Specially hardened stainless props ?

[phillnjack]

Ok so I have had a fair few stainless props over the years including over hubs and thru hubs. all different makes inc Omc Mercury Volvo Suzuki Attwood etc.
most of them I have polished and most of the thru hubs I have drilled vents in them.
Just last week I finished a 13 3/8 x17 OMC prop 389938 stainless with a nice set of 12mm vents, also added extra tip cup and polished it up to mirror finish.
pretty decent job done and I am very happy with it.

Yesterday I started on my 12 3/4 x 21 OMC 389512 stainless and cant believe how tough this prop is !!!
I have never ever had a propeller this tough, when trying to drill the vents on my bench drill it was like its extremely hardened material.
First I normally drill a 1/8th hole then go up in stages to eventual finish size.

The very first drill bit would not cut and barely made a mark, second went on to make the initial hole but struggle.
Then I go to 1/4 and that was a joke, I burnt out the first drill and the second one grabbed and broke, so then it was a nice new 5/16 drill bit and that only got
2 of the three holes done before that was blunt and needed to be re-dressed etc.

Then I took the jump to 1/2 with a drill that I often use on stainless of 1/2 thick, but this drill bit just did not want to know /

so I get a 10mm carbide drill bit and struggle even with that to drill the 3 holes.

Then I re-sharpen 4 different high quality HSS drill bits and proceed to drill the 2 vents to the 1/2 size I wanted. this whole process took about 1 hour to
drill 3 simple 1/2 inch vents in what is normally a 10 minute job.

After this was finished I got a scrap piece of 316L 12mm stainless and drilled that, very easy, then trued a piece of 304 same very easy.
then trued 1/2 inch hardened steel and even that was easier to drill through.

I started the process of polishing this was crazy,
So far its been worked on for 3 hours and got just 1 blade nearly ready for the second stage of 3 to start getting a shine ?
so on a different blade I get out the 4 inch angle grinder with a 400 grit flap wheel, that showed just how hard this material is realy hard.

over the years I have probably vented about 40 different props, over 30 stainless, I have polished roughly about 14 of them.
I use proper polishing wheels on a very large old English Elliot drill press and this has never been so hard before.

if this was my first prop to drill or polish it would of definitely been my last too

my question is,
was there a time when omc used some special hardened stainless to make their props ?


.

[staylor]

I recall that many years back OMC used 410 SS for awhile. This was very tough material- especially if you're drilling it. You could spot the 410 props because they had a little bit of rust that would form where the blades meet the hub- typical of most 400 series stainless'.
Doug

[phillnjack]

Thanks Staylor

sounds right for hardness, but I thought 410 was magnetic, this prop is not magnetic as far as I know.. will be checking that out tomorrow.

[Steelborn]

Be sure you don't create heat by polishing it or it will warp, stainless is notoriously know to warp under friction

[phillnjack]

this is an omc prop, its very thick and well made, no chance of this thing warping from polishing heat.

If you dont create heat then you will not get a mirror finish on thick stainless props, its not like aluminium, stainless takes a lot more to get it polishing.
all the stainless props get very hot when you polish them, its a part of the process to get a real shine.

ive got a ballistic that is thin and that probably would warp, but not the omc 389 range of props, they are realy meaty.

[NeedOne]

If it is 400 series SST, it may be heat treated... 440c HT will be hard like A2 tool steel

[phillnjack]

All I know is this bas***d is realy tough, drilling the vents was a nightmare, and polishing it is so time consuming.
Ive got the 3 blades almost done now just have to finish the hub.
Like I said I have polished loads of props and used to do them by hand working my way up the grades to get almost mirror finish.
I tried 120 grit wet n dry and all it done was wear the paper out, a 80 grit flap disc on angle grinder is even hard work to TRY AND
shift some marks.

Definitely something extremely tough, and its also a pretty heavy prop too, its only 12 3/4 x 21 omc (looks like a SST2 style) yet 2 pounds heavier
then my 13x19 omc that is very similar apart from the bronze divergence ring v welded on flare on this one.
the 17 pitch SST was easy to drill the vents and not too bad to polish it .

I have a fair few scrap bits of stainless in different grades under the bench but nothing this tough.
No wonder OMC painted these things black ha ha .

this is what it was like under the black paint, will post another pic of it when I have finished polishing it,
( I will just do a bit each time in the garage as I know this is going to be an epic ).
.

[roadkill636]

DAH told me that there were 2 diffrent styles of SRX made. The early ones were painted black because it was difficult to pollis3the harder ones. Later the softer ones were made and easy to polish.

[rjdubiel]

DAH told me that there were 2 diffrent styles of SRX made. The early ones were painted black because it was difficult to pollis3the harder ones. Later the softer ones were made and easy to polish.

I am sure you are correct. Last year I sent a stock black SRX to them to work and it came back nice and shiny. There is sill the black paint/teflon or whatever it was in the numbers on the trailing edge of the blades by the hub. Interesting though, if DAH guys said it, it is usually is correct. They know their sh%t!