[andy_ck87028]

Hi

I have a need to cut oval holes in stainless steel tube that has 1.6mm thick walls.

The tube is 31mm dia. and each hole needs to be 5mm by 10mm at intervals along the length of the tube.

Altogether I need to cut around 16 of these holes.

My concern is that I want to do it as fast as possible without introducing excessive heat.

I have been suggested the use of a drill followed by a tungsten carbide tipped burr. I am assuming that I will be able to use coolant on the burr.

Is there a better method?

I have a drill press with a cross slide table that enables me to control each cut.

I started off using an angle grinder but I am concerned about heat distortion using that method. It is faster and less precise but adequate (sort of!)

Any ideas anyone?

Andy

[damae]

Stainless generally has about 50% the machinability of regular steel. A book I have suggests that slow speeds, sharp tools, and positive feeds are the keys to cutting stainless.

The positive speed in particular is interesting. The book suggests that 'if you hesitate on the downfeed while drilling, the drill point can cold work the dwell area to hardnesses as high as 50HRC, and further drilling is impossible.' The same applies while milling, if you let the end mill kiss the surface, it will work harden the surface.

But if you can make the slot you need with a grinder and it's _almost_ passable, then you probably don't need high tolerance slots and you should be ok, as long as you keep a positive feed on your cutting tools.

[andy_ck87028]

Thanks Damae

Should I be concerned about distortion if using an angle grinder? The work got hot on the test run and the stainless discoloured around the cut. (31mm tube with 1.6mm sidewall).

I was thinking of repeatedly cooling down when grinding to alleviate the problem. Would that work?

Andy

[damae]

It stands to reason that if you succeeded in making one cut without distortion, then as long as you repeated that process (cooling between cuts) then you wouldn't distort it.

The only caution is that if you cool too fast (ie. quenching) then you could quench harden the material. The exception are the ferritic and 'duplex' stainless varieties.

[kevingambrell]

Look I know this may seem like a terrible idea, but looking at the problem wouldnt a hand file and a bit of elbow grease give a better finnish with no heating problems. SS cuts fine with hand tools its harder to work than MS but still ok.

Kevin

[andy_ck87028]

Kevin

I think you are right.

Yesterday, I made my cut with the drill press set at lowest speed, plenty of coolant and a sharp drill. It went straight through..... apprehension over

WIth a new rat tail file, I should be able to make my oval easy.

Thanks Kevin and Damae

Andy

[kevingambrell]

Im glad the job is going ok for you. As a rule I dont work much SS for the most part its 6061 but from time to time I come across a job in SS. In general the trick is a very sharp tool and plenty of coolant.
In my training days I spent my first six months with only a hacksaw and files. have to say at the time I hated it but looking back im glad I did it. i had a job a few weeks ago that called for a slice to be cut off of a 3inch MS bar. No bandsaw blade so I cut it with a hacksaw bought back a lot of memories and an apreciation for the way my father worked.

Kevin