Max stick-out for light facing cuts?

[tome9999]

I’m making a 4.8” long part and I am starting with a 1” dia steel bar, 3-4’ lg. Bar will be inside spindle liner behind chuck. I want stock to stick out of the chuck 5” and then take a couple light facing passes to clean up the end. I will then spot drill it (with a live tool) and bring a center in to hold it for turning. Is 5xD ok for facing as long as I keep the rpm down and a light DOC, ~0.010 or less? Im more worried about safety than about finish because most of the dia is getting turned down and there will be the center hole, but I want it to be better than the saw cut on the bars. I can face shorter and re-position but would like not to if possible…
-Tom

 

[wmpy]

You should be fine. I'm currently doing worse than that and getting away with it consistently. I get a little chatter but not bad.

 

[706jim]

5:1 stickout is pretty much the max. I tried a "light" facing cut on 7/8"SPS bar with about 5.25 stickout. Part climbed right up onto the tool.

 

[tome9999]

Thanks for the replies. I’ll give it try and see how it goes.
-Tom

 

[CITIZEN F16]

Just keep the RPMs down.

 

[Rogue_Machinist]

I do some sketchy work like this. But I always try to stay as close to the jaws as possible I know its not always possible. But usually 4xd is the max you want outside your jaws.

 

[guythatbrews]

I will then spot drill it (with a live tool) and bring a center in to hold it for turning.
-Tom

I agree with .010 cuts and keep max rpm down should be ok and sounds like it's through the chuck so you can't throw it out.

Why use a live tool for the center drill? Almost sure to wind up with center eccentric to some degree.

 

[tome9999]

I agree with .010 cuts and keep max rpm down should be ok and sounds like it's through the chuck so you can't throw it out.

Why use a live tool for the center drill? Almost sure to wind up with center eccentric to some degree.

Yes, it's bar stock so there will be plenty behind the jaws, if it bends it won't get thrown. My center drill just happens to be in a live tool holder because it was open. I guess I could put it in a static boring bar holder. I put a pin in a collet in the live holders (as well as the static boring bar holders) and tweaked them concentric with the main spindle, are you saying that even still live holders are going to be off center for some reason?

Thanks,
-Tom

 

[guythatbrews]

I put a pin in a collet in the live holders (as well as the static boring bar holders) and tweaked them concentric with the main spindle, are you saying that even still live holders are going to be off center for some reason?

Thanks,
-Tom

If I want a hole drilled on the axis of a lathe part I will usually use a dead tool.

Try thinking of it this way. Imagine your shaft is perfectly stiff (sorry!) And the center drill is perfectly aligned and stiff be it either live or dead. No worries everything will be concentric. But if a live tool is not perfectly aligned(more often the case than not) the center will be eccentric, perfectly stiff or not. But the eccentric (within reason) dead tool will cut a true center. Granted it's harder on the center drill but if the center drill is off a few thou TIR the center will still be pretty true, whereas the live tool will always be off.

Probably not quite that simple with a flexible shaft that can walk around the point of a dead center drill, but you get the idea.

If you've got a great machine and confident of all alignment probably ok either way.

 

[wmpy]

You should be fine. I'm currently doing worse than that and getting away with it consistently. I get a little chatter but not bad.

For reference, the job I'm doing now uses 13/16" diameter 416 SS material and is sticking out 6.5". This is a job that is running with a bar feeder (no operator), so it has to run reliably. There have been no problems after a couple thousand parts.

 

[tome9999]

I kept the rpm limited to 1000 and cut 0.010 and it worked just fine. No chatter and a good finish on the part, though that is unimportant here.
-Tom

 

[CNC Hacker]

If I want a hole drilled on the axis of a lathe part I will usually use a dead tool.

Try thinking of it this way. Imagine your shaft is perfectly stiff (sorry!) And the center drill is perfectly aligned and stiff be it either live or dead. No worries everything will be concentric. But if a live tool is not perfectly aligned(more often the case than not) the center will be eccentric, perfectly stiff or not. But the eccentric (within reason) dead tool will cut a true center. Granted it's harder on the center drill but if the center drill is off a few thou TIR the center will still be pretty true, whereas the live tool will always be off.

Probably not quite that simple with a flexible shaft that can walk around the point of a dead center drill, but you get the idea.

If you've got a great machine and confident of all alignment probably ok either way.

Good opportunity to run the lathe chuck and live tool in opposite directions simultaneously and drill. I do that when I can to get really straight holes on millturns.

 

[deltap]

Center drill first, then face end while supported by center.

 

[tome9999]

Center drill first, then face end while supported by center.

Haven’t ever done that. Seems fraught with danger to the center/insert if I don‘t get the center drill depth and center geometry perfect! But then again, that’s why we have precision machines
-Tom

 

[Mtndew]

Center drill first, then face end while supported by center.

And how do you propose the entire face gets machined with a center in it?