De-tongued my first prop today

[David Santistevan]

I just finished detonguening (sp) my first prop today. It was actually much easier than I thought the process would be. From start to finish it took about an hour and a half only using a small metal file, a set of tile nippers and some 320 grit sand paper. I am very leary of the dangers of breathing berillium/copper so I did not use any power tools. After drawing my initial shape on the blade with a sharpie I used the tile nippers to do the initial cut of the blade. Using the small file I then fine tunned the shape and then began thinning the blade to create the new edge. Once I had that blade done I made a stencil using masking tape on the back of the semi-finished blade. I layed across the entire blade (it took a couple of pieces because the shape of the blade. I then using sissors cut the masking tape around the blade shape and then triimmed it even closer using and xacto blade. I then just lifted the masking tape stencil off the blade and placed it on the new blade. Using the tile nippers I again cut the rough cut of the new blade and then worked the final shape and thinned the blade using my file. When I was done I took some play-doh and made an impression of one of the blades and checked the shape against the other blade and it was spot on. I just then finished thinning to the edge (sharpening it) and the cleaned the whole mess up with some 320 grit sand paper. Checked the final balance and threw it in the tumbler for a couple of hours to finish polishing it and cleaning it up. I will check the balance one more time when it comes out and see how bad I screwed it up when I run it tomorrow! :blink:

 

[57fairlane500]

What prop did you do and for what boat? Lets see a picture of your work.

 

[David Santistevan]

I was working in on a X438 for a Lynx tunnel. When it comes out of the polisher I will post pics.

D

 

[Tom Foley]

1 " beltsander ....2 minutes !!

 

[57fairlane500]

I agree with Tom, but get a good mask first.

 

[David Santistevan]

These are the original and the detongued version of the same prop.

I have an 1" beltsander, I have been really worried about spreading "radioactive" dust all over my shop so I have been doing this in any way that prevents the creation of a lot of grinding dust. Maybe I am being a little too careful. Oh well, go the job done.

 

[shoboat]

David,

It looks nice.

You will need to thin it out a little more for great performance.

Did you remove some of the trailing edge cup already? It has

too much for a stock for 21 Tunnel.

Thanks For Sharing,

Mark Sholund

 

[David Santistevan]

Thanks Mark,

No I have not removed any cupping yet, that is probably a little outside my skill level yet but I will start researching that. Does the entire blade need to be thinned or just the leading edge? Question (and pardon my lack of understanding here) if the boat could pull this prop before detonguenging then why can't pull the prop after? The max pitch hasn't changed? Also did I remove enough of the tongue?

Thanks for the help.

D

 

[shoboat]

David,

It will pull it, but not with great RPM!!!

The X-438 has too much cup stock.

I just measured a new one at: 4.29" of trailing edge cup

2.67" of center of blade pitch and 38.87mm stock.

I think you would need aprox. 3.00" of T.E. cup for great

RPM and when you reduce the cup the center of blade pitch

will come down also. I would shoot for leading edge thickness

At aprox. .020" to .025" thickness. Take the belt sander outside.

Check your PM box. Call Me.

Just A Few Things To Think About,

Mark Sholund

231-590-3023

 

[David Santistevan]

So here are some questions I have, for some of you these may be obvious but to me I feel like a deer in the headlights:

1) Why are props not made of a less toxic and lighter material like aluminum? I understand that the aluminum props would bend more easily but ultimately the whole safety things is a big deal to me.

2) Why are all the casts so rough and require so much work, seems to me current manufacturing technologies could product a better first step prop. Infact, why aren't these props CNC'd, a specific designed could be copied and perfectly matched every time. The finish would be imaculate, the props would be prefectly balanced...

3) Does someone have some information that explains the different prop characteristics like what part of a prop produces lift or cavitation etc.

I am a technical hobbiest. I like to understand all aspects of my hobbies, that is part of the enjoyment for me. When I flew helis I knew every theory and principal that made those lawn mowers fly. Right now props are black hole for me and more importantly I am not excited about the issues of working with BEC.

