How do I spin a small cylinder longways?

[StevenRice]

TL;DR Summary

Spinning a small cylinder precisely.

Imagine laying a pencil down, and spinning it on its own graphite. What do you call that, "spinning" or "rotating"?

 

[shjacks45]

Dictionary same. Synonyms. Spinning usually implies rapid rotation. Trying to ballance my pencil on its graphite point and it falls over. Stuff with lower center of gravity, like a dreidel, spin better. Coins spin pretty good on edge, fall over when rotation slows.

 

[StevenRice]

Dictionary same. Synonyms. Spinning usually implies rapid rotation. Trying to ballance my pencil on its graphite point and it falls over. Stuff with lower center of gravity, like a dreidel, spin better. Coins spin pretty good on edge, fall over when rotation slows.

Dictionary same. Synonyms. Spinning usually implies rapid rotation. Trying to ballance my pencil on its graphite point and it falls over. Stuff with lower center of gravity, like a dreidel, spin better. Coins spin pretty good on edge, fall over when rotation slows.

Good answer, thanks. You might even be able to help me with my main question. I'll be creating a new topic for that.

[Mentor Note -- No, your two threads on the same subject have been merged. Please check your PMs. Thanks]

 

[StevenRice]

The dimensions are 6 inches long, and about an inch diameter. How do I lay it down, and spin it precisely, with absolutely no shake?

I understand that I need to know the exact radius, and find the center of each side. But, what do I do next?

 

[Baluncore]

1. Will the axis of the cylinder be horizontal or vertical?
2. Will it spin about the vertical or the horizontal axis?
3. How will it be mounted, what will it rest on?
4. How will you couple energy into it to start it spinning?
If you spin it on Earth it will be influenced by the rotation of the Earth.

 

[Tom.G]

Summary:: Spinning a small cylinder precisely.
How do I lay it down, and spin it precisely, with absolutely no shake?

If you are you asking about the technical requirements:
Make sure the spin axis goes thru the objects center-of-gravity; and that the object is dynamically balanced.

The first part is (relatively) easy with a dimensionally symmetric object.
If the mass is uniformally distributed about each of the three axes, you are done.

If you are asking about the manipulation and gripping details, see the post above by @Baluncore, who typed faster than I did.

Cheers,
Tom

 

[StevenRice]

1. Will the axis of the cylinder be horizontal or vertical?
2. Will it spin about the vertical or the horizontal axis?
3. How will it be mounted, what will it rest on?
4. How will you couple energy into it to start it spinning?
If you spin it on Earth it will be influenced by the rotation of the Earth.

Thanks for the scientific response. Aren't question 1 and 2 the same? I think I should say that I need it to spin on the vertical axis, if it was standing up. The horizontal axis, if it was laying down. But, I usually say: "Iimagine a pencil laying down, and spinning it on its own graphite." Is that the vertical or horizontal axis?

 

[Baluncore]

Questions 1 and 2 are different, but connected.
Do you know what the principle axis of a cylinder is ?
Do you know the difference between a vertical axis and a horizontal axis ?
Then you can answer the first two questions one at the time.

"But, I usually say: Iimagine a pencil laying down, and spinning it on its own graphite."

Do you mean it's point where the graphite is exposed?
Or do you mean spinning about the principle axis that follows the centre of the graphite along the pencil ?

Things spin about an axis. Things spin on a support.
How would it be supported ?

You need to describe it clearly by answering the questions, or attach a sketch.

 

[StevenRice]

I am not a great artist, but I drew this on my Android phone. The spin I'm talking about actually has almost NO movement. I asked my brother about it, and he said that I should put it on something like a rotisserie.

 

[Rive]

Summary:: Spinning a small cylinder precisely.

with absolutely no shake?

That may be an absurdly stitch requirement. But if what a ball bearing can provide is acceptable then you may put in or around your cylinder a bearing. For any general usage it should do.

 

[StevenRice]

I believe that a bearing may be a good solution. But, how do I attach the bearing to the cylinder?

 

[Baluncore]

Bearings come in many types and sizes. https://en.wikipedia.org/wiki/Ball_bearing
Push the cylinder into the bearings. House the bearings in holes bored in parallel walls.
The type of bearing will be important. What is the cylinder diameter?

The cylinder will sag due to gravity, so you may need two or more bearings, at maybe 25% and 75% of the length depending on requirements.

How fast will it spin? At some speed the cylinder will become bowed and will twirl. It will need to be controlled by positioning bearings.

You have not yet provided sufficient information to answer your question.

 

[berkeman]

I asked my brother about it, and he said that I should put it on something like a rotisserie.

If you used clean new hot dog rollers and added small thrust bearings to constrain the movement in the axial direction, would that work?

https://www.restaurantsupply.com/me...0ea9ea74156d57dd117fae31f3703/4/0/40821_1.jpg

 

[StevenRice]

If you used clean new hot dog rollers and added small thrust bearings to constrain the movement in the axial direction, would that work?

https://www.restaurantsupply.com/me...0ea9ea74156d57dd117fae31f3703/4/0/40821_1.jpg

View attachment 266936

Thanks for the idea of using bearings. Hot dog rollers won't work for this project. But, I found perfect bearings. Now, I am wondering how I should have the bearings held to be able to spin the cylinder precisely, with NO shake. I might use some Loctite to secure the bearings to the cylinder. But, I don't know how I should have them held?

If you're wondering, you can see it here :

 

[Baluncore]

Now, I am wondering how I should have the bearings held to be able to spin the cylinder precisely, with NO shake. I might use some Loctite to secure the bearings to the cylinder. But, I don't know how I should have them held?

Loctite will be uneven and may create a balance problem.
A press fit would be a better solution.
We need to know what you are trying to do, and why you are trying to do it.
1. How much vibration can you tolerate ?
2. How fast will it rotate, in RPM ?
3. What will drive the rotation ?

 

[StevenRice]

Loctite will be uneven and may create a balance problem.
A press fit would be a better solution.
We need to know what you are trying to do, and why you are trying to do it.
1. How much vibration can you tolerate ?
2. How fast will it rotate, in RPM ?
3. What will drive the rotation ?

I won't be able to tell you everything you say you need. Because I fear that someone might steal my ideas. But, I can answer some questions.
1. I can't tolerate any vibration
2.+3. I have no idea what the RPM will be. I might be trying to use a cordless drill to spin it. But, nevermind.

 

[Baluncore]

If you start it with a cordless drill, then vibration will be a problem, the drill coupling will introduce so much vibration that it will probably damage the bearings.

A gyrocompass operates with a horizontal axis, spinning at between 15,000 RPM and 40,000 RPM, usually driven by an electric motor.
https://en.wikipedia.org/wiki/Gyrocompass

The spindle in the head-stock of a precision lathe must rotate without vibration. Lathes use accurate high grade spindle bearings, that are arranged to control the alignment of the spindle.

I won't be able to tell you everything you say you need. Because I fear that someone might steal my ideas.

That suggests you are so far behind, that you think you are first.

 

[PeterDonis]

I won't be able to tell you everything you say you need. Because I fear that someone might steal my ideas.

Personal research is out of bounds for discussion here at PF.

Thread closed.