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  1. #1
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    Real uses for 3d printing - what are the benefits vs. subtractive machining.

    Total newbie here. I'm exploring this site because it was mentioned on the CNC Zone forum where I have been gathering information on CNC machines. I'm trying to weigh the benefits of both processes and how they will apply to me.

    My background - took high school drafting ions ago but have always been interested in everything mechanical. With that said, I've been toying with the idea of tweaking gear in one of my passions in life, fishing. I have ideas and plans for parts and luckily, I have friends that are engineers and designers to help me out.

    My guess is that speed is the main benefit of 3d printing. It would be nice to have a physical part for prototype assembly but I would think accuracy may suffer and testing strength would be difficult. My task is to figure out if making a 3d print of a part is going to satisfy my needs. I may be wrong but, won't I be able to figure out how well parts fit together in the CAD process? Why would I need to make a "plastic" part to tell me that? Most all parts in the finished product will be aluminum. My original plan was to get a 4-axis benchtop CNC machine for the journey (figure it could also make some parts for my RC hobby down the line as well.)

    If it were for making just a few parts, I would just send them out to a shop. If acquiring the right CNC mill at the right price made it feasible to make a few more parts for others and offset some costs, then it would be a no brainer. If it were something that went commercial, then it would be back to sending it out. I'm wondering how everyone is using their 3d printers in their design process? Do you also have machining facilities at hand or do you send them out? What are the benefits of 3d printing vs CNC machining in the design process? I would appreciate any comments on whether I'm thinking about 3d printing the wrong way, what could it do for me or if a CNC mill would be a better way to go.

  2. #2
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    I am only starting with both cnc machining and 3d printing for my hobbies. so YMMV. I also design a variety of parts for my real job. Cad is great for theoretical fitting, but does not cover everything. If you have two gears that need to mesh, depending on the cad program you may be able to rotate the parts and get collision detection. I work with automotive companies and they make 3d printed prototypes of almost everything I touch, and they have a lot more advanced cad than I will ever use.
    I feel ergonomics is a very good use for 3d printing. I enjoy fishing too, so here is a simple example. You are designing the handle for a spinning reel, or rather just the spinning knob that you hold on to. How does it feel in your hand? You could have a machine shop make the part, or you could even make one on your own cnc machines. Then you hold it... nope the size is too small, it feels like crap. So you change the drawing and re machine. Several hundreds of dollars later, or hours of machine time you make do with the last iteration because it is good enough and you are broke or sick of working on it. With a 3d printer you could print that part in 15-30 minutes and iterate until it is "perfect", then get your parts machined knowing you like the part.
    True that strength testing would not be a fair comparison in all situations, somewhat depending on the filament. Nylon could be a fair comparison to a molded or machined nylon part, as abs to abs could be (disclaimer:I am not a plastics expert).
    One of my projects I will use the 3d printed part to test if a design is going to fit and function, then print a scaled up version for the sand casting guy to make a mold to pour bronze parts for production. Very cheap and easy to do with a printer, I don't even know how many tens to hundred hours this part would take to machine, then machine again scaled up to allow for shrinkage.
    The easy answer is, I personally don't feel it's an either or thing. Eventually you will likely end up with both.
    I do know this. If you are designing parts to send out to have multiples made, you better have a functioning sample to make sure you aren't wasting time and money.

  3. #3
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    Thanks, maker of things, for your point of view concerning this matter. I appreciate it very much.

    Regarding the automotive companies producing printed prototypes for you to deal with, is that a function of cost or time or both? I bet those must be some real nice SLA models to deal with. I would have to guess that many on this forum won't have the same 3d printers in our house that those automotive companies will have down at R&D. I know I sure won't. Also, I know it's hard to estimate but, how many design changes do those part go through?

    As for the ergonomics, I guess I'm a little old school for this new fangled, 3d printing stuff (haha). Funny you used the handle of the reel as an example. That was a part that was modeled... in clay to get a "feeling" for its ergonomics. Only had an approximate size from existing handles as a starting point. Off the top of my head, I wouldn't be able to tell you to start at a 0.50" here, then taper to there then bend to that and round this off here. I needed that thing in hand before it could be put on paper. My buddies, on the other hand, were spinning it in 3d in their heads when I was telling them about it.

    A concern I have regarding the ergonomics and printing parts would be the balance of the assembly which, I don't think can be achieved as easily as a machined part. Some of the parts we are dealing with are off the shelf and the other parts we are making. We have designs/parts for a new, complete reel while other parts are for upgrading/modifying our existing reels. Dealing with materials close in weight to finished parts would be helpful. But I see the value in, like you said, printing a complete model to verify function. I guess, for me, fit and tolerances are a concern in dealing with a printed vs machined part. It's not like we're making Swiss watches but there are a few places where I think it'l be tight. Maybe I am not yet convinced that a printed part will suit me when prototyping a model.

