learning cad

Discussion in 'Software and Programming' started by jixxerbill, Feb 24, 2013.

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  1. Mar 8, 2013 #61

    lohring

    lohring

    lohring

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    Thanks for all the suggestions. The drawing is from an Aprilia 125 cc motorcycle cylinder. The engine develops 54 hp and is considered to be the state of the art in high power, small two stroke engines. It was developed without the use of CAD so I suspect the 3D rendering is built from scans of the core patterns. I could build models like the 3D picture to cast molds to make the cores like the pictures of sand casting core molds below. However, I thought I would try solid modeling since it has lots of advantages when combined with 3D printing for scaling or altering parts to test the effects of small changes.

    I'm studying lofts in Alibre and it looks like I can loft a section along a curve. That will be a good place to start. I can work up to a series of sections along a complex curve if needed. It still looks easier to build a physical model, though.

    Lohring Miller

    Core2.jpg

    Core3.jpg
     
    vascon2196 and littlelocos like this.
  2. Mar 10, 2013 #62

    wildun

    wildun

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    LOHRING,
    The name Jan Thiel rings a bell from the late sixties, was he the guy who was involved with designing the 50cc racers for the Dutch Jamathi team of the late sixties/early seventies and later moving to Derbi?
    If that is the case, then his knowledge of two strokes would be second to none.
    BTW, my school French was not quite up to scratch for the forum but I was able to get the gist of it!
     
  3. Mar 10, 2013 #63

    Auzzie53

    Auzzie53

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    send me your email address and I will send you some material

    Regards
    John
     
  4. Mar 10, 2013 #64

    dman

    dman

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    lohring that looks like a learning experience recreating that in cad. I'm just curious, what are you planing to do with all this? do you have an aprilia and looking for even more power? or trying to learn from it and reproduce it on something else? I'm thinking about getting into 2 strokes on a modification and performance level myself.. I'd really like to see where you go with this.
     
  5. Mar 10, 2013 #65

    petertha

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    Wow those core patterns are very complex looking. Yet another example of trade craftsmanship achieved long before computer drafting. Seeing those, I think my earlier examples may be barking up the wrong tree for you. I was attempting to show simplistic 'cuts' from a solid, kind of like port passages in a typical RC 2-stroke crank case.

    Here is another example along the lines of the one core piece you show. It’s a similar principle oflofting a port shape into a main trunk body. But more along the lines of 'adding’ material to build up some solid shape. I made 3 sections & a spline curve, lofted the solid into the cylinder & filleted the top. In this case I’m just radially copying the exact same arms for illustration, but nothing stopping you from having uniquely shaped and/or un-equalspaced octopus tentacles.

    Now what you do with this positive shape is beyond myability. Possibly it could be submerged within a crankcase block & cut away yielding thecavity. SW has such tools & I mentioned other cad packages do this byboolean solids (adding or subtracting). One can also offset or shell a solid.The Cad raw ingredients are there, but how you physically go about designing it isa bit above my head. Fascinating stuff.

    2013-03-10_111642.jpg
     
    Last edited: Mar 10, 2013
  6. Mar 11, 2013 #66

    lohring

    lohring

    lohring

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    I'm designing a high power 26 cc two stroke. I race model boats and even the best available engines are considerably behind the state of the art. My inspiration is this quote:

    "The best horsepower we attained at Aprilia last year (2007 125cc GP) was 53,9 HP at 13000 rpm. This means a Pme of 14.88 at a piston speed of 23,6 m/sec. Using these same values means that a single cylinder 50cc would give 29.5 HP at 17850 rpm and a 50cc twin would give 39 HP at 23600 rpm, measured at the gearbox output shaft. I am 100% sure these values can be attained although it never will be proved due to lack of interest and money. Remember that 50cc development was stopped in 1983 and enormous progress was made in the following 24 years. Now, sadly, also the development of the 125cc two strokes has stopped, the two stroke will only survive in karting but there will be no progress because of the very strict regulations!"
    Jan Thiel 2008



    That would mean that my 1/2 of a two cylinder 50 cc engine could produce 19 hp rather than the 8 hp at around 18,000 rpm the very best current engines have. I would be happy with anything over 10 hp. I was involved with the current RC gasoline engine powered speed record of 109+ mph set in 2004 that still stands. The last complete engine I built was in high school over 50 years ago. I belong to a restricted forum of two stroke builders that made the above pictures available.

    I'm trying sweep cuts in Alibre to generate the transfer passages. I hope to create one plane for each side of the transfer then sweep the shape shown in the 2D cross section around the bore from one plane to the other. I can then fillet the edges of the shape. So far it isn't working, though.

