Lathe material unsupported how much?

[pcd]

I run a repeat job where I chuck a 6" length of 3.5" diameter bar and salami slice it into wafers. A 12" blank is too long even though that's only about 3 diameters unsupported. Turning or facing is easy at 3 diameters; parting is not. The only reason I do it this way is that I don't have a saw that's good enough to make really thin burr-free wafers.

Your part is thick enough that it would be easy to saw blanks. Either pay somebody else to do the sawing or get a used automatic bandsaw like @EmGo suggested or maybe an auto cold saw.

Parting 3" bar is troublesome and will leave a poor finish. Aluminum smears when parting and chatter will be a problem out at a few diameters. Your supplier that was finishing the back with a parting tool was probably doing it right at the chuck and may have been plunging the tool a few times offset along Z to avoid smearing from the chip rubbing against the finished face.

I just don't want to be leashed to it, feeling these pucks in.

You're going to be leashed to the lathe whether the blanks are 8" long or 0.8" long because an 8" blank will be done before you have time to do anything useful. Handling small disks will be less strenuous than 8" bars. The only way to not be leashed to the machine is using a bar feeder and a sub-spindle.

If you're feeling really cheap you could get a turret lathe. But then you'll be taking a shower in hot chips for 3-4 weeks.

I would love to get a dual spindle Y-axis lathe.

How would a Y-axis be useful?

I then will have to manually deburr the backside center through the hole from the part off op. But if this would work, it's a one op part.

Deburring is a 2nd op. I guess a drill press next to the lathe for deburring might be not so bad.

If you go the sawn blanks route an automatic door on the lathe might be a good investment. A cheap thing to make life easier would be using diamond inserts with laser chipbreakers. They eliminate bird's nesting without having to resort to excessive feed.

 

[eKretz]

I run a repeat job where I chuck a 6" length of 3.5" diameter bar and salami slice it into wafers. A 12" blank is too long even though that's only about 3 diameters unsupported. Turning or facing is easy at 3 diameters; parting is not. The only reason I do it this way is that I don't have a saw that's good enough to make really thin burr-free wafers.

Parting 3" bar is troublesome and will leave a poor finish. Aluminum smears when parting and chatter will be a problem out at a few diameters. Your supplier that was finishing the back with a parting tool was probably doing it right at the chuck and may have been plunging the tool a few times offset along Z to avoid smearing from the chip rubbing against the finished face.



You're going to be leashed to the lathe whether the blanks are 8" long or 0.8" long because an 8" blank will be done before you have time to do anything useful. Handling small disks will be less strenuous than 8" bars. The only way to not be leashed to the machine is using a bar feeder and a sub-spindle.

If you're feeling really cheap you could get a turret lathe. But then you'll be taking a shower in hot chips for 3-4 weeks.



How would a Y-axis be useful?

Your part is thick enough that it would be easy to saw blanks. Either pay somebody else to do the sawing or get a used automatic bandsaw like @EmGo suggested or maybe an auto cold saw.



Deburring is a 2nd op. I guess a drill press next to the lathe for deburring might be not so bad.

If you go the sawn blanks route an automatic door on the lathe might be a good investment. A cheap thing to make life easier would be using diamond inserts with laser chipbreakers. They eliminate bird's nesting without having to resort to excessive feed.

Depends on the lathe, or possibly the tooling setup, I'd guess. I don't think it's the material you're having trouble with in that scenario, personally. It's the machine rigidity or tool setup. I've parted both aluminum and steel at way farther than 3xD with no issues, but that was with a stout machine and with bearings well adjusted.

 

[pcd]

I've parted both aluminum and steel at way farther than 3xD with no issues

Do you have any photos of the finish on the face of the drop from a 3" steel bar that you've parted >9" from the chuck without a steady? How was your insert life? Was it a quick and worry-free operation that you'd want to repeat all day?

I agree that it's the machine / setup rather than the bar itself flexing.

 

[MwTech Inc]

Dumb question....possible to use lathe to make the pucks?
Is there a parting blade that would work just to knock them out quick and not worry about finish?
With a bar puller seems it may be faster than sawing?
Then, I agree with EmGo and do a 2 op for the nice finish.

 

[eKretz]

Do you have any photos of the finish on the face of the drop from a 3" steel bar that you've parted >9" from the chuck without a steady? How was your insert life? Was it a quick and worry-free operation that you'd want to repeat all day?

I agree that it's the machine / setup rather than the bar itself flexing.

Nope, sorry. I'm mostly out of the shop these days, and I certainly never thought to take pictures of a parted off bar end... I've done it plenty of times on older U.S. made manual machines, which are, granted, probably a heck of a lot stiffer than most CNC lathes. And yes, very smooth cutting, quick and easy (with full flood coolant). What width cutoff insert are you using?

 

[bigjon61]

If you can barfeed it, sawing and chucking parts should be a last resort. Depending upon your requirements of surface finish on the back side (which, judging by your picture isn't great) you could run a second op after cut off. It makes no sense to saw and run two operations if you have the machine capacity.

 

[pcd]

Nope, sorry. I'm mostly out of the shop these days, and I certainly never thought to take pictures of a parted off bar end... I've done it plenty of times on older U.S. made manual machines, which are, granted, probably a heck of a lot stiffer than most CNC lathes. And yes, very smooth cutting, quick and easy (with full flood coolant). What width cutoff insert are you using?

Good to know. I use a .122 GTN on that job.

So, are you saying that the OP should buy a lathe with less than 3" bore and salami slice 1' blanks?

