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madman
07-06-2007, 09:42 PM
Im gonna be doing a 304 Stainless Machining Job. Im kind off intimidated by this stainless material, I did some research on internet and everyone has just bad things to say about it. I need to turn outside diameters of 5 inch to 4 inch .682
o/d. Also drill bore to 3 inch inside diameter. I wonder how the heck to do this with what type of special cutters??? Is coated carbide required?? Also have some tubeing 5.563 outside diameter that also has a 5.293 inside diameter. (schedule 10 5 inch Pipe) It needs 1.330 diameter holes produced radially every 90 degrees. I am purchasing building a coolant pump system. I am just worried that my equipment and current tooling may not cut it. What type of cutting tools do you suggest i use?? Thanx Mike

Mark Hockett
07-06-2007, 11:35 PM
Mike,
What kinds of machines do you have for this job? What types of tool holders for the lathe. There are a lot of new lathe insert styles and coatings that work well on stainless but usually require high HP and rigidity, I would need to know what you have to work with to make an accurate recommendation. For drilling Cobalt drills work OK in that material, best if you can use coolant. Stainless work hardens very easy so you have to hit it fairly hard and fast which is why you need high HP and rigidity.

rake60
07-07-2007, 01:00 PM
As Mark already said, work hardening is a big issue with 304 stainless.
At work we hit it hard and flood the coolant.
At home I don't have coolant so I take take an opposite approach. I use
positive rake inserts and tools to reduce tool pressure. 304 is not free cutting
at it's best, but doing what you can to reduce the stress of the cut will
reduce the work hardening.

I HATE 304 stainless!

madman
07-07-2007, 06:32 PM
Bridgeport Mill ing machine and a cincinatti toolroom traytop ;athe. Quick change tooling on lathe r8 collet system on mill.

b2u44
07-08-2007, 12:52 AM
I'm no expert, but I spent several long weeks last summer machining a lot of 304. It can be a real pain, as you have read, but there are a few things that may help...

A lot of bars that are sold as 304 are actually 304L. I believe that this variation of 304 includes additional Lead which reduces the extent to which it work hardens (much like 1214 Steel versus 12L14). It's still not 'free machining' but it's a lot better. Infact, I don't mind turning 304L.

In addition to work hardening like crazy, 304 has a lot of carbides included in the metallic structure, meaning that it is very abrasive. I have worn through TiN-coated carbide cutters very quickly because of the abrasive nature. Addressing both of these problems requires aggressive cuts that remove the previously work-hardened area on each successive cut. I used very beefy negative-rake tooling to rough the parts to size, and finished with a normal brazed-carbide tool (which I had to constantly re-sharpen). As a side note: I was using a Clausing Colchester 15 lathe with a CXA toolpost. The BXA toolpost on a smaller lathe couldn't withstand the forces caused by the negative-rake tooling.

Unfortunately, I cannot address the 3"-ID boring operation. I had to repeatedly perform a similar operation... each of which killed one corner of a triangle-insert boring bar. I did not use coolant as it was not available for that machine. Perhaps a coolant bath would extend the tool life.


Correction: Thanks to Peter Neill, the L refers to a "low-carbon content." My mistake, but thus why I prefaced it with "I believe..."

Peter Neill
07-08-2007, 04:10 AM
Btu44, the "L" means that it is a low-carbon content grade of stainless.

There is no lead added to stainless steel grades.

Peter

Swarf&Sparks
07-08-2007, 07:35 AM
Don't let em scare you off
I've machined plenty of 3xx stainless and inconel/incolloy on a 9x20 lathe.
IMHO, flood coolant is mandatory, but I just use a 12v camping shower pump and soluble oil.
0 top rake on HSS and as high a speed as I can get away with.

A.K. Boomer
07-08-2007, 08:53 AM
Just be careful pulling out the swarf, esp. on a lathe cut, that stuff can lay a finger wide open with no pressure at all, it can get razor sharp and remains very strong even in light strands, Iv cleared light aluminum strands away from the quick change area while the chuck was spinning but to do this with 304 could mean that your minus a finger at the end of the day if the piece caught the chuck...

Rustybolt
07-08-2007, 09:37 AM
When milling the stuff with HS cutters I usually run it slower that I would for steel. It doesn't seem to workharden that way. Same goes for drilling. My experience is different from AKs. but we only have positive rake inserts. So again I slow down the rpms. Use lots of coolant.

Swarf&Sparks
07-08-2007, 10:45 AM
Boomer has it right, I have kevlar gloves I use to clear the swarf.
SS swarf will cut to the bone!