# Working with 316 Stainless



## RobinHood (Sep 7, 2018)

This project came into the shop because the parts are for a centrifuge from Europe built in the ‘80s; parts are hard to get (if available at all) and very, very expensive if you can get them. So i was asked if we could help out...

Here is what we had to start with (the part had lived a very hard life....)





And the back side (note the welded on nut as a temporary repair for a stripped out helicoil)





So we bought a 10” OD by 2” thick disk of 316 SS and went to work. I was first going to try and trepan a slug out of the middle. That idea went away quickly as my lathe is barely big enough to hold this thing and we needed a trepanning tool that was able to cut at least 2” deep. So we used the 12” rotary table and 3/8” HSS endmills to cut a circular slot all the way through the disc. We only went halfway through and then flipped it over to cut the rest from the other side as we got increasing chatter with the longer endmill the deeper we went.









We did make it through: 0.025” DOC at a time...





We then turned the OD, ID (and ID features: step on one side, chamfer on the other) and thickness on the lathe.





Then back on the rotary table and mill for 4 bored through holes spaced at 90* to each other and 4 M16x2.0 threaded holes spaced 21* off their respective through holes.





And a close-up





The ring completed; front and back images









3/4” round 316 SS bar was used to make three new pieces to replace this part (the round “head” threads onto it and is then welded permanently to the rod to make a solid unit). Here is a pic of the original bent part with chewed up threads





Next we needed 4 new (plus one spare) aprox. 21cm long M16x2.0 bolts to fit the new ring. They had used 5/8-11 threaded bolts in the M16x2.0 original holes.... Like i said, the ring had had a hard life. These were made from 1” 316 SS hex bar. Thurned and threaded on the lathe....





... and the hex milled down to 24mm (the metric standard for an M16 bolt) on the mill using the dividing head. Each bolt also needed a 2.5mm hole for a retaining pin 45mm below the bolt head.





Here is an image of the original 5/8-11 bolt (as given to me; i doubt that this came out of the factory in Europe back in the ‘80s like that...)  that was threaded into the M16x2.0 holes in the old ring. The round “head” spins on the bolt and is retained by a little pin through the shank just below it. You can see the 2.5mm hole.





Here are all the parts ready for shipping to the customer.





A mix of HSS and carbide tooling was used on this job. Speeds and feeds were experimented with until the desirable surface finishes were achieved. Other than a bit of Scotchbrite, no other surface finish treatment was used. Chip control was a huge problem for me as we did not have the correct inserts for the most part and my lathe is not powerful and rigid enough to take really big cuts to break the chip. To quote John Mills (doubleboost on youtube), we did get some “stringy bastard chips”. 316 SS is quite chewy, but it is possible to machine to a nice finish with some patience.


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## PeterT (Sep 7, 2018)

Nice work. My limited machining experience with SS has been hit & miss, but the finished parts sure are nice. I cant think of another way to take out the middle material to make a donut blank other than send it to a waterjet or laser shop which costs money.
- what kind of centrifuge? (like dairy or fluid/particulate or ...?
- did you do metric or imperial threading on those replacement studs?


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## RobinHood (Sep 7, 2018)

PeterT said:


> I cant think of another way to take out the middle material to make a donut blank other than send it to a waterjet or laser shop which costs money.
> - what kind of centrifuge? (like dairy or fluid/particulate or ...?
> - did you do metric or imperial threading on those replacement studs?



We were considering both waterjet and laser. That would have been option two to save the raw material if the milling operation did not work.

I believe it is a milk separator/centrifuge

We stayed with all metric, just in case the machine ever sees European soil again. Even the ring dimensions were metric. I just wrote the rough numbers on in SAE because that’s the rule i had in my hand when the part first came into the shop...


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