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  1. #1

    Questions to consider before buying a 3D printer

    I am helping advise a company in South India on the purchase of a 3D printer. I was involved in this years ago, trying to find a suitable 3D printer for prosthetic eyes. That search went well, until we tried to find a 3D Scanner - back then, we couldn't find what we needed.


    What I'm looking for in this forum, is what kind of list of requirements do we need, in order to select an appropriate printer. I think I know some of them, but maybe I'm missing others that are equally important before they actually start looking for "the" best printer for their needs.

    I have asked them to give me the size of the largest part they expect to print. (That makes me wonder if printing small parts will be limited by a printer that is "too big".)

    I need to find out what kinds of parts they plan to print. I know they are likely to make fairly small prototype parts, and at some point some of those parts might be made in a larger quantity. I see printing speed as being important, but not the "most important". Slower speeds for better quality would be fine. The parts would mostly be connected to medical parts related to eye surgery and care.

    Quality is very important. I have seen some parts they want to make prototypes of that are about an inch in length. I can post a photo of one of these, if it would help. I think the quality of the part is near the top of the list in importance.

    One of the decisions that is needed is how many extruders to get. Having watched the Stratasys videos, and their use of "support material" to allow printing parts including unsupported areas, to me that seems like a must-have. Is this true?

    They have told me they would like a mechanism to verify that the printing "table" is level, before printing starts. Is this something common?

    Finally, there is a question of what materials to use for printing. They have told me they would prefer a printer that accepts a wide variety of printing material. I know very little about this, other than it is unlikely that they will need to print metal.






    There is also a question of cost, and the budget. My own preference would be to start with the requirements, and only then consider the cost, and if the cost is too high, decide which requirements might be needed to bring down the cost. This can happen later.

    They also want to purchase a 3D Scanner. I'll leave that to a separate discussion.

    They plan to use their existing 3D software for designing the parts.


    If I were to make a "check list" for selecting a printer, are there things I have left off the notes above, that they need to think about before selecting a suitable printer?

  2. #2
    This is a list of "requirements" I have put together so far.


    • Size 150 x 150 x 150 mm capacity (around 6” cube)
    • Roughness rating 0.5 micron. (Maybe still need post processing??)
    • Preferably capable of using these materials:
      • ABS Plastic (PLA)
      • Nylon
      • PP Rubber and Silicon
      • If possible, metal

    • Automatic calibration for base flatness
    • Cost limit approximately $15,000
    • Should use a wide variety of consumables
    • Filament size 1.75 to 1.85
    • Capability to make “body parts”
    • Time frame approx 6 months
    • Need appropriate scanner as well


    Also:
    1.machine should be capable of printing functional protos.
    2.multijet/polyjet machine
    3.sla/sls process
    Last edited by mike@aravind.org; 02-21-2017 at 11:06 AM.

  3. #3
    Here is a top and bottom view of one part that needs to be scanned and printed. I have entered a separate thread to ask how to scan "transparent" parts.

    (http://3dprintboard.com/showthread.p...644#post105644

    The printer needs to be able to print parts like this...

    image002.jpg

    image001.jpg

  4. #4
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    You'll probably need a resin printer for parts like that, since the detail is more than a FDM-type printer could deliver. The Form2 could do it, and it has a transparent resin available. But aside from the part volume and "sla process" it doesn't meet your other requirements; it works with a limited number of resin-based materials, none of which are food-safe as far as I know, much less being suitable for "body parts". But with your budget, you might be able to get one of those and another machine for other materials like rubber - you might ask Davo at Hyrel about that.

    As for scanning a transparent part; either use a non-optical scanner, like a touchprobe, or paint the thing white before scanning it. You'll still have to do some reverse-engineering, to construct things like the interior volume which won't show up in the scan, but the scan would get you started. The other thing you could do is just model it from measurements.

    Andrew Werby
    www.computersculpture.com

  5. #5
    Thank you 'awerby'. I had suspicions that a 3D printer designed for small parts an inch or so in length would be printed better on a small machine. While the request was to find a single printer that does anything, my previous impressions of "all in one" devices has been that it doesn't do anything "the best", as it makes compromises to do so many other things.

    "Body parts" was intended to mean parts such as a prosthetic eye, which "looks" like an eye, but is placed inside a person's head. There is a "socket" behind the eye, and we currently make a mold of that socket, and eventually end up with a part that would go into the socket perfectly. That's where the idea came to scan the mold, to get the information for making a part that would fit.

    I need to read up on a "resin printer". I think extreme accuracy is one of the essential requirements, but I'll need to get help from people at the company/hospital to define what I mean by "extreme accuracy". The part in the photo was given to me as a sample of what they need to be able to print.

    Regarding scanning the transparent part, I was wondering if the part could simply be covered in "Dykem" die, hopefully allowing the scanner to see it properly. I don't know if Dykem will work with "plastic" though.

