No Lathe - Using the VMC - Any reason why not?

Rick_H · Apr 6, 2014

Hi Guys.

In our shop we are CNC Mill only, no lathe - we don't usually do job-shop work but have been approached by a friend of friend with a job that I would consider to be definitive lathe work.

They need some circular inserts making - 70mm OD -0.00mm +0.05mm, concentricity is 0.01mm and this dimension is to be cut 15mm deep.
Material is 6061 Al- Other dimensions have no real tolerance.

If I take it on it would be for 2000pcs a year in 200pc batches.

We have a couple of less than year-old VMC's so wouldn't be making them on worn out iron.

Do we cut some bar-stock up and chuck them up on the machine or give it over to somebody with the lathe? I suppose the only reason I am questioning things is that I know they are currently being made on a lathe....

Thanks, Rick

upnorth5axis · Apr 6, 2014

we used to do this when needed but we have a lathe now. most parts you will not be able to as fast as a lathe but you can still be them done

Rick_H · Apr 6, 2014

Thanks, we don't have any mic's that go upto this size so will get hold of a decent one and measure concentricity - that's what I am most worried about, especially at the quadrant lines....

LKeithR · Apr 6, 2014

I think the first question I'd ask myself is: "What else can I do on the VMC?" If the job you're considering is the only one available then it's certainly better than nothing but if there is more appropriate--and potentially more profitable--work available for the machine then you're probably better off going in that direction. If you can find someone with a lathe to smoke these pieces off for you you might be able to sub them out and tack on a small profit as well...

DavidScott · Apr 6, 2014

Works fine, just take light cuts. You can even gang multiple tools with separate offsets. If you can load and unload parts from the tool holders while making parts it can be fairly efficient.

upnorth5axis · Apr 6, 2014

Rick_H said:
Thanks, we don't have any mic's that go upto this size so will get hold of a decent one and measure concentricity - that's what I am most worried about, especially at the quadrant lines....

So you must be going to mill your part if you are worried about quadrant lines? I was thinking you would mount your stock in a tool holder and your turning tool in a vise or on the table and turn the part.

Rick_H · Apr 6, 2014

The part is only 25mm tall and needs a through hole, that and it being 70mm od and having no experience turning on the vmc leads ne to just wanting to mill it conventionally.

Tonytn36 · Apr 6, 2014

I'd stick it in a collet holder in the spindle. You can drill the hole, turn OD and part off with one clamping and not worry about concentricity.

Zonko · Apr 6, 2014

Tonytn36 said:
I'd stick it in a collet holder in the spindle. You can drill the hole, turn OD and part off with one clamping and not worry about concentricity.

Riiiight
70mm collet holder.....for a mill spindle ? No ?!

They did make huge collets for instrument makers lathes........but for VMCs...why on earth would anyone do that...

dstryr · Apr 6, 2014

What kind of VMC do you have? You could reverse mount a boring bar in a boring head to turn the outside with the part clamped to the table. Then drill and bore a hole with another boring head setup. Rough both OD and ID with an endmill first. Shouldn't have a problem holding that tolerance as long as your machine is any good....

Philabuster · Apr 6, 2014

Rick_H said:
Hi Guys.

In our shop we are CNC Mill only, no lathe - we don't usually do job-shop work but have been approached by a friend of friend with a job that I would consider to be definitive lathe work.

They need some circular inserts making - 70mm OD -0.00mm +0.05mm, concentricity is 0.01mm and this dimension is to be cut 15mm deep.
Material is 6061 Al- Other dimensions have no real tolerance.

If I take it on it would be for 2000pcs a year in 200pc batches.

We have a couple of less than year-old VMC's so wouldn't be making them on worn out iron.

Do we cut some bar-stock up and chuck them up on the machine or give it over to somebody with the lathe? I suppose the only reason I am questioning things is that I know they are currently being made on a lathe....

Thanks, Rick

Buy a CNC lathe and make this job profitable. Do not fiddle fuck around on a CNC mill when a 30 year old CNC lathe would be more than adequate for this stuff. Not to mention, you could also take in more CNC lathe jobs and do second OP milling if necessary.

