Titanium Propellers

Figured I would share what I have been working on. I cnc'd these titanium propellers out of a solid bar of 6al-4v titanium and anodized a couple of them too. Let me know your thoughts. I know

the edges are a little jagged in spots. I still need to buff them smooth and polish them but that's how they came off the machine.

Man that's a lot of whittlin"!  Nice work tho.

What machine are you running them on?

We have a little 30 taper ares. It's just like a robo drill if your familiar with those

What pitch is it? It looks a little lite on pitch...

It's a 38 1.9

What 3D modeling program are you using?  I've been doing parametric propeller designs in Fusion 360.  So far I can model propellers with the number of blades, pitch, rake, cup, blade thickness, blade area, and hub size as variables.  Progressive pitch would be my next step.  My plan was to 3D print the pattern and investment cast it.  However, machining the prop should allow thinner blades.  You would need to support one side with a low melting alloy while machining the other side.  Grinding should work even better.  Material strength is what allows thinner blades.  I would consider an air hardening tool steel for SAW props.  We ran knife blade rudders with a considerable speed improvement over aluminum rudders. 

A long time ago I built a jig to machine propellers on a conventional mill.  It used tracing on a sheet metal pattern to get the blade shape.  It gets clamped in the milling vise at an angle to generate rake.  I haven't used it to actually make a propeller, but it was a good exercise in understanding propeller geometry.

Lohrig Miller

RYRYCNC.. thanks for joining the board.. we love having you.. 

It is with mentioning you MUST have our full name in your signature if you used a "alias" as your sign in.

Thanks

Grim

"Figured I would share what I have been working on. I cnc'd these titanium propellers out of a solid bar of 6al-4v titanium and anodized a couple of them too. Let me know your thoughts. I know the edges are a little jagged in spots. I still need to buff them smooth and polish them but that's how they came off the machine." Very nice work!! What I'm wondering is, why did you choose 6AL-4V Titanium? Even when heat treated it would have a lower ultimate tensile than typical model boat propeller alloys such as C-20, Modified C-20, 17-4 PH, 15-5 PH, CoCh, 416 Stainless, etc. Some of the mentioned alloys are suitable for casting in very thin sections & casting with molds is the cheapest methods to make model boat propellers. Modern day propeller molds are made in 3-D printers. Contact Jim Schaefer of ABC props for more in depth information. 614-475-4247

I chose titanium because it has one of the highest strength to weight ratios of any material plus it's more corrosion resistant than any stainless. I believe it will be plenty strong for rc use if it's not i will go the other route and make them out of maraging steel which has the highest tensile strength of any material. Honestly I hate castings. The material isn't near as good as billet. Dimensions can be all over the place. You can have air pockets etc it's just not good imo. I'm looking to make the best thing out there not the cheapest.

Jim i found a 2 inch bar of maraging on ebay for a good price so i got it.  I will do some testing vs the titanium. With the maraging I will be able to make the prop blades super thin this may help the prop cut through the water faster. Also it heat treats to 54 rockwell so it will be able to hold an edge much better than those stainless steels you mentioned. Most of those are 200,00 tensile or below and 42 rockwell. Maraging is 300,000 ultimate tensile and yield and is a lot more ductile than 17-4 15-5ph it's just super expensive stuff it's actually more expensive than titanium.

Ryan,

I am very familiar with all the grades of Maraging steels, both Cobalt strengthened, Titanium strengthened, their uses & how they can be heat treated. The actual ultimate tensile of the C-350 is 350,000 psi with a yield strength of 340,000 psi. at 55/60 Rockwell "C" hardness. Since these steels are Carbon free, protective atmospheres are not required during martensitic precipitation aging. They are exceptionally stable during aging, with predictable uniform shrinkage on all dimensions & they are distortion free. I use the C-350 alloy to make machined retainers for both gas & nitro engines. The machined retainers are heat treated 4 or 5 hours at 925* F. 

Even though I do not know of any model boat propellers made of maraging steels, I think the alloys would be suitable for very thin, very high RPM model boat use. The C-350 grade would be ideal for high speed, instant high RPM electric type boats. Please keep us posted on your results?

