Reuleaux triangle

[Mickwhitt 4,593]

Hi guys.

Following on from the drilling square holes thread I filmed a short video of the Reuleaux triangle I made on the lathe. 

Purely an exercise in machining a complex shape to see if I could do it.

Whenever I show the triangle to people they assume it will not roll because it is not round. But it confounds them as it does have a constant diameter. 

 

 

[CCW 1,292]

Would love to see how you actually produced it on the lathe.

[JoeM 7,871]

3 hours ago, Mickwhitt said:

Reuleaux triangle

Now you need to make a little crankshaft and fix yourself up a mini Wankel Engine! 

[Pullstart 62,801]

Wow Mick, awesome fidget toy!

[953 nut 55,098]

I was thinking the same as @JoeM.           make yourself a tiny Wankel.

[Mickwhitt 4,593]

Lol if only I had the time to build a miniature wankel engine.

Besides, the real reason that kind of engine failed to succeed here is that the word contains a pretty funny swear word in English and no one wanted to show off their shiny new car complete with a WANKel engine.  

[Mickwhitt 4,593]

I will set up the method of turning that I used. To show how its done. Its one of those things you do to see how its done, then never use again. Lol 

[WVHillbilly520H 10,373]

1 hour ago, Mickwhitt said:

Lol if only I had the time to build a miniature wankel engine.

Besides, the real reason that kind of engine failed to succeed here is that the word contains a pretty funny swear word in English and no one wanted to show off their shiny new car complete with a WANKel engine.  

I hope they don't check it on "urban dictionary" ... 

[Jeff-C175 7,199]

3 hours ago, Mickwhitt said:

the real reason that kind of engine failed to succeed here is that the word contains a pretty funny swear word in English

 

It's not likely that something called a "Jerk Off Engine" would sell well anywhere!

[Handy Don 12,163]

3 hours ago, Jeff-C175 said:

 

It's not likely that something called a "Jerk Off Engine" would sell well anywhere!

Think of the fellow who invented the engine and had it named after him.

[Mickwhitt 4,593]

Good old Felix Wankel. Shame the engine never really took off. Looks like the electric motor will replace all IC engines in due course in any event. 

Here is a short video of the method used to turn the Reuleaux triangle on the lathe. First off you have to carefully make a pair of accurate work carriers with three off set centre drillings. 

Then its a case of turning each face of the triangle in turn.

Its pretty straight forward but a good test of your accuracy in marking out and machining. You have to be really gentle with the cutting between centres. 

Mick 

[Pullstart 62,801]

1 hour ago, Mickwhitt said:

You have to be really gentle with the cutting between centres. 

I can only imagine that getting hung up on too big a cut and it goes flying into never land!  Awesome jig, Mick!  Where do you get your figures for the machined holes?

[Mickwhitt 4,593]

The maths of this shape is pretty simple. An equilateral triangle and an arc drawn from each point passing through the other two points.  

I can't for the life of me find where I saw the method for turning a Reuleaux cylinder between centres, it has to have been on the net somewhere but I can't find anything like it.

I will measure up the jigs I made to let you know the dimensions to make the cylinder I did.

That can be scaled up pretty easily.

By the way I said it was a shape of constant diameter, its not. It is a shape of constant width. There is a difference.

Put an axle through the centre of a circle and you have a wheel. It rolls about the centre point as it is of constant diameter. 

Put an axle through the centre point of a Reuleaux triangle and it will not behave like a wheel, because it is of constant width, not diameter. Lose the axle and a Reuleaux will act exactly like a circular roller, so the ancient Egyptians could have easily used them to move their rocks around.

You might have seen Reuleaux triangular section pencils, they don't roll off the desk because the centre of gravity is not the centre of mass of the shape.

I'm going for a lie down now, my head is aching after all that maths (math) and it needs to rest lol.

Mick 

 

[formariz 11,987]

This brings back memories of a long gone family member who was an absolute master gunstock maker and a master carver. To watch him on a treadle lathe turning  gunstock blanks on offset centers was something to treasure. Lathe's pedal return was assisted by a long  branch attached to ceiling using a rope from end of it to treadle. One of those things one has to see it to believe it. Its a shame there were no video capabilities back then. What a loss that none of his children cared about it or followed in his footsteps. He was a big influence on me and I am lucky to also have inherited a few of his tools.

[wh500special 2,163]

It’s really strange and coincidental timing that your post corresponded to a conversation that happened in my office on Monday. 
 

I had a bottle of generic pepto bismol on my desk and was looking at the wankel rotor cross section. Noticed it looked a lot like the triangular/tri-lobe holes you get when you drill a thin piece of metal with a large two fluted drill bit when things aren’t rigid. 
 

I wondered if the width was fairly constant so I rolled it across my desk.  Sure enough, you could see the thing rolled just like the piece in your first video.   Made me smile.  Curious coworkers engaged the issue. It was fun. 
 

Then I saw your post here today.  Wild.  
 

At a previous job I remember we would periodically get those triangles out of the centerless grinders every once in a while.  The smart aleck operators could see they weren’t round but could still measure the right diameter with their calipers so would argue the parts were in spec.   Each time it would happen it would launch a marathon of meetings and a dissertation’s worth of findings to determine the causes.  
 

Thankfully it was somebody else’s department so I could look on as a spectator. 
 

neat stuff. 
 

steve. 

Edited March 16, 2021 by wh500special

[lynnmor 7,302]

1 hour ago, wh500special said:

At a previous job I remember we would periodically get those triangles out of the centerless grinders every once in a while.  The smart aleck operators could see they weren’t round but could still measure the right diameter with their calipers so would argue the parts were in spec.   Each time it would happen it would launch a marathon of meetings and a dissertation’s worth of findings to determine the causes. 

 

Instead of holding meetings, they should have purchased the proper tool.