  6. #6
    (Another question - why were the posts I type here using my MacBook Pro showing up so narrow before? How can I get them to fill the screen, so they look normal? It's working now, but I don't know what I "fixed"...)

  7. #7
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    The resin parts might be used as masters for molding; then you can cast them in a material that's approved for body implantation. I don't think these photo-reactive resins qualify. Dykem is blue, so it might help with a blue-light scanner, but usually white is preferred. If you get rid of the "sponsors" pane on the right side of the screen, the posts will have more width.

    Andrew Werby
    www.computersculpture.com

  8. #8
    I still have my original goals about finding a 3D printer, but you've given me what I think might be my answer to my problem two years ago.

    When a person loses an eye completely, all that is left is the "socket" that used to support the eye. The hospital makes a series of molds, and eventually ends up with a replacement eye that looks realistic. So, if they were to make a mold of the socket (first step they do right now), and use.a scanner such as the one you suggested to scan that mold, they would get an engineering design showing that part of the replacement eye, and they could add on additional features as needed. With the resin printer, they could print this out very accurately, in resin, and from that part they could make a mold and cast the actual part later, using the appropriate materials that can be used inside a body.

    I will be back at the hospital in April, and take detailed photos of how this is done. I'm not sure what their budget is for this, but it sounds a lot more plausible right now than two years ago. Maybe they need to purchase two 3D printers, one of which will be a resin printer.

    Thanks..... to be continued...

  9. #9

    Requirements for 3D printer

    Feedback from the hospital added to my notes and questions..... My text is in black, and Rajasekar's feedback is in red....


    ==================================

    What parts will we scan? Most likely “machine tool” type parts, no larger than 6 inches in any dimension, and I would expect not much smaller than an inch or so. I can picture machining a prototype part, and once it’s finished, scanning it to allow us to make more parts the same way.

    Metal and plastic parts (opaque transperant,translucent)(medical devices), 6 inches in any dimension ok- less than or slightly more than one inch also needed.
    Inner profile and shape also to be scanned. What 3d modelling/cad software needed to join different surfaces of a part after scanning.(stiching), what will be the prerequisites of the technical staff to do this job?



    ==================================

    How much accuracy and resolution do we need... I will try to get figures that relate to our needs. For accuracy, I’m pretty sure 50 microns will not be good enough and 5 microns is more than we need. I will ask Rajasekar, along with a question about the required resolution.
    5 microns may be ok

    ==================================

    How fast do we need it to scan? I don’t see that as a main concern. We are only going to be scanning “static objects”. If scanning more slowly gives us better results in a longer time, I think that will be acceptable.
    yes

    ==================================

    Data storage: After the scanning is completed, I assume the data will be stored on our computer system, possibly for use in re-creating the object in a 3D printer, possibly with modifications. I already know of parts such as a mobile phone “case” that we may scan, so that we can print more of them.

    Sometimes scanned data copied to 3d modelling software like solidworks/pro-e, do the required changes if required and converted to a file format suitable for 3d printing

    ==================================

    I assume the scanner will be set up in an “office” environment, or a separate room kept more or less like a laboratory. Not knowing more about scanners, I’m not sure what else we might have to do, other than cover it when not in use. I’m assuming normal office lighting won’t interfere with the scanner. If it did, we would change the lighting to something more appropriate.

    Normal office environment

    ==================================

    I assume the above answers will allow us to calculate the cost range for the scanner. I don’t see us trying to make something fit into a budget, but I do see us trying to keep the cost reasonable by not including features or capability that we don’t expect to need.

    ==================================

    We have an engineering department. As a group, I assume they will learn how to use the scanner. As with anything else, learning how to use the scanner effectively will take time, but I don’t understand enough to say much more. I assumed we would put a part in front of the scanner, start the scan, and after a certain amount of time, the scan would complete. As with a camera, there are probably a lot of settings to adjust before the scan – but I don’t know anything about these, let alone how difficult they are to learn.
    Yes

    ==================================


    Well, that's the best I've been able to come up with to suggest what we think are our requirements. I have a feeling that we may need to re-evaluate some of these requirements, as I think the cost of what I've described is going to be more than will be approved. I read that an accuracy of 5 microns would be very costly. Other than that, everything seems reasonable to me, which is scary as I don't know enough yet to say that. Maybe I should say it sounds in line with what I've been reading over the past few weeks.

    There will be one other requirement - I should have listed it long ago. The printer is going to be use in South India, and it would be best if we were to purchase it from a company that provides support in that part of the world. I guess that can come later on - the first step is to find which 3D printers can do these things. Thanks!!!!!!!!!

  10. #10
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    Quote Originally Posted by mike@aravind.org View Post
    Feedback from the hospital added to my notes and questions..... My text is in black, and Rajasekar's feedback is in red....

    [AW: My responses are added in square brackets.]


