Saturday, 13 November 2010

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.



  2. You can use bolt adhesive to secure the nuts from loosening.

  3. Yes I can lock the bolt in the nut with glue, but I am not sure whether I might need to tighten it further when the plastic creeps.

  4. There's a discussion going on over at the MakerBot Operators group about that extra outline around the print in the last photo and how you did that.

    Could you shed some light on how you did that?

    Thank you,

  5. Since my machine is driven from Python script, I simply write a few lines of code to add a square to the bottom layer which is slightly bigger than the bounding square.

  6. just epoxy the pulley onto the motor shaft. that's how our mendel is working so well. it will never come loose.

  7. No but the extruder gear wears out eventually, so needs to be replaceable.

  8. Hi Nophead.

    What skeinforge settings do you use on your mendel? Do you have them availible for others to use? I'm fedup with the reprap host software.


  9. I only use Skeinforge to slice, I don't use it to control feed rates, flow rates or temperatures, so the only settings I use are those in Carve, Fill and Multiply where I set the layer height I want, number of shells, infill solidity, etc. I.e. nothing machine specific so I don't need to re-slice when I change my machine, or use different machines or plastic.

  10. What temperatures are you using for your crosshatch support structures? They look like they come away from your parts really cleanly! (Or at least, alot cleaner than mine!)

  11. I haven't done anything to detect support structures yet so they are printed at the same temperature as the rest and are not easy to remove. I did a lot of whittling with a penknife.

    I plan to detect support material in my software by the fact they are non-closed paths, which makes them look like infill, but they are not inside an outline. I will then reduce the flow rate a little so they have a smaller contact area. I don't see much point in changing the temperature because they object has to be extruded at the right temperature to bond to itself, so it will bond to the support just as well, regardless of what temperature the support was extruded at. That will only affect how well it bonds to itself.

  12. That makes a lot more sense, I had been under the impression that the support material was just that, and had no need to be structurally sound since all that would happen after finishing the part is it gets tossed in the recycle bin. The part wouldnt necciscarialy have to bond to the support structure provided you were using PLA or some other plastic that didn't suffer from warping. Your method makes more sense than mine!