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Thread: Turning A Model Into A Negative For Mold Applications

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    Default Turning A Model Into A Negative For Mold Applications

    In the near future I will be having an existing item 3D scanned in order to get as close to precise a digital model as possible. I use Solidworks 10 and I have been able to draw up a model to pretty close to the matching geometry but, I'm wanting to get closer than just "Pretty Close". If possible, I'm wanting a "Dead-Nuts" match.

    The item being 3D scanned is a small circular high pressure Piston Seal used in air guns. It's made of PolyUrethane and the face of this Piston Seal is the real critical part that I need an absolute match for. My problem is that I'm self-taught in Solidworks and I have NOT been unable to teach myself how to create a Negative out of the 3D scanned digital model using Solidworks. When you are self-taught, you have a situation where the teacher is just as ignorant as the student.

    Back when I first started playing around with CAD software I did manage to acquire a software called AutoCAD. (which I no longer have) It had a feature called "Booleen" or something like that where I could do a sort of digital "Lost-Wax" thing wherein I had my original model; the one I wanted to make into a Negative, so all I had to do was to draw additional width, length or thickness all around the original and then select that original model and then delete it. This would leave a cavity within the remaining model that was the exact shape of the item I had just deleted. (this is just an example of what I'm wanting to do within Solidworks)

    With my scanned Piston Seal, I'm wanting to do something similar but I don't know if it's even possible in Solidworks. Can one of you guys clue me in? With my 3D scanned Piston Seal, what I really need to make a negative of is the front face of the Seal. The curves and other geometry of this front face makes it impossible to get precise measurements with any of my measuring tools.

    What I'm wanting to do is like pressing the face of this Piston Seal into some clay in order to leave an exact matching imprint of that front face; except I'd be using digital means to do so.

    A little help Please.

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    Default Re: Turning A Model Into A Negative For Mold Applications

    Hi, Need to make a precise mold of scanned data?
    DIY ? or seek expertise ?

    Over a few years i have developed methods to do this correctly.
    And produce good results.

    Can you show the data or is it under NDA?
    Who and how scanned and resolution ?

    I use a serious lofting system to do this work,

    Attached Thumbnails Attached Thumbnails Turning A Model Into A Negative For Mold Applications-detail-7-jpg  
    Been doing this too long


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    Default Re: Turning A Model Into A Negative For Mold Applications

    Hi bostosh:

    And thanks for the quick reply.

    The model in question has not yet been scanned. I'm presently looking for someone to actually scan it if it can in fact be scanned at all. It's a very small part; about 1 1/8" diameter by 1/4" thick.

    I have no clue what "NDA" is the acronym for but am open to learning.

    One of the major problems I've encountered when asking for help from knowledgeable folks in this field is that their expertise leads them to offer genuine helpfulness in the form of technical jargon beyond the knowledge of hobbyists like myself. If possible, could you clarify by using words or descriptives that a two year old could understand; perhaps a link to diagrams showing what you are referring to? I'm not trying come off sounding ungrateful or smart-alec. I'm just trying to figure this out.



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    Default Re: Turning A Model Into A Negative For Mold Applications

    OK; I think I've figured out how to do it. YouTube comes thru for me again.

    I want to thank bostosh for taking the time to reply to my dilemma. I know I can always count on the good guys here on cnczone to help a guy out; or at least try.

    MetalShavings



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    Default Re: Turning A Model Into A Negative For Mold Applications

    Something that small should be handed to a jewelry place. for super fine resolution.



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    Default Re: Turning A Model Into A Negative For Mold Applications

    You say this part is a piston seal? Does it look something like this?


    Turning A Model Into A Negative For Mold Applications-04-11-14-02-diana-piston-seal


    If so I don't think scanning is needed or even appropriate. Anyone that's good with a caliper should be able to reverse engineer that into a 3D model in about 10 minutes. If you really want to be super accurate about it you could use an optical comparator instead of calipers, but even that's probably overkill.


    As far as making a mold for it, there are a few ways to do it in Solidworks. Probably the most typical way is to model the seal first, model the mold block around it, then use the "combine" command to subtract the seal from the mold block. This would be the Solidworks equivalent to the boolean command in AutoCAD. But if this part is similar to the picture above, you could most likely cut the negative shape from the mold with a single revolved sketch.


    C|



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    Default Re: Turning A Model Into A Negative For Mold Applications

    Quote Originally Posted by cygnus x-1 View Post
    You say this part is a piston seal? Does it look something like this?


    Turning A Model Into A Negative For Mold Applications-04-11-14-02-diana-piston-seal


    If so I don't think scanning is needed or even appropriate. Anyone that's good with a caliper should be able to reverse engineer that into a 3D model in about 10 minutes. If you really want to be super accurate about it you could use an optical comparator instead of calipers, but even that's probably overkill.


    As far as making a mold for it, there are a few ways to do it in Solidworks. Probably the most typical way is to model the seal first, model the mold block around it, then use the "combine" command to subtract the seal from the mold block. This would be the Solidworks equivalent to the boolean command in AutoCAD. But if this part is similar to the picture above, you could most likely cut the negative shape from the mold with a single revolved sketch.


