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View Full Version : Shoulders and features when turning at high speed on stainless ?



nheng
03-31-2007, 08:38 PM
Ok, so stainless can be a b-tch to work with but I've got it down to the speed and feed with carbide to yield near mirror finish. The only problem is I can't stop turning.

Higher speed and feed are fine but how the heck do you guys stop at a shoulder or other feature that needs slow, careful work on a manual machine? At the speeds and feeds that give the nice finish, stop for a second and ... SCREEEEECHHH ! ... instant hardening at the point of contact. Den

garyphansen
03-31-2007, 08:51 PM
Are you using flood coolent? Gary P. Hansen

motorworks
03-31-2007, 09:10 PM
Stainless:
Flood coolant is a must if your are using carbides.
Use a mag back clock and set it to zero at your shoulder.
Give yourself about .100" of dial before the "zero" at the shoulder.
Throw out the feed lever at about 0.050" on the clock and finish to shoulder by hand.
Make sure you are getting "6 and 9" chips not long strings.
The long strings and bird nets can be danagerous!
eddie

see ebay item for sample of dial:
http://cgi.ebay.com/Magnetic-Base-with-direct-mount-back-Brand-New_W0QQitemZ160028165945QQcategoryZ25272QQrdZ1QQs sPageNameZWD1VQQcmdZViewItem

nheng
04-01-2007, 09:32 AM
It seems like once the work is done (except for the shoulder), you'd have to get the tool off the work surface and cut the speed. Or does the flood coolant allow the tool to remain in contact?

I'm using Mobil Omicron dripped from a syringe. For only an occasional part in SS, it should be ok. Works great on most materials but probably not the best thing for the carbide.

Swarf&Sparks
04-01-2007, 09:43 AM
I do quite a lot of 316, mostly to fit, not spec, but finish is important (shiny stuff for boats)
Flood coolant and HSS tooling, no carbide necessary.

pntrbl
04-01-2007, 10:56 AM
I'm working with 303 again. And again, at my level I don't know nuthin', but it seems to me it's the temp the material is reaching that causes all the ugly. Those guys with flood coolant can keep the metal cooler. Swarf even gets it done with HSS!

For those of us without flood capability going hard and fast gets it over with sooner and the metal doesn't have a chance to get so hot.

Parting's my issue but the faster I feed the cooler the part is and the better it looks when it pops off.

I'm about ready to try a spay can of good old WD on one just to see if I can keep it cooler that way.

SP

BobWarfield
04-01-2007, 11:19 AM
Feeding faster is thought to keep the work cooler because the heat is carried away in the chips. The work hardening is not so much due to the temperature however, it is literal the contact or "work" being done on the material. For that reason, you're going to encounter work hardening if you have to stop feeding and leave the tool rubbing the material, there just isn't much way around it.

You can try to set up as has been suggested with the dial indicator so you can work really fast near that shoulder. Another thought is whether you can focus on disengaging quickly while turning to size and then go back and machine the shoulder to precise spec afterward when you aren't feeding into it.

If you're really bothered by the work hardening there are stainless grades that have higher machinability and no work hardening (or I should say minimal as most steels will work harden a little bit).

Best,

BW

wierdscience
04-01-2007, 11:30 AM
It's not so much temperature on stainless as is it's ability to cold weld to cutting edges.Keeping the part and tool cool is always good,but on stainless the little bit of oil in the coolant is what does the trick by reducing the tendancy to cold weld.Read the bottle on some water-sol coolant and the ratio of water to oil decreases as the alloy increases.Where 1018 steel would have a ratio of 25:1,stainless would be more like 15:1.

A note on carbide and coolant,either run carbide dry or flood it,those are your choices there really is no in-between.Intermitant cooling causes carbide to flake and crater as the result of micro-cracking.The temps at the cutting edge can run 1200F or better so imagine what cycling back and forth between 200 and 1200F will do to a carbide edge in the case of intermittant cooling.

pntrbl
04-02-2007, 02:19 AM
I've heard about flood coolant being the answer to stainless so many times I just had to do something about it. No flood here and I get me some ugly when parting 303, so I got me that spraycan of WD40 just to see what'd happen. The difference is absolutely amazing.

I could tell as soon as I picked up the part. And I mean without looking! LOL! It wasn't burn your fingers hot no more. Used to be I'd get a rag ready to toss it in cuz you sure couldn't hold on to it. Now I can pick it up and hold it as soon as I can find it.

What I did was start the feed and get the tube ready. As soon as I saw the first chip I pushed the button and kept that tube right there in the slot until the part dropped. Full flood all the way. It did get a little messy. Let's tell the truth, it was all over the place!

But now with a bit of emery the part looks just as good as a face cut. Very nice. I've seen the parts they've bought in the past and mine will have a better finish. I may have to buy spraycans of WD by the case but smooth and shiny gets me every time.

I thought about trying some Brakekleen cuz you know cold that stuff makes your fingers, but after reading the can it sounded like a good way to start a fire! :eek: I keep extinguishers handy and have had to use them in the past, but who needs that mess?

SP

Swarf&Sparks
04-02-2007, 02:50 AM
I don't understand the reluctance to use flood cooling. If you've got a chip-tray, you're halfway there.
The rest of my system is just a 12v camping shower and a plastic bucket.
Of course, I replaced the shower rose with a mag-base nozzle :D

pntrbl
04-02-2007, 11:23 AM
Benchtop here Swarf. No chip tray. But I do keep a cookie sheet under it so I can unload most of the chips in one dump. :)

Nheng doesn't say what alloy he's using but with 303 I'm not having a problem with dry carbide on anything other than parting cuts. A kiss of the emery and it gets real smooth on your fingers. Definitely commercially acceptable in the mfg world.

Haven't tried threading it yet tho. :rolleyes:

I'm also not seeing the "rubbing" I've heard reference too. I've read many times where you need at least .002-.003 DOC on stainless or the tool just rubs, but I'm not seeing that here. Maybe it's the 303. I have no experience with any other so I wouldn't know.

SP