Sunday, April 20, 2008

I hate Stainless...

Some notes on how I design things. Some people make detailed 3D cad models of their complete vehicle. I do some dimensioned drawings, but I don’t make them a complete detailed cad model. The drawing below was my layout for the Jet Vanes.Vanefirst

This drawing was done in Rhino to scale. but as a flat 2d drawing. When the vane mount got welded to the exit cone if was about 0.1875 too far down. This caused me to redo my vane bearing mounts and redo the jet vanes as the bearing is now 0.2” farther from the exit cone. 

Once I have a scale drawing of the parts I make a simple dimensioned drawing I can take out to the shop or use to generate CNC code for the lathe. I don’t have a good lathe CAM program so all the Lathe CNC code is generated by hand or by writing a program to generate the CAM file. The CAM generation on the mill is automated from the drawing.


This is the drawing for my new corrected vane. I got up this morning and went to two places, IMS to get more 316 stainless shaft to make vanes out of, and to Marshals Industrial hardware to get some more carbide end mills to cut the stainless. So after working from 8 am to 1:30 am I have the following:


The three parts on th left are not yet destroyed. All the parts on the right are toast in various ways. The four that look relatively complete are done to the original drawing and are now the wrong dimension. Some of the bad ones have the wrong bearing dimension (They are loose on the bearing), I had a problem in my hand crafted lathe code where I made 4 exact errors…. The other two are the result of milling problems, the new carbide bits I got today just aren’t lasting. MY last set that I ordered from MSC would do two vanes before they were dull, the ones I picked up today last for 1/2 of a vane.  So since I went through all my carbide tooling I though I’d try a big 3/4 TAIN coated HSS end mill, real slow…. The one in the middle left with the notch is the result of that experiment. The bit cut just fine … for awhile then it suddenly welded it self to the work piece and when I based the mill to recover it bent the vane. The three parts on the left are done with the lathe work (sort of) and now need milled. The one on the bottom left that looks like it was gnawed by a rabid squirrel is the result of trying to part off the  vane and having the parting tool die. I really should not be parting solid stainless on my Lathe its just not rigid enough, but I don’t have the shop space for the proper tool, a metal cutting horizontal band saw. I even tried the Armstrong method, I bought the highest quality hacksaw blades I could find at home depot and after two strokes the stainless removes all the teeth. 


Lastly the lathe makes miles of razor sharp stainless turnings, They get tangled with everything and cut you if you just look at them crooked.Stainlessknives


 As a general rule I don’t wear gloves near machine tools, its a good way to loose your hand. So in the last 24 hours I’ve bled from 5 of my 10 fingers.


The vanes are bieng used in a hot oxygen stream so I need the maximum oxidation resistance, otherwise I’d use 303 stainless a lot easier to machine. Did I say I hate Stainless?  Hopefully today will go better…




Rocket Dude said...

Would you consider outsourcing these parts to a machine shop? I've used quite a bit and have been very happy with their work. I drew up your vanes in about 20 minutes. Price was ~$500 for 10 in 316 with a lead time of 4 weeks. They are usually faster than promised however.

I'm sure you don't want to wait 4 weeks but you could make some yourself out of an easier to machine material to use while you're waiting for the 316 versions.


James said...


Just as a guess, try increasing your feed rate. As I'm sure you are aware, work hardening is the main problem with machining stainless. Get rid of any dwell you have and run some sort of coolant. Even if it is just you squirting tap magic on to the tool as fast as you can while breathing rolling clouds of smoke. It will help.

Cobalt end mills should be fine for 304 and may work better than carbide if your machine isn't rigid enough. I use some 1/2" M42 cobalt roughing end mills and they cut 304 SS just fine.

I suspect again that your lathe parting problems are from not enough feed pressure with your parting tool. Skip the coolant while parting and really feed the parting tool hard. You are either going to get a very nice cut or the tool will blow up on you. Stand off to the side and wear appropriate personal protective equipment.

I once made a little dremel tool "tool post grinder" for my lathe. With the abrasive cut off discs you could part your stainless. Photos at:
towards the end.

Or just use an angle grinder with cutting disc to roughly get it to length. Then rechuck it and use a carbide tool to face the rough cut off.

Following up to what rocket dude said about outsourcing. I've used a few times and have been pleasantly surprised at the responsiveness and price of some of the vendors. Certainally not as fast as doing it yourself, but definitely frees up time.

Can the jet vanes be made as a welded assembly? Cut the vane from sheet. Turn the shaft and then slit the top. Tig weld together.

-James Jarvis

Carl Tedesco said...

Is there a reason they have to be monolithic? How about turn the shafts using stainless rod. Then have the vanes water jet cut from stainless plate. Grind in the sharp leading/trailing edges. Then have your welder join the two parts.

Carl Tedesco said...

Oops... I should read all the posts before I reply... what James Jarvis said at the end! :-)

Johh Kasunich said...

I know it's already been said, but I have to agree - weld those things!

You are spending lots of time and tooling turning expensive steel into chips. If you did a welded assembly you could start with 5/8" bar instead of the 1-1/2" (or bigger) bar you are using now. Turn the bearing seats, then mill a shallow slot across the 0.600 diameter end to locate the blade.

Blades could be waterjet cut from sheet, including a 0.600 wide notch at the shaft end to locate them on the shaft. Waterjet cutting rates are pretty reasonable - I bet $200 would get you a dozen blades if not more.

(BTW, I hate stainless too, ever since I watched the end of a drill bit literally turn red and crumble before my eyes. I was using a drill press and I eased up on the pressure for just a fraction of a second.)

Ed said...

Check out this tool cutting steel like butter:

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