Well, even though I have been at work the last couple of days, I have still managed to to some design work. Before work on Wednesday I did another drawing of the extruder from another angle to help show some of the features a tad better.
This shows the drive gear being directly driven by the motor. This has since changed a number of times. After the direct drive idea, I though a worm drive would be a better idea. This worked until I started designing how to attach the extruder to the frame. The worm drive gear was then thought could be used in combination with helical or bevel gears but I realised these would be too hard to machine at home on our mill and lathe as we don't have a geared dividing head. At this point I better add why I want to use a worm drive. This because I firstly want there to be plenty or torque for pushing the filament and second to that but not as important in this case, accuracy of how much is being pushed down the nozzle. I have finally gone with simply using two gears with a high enough gear and torque ratio. I haven't yet drawn an illustration of this situation. I still reckon I will use a worm drive on the Z slide though as the torque would be very useful for pushing the slides up when gravity is trying to push everything down.
I next sat down, and with a copy of the previous design (as shown in the last post), and drew over it.
With this, I tried to decide on materials for each section of the frame. In the last post I had been thinking of using angular or channel extrusions for the X slide. I realised that this would not work due to the unsymmetrical mass and thus twist of the materials would occur and cause inaccuracies and possibly breakages after a time. That is what all the pictures of beam types are in the top corner. I've written around them why I haven't chosen them. The Y slide I'm going to go with angle regardless as its otherwise too hard to attach the X slide. I'll instead just make this sturdy enough that twist won't be great enough to worry about. This drawing also shows that the bar on top, needs only be a tie bar for strength purposes. It may still not just be used as a tie bar due to aesthetics. The main frame, as in the materials for the Z slide and base will all be square tubing. With the base, I came across a page on the reprap site about calibration and it recommended if there was a heated bed, that it be 110˚C for PLA. With this in mind, I'm going to install insulators between the bed and the frame itself. I don't think I've said anywhere else so may as well state the sort of obvious. The frame at the bottom will also have a bar attaching the two legs of the frame together. This is obviously needed for strength and to tie the frame together.
So the type of material I decided on for the X slide was an I beam. This was due to twist and sturdiness.
I think I will join the X and Y slides similar to the above picture, but I haven't done any analysis on this joint so has potential to change. The green part (the colours are just to show different parts) bends down the back of the red one so it can slip forwards too much. I may be able to put a grove in the back of the red part so the green one latches in and is unable to fall out.
The next day at work, I decided I would have a go trying to think of how to fit an extruder onto this I beam. I came up with a nice carriage idea and a new extruder that had an angled/L shaped nozzle.
I soon realised that an angled nozzle was a bad idea as it had the forces in the wrong direction to get the filament down the other end and would be very hard to clean which would be needed if a change of filament colour was wanted. So I scraped this idea and went back to the original extruder. I'll balance out the weight by moving the motor to the other side of the carriage from the nozzle and the rest of the drive. The carriage shown also has the slide drive above the carriage. I think I will move this to one of the sides so that it takes away height, plus I can have this motor on the top and the motor for the Y slide underneath. This would mean that I can use that space used by the motor on the Y slide more effectively. To make more sense of the image above I also made another image showing one side of the carriage wheel arrangement.
This arrangement works by having wheels in the Z direction pushing against each other and so making the carriage centred in the Z direction while taking out bumps. The wheel in the Y direction is used to centre the carriage in the Y direction and is used by pushing against the wheel on the other side of the I beam. The arrangement of three wheels for the Z direction on each side is so the carriage doesn't rotate.
Hopefully in the next few days, I'll do a proper mechanical sketch which will combine all of these ideas into one image. I was going to do it today but I have had to do some other wood work so to start tidying up dad's shed for his use.
Other ideas I have had for the frame is too have gyroscopes on the head/carriage and one on the bed so corrections can be made automatically for any twist. This idea was always the case, I just needed to write it down. I will put micro switches on the slides so the electronics can work out its maximum travel distances. I'm also going to have to weigh the stepper motor sometime so once I've done the basic design, I can check material strengths and balance out the weight on parts such as the extruder carriage.
One last thing before I finish this post. A while ago I posted an invention that you could use to melt down old plastic bottles and convert to filament. During the week I was thinking about this and I think I will make one of these almost as soon as I've made the printer. This is because its far cheaper to melt down plastic you already have and recycle rather than always buy it. I also had a quick look on the net and found you can buy plastic pigment for colouring so this could be added to get colours. With this machine, if I was to make one, I would try and make it mostly automatic and so it would melt down the plastic given, add the pigment and mix then extruder out through a hot nozzle into a cold nozzle and then automatically roll it up. The cold nozzle is used so the plastic doesn't melt together when rolled up.
Well that is all for this post, hopefully tomorrow I'll have a new image of all the above components together but it may be Tuesday or Wednesday before I get it done.
