Inventor HSM Rest Machining "Not Valid Toolpath" Error Fix

Rest Milling is an acronym for remaining Stock required to be machined. Rest tool paths only remove material left by previous machining operations. They do this by calculating what stock has been previously removed and comparing it against the finished model. This is far more efficient than re-machining the entire part with a small tool just to create a few small features.

Rest paths are calculation intensive. A good practice whenever possible is to use a tool whose diameter is slightly smaller than the smallest feature to be machined. This makes the rest calculations simpler and more effective.

remachining rest calculations hsm inventor

Autodesk Inventor HSM Rest machining using 2D pocket

I ran into an issue the other day with machining a 2D pocket with a DIA 12 flat end mill as shown below and leaving radial stock of 1mm to finish off with a smaller tool.

remachining rest calculations hsm inventor 2d pocket 1mm

After the first 2D pocket I duplicated the command in the CAM browser and edited it by changing the tool to a DIA 8 flat end mill for removing the remaining stock left by the previous operation. On the geometry tab, I used the rest machining option and inputted the tool size for the last cut. Tool diameter was 12mm and tool corner radius was 0mm as the first tool was a flat end mill

remachining rest calculations hsm inventor 2d pocket 12mm

To my surprise, it did not work as expected and when I selected simulate I got the message no valid toolpath. By right clicking on the 2nd pocket in the CAM browser and selecting generate toolpath I was greeted with another dialog box the selected operation has a valid toolpath. Was I doing something wrong or is there a bug in the software.

remachining rest calculations hsm inventor errr valid toolpath

After doing a bit of research on the web, where there were a couple of people with the same problem and trying a few of the suggestions nothing seemed to work. I was not going to give up so I started playing around with some settings.

The solution I found that worked for me was to add a 1mm radius to the corner radius for the rest machining option of the second pocket operation. Wow it worked! which seems quite strange as my first tool was a flat end mill.

remachining rest calculations hsm inventor corner radius

Must be a bug in Autodesk Inventor HSM that I just thought I would share with others who are experiencing the same problem. Below are the 2 pocket operations as I wanted them.

remachining rest calculations hsm inventor pocket operation

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