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  1. #493
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    This is a fascinating thread. I have contemplated building a scaled engine but, I never got past the CAD/CAM stage and 1 test cut to prove my tool path. It was mentioned that machining a helical rotor would require a 4th axis. My test cut machined 1/3 of the profile of a helical rotor on a 3 axis CNC milling machine. The full profile would have required indexing the rotor twice at 120° increments. There is a small shelf in the tool path so it requires using a 220° back cut spherical end mill. The tool path was generated with a lobe at 180° as shown in the last picture. The basic rotor profile is comprised of 324 arcs (involute curve) with varying radii. Excluding the right hand rotor you can see that there is basically a straight line between the inside of the high lobe at each end of the rotor.

    Due to the small shelf at each end of the rotor you cannot use a surface generated tool path. I offset the rotor Geometry (1/3 of the profile or rotor tip to rotor tip) by .25" for a 1/2" diameter 220° back cut spherical end mill, generated points along the section of the Geometry spaced at .015", translated the Geometry with points at a distance equal to 1/10th of the overall length of the rotor and then rotated the result at -6°. After having translated Geometry twice I now had three of what I refer to as bulkheads. I created a spline using a common point on each of the three bulkheads. After creating the spline I deleted the three points so as to prevent confusion. When all splines had been created I had a 1/5th segment of the rotor tool path. By translating and rotation the 1/5th segment 5 times I had the full length rotor length. Next I tied every other spline together at the start and end of the rotor tool path. That resulted in a zig-zag tool path with a 60° helical twist. It was extremely slow and tedious but, It resulted in an almost polished surface finish.

    Well I forgot to account for a lead into the tool path so you need to translate and rotate the 1/5th segment beyond each end of the rotor. That maintains the helix and you can trim the length afterwards.

    ROTATING ROTORS IN CONSTANT MESH: http://flickcabin.com/public/view/full/153169 < SLOW TO LOAD

    TEST TOOL PATH:


    STATIONARY ROTORS IMAGE:


    Last edited by RFB; 03-19-2013 at 10:23 PM. Reason: Added picture


  2. #494
    Registered cforcht's Avatar
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    RFB your model Looks good. in fact it looks very much like the real rotor design of a roots blower with the lands on the ends of the lobes. although I didnt understand most of your explanation and would really like to. but its early and I havent had but half a cup of coffee yet. I have been dabbling in learning solid works the last couple weeks. pretty slow progress since Im doing the self taught method like I normally do. But in doing so I have revisited my engine and getting back into the engine mode. Maybe I will get some work done on it sometime soon. its still sitting here on the desk waiting for me to come back to it. after much deliberation I think I am going to re-make the crank. I just dont have much faith in the multiple piece crank idea. yes I have them made but I just cant get past the idea that one piece would be more reliable than multiple pieces bolted together. getting back to your helical rotors. I would like to have a look at your CAD model if you would be so kind. I tinkered with the helical design a bit and was less than pleased with my results. the mesh didnt come out right and kept having to alter the profile and still just didnt seem right. please contact me if you would. heres a couple renderings from my solidworks tinkerings.






  3. #495
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    Craig,

    Im doing the self taught method like I normally do
    Good on You! There is no better teacher than one's self. When I purchased Mastercam (1st Windows version) the sale include ? hours of tutoring. I never attended class. I have always believed that if you have to read the instructions or be schooled then you are probably not smart enough to use the technology.

    The images were developed using the Mastercam shading studio. My learning process dropped off prior to Solids. Surfaces are the extent of my knowledge and that has satisfied my needs. However I'm so picky that I don't like the result of most surface/s developed tool paths. When exact precision is required then I prefer to create the Geometry myself. I program in Mastercam v7 or v9 depending on my location. All of the blower prototype was done several years ago and the tool path no longer exist. However I do have the CAD files but, you would learn nothing if I were to give them to you. I will show you how to generate your own profile. You can then use your own discretion for who you share it with. My only request is that you do not share it with anyone that will market a product using the technology. If they plan to make money then let them do their own homework!

    The technology is highly sought after. With the exception of the epicycloid and hypocycloid profile <(read on) it is the only thing that I have not been able to locate on the internet. Just recently there was a person from India that posted in CNC Zone and openly asked for the profile because his company could not develop a working profile. Next he attempted to contract with someone to write a program for their Hass. I can proudly state that I dropped the hammer on him both times.

    Send a PM with your e-mail address so we can exchange information. I do not have Windows 7 e-mail setup so I cannot use the CNC Zone PM.

