Safe wall thickness on oscillator crank? and how to pack a bearing

[student123]

On a novice build of the littlemachneshop oscillating engine

http://littlemachineshop.com/Projects/OscillatingEngine.php

I've added a bearing & done the crankshaft differently, (pic below)

Both the crankshaft & upright is ali. After some problems, I ended up d/t the flywheel centre with 6mm int thread.

Bearing inner diameter is approx 6.8mm . Ive turned the crankshaft so the bearing goes on as a tight fit
so outer diam of crankshaft is approx 6.7mm. I've d/t an iner diameter for a 6mm thread, so wall thickness is approx 0.35mm. It feels ok to me + will have a bolt going in , so I'm assuming it will be safe one the engine is running
( presumably there must be a point where a thinner wall would become unsafe)


If its relevant I also plan to do a similar internal thread to fit the crank disc to the crankshaftother side of the upright.

'Is my assumption about 0.35mm thickness being safe correct ?



Hands up I cut the recess for the bearing in the upright the wrong way (a hack with drill , mill, Dremel & file)

So now need to pack the upright around the bearing. I have a pack of modelling clay in the shop. Dries hard in air. Is using clay a not-so-clever idea?? If so, whats best to pack around the bearing?


Mike

 

[Kermit]

Perhaps something in the epoxy class would be better than a clay?

 

[radfordc]

Hands up I cut the recess for the bearing in the upright the wrong way (a hack with drill , mill, Dremel & file)

So now need to pack the upright around the bearing. I have a pack of modelling clay in the shop. Dries hard in air. Is using clay a not-so-clever idea?? If so, whats best to pack around the bearing?

From the picture I would have guessed you used an axe. :big:

Yes, use a filled epoxy such as JB Weld, PC 7, etc.

Charlie

 

[Deanofid]

Mike, that's a pretty thin wall in aluminum. About .013" doesn't sound sufficient to me.

You may have another problem, too. You have a sealed bearing there, and they have
a significant friction factor built in because of the rubber seals. Your engine may not even
make enough power to spin the bearing.

I don't want to sound like a kill-joy, but you've had a few troubles the past month or two.
Is there any reason not to just build an engine exactly as the prints show? I mean, simply
do what the prints say, and work on building modified engines after you get good at this
machining stuff?

We want you to be successful. Sometimes, going by the numbers is the best way.

Dean

 

[student123]

From the picture I would have guessed you used an axe. :big:

I might yet take an axe to this project...!

Thanks for the replies. Dean I didnt know a bearing would increase the friction , thinking 'a bearing - will aid the crankshaft spin round easier '.
So thanks for that.

Off now to have a think on this...

Mike

 

[Royal Viking]

Mike,

What Dean said was that the seal would add friction. You could remove the seal, you may loose some grease in the process. With low load you may get away with it.

Roy

 

[student123]

Roy,

Thanks for the feedback.

Dean,
I jsut want to say thanks again for the reply, particualrly about the wall thickness, which was the main aim of the OP. I'm guessing potentially there could have been a problem laying dormant to surface unexpectedly in the future. I've abandonded that approach on your advice.

Mike