ctwo wrote: ↑
Thu Apr 19, 2018 12:08 am
I think all we really need is a fast enough spindle.
Well, be careful!
I've had soft jaws release parts on more than one occasion, due exactly to the thing you suggested. If the jaws are heavy, and some of mine are, enough speed causes them to release. It's a strange thing to see a part slip while cutting--when you know it should be rigidly gripped.
I should make mention---if fragile parts are being machined, I tend to use very light chucking pressure, to avoid distorting the parts. That can include using broad jaws, which exacerbates the problem (greater weight, but less chance of distortion). Because I specialized in small work, it wasn't unusual to find my lathe running @ 2,000 rpm, even with my 3 jaw.
Anyway, sure for soft jaw applications and what you are typically working too, then I agree it gets much more critical.
Thanks for understanding. I realize that I often sound like I've lost my mind, but the world I served demanded exacting performance. The slightest thing would often result in unacceptable results. While the majority of it seems like overkill, if you acquire good work habits, tough work becomes routine. The guy who thinks "close enough" generally struggles when called upon to do tough work, so there's a huge reward in spending enough time in learning to do it right. The best possible lessons are learned that way.
Hard fixed jaws already seem to be compromise, and a lot of times I have a gummed up shim in there. There is some motivation to revisit that item - it's on my rotab now.
I agree that hard jaws are a compromise, a lesson I learned only when I was forced to use soft jaws for non-critical work. If I haven't made mention previously, my three jaw was sitting on the compound of my Graziano. I took my hand off it and leaned to pick up my air hose. Chuck rolled off and landed on the concrete floor, on a jaw, shearing the teeth. The scroll appeared to be unharmed, and has been in use ever since. This occurred way back in the late 60's, not too long after I purchased the lathe.
I inquired of the dealership if they could get me a set of jaws. They said they could, but in the mean time they had a badly used (or abused) set they allowed me to use. They fit poorly, although they did work. I was not impressed with their general condition, nor of their lack of concentric gripping, so I installed the master jaws and bored a set of straight through jaws. I was shocked at the results, so I decided to stick with them instead of the hard jaws. That was a respectable decision, as the set of jaws I requested from them never were delivered.
I am now so comfortable with the soft jaws that I rarely use the hard jaws. There are occasions where they fit the bill for a project, so they do get used occasionally. Mean time, I'm a died-in-the-wool user of soft jaws.
The rotab issue. Because I often needed my lathe when doing mill work, the idea of tying up my three jaw on my rotab wasn't acceptable, so I purchased a nice Rohm (with master jaws), which I used only on my rotab. A permanent base plate was made (about 1" thick aluminum) which mounts directly to the chuck and rotab. Do keep in mind, this was when I worked for gain. I am not the least bit critical of your choice, and would likely do the same thing now if I didn't already have the second chuck (which rarely gets used).
A spider isn't the best possible way to machine jaws, be they hard or soft. However, it is the fastest and least demanding of all systems. With one spider and three sets of screws, a huge range can be covered, while most other methods require rings and other devices in large numbers. It also eliminates the problem of not having on hand a component for the system you may use when you hope to make a quick setup. I use a spider and spend the necessary time (generally just a few moments) to ensure it functions as it should. For me, it was the best solution. I got tired of hunting for the just-right-size piece of stock that would load the jaws, and learned quickly that a spider allows for removing just a few thou from the jaws, so they enjoy a very long service life.