Jim Allen

Note: Photo of a typical precision machined retainer made of C-350 maraging steel. Machining the retainer allows 14 rollers to be used on the standard 10 mm (.3937") crank pin, instead of 9. Rollers & crank pins are made of M-2 steel.

That sounds like a good alloy.  I picked tool steel because that's what I can harden easily.  Air hardening tool steels don't change shape much with hardening either.  I still think grinding after hardening would be good.  My former partner, Mike Bontoft, used his CNC mill to grind a square on a Zenoah crankshaft .  He had a 10,000 rpm spindle.  At the time we tried making a propeller but had issues with my 3D modeling program and Gibbs Cam not working together. 

Keep on working on the props.  It's one of the best areas for improvement.  Jim Schaefer at ABC has been working with the electric racers on his latest designs.  They are more efficient at converting engine power to thrust than earlier designs.  However, his bronze alloys can't be thinned as much as steel alloys can.  Titanium is great for corrosion resistance but that's not a problem in model boating.  All you need to do is clean and apply oil after running.  That's standard with our model's steel shafting.  Really high performance props have been made with cast chrome cobalt alloys.  Dental labs have been very accurately casting them with fancy vacuum melting equipment for decades.  These days 3D printing is starting to replace casting, though.  I believe cast chrome cobalt is the the prop alloy Joerg used for his close to 200 mph record runs.  Some finishing is still needed, though.

Lohring Miller

Jim i got c300 for the props. I am working on a gear drive .21 lower unit that I am using c350 in for the gears. I will also nickel teflon with nano diamond plate them. I live at the shop i work at so i have access to the equipment whenever i want. I have a lot of things I want to play around with like carbon carbon pistons and sleeves. I do my own plating and heat treating as well.I like doing everything myself for total control of the process and not getting killed on lot charges.

Here is a mock setup I made just to see how the gears would mesh

Ryan,

Also consider unleaded 4340 heat treated steel for any model boat gears. This is the same material used in John Bridges Lead Sled hydro of years past. If you try to use this alloy, make sure the material is certified, "UNLEADED". Pre-harden the gear blanks & anneal to 38/40 Rockwell "C". The gears shown were precision hobbed after heat treating to + or - .0002" tooth to tooth & + or - .0002" on the major diameter. All the tapered split collets & their seats in the gear blanks were machined in  the same setup before hobbing. The class 11 gears run dry & have excellent wear resistance at RPM's of 35,000+. Keep in mind that if the gear mesh is a little loose, nothing happens, except a little noise will be generated. However if the mesh is a little tight, the gears will rapidly wear out. It's nice to see someone using real tools to modify or build model boat stuff! 

Note: The gear ratio used in this setup is 1 to 1. The torque & HP are doubled while the RPM's stay the same (minus any gear loses). Properly designed spur gears typically have efficiencies greater than 98%. (Dudley's gear Handbook; 2nd edition; chapter 12)

Jim Allen

Jim i have been working on making the lightest strongest motorcycle chain on the market and used everything from titanium to maraging and also played with 4340. I made some links of 300m/4340 modified and pulled for over 10,500 lbs on the tensile test I then made some regular 4340 links and they were hit and miss. Some were brittle and snapped some were fine. The 300m that carpenter makes is vacuum melted and it makes all the difference in the world on the purity of the metal and ductility. I highly highly recommend 300m it's worth the extra coouple bucks a pound cost

There are many manufacturers & suppliers of Vacuum Melted Steels. Teledyne Vasco, Service Steel Aerospace Corp., Magellan, Allegheny Technologies company, Carpenter, etc.  Make sure your getting vacuum melted stuff!

JA

I get all my stuff through Service steel but it's carpenter that they are buying 300m from.

Ryan,

The problem you'll find with Ti is that it is fairly flexible. This is actually where it's "strength" comes from. I has a very good "memory", meaning it will return to its original shape after being flexed. It has to be formed WAY past your target angle when bending, as it springs back. What you will find is that the pitch will vary widely with loads, and yield far less than desirable results while in use.

I've always thought 17-4 would be a really good choice for CNC props, as it machines easily, can be heat treated with minimal distortion, and its REALLY strong after HT.

Nice work on the props, though. Not beyond my understanding, but far beyond my current machine capabilities.

Thanks. Brad.

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