# Building a Prony Brake



## T70MkIII (Jul 16, 2010)

Tubal Cain has posted a 2 part facetube on building and using a Prony Brake dyno that may be of interest - well, it captured my interest, being new to all this stuff. I'm not sure whether accuracy changes significantly with lower torque engines. Useful for an indicative reading for a small multi cyl engine, perhaps?

Part 1:
[ame]http://www.youtube.com/watch?v=9Wi51Kf8bzA&feature=uploademail[/ame]

Part 2:
[ame]http://www.youtube.com/watch?v=weJhTdnlUAo&feature=uploademail[/ame]


----------



## steamer (Jul 16, 2010)

Works fine for small engines! ;D






I wouldn't mount weights loosely though...you might eat one......

I used an electronic fish scale and a heavy fishing line, pulling through a pulley.

The scale reads in pounds, so I made the brake 1 foot long so I could read the scale in "pound feet".



Dave


----------



## Dan Rowe (Jul 16, 2010)

Dave,
Very nice marine engine. Is there by chance a thread on the build? I made a failed search atempt to find it.
Dan


----------



## Deanofid (Jul 16, 2010)

That's a neat thing. I've read about them, but it's a lot easier figuring out the thing seeing it work.

So, Tubal Cain was an American dude from Chicago, then... And all these years
I thought he was another one of those crafty British fellows.  :


----------



## mklotz (Jul 16, 2010)

Tubal Cain is a character in the Hebrew bible,

http://en.wikipedia.org/wiki/Tubal-cain

supposedly the inventor of metalworking.

I believe that, over the years, a number of amateur metalworkers have adopted his name as a nom de plume.


----------



## cidrontmg (Jul 16, 2010)

The British Tubal Cain wrote some 20 books (and many articles for the M.E. magazine) but he also wrote a couple of books with his real name, TD (Tom) Walshaw. BSc (Eng), DLC (Hons), AMIMechE, AMIPE, and one-time lecturer in mechanical engineering at the University of London. Sadly passed away in 1998.

The biblical Tubal Cain is the supposed inventor of the forge, and thereby all metalworking.


----------



## Deanofid (Jul 16, 2010)

mklotz  said:
			
		

> Tubal Cain is a character in the Hebrew bible,
> 
> http://en.wikipedia.org/wiki/Tubal-cain
> 
> ...



I know about the Tubal-cain in the the Bible, and that Tom Walshaw, the famous person (in model 
engineers' terms) used that pen name. Considering who Walshaw was, and the huge contribution he
made to our hobby, it seems cheap and unseemly for another person to use the name. Like a third 
rate soap opera actor using the name John Wayne.

About the historic guy, my Bible just says: "an instructor of every artificer in brass and iron". 

Dean

EDIT: Sorry Cidrontmg, I missed your post while I was typing!


----------



## T70MkIII (Jul 17, 2010)

I assumed they were one and the same, having heard the name held in great regard but not yet having read any of the lauded authors' books


----------



## bearcar1 (Jul 17, 2010)

I know what you mean about the name thing Dean and I agree. 

BC1
Jim


----------



## mklotz (Jul 17, 2010)

Dean,

I missed your point the first time around but, now that you've explained, I must say that I agree.


----------



## steamer (Jul 17, 2010)

Dan,

My Launch engine is Pre HMEM.  I can send you some photo's if you like...but not here... 

What about eddy current for a Prony brake....no contact.


----------



## gmac (Jul 17, 2010)

Dave;
Add me to the "interested" list - even if it's just a few more photo's of the dyno setup.
Thanks
Garry


----------



## Tin Falcon (Jul 17, 2010)

For those of you that like digging into old technical books look here:

A handbook of engine and boiler trials and of the indicator and Prony brake:
Around pg 290 it starts explaining the prony break. 
Tin


----------



## steamer (Jul 18, 2010)

Garry and Dan,

I've still got the brake portion somewhere in the shop...I'll see if I can dig it up.

The ball bearing pulley comes from a sliding glass door, mounted on an angle bracket.

I made one turn around the pulley before I tied off to the scale with the torque arm in the horizontal position.

I clamped the fish scale in a make shift wooden clamp. As it is the electronic type,and not the spring scale type, under load the torque arm doesn't move at all.
All of it was mounted to this piece of scrap particle board for the test. Make sure the engine is strapped down securely before you do this.

I got 3/4 HP on 80 psig WET steam @ 600 rpm or about 6.5 pound feet of torque.
with a very satisfying "Bark". That was all the pressure that particular boiler had at the time as my boat boiler wasn't completed yet.

HP = 2 Pi N T/33000....she was and is designed for 600 rpm @ 160 psig with a vacuum...somewhere in the 2 HP range or about 17 pound feet of torque...she runs much better there.... ;D

Dave


----------



## steamer (Jul 25, 2010)

I dug up the brake....here's some photo's of it in position.




































Dave


----------



## gmac (Jul 26, 2010)

Dave 
Thanks for taking the time to post the photo's.
Cheers
Garry


----------



## steamer (Aug 10, 2010)

Here's a few...browse thru if you like.

http://i164.photobucket.com/albums/u27/mcandrew1894/P7250034.jpg
http://i164.photobucket.com/albums/u27/mcandrew1894/P7100057.jpg
http://i164.photobucket.com/albums/u27/mcandrew1894/P7100058.jpg
http://i164.photobucket.com/albums/u27/mcandrew1894/P5250141.jpg
http://i164.photobucket.com/albums/u27/mcandrew1894/P5250142.jpg
http://i164.photobucket.com/albums/u27/mcandrew1894/P5250143-1.jpg

Thanks for the interest.

Dave


----------

