How do i get the perfect angles for welding?

You might want to try using math.rad

You typically want your angles in radians

Here is a simple example of what I mean:

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NonRadPart = Instance.new("Part",workspace)
NonRadPart.Anchored = true
NonRadPart.Color = Color3.new(1,0,0)
NonRadPart.Size = Vector3.new(10,1,10)

NonRadPart.CFrame = CFrame.new(0,25,0)*CFrame.Angles(90,0,0)

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RadPart = Instance.new("Part",workspace)
RadPart .Anchored = true
RadPart .Color = Color3.new(0,1,0)
RadPart .Size = Vector3.new(10,1,10)

RadPart.CFrame = CFrame.new(0,50,0)*CFrame.Angles(math.rad(90),0,0)

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Notice how the green brick is what you typically see as 90 degrees while the red brick is nowhere near 90 degrees.

If you check the orientation on each of the bricks, you can notice that the green RadPart brick has an orientation of 90,0,0 and the red NonRadPart brick has the orientation of 63.38, 180, 180.