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CNC Lathe Options for Small Diameter Bar Work

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May 16, 2017
I am looking for options for cnc lathes suited for small diameter bar work. Most of the work I am looking to do is producing small volumes my own product. The primary parts are all custom configurations(1-3 pcs the same) within the a "family". This involves 440 or 17-4 stainless, turned OD (.125"-.5"), .375"-2" long, couple OD grooves, blind hole drilled 80% of the length (.025"-.30" ID) and a .010" smaller through hole. On the ones with really small drilled holes, the through hole may need to come from back after flipping or handing off the part to a sub spindle. Sometimes there will be bored profile in the id.

The priority is on minimizing operator setup and attendance time over cycle time. The goal is to be able to program and tool up 3-4 different parts and walk away once we are comfortable with running this family of parts. This way we can work on the next setup. Ideally I will figure out a set of tools that will work for most of these and can leave the turret full or maybe just swap some drills. I would be happy to leave the same .5" bar in the machine and just turn it down when needed.

The reason for bringing this low volume operation in house is to reduce lead times to a day or two. These parts will go on to get EDM'd details. This lathe may be used to produce electrodes in a similar manner, but I am still working out the requirements of what we will run for electrodes and if running graphite on this machine would be viable given our small volumes. Tolerances on electrodes would be a few tenths. I think i could come up with reasonably effective vacuum fixturing, but long term, things would be a mess. We will also produce other parts for our own use as it makes sense, but those aren't a strong reason for bringing this equipment in.

As far as machines I am thinking small slant bed turret lathe, collet chuck, sub spindle for pulling stock or maybe a bar feeder, tool eye, 5000+ rpm. For the small drills I might need some more rpm, those might need to be a live tool or in an air spindle. I would like to stay below $50K, so I am looking used.

This Hardinge seemed to tick a number of boxes, and seemed to be a decent deal, but sold while I was investigating the logistics: Hardinge T42SP super-precision CNC lathe w/ bar feed

Besides Hardinge, what should I be looking for? This will be my first CNC machine, point me in the right direction if I am out of line.
 
How many tools would you like to have in the machine at a given time?

If the number is 4-8, I would lean towards a gang tool lathe. They are quick, compact & cost effective

IME, especially with smaller tools/drills, the indexing of a turret is not always supremely accurate. We have mostly

hydraulic turret machines.

Maybe my machines are just kaput, but if i needed to drill holes as small as .01" I would definitely avoid a turret.
 
The number of tools needed would depend on how many different parts I was making. For a single part I could get away with 4-5 tools, add 2-3 more and I can get a second variant. Looks like there are tools you can mount to pull the bar, so a sub spindle wouldn't be required. A gang lathe is also probably better for turning electrodes as it is one less mechanism to fill with dust.

Setup would seems like it would be faster, but maybe need to happen a little more often. Can you work out all your offsets outside the machine with a height gage? How accurately do the plate mount in the machine? I could have a couple plates set up for various sizes.

Any particular models I should look at?
 
Unfortunately I don't have any direct experience with gang lathes. I'm sure someone else can who does can chime in.

But another advantage to gang lathes, is that you could make your own tooling block to suit your needs and swap out the

entire block rather than tool by tool. This could make your setups very efficient. Although it would be comparably

expensive. One draw back to gang lathes is tool interference. some times it can be time consuming and a pain to set up

all the necessary tools in such a way that does not cause a crash or interfere with other tools.

There are a lot of manufacturers that produce a gang lathe, I was looking heavily into a used Doosan Lynx 220G

a few months ago. But the job fell through and blah blah blah...

Just make sure whatever you buy that you have plenty of service/support.
 
Hardinges are good machines...I have four T42's but they are a large machine for what you are trying to do (42mm = 1-5/8" through hole) and would be at least 50% longer cycle time than a small swiss-style lather.

Aside from "sometimes there will be a bored profile in the ID" it sounds like all OD turning and on-center drilling, in which case $50k could get you a nice used 12mm swiss with 8 turning tool stations and four on-center drilling spots and a sub spindle to hold the parts while parting off so you don't have to worry about burrs/tits to deal with off-line. I bet you could even get one with a magazine bar feed to load bars for you automatically within that $50k. It might be overkill though for your short runs but I totally understand the importance of reducing set up time and having strong process stability so maybe not!
 
I'm wondering if a Swiss style lathe wouldn't be better for the parts mentioned.

However, if a conventional lathe is more to your liking, there are scores. If going used, it's quite literally, a buyers market. LOTS of decent machines in great shape for reasonable prices. If going new, it's a great time to buy as well, as machine capabilities, even standard 2 axis machines, have gone way ahead of what was available even a few years ago.

Granted, I'm biased as I work for a major tool builder in addition to being a shop owner. A six inch chuck machine with a Tool Setter, multi station turret or gang tool, and a high quality collet chuck would do you right, I think.

A 20 mm Swiss with multi tool stations would probably work better. Depends on your budget.
 
A Hardinge CNHC is a great machine for small parts and pretty flexible for tool set ups. They can be found in good shape for under 10 grand.

Make Chips Boys !

Ron
 
I mean, you're literally describing Swiss lathe bread and butter. You'd ALMOST be stupid to look anywhere else, except that a decent gang tooled lathe will cost 10% as much. If you can make it do what you want.

But seriously, that's Swiss lathe territory, they'll do the same small part, day in, day out, operator or no operator, and hold tenths, as long as your tools don't wear out (which is on the programmer).
 
Thanks for everyone's input.

I mean, you're literally describing Swiss lathe bread and butter. You'd ALMOST be stupid to look anywhere else, except that a decent gang tooled lathe will cost 10% as much. If you can make it do what you want.

But seriously, that's Swiss lathe territory, they'll do the same small part, day in, day out, operator or no operator, and hold tenths, as long as your tools don't wear out (which is on the programmer).

I know these parts are very well suited to a swiss machine. This lathe will be the first in my shop though, so I am concerned about the limitations of a swiss machine in terms of versatility. I am making a really small number of parts, generally each one unique. There is still an R&D aspect to what I produce and if I need to modify something, It would be nice to have a chuck to put the part in.

I think a swiss lathe will likely be my second lathe. I have some small core pin type parts that currently get ground that I think would run well on a swiss machine. No one wants to run 3 simple parts on their swiss for me, but the grinders are used to these quantities. There is a local shop selling a few late 90's early 2000's Citizen machines I am going to check out next week. If the price is right, I could go the swiss direction. I think I would still need to pick up a lathe or run electrodes on a mill (maybe reverse with the electrode in a tool holder?). I'm still working out my EDM needs. Graphite comes in 6" and 12" lengths typically, which don't think will work well on a swiss machine.

For a CNC chucking lathe, it seems like I should be looking at 42mm/6" chuck class from the major manufactures.
Any favorites on the used market I should be looking at?
 








 
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