 

[r1xlx]

auto saw and chucking auto lathe is probably best and fastest for mass producing these.
deep parting off is ok if the bar is gripped properly in perfect fitting soft jaws.
I used to part off and trepan out all sorts of metals on old turret and capstans.

 

[r1xlx]

Sandvik Coromant

www.sandvik.coromant.com

Coromant can go through a 100mm bar.

• First choice for parting off Diameter: 38–160 mm (1.5–6.3 inch)Cutting widths (CW): 1.0–8.0 mm (0.04–0.315 inch)

 

[eKretz]

Good to know. I use a .122 GTN on that job.

So, are you saying that the OP should buy a lathe with less than 3" bore and salami slice 1' blanks?

I didn't see myself say that. Did you?

 

[3DM]

@Ox Great info; thank you. It makes sense that the part of the blade can be used to chafer, etc. I will have to try it out to learn more about it. Thank you for the tips on holding the parts pryer to the full part off. Snapping them off or a quick whack with a soft-blow hammer is great. I do that now for nesting small laser-cut steel parts that all have the same forming. Form 10 parts in one press, then snap them apart, touch on a green wheel, and done.

@EmGo That makes total sense. The half-pound part dropping inside the lathe does seem wrong. We may just end up doing just as you described and handloading with two back-to-back Ops. Good time for a robot on the lathe. (not for $30k all in). An automated cold saw would be nice in-house, but paying that $1.25 per cut to make the pucks may just be what is needed with the metal vendor for now.

I sure appreciate the info, everyone. CNC Lathes have just evaded me all these years. I turned cranks a few times and hand ground tools in JC machining classes in the 90s, but that's it. I make all my proto-round stuff on my mill; it does fine, but clearly, it is not a production solution.

 

[3DM]

How would a Y-axis be useful?

For this job - not at all. But if I am talking duel spindle, then at that point, I will want the Y-axis for other jobs. For now, I don't have the budget for what I want. I have to get what I can afford. I'm just not willing to take on another machine payment the month after I paid off my mill! I can limp along with some older, slightly clapped-out tools. I have to learn how to drive it. Like my first car I learned to drive on, it took hits and crashes and only cost $1200. Rather, I learn from the old tool, so when I replace it with a fancy new one at some point, I can operate the new machine with some experience.

Deburring is a 2nd op. I guess a drill press next to the lathe for deburring might be not so bad.

If you go the sawn blanks route an automatic door on the lathe might be a good investment. A cheap thing to make life easier would be using diamond inserts with laser chipbreakers. They eliminate bird's nesting without having to resort to excessive feed.

Correct deburring can be an op2. Yes, a drill press next to the tool is good old-fashioned operator-side work. I like @Ox idea of pre-chamfering with the threading tool prior to part off.

There are no auto doors on the lathes I am looking at, but there is nothing a 40" stroke air-actuated cylinder could not handle as long as the door was not janky to open/close. The door could be opened with a trigger inside the lathe with a tool and closed with a foot switch. It would be total booty fab, but it would probably work fine. The age of the tools I am looking at does not have door locks!

As for a future nice lathe, I honestly think a robot makes the most sense. Large part loading/unloading + flipping, so no second spindle is needed. Meh, for now, I need to focus on the now. Another good reason for getting some old things is to learn what I really need in the future versus guessing now. It's kind of like some large company where someone in an office buys the machine for the guys in the shop to use since they liked the color or the salesperson was attractive. Vrs. just letting the guys who actually use the thing pick out the new tool that will do the best job.

 

[EmGo]

paying that $1.25 per cut to make the pucks may just be what is needed with the metal vendor for now.

If you think about this a second - I used to charge $60/hr. That's gone up I am sure. But even at $60/hr that's two minutes and doesn't count the cost of the inserts or holder and figuring out how to catch the part and experimenting to find out just how far you can stick out, what to do about the shitty finish, bla bla bla.

If it's really $1.25 each to have them sawcut, looks cheaper and better to me. Quote it on the basis of partoff then have them sawcut, you can make a profit on someone else's work, mwa ha haaa.

btw, since you said you are new to turning ... I loves me them knux'es. Good to have at least a right and left holder and one box of inserts in your cabinet. Them's some good inserts for any time you want positive rake.

 

[Houdini]

We ran some similar 3" 6061 with a LNS bar feeder and 3' bars, machine didn't like 4' bars as well.
part off looked fine. 1/4"NPT
parts were heavy and would dent each other in the parts catcher, put a slider then conveyor on the parts catcher bucket. rubber lined everything.

The parts went on either end of a 3" x 12" clear acrylic tube,
looked like a penis pump.

So I called them that, eventually over time all the new guys didn't know what they actually were, they all called them penis pumps.
Some thought that is what they actually were.
Gcode and files said penis pump end caps

Owner HATED it, would get so mad, because no one knew what he was talking about if he said desiccant tube ends.
I got chewed out a few times, because he had to call them penis pumps so people would know what he was talking about.

 

[EmGo]

looked like a penis pump.

We made chalk sticks for the SF meter maids about once a year. No big thing, just a quick and dirty, make a few bucks. Aluminum tube, sqush one end and zap a chalk-holding thingy on it, put a motorcycle handgrip on the other end.

One year Mikey had a brainstorm and went over to the sex shop instead of Dudley Perkins, picked up fifty cheap soft dildos and used them for hand grips. The cops thought it was hilarious, not sure if the meter maids were quite as pleased. You'd probably go to jail for that now.

SF used to have a sense of humor

 

[???]

The age of the tools I am looking at does not have door locks

Whats a door lock, i thought that is where you keep a extra cable tie so you don't have to walk to your toolbox