“The cure for chatter on the tool in a keyway is just spending time fiddling with it in terms of speeds and feeds and lube (if any) and the tool rake.
“I have had chips just peel off silently (like a wood plane) when I finally got the right speed and feed and rake - and I think I put a drop of some mixture of machinist's "snake oil" such as kerosene + cutting oil 50-50 or some such. A sharp tool is necessary, since you've got to think of the tool as a slow-moving chisel, with no “blasting through at high speed”. As with parting on a lathe, you might also do a small sideways set of cuts with an offset of 15 thou to provide clearance to the side if you have a straight-sided tool. A slight "VEE" on the top of the tool would also work as a chip breaker or chip bender to drift them away from the sides of the cut. Old time shaper operators had "pet" tools for each job and kept them sharp - even touching them up with a pocket stone halfway through a job.
“Regarding the small sideways cuts. If you are doing a "plunge cut", the tool is the same width as the groove you want. This requires all the chips to be moved past the walls of the cut and out. In real life, a few chip bits want to jam between the tool side and the wall – galling, scoring, and perhaps chattering. The “VEE” profile idea is to make the chip a slight “V” so it is narrower - hence can escape. What I have used is not a true full-width plunge cut, but a series of slight sideways or zigzags as part of the down feed (shaper) or in feed (lathe) - if the chips do not come off the front in a nice curl. So for a 1/4-inch keyway use a 0.235 inch wide tool. Start your cut on center, go down perhaps 60 thou, or maybe to 100. Then shift sideways 5 thou for the next cut, then back the other way 10 thou for the next cut, etc. This gives 10 thou clearance for chips. A kind of rocking back and forth in the cut. You then have 5 thou left - call it 3 thou per side for trimming up the edges. It all depends on the material, lubricant, speed, feed and the machine rigidity.
“I found doing this with some of the CNC programs to make a plunge cut with a milling cutter also works. Sort of like the Panama Canal terraces in miniature. Then doing a final pass along the sideways surface to true it up. The cutter does deflect a little, so you end up with a slight slope in the wall unless you make a couple of passes.
“The shaper has chatter caused by alternate compression - release waves between the tool and the work making ripples and chatter. This is machine rigidity and “speeds and feeds” stuff. A minimal front rake, say 2 degrees acts as a "stop" for the sudden “in-plunge” of the tool since it actually rubs against the work. Of course, you then get some burnishing or work hardening. So too little front rake is not an optimal method but still might solve the chatter problem.
“Chatter big enough to see and feel is usually parts sliding up and down at the mechanical level. Noise ("squealing") chatter is more the workpiece and tool vibrating (at a few kilohertz and up).
“The geometry of the "gooseneck" tool, where the cutting edge is behind the front surface of the clapper box, allows the tool to vibrate at much higher frequencies, resulting in a smoother surface. If you have a contact microphone with a good high-end range, you might put it on your shaper tool and get the frequencies.
“My own guess is that the gooseneck style has a slight lift-away to the back as it digs in, and the return speed is perhaps 10 times or more of the forward speed.
“This results in the tool actually traveling at, 400 feet per minute over the 3 thou of travel. So the tool is "buzzing" like an ultrasonic engraver. The old-timers "tuned" the tools by length and also clamping pressure, which I think shifted the frequencies. This was all “cut and try” stuff back then, but I suspect the tool-vibration issue is what helps to make some of those wonderful glass-smooth cuts a shaper is capable of.
“The empirical approach of the old-timers was such that the "master craftsman" had his little trade secrets, which thus made him more valuable to the company. A newcomer to the shaping department soon learned that it was not as simple as it looked and the old-timers would dole out a tip or "secret" one at a time to the individuals they liked and wished to stay in the department. The ones who didn't get the tips soon were fired or transferred.
“The ones who ran shapers in shops got their tooling "tuned" and optimized for the material at hand. The amateur who sets the work in the vise and selects a lathe tool and starts cutting is far from optimal. This leads to all the horror stories on how difficult it is to get a good cut with a shaper. It is machine, material and tool geometry specific. There is a learning curve for each cut.
“A part of the shaper operator's toolbox should be some samples of workpiece materials (scrap) to set up the tooling first and do a few trial cuts. That beats spoiling the one and only part, and in the case of the model engineer who has a casting from a defunct supplier, reduces anxiety. Always do your shaper setting and tuning on a scrap bit of material first (or on a hidden portion of the actual workpiece).
“Recall, too, that the shaper speeds are low, almost off the bottom of some of the charts for speeds and feeds for HHS and Cobalt, etc. These are low speed, heavy feed environments. No place for carbides!
“I have often been discouraged with my shapers when I try this, and that, and then this, and then that - making scrap. However, once you do get the right combination, remember it and note it so you won't have to reinvent it the next time.
“Lindsay's South Bend book “How to run a Shaper and a Drill Press”... page 14 is figure 31A showing a roughing vertical cut with two or more finishing cuts (at presumably finer feeds)... the text is on page 21. What I was describing is the same idea with the vertical roughing cut. If chatter occurs - just cut the bottom on one side, then the other side as part of the roughing procedure and you could shift the table the 10 thou or more and do three or four down cuts, then shift it the other side and do a few more down cuts.
“Home Shop Machinist had a short article a few years ago on a massive shaper tool which was very stubby - like your thumbnail sticking out from a big clapper. It was reported to make a smooth cut.
“Shaper tool philosophy and design seems to go between the long slender tools to the short stubby ones. Each for a purpose and style of cutting.”
Thanks, Jay, for that great explanation.
Keep sending email with questions and interesting shaper stories.
My email address is KayPatFisher@gmail.com.