    The test cut that I showed was actually developed from a different profile. The old profile did not maintain a constant mesh and I was not driven to perfection back when the profile was developed. The more recent development was a Do It or Die Trying effort. First I schooled myself in developing epicycloid and hypocycloid curves for a constant meshing rotor profile. The process did developed a constant meshing rotor profile. However the rotors had a very large mass and would have been very inefficient. Learning the cycloid method was entertaining but, otherwise a total waste of time. Without having a CAD/CAM program I would not have been able to create the profile. The GMC 6-71 supercharger is rated at 411 cubic inches of displacement per revolution and my profile produces 410.6 or 411 when rounded. The profile maintains a constant mesh with zero interference so I did it before I died. It is so damn simple that I cannot believe the amount of time I spent before figuring it out.

    Below are pictures of the HTD belt drive system I built back when I was racing gokarts. They are 8mm but, could easily be scaled to 3mm or 5mm. The ones without a flange are two piece and were used on the rear axel. Each tooth count had it's own profile so as to prevent the belt cogs from scrubbing on departure. The sprockets were machined with a Woodruff type cutter with a full radius and multiple sprocket teeth were machined at each index. That is why the index plate looks strange. Inside of the square block is a piston the actuates the index lock pin. The lock pin also serves as a spool valve which controls the actuation cylinder. The actuation arm on the pivot has a sprag bearing so that it does not drag the spindle back when the cylinder retracts. The process had to be coordinated and activated with a single pneumatic valve.

    The engines were Italian road race motorcycle engines with a six speed transmission. The splined output shaft presented a problem with aluminum sprockets. Others had tried pressing steel hubs in the aluminum sprockets but they would come apart in short order. Solid steel sprockets would cause the output shaft to break due to the weight. Every engine came with a 13 tooth sprocket which nobody used so they were plentiful. Unfortunately I did not preserve an image of the back side of the drive sprockets. My approach was to machine a cavity in the shape of the 13 tooth sprocket which would facilitate mounting the aluminum HTD sprocket over the 13 tooth chain sprocket and then secure both with a cap nut.







    RFB



  4. #496
    Registered cforcht's Avatar
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    RFB
    way back when, I started on mastercam 286 which is really old. it ran on an old 386 computer. man was that thing slow. all I had was a slim manual and no idea what I was doing. it was the first CAM program I have ever laid eyes on. In fact up to that point I had always done it on the machine. I didnt know there was a PC program that would do that kind of stuff. since then I have followed through with the various upgrades. I stalled on Ver 9 though. I was shown X version and hated it. it took so many more clicks to do the same thing it seemed like I was just trying to check the mouse's cyclic rating. but once I bought the live tooling lathe I saw the benefits of the X version. I handled the C axis much easier than Ver 9 did. so I made the switch. My CAD program has been historically Autocad. I have been a true blue fan of it for many years. But a friend of mine talked me into actually giving Solidworks an honest try instead of the precursory glance I had always given competing CAD programs. I have to say I do like it. its different thats for sure. but we're starting to see eye to eye. still have a long way to go. but i can usually get things done.

    right now Im in the process of getting my 4th axis working with my machine. more or less Im just waiting for my service guy / friend to get here to tie it into the machine. its was a Yuasa cnc indexer I picked up on fleabay a few years ago. It did work. but I have since adapted a larger Fanuc servo to it and got it ready for full 4th axis use instead of indexer. of course now I have a cnc indexer control and servo I dont know what to do with. oh well. it might go back on ebay someday unless I can find some use for it.

    anyway gotta keep it short my lathe is waiting for me.



  5. #497
    Registered 1970chevelle0's Avatar
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    Hello,
    I'm brand new to the site and just read this whole thread it's great. The last post I see is from a year ago was there a new thread started or am I missing something?

    Thanks


    Sent from my iPhone using Tapatalk



  6. #498
    Member stevehuckss396's Avatar
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    I think work picked up and he got busy so there hasn't been much progress.



  7. #499
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    Quote Originally Posted by stevehuckss396 View Post
    I think work picked up and he got busy so there hasn't been much progress.
    Ok thanks I just wanted to make sure there wasn't a second thread or something I didn't know about.


    Sent from my iPhone using Tapatalk



  8. #500
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    Default Re: Steve Huck's Demon V8 version 1.5

    awesome thread ....

    you can post work stuff if you like , im sure there wont be too many complaints

    but progress would be great, *nudge nudge*



  9. #501
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    Great work,



  10. #502
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    Hi can you tell me what angle on the block to machine where heads fit is it 45 degrees? I have purchased these plans but I cannot see where it tells this thanks in advance.Rocky



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