[Geof]

.....your feed rate just sounds a little fierce for a good finish - no probs if job requires 2nd op.

ST

Time is money, 0.01 inch per rev goes through a lot faster than 0.04.

On the 2" and 2-1/4" diameters we cannot get a finish that is acceptable no matter how slow we go; good but not like a faced surface.

[star-turn]

Geof - totally agree! however paying an extra operator to face jobs is even more $$$

i have closed shop for thr christmas break, but when i go back i'll try and remember to pick up a component or two and post them on here to see if you think the finish is acceptable.

ST

[harpman28]

I just tried the empire e3000 twin tip cut off and it worked much better but still not where I want it to be. Geof are you bar pushing? I am noticing a lot of machine vibration possibly caused by the bar material that is behind the chuck. I also noticed that after correcting my facing tools height I am still getting some slight chatter on the face. The finish looks very nice except you can see when light is reflected off of it that there is some chatter going on. I think I will try a shorter bar. Any ideas?

[Geof]

We are doing bar work but have never noticed any connection between the bar rattling inside the spindle and the finish either on facing or parting. Most times, however, our bars are supported with liners inside the bar feed so they run tru and do not shake.

[harpman28]

We are using the supplied liners as well. Argh.

[Delw]

We part-off 6061-T65 round bar all the time and have never been able to get a finish that is good enough so a second operation is not needed. It is not a problem for use because nearly every part needs holes drilled and counterbored so we finish the parted surface at that time.

I have attached three pictures showing a typical finish. These are 2" O.D. and the through hole is 0.69". For parting rpm was about 1500 - 2000 with a feed of 0.01 ipr using a peck of about 0.05 and a retract of 0.005" using flood coolant. The pecking is used to avoid getting a long chip that gets wrapped around everything and occasionally jams in the groove. At about 0.05" (radius measure) from either the point where the solid part breaks off or away from the through hole the speed is dropped to 500 rpm and the feed to 0.002" so the piece drops off rather than getting flung off.

I think the mottled surface comes from the parting tool vibrating sideways as the chips curl up from the chipbreaker.

One idea I had, but have not tried yet, to get a good finish is to part in as quickly as possible to within 0.05" of the finish using a thin (3mm) tool then change to a 4mm tool and go in centered on the existing groove at a much slower feed rate. The wider tool will only take off about 0.02" on each corner and it should be possible to do this without pecking. With an internal vee groove, as mentioned in an earlier post, it may be possible to part off with a good surface finish and leaving only a very small burr that can be taken off with a hand scraper.

Geof
No offence man but that finish looks pretty bad. I will try to pop some pictures off of some of our part off piece they requier no second ops, just a light lap job on the back end and they are good to go 63 and 125 finish are usally no problems at all.

The main propbelm with parting off is vibration. there are a few tricks to do.
Stock spindle liners pretty much suck unless you have less than .020 clearance anything more and your going to have some trouble.

For a chuck:
you need to use 3" long jaw's with the heaviest grip your chuck will allow.
Its also very very important that you cut your jaws for this Dia.
While some shops don't like to waste the 50bucks for a set of jaws for each size it is well worth it in the long run. We had every nominal size cut in out jaws and they were marked for each size as well. they never were bored out after the initial bore. Kitagawa chucks always held them right on the money for years.

for spindle liners we had them for every size and every size in between. If the company that we used didnt have a spindle liner that was tight enough we would take delrin and bore it out leaving .020 max freeplay. and press it in the spindle liners. sure it was a pain cause depending on what dia. you had to cut them in 6"-12" lengths and press them in.

if you do lots of barfeed work like we did it paid for itself the second time you had the job.

for collets:
the only thing that we would do is modify the spindle liners like above.
we used 16c 20c and 5c collet noses. the 20c's were the best but not always practicle.

if you can't fix the the rigidity or the vibration your always going to have problems.

before I started my own shop I worked at 2 machines shops. both shops did tons of second op stuff cause they didnt know how to do it right in the first op.
when your using a machinest and machine to just chamfer face and chamfer your wasteing tons of resources. one day I got kinda tired of the waste so made the liners and jaws. it took some time Boss's didnt like it but no biggy I ran the place anyway. They really liked it when it was done and we could have our only 2 barfeed capable machines running to jobs at once on two separate machines unatended. then number showed more profit in the long run and more jobs getting out faster with less tooling and machine cost as well. The machine operators liked it also cause they didnt have to work so hard. 1min cycle times times drive the operators up a wall. some don't mind sitting there putting parts in the machine every 1-2 mins but I personally hated it ( I am not a production type of guy lol).

Sure we would get some bad parts every once in a while from the chuck jaws, which later I discovered that if you cut the jaws at a angle and set the face's of them back an inch or 2 you would get pretty 100% perfect parts with no dings.

to have a second operation that takes set-up time an operator and a machine for the sake of reducing your cut off to slower feeds by 15-20 seconds is pretty much a waste of time. It looks good at first glance due to shaving off 20 seconds on a 2-5 min part but then you add the time it takes to chuck a second part and run it with 3 tools ( chamfer id face and chamfer od) is a waste. our shop always looked at what it takes for the first operation and disreguarded the second op becuase of out of sight out of mind mentality.

we did everything from brass to stelite and everything in between.
when I finally set my shop up back in 1990 I was by myself with 4 bar feed machines and very rarely had to do second op work unless its was like ods and such on the back side, even then most were done in one operation. Back in the 80s and 90s tooling was limited so we made our own tooling ( gotta love manchester cut off tools ). we did threading on the back part of the parts as well. along with grooves and some o ring cut outs on the back sides in one operation.
the tooling is there and if its not you can make it. just need to use your imagination sometimes and think outside fo the circle. one guy 4 lathes and one fadal and I was able to sit and play video games LOL. I didnt have to higher anyone till we started doing slug work and casting work. I didnt do it to make it easier I did it cause I had to find a way to keep the work coming in the shop and pay for the machines. 1 of our machines ran unattended over night and on weekends with a 2 min cycle time. I had to design a conveyor belt parts catcher for the supermax so the parts wouldnt get loaded up in the chuck when I came in , in the morning.

the nice part about barfeed work is that in most cases you supply the material so you get a little more when you order it and you can get the process right on the money, saving time which is money.

our barfeed machines were hitachi seikis and supermax's with thru spindle dials of just over 2", 6" and 8" kitagawa chucks I never owned nor ran a big bore machine for barfeed work.