Sketching issue using fractions

[TPrice_71]

I have a problem with sketching. I went into  “preferences” and changed my settings from decimal to fractions. My problem is when I try to dimension profiles in my sketch, the profile moves around.

I made a quick screen cast to show you what I mean. I imported this profile from a vendor for a piece of trim molding. You can see in the video how the profile distorts as I apply dimensions. When I change the settings in preferences back to decimal, it no longer does this. I thought maybe it was a precision issue on the fractions, so I turned the value up with no change.

Any ideas on what could cause this?

https://knowledge.autodesk.com/community/screencast/d7c8ca82-e603-4108-870b-4f2bd6713bb3

[wmhazzard]

With no constraints on a sketch, that behavior is to be expected. Place a vertical constraint on the line above the origin and a perpendicular constraint on the top line and things should go back where they were. Of course you will need more dimensions and constraints to fully define the sketch. 

[TPrice_71]

Why does it not do it when I switch it back to decimals?

[demong]

Hi @TPrice_71 ,

I do not use fractions myself, but as an educated guess, I believe it is because the fractional mode forces rounding. When using decimals, that second dimension you made would have stayed at something like 0.618... in to as many decimal places as Fusion calculates. It appears with fractional mode, Fusion forces the nearest fractional dimension, 5/8", or exactly 0.625 in, thereby rounding up the dimension of the line and increasing it's length.

Similar behaviour occurs in fractional if you specify a different dimension from what is originally drawn/suggested. That all being said, I agree with @wmhazzard . This appears to be normal behaviour. The sketch just needs a host of dimensions and constraints to lock everything down.

Hope that helps,

Jon