    ==================================

    What parts will we scan? Most likely “machine tool” type parts, no larger than 6 inches in any dimension, and I would expect not much smaller than an inch or so. I can picture machining a prototype part, and once it’s finished, scanning it to allow us to make more parts the same way.

    [If you've machined it with a CNC machine, you've probably had to create a 3D model to base the toolpaths on. This model would be more accurate than any scan you made from the finished part.]

    Metal and plastic parts (opaque transperant,translucent)(medical devices), 6 inches in any dimension ok- less than or slightly more than one inch also needed.
    Inner profile and shape also to be scanned. What 3d modelling/cad software needed to join different surfaces of a part after scanning.(stiching), what will be the prerequisites of the technical staff to do this job?

    [If there are interior volumes that need to be scanned, no optical scanner will do that. If your hospital has access to a CAT scanner, that might work. Otherwise, you'd need to fill the volume with something, remove the outside (by dissolving it in acid?), scan the resulting form, and subtract it from the scan of the exterior. Scanners are often sold with software that is used for integrating the various sub-scans that they make into a solid printable object, but if not, one good one is Wrap, from Geomagic (3DS). The staffers assigned to this part of the job would have to learn how to use it.]


    ==================================

    How much accuracy and resolution do we need... I will try to get figures that relate to our needs. For accuracy, I’m pretty sure 50 microns will not be good enough and 5 microns is more than we need. I will ask Rajasekar, along with a question about the required resolution.
    5 microns may be ok

    [The Capture Mini can resolve details down to .034 mm (34 microns). There may be scanners that can do better, but they will be correspondingly more expensive. It may be that you're expecting more from a scanner than is reasonable; if you need extreme accuracy in your prints (or toolpaths), you won't be printing directly off your scan data; you'll need to go through a reverse engineering step, using a program that constructs clean CAD data from the scans.]

    ==================================

    How fast do we need it to scan? I don’t see that as a main concern. We are only going to be scanning “static objects”. If scanning more slowly gives us better results in a longer time, I think that will be acceptable.
    yes

    ==================================

    Data storage: After the scanning is completed, I assume the data will be stored on our computer system, possibly for use in re-creating the object in a 3D printer, possibly with modifications. I already know of parts such as a mobile phone “case” that we may scan, so that we can print more of them.


    Sometimes scanned data copied to 3d modelling software like solidworks/pro-e, do the required changes if required and converted to a file format suitable for 3d printing


    [Things like that work better if you go through the reverse-engineering step I talked about above; generally scanners produce "point clouds" which normal CAD programs aren't equipped to deal with.]

    ==================================

    I assume the scanner will be set up in an “office” environment, or a separate room kept more or less like a laboratory. Not knowing more about scanners, I’m not sure what else we might have to do, other than cover it when not in use. I’m assuming normal office lighting won’t interfere with the scanner. If it did, we would change the lighting to something more appropriate.

    Normal office environment

    [That shouldn't be a problem; scanning is a fairly clean process.]

    ==================================

    I assume the above answers will allow us to calculate the cost range for the scanner. I don’t see us trying to make something fit into a budget, but I do see us trying to keep the cost reasonable by not including features or capability that we don’t expect to need.

    [Look seriously at the tolerances you're calling out - if you really need to hold 5 microns, be prepared to pay for them.]

    ==================================

    We have an engineering department. As a group, I assume they will learn how to use the scanner. As with anything else, learning how to use the scanner effectively will take time, but I don’t understand enough to say much more. I assumed we would put a part in front of the scanner, start the scan, and after a certain amount of time, the scan would complete. As with a camera, there are probably a lot of settings to adjust before the scan – but I don’t know anything about these, let alone how difficult they are to learn.
    Yes

    [Scanners often come with a turntable that semi-automates the scanning process, but anything not in the line of sight will manifest itself as a hole in the scan mesh. If you want more or less whole objects, you'll generally have to scan at least twice with the turntable, and then register, align and merge the two sets of scans to make a solid object.]

    ==================================


    Well, that's the best I've been able to come up with to suggest what we think are our requirements. I have a feeling that we may need to re-evaluate some of these requirements, as I think the cost of what I've described is going to be more than will be approved. I read that an accuracy of 5 microns would be very costly. Other than that, everything seems reasonable to me, which is scary as I don't know enough yet to say that. Maybe I should say it sounds in line with what I've been reading over the past few weeks.

    There will be one other requirement - I should have listed it long ago. The printer is going to be use in South India, and it would be best if we were to purchase it from a company that provides support in that part of the world. I guess that can come later on - the first step is to find which 3D printers can do these things. Thanks!!!!!!!!!
    [I think you're doing the right thing by asking questions and getting information on the process before spending your hospital's money. The 3D printer is just one piece of a rather complex puzzle you're trying to solve, but it sounds like one that's worth solving. Have you investigated how other health-care institutions are dealing with these issues?]

    Andrew Werby
    www.computersculpture.com

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