Can't find a way to lock 3 lines

[iuliancalin22]

There are 3 lines that are curved, those cannot change in any way, i tried using the lock with no success. The sketch is only half, but as soon as those lines are locked i will use mirror on everything. 

if you know a way to fully constrain the sketch please let me know. 

The sketch in question is "sketch3" 

Document is attached. 

[TrippyLighting]

Mirroring a sketch is a bad idea. Extrude the shape and then mirror the solid body!

Instead of haphazardly  dimensioning this, you could have simply used the fix constraint.

[iuliancalin22]

as i said, using the lock on the lines does not contraint the skech, i already tried multiple times

[TrippyLighting]

I had attached a model to my post. I am assuming that escaped your attention 😉

[iuliancalin22]

i did check that and it's not locked

usually when a sketch is fully contrained it has the red lock on the left side menu, and your example is not locked. 

also there are some dimensions that cannot change that's why i used dimensions to try and lock it. 

some of those dimmensions can change but not all 

[iuliancalin22]

ok, i tried something new and it worked but i don't really like that. 

taking the lock and drawing over everything locked the sketch. 

now, why is it better to mirror half body over the sketch?

[TrippyLighting]

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@iuliancalin22 wrote:

ok, i tried somaething new and it worked but i don't really like that. 

taking the lock and drawing over everything locked the sketch. 

now, why is it better to mirror half body over the sketch?

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When you mirror an entire sketch, you will add loads of constraints to the sketch. These constraints will have to be evaluated continually, which uses computational resources. So the simpler the sketch, the quicker your model is.
Also, fewer constraints means that a sketch is much easier to debug.   

Also ii is wise to start sketches that are symmetric at the sketch origin.

The reason your sketch is not fully constrained is because the tangent handles of the three splines you uses are not constrained. I personally would actually not constrain those. 

As you can see, all other sketch elements have turned from blue to white, meaning they are constrained.

While you will not get that red padlock icon, the sketch is constrined enough and should respond better to dimensional changes.

I you want to use splines and constrain them, I would suggest using a control point spline.  

Edit: even if you constrain the tangent handles you won't get the padlock icon.

I can say that there still are many situation where Fusion 360's sketch solver does not properly recognize a fully constrain sketch. They'll get there eventually (The Fusion 360 team that is), but it'll be a while.