View Full Version : Bike fork using Maya NURBS

02 February 2005, 04:17 AM
Regards all,

I searched the archives here as well as a couple other sites for this answer and only cam eup with a rhino tutorial I couldnt really apply to my current knowlege of the maya toolset. The motorcycle tutorials were not quite what I needed as the shape I am going for is more like a tuning fork with a single pipe that splits into two sections.

I am trying to model the front wheel fork of a bicycle using NURBS. I assume this is a loft option that forks into two branches. How would one accomplish this? Should I be looking at the birail tools instead?
I really want to accomplish this in NURBS and I want to avoid booleans and polys.

Thanks for any input you may have,

Scott Spencer

02 February 2005, 02:32 PM
so basically u want a Y shaped tube?

u can do this by making two objects, one for the V part and one for the | part. then place them over each other like u want, and "circular fillet" them with "create curve on surface" on. then just trim the overlapping areas and u get a Y shape, or a T shape or whatever. group them together and there u go...

hope that helped
03 March 2005, 06:05 AM
hey you could get shape in a number of ways
1 loft between three curves
2 b rail 3 tool
3 or extrude along a curve with a scale on it

03 March 2005, 06:59 PM
i think lofting would be the easiest way to make a fork.

loft the two main parts separately and than, bring them togther. after that you could use that as a base for the more detailed parts like the headsets....

03 March 2005, 05:17 AM
Thanks for the input everyone! I think I am going to try a birail or even more difficult a stiched surface. I am still not clear on how topology works in NURBS ie when and where you want isoparms to line up but I am learning : )

Thanks again all!


03 March 2005, 04:56 PM
Sorry to drag this one up again but I'm having trouble getting my head round the birail method of achieving this. How would you get the birail to actual split into two seperate 'tubes'?

03 March 2005, 06:53 PM
if using birail, i'd build in halves or quarters. if quarters, split Y left and right. build using four curves. 2 profiles. 2 rails. align your CV's at mirror locations to control tangency (or continuity) for later dup/attach.

select each curve and create an extrude surface away from the quarter fork. hide curves. now birail using those surface edges - but birail with continuity on all four [edit - should be "continuity on profile curves"]. might need to modify result by tweaking CV's. just stay away from mirror edges (the nearest two CV's don't move or you affect tangency). then mirror it and attach.

i use this same technique with regular CAD (birail=swept blend). except there's no tweaking CV's so there are more curves for control.

hope that helps.

03 March 2005, 05:15 PM
Thanks Csven, I half understand that. I don't suppose you have an image or even reference file I could have a look at?



03 March 2005, 05:23 PM
no. but i can whip out a quick sample.

03 March 2005, 07:50 PM
That would be much appreciated - please feel free to msm me if it's easier? I can host the file as well for other people to use if neccesary.

Cheers, Jules

03 March 2005, 09:25 PM
did a quick sample. ugly. but it might be helpful. includes the curves, the extrudes and a final shape. should correct myself re: above - you can only keep continuity on profile curves. the profiles here are the arc'd curves. rails are planar.

after creating the birail surface using the extrude surface edges (continuity checked for both profiles), i tweaked CV's, added isoparms, tweaked, rebuilt a couple times, and generally did what i needed to get something to duplicate. then i dup'd along Y-axis. attached the surfaces. tweaked a little more. arc'd the fork upward and then did a final dup along Z-axis. then scaled it a couple times.

i didn't pay any attention to alot of details i'd normally look at. aligning CV's and the like. it's really just the basic shape to help you figure it out. if you have a Square tool, you can control the continuity along all four curves.

i'm no master at Maya, so hopefully someone who is will come along and give better advice than i'm capable of giving. good luck.

03 March 2005, 01:44 PM
Hi Csven, Thanks loads for the effort! I understand it now. The reason I wasn't following was because I was thinking of a bike fork with an 'open' top. Ie a tube that pyhsically splits into two. I was thinking that this sort of model shape would be possible with birail but i guess not because you would always end up with a five cornered nurbs surface which i guess ins't possible with the birail tools?!?

Not sure if that makes any sense, but have attached a pic of what I was thinking.

Thanks again for your help


03 March 2005, 02:47 PM
in this case i'd trim this shape above the branch. it would need to go to a cylinder and tweaking CV's isn't the way to get that shape imo.

closest thing i've done to this was a mop ( i did in CAD. in that case the "Y" was cut out of the form. you could do the same thing here. loft from the fork up to a cylinder then trim away. and there's probably alot of other ways to do this shape. method probably depending on what element is most important and how creative someone gets in construction. i enjoy seeing how people model bc it's usually different than what i would do; and quite often i learn something i can incorporate into my process.

03 March 2005, 06:30 PM
I couldn't agree more, I wanted to explore the potential of birail to the full, and learn about how people use this tool, and what it's strengths / weaknesses are, i knew that trimming etc would be a way to zchieve this, just wondered if I was missing the something. Thanks a lot for your help, I'm very grateful for the time you put in.

Your work is mighty fine too.


03 March 2005, 03:16 PM

I was away from the thread a little while and some great info got posted! Thanks csven and Droolz!

I tried downloading the sample file and it appears the archive is corrupt. I tried twice. IUs anyone else experiencing this? Could you possibly upload it again?



03 March 2005, 10:14 AM
Hi Scott,

Hmm ... I can download and open the zip and file fine. I'm using maya 6.5., and I guess csven is too so that might be your problem if your on 6 or less. Not sure if you can do anything about that.



03 March 2005, 12:18 PM

I get an error from winzip saying it is an invalid archive before I even can unzip it. I am using winzip 8.1

What version of winzip are you using?


03 March 2005, 01:21 PM
version 9...guess give that a go.

03 March 2005, 10:40 PM
Same with 9 on 6 different computers. two different networks... Have you downloaded this file recently and it still worked? I cant imagine anything other than a file issue since I have tried on so many different systems and 2 locations.



03 March 2005, 10:39 AM
Very odd, tried it first thing - worked fine. Have re-attached it to see if that makes any difference.

03 March 2005, 11:51 PM
thats so bizzare... Same problem.

I dunno... Whats in the archive? Is it just a mb file? Could you possibly just attach that?
Sorry for the trouble.



03 March 2005, 09:50 AM
use firefox ( instead of iexplore to not get any corrupt-file problems

03 March 2005, 02:14 PM
Yeah - I agree I'm on firefox.... not allowed to upload attachments with .ma extensions...

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