Trackpad excersise anyone?

ah sorry…

Im a bit better at edgesrf and sweep 2… but cant loft!! why cant i loft this shape please? you can see ive kept it super simple…

I can do a nice 1 rail or 2 rail sweep… but no loft

With loft, pick order and placement counts. You want to pick consistent spots for the three curves you are lofting, in the image below, spots 1, 2, and 3 would be an option. Before the loft though, you want / need to make your center line curve match the edge curves. I did this first by copy inPlace, and locking so I had a reference of the original, then using match on the two halves of it, choosing curvature and the merge option. I then look a look at the structure of curves 1 and 3, which are 6 points, degree 3 (changing their degree to 5 would make them single span, but that isn’t critical here, but not bad practice). Rebuilt the center line curve to match, point edit to get it back in shape, then loft.

Also, you have the line drawings available, so you can place them in the file so you can use them as reference and get your curves closer to the drawing.


None of this makes any sense unless you have done it before. Ive just spent 400 quid on classes taht im lost in… why cant

TRACKBAD.3dm (4.2 MB)
i even trim this now?.. Im despairing…
am i that stupid?? how did you all learn??

I need to take a break. sorry if im being stressul

By messing up, regularly and repeatedly, then asking for help. If you never have used tools like those found in modeling applications before, it is no surprise the tools are foreign and awkward to learn. It is not stupidity, but simply unfamiliarity as one would expect of any beginner. That is remedied with practice, learning lessons from failure.

If you keep at it, you will get there. At this point, every problem you are encountering is something brand new to you, so reasonably you don’t know how to approach it. Eventually, with increased familiarity, that will change.

If you don’t understand why someone has offered some piece of advice or technique, ask why. The why can be as informative, or more so, than the how.

As for your TRACKBAD model, is it not trimming on your side? Here it seems to trim OK. I would however encourage the loft approach, as it yields a clean result, and with correct input curves doesn’t need to be trimmed.

Thanks Sam,

Could you just explain both ‘loft’ and trim for me?

I dont understand for example why i need to match or merge. or even what that means. Im happy with my curves and I cant see whats wrong with them, what is wrong with them? how do they not match and merge?.. and why would be truing to do it. And in the loft in the taught manual it isnt clear what im actually trying to do… how do you actully loft? when it says … select curves to loft… which of my curves is it asking me to select? could be any of them… and ive tried all!
And with trim… I drew a neat line… as Pascal suggested… but the command in the excersises were 2d trims… how am I supposed to trim a 3d shape with a 2d line?..
sorry if I am embarrassing myself… but this is my only resource.

Loft is the most basic surface creation tool, Draw 2 arbitrary lines and then run loft. Add another and try it. You should see that loft ( normal style) will create a surface that passes rhrough the lines

One thing you need to know about loft is that it is important to pick the curves in the right order and important to pick each curve in the right place. This tells Rhino how you want the curves used to make the surface. You can preselect the curves and Rhino will guess how you want the curves ordered and arranged, but Rhino may guess wrong.
So with your 3 arbitrary lines you should be able to see how you get different surfaces depending on the order you pick and which end of each line you pick. So there are 6 different surfaces that you could get by lofting 3 arbitrary lines.

Here is a file showing how you can make something like this by lofting 5 curves in 4 easy steps. TRACKPADx.3dm (90.9 KB)

The purpose of inserting knots in step 3 is to create a flat bottom (it will be perfectly flat between the knots). if you don’t need that then skip the insert knots part.

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I see jim beat me to it, but I was almost there, so I’ll continue :wink:

Are you referring to Pascal’s TrackBallBody.3dm example? In his second step, call loft, and pick the curves in the order shown:

Loft is stringing a surface through all these curves, in the order you picked them, and in the direction you picked them. If you mess with the pick order, or the sides of the curves that you picked, you will see the outcome will be different.

Turn on the control points for the resulting loft, and you should see that there are not many points, 6 in one direction, and 5 in the other. It is so clean in Pascal’s model because his input curves are clean, and they match each other. They are all 6 points (they are also all degree 5, but we don’t need to worry about that right now). Curves being the same point count and degree is not a requirement for loft, or any other surfacing tool, but if you want to make nice, clean surfaces, it is something to pay attention to (if they don’t match, Rhino will make them all match the most complex curve in the set). Loft is a very basic surface creation tool, so if you pay attention to your input curves, you can get very reliable, clean surfaces from it. It takes any number of curves to work with, as long as the number is 2 or greater. The downside of this, as Mary pointed out, what you gain in simplicity, you lose in control.

What was happening in your TRACKPAD-VERSIONMILLION.3dm is that the curves were not really set up well for a loft:

The fillets on the edge curve, the edge curve being all joined together, and the center line curve being made up of two curves were the biggest problem. So you need to explode the edge curve (all curves in a loft need to match open / closed-ness, you can’t have a mix of some open some closed). What I was trying to describe with the match with merge option was a method of turning the center line curve from two curves into one. You could have just joined it, but then the loft result would be a polysurface (because Rhino has to rebuild this simpler curves to match the more complex one). The Rebuild was to try and get it to the same point count as the edge curve. That step was not required, but a recommendation to get the curve structure the same for all curves.

With trim, you can always trim a 3d thing (surface or polysurface) with a 2d line, Rhino will automatically project it for you. It is functionally the same thing as if before you called trim, you called Project, selected the trim curve as the thing to project, and projected it onto the thing you are trimming. The projection will always be in the current CPlane Z direction (both positive and negative, so it doesn’t matter if the curve is in front or behind the thing you want to trim). This is why Pascal corrected himself to say the trim needed to happen in the Front view, as in the Front view, the (projected) curve fully intersected the object to trim.


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Ah Sam… thankyou. So much information. really appreciate it. I love learning all this… Ill pay back all this attention when I get good enough one day! Im on another project for a bit but looking forward to having another attempt over the next few days. :slight_smile:

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