The Velleman K8200 - the Big Build!

Chris Calver

The Velleman K8200 is the most affordable 3D printer on the market. Part of the deal, however, is that you must assemble it first. But how long does it take? What skills do you need? More importantly, how many cups of tea do you need? Rapid's Education manager Chris Calver (right) built it and explains what buyers should expect before they can start printing.

When I received my K8200 3D printer, the first thing that occurred to me was how small the box was. Then you open the box and realise just how many parts there are!

Thankfully, Velleman have packaged all the parts in smaller bags containing just a handful of pieces. Each of these bags is referred to in the instructions as you progress through the build which makes it nice and easy to find the right parts and keep track of what you have used.

Let the build begin!

I used the online instructions for building my kit but you can download and print a PDF if you find it easier. The instructions have plenty of pictures in and the text is easy to follow.

Velleman ease you into the build gently by getting you to build the support for the filament spool first. Once this is done it is on to the serious business of the X-axis carriage which involves fixing the linear bearings into their clamps. These are retained with fairly large circlips which need a pair of circlip pliers to apply them without launching them across the room. If you don’t have any, beg, borrow or buy a cheap pair which are available for about £4. Y axis is then fitted on top of the X-axis, again using circlips to fix the linear bearings.

The next step involves adding the first stepper motor and drive belt to move the Y axis. The belt is cut from a continuous length so be sure to count the correct number of teeth. The belt is then fixed to the bottom of the Y-axis by means of a plastic clamp. Care needs to be taken when tightening this to avoid cracking the plastic. Luckily for me, Velleman included a couple of spares in the kit!

The first stage of the build is concluded by adding a limit switch which the printer will later use when setting it’s datum points before each print. Once this is fitted, you’ll be left with a really nice looking piece of hardware for which you are likely to reward yourself with a nice cup of tea.

The completed X-axis carriage

The next phase is to build the printer’s base. This is constructed from 4 lengths of aluminium extrusion which is fixed together using some ingenious 90 degree clamps with captive fixings. You simply slide them into the extrusion and tighten the allen bolts. There are a number of square nuts that also need to be inserted during assembly of the base which will be used to secure other pieces to the frame later. Finally, the X-Y assembly is added and your printer is starting to take shape.

The printer's base

Now it’s time for the Z-axis. Again, this is built using aluminium extrusions and the clever 90 degree clamps. The Z-carriage is then added which uses more linear bearings and circlips. The horizontal bar which will eventually carry the extruder is then fitted. The Z-axis is controlled by a threaded rod which runs up the left hand side of the printer. It is attached to a stepper motor at the base and is retained in a bearing at the top. Personally I would like to have seen a sealed bearing used here, because in the workshop environment I can see this open bearing accumulating dirt and becoming an area for regular cleaning/maintenance.

At this point, you will have something that pretty much resembles a 3D printer. Make yourself another cup of tea though, you are only a quarter of the way through the build!

The drive train and extruder body

The next stage is the last part of the drive train and involves adding the stepper motor and drive belt for the X-axis. Again I have a little grumble in that open bearings are used in the belt tensioner which will need cleaning occasionally. The same high quality stepper motor is used on this axis as on the pulley and belts and are nice heavy duty items. The belt itself clamps to the X-carriage using aluminium clamps which feels much better than the plastic item on the Y-axis.

Only a couple of mechanical bits to go now - the main one being the extruder body which will feed the plastic into the ‘hotend’, the part which actually melts and dispenses the plastic. This part of the build only concerns itself with the feed mechanism with the hotend being one of the last things to go on.

The feed mechanism is operated by a stepper motor which drives a special “hob bolt” via two plastic gears. This hob bolt has splines cut in to the thread and it is these splines that will ultimately pull the element into the hotend. The plastic gears seem well moulded and are really tough.  The rest of the body of the extruder is more high quality CNC aluminium which sandwiches a plastic housing. Part of this plastic housing forms a spring loaded tensioner which keeps the filament in place. Again, my only criticism is the open bearing…

The extruder housing

The extruder housing is then mounted to the rest of the frame via some captive nuts in the aluminium extrusion of the Z-Axis. 

Assembling the heated bed 

 

The K8200 has a heated bed which prevents the plastic warping as it cools and is said to allow higher quality prints. This heated bed is like a PCB with an element running throughout it. The bed is mounted to an aluminium carrier with an insulating layer in between to prevent the heat sinking through the frame of the printer. There is a slightly fiddly moment here when a surface mount NTC thermistor needs to be soldered to the bottom of the bed. This thermistor will allow the control board to keep the bed at the right temperature so it is vital that it is correctly installed. A pair of tweezers makes this task a bit easier!

The NTC Thermistor

The rest of the bed assembly consists of adding some thumb screws which will allow the extruder to be calibrated later in the assembly.

There are three microswitches, one on each axis which allow the printer to detect when it has reached the end of its travel. The controller uses these to set datum points before each print so that it knows the exact position of the extruder in relation to the bed. These are vital to the calibration of the printer and ultimately to the accuracy of the printer. As a result, I was a little disappointed to see that the switch on the Z-axis is only retained by one bolt, meaning that despite the toothed washer behind it, it is too easy for this switch to be knocked out of alignment. My preference would have been for this switch to be mounted through two holes and I will be making my own bracket to make this possible.

Attaching the switch to the Z-axis

The controller board for the printer is the heart of the machine and will control all the stepper motors, limit switches and heaters. It also handles all communications to your PC via a USB interface. The PCB is supplied ready assembled so it is just a case of bolting it to the mounts on the side of the printer. 

It looks a little exposed, but one of the first jobs for your printer will be to print a case to protect the board. What a neat little idea. Velleman supply you with a CAD model for the case so this can be used to calibrate and test the printer!

The controller board assembled to the frame

The wiring loom 

 

The next task is a big one and is the one that probably requires the most care as well as being the most time consuming – assembling the wiring loom. You are presented with a length of ribbon cable and a whole bunch of ‘Molex’ style connectors. Thankfully, these are at least prewired and stripped but there is still a lot of work to do here.

As with the whole of the build, the instructions are very clear and there are loads of pictures to help you on your way. Each core in the ribbon cable needs to be carefully stripped and tinned, then each needs to be carefully soldered and protected with heatshrink tubing. Remember to put your heatshrink on before soldering the wires as these can’t be added afterwards! 

If you have soldering experience, you will find this job quite easy and you may prefer to assemble the loom off the printer rather than on it as the instructions suggest. For these with less soldering experience, it is worth following the instructions to the letter and taking your time. Errors made here would take a long time to fault find later so check, check and check again.

The final part of the assembly is the hotend which consists of a copper nozzle which runs through a heater block. Another fiddly part coming up - there is a tiny glass bead thermistor which needs to be mounted in a small hole in the heater block. Again, it is crucial to the operation of the printer as this will be responsible for the regulation of the temperature of the heater so it is worth taking your time to make sure you get this bit right. 

The heater block with thermistor fitted

The assembled hotend

Once the hotend is bolted on to the extruder, the heater element and thermistor of the hotend need to be soldered in to the wiring loom. You can now stand back and admire your work; the build is complete!

Mission accomplished

All in all, this took me the best part of seven hours and copious cups of tea. However, if you have some basic soldering and circuit assembly skills it's still fairly straightforward and quite satisfying to build. I hope to blog again soon about the calibration, set-up and software, but this will do for now. If you've got this far with the build you've more than earned yourself one of these:

Remember, the K8200 is available from Rapid for under £700.