3D Props

[Michael Caruso]

If you guys have wire frame models of the props your working on,.. if you send me the models I can surface them very quickly.. send you .stl file it .stp that can be used for all types of rapid prototyping.

Very interesting thread anything new happening?

 

[Christian Lucas]

Hi Michael,

no ,there is no News . Lohring is anxious to send me the propdata . I want to start a new propeller line with Graupner as they want to go on producing modelboatpropellers after going down and now with the new owner there is some light at the horizon . will see and keep you informed . With my friends we start some of the very strong propellers for tethered line boats as a other friend has Problems with the current ic tethered line props when he drove them with electric drive line . Electric has to much torque and bend the propellerblade .

 

[lohring]

Since I started this thread a lot has happened. We did set a new gas scale two lap record with Kelley Gruol driving but with a borrowed prop that I had to give back. The same weekend Brian Buaas and Tyler Garrard bent and broke a lot of props trying to set electric SAW records. We are working on the problem from several directions.

Tyler is the modern CAD guy so he's in charge of refining my design methods. He has a real job so progress may be slow. I've been sending out a sample model to 3D printing shops for quotes. I also talked with a dental lab I've worked with for decades on casting props in chrome cobalt alloys. He has very modern casting equipment and said it would be no problem. Props would cost $80 to $100 by this method. I'm also building a simple fixture to machine props. It's easy with manual machines to mill any straight blade. You can control cup, rake, and pitch progression with a helical milling fixture. Another fixture can cut the blade outline. As soon as I build the fixtures I'll start with machinable wax that we can turn into investment cast props and then try harder metals.

Brian is the design guy. He has the best feel for what works of anyone I know. We'll get together soon and pick some props to measure their parameters. We'll see if the duplicates made by the various processes work as well.

Lohring Miller

 

[Terry Keeley]

Very interested in your team's progress, please keep us informed!

 

[Kris Flynn]

Lohring, have you spoken to Peter from CoCr props over here in Aus?

 

[anthony_marquart]

This is very interesting. Actually controlling the surfaces of a prop is not easy at all. I was an advanced surfacing guy for a long time and it would still be a challenge to manage variable pitch prop geometry in cad. Lots of packages would lead you to think that you are doing that. But when you actually cut sections thru the solid and do the calculations you find some thing different than you planned. Would like to check out the data.

 

[lohring]

Lohring, have you spoken to Peter from CoCr props over here in Aus?

I ran one of his props on my $ Bill for Kelley Gruol's gas scale two lap record. It looked very nice and similar to the modified Prop Shop props many gas racers run.

Lohring Miller

 

[lohring]

This is very interesting. Actually controlling the surfaces of a prop is not easy at all. I was an advanced surfacing guy for a long time and it would still be a challenge to manage variable pitch prop geometry in cad. Lots of packages would lead you to think that you are doing that. But when you actually cut sections thru the solid and do the calculations you find some thing different than you planned. Would like to check out the data.

I used the helical revolve feature. It allows variable pitch and should produce the expected result. One thing I forgot is to adjust the blade section thickness for the pitch angle. The props at the beginning of the thread get very thin, especially at the hub because of this. You also need to correct for the rake angle, but this is small until you get into large rakes.

Lohring Miller

 

[lohring]

Let me explain how I generate a prop.

First I create the hub and draw a cross section of the blade.

Note that the section at the hub in this view is quite thick. When you rotate the section 71 degrees (the pitch angle for an 82 mm pitch at the 9 mm diameter hub) it's only 1 mm thick. The pitch angle at the tip is much less and doesn't significantly change the thickness. The 10 degree rake also has little effect.

Next I generate the main blade helix.

The helix generator allows the selection of pitch and number of revolutions. I picked 82 mm pitch and 0.2 revolutions. You can add progressive pitch with the same helix generator to either increase (not usually) or decrease the pitch toward the leading edge. This example used a straight helical pitch.

The cup section is generated in the same way from a new plane. My program won't generate two helices from the same cross section so I created a new plane a tiny distance away from the plane of the section in the first picture and drew an identical cross section. I then generated a new helix away from the first with a different and increasing pitch. In this case I picked a 150 mm pitch with a 1.5 pitch increase for a 2 mm height. The earlier examples used the same pitch over a greater distance with a larger pitch increase. It all depends on how you want to portray the cup.

Finally I duplicate the blade to greate a two bladed prop and then cut the blade shape and the drive dog slot using extruded cuts.

You now have an approximation of an ABC 1818 prop. The blade will need to be sharpened on the leading edge and has a steeply sloped trailing edge. It also may need a radius at the hub. I'll leave all these details to someone who didn't learn drafting in the pen and ink era.

Lohring Miller

 

[Michael Caruso]

Hi Michael,

no ,there is no News . Lohring is anxious to send me the propdata . I want to start a new propeller line with Graupner as they want to go on producing modelboatpropellers after going down and now with the new owner there is some light at the horizon . will see and keep you informed . With my friends we start some of the very strong propellers for tethered line boats as a other friend has Problems with the current ic tethered line props when he drove them with electric drive line . Electric has to much torque and bend the propellerblade .

Thank you for the update.

 

[Michael Caruso]

Since I started this thread a lot has happened. We did set a new gas scale two lap record with Kelley Gruol driving but with a borrowed prop that I had to give back. The same weekend Brian Buaas and Tyler Garrard bent and broke a lot of props trying to set electric SAW records. We are working on the problem from several directions.

