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  1. #1
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    Stratasys Dimension SST 768 Head Re-design

    Hi, our school has a Dimension SST 768 printer that has been collecting dust since 2010 because nobody had the time to fix a problem it was having with extrusion.

    Turns out the head wasn't extruding the filaments properly (maybe because they are all dated for 2007, haha), so they ended up having a secondary company re-design the liquifier pipe because there was a hole in it or something. Anyway, the support filament wouldn't come out, and it was just a mess, so it ended up sitting around for 4 years.

    I got permission to try and mess with it and fix it, and have tried a lot of things. I replaced the liquifier pipes, brazed them onto the nozzle head, put everything back with the high-heat adhesive, but just can't get it to work. The filament will extrude for a while, but when I pause and try to start again, it gets soft at the pipe entrance and breaks off or the rollers spin without pushing the filament in anymore.

    I tried about 5 or 6 times to re-align the pipes and do everything correctly, but nothing works out. So, I decided to redesign the head and machine it out at the school.

    There are some concepts I have so far, designed in Autodesk Inventor. I separated the nozzles alot, but am hoping that with the XY calibration settings, I should be able to use these dimensions...here's to hoping.

    HeatAssemblyRender005.jpg
    HeatAssemblyRender002.jpg
    HeatAssemblyRender003.jpg

    Anyway, I am hoping that by separating the model and Support filaments like this, they will be able to maintain the different temperatures they need easier. I also wanted to use the Makerbot Nozzles, because they are so cheap, and make the pipe with one bend instead of the slanted version stratasys had, which I think causes too much stress while trying to push the filament through.

    What I am trying to figure out now, is a way to hold the pipe around the bend area, without using adhesives, or having the heated sections heat it up. (want to keep the pipe as cool as possible as long as possible.)

    Will keep this forum updated as I go along.
    Attached Images Attached Images

  2. #2
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    The Stratasys is designed to melt the whole of the pipe full of material, not just the end immediately before extrusion. If the original head had the problems you describe then the problem was an incorrectly inserted thermocouple and very damp support filament or a faulty fan. Do not assume that because the fan is rotating it is moving the right amount of air. That head fan is the biggest failure point on these printers.

    While I am sure you can do this you will also have to hack the software to correct for the new head offsets and that is not easy to do.

    The isolation between the two extruders is carefully designed such that if you are printing with the model head and the support head heater is off then the support material sits at just under the glass transition temperature so that it can be warmed in minimum time to extrude temperature.

    You will not improve on the original design, if you are going to make a new head then copy the original Stratasys one.

  3. #3
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    So, the model-side thermocouple can be on while the support-side is off, to keep the support-side cool enough that there is no leakage, but warm enough for a speedy warm-up when support material is needed? I guess that makes sense in a design where energy consumption is important. But doesn't that mean when the support is running, the model material will be above its glass-transition phase, and might leak a little while support is printing? I have never had the opportunity of seeing the machine running by itself, so I don't really know...

    Well, here is an earlier design I was working on, but I switched to the one in the above post when I thought I could just modify the XY-axis through the adjustment settings, because it would mean I could use the makerbot nozzles, which are threaded and already pretty accurate. They are just a little too big for the original design spacing (about 6.1 or 6.2mm) I didn't want to have to use the lathe for this...

    But now that you mention it...of course the model material and support material aren't being printed at the same time, so there is no reason to separate them with a gap because the temperature for each nozzle will always be correct...doh! Thanks, I didn't see that, haha.

    hotend1.jpg

    Hmmm...back to the thinking board. I guess I could look at the fan again as well, and see what issues we are getting there.

  4. #4
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    Does anyone know what the nozzle diameter is for model and support? 0.25mm or something? Can't find that spec anywhere, but it is super important.

  5. #5
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    0.3 mm

    minchars

  6. #6
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    Quote Originally Posted by Mjolinor View Post
    0.3 mm

    minchars
    Thanks, that was pretty helpful. I have another question though, the head is made up of several parts:

    1) Motors
    2) Backplate
    3) Heat Block + nozzle

    I was wondering if you knew what the screw sizes were for fastening the Heat Block to the Backplate? There are four of them, but they are the same screw size as those that fasten the motors to the backplate.

    Our school only has metric measuring equipment, and all I know is they have an Outer Diameter of 3.4mm, and a round head with a hex cut for tightening. The hex cut fits a 7/64 allen wrench.

    I don't have the tools to measure the pitch, and I can't run to a Home Depot to test the screws out, so I'm screwed. (^_^) Any help would be great. Thanks!

  7. #7
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    They are not metric, that is for sure but other than that I can't help. I just routed about in my spare screw box till something fitted if the originals were knackered.

  8. #8
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    Just wanted to put up an update.

    I've got a design I like, and the concept is pretty much summarized as "press-fit" for securing pieces as opposed to the high-heat adhesive option.

    Still only cutting out and testing the designs from wood, but it looks like when I get a few more of the design flaws out I should be able to move on to Aluminum or a brass material within the next two weeks, and actually try a working model. After that is checking extrusion rates and dimensions.

    A step at a time.

    20150325_151828.jpg

    20150325_184245.jpg

    20150325_184618.jpg

  9. #9
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    Hi, I was wondering if anyone knows whether the maintenance software for the Stratasys SST 768 (maraca?) can edit the offset between nozzle tips? For example, in the current design, the offset between tips seems to be around 6.1mm (x-axis direction). I was wondering if it were possible to modify this so the system prints assuming the space between support and model tips is like 28.5mm?

    Or does the tip setting only affect the offset in a "circle" so that the offset between tips is always 6.1mm, but the tips could be "twisted" so that they don't line up horizontally? I've attached a picture to help explain what I mean...

    Any help would be great!

    tipoffset.jpg

  10. #10
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    Think I found the answer. There seems to be a setting for the Z tip-to-tip offset, and this is the number you change to set the distance in-between tips. Finally I can get away from that 6.1mm gap! That has been making these designs really rough.

    I cut out a piece in Aluminum, will do some re-adjustments and go for the final copy. Things are starting to turn out a little better, just a little more to go.

    After that, it will be running through temperatures tests and trying to get the P400 ABS up and running. I got a quote on a head replacement being around 4,000 USD. Seriously?

    Also for reference, this is from the Stratasys

    WO 2007130220 A2
    Furthermore, the calibration routine may include calibrating an X-axis and Y-axis tip-to-origϊn offset to ensure that the system knows the spatial relationship between the extrusion tip and an origin on the substrate. If multiple tips exist, the calibration routine also includes a Z-axis tip-to-tip offset, an X-axis tip-to-tip offset, and a Y-axis tip-to-tip offset. Without calibration, the position of the extrusion tips relative to the base and relative to each other may be incorrect, which may result in the inability of the modeling system to build accurate, error-free models.
    Last edited by breadvsrice; 05-17-2015 at 07:03 AM.

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