I missed to copy&paste some really really critical holes and vents into the bottom frame.

Rostock Mini motor end

Rostock Mini motor end

Fortunately acrylic glass is easy to process so I printed the correct bottom part on paper and used it as a template to drill the missing holes into the plate.

So after all this mess this it what my Rostock Mini looks like now. Look at those beauties !

Rostock Mini assembled

Rostock Mini assembled