Bob,
I like the idea of using a lathe dog on the bit and will have to get some dogs.
I am new to this machining stuff and don't know the right or best way to achieve an end goal. So given my experience and the size of my lathe what would be the best way / sequence to make large holes, in mild steel? Is using the toolpost the right place to mount drill bits? What maximum drill size before switching to boring? I have had problems getting a boring setup just right and find it easier to get it working when I start with a larger hole. Even with a 7/8" hole for boring start up it took me a few tries to get the tool undercut, height and angle just right. If there is a better way, I am all ears (well, eyes on the forum).
I seem to get rubbing and squealing quite often. I am starting to understand when something is not right and getting better at finding a cure but this will only come with more experience and helpful guidance from the only place I can get it, here on this forum.
RJ
Your description is good and I understand it. I will try joining the forum again. I have also tried to join Projects in Metal several times and cannot get on. They have a lot of G0602 info too.
It looks like my approach to making large holes may be wrong and there may not be a need for me to beef up the tailstock, at least not right away. I have a lot of other projects that need attention too.
If you use lathe dogs on your drills, grind a flat spot on the shank of the drill below the end of the flutes for the lathe dog set screw to bite into. When you want to use drill bits at the maximum possible size for the work and the machine, make sure the drill is in perfect working order, clean and dry Morse tapers without burrs and dings on the mating tapers (stone them down), properly ground with sharp cutting edges, equal cutting edge lengths and proper cutting and relief angles for the material you are drilling. You can use lathe dogs on Silver and Deming (1/2" shank) drills as well, mounted in a good drill chuck, but remember that the dog is taking a large percentage of the torque load, and make sure it is as solid a setup as you can make.
What is the biggest size? It depends, on many things. 6061-T6 aluminum is a totally different animal than hot rolled 4140 and some stainless steels. Tough metals are tough to machine, free machining metals are much more forgiving. The lathe also makes a big difference. What you can do on a 20" Monarch lathe is much different than what is possible on a small bench lathe, especially if it is well worn and loose as a goose. Rigidity is king, in machinery, tooling, and setups. Sharp tools make a big difference, too.
Import brazed carbide boring bars are often ground poorly, and the lower part of the carbide and the shank below can rub on the bore. Look for indications of rubbing. You can grind the steel below the the carbide pretty easily, but the carbide will need diamond grinding equipment to grind them properly. If you rotate a tool like that so the cutting edge meets the work at a slightly downward angle (negative rake), that often works OK and is an easy workaround if rubbing is an issue. Rotating the tool gives more relief against rubbing.
Edit: Watch out for good luck. Sometimes we can get away with doing something stupid for a long time before it bites us in the butt. But when it does, it can be expensive and can set back the confidence we have been building in what we are doing, making us gun shy and afraid to run the machine again, even possibly giving up the hobby entirely when something scary happens. When we are new to the hobby we need to be extra conservative with what we are willing to try. Study, learn, practice, talk to people with much more experience, and try not to do anything too stupid. We all do stupid stuff, but some of us learn from it, and work at avoiding problems in the future.
