Well today I actually got some CAD done! I modelled the nozzle for the extruder and the insulator, which I posted about yesterday. The designs I had yesterday weren't complete as they had no dimensions and were really just pretty pictures (not even very pretty some of them). I also changed a few things about them along the way. Just of note, I'm going to post my hand drawn designs as well as the CAD ones in this post which I won't do normally as there isn't much point in uploading both except for looking at my effort at drawing and seeing how it fairs to what I actually design. So here is the page of designs.
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As you can see from this, I have designed and given numerical values to dimensions except where I'm unsure or I'm going with a standard. Next thing to notice is that I have started to assign part numbers. I wasn't going to do this but I realised when I was drawing these that if I do a parts list on Inventor that it always shows a parts list plus when I save the files it makes it neater to have standardised file names rather than the hodgepodge that I normally do have. I thought for ideas I better have a read about part numbering and found that some company called Arena Solutions had some nice pages about part numbering
here and
here. I then went with a 11 character (excluding dashes) with an extra 2 digits if needed. There were as follows:
3 characters for the significant (major) location or use of the part
3 characters for the minor location or use of part with the significant one (major)
4 numbers for the revision
and the optional 2 numbers that are used for types of a part such as with the nozzle, there will be at least two versions of the same nozzle, one with a smaller extrusion hole (ie the bit where the plastic comes out) and one with a larger one hole.
While I was looking round for dimensions for the nozzle I also came across a page on the RepRap site that had some
variations of the standard nozzles. One of these used PEEK plastic for something and was attached to the nozzle so I checked it out and its melting temperature is 343 degrees according to wikipedia so is another contender along with the ones mentioned in the last post which were polyurethane (no melting point), Kevlar (500˚), Twaron (500˚), Nomex (390˚) and PTFE (330˚).
Another page I found when wondering about the size of filament to use was a forum
page talking about the best sizes. This explained that larger nozzles can actually be better for larger prints as sometimes these don't need too much detail and so a larger nozzle will be faster. The page also recommended starting with a 1.75mm filament that although slightly more expensive, would melt quicker and so easier to use and not as much pressure would be required.
The red note (which was partially cut off by the scanner) in the bottom of the page is about the potential of plastic to melt into the crevasse between the end of the nozzle bolt and the nozzle tip. I had thought this would be an issue and have to create a revision that had all the tubes and diameter changes all part of the bolt and just use the tip as metal mass and for using as the storage for the heating element and sensor (with some heat sink fluid between the two parts). After some thought I decided this wouldn't matter as it would fill up and stay there. It could also be fixed using a high temperature sealant such as silicone of which there seemed to be plenty selling online. We shall see how it turns out once we make it. The only reason to be worried is for cleaning and changing the colour of the filament used.
So after all of that, here is my CAD version of the nozzle.
I had to upload it as a PNG rather than PDF so its lost some of the detail and the page size which is supposed to be A3. Here is a link to the
PDF version on my Google drive. The only real difference between this and the design I had yesterday are that the locations for the heating element and temperature sensor are now holes that go straight through the nozzle rather than being at a weird angle. There is also one dimension that I've added a numerical value to but will have to be adjusted. This is the length of the thread on the bolt as it depends on the thickness of the casing/wall that holds the nozzle.
So that covers what I've done with the nozzle today. As I said I won't write up everything from the preliminary designs in the future I don't think but we'll see how I feel on the day.
The other thing I did today very briefly was to think about the materials for the frame. I'm still working off the design I posted a while ago.
Apart from I'm going with what I said yesterday which was to use U shaped channel for the X slide. I think I will also use it for the Y slide now too. This is because it is much stronger laterally that just a bar which is what I had drawn in my original design and even today was thinking about. I think the bulk of the main frame will be out of
square hollow tube with the sides being either 45 or 50mm. I was also thinking of using a special type of aluminium extrusion for the Y slide and top. It looks similar to the next image which I had seen when I did a tour round a high speed boat builder site. I think though it was specially made and most likely wouldn't be made small enough.
This was the stage were I thought flat bars would be a good idea but as I said above I've reconsidered and think channel will be a better idea.
Well that is all for this post. I'm working the next few days so won't be able to write any more posts but I'm sure I'll be thinking of ideas as I'm working.
