Making Special Bolt

[Splat]

Guys, I need to make a special bolt used to hold saddle bags on a motorcycle. The price the manufacturer wants per bolt is crazy high. I'd like to make my own for two reasons. (1) Price. (2) there are many reports of this bolt breaking in use. Users report not loading the bag(s) down, but that's subjective. I wonder if it's more from improper install of the bags or mounting device(s). I'd like to make mine from better stock, if possible. The load is perpendicular to the bolt. I don't know how I'd go about turning this bolt so any help appreciated. Also, these don't appear hardened at all.

It is a M8 x 1.25 thread, with the total length about 4".
I don't believe I need the flatted nut-like section if I mill flats onto the bigger (about 5/8" diameter) spacer.
What steel would you recommend?
Should I turn this bolt from an existing 10.9 bolt?

Thank you.

 

[martik777]

Are the bolt and spacer part of the shaft or press fitted on? You could machine the whole part on the lathe except the bolt flats, so cut it round then cut the hex flats on the mill with a rotab or hex collet block.

If used outside I would go with stainless 303 otherwise 1144

 

[Splat]

Sorry, I should have noted it is all one piece.

 

[martik777]

Does it need to be one piece for strength? It would be easier to make in separate pieces. Thread up to where the bolt is and locktite and/or pin the bolt and spacer on.

 

[mikey]

Guys, I need to make a special bolt used to hold saddle bags on a motorcycle. The price the manufacturer wants per bolt is crazy high. I'd like to make my own for two reasons. (1) Price. (2) there are many reports of this bolt breaking in use. Users report not loading the bag(s) down, but that's subjective. I'd like to make mine from better stock, if possible. The load is perpendicular to the bolt. I don't know how I'd go about turning this bolt so any help appreciated. Also, these don't appear hardened at all.

It is a M8 x 1.25 thread, with the total length about 4".
What steel would you recommend?
Should I turn this bolt from an existing 10.9 bolt?
What would you recommend for order of ops?

Thank you.

It seems to me that if these bolts are breaking under load then something about the design is wrong. You have an 8mm bolt locked down and its breaking? Time to look at the system design.

Assuming you just want to go with the original design, I would personally use 1144 steel. It has more than enough tensile strength, is easy to work with and is readily available.

Here is how I would do this part:

• Cut the stock to a little over 4" long and face one end and center drill it for a live center. Extend it and support it with a live center.
• Turn the part to the OD of the round part behind the hex, then turn the part that will become the hex to size.
• Turn the shank of the long part beyond the hex down to 8mm size and screw cut the 1.25 threads.
• Put the shank of the threaded part in a hex collet block and mill the hex.
• Flip the part, chuck up on the round part behind the hex and turn down and thread the short threaded section.

 

[Splat]

Thank you, sirs. Mikey, I think there's gotta be more people not having problems. I don't think Kawasaki would keep this design for quite a few years now if that many were breaking. Maybe I'm making something out of nothing...I just don't get a warm and fuzzy thinking one bolt fails and my back wheel gets a bag mount into it.

This bolt is used, two per side, when you have a backrest and the saddlebags mounted. Here's the page that shows the backrest, saddlebags and mount.

 

[mikey]

Something is moving and vibrating, which has to be causing metal fatigue in the bolts. If you don't address that the bolts will just keep breaking.

 

[Splat]

Something is moving and vibrating, which has to be causing metal fatigue in the bolts. If you don't address that the bolts will just keep breaking.

I just got the bags and haven't installed them yet, Mikey. I definitely agree that it's either the way some folks are installing everything or maybe they're putting too much weight into the bags. With that much stickout they shouldn't be loading them down like crazy.

 

[ErichKeane]

I just got the bags and haven't installed them yet, Mikey. I definitely agree that it's either the way some folks are installing everything or maybe they're putting too much weight into the bags. With that much stickout they shouldn't be loading them down like crazy.

If that is the case (and I am envisioning this bolt's use), then I wonder if just increasing the size of the large diameter would be more helpful. The larger diameter of the shoulder that contacts the bike, the less load would be on those threads.

How are these breaking? Do you have photos of a common broken one?

 

[Splat]

If that is the case (and I am envisioning this bolt's use), then I wonder if just increasing the size of the large diameter would be more helpful. The larger diameter of the shoulder that contacts the bike, the less load would be on those threads.

How are these breaking? Do you have photos of a common broken one?

I thought of trying that too, Erich. I only found one picture and the break was at the longer threaded end that would go thru a saddle bag right about where a nut would thread on.