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Old 05-20-2015, 08:09 PM   #11
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Originally Posted by terryp View Post
I was thinking maybe the broken bolt could be drilled out, and a nut welded to the back of the plate, over the old head, but there's not enough space.

What if I drilled and tapped a couple 12-24 holes in the plate, one on either side of the broken bolt, then drilled holes in the wheel for bolts? The plastic would have to be cut away around the new holes so the heads could rest against the metal insert in the wheel. I'd also use lockwashers and thread-locker.

Do you mechanical types think that would work?
The wheel plate and those bolts are pretty well balanced. Replacing the broken bolt with a similar piece (like at a welding shop) or an option similar to that may work for you.

Drilling new bolt locations, and modifying the wheel to match are less likely options to be successful with. At this point, you accidentally broke a bolt, which has resulted in a wheel flange with 2 1/2 bolts instead of 3. It may eventually require you to replace a transmission because of it.

At some point, drilling and tapping, and modifying a wheel seems like a project that may be more likely to make things worse than better. Getting the exact placement will be difficult. I suppose you could mount the wheel with the other two bolts, then thru drill the wheel and flange at the same time, but the flange is hardened steel, and the plastic wheel will not give the same or even similar resistance.

Also, there are stiffeners inside the plastic wheel, and their exact placement may be difficult to deal with when mounting bolts in other places than factory expected...

As a 'mechanical type' I would offer that there are better solutions to try before this route.

Of course, it is your machine, and you can and should do whatever you want. You and only you can judge what you can do, and what you cannot do.

Good luck on whatever you try, and keep us posted.
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Old 05-20-2015, 09:48 PM   #12
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Default Carl is right

The flange is hardened, and a standard bit barely makes a dent. Special drills and taps are available, but would cost as much as a new gearbox.

There aren't any machine shops nearby, and I haven't ever seen a used 2nd gen gearbox offered on ebay, so I'll just bite the bullet and buy a new one and consider this another hard-learned lesson: When in doubt, look it up.

Thanks for your suggestions.
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Old 05-20-2015, 10:45 PM   #13
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I'm wondering if the transmission can be disassembled for output shaft / mounting plate removal, and take it to a machine shop to have a new lug installed.

Quite an oversight for the assembly to be designed such that a wheel lug can't easily be replaced...

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Old 05-20-2015, 11:32 PM   #14
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A wheel bolt shouldn't ever break unless some idiot (see picture at left) exceeds the published torque spec.

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Quite an oversight for the assembly to be designed such that a wheel lug can't easily be replaced...
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Old 05-21-2015, 06:57 AM   #15
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A wheel bolt shouldn't ever break unless some idiot (see picture at left) exceeds the published torque spec.
I am thinking it is a testament to the overall quality of the segway build that it could withstand the stress involved in snapping this bolt in the first place.

I do not mean to be harsh, but it takes a pretty large amount of force to snap one of these bolts. Of course, a bolt may be manufactured in a faulty way, or some other unusual factor can be involved, but mostly, it takes human interaction with a mechanical advantage (large wrench with a lever action) to give the strength needed to snap these things.

If this were a situation where you had a wrench on the head of the bolt, and another on the nut of the bolt, the stress can be isolated to the bolt itself. That is how thru bolts break.

But in this case, the head is press fit into a pretty thin piece of hardened steel, which is press fit a few inches away onto the output shaft of the transmission. That heavy stress that caused the break has no choice but to be transmitted at the other end thru the flange to the output shaft, and therefore any seatings for that shaft.

I do not believe that a situation with enough force to snap a bolt like this is isolated to that bolt. All the other components have been taking the stress of this overtightening for some time, and they have survived.

The question is, how well have they survived? Can they take more stress?

I think the segway components are very well built, and we really have heard of very few failures of a mechanical nature. But... Will this transmission deal well the added stress of a machine shop repair?

One suggestion was to take the tranny apart and replace the output shaft or last gear and output shaft, with a new one with a good flange on it. While in theory this may work, I believe the individual parts may be as hard to come by as an entire transmission, the question remains in my mind, how well with these shaft seals and seats take to a new shaft? They have already been stressed with what took out the bolt.

