# Videos > Instructional Videos >  Bearing Block Sheath Demonstration

## crashdive123

It wouldn't be right to make something and not field test it.  Worked out a big kink in the process.  The three strand sisal twine cordage broke on the third use.  I braided another piece and the same thing happened on the third use.  I switched to 550 cord.  I don't think there will be any breaking issues with it.

----------


## COWBOYSURVIVAL

Way to go Crash!

----------


## mosquitomountainman

Good video.  Thanks

----------


## Winter

Never saw that before Crash. That's an awesome idea. Can't have too many plan B's.

I'm impressed.

----------


## rwc1969

That's pretty neat. Hey, was it raining? LOL!

----------


## Skinner

Lookd Great and Good Thinking Ahead With the Skate Board Berring. Man If you did this Yesterday It Was 101 here In Woodvill Florida I Can Understand the Sweating ,LOL

----------


## your_comforting_company

Great job Crash! I like the way you've blended ancient technology with modern. 
Watch that paracord tho.. it will break, just not as quickly as the twine. The outer sheath seems to "slip" causing friction inside the cord. I've broken paracord twice now on the bow. 
I hadn't thought about it, but I have several old broken skateboards. Might consider throwing a wheel in my kit.

----------


## crashdive123

> That's pretty neat. Hey, was it raining? LOL!


Very windy.  34 wildfires burning in the area.  Didn't want today's headlines to read 35.

----------


## finallyME

That is a cool idea.  Is the bearing a sealed one?

----------


## welderguy

That's an awesome idea, thanks

----------


## tuxdad

My question is where do you get the bearings ?? I'd like to try that as well..
Great vid !!

----------


## crashdive123

Most sporting good stores should have them.  I bought mine at Academy Sports.

----------


## Pocomoonskyeyes3

Have you tried using leather or rawhide for your string? That is a great job Crash. A really cool innovation.

----------


## crashdive123

I have not tried leather or rawhide.

----------


## tuxdad

Will have to take a look around my area.. I only found skateboard wheels in walmart, and wasn't too sure of how to get the bearing out of it other then melting it...lol 

Thanks

----------


## crashdive123

If you have the wheel/bearing combination, I'm pretty sure the bearings are just pressed in.

----------


## crashdive123

> That is a cool idea.  Is the bearing a sealed one?


Sorry I missed this when you asked.  I'm pretty sure they are shielded bearings and not sealed.

----------


## tuxdad

> If you have the wheel/bearing combination, I'm pretty sure the bearings are just pressed in.


Will have to check the next time I'm in walmart...

----------


## crashdive123

I looked in one or the local WalMarts and they did not have replacement bearings.  I think a sporting goods store might be better.

----------


## tuxdad

Thanks, will check the "dick's" and "dunham's" up here...

----------


## tuxdad

Check both those places out that I mentioned... I'll have to wait a bit before putting $35 into bearings(wheels and bearing kits)... I'll check the local bike shops as well to see if they have any cheaper...

Thanks again

----------


## crashdive123

I paid $15 or $20 for a pack of 16 bearings.  If you want a couple, PM me your address.

----------


## tuxdad

I check around some more first.. Will send a PM if I can't find them ...

Thanks !!

----------


## tuxdad

Looks like I'll have to take you up on your offer Sir..... 

Having a devil of a time finding any of just the bearings....

PM sent...

----------


## crashdive123

Got the PM.  I'll get a couple out to you this week.

----------


## tuxdad

Thanks Again  Crash !!

----------


## tuxdad

Just got presented a package by my beloved as I walked through the door... 

Thank you Brother Crashdive !! :Wavey:

----------


## crashdive123

You are quite welcome.  Make sure you post pictures of what you end up making with them.

----------


## whitis

Neat idea.

I do have some constructive criticism:
- you are using a radial bearing for a thrust load.    At least it is probably a deep groove bearing so it will take some thrust load but if you put too much force on it the bearing may pop apart.   Depending on the bearing, though, it might be able to take a couple hundred pounds.   A regular groove bearing can easily pop apart with hand force.
- on the back side of the bearing, you need to apply force/contact only to the outer race.   If the inner race rubs, which will be the case with a flat surface, you don't really have a ball bearing.   I see no explicit design feature in your construction plans to allow for this.
- you appear to be applying force through a hollow section of the sheath, though this may be partially filled by the knife.
- basic skate/skateboard bearings are very low quality (though some sites sell real bearings as replacements).   The balls and race grooves are about as round as percentile dice.   Hence the noise.   Not very critical in this application but it is possible to reduce the noise with normal quality bearings.

In your test, the leather may be cupping some under load taking pressure off the inner race, such that flaw #3 is canceling out some of flaw #2.

At least the bearing noise suggests the inner race is turning, though not necessarily at the same speed as the stick.   This was not a foregone conclusion.   If the coefficient of friction between the steel and leather exceeds the coefficient of friction between the steel and wood, the inner race can remain stationary.   Both are typically in the 0.2 to 0.6 range.   Oily leather and a dry stick and the inner race turns (but wastes energy).   Wet stick and dry leather and it may not.   Dry wood on wood has a coefficient of friction of 0.25 to 0.5 - not necessarily any worse than a bearing that has been reduced to a bushing.  The coefficient of friction for a sealed ball bearing might be around 0.004 - around a hundred times better.   Do you want 50% of your effort delivered to the stick to go into making fire or 99.5%?

You haven't really demonstrated that it works better than a plain wood, steel, polyethelene, or leather bushing or an ordinary snap fastener used as a bushing.  At one point in the video, you show that the stick spins freely in the bearing but there is no significant load.

Given the effort put into it, I would assume you want: 1) the effort expended to go into producing fire, not waste heat in the wrong place, 2) long life, and 3) to avoid the embarrassment of the sheath catching fire instead of the wood.   I.E. you want it to work as well as possible, time after time, under adverse real world conditions where an improvised bushing may not.

Normally, the bearing mount would consist of two concentric flat bottom holes bored in a piece of metal.   The deeper whole is about the same size as the inner diameter of the outer race and the shallower hole is about the same size as the outer diameter of the bearing (normally very slightly undersize for a press fit but that isn't needed in this case if you have a way to retain the bearing).   The difference in hole depth must be enough to prevent the inner race from bottoming out at maximum deflection under load and the remaining thickness of metal supporting the back side of the outer race must be thick enough to not shear off under load.   The smaller hole can go all the way through (but you can't allow the leather above to deform into the hole enough to touch the inner race).   As an alternative, bearing shims can be used but in this case they may not stay put.

----------


## tuxdad

> You are quite welcome.  Make sure you post pictures of what you end up making with them.


Will do !! Unfortunately it won't be for a couple of weeks... Heading up to see my stepson graduate from boot camp next weekend, and this weekend is getting preps done for the trip(12 or more hours of driving)....

----------


## crashdive123

Tell your Stepson thanks from all of us.

----------


## tuxdad

> tell your stepson thanks from all of us.


will do !!

----------


## Cousin-IT

cool idea crash..... but going on from what whitis said.... bearings get dirt in them.

why not a solid chunk of metal with tip of a 1/2" drill in it and add lard or spit for lobe?
-so the metal chunk would look like this:

|"""\/"""|

...hell you could incorperate it into a knife handle  :Smile:

----------

