Safety chains - choices, choices, choices - Page 3

**Bill** · 10-02-2008, 06:42 AM

Dave -

The drawing helped - thanks for including it.

I'm not a mechanical engineer, but it looks good to me. Since the chains will be crossed under the hitch, they will exit from the channels more or less straight, which is a good thing, since they will be less likely rub on the channel ends and wear them. I thought about suggesting a sleeve of some kind over the bolts for the same reason - avoiding wear at the middle of the bolt - but a sleeve would hold water and might encourage the bolts to rust. I guess the possibility of hidden wear/damage is my only reservation, and it seems no more likely in your approach than with the standard approach.

Bill

**ShrimpBurrito** · 10-02-2008, 10:00 AM

I thought about water getting into the channel and rusting either the channel or the bolts too. I didn't think the channel would end of being a big deal because of the nice big holes the tension rods go through.

I could use a stainless or galvanized bolt, but it's my understanding that neither are as strong as a grade 5 bolt.

Dave

Wavery · 10-02-2008, 11:43 AM

Quote:

Originally Posted by ShrimpBurrito

I thought about water getting into the channel and rusting either the channel or the bolts too. I didn't think the channel would end of being a big deal because of the nice big holes the tension rods go through.

I could use a stainless or galvanized bolt, but it's my understanding that neither are as strong as a grade 5 bolt.

Dave

S/S is made to be pretty, not strong. Also it is called "Stain less" for a reason. S/S will still corrode and as it does, it's strength quickly degrades.

Fine thread Grade 8 bolts should be used in places where there is extreme stress (not applicable) or the possibility of shock loading, like in safety chains. Grade 8 bolts are less susceptible to corrosion too. That's one of the reasons that they are used in the suspension of your car. All suspension bolts (and some assembly bolts) on vehicles are required to be grade 8 by law (fine threaded bolts are stongest because the threads are not cut as deep). This is because of the superior strength and resistance to shock-loading. When using any steel bolts, it's always a good idea to use an anti-seizing compound (on the threads of the bolt) and lock-nuts. Double nutting is best. If you are concerned about aesthetics, you may want to use a nylon-insert lock-nut.

I'd be careful about drilling holes in the trailer frame. It should be avoided if possible. Cracks can develop from the holes due to the constant flexing and working of the trailer frame. One tip for drilling through the frame is to drill a larger hole and have a piece of pipe welded into the hole. This will avoid crushing, water intrusion and cracking. A better idea might be to weld a thick 1/2" nut on the outside of the frame and use that to bolt the chain to that nut.

Most holes that come in the frame from the factory are stamped, not drilled. It is rare to find any holes in the tongue area due to stress and flexing.

If you are concerned about the strength and corrosion of the chains, you may want to look into "high tensile" boat anchor chain. It is corrosion resistant and extremely strong. It can be purchased by the foot at most marine supply stores relatively cheaply. 3/8" Proof Coil anchor chain (which is not high tensile) has a 10600lb breaking strength and is around $2.50 per ft. High tensile chain is about 40% stronger but over double the price. I would avoid chain from hardware stores. They are mainly meant for fencing and there are no set quality standards or testing. Very dangerous stuff for this application IMO.
http://www.westmarine.com/webapp/wcs...FQ89awod3We1Fg

I would not feel comfortable with plastic coated cable. Although it is more aesthetically pleasing, water can (and most likely will) get into the plastic and you may not see the corrosion until it is too late (if it is colored coating, you won't see the corrosion). Once the water gets in, it cannot escape. Cables also tend to corrode from the inside out. With chain, what you see is what you have. I'd much rather have a rusty chain that I can see than a plastic coated cable that I can't see.

If you have a clear plastic coating on the cable, inspect it regularly and replace it at the first sign of discoloration.

Bolts are graded at their "Breaking point":
http://dodgeram.org/tech/specs/bolts..._strength.html

It is true that softer bolts will stretch before breaking. However, they will ultimately break at a much lower load.

BTW, the weakest point in the safety chain system is often the attachment to the TV. If you are clipping to the attachment points on your hitch, it is probably soft cold rolled steel bar welded to the hitch. The weakest point in the entire system may well be that weld. Check that carefully for gaps and cracks.

**Bill** · 10-02-2008, 02:39 PM

I was under the impression that a hole midway up the sides of the channel isn't a big deal. This is the so-called neutral axis - the steel above the center is in compression, and the steel below the center is in tension. That's why it is legal to bore holes in the center of the pre-made wooden I-joists (simlar to I-beams) that may support your house.

And FWIW, both of my TMs had/has two cables, each attached to the frame via a bolt through each frame channel, with the chain captured under the head of the bolt.

