Question Milling underside of project from Fusion 360

I've created a project in Fusion 360 that involves milling both sides of a piece of wood. Up until now, I've only milled the top side of projects.

In fusion 360 it seemed that I could easily design a tool path for the underside by changing the tool orientation z-axis to be able to approach it. The problem arises with the stepcraft post-processor not liking the produced data.

I imagine this is a common requirement, so there must be a simple way to work around this.

Is anyone able to help with this, or point to where it's already been discussed?
I'm fairly new to Fusion 360, but have had success with simple projects and self-learning so far.

Thanks!

Ben
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resulting G-code excerpt with error codes:
Information: Configuration: STEPCRAFT UCCNC
Information: Vendor: UCCNC
Information: Posting intermediate data to [snip]
Information: Total number of warnings: 1
Error: Failed to post process. See below for details.
...
Code page changed to '1252 (ANSI - Latin I)'
Start time: Friday, August 18, 2017 3:09:44 PM
Code page changed to '20127 (US-ASCII)'
Post processor engine: 4.2.1 41465
Configuration path: [snip]\Autodesk\Fusion 360 CAM\Posts\stepcraft uccnc.cps
Include paths: [snip]
Configuration modification date: Saturday, August 12, 2017 11:31:52 PM
Output path: [snip]
Checksum of intermediate NC data: [snip]
Checksum of configuration: [snip]
Vendor url: www.cncdrive.com/
Legal: Copyright (C) 2012-2017 by Autodesk, Inc.
Generated by: Fusion 360 CAM 2.0.3253
...
Warning: Work offset has not been specified. Using G54 as WCS.
Error: Tool orientation is not supported.

Sorry - soon after posting this, I discovered the solution.
I needed to make a second setup, and leave the tool orientation alone.

If anyone else is trying to solve this problem too:
Rotate your view of the model (shift-middle mouse button press, move the mouse)
When it's oriented in the desired position, create a new setup, then proceed as per usual.

forums.autodesk.com/autodesk/attachments/autodesk/2070/2567/1/09_CAM.pdf
page 27 references this.

Sorry for the unnecessary post, and perhaps this will help someone else.
Ben

I've been using Vectric Vcarve Pro for this, which works well, and has some specific features for double-sided milling that are really nice. Unfortunately the software is pretty pricey. I made a dedicated backboard, with nylon 30mm M8 set-screws (hot) glued into to it in such a way as only the threaded portion sticks through the MDF backboard. "Blanks" were then cut to shapes that are symmetrical in one axis only, which are then temporarily bolted down onto the backboard with nylon wingnuts. Nylon is used so that if a toolpath goes awry, and cuts through the bolt or wingnut, it won't do the end-mill a mischief. Obviously colliding with a steel bolt etc would pretty much write off most endmills. The blanks have 7.85mm D holes in them that match the positions of the M8 backboard threads, as a fairly tight fit, ensuring maximum accuracy.

Pic attached shewing the principle. Once you've done one side eg "top", you simply flip it, and run the "bottom" toolpath generated in Vectric Pro. I have read elsewhere of people using wooden dowels, but I find the nylon wingnuts/set-screws a slightly better proposition. Making the blanks/backboard is extra work, but I fear without it, you'll find double-sided milling profoundly frustrating.

Interesting setup - thanks for the suggestions!