Additionally some machinists believe that the number refers to the maximum size cube that can be machined on the shaper. In this case a 7 inch shaper could then be relied upon to completely machine a 7 x 7 x 7 cube. Although I have never seen this definition in any shaper manuals or text books it does seem pretty accurate. In this case the conservative rating is necessary because if you need to cut a cube 7 inches then you better have a stroke somewhat more then 7 inches.
I doubt that many large shapers would have a vertical travel with their tool slide equal to their ram stroke. In order to cut a 7 x 7 x 7 cube you would first have to cut the top. Then flip it 180 degrees and cut the bottom. Then flip it 90 degrees and clamp it to a good angle block, et cetera. Most shapers do have sufficient vertical travel of their tables to machine the side but that is not an accepted procedure.
At last we get to the horizontal travel of the table. Every shaper I have seen has more horizontal travel than ram throw. That may not be true for all shapers. If you know of some exceptions please let me know the details. This large horizontal travel in combination with the conservative rating of the stroke gives you the ability to machine a 7-inch cube on a 7-inch shaper.
Perhaps more important than the raw capacity of the shaper is the fact that all shapers (that I know about) have the ability to true their own tables. If you know of any that can't please let me know. This is a fascinating capability that is unparalleled in the rest of the machine industry. A lathe can't true it's ways. A mill can't true up it's own table (well not very precisely). But a shaper can take a cut across it's own table.
This is something you want to reserve and use it only when absolutely necessary unless you have a large stock of replacement tables. This allows you to semi-permanently mount an auxiliary table on top of your table. In this auxiliary table you could have several handy holes tapped. You could true it up to be nearly perfect. It could be a combination vice and mounting plate. As my grandson would say - "It could happen!" Looks like a good application for that half-inch slab of aluminum plate you've had laying around for the last few years waiting for just the right project.
Keep sending email with questions and interesting shaper stories.
My email address is KayPatFisher@gmail.com.