Need some design help

[Gary_in_Indiana]

We're thinking the same here. I was thinking I'd have to remove the upright to turn it the 180 degrees because I'd be using 4 x 4 x 1/4 square tube over something like 3 1/2 x 3 1/2 square bar stock.

Your way has it so I'd just remove pins and spin it around then replace pins to lock it in place, right? Are you talking about using round stock there or what? That's where I lost you.

The drawings are great. Thanks.

 

[hazmat]

<font color=blue>Your way has it so I'd just remove pins and spin it around then replace pins to lock it in place, right? Are you talking about using round stock there or what? That's where I lost you.</font color=blue>

Yup, round "pipe" for the upright. Pull pin, swivel, reinstall pin. The drawing does show as a square tube/w3tcompact/icons/blush.gif

<font color=blue>The drawings are great. Thanks.</font color=blue>

You're welcome

 

[Gary_in_Indiana]

OK, I'm with you now. Now for the next question. Isn't 4" x 1/4" square tubing stronger than the same wall thickness 4" OD pipe?

If that's true, then I have an idea to keep the strength I want. Instead of using pipe as my outer upright piece coming off the dolly tongue to the 90 degree turn to the fifth wheel tongue I can still use 4 x 4 x 1/4 square tubing IF I use something like 3 1/2 steel rod or 1/2 walled pipe coming up off the dolly tongue for the square tubing to fit over and pin through. I could even taper the top to make mounting easier. /w3tcompact/icons/clever.gif How does that sound?

 

[Anonymous Poster]

Gary, I'm dropping back to Plan 1, with a stretched Z adaptor to convert a standard towing dolly. You could make the Z from 3" pipe, about 10 feet long, and a trailer ball along with a shackle that slips over the toung of the standard dolly.
If necessary for transport purposes, the Z could be made in 2 pieces that telescope together.
We have a similar toung extension setup on a box trailer for hauling long loads, made from 3" pipe, and it has never presented any problem.
If you know an electrical contractor with a hydraulic bender, he can bend the Z and eliminate much of the welding.
If I knew how to do a drawing of this, and post it, the explanation would be a lot easier.

 

[hazmat]

<font color=blue>OK, I'm with you now. Now for the next question. Isn't 4" x 1/4" square tubing stronger than the same wall thickness 4" OD pipe?</font color=blue>

Yes, less metal

<font color=blue>
If that's true, then I have an idea to keep the strength I want. Instead of using pipe as my outer upright piece coming off the dolly tongue to the 90 degree turn to the fifth wheel tongue I can still use 4 x 4 x 1/4 square tubing IF I use something like 3 1/2 steel rod or 1/2 walled pipe coming up off the dolly tongue for the square tubing to fit over and pin through. I could even taper the top to make mounting easier. How does that sound?</font color=blue>

You're idea will work. But, If you are concerned about strength, you'd be better off to go to 5 or even 6" pipe for the upright than the square tube over round peg.

The pipe over pipe will give smoother operation w/ less chance for binding. It also provides a better bearing surface.

Hmm, just came up with an Idea, let me model it up and then I will post again. To wet your appetite, it involves a "lazy susan" at the dolley-tongue interface.

 

[hazmat]

Add a plate to bottom of square tubing upright. Add gussets as needed. This plate would have a pipe welded to it. The pipe would go inside the square tubing.

The dolly has a corresponding plate & male post that fits inside the pipe above.

You may want to have a machine shop fab these parts for you for better tolerance control (vs. hand tools etc.) Be sure to grease the mating parts to prevent them from rusting together.

 

[Gary_in_Indiana]

That looks great! I'd have round in round for full contact and still have the square tubing for the upright. I'd also have the two round, flat plates for additional strength. I'd never have to have a driver lift anything at the location of the semi tractor. All he'd have to do would be pull a couple pins, pivot the fifth wheel tongue around and pin it in place again. Then he could make any adjustments to the length of the fifth wheel tongue with a couple pins there, too.

I'll still need to make that piece adjustable. Would using 3.5" x 3.5" x 1/4" square tubing attached to one end of the two piece fifth wheel tongue to slide inside the 4" x 4" x 1/4" square tubing material be strong enough to use as my adjustment mechanism for the fifth wheel tongue? I'd probably have to have it be adjustable from zero to three feet of extension.

I think we're on the home stretch of this and I have to say I think it's going to be far better than what I'd have done without all the help. /w3tcompact/icons/smile.gif

 

[hazmat]

<font color=blue>I'll still need to make that piece adjustable. Would using 3.5" x 3.5" x 1/4" square tubing attached to one end of the two piece fifth wheel tongue to slide inside the 4" x 4" x 1/4" square tubing material be strong enough to use as my adjustment mechanism for the fifth wheel tongue? I'd probably have to have it be adjustable from zero to three feet of extension</font color=blue>

The 3.5" "extension" will be strong enough. Any reason not to just leave it long? I'm assuming you are accounting for the difference between a single rear axle truck & dual or triple axles.

<font color=blue>I think we're on the home stretch of this and I have to say I think it's going to be far better than what I'd have done without all the help. </font color=blue>

Glad we could be of help.

 

[Gary_in_Indiana]

<font color=blue>"Any reason not to just leave it long?"</font color=blue>

That's an excellent question. In considering it the only thing I can come up with is that I assumed I wouldn't want a big gap between the upright piece and the back of the tractor frame. In actually thinking about that I can't come up with a good reason why that would, in and of itself, be a particularly bad thing. Is there any advantage or disadvantage to that distance being substantially longer than is needed to clear on turns?

 

[hazmat]

<font color=blue>Is there any advantage or disadvantage to that distance being substantially longer than is needed to clear on turns?</font color=blue>

Longer "trailer" will track better, More potential for hopping curbs if you don't swing wide. But still pretty darn easy compared to a 53 footer.

Shorter "trailer" turns quicker when backing. (good if you are trying to manuver it, bad if you've got a long relatively straight section to reverse)

Shorter is of course stronger, (linear relationship IE 2X longer -= 1/2 strength) so I wouldn't go too overboard.