Bill

Wavery · 10-02-2008, 03:04 PM

Quote:

Originally Posted by Bill

I was under the impression that a hole midway up the sides of the channel isn't a big deal. This is the so-called neutral axis - the steel above the center is in compression, and the steel below the center is in tension. That's why it is legal to bore holes in the center of the pre-made wooden I-joists (simlar to I-beams) that may support your house.

And FWIW, both of my TMs had/has two cables, each attached to the frame via a bolt through each frame channel, with the chain captured under the head of the bolt.

Bill

The load on a trailer is different than a structure. The trailer is suseptable to flexing (in both directions) that effects the entire beam. The weight isn't the issue....it's the flexing.

If there is a hole in the frame from the factory, it is more than likely stamped and not drilled.

You could probably get away with drilling through the frame just as you described and never have an issue. However, I just thought that you might like to know that cracking is common when there are drilled holes in flexing metal.

Try taking a piece of metal and flex it back and forth until it fails. Try taking a similar piece of metal and drilling a small hole in it. Flex the metal back and forth. It will fail 50% sooner and it will always fail at the point of the hole.

I'm not saying that it is "Dangerous" to drill the holes that you are talking about. All I'm saying is that welding a nut on the frame might be safer method.

**Bill** · 10-02-2008, 03:45 PM

Sailor -

I'm certainly not going to disagree. As I say, I'm not an ME. Welding a nut or a pipe, to relieve any point stresses at the microscopic scale, and thereby stop cracks, sounds like a good idea.

I have no idea whether the holes in the frame members of my TMs are drilled or stamped. And I don't even know how to tell.

I'm not sure I buy the "flex a piece of metal until it breaks" argument, though, since the flexing is in a different direction. In your argument, the flexing is back and forth across the plane of the hole (like breaking a cracker). In the I-beam case, it is parallel to the plane of the hole, which is much harder to do.

Where is Larry Loo when we need him?

Bill

**ShrimpBurrito** · 10-02-2008, 04:18 PM

Interesting. But is the weakened strength from a 3/8" or whatever hole really relevant when you have holes this big in the frame just a foot or two behind where the bolt would be? And these holes are definitely not stamped. They look they are maybe cut with plasma....I don't know.

Dave

Mr. Adventure · 10-02-2008, 06:44 PM

Quote:

Originally Posted by Bill

Sailor -

I'm certainly not going to disagree. As I say, I'm not an ME. Welding a nut or a pipe, to relieve any point stresses at the microscopic scale, and thereby stop cracks, sounds like a good idea.

I have no idea whether the holes in the frame members of my TMs are drilled or stamped. And I don't even know how to tell.

I'm not sure I buy the "flex a piece of metal until it breaks" argument, though, since the flexing is in a different direction. In your argument, the flexing is back and forth across the plane of the hole (like breaking a cracker). In the I-beam case, it is parallel to the plane of the hole, which is much harder to do.

Where is Larry Loo when we need him?

Bill

Bill,
I'm going with your intuition on this one. It's hard to imagine a point in the web of the front of a trailer frame where drilling a 3/8 hole is going to be a failure factor, considering that the point of maximum bending load is going to be over the axle (rated for 4000# plus on a trailmanor), and you have the same steel cross section dimensions all the way to the tongue (even PopBeavers can only come up with 1100# or so in tongue weight on a 5000# trailer) (but tell me about a crack ever caused by somebody drilling a hole anywhere on a trailer frame, and I'll cheerfully catalog the experience).

For anybody who'd like to do the math:

http://en.wikipedia.org/wiki/Beam_(s...General_shapes

Wavery · 10-02-2008, 06:58 PM

I thought that we were talking about the trailer tongue here. Big difference.

Besides, I think this is getting a bit blown out of proportion. All I am saying is, when you drill a hole in the trailer tongue, you risk the chance of the hole developing a crack over time and it may be safer to weld a nut on the surface.

It's a suggestion, not a danger WARNING!!!......you're gonna die if you do that....

When a poster asks a question, one assumes that the poster is looking for suggestions for the best way to do something.

Virginia Deacon · 10-02-2008, 07:16 PM

I don't know if any of you have ever had a hitch break or come loose from the hitch ball, but I have. And, the crossed chains caught the hitch, just like they are supposed to, I gradually slowed and stopped, and was even able to pull to the side of the road. IF the hitch had hit the ground, as some have suggested here might be a good idea, it would have hit one of the tar strips or potholes in the road and -- maybe, flipped the trailer up and into the car, thrown the trailer into the on-coming lane of traffice -- who knows. Not to mention the propane tanks and what a situation involving them would look like!

Having had that experience and having read about an improperly connected rental trailer killing a women on her way to work here - after traveling several hundred feet across a median between northbound and southbound lanes and striking her car's driver door... I wouldn't want to experiment connections. Sounds to me like the cable arrangement on the new TrailManors might be worth looking at. Does anyone have pictures?

Happy Camping!