Wrong hobbed bolt?

I wanted to try a knurled bolt and I bought one like this: [www.ebay.es]

Shipping was fast but bolt seems useless as the bolt area won't go through 608 bearing. Seller seems unresponsive and I made the mistake of providing positive feedback before testing the bolt first.

Did anyone have a similar problem? Did you fix it?

I still can open a PayPal dispute, but I hate when sellers force me to do this dance.

That bolt is imperial - it will never fit a metric (608) bearing.

You need a 1603ZZ bearing - that *might* fit.

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- akhlut

Just remember - Iterate, Iterate, Iterate!

[myhomelessmind.blogspot.com]

The problem as I mentioned is that the knurled area won't go through the 8mm hole of 608 bearing. I know that bolt I've bought is imperial 5/16". But according to my calculations

5/16inches*25.4 mm/inch = 7.93mm so the diameter of a 1603ZZ bearing would smaller and not larger than 608.

I guess the knurling raised the surface beyond the original dimensions of the bolt. But sanding it down would entirely defeat the purpose :-(

Thanks for the hint, though.

I'm here in the usa, and have my calipers handy.
measurements are at bolt head and before threading.
I just grabbed 1 8mm and one 5/16.
metric 8mm bolt is 7.92mm- 7.84mm
imperial is 7.82mm 7.77mm

I would bet the next time i pick up similar bolts the measurements reverse!

as for knurling, it does push up the surface. I would bet that metal bolt would shrink if it is refrigerated for 10 minutes in your freezer, then just slide it thru without damaging it, let it cool in place, do not torque down on it until back at room temp.

akhlut Wrote:
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> That bolt is imperial - it will never fit a metric
> (608) bearing.
>
> You need a 1603ZZ bearing - that *might* fit.


5/16" is smaller than 8mm.

I imagine, as mentioned, that the knurling raised the surface of the bolt. Try the freezer thing.

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Freezer thing sounds promising.

Thank you guys!

Oops! I got it backwards! That's what happens when you read the forums at work...

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- akhlut

Just remember - Iterate, Iterate, Iterate!

[myhomelessmind.blogspot.com]

Maybe I can buy myself a reprieve. Get a drill,mount it in a vise and put the bolt in the chock. Spin it up and lightly file down the knurled area.

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- akhlut

Just remember - Iterate, Iterate, Iterate!

[myhomelessmind.blogspot.com]

Unfortunately -22C was not low enough for the bolt to go through the bearing. I guess plan C is to make the bearing hole larger.

You could also try heating the bearing while you cool the bolt. Not sure how hot you can get it without damaging it, but bearings are cheap.

Bearings are packed with grease so you can't get it too hot.

I don't think the amount metals expand and contract is the same order of magnitude as the height that knurling creates. The bolt seems like a floored concept to me.

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[www.hydraraptor.blogspot.com]

The thread is titled Hobbed but the subject part is clearly knurled. When you hobb something material is removed. When you knurl something material is not removed but deformed using a knurling tool (basically a raised cross pattern on two two rollers) using a lathe. So no matter what bolt you start with, that is close to 8mm, the knurled zone will be over 8mm. If you file it back to 8mm you loose the tips of the dimonds and not grip the filiment. So unless you support the bolt in some other way other then using the bearing ID, I don't see how knurling can work. There a plenty of posts describing how best to hobb extruder bolts.

You need to reduce the bolt diameter where you are going to knurl. If you knurl a threaded rod, you don't need to do that. I used one for a while, until a tiny piece of the knurl came off and plugged the hotend.

Or fit the bearing from either end, like if the bolt was threaded on both ends a bit like the new Arcul bolt. (his is hobbed not knurled).

@dean448: You are right about the subject, knurled and not hobbed.

@stepherrc: oops, knurling a threaded rod is now in my not-to-try list.

@rcs: It's an idea I could not use as my knurling are is already pretty off-center, cutting the bolt head and threading the bolt collar will get the knurling area off the filament hole in standard extruders.

I have no knurling experience but the purpose of my topic was twofold, on one hand to get help in case there was something I could to to use the knurled bolt I've bought, on the other as a warning call to other reprappers that might buy the same thing from the same add and run into the same trouble I am in.