316 Stainless tips?

'noon all, Ive got to make 8 'corner pieces' (for want of a better description) they are 1"1/2 316 stainless bar, with the back cut out to cover
a mitre joint in some 304 angle edging. I managed to part off 1 blank last night before my parting tool gave up the ghost (cheapo chinese screws have stripped ) I think Il get a carbide insert one from JB to replace it, but then I still have to remove the 'corner' from the inside of the bar blanks.
Any tips? This is the first stainless machining Ive done. I plan to use a reasonably sized (1") endmill to plunge a good chunk away, then 'refine' the corner with a smaller one. The inside bit doesnt have to look pretty, its inside and underneath, but Id rather not break any tools (or me) whilst making them.
cheers
Dave
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On Wed, 7 May 2008 05:23:59 -0700 (PDT), dave sanderson

Any particular reason why you're using 316? Because it's there? I've got some scrap 1 1/2" prop shafts in free cutting stainless if you're nearby (Cheshire) & want to try one.
Main thing is lots of lubricant & keep up a steady feed, don't pause or it'll work harden.
Tim
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Im using 316 because thats what Ive got... As it happens its an offcut from the propshaft of my cousin John's new canal boat. (might not be 316 then, but the only markings on it were the number 316, so I assumed) It certainly work hardens, I knackered a hacksaw blade before I though of using the lathe.... (bit dim sometimes, and parting off that size from a bar scares me somewhat) Id take you up on the free cutting stuff but I over in leicestereshire, and afaik Im not due over your way any time soon.
I thought the work hardening bit was the main thing, nice to have it confirmed :)
Dave
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On Wed, 7 May 2008 09:38:33 -0700 (PDT), dave sanderson

Boat prop shafts ought to be 316, but it seems that most of those 'mass produced' for the inland waterways market are made from free cutting stuff (303?), presume that keeps manufacturing costs down although it doesn't last as long as 316 in service.
Tim
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It'll be 316 then, Johns boat is definitely not build to a price as such, he believes in doing it properly :) Is 303 a lot easier to machine then? If so I might try and find some locally, I only need about 18" of it.
Dave
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On Wed, 7 May 2008 11:08:12 -0700 (PDT), dave sanderson

Greetings Dave, 303 is much easier to machine. It is also a different color than 316. 316 and 304 match pretty well color wise but 303 is greyer and not as blue. 303 more closely resembles brushed nickel in color than it does 304 or 316. Cheers, ERS
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dave sanderson wrote:

Sharp tools, carbide for preference (especially for parting), everything rigid (if a slide isn't going to be moved deliberately, lock it), lots of suds, and most important "gie it laldy", ie don't sneak up or take small cuts and don't stop or slow the feed down.
I don't know what machines you have, but plunging a 1" endmill will take quite a lot of power - slow-to-medium speed, medium-to-fast feed.
The main problem is work-hardening, the lesser problem is gumminess and tearing. "Laldy" and suds will cure the first, sharp tools the second.
-- Peter Fairbrother
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I have a TOS FKN25 mill to do the milling bit, think of a grownup bridgeport... IIRC the bottom speed is about 56 rpm, I was only going to plunge about 1/4 or so of the end mill, and so sort of 'nibble out' the hollow bit but in quite big bites IYSWIM. Ill have to read the manual about plunging, the quill has a feed, but the knee doesnt, and Im not sure what the quill feed is rated for (diameter and speed). Cranking the knee up and down gets old really fast.
The parting off was with a harrison at 22 rpm, but 'leaning' on the crossfeed handle quite hard. Copious lubricant from an oilcan with the other hand. Seemed ok but I did have builtup edge problems, and the tool seemed to 'weld' itself to the work occasionally, giving an almighty bang as it freed itself. The tool holder clamp couldnt cope with the force and the blade moved slowly backwards, and eventually (just about 1/4" to go) it snapped! EEEK!!! Scared the Sh1t out of me, hence Im going to invest in a proper inserted carbide tool.
Dave
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dave sanderson wrote:
[..]

Sounds good enough to me - but give the 316 no respect, be brutal with it, and work the machine as hard as you can.
Lower speeds than eg mild steel, as-fast or faster feeds. Carve it up quick, with sharp tools (because you are a good craftsman who always uses sharp tools anyway), ... don't play with it and give it a chance to bite you.
[..]

Continuous suds are more useful than occasional oil here - they cool the tool and workpiece better, and are _always_ available at the cutting edge. They also move chips out of the way better, and deter sticking.
If, as it sounds, you are using a blade-type parting tool then the side of the tool is going to be very close to the cut edge in the workpiece - and a small chip which can get into the tiny gap will cause all sorts of wonderful and loud problems, especially with gummy stuff like 316.
Better carbide tools are wider at the cutting edge than along the sides to prevent this (you can also grind a HSS blade that way, but you end up only being able to use a small percent of it for parting - cost-wise it's not a bad option though, especially for brass, mild steel etc, as blades are cheap).
Making everything rigid helps here too - the parting tool (or workpiece) is not going to move a thou or so sideways and dig into the side of the cut. If the piece is gummy like 316, then ... it sticks
-- Peter Fairbrother
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