Capto

[PeterBrown]

Has anyone a method of modeling a Sandvik Capto shank? This is now an ISO standard 26623, and looks kind of like a Wankel rotor. TIA

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[DavidButz]

Peter, I'm intrigued by your question. 1. How does modelling the shank relate to Curve by Equation? 2. Can you tell us what "beep" is, in terms that can get by the mysterious censor? David

[DavidButz]

P.S. Whatever the answer to question #1, I have found Curves-by-Equation very disappointing in the past. You can create this very cool and sophisticated Curve, then not use it to drive solid geometry such as Sweeps.

[PeterBrown]

Hmmm... I can't believe it got beepe! Okay, it looks like the rotor that Mazda puts in the RX8. Invented by a German name Felix W A N K E L. Kind of a triangle with curved edges. TIA

[DavidButz]

Peter, Yes, I was just eating supper,and started laughing when it dawned on me why they beeped it (in British slang, what every lad does, and few admit). I had answered question #1 by down-loading an arbitray tool from the Sandvik site, but couldn't find the equation for the tri-lobe profile without paying ISO for it. Anyway, I tried an arbitrary Curve-by-Equation curve, and, sure enough, it would not extrude, BUT if I created a new curve and simply copied the C-b-E in Sketcher, it did work, IF that was your issue. BTW, what is the Equation? David

[PeterBrown]

http://kotuha.com/file/qQ7Vk-22.html

[DavidButz]

Peter, The attached was created using an arbitrary test Curve-by-Equation, to wit: r=(sin(t*1080))/8+2 theta=t*360 z=0 Created a Sketched Curve to copy the C-b-E, Extruded, and added Draft. Hmmm? Wonder if this would be useful as a UDF. David

[PeterBrown]

Hey Dave, Shape looks right but the equation you're using has me. If Dm was 28mm and e=0.9? TIA

[PeterBrown]

[DavidButz]

Peter, My equation was just meant to be a rough stab at the shape; I still don't have the proper info. Couldn't make sense of your link in the earlier post as far as accessing what we need here, and the image you sent in the later post doesn't show. You must have been trying to give me the info, 

[DavidButz]

In other words, I didn't know what to do when the link took me to Kotuha, which I haven't used before. Tried to Browse for your file, but had no luck.

[DavidButz]

Peter, Need my eyes examined; 10th time was a charm; I now have the jpeg; let me see if I can figure out how to translate it into the necessary t-parameter equations. David

[DavidButz]

Peter, OK, here it is per the correct formula, except that I arbitrarily made it 18mm high with 5deg draft, not knowing what those two values should be. The formulae to create the curve using the parametric method were as follows (remember it evaluates continuously from t=0 to t=1 and then stops): x=14*(cos(t*360))-1.8*(cos(t*720))+0.9*(cos(t*1440)) y=14*(sin(t*360))+1.8*(sin(t*720))+0.9*(sin(t*1440)) z=0 David

[DavidButz]

Peter, Thanks for the email clarifications; I see that the height should have been 24mm, and the angle that common one known to the man-on-the-street, namely 1deg26'21" (1:40). David

[TimBrotherhood]

All, This type of rotary engine uses an epitrochoid shaped housing and Reuleaux shape piston. The piston can easily be drawn with a compass. 1. Draw an arc. 2. Move the compass point to a point on the curve and draw another arc. 3. Move the compass point to the intersection between the two arcs and draw another arc. The area inside the three curved arcs is the rotor shape. Wikipedia has a fuller description. As an aside, the Reuleaux shape works as a perfect roller because it has constant diameter. The UK 50 pence piece is based on the same principle but with 7 sides. Cheers Tim[/img]

[PeterBrown]

Tim, True - the Mazda rotary engine uses a Reuleaux triangle. The Capto, while sort of similar, is a polygon curve. I only described it as such because it was easier to convey since the Mazda is more widely known. Regards

[DELETEME]

"Peter Brown" wrote:

Tim, True - the Mazda rotary engine uses a Reuleaux triangle. The Capto, while sort of similar, is a polygon curve. I only described it as such because it was easier to convey since the Mazda is more widely known. Regards

[PeterBrown]

 The Reuleaux triangle is comprised of 3 constant-radius arcs - you could draw one with a compass. The Capto is a polygon curve where the radius is constantly changing along each of the 3 lobes. Pete ps. 

[DavidButz]

Besides, if we want to follow the ISO standard, we want to use the equation and it's parameters, not a series of arcs. BTW, if you are doing a lot of these, especially if using some of the different nominal sizes, a Family Table UDF could be very useful. A special start part wouldn't be bad either. David

[PeterBrown]

Dave, I tried the equation but the feature fails. Also tried changing the accuracy to absolute and it still won't generate the curve - can you double check it? TIA

[PeterBrown]

Ah, the csys system is Cartesian, not cylindrical......... Thanks, Dave