Screw size for mounting 608 bearing

[zohar golan]

Hi All,

What screw size are you using with 608 bearing in your projects?

608 hole diameter is 8mm, 5/16" screw is ~7.4mm, M8 is also around the same, and M10 is too big.

In my CollapsiRap  printer I am designing, there is too much slope in the bearing when I am using the 5/16 screw. I am considering using a much smaller 1/4" screw and make an adapter between the 1/4" hole size and the 8mm cylinder for mounting the bearing.

Any other ideas?

Thank you,

Zohar

[jorwex]

I believe I'm using 5/16". Seems to work nicely. 

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Jordan W

[Ken Snyder]

M8 is much closer to 8mm.  That's why they are called M"8".  Mine measure 7.85mm.  You don't want them to be exactly 8mm.  They should be just right for the 608 bearings.

Ken

[Bill Seiler]

Where is the meeting tonight?

San Jose TechShop?

[zohar golan]

Hi Ken,

I've tried the M8 in OSH and they the bearing also have a huge slope on them. The bearing measurement is pretty good thou. I guess I will have to have adaptors there

Zohar

On Wednesday, July 2, 2014 9:47:09 AM UTC-7, Ken Snyder wrote:

M8 is much closer to 8mm.  That's why they are called M"8".  Mine measure 7.85mm.  You don't want them to be exactly 8mm.  They should be just right for the 608 bearings.

Ken

On Wed, Jul 2, 2014 at 9:18 AM, jorwex <jor...@gmail.com> wrote:

I believe I'm using 5/16". Seems to work nicely. 

On Wednesday, July 2, 2014, zohar golan <zohar...@hotmail.com> wrote:

Hi All,

What screw size are you using with 608 bearing in your projects?

608 hole diameter is 8mm, 5/16" screw is ~7.4mm, M8 is also around the same, and M10 is too big.

In my CollapsiRap  printer I am designing, there is too much slope in the bearing when I am using the 5/16 screw. I am considering using a much smaller 1/4" screw and make an adapter between the 1/4" hole size and the 8mm cylinder for mounting the bearing.

Any other ideas?

Thank you,

Zohar

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[John Asay]

5/16" = 7.94mm not 7.4mm.  Are you using shoulder screws or fully threaded screws?  

Dimensions below from Machinery's Handbook 28th edition.

Depending on thread pitch and class of threads Standard 5/16" screws should have a major diameter between .2982" and .3125".  This is 7.57-7.94mm.

Shoulders should be .002"-.004" below nominal so a shoulder on a 5/16" should be .3085"-.3105" or 7.84-7.89mm.

8mm thread major diameter, again depending on pitch and class, can range from 7.76-8.00mm

8mm shoulders should be be something like 7.95-7.99mm

I have no idea what the tolerance on the bearing is.

John

[Elliot]

Zohar,

Have you considered a printed part for the bearing to ride on?

[zohar golan]

Yes I did.

Its actually in my first post ;-).

I was thinking to print an adaptor from the 8mm to 1/4" screw hole, but I wonder if there is an already made solution. Doesn't look like I have a choice.

Zohar

[danman]

5/16th is what I use - keep in mind that it's a good idea to tighten down the bolt until it clamps the center portion of the bearing so that it is stationary. That way you have almost no wobble (only wobble from the bearings/housing) and the bearing will spin fine.

-Dan