Left Hand Metric Bolt Needed

[ErichKeane]

I wonder if you'd be better off rethreading the LH thread into a RH thread and just using loctite to keep it from spinning out? That way you can use the same bolt for each side.

 

[mksj]

A little of a challenge figuring the setup for doing left hand metric thread, fotunately my lathe has a universal gearbox and easy to change the carriage direction relativve to the chuck direction. I started with 12.9 Alloy Steel M10 160mm Allen head screws and cut the threads off, then cut the shaft to 120 mm. I then cut my relief and I was able to use it as a zero reference for my proximity stop system, so the thread starting point was always be in the center of the relief groove. When I thread I do not disengage the half nut until the thread is completed and advance with the cross slide so the cutter tip position doesn't change position. All my reflexes were a bit backward, but was able to turn out two left hand bolts and used left hand nuts to verify the fit. Will ship shortly.

Two right hand and two left hand M10-1.5 120mm, stock threads are just under 35 mm, I cut the left hands to 32 mm per the spec. requested.

 

[lesrhorer]

I wonder if you'd be better off rethreading the LH thread into a RH thread and just using loctite to keep it from spinning out? That way you can use the same bolt for each side.

Why would anyone do that? It's no more difficult to properly thread a blank than to double-thread an existing screw, and far, far stronger. These bolts need to be quite strong. Indeed, they need to be at least a bit stronger than the original setup required, and the original bolts were quite properly tightened down under a lot of torque. It was difficult to break them loose.

 

[ErichKeane]

Why would anyone do that? It's no more difficult to properly thread a blank than to double-thread an existing screw, and far, far stronger. These bolts need to be quite strong. Indeed, they need to be at least a bit stronger than the original setup required, and the original bolts were quite properly tightened down under a lot of torque. It was difficult to break them loose.

I mean drilling out & helicoiling (or similar) the LH thread and just using a RH thread. Rolled threads (like in factory bolts) are an order of magnitude stronger than cut threads, so the tradeoff would, IMO be worth it.

Typically you use a LH thread to counter rotation of the wheel, but a good thread locker makes this completely unnecessary. From what I can see by the rest of the construction, this is a pretty low load axle (let alone using a bolt as an axle!), so using a LH thread rather than some thread locker seems wasteful...

EDIT: Another consideration: Unless these wheels go 'really fast' (fast enough that centripetal force is the major component), the load on the threads themselves is going to be fairly minimal. A cantilevered wheel like that puts most of its force perpendicular to the threads holding force, not in line with it. SO the force required to hold it in is, comparatively, quite minimal. The BOLTS might need to be strong (to contend with the bending force) but the threads themselves dont.

 

[lesrhorer]

Oh, I see. Well, the bolts were originally installed with thread locker, as it happens. You are of course correct the issue is not the longitudinal force on the bolt, although that is significant. It is the shear force which will likely be greatest, and that force falls right on the threaded portion of the bolt, which is also the thinnest part of the bolt. It also happens to fall on a part of the bolt with a very small radius - a crack already starting to happen. With the extension, the torque perpendicular to the bolt is also much, much greater than the original setup, since the end of the lever is now almost 3" away from the fulcrum, rather than under an inch. 'Somewher between 3 and 5 times longer.

In any case, the point is moot, since mksj already did a great job of threading the bolts.