Frame design for new build

[jdaan]

Here's a pic of a frame design I'm thinking about for a 4x8, fairly lightweight tear. The basis is the new cub frame design with a beefier tongue (2x3x1/8 instead of 2x2x1/8. The rest is in 2x2x1/8 tube with 2x2x1/8 angle bracing the tongue for stiffness. I really like the look of a single tongue but want to avoid the "swaying" problems others have encountered. Would these two short sections of angle take care of that? Also, I'm planning to use a Dexter axle.



Any comments?

Justin

[WarPony]

Hey Justin, welcome aboard!! Me thinks the frame you planned may be a bit overboard for a "lightweight" Cub. I think a 2 X 2 14ga. (1/16" wall) would be plenty for the box part and a 2 X 2 1/8" for the tongue will be strong enough. I like the A-arm braces but if you use a Dexter axle, that will act as a center brace so that one you have drawn up may not be needed, or maybe moved a little to the front. The swaying part you worry about can be taken care of with the proper placement of the axle.

Just my opinion...... others can chime in if I'm guiding him in the wrong direction.

Jeff

[Trackstriper]

Justin,

So you're about to jump in after doing your homework! Welcome.

I thought I'd inject some food for thought for trailers with a single tube for a tongue. It seems like the standard tube is the 2x2x11 gage (.120 or 1/8") that is mentioned in most of the plans. When builders move up to a heavier tongue, they will sometimes go with the 2x3x11 gage that you mentioned, aligned so that the 3" side is vertical. This makes sense for the greatest vertical strength. But....

I have a small 4'x6' Pace American "Journey" cargo trailer, model JT46SA that I've used for the past six years. The trailer has a GVWR of 2000# with 5.30x12 load range C tires and I've had it on the scales nearly maxed out. Here's where I'm going....the side frame members are 2x3x11 gage vertical, but the tongue is 2x3x11 gage, aligned horizontally. I seems like maybe the engineers were more concerned with the horizontal loads on the tongue than the vertical loads. I just haven't notice anyone aligning the tubing this way on the forum, but the Pace engineers have got to be pragmatic about what works as they are building a small trailer for the general market, who will abuse and certainly overload the trailer. It seems to resolve the horizontal load issue without needing additional bracing.

The frame under my trailer is fairly similar in size as the one you wish to build, 4' wide by six feet long with a 42" tongue. You might look into this as an option.

Perhaps Andrew will chime in and let us know what the vertical strength difference is between 2x2x11 gage and 2x3x11 gage aligned horizontally. I suspect the 2x3 is somewhat stronger but I can't do the engineering on this one. Help?

Regarding Jeff's helpful previous post, you might be able to use lighter 14 gage tubing elsewhere as he suggested, but 14 gage is about .083 wall thickness. He mentioned 1/16" thick wall which is basically 16 gage. It's a small detail, but worth noting for strength and weight of the trailer. Seems like someone in a way back post mentioned using 2x2x16 gage for the under-the-body portion of the frame, but I can't remember who.

Hope this helps.

J.B.

[doug hodder]

The last couple of tears I've built I've used the 16ga. I do make up a composite tongue however, using 2x3x.090 and angle iron. For materials strength check the design library, tongue strength. There are a lot of different materials stats there. The difference according to Andrews chart is:

2x3 11 ga. 28000# vertical strength...3.9# /ft weight
2x2 11 ga. 15600# vertical strength...3.05 #/ft weight

I think it's a little beefy for what you want, but everyone needs to build to their own comfort level. Thin wall tube isn't for everyone when it comes to welding, but if you feel competent to do it, I'd say you'll be able to save a lot of weight. The body will give it a lot of strength. Just my opinion, others may vary. Doug

[asianflava]

I'm going to totally contradict Jeff here. The "A" supports will cause you headaches if you plan on letting the front arc overhang the frame. You could stiffen the tongue by using 2x3x3/16 for just 11 extra lbs. Like Jeff said, you could go down a size for the frame portion but it is only a savings of about 20lbs.

Another thing to consider is when you are placing your order, it is cheaper to order all the same material, one stick of 2x2x1/8 and half stick of 2x3x3/16 should do it, using part of it as the cross brace, it might cost more to get a short piece of 2x2.

Not saying that you can't do the composite tongue, but you will have to plan for it. There isn't much detail in that area so I had to make it up as went along. You will need to keep the cross brace to stabilize the tongue.

[jdaan]

Thanks for the input. I'm glad to hear that some think it is too beefy. I don't want to under-build, but at the same time I'd like to avoid over doing it.

Asianflava: I am expecting the front arc to overhang, but only as low as the rectangular frame. The tongue (and the a-frame) would be welded under the frame, like so:



Hopefully this makes it less of a headache.

Here is another version I'm considering which would allow doing away with angle bracing. It also incorporates 2x2x14gauge as recommended, hopefully saving money and weight.



Or an alternate version leaving out the x-member:



This seems to be the simplest and (hopefully) plenty strong enough. I'm having a professional weld it, figuring it's not the place to scrimp. This should make using a lighter gauge ok. Thanks again.