    Lohring Miller
     
  7. Mar 12, 2013 #67

    dman

    dman

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    that'll get you sorta close but you may wat to try it with a mesh so things can be manipulated to get some of the more organic aspects of it closer. do you have a more readable copy of that blueprint? maybe in a .pdf or other vector format? mabe i'll try to draft someting up. it's been a while since i've done anything close to this. it turns out that this kind of drafting is rarely needed in what i'vw been doing
    .
    just for fun i ran some of those numbers for some popular 2 stroke engines to see what they could make in full race trim.. (assuming the bore/stroke ratio is close, i really just ran the numbers as if the aprilia was scaled.) an lt500r quadzilla could make around 135hp at 8200 rpm. a banshee or rz350 could also make 135hp at 11,600 rpm. (weird how that works isn't it) and a 250cc engine could make 86hp at 10,300 meaning a kawasaki h2 machiv could make a scary 258hp and even an h1 could make 196hp at 11,800.

    what i think is interesting is the numbers are around twice what the best stock japanese engines made when 2-strokes ruled motocross but the rpm isn't too much higher. sounds like aprilia had a lot going on in this engine. maybe my next motorcycle will be a 2-stroke.
     
  8. Mar 12, 2013 #68

    lohring

    lohring

    lohring

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    Thanks for your offer to help. So far I think a series of cross sections along a 3D curved line is the only way. The only drawings I have of the Aprilia cylinder are .jpg. Below are the rest.

    Lohring Miller

    PS I've at least been able to model propellers. See below.

    Ap125-02.jpg

    Ap125-03.jpg

    Propeller 72 x 100 with cup.jpg
     
  9. Apr 7, 2013 #69

    DanP

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    Hi
    I was not sure where to ask this but I thought I would start here. A friend of mine is using a Mac drawing program, I don’t know what it is and he doesn’t seem to know either. I am using AutoCAD 2006. We have been collaborating on a Gauge 1/ Gauge 2 layout plan. When he sends me his file in either DWG or DFX I can open them with AutoCAD and use them, add to them, change them, whatever I can do with a normal AutoCAD drawing. When I send them back to him in either format he can see them but not use them. I save them as 2000, because that’s what he says he needs. So, the question, what are we doing wrong?
     
  10. Apr 7, 2013 #70

    ausdier

    ausdier

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    Hi Dan,
    Does your mate have an educational copy of the program he is using ?
    This sometimes means it wont open non educational drawings.
    Cheers.
     
  11. Apr 7, 2013 #71

    dman

    dman

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    sounds like an auto cad licensing thing. i hate to agree with richard stallman mostly because i think he's insane but when he pushes open source or otherwise "free" software it's things like this he wants to FREE people from. not free as in free of cost. free as in who the hell are they to tell me how i can use my computer to manipulate files? you both should try draftsight unless you need 3d. it's very intuitive to autocad users. there is also freecad for 3d but it has a learning curve.

    i personally think proprietary is fine as long as it's not malicious but it too often is.
     
  12. Apr 7, 2013 #72

    DanP

    DanP

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    I found out what program my friend has, MacDraft Profesional 5.6.6, maybe this will help answer my problem.
     
  13. Apr 7, 2013 #73

    GailInNM

    GailInNM

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    Dan,
    If you want, send me a file that is giving problems. Send it in ACAD2000 format as I have 2000 in native format and I will see if I can manipulate it. If I can then the problem is probably at Jim's end. I have not had any problems reading the files that he has sent me in 2000 format but I dont think that I have sent him any since his last software upgrade. Just use my regular email address that you have.
    Gail in NM
     
  14. Apr 7, 2013 #74

    Draw-Tech

    Draw-Tech

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    Try having your friend go to autodesk.com and download the dwg viewer it is free, he will be able to read dimensions and measure the parts at least.

    Hope this helps

    Draw-Tech
     
  15. Apr 8, 2013 #75

    kf2qd

    kf2qd

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    Or have him download the Mac version of Draftsight.

    DXF is NOT a proprietary format. DWG is. His version may be looking for some ID info in hte DXF file, or it doesn't use some feature in a 2000 compatable DXF. You could try sending him a R12 or R14 DXF.
     
  16. Apr 8, 2013 #76

    kjk

    kjk

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    I don't use autocad, but with many software products a program will read all files created by previous versions of the software but not files created by newer versions.

    CAD software I use offers the opportunity to save files in formats used by other versions - does Autocad 2006 allow you to save in formats for previous versions of autocad?

    Also - it may be that your friend's software only recognizes text files and not binary.
     
  17. Apr 8, 2013 #77

    DanP

    DanP

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    My friend can view my files but can't change them. When he sends me a file I not only can see them but change them. Gail in NM knows who I am talking about and we will see if he can tell us why, I will let you all know what I find out.
     
  18. Apr 11, 2013 #78

    DanP

    DanP

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    It only works when I initiate the drawing. I save them as R12/LT2DXF. If he initiates the drawing then all he can do is look at it and zoom in & out. Gail in NM suggested it's a Proxy thing. Oh well, on to more pressing matters.
     
  19. Apr 13, 2013 #79

    Chriske

    Chriske

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    Hi guys,

    Don't know if this has been mentioned before.
    As in 2DCAD programs also in 3DCAD programs files easily can be exported to be sent to other 3D CAD users anywhere.
    STP or STEP format has to be used to export files. Almost all 3D CAD programs can open this type of files. No need to save all parts separately, just the complete assembly will do. If opened in another 3DCAD program all part from the imported assembly can be extracted and opened in a single file.

    Very handy..!

    Chris
     
  20. Apr 13, 2013 #80

    kjk

    kjk

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    I received some drawings from a friend which I could not modify. For some reason as received these files were read only.

    Try saving the files under another name, then re-opening them.
     

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