Hi
_Connect not works by Arc.
ExtendArcsBy=Arc works same as a Line.
Why it is happened?
Bug?
R5 sr13
Seems to work here… Are you sure your curves are both arcs?
–Mitch
Can you post the arcs? --Mitch
uploaded arcs.3dm
Where?
Sorry
it is here
arcs.3dm (361.4 KB)
Ok I see.
I assumed that the _Connect by arc has to work same as a _Extend by Arc
_Extend
Type=_Arc
Any idea?
No, the options in Connect simply extend either line or arc objects “naturally” to meet if possible. Simply use Extend>Arc on both curves past the point where they cross, then use Trim or Connect to trim them to each other.
–Mitch
Is it possible to make the automatic trim at the intersection?
If the curves are on the same plane, you can use Fillet with the radius set to “0”. This is still an extra step but quicker than Trim.
Connect is an alternative command to trim overlapping curves to each other. Connect and click on the parts of the curves you want to keep.
Thanks Nick and Davidcockey
This was useful information.
I did not know that these tools are able to work with intersecting curves 
I have written a small macro to a bit automate the process with curves having a break.
It is a pity that the _Flet and _Connect can not simultaneously select two curves completely. Then It would be possible to make full automation
Extend _Enter
Type=_Arc
Pause
Pause
Pause
Enter
Enter
Sellast
Trim
Pause
Pause
Pause
Enter
SelNone
and
Extend _Enter
Type=_Arc
Pause
Pause
Pause
Enter
Enter
ConnectBoth commands depend on screen picks to determine which ends are to be filleted/connected. So a full automation such as window pre-selecting 2 curves and then calling the command is ambiguous- it will not know which ends to connect. It is possible to always connect the end points that are closest, but there will certainly be situations where the result will not be the end you want.
–Mitch
it is interesting.
Identify short pieces based on the intersection. And in the macro to use the trim for short
It’s real?