[Trackstriper]

Thanks Doug. I went back and edited my post to hopefully make it a little more clear about the vertical strengths of the tubes. My small Pace trailer has the 2x3 tongue tube laid "flat" so that the 3" dimension is on the top and the 2" dimension is on the sides. This contradicts the way we tend to think about tongues. I couldn't get useful data from Andrew's tables with the tongue set up this way as his chart is for a vertical alignment of the tube, that I'm sure of. It will take an engineer's head to sort out the numbers with the tube "flat". Some other small trailer manufacturers do it the same way for their 4x6 cargo models, so it must work. Might be very applicable for teardrops.

I'm with you all the way on the thinner wall tubes. I'm using 2x3x11 gage in the conventional way, and with an "A" frame tongue, but I've got a kinky frame design for my soon to be started TTT.

J.B.

[Trackstriper]

Correction to self: the numbers are in Andrew's table, if I were to read the chart correctly.

Since the tubing is "flat" the horizontal strength on the chart is now the vertical strength, so 2x3x11 gage would have a vertical strength of 22,300# or 43% more strength than a 2x2x11 gage square tube. The horizontal strength would be the 28,000# that Doug mentioned which is 80% stronger than 2"x2" square listed at 15,600#. This is assuming that the tubing for the tongue is mounted the "wrong" way.

Justin, I really like that last drawing. That should get you a light frame and a vertical tongue strength 50% greater than a single 2x2x11 gage tube. The Dexter axle will fill in for your central cross tube. Good call.

[Trackstriper]

Justin, too much time on my hands tonight. Was thinking more about your frame as you indicated that you liked the look of a single tube tongue. How about this:



By your dimensions, you will be using a whole 20' stick of 2x2 for your perimeter frame. Pick your own wall thickness. You will still have to buy or scrounge tubing for your tongue. I have shown a 2x3x11 gage tube laid flat which is plenty strong...see earlier posts. The weak member would be the front cross tube, but nobody seems to have trouble with that. Maybe use 1/8" wall tube for your perimeter frame. I think that you could judiciously weld the Dexter right to the frame (or get the brackets) and then weld the tongue to the center of the axle tube, or make a bracket for it to bolt to so that the axle could be removed if necessary. I think warnings about not welding to the axle tube would affect primarily the areas where the rubber is, and it's not in the center section of the axle tube. The axle tube will have a slight camber bow to it so this sketch is schematic only.

You could support your floor with wood spacers above the tongue tube and axle tube.

[asianflava]

I don't think it would be a good idea to weld onto the Dexter axle. The heat could damage the rubber inside of it. Plus, it is arched so it may not be in the same plane as the perimeter frame.

I mentioned using 2x3 (placed wide side up) as a crossmember for the exact reason you mentioned, because an entire stick would be used for the perimeter frame.

[jdaan]

I have the same reservations about welding directly to a Dexter axle, based on what I've read here. One way around that would be to have a 2x2 tube x-member and axle stubs welded to it, although apparently that's a bit complicated to get lined up properly. Here's a revised single tongue drawing with a 2x3x1/8 tongue mounted "sideways" and a 2x3 x-member. The weight on that without the axle is around 83 lb. Next to it is the simple a-frame design weighing in at 71 lb.



Does it make more sense to use the 2x3 cross-member for the forward one?


Justin

[asianflava]

I'd keep the tongue like you originally had it, narrow side up. When placed that way, it will have more vertical strength. Increasing lateral strength is done by going one size thicker (or adding the diagonals that you originally designed) you may not even have to go thicker since 2x3x1/8 is stiffer than the 2x2x1/8 that I used. So 2x3x1/8 with diagonals or 2x3x3/16 without them, a little bit of overkill but I'm just a bit paranoid now.

I'm not disagreeing with Trackstriper is saying, Pace probably placed their tubes like that for a reason. 2x3x1/8 placed wide side up is still much stronger then the 2x2x1/8 that I originally had.

On Andrew's Tongue Strength page you can see the strength of a piece of 2x3 is much stronger vertically than horizontally.

For example:
Rectangular Tube 2" x 3" x 3/16" 38,800 Vertical capacity 30,600 Horizontal capacity

Oh I just happen to like the looks of a single tube tongue...but that's just me.

Hope I didn't muddy the water too much.

[asianflava]

Awww nuts, I just remembered that you are doing a 4x8....I was thinking 5x10. All my thinking will be a bit high. 2x3x1/8 with no digaonals should be fine for a 4x8. Either way you put it wide or narrow side up, will be fine.

[jdaan]

My estimated max weight is around 800 lb. 2x2x1/8 comes close to being strong enough, although out to a 42" tongue length it seems a bit weak. That and we've seen a couple photos on here of broken 2x2x1/8 tongues. Like you said, the 2x3 is fine in either direction. I'm wondering if by having it 3" side up, it would have a little more lateral stiffness and prevent swaying.

Does it make more sense to have the 2x3 cross-member in the front or middle?

Thanks

Justin

[Alphacarina]

While a single tongue is neat and clean (at least it is with nothing mounted on it) if you ever do plan to mount something there (battery box, generator, etc) it's much easier/neater to do with a Vee tongue

My Little Guy has the single tongue and I have all sorts of plans for mounting stuff up front, so I wish it have a Vee instead

Don