Rick_H · Apr 6, 2014

Lathe purchase is not an option, we don't have physical space for it in the shop, have no lathe programming experience, would have to buy tooling and I simply don't have time to scour the uk for a suitable cheap machine, hand chucking would be just as much of a pita and bar fed 70+mm capable lathes are lots of coin.

As above, we are not a job shop and have no need for lathe right now - this is a friend of a friend type job.

Like the idea of the 'reverse' boring setup, we have a small one but it won't go up to the size we need - it may be difficult to find one I'm assuming as the bar usually mounts toe the side of the head above a certain diameter on most I have seen?

AHC · Apr 6, 2014

Rick_H said:
Lathe purchase is not an option, we don't have physical space for it in the shop, have no lathe programming experience, would have to buy tooling and I simply don't have time to scour the uk for a suitable cheap machine, hand chucking would be just as much of a pita and bar fed 70+mm capable lathes are lots of coin.

As above, we are not a job shop and have no need for lathe right now - this is a friend of a friend type job.

Like the idea of the 'reverse' boring setup, we have a small one but it won't go up to the size we need - it may be difficult to find one I'm assuming as the bar usually mounts toe the side of the head above a certain diameter on most I have seen?

Sounds like a loser proposition all around to me. You're going to lose money doing a job in a machine not designed for it, the end customer is going to get parts that will not be like what he is expecting to get and your friend is in the middle.

gustafson · Apr 6, 2014

I turned several different parts in the spindle of a cnc over the years. Depending on what the part is I would turn it in the spindle with a tool held in the vise or if it works out machine it 'normally'

or maybe a combination of both

Greg White · Apr 6, 2014

Try it on some scrap,i have used many mills as lathes,not perfect,but I aint either.
get er dun!

Gw

macgyver · Apr 6, 2014

If it is only 200 pc batch size, what about a small manual lathe, maybe even a little turret or second op? I have one that will handle this size part and is only 3x4 ft foot print. Got it cheap too. Do you have a manual lathe in house?

sable · Apr 6, 2014

Problem with this job is that it sounds like a nice regular job for a lathe so the customer should get a decent price ,trying to do it in a VMC is likely to be more costly ,so either you don't make much on it ,or the customer pays too much .

Having said that it is difficult to say without actually seeing what the part looks like whether it is a good idea or not, there are plenty of jobs that look like a lathe job but can be done easier on a VMC, but usually it is only economic to use the right machine for the job, a 200pc batch is a lot to do with a half arsed setup.

jrmach · Apr 7, 2014

You can hear the wisdom of experience in some of these posts.Fiddle Fucking don't pay well,that's for sure.

Rick_H · Apr 7, 2014

jrmach said:
You can hear the wisdom of experience in some of these posts.Fiddle Fucking don't pay well,that's for sure.

Agreed - the part is basically a top-hat insert, I believe it will replace a version which has a rubber centre - Looks similar to this except the larger diameter is much taller (picture is just a random google image)

I think I will pop some scrap in a vice and take a look at what our machines can do, we have a few hurco VM20's that are nearly new (less than 6 months) and an old Cincinatti Arrow so wouldn't be doing them on worn out iron.

Essentially, this would be a job run 'after hours' so to speak as we have enough work to keep us busy atm.

Thank you for the advice guys, looking like it may be passed onto somebody with a lathe....

hanermo · Apr 7, 2014

You should be very, very easily able to do this with the VMC alone.

Rough it with the VMC, then grab it in a collet, and finish the last 0.1 or so mm against static fixed lathe tools.
You can machine a round in the stock to then hold it from in the collet, and the last op drops it off.

2 cycels, maybe half a minute - one minute each to finish. Sat 0.1 mm cut, and then 0.02 mm for finish.
Should leave perfect finish, and be very fast, and much better than 0.01 mm concentricity.

No Lathe - Using the VMC - Any reason why not?

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