101 Mendels

From March up until a week ago I have run my Mendel as close to 24/7 as I can and it has printed 101 Mendels, with a bit of help from HydraRaptor. During all that time I have been able to sell them as fast as I could print them but there has been a dip in demand running up to Christmas, so I stopped printing on Monday, having built up a small stock.

I have shipped parts to England, Scotland, Isle of Man, Ireland, Sweden, Denmark, Belgium, Netherlands, Germany, Austria, Poland, France, Spain, Portugal, Italy, Tenerife, USA, Canada, Australia and Singapore.



It seems weird now to have a quiet house and not have to stay up until midnight every night to start the overnight build. It does mean that I have time to blog again though, and print things that are not Mendel parts.

I have been printing parts of a Milestag laser tag gun for a friend of mine. I recommended CoCreate to him and he has taken it and run with it. His first design is way more sophisticated that anything I have managed so far. It is a large device broken up into parts that just fit on my 200mm bed. Here is one of them: -



You can see the rest in Tony's blog http://funwithelectrons.blogspot.com/2010/12/milestag.html.

I think a machine printing 101 copies of itself must be a bit of a milestone in the RepRap project. That is about 100kg of plastic and not far off 4800 hours of printing in about 6000 available. It is testimony to the reliability of the mechanical design and if anything, the quality of the parts is getting better as I tweak the settings.

Crème brûlée

This is what happened when the thermocouple fell off my heated bed: -

It happened while both myself and my wife were at work so the machine finished the build. When I came home the room stank of fumes.

The bed temperature will have been limited to about 170°C by the thermal cut out I have in series with the heater for safety. Since it was making a bed of six and it went wrong about 1/3 of the way through the build, they will have been cooking for about 4 hours.

Unsurprisingly the bottom of the object shrank and went brown. What was surprising was that the bottom layer became transparent and glass like. So glass like that I cut my finger on it. The meniscus edge was razor sharp. It seems to have softened over time though, this happened a few weeks ago.

Perhaps it might be a useful process if you want a transparent window on the base of an object. You could lay down a single layer and then cook it for a few hours at 170°C and then deposit the rest of the object on top of it.

Monthly maintenance

So, after just over a month more of continuous use of my Mendel, I noticed the filament not spanning gaps well. It had also gone curly again. I measured it at about 0.6mm extruded into fresh air, so decided it was time to bore out the nozzle again. I do this with a 0.5mm bit held between my fingers with the nozzle hot. This restored the diameter to over 0.7mm again, so it is able to extrude 0.6mm filament with enough stretch to span gaps. Looks like this needs to be once a month maintenance.

Another failure I had was two of the bed support lugs sheared off the 360 y-bearings: -

 

These are under more load on my machine because I have a heavy metal bed. They also get some strain when parts are being removed from it. Rather than strip the machine down and replace the y-bearings, I made a new part that sits between the two y-bearings and supports the bed on three rather than four points.

 

If the bed is slightly flexible, for example when made from Dibond, then all four corners can be levelled independently. When it is stiffer, for example 6mm aluminium, then you can only adjust three points independently. In fact, one of those can be fixed and then there are only two points that need adjusting.

I made this using the support material option of Skienforge for the first time. To use it I have to enable the raft module but then disable the raft by setting the base layers and interface layers to zero. Without the cross hatch option the support material is easier to remove, but it tends to come away from the bed. For raft-less support the first layer of the support could do with being solid.

Other persistent problems I have are connectors losing contact, so reseating them once a month is good idea. The constant vibration and heat cycling seems to make connectors unreliable. Screw terminals with ferrules over the wire end seems to be the way to go.

The M8 nuts on the frame shake loose, I wish I had used lock washers! Also the grub screw in the pulleys eventually work loose after months and the one in the extruder drive gear needs tightening after a few weeks. It seems to be impossible to keep anything tight in plastic, especially when it is oscillating backwards and forwards. The plastic gives a little and that movement causes screws to work loose. Perhaps some thread-lock in the set screws would do the trick, but I am not certain that the screw might need to be tightened to take up slack caused by the plastic creeping.

Of course running a machine 24/7 is not what most users will do, so it will take many months of normal use before these types of fault manifest.