Arcs and splines on points

[Anonymous]

Hi,

I've been using turbocad for a while, but after poor service and support from them a friend of mine recommended trying out Fusion 360. 

Hope you guys understand something of what i write.

I build skis and i'm currently trying to learn fusion by drawing some of the skis i make. 

The skis i'm drawing now is 182cm with the dimensions (in mm) 133-98-113, and a radius of 21,5m. The center of the ski is at 55% of the skis length, so it's situated at 100,1cm at the 98mm point of the ski. It's really important that the midpoint of the ski (98mm) is exactly on 55% or the ski will become unresponsive when skiing. So, to the problem; When i use either the spline or 3 point arc between tip-tail-mid, the curve of the arc/spline on the midpoint continues behind/below the midpoint making it narrower and offsets the midpoint about 5-6cm. Which will make a huge difference in the skis behaviour. I want the narrowest part of the ski to be at 55% and for the curve to "lift" from that point to the tail. I can somehow use the spline and adjust the tangent to make it"right", but the geometry of skis is quite sensitive to small changes regarding radius and sidecut. Any help or tips will be much appreciated!

Cheers!

[SaeedHamza]

Hi,

according to what I see here, your problem is that when you try to set a 3-points-arc, the arc starts going down a bit from the middle and then goes up

if that is the case it can be solved by carefully adding the 3rd point which decides the point on the arc

and that will give you a clear start from mid point up, and as you said, it's a lot better than adjusting a spline

like this :

please let me know if I misunderstood

Regards

Saeed

[Anonymous]

Thank you for the reply. If i understood you correctly, i would be drawing two seperate 3 point arcs from tip-mid with a point in between them and another arc from mid-tail with a point in between those again. I tried, but it creates a bit of an angle at the midpoint where the arcs meet, which is not optimal. And it's hard to set the correct place for the 3rd point, to get the correct radius. Could the problem be that the radius between the tip-mid and mid-tail is different, that the problem lies there? And the midpoint is closer to the tail than the tip? 

And as a follow up question, when i draw an arc the radius appear at the bottom right. So it says 2.692E+0,4mm, does it mean that the radius is 26m? 

[davebYYPCU]

I am following your description, my sketch is telling me that a 21.5m radius arc, is not fitting the geometry.

Both arc need to be tangent from the 55% line, both arcs will be different radius, and i have got the following result.

With 133 line, a 28640 mm Front arc to the 98mm line at 55% to the rear, then 44710 mm arc to the 113 line at the rear.

[SaeedHamza · Accepted solution]

No it is one arc

This is what I meant by the 3rd point

[Anonymous]

Thanks a lot! I don't know if i understood you right, but i somehow managed to get the arc going upwards from the midpoint. When i got the stapled line that indicates the length between tip and tail when using the 3 point arc, pointing upwards, the arc came out perfect. When the stapled line indicating length showed under, the arc came out wrong. 

Anyways, thanks for the quick replies. And regarding the radius, the widest parts of the tip and tail is drawn towards the center of the ski. So the actual effective length is 142cm, which will come out around 21,5m radius between the tip-mid and tail.

Cheers guys!