Another suggestion was to go to a machine shop, and have them potentially cut out and weld in, or add on another section of threaded rod. This too may well work, but can that assembly take the stress of the heat of welding, or other stresses, considering its age and previous stresses that it has already endured?

I always dread taking my car to the mechanic for repairs, because I have found that in any mechanical system, once you disturb a process that has been working for some time, you introduce new problems. I don't know how much is actual, and how much is psychological, but whenever I get a car back from one repair, I notice other issues wrong.

I wonder the same on this. This bolt gets replaced or repaired, and other issues are then noticed about this transmission, or the track and feel of the segway.

If this activity (50 pounds of pressure) has been applied to all 6 bolts, perhaps new trannys need to be on the short list of what to find. For me, it would up the ante on finding a broken segway, one that is available cheap for electrical or battery problems, and then have the new transmissions both for this side, and a spare for the other side.

In this case, since the segway transmission is pretty well sealed, you can even take a water damaged unit and have no problems.

I believe there are many segways that are no longer used for battery or electrical problems of one sort or another. The cost of repair of these issues is high enough to keep most from ever being repaired. The new problem is how to find them...

Good luck...
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Old 05-21-2015, 08:54 AM   #16
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Quote:
Originally Posted by terryp View Post
The flange is hardened, and a standard bit barely makes a dent. Special drills and taps are available, but would cost as much as a new gearbox.

There aren't any machine shops nearby, and I haven't ever seen a used 2nd gen gearbox offered on ebay, so I'll just bite the bullet and buy a new one and consider this another hard-learned lesson: When in doubt, look it up.

Thanks for your suggestions.
Drilling out hardened bolts my be difficult but not hard to do...

The harder the metal the slower you drill....Keep it (bit)cool and lubricated, this is not difficult, I drilled out many bolts on engines ...

Use small drill bits and go larger... It will not cost $500 in drill bits!
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Old 05-21-2015, 11:09 AM   #17
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A bit of an exaggeration, but at least $100 for the pair.

I'll eventually take the old gearbox to a shop to see if there's anything they can do without having to open it. I'll also watch for a used machine with other problems for the right price. But for now, I've ordered a new gearbox.

As for Carl's suggestion that something else might have been damaged, I think that's very unlikely, considering how much torque gets delivered to the wheels.

I'll also pick up a smaller torque wrench. Mine goes up to 150 ft-lbs, so probably isn't very accurate around the 25 mark. It was the only choice at the local auto parts store.

Finally, since the other bolts have survived 50 ft-lbs for years, I'm not too worried that one's going to snap while riding now that I've reduced the torque to half that. <Knocking on wood>

Quote:
Originally Posted by airdale View Post
Drilling out hardened bolts my be difficult but not hard to do...

The harder the metal the slower you drill....Keep it (bit)cool and lubricated, this is not difficult, I drilled out many bolts on engines ...

Use small drill bits and go larger... It will not cost $500 in drill bits!
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Old 05-21-2015, 07:53 PM   #18
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Quote:
Originally Posted by terryp View Post
A bit of an exaggeration, but at least $100 for the pair.

I'll eventually take the old gearbox to a shop to see if there's anything they can do without having to open it. I'll also watch for a used machine with other problems for the right price. But for now, I've ordered a new gearbox.

As for Carl's suggestion that something else might have been damaged, I think that's very unlikely, considering how much torque gets delivered to the wheels.

I'll also pick up a smaller torque wrench. Mine goes up to 150 ft-lbs, so probably isn't very accurate around the 25 mark. It was the only choice at the local auto parts store.

Finally, since the other bolts have survived 50 ft-lbs for years, I'm not too worried that one's going to snap while riding now that I've reduced the torque to half that. <Knocking on wood>
I don't mean to be difficult, but I cannot understand how you snapped it with only 50 pounds of force. That bolt, if not damaged, should easily withstand that pressure.

