Hi everyone,
Is there a way to use a arc blend function with fixed radius, so when drawing curves for pipes I would get a straight line between the radius? This would be very handy when drawing pipes. Or some kind of a auto routing system as Solidworks and other cad programs have?
Best regards
Bjørn H
Hi Bjorn - there is nothing in Rhino secifically for piping, though there may be plug-ins available on Food4Rhino.com. If your radii are all the same, you can make a polyline and FilletCorners when done…
-Pascal
Hi Pascal,
Yes usually I use the fillet corners when done, but in some or I would say often cases I want the bend to start at the flange without having a piece of pipe before bend. To do this I have to make a circle first and then use the tanget from curve tool. This can sometime be tricky in some cases. If you ad such tool in Rhino 8 it would be very helpful for those who draw a lot of pipes in rhino.
Bjørn
It might be simplest, for now at least, to make an extra starting or ending segment on your polyline and then simply delete the part of that segment that is left (ExtractSubCrv) after FilletCorners.
Also, @bjorn.hatlehol - in case it helps - you can, although the workflow seems a little convoluted, draw the polyline with the arcs included by switching between line and arc mode when drawing. Note that switching from arc to line is not very intuitive in that the line is only constrained to be tangent if you invoke the Length option, so it makes for a lot of option switching to make a polyline of any complexity.
RH-64686 Polyline: Constrain the line to the previous arc tangent
-Pascal
I also find the proposed tool as something that could make the design process more convenient. 
Added a file of DN500 pipe. Here is two fixed points were you want the bend to start at both flanges. For big pipes it is very important to use as little welded parts as possible since it usually takes up to 1.5-2 hours just to weld one seam. Have not found a plugin that could solve this kind of issues.
Bjørn
Hi Bjorn - so the problem is you need to start at the flange, you do not know where the polyline vertex will fall, correct? Presumably the arc comes off normal to the flange in all cases?
-Pascal
Hi Pascal,
Yes that is the case.
Bjørn
Hi Bjorn - if you come off the starting point with an arc, and you do not know the vertex location for the underlying polyline, but you do know the radius of the arc, how would you like to specify the direction for the next straight segment? By angle from the starting direction (the normal to the flange) ?
Also, is this a one-shot tool, you are looking for? By that I mean, arc from the start point > straight > arc to the end point, and you’re done, no need to continue drawing?
-Pascal
Hi Pascal,
It would probably needed to be a short polyline inside of the flange, since I guess you would need to know from what angle to arc from so you could do a kind of a curve blend with fixed radius so you would get this straight polyline between the arc. So yes as you write “arc from the start point > straight > arc to the end point” This would be amazing tool to have.
Bjørn
Hi Bjorn - So you would like to input start point and direction, end point and direction (direction can be derived from a plane, an existing line segment, two points etc) and arc radius, correct? and get the resulting arc-line-arc from that input? That should be possible.
-Pascal
Hi Pascal,
Yes, but how to do it I don’t know
Bjørn
I am thinking… I mean it should be possible to design such a tool, not that it exists now…
-Pascal
I am sure you will find a solution on this. Drawing pipes from curves in Rhino is very good and this is really the tool a lot of naval architects is missing. Ref. Discussion with my colleagues who is working in autocad who also has this problem.
Bjørn
This is exactly how I would imagine it to work.
Method if the end tangent vectors are coplanar:
Arc Blend Coplanar DC01.3dm (2.8 MB)
Direction lines are coplanar in a plane which is parallel to Cplane
Circles tangent to ends of direction lines.
Line tangent to the circles.
Note: The circle for each direction line lies on the same side of the direction line as the end of the other direction line.
Hi David,
This is how I usually do it if coplanar, but often the start and stop is not coplanar.
Bjørn
Hm, well, having directed all three of my remaining brain cells at this, I am not sure the problem is solvable in the general case. It looks to me like there might, in many or some cases, be an exact solution, but so far I do not see how, with the needed inputs, it can be found from arbitrarily oriented lines. I’ll ask a bigger brain.
-Pascal
I’m sure when all McNeel’s brains come together, they’ll find a very good solution to this. Wish you good luck .