    C|
    Hi Cygnus:

    Yes: the piston seal in question is very similar to the one pictured here but the actual factory piston seal has a geometry with slightly different features. It's these different subtle features that I was hoping to nail down with a 3D scan.

    It's true that a guy with accurate measuring tools can come close to the factory dimension. I've done this myself but, I'm trying to do better than just come close. I'm hoping to achieve a "Dead-Nuts" match if possible.

    I've come across a couple of youtube videos that have helped me out a lot in turning my hand-measured model into an injection mold. Before I go any further with it I want to be sure I've exhausted all my efforts at getting it 3D scanned.

    Thanks for your reply. It was helpful.

    MetalShavings



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    Default Re: Turning A Model Into A Negative For Mold Applications

    What level of accuracy do you need (in numbers)? +/-0.005" is pretty doable with a caliper, and on geometric parts you can many times do even better. If you need more accuracy than that it will take a fairly good scanner, and one that's intended for small parts.


    C|



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    Default Re: Turning A Model Into A Negative For Mold Applications

    There is a big chance that a seal is an off the shelf part available from some place like McMaster-Carr (Mcmaster.com)

    A point cloud will not be processed in Solidworks in any easy manner. It was never intended to process point clouds. There are some plug ins but with that version of Solidworks you will not find it. So you will just get a huge number of points or triangles that are tough to do anything useful with unless you have lots of time and lots of experience.

    But once you get your point cloud of scan you will need to turn it in to a "water tight" solid model. Don't worry about the mold until you have the part as a 3D part model with no gaps between surfaces. Once you have that you will create a box that envelopes you model. Then do your boolean subtract and you will have the core. Draw a sketch along the parting line and then split your solid in to your mold halves.



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    Default Re: Turning A Model Into A Negative For Mold Applications

    Quote Originally Posted by warrenb View Post
    There is a big chance that a seal is an off the shelf part available from some place like McMaster-Carr (Mcmaster.com)

    A point cloud will not be processed in Solidworks in any easy manner. It was never intended to process point clouds. There are some plug ins but with that version of Solidworks you will not find it. So you will just get a huge number of points or triangles that are tough to do anything useful with unless you have lots of time and lots of experience.

    But once you get your point cloud of scan you will need to turn it in to a "water tight" solid model. Don't worry about the mold until you have the part as a 3D part model with no gaps between surfaces. Once you have that you will create a box that envelopes you model. Then do your boolean subtract and you will have the core. Draw a sketch along the parting line and then split your solid in to your mold halves.

    Even though I have limited knowledge and even less experience with 3D scanning, with the little bit of research I've done on the subject I figured as much. I mean, my ideas of how to go about getting an ultra accurate 3D scan slowly started leaning back toward manually measuring the Seal in question.

    It's been a while since I initially posted this search for wisdom. Since that time I decided to take another crack at it by sacrificing a brand new Pressure Seal to get a vertical split view in order to put my most accurate measuring tools to it. I took a razor blade to it and split it down the middle. I was just hoping that the 3D scanning technology had evolved enough to make it practical to scan such a small part. It appears that for my particular needs, it's still to far out of the financial realm. At least that's what it seems like when deduced from the few replies I've gotten on this thread.

    I am grateful for those who took the time to reply at all and I did learn a few things.

    MetalShavings



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    Default Re: Turning A Model Into A Negative For Mold Applications

    Quote Originally Posted by MetalShavings View Post
    Even though I have limited knowledge and even less experience with 3D scanning, with the little bit of research I've done on the subject I figured as much. I mean, my ideas of how to go about getting an ultra accurate 3D scan slowly started leaning back toward manually measuring the Seal in question.

    It's been a while since I initially posted this search for wisdom. Since that time I decided to take another crack at it by sacrificing a brand new Pressure Seal to get a vertical split view in order to put my most accurate measuring tools to it. I took a razor blade to it and split it down the middle. I was just hoping that the 3D scanning technology had evolved enough to make it practical to scan such a small part. It appears that for my particular needs, it's still to far out of the financial realm. At least that's what it seems like when deduced from the few replies I've gotten on this thread.

    I am grateful for those who took the time to reply at all and I did learn a few things.

    MetalShavings
    From the sounds of it you were after a measurement accuracy orders of magnitude higher than normal, but you do realise that in slicing the part in two, you've potentially exposed internal stresses or flex that may skew the measured results, given the extremely high degree of resolution you were after?

    cheers, Ian

    It's a state of mind!


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    Default Re: Turning A Model Into A Negative For Mold Applications

    You can indeed get an ultra accurate scan of this part. But what do you do with 1,000,000 points or a massive triangle mesh? You still need the "something" to turn it in to useful information with which to make a mold. SW does not know what to do with them. They are just 3 dimensional locations with no surfaces, unless it is exported as triangles. And then you only deal with the resolution of your scanner.



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    Default Re: Turning A Model Into A Negative For Mold Applications

    In SWX 10 as I remember you can create a use the "cavity" routine to create a negative of the part. See the "help" menu. The part has to be a true solid(called water tight) with no surface imperfections.

    Mike



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