Kevin J has some solid advice. I had the advantage of learning about shapers from some old hands (some were a few digits short) back in the 1970's. We used a Tegle and Sonner shaper, with a 150 lb flywheel, so even a major accident did not slow it a bit.
Most of our cutters were notch edge 'shaper' steel knives that fit into grooves in the upper and lower discs - one had Allen screws for adjusting knives in or our, and one collar had a bearing that the stock could ride against. All these knives were hand ground, using the squint and spark method, so profiles were not matched, even if you could adjust them as close as you could.
The best advice I ever got was to 'hold it on 3 sides" - table, fences (or bearing) and feeder (or pressure bar). This kept you on track and if during a set up you realized you did not have 3 means of support, you could stop and re figure, adding that third side. The big shaper had an overarm hold down that was firm but had some give, so you could adjust for a really firm hold down, or something light and hardly holding it down at all. This overarm had a block of wood screwed into it, so you could even run it into a running cutter to get good coverage. The block was between you and the cutter, about 2" thick, 3" wide and 10 -12" long. It was to be placed so that the stock was well under the block/hold down before the cutter, and same on exit.
When we finally got a 3 wheel feeder, it replaced the overarm, but the function was the same. 52 years in the shop, and I have never had nor seen a shaper accident involving blood.
One thing we use a lot of is pressure bars. A 1'' x 2" pc of hardwood, the length of the table or fences, with blocks at each end. The blocks hold the 1x2 away from the fence but close to the cutter, parallel to the table, same thickness as the stock. Clamping the end blocks to the wooden fences allows for increasing or decreasing pressure on the parts. Adjust until the parts are firmly held, but can be pushed under the bar. Wax may be employed. Starting out, it seems an easy push, but after a whole day, you will discover muscles you never knew you had. The pressure bars are great for slight curved to heavily curved parts - like arch top raised panels where the tongue rides on the bearing and the pressure bar holds it all down.
Another shop made item that comes in handy is a feather board. Shop made for length and strength as needed, these are clamped to the shaper table to hold stock up to the fences or shaper bearing. Often paired, one holds to the fore table, and a second holds against the aft fence. Again, adjustability is the key. But all that holding has a price. It can be exhausting pushing lumber all day. Gawd love the power feeder.
Kevin mentioned a power feeder was not much good on curved parts. We take off wheels to make it a one or two wheel feeder, and then we can wrestle the parts thru the machine. A commercial feeder maker has a one wheel curve feeder with a larger, spongier wheel that allows the wood to be manipulated as it goes forward. With our 3 or 4 wheel feeders, we do two wheels for lay down or stand up curve profiling - one before the cutter and one after. Curve brick mold at an 18" radius going thru in stand up mode with two wheels on the shaper works fine. But the complex set-up is time consuming (an hour to set up, 10 minutes or less to run), so it is best if we have several jobs to run while the machine and accessories are up and running.
And finally, at my first World Machinery Fair in 1973 in Louisville, KY, I met a machinery sales rep at a lunch counter, and we spent about 3 hours talking. Being off our feet and enjoying the food were part of it, but he talked about safety manuals and machines, lawyers and legal departments. He claimed that no machine maker would ever illustrate what the machine could do, since that would terrify a jury. The best machine designers could do was to state that all safety equipment, hold downs, and warnings should be strictly adhered to at all times. Of course, back then, advanced shop classes were common as were shops that would take the time to find talent and train from there.
I want to stay as close to the edge as I can without going over. Out on the edge you see all kinds of things you can't see from the center.
- Kurt Vonnegut