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  1. #11
    Thanks--all good stuff. I bought the Creality on my own nickel as a trial basically-and at $350 bucks it has already paid for itself in making optical bench parts that can cost $1000 of more, But I am sure it is over-advertised and maybe a bit obsolete. As I mentioned that parts are all "generic" so it can be maintained forever--sort of like a model A ford. (;->
    . But if we decide that 3D has use in the lab (and it does) we will probably opt for a better machine when the time comes. Your Sapphire shines here. And now that I have an inkling about what I am doing, I can pay more attention to the items that you mention.

    Software is another issue--I work 2 contracts right now and am split between Solidworks, Inventor and Fusion. I only know option 3 and have ME"s do the designs on the other 2. Software breeding is a real problem in the engineering field-I have the same problem with electrical design. Someone landed an Altium circuit on my desk the other day and at $7000/seat I told them to redraft it. Besides I haven't used it in 10 years.
    I never can be sure what software methods are really best--I think a lot of skill goes into that and I admire that vendors like Fusion even write it. I cobbled a crude python script to break out the Gcode, and comparing fusion to Cura for example reveals a lot of differences. Both make sense of course --so which is best! I certainly am not the guy to know. Simplfy3d is priced right and I would guess it is tuned pretty well since that is their main focus. All fun stuff of course-this took a whole new life since 50 years ago!

    Thanks
    Fritz

  2. #12
    Engineer-in-Training
    Join Date
    Aug 2020
    Location
    United Kingdom
    Posts
    249
    hi Fritz I thought there might be a music connection there some where - wasn.t sure about the name of the cleft you use as a logo I am a rather poor piano player as an English comedian remarked " all the right notes but not necessarily in the right order") and our music tends to have only the treble and Base cleft.It sounds like we have had very similar careers but on opposite sides of the Atlantic, but I did spend some time doing research in Boston and living in Concord MA.On the question of Aspherical mirrors a few years ago we did quite a bit of work on metalizing mirrors for automotive prototypes which had been produced by 3d printing. The main problem we encountered was build lines including slight layer shifts and surface texture. To cut a long story short we found that sanding and painting then sanding some more was very laborious. In the end with the aid of a polyester resin manufacturer we developed a special spray coating with a very small "shrink back" and ease of sanding. Though the quality of 3D printing has greatly improved we still use this process.Taking a automobile head lamp as an example the process consists of using conventional spray painting techniques to "bury" the surface texture the applying, again spray painting, an extremely thin film of an epoxy resin on the surface of the mirror.Once the epoxy is fully cured using a water based process similar to the traditional way of silvering say bathroom mirrors we deposit a reflective silver film which we then passivate with Tin to reduce tarnishing.

  3. #13
    Recommended speeds range from 1800-6000mm per min or 30-100mm per sec and the most efficient speed will depend on what type of filament you're using. If you retraction is too low, you may find filament slowly coming out of the nozzle before your printer head finished moving.

  4. #14
    Yes--I am finally getting that. I had to print some optical "easy" parts last weekend so I went all out at speeds up to about 80mm/s. Everything worked out fine so I will gradually adjust my speeds up in due time.
    I was seeing "drip" from the nozzle as it ran between areas so I see what you mean there.

    Other interesting thing is that I see a little "sag" -- holes for example out of round, flatter in the vertical direction----at higher speeds. I presume the extruder returns to the next pass while the last layer is still soft--but then I am bringing down my temperatures a bit so it may cure that.

    All told I am realizing that there is a lot of adjustments that can be made-I expect a lot of this is worked out already but for lack of decent books on the topic I have to "re-invent" the wheel so to speak.

    Thanks for your comment
    Fritz

  5. #15
    Engineer-in-Training
    Join Date
    Aug 2020
    Location
    United Kingdom
    Posts
    249
    Yes holes in flat horizontal surfaces are usually OK but holes in vertical surfaces often distort if they are more than a few mm in dia. when designing a part for printing it is a good idea to work out the orientation you will be using for printing and using that a guide for placement of holes. 3D printing doesn't do overhangs well and so sometimes it is necessary to print a piece in more than one part with different orientations -just remember at the design stage to build in registers for joins between each part.
    Almost all the polymers can be securely stuck together with one or the other specialist "superglues".

  6. #16
    Usually I am not doing parts that are overly precise. I find that a 1cm test cube gives a size of about 10.03 to 10.08 cm on a side, the "shorter" dimension being in the vertical. I do think I am seeing some type of relationship between speed, temperature and "sag" however--so I expect if I can get that under control it will make things closers. I guess the one thing that is tricky about speed--is that it can be "too slow". That apparently gets into all types of dogma regarding cooling fan speed etc-. If I was running 100 parts maybe worth the time, but for one offs I am trying to get the best compromise.Thanksfritz

  7. #17
    Yep - In find top and bottom shells to be problematic to begin with. Unlike the side shells--which are smooth within the realm of the layer height--the cross-hatched top and bottom always look rough. After 3 slicers I guess this is just a fact of life although I am not sure why--I would think a set of parallel lines of plastic spaced by the nozzle width would look nicer. I don't know of anything in the GCODE generators that controls this (or a lot of other things).Another issue I am having with speed is "sag". I find my bolt holes to be obligated --Maybe piling on on layer before the previous one has cooled---or fan speed---etcFritz

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