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Smokedaddy
10-19-2011, 11:58 PM
Any tips or suggestions are appreciated. I have a few blind flanges that I was asked to bore a 1.9" hole in. I have a old Bridgeport. I did give one a shot but once I got up to around a 3/4" hole (via a drill bit) the bits were being destroyed. The SS must of work hardened. I don't have flood coolent and was using cutting oil (from a pipe machine). I could of made some decent money doing a bunch of these but not if my tooling is being trashed.

1. Once it work hardenes what is the next step?

2. If I were to do it all over again, what should the process be?

Regards,
-SD:

Kiwi
10-20-2011, 12:33 AM
Don't let it get hot keep drill bits sharp. I have used a large oil can full of fluid ( water soluble oil ) does the trick or a can slung up to a roof beam and a hose down to the job a valve on the can to control the flow is good

Toolguy
10-20-2011, 12:39 AM
I would use a 1-7/8 Rota Broach hole saw running slow, 90 - 120 RPM with oil to make the hole, then bring it to size with a carbide tipped boring bar running 150 - 200 RPM.

T.Hoffman
10-20-2011, 12:46 AM
I just did a little work in stainless, my first outing with it.

Not sure of the actual type of stainless I was working with, but I had to really go slow. As your boring bit is spinning at each larger dia, the surface speed is going up too....

I was just using LPS cutting fluid and it seemed to work ok.

Mike Burch
10-20-2011, 03:58 AM
To answer your questions, once it work hardens, either get very brutal with it or throw it away.
If you let the tool rub instead of cut, the stuff will work-harden in an instant.
You MUST keep the pressure on the tool. And you must keep it cool, with slow speed and lots of lube/coolant.

lakeside53
10-20-2011, 11:56 AM
I've drilled 316 and 304 with 3/4 and 7/8 inch drills high quality ($$$) on my lathe (pre-drilling for boring) . Usually 55-80 rpm (or less), lots of pressure and tapmatic cutting oil. I drill about 3/8 - 1/2 inch at a time, then back out and relube. You must keep the pressure up and constant. If the swarf is coming out a two nice sprirls, I keep going - most of the heat is in the swarf.

If it does work harden (it will in places) , it's still not all that a hard - lube, and pressure though it.

Smokedaddy
10-20-2011, 10:04 PM
I would say a high majority of things I machine are aluminum, some 303 SS now and then and brass. Looks like I need to figure out how to put flood coolent on my mill. I don't want a mess to clean up, so I'll have to look and see how others accomplish this.

Thanks again,
-SD:

boslab
10-21-2011, 02:15 AM
once it gets a chance to go fridgid on you ive managed to turn the drill dull red and collapse on me!,
mark

Forrest Addy
10-21-2011, 05:06 AM
Stainless 316L cuts readily but it is tough and it will work harden forming a rind that can be difficult for a tool to penetrate. If it does work harden you might have to sharpen the tool several times before you break through it.

You can hold close tolerances on low power machine tools if you don't try to over-do it. Take light but definite cuts and don't let the tool dwell.

Try to keep the spindle tooling as short and rigid as possible. Keep the surface speed to 35 - 40 feet per minute, use sharp tools with relatively small nose redii (4 to 5 times the feedrate per rev), 7 degrees end clearance and no more than 10 degrees positive rake.. Avoid fine feeds (0.005inches per rev, dial in a minimum depth of cut 0.010" or more, and, again, don't let the tool dwell in the cut. Don't re-cut chips. Sweep them clear or vacuum them up as you make them.

A little coolant will help. I suggest a soluable oil drip or squirts from a laundry bottle. Flood is not really necessary unless you are seriously milling with HSS and need to remove heat from the cut. Keep the cut wet.

If your object is hole making for fastener clearance etc an annular cutter (slug cutter) is a good choice but the feeding forces will be high. make the tool cut. If you have a choice, keep the spindle RPM in the 35 FPM (about 70 rpm) and don't let the cutter dwell. Use plenty of oil. Break the stringy chips by pecking frequently - and be careful, the chips are like razor wire.

Toolguy
10-21-2011, 11:12 AM
I would say a high majority of things I machine are aluminum, some 303 SS now and then and brass. Looks like I need to figure out how to put flood coolent on my mill. I don't want a mess to clean up, so I'll have to look and see how others accomplish this.

Thanks again,
-SD:

The 303 Stainless is one of the easiest ones to cut. You don't really need coolant for that. The 304 is one of the harder ones to cut, coolant advised.

lakeside53
10-21-2011, 12:30 PM
Yes... I really like working with 303. Unless you need to weld it, or have a paricular enviromental condition that requires 316, just use 303... Easy to say, but I couldn't find 303 in schedule 40 pipe when i needed to.:(