Tyler is the modern CAD guy so he's in charge of refining my design methods. He has a real job so progress may be slow. I've been sending out a sample model to 3D printing shops for quotes. I also talked with a dental lab I've worked with for decades on casting props in chrome cobalt alloys. He has very modern casting equipment and said it would be no problem. Props would cost $80 to $100 by this method. I'm also building a simple fixture to machine props. It's easy with manual machines to mill any straight blade. You can control cup, rake, and pitch progression with a helical milling fixture. Another fixture can cut the blade outline. As soon as I build the fixtures I'll start with machinable wax that we can turn into investment cast props and then try harder metals.

Brian is the design guy. He has the best feel for what works of anyone I know. We'll get together soon and pick some props to measure their parameters. We'll see if the duplicates made by the various processes work as well.

Lohring Miller

A very nice team effort I like that. Keep up the great work the rewards are worth all the work.

Best to you and the guy's.

Mike

 

[Andy Brown]

Nice work everyone!...on all the CAD and CNC prop designs!

Here are photos of a CNC prop that I made in 2008.

Machined from 4340 prehardened to 42 RC.

Diameter- 42mm

L.E. 2.4"

T.E. 3.3"

Progression - 38%

Rake - 15%

Blade thinckness 50% out from hub-

T.E. - 0.8 mm

Mid. - 0.6 mm

L.E. - 0.2 mm

These dimensions are measured from the prop straight from the machine. No hand thinning has been done. Only hand work was to cut the L.E. back a small amount because it came off the machine at less than 0.1 mm (.004") thick.....razor thin!

I tested this prop on a .45 nitro rigger for durability. It survived the test with no change in dimensions.

 

[lohring]

Though my first prop machining efforts will be in aluminum, the electric SAW racers have been breaking and/or bending bronze and aluminum props. The first prop I ever broke was on an electric model in 2006. I was very surprised. I think tougher props in cast stainless steel or chrome cobalt alloys will be needed. Dental labs have been casting these materials a very long time and can produce exceptionally accurate castings from wax models. Those models can be 3D printed or machined. That's the way Joerg made his 140 mph props.

Lohring Miller

 

[Mike Rappold]

Nice work everyone!...on all the CAD and CNC prop designs!

Here are photos of a CNC prop that I made in 2008.

Machined from 4340 prehardened to 42 RC.

Diameter- 42mm

L.E. 2.4"

T.E. 3.3"

Progression - 38%

Rake - 15%

Blade thinckness 50% out from hub-

T.E. - 0.8 mm

Mid. - 0.6 mm

L.E. - 0.2 mm

These dimensions are measured from the prop straight from the machine. No hand thinning has been done. Only hand work was to cut the L.E. back a small amount because it came off the machine at less than 0.1 mm (.004") thick.....razor thin!

I tested this prop on a .45 nitro rigger for durability. It survived the test with no change in dimensions.

Andy,

On the material, out of curiosity how did you choose 4340 vs some other material?

Also by "prehardened" am I understanding corrrectly that you heat treat the entire blank to 42 before any machining?

Mike

 

[Andy Brown]

Nice work everyone!...on all the CAD and CNC prop designs!

Here are photos of a CNC prop that I made in 2008.

Machined from 4340 prehardened to 42 RC.

Diameter- 42mm

L.E. 2.4"

T.E. 3.3"

Progression - 38%

Rake - 15%

Blade thinckness 50% out from hub-

T.E. - 0.8 mm

Mid. - 0.6 mm

L.E. - 0.2 mm

These dimensions are measured from the prop straight from the machine. No hand thinning has been done. Only hand work was to cut the L.E. back a small amount because it came off the machine at less than 0.1 mm (.004") thick.....razor thin!

I tested this prop on a .45 nitro rigger for durability. It survived the test with no change in dimensions.

Andy,

On the material, out of curiosity how did you choose 4340 vs some other material?

Also by "prehardened" am I understanding corrrectly that you heat treat the entire blank to 42 before any machining?

Mike

Yes, that is correct Mike. The 4340 blank was heat treated to 42 RC before machining. The reason for using the heat treated 4340?.... I had it on hand!

I used a carbide tool made for milling materials up to 60 RC to do the job.

How is the Speedsports team doing?

 

[dwilfong]

can't wait to play with my new prop.

 

[lohring]

I also have some heat treated 4340 on hand, but am not sure my fixture is heavy duty enough to cut it. I also considered A1 tool steel because it hardens without too much distortion. I'm sure I can cut machinable wax and that can be cast in high strength alloys. The big advantage of machined props is the ability to carefully control one factor at a time and run comparison tests. NC machining is easier, but the machine to do it is seriously expensive. 3D printing may eventially be the answer, but for now I'll try old time manual machining with a fixture.

Lohring Miller

 

[Terry Keeley]

I'm sure I can cut machinable wax and that can be cast in high strength alloys.

Lohring Miller

That's what I'd do if I had the capability...

 

[RaceMechaniX]

Hey Andy,

You can send that 42mm prop to me and I will "flex test" it free of charge

TG

 

[Andy Brown]

Hey Tyler!

On the right boat it will definately be good for a new record. It is very thin... has about 200psi tensile. It is tough and fatigue resistant, not brittle.

It is low enough in lift that it could work on many boat types.