  4. #4
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    Actually most of the prototype parts I see are FDM. SLA is too expensive for most of the applications I get involved with. It is a function of both cost and time. Basically if they have a mold made and start producing parts and there is any little flaw, it is a nightmare to fix. Much of that could have been caught with a simple fdm that verified that all the pieces fit together before they have the mold cut. From what I have seen so far, other than size, the parts don't look too different to what I can print. The commercial machines print support so they can do much more detailed shapes than I currently would be able to do.
    The funny thing about cnc machines is that they all need the same info. My experience has been that if you go to a machine shop and tell them to start at .5" and taper and round off, you will likely get a blank stare. Most shops won't even give you a quote without prints or cad data. If you can produce the information to print a part, it is very likely that the machine shops can then machine it too.
    My old school is 2d cad so this here fancy parametric 3d cad is taking me a bit of getting used to. Back in the day of drafting and 2d cad, we would print the 3 view drawing and double check the measurements before we sent an order out for parts to be made from the print. Think of it that way. If the drawing is in 3d, why not print a 3d "drawing" to verify.

    3d printing plastic is not the be all end all solution, nor is it the best for everything. Even though the media likes to get all excited because it is possible to print a gun, I bet my mill and lathe would produce more usable results. Then again, a new set of custom side plates for the 1911 would take less than 1 hour on the printer...

    It's your money go with what you feel most comfortable with, but don't be surprised to end up with both.

  5. #5
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    When I started my RC business a few years ago, I bought a CNC mill for my basement. I knew that I would be making the production parts as well as all the prototypes, so the mill purchase was an easy choice. Speed isn't really the benefit I see with 3D Printing...I think it's cost. If you don't have a mill to make your own prototypes, a local shop will gladly do it for you...for a price!

    You have to ask yourself a few questions. Are you just making these parts for yourself? Are you going into business? Does it make more sense to design the part and have someone else print or machine it?

    Our printer at work has already paid for itself many times over, but then again so has our machining centers.

  6. #6
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    When I was building my first 3dPrinter my sons kept asking what I was going to print.
    I told them I didn't have anything to print, but I just had to make the machine.
    And I haven't stopped making more machines and printing stuff since!

  7. #7
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    Thanks for all the replys. It's much appreciated info added to the tank.

    maker of things - Would you happen to know what the resolution of the models presented to you? What tolerances do you have to deal with concerning those models? I guess from what I've seen printed from fdm/fff printers, the resolution doesn't look sufficiently useful yet. All parts that I'll be dealing with will be machined. Thought of having one of the parts powder forged since it has many complex curves but the cost of tooling for that piece x the different models could offer = too much money. I know a printer can be a useful tool in the design process but I am still considering how useful it will be in our case. My thought process is that having a completely finished part, or similarly manufactured part, for prototyping would allow us a better understanding utility and making corrections. I guess I still have to determine out exactly out needs.

    C*H*U*D - So how does the printer get implemented nowadays; are you frequently redesigning products? I guess the RC market has so many different manufacturers and models that designing could also be non-stop and the printer would be in continuous operation. Initially, these parts are for me. It would be for upgrading existing parts for fishing reels and building a completely new reel from scratch. The complete reel has outside interest but, bringing it to market would be a long way away. If feasible and the tolerances can be kept, I would manufacture some parts in house.

    p.s. Was thinking of getting a scale crawler and making parts for that would definitely be on the list! Already have ideas for parts on my rc10.


    jmkissell - I won't even tell my niece about it. She would be over all the time printing new stuff for her Monster High dolls and I'd never see it again.
    What printers are you making, what kind of tolerances do they hold, what are the capabilities of the print (size) and what kind of objects are you printing? Anything for end use or just for design and verification?

  8. #8
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    Quote Originally Posted by chipmcd View Post

    C*H*U*D - So how does the printer get implemented nowadays; are you frequently redesigning products?
    Our printer at work gets used for a number of things. A lot of mechanical parts get printed to test for fit and function, but the big money saver is when we print out parts that our Marketing department needs to approve. Things that the end user will have to interface with. Being able to actually hold something in your hand, even if the material is different, can tell you things that a computer model just can't convey. We will print out 2 or 3 different versions, and people can get together and actually get a feel for each piece and decide which they prefer. Having each piece injected molded would not be financially feasible so the printer is invaluable.

  9. #9
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    The parts I'm involved with are not for cosmetic testing, only for physical size and fit. The layering is very much evident. If I had a dual head extruder with support filament I'm sure I could get very close to matching the quality of the industrial prints. C*H*U*D describes the process pretty well, even if you are your marketing department.

  10. #10
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    I have my eye on a couple or printers but just curious on which make and models are being used by all of you? And why did you go with that particular printer? Strengths? Weaknesses?

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