Many times, a nut may be stripped, or cross threaded, and then the effort to get it tight is not a function of torque at the tightened point, but trying too hard to get the nut to clamp down on the wheel surface.

In other words, you should be able to make the nuts snug to the wheel with your fingers, and then tighten them down with a wrench (to 25 or whatever poundage torque you want).

If you cannot tighten them down with your fingers, but must use a wrench to just get the nut in contact with the wheel, then there is some other impediment to the threads working as they should. That bind can cause a bolt to break.

In this case, I see from some on line segway manuals that the wheel bolts on an i2 should be at 30 N-m, which is 30 newtons at a meter. That converts to about 22 foot pounds of torque, and even the Gen 1 that were at (I think 50 N-m were only at 36 foot pounds.

I found no reference from segway to either 50 pounds of force, or 25 foot pounds of torque for any wheel bolts.

I work with similar hardware all the time. 25 inch pounds is not much at all, and 50 is not either. Even 50 foot pounds is not too much for this bolt, I believe, but I am not here to debate the factory specs, but to say that there may be some other factor involved in the breaking of this bolt.
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Old 05-22-2015, 02:00 PM   #19
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I don't mean to be difficult, but I cannot understand how you snapped it with only 50 pounds of force. That bolt, if not damaged, should easily withstand that pressure.

Many times, a nut may be stripped, or cross threaded, and then the effort to get it tight is not a function of torque at the tightened point, but trying too hard to get the nut to clamp down on the wheel surface.

In other words, you should be able to make the nuts snug to the wheel with your fingers, and then tighten them down with a wrench (to 25 or whatever poundage torque you want).

If you cannot tighten them down with your fingers, but must use a wrench to just get the nut in contact with the wheel, then there is some other impediment to the threads working as they should. That bind can cause a bolt to break.

In this case, I see from some on line segway manuals that the wheel bolts on an i2 should be at 30 N-m, which is 30 newtons at a meter. That converts to about 22 foot pounds of torque, and even the Gen 1 that were at (I think 50 N-m were only at 36 foot pounds.

I found no reference from segway to either 50 pounds of force, or 25 foot pounds of torque for any wheel bolts.

I work with similar hardware all the time. 25 inch pounds is not much at all, and 50 is not either. Even 50 foot pounds is not too much for this bolt, I believe, but I am not here to debate the factory specs, but to say that there may be some other factor involved in the breaking of this bolt.
The reason you don't find a reference to 50ft-lbs is that there is none; it was in my head. Page 107 of the PT manual specifies '35N-m (26ft-lbf)'. If Segway now specifies 30N-m online (just checked - they do for the SE), then they've reduced it by ~14% since my 2006 manual was printed. I wonder why.

I've always hand-tightened the nuts against the wheel before using the wrench, so there was no cross-threading or stripping involved.

I clearly remember that trying to reach 50ft-lb resulted in what I thought at the time must be the bolt heads slipping in the plate (not just one). The pointer hovered just below that mark as the wrench continued to move. It's obvious now that I was twisting/stretching the bolts. I should at least have been suspicious and double-checked the spec before continuing.
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Old 05-22-2015, 04:11 PM   #20
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one other potential factor to consider is the type of tool you use to determine the amount of torque you are applying.

I use a torque wrench at work that has a pivoting head, in that when you reach the dialed in torque, the head will 'pop' or pivot about 10 degrees. This action is pretty noticeable, if you are looking for it.

Unfortunately, this type of torque wrench does not quit applying torque at that point. It is designed to tell the operator it has reached the dialed in torque, but you can easily continue to tighten bolts till they snap.

I have used better torque wrenches in the past, where they will simply ratchet freely after the dialed in torque is reached. In other words, you cannot over tighten bolts with this type.

A third type of torque wrench exists, and I have used them in the past, but not for decades, is a wrench that has a scale and long pointer that indicates the torque on the shaft of the wrench. The harder you push, the farther the needle moves. I believe you need to be careful with this type, as you can over toque pretty easily. The needle may not be reflective of the actual torque involved.

Just curious. What type to you use, and do you agree or not with me on some of my observed differences in these tools?
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