When I was in the hobby back in the late 70's and early 80's I polished 70 or more props using a dremel tool, files and sand paper and NO mask. With no warnings and being 18 years old (my brain had not solidified yet), I didn't have a care in the world so I still may have to pay for that ignorance....

D

 

[RodneyPierce]

give mark a call. he will explain anything prop related in great detail.

 

[John Knight]

I can respond to numbers 1 & 2.

1. Take a look at the full sized props, from the big tankers to the rec boats. They are bronze/alloys or stainless for durability. Alum is not a strong material and will ultimately fail by bending or breaking. Durabilty is a big factor so a small amt of beryllium is added for strength.

2. CNC work is computer based and is a high dollar machine investment. Then the software is added for an even higher cost. Process is slow for quantity work. Price is determined by initial investment cost, material cost, speed of manufacture and that finally determines the cost per unit. Casting is much faster, less costly and can achieve economies of scale where CNC cannot. However the finished product needs work. I agree the moulds can be improved a lot but how much more will the completed props cost? I suspect the price would be a least double before finishing them to be able to run. Economics drive this train.

BTW, I am a business major, hence my business angle to the equation.

 

[David Santistevan]

Results of running my new worked prop was a significant increase in speed. However, as Mark noted it does seem be laboring and not reaching max RPM. Next step learning how to take some of the cup out of the prop.

D

 

[Tom Foley]

Wear a dust mask if you wish , Have a fan sucking air away from you right at the area you are working and then sweep up the rest . We are not removing fuel rods from a reactor here . I live in the industrial disease world grinding aluminum , stainless , etc . Our tungsten electrodes that we grind for welding everyday contain 2 % thorium .Been welding , glassing , painting etc for 40 years , still have a clean bill of health . I'm not worried , I've sucked nitro fumes from Fuelers , RC boats , dirt bikes , alky hydros ... still here and a clean bill of health !! Paints and solvents present real risks and should be dealt with cautiously as well . be careful of course but don't be afraid of grind on a prop . Stay thirsty my friend .. .

 

[David Santistevan]

Tom,

Thanks for the relief. That helps to know I am not working with a infectious disease or anything. I have a large shop vac with a hepa filter in it that I place right in front of where I am working. Interestingly enough I am going to order some props from Mark, if that works out I may just go that way since I don't like doing the prop work anyway.

Thanks everyone for the help, and it was interesting going through the process of the detongueing of the prop.

D

 

[Tom Foley]

Tom,

Thanks for the relief. That helps to know I am not working with a infectious disease or anything. I have a large shop vac with a hepa filter in it that I place right in front of where I am working. Interestingly enough I am going to order some props from Mark, if that works out I may just go that way since I don't like doing the prop work anyway.

Thanks everyone for the help, and it was interesting going through the process of the detongueing of the prop.

D

Mark does outstanding work , much better than I could dream of doing myself !! His and Andy Brown's props are the ticket to any speed I thought of having !! They are top notch !!

 

[mark voorhies]

Tom,

Thanks for the relief. That helps to know I am not working with a infectious disease or anything. I have a large shop vac with a hepa filter in it that I place right in front of where I am working. Interestingly enough I am going to order some props from Mark, if that works out I may just go that way since I don't like doing the prop work anyway.

Thanks everyone for the help, and it was interesting going through the process of the detongueing of the prop.

D

Mark does outstanding work , much better than I could dream of doing myself !! His and Andy Brown's props are the ticket to any speed I thought of having !! They are top notch !!

Tom, I have to agree with you on the prop guys knowing their stuff, I have tried many times on doing my own and it takes

me hours, and still they are not quiet right, throw alot away after testing. I have bought props from Andy, Mark and

Ernie Lafleur, and all are top notch to race with as you receive them. For guys wanting to try, it's a lot of work, and you

will fail sometimes, but you can get it right if you have the time and patience. Otherwise the guys that know how to do

the props deserve every penny they get for that service. It will make huge difference in performance!