Built me a towbar

[jrou111]

I'm interested.

If you need a test bed, I'll be recovering my pair of deuces in a couple of weeks from Redstone. I have a friend's house about 15 miles away I'm taking them for a short test or back to Birmingham (100mi) for a longer test.

 

[cbvet]

M16ty,
No offense intended when I questioned your towbar's strength. And the "test" pull you did seems to prove me wrong.
What I should have said was that I didn't think yours was as strong as a military tow bar.
That's not to say yours isn't plenty strong enough.
Eric
CBVET

 

[otisroy]

I'd definitely be interested in one if you get them in production.

 

[m16ty]

M16ty,
No offense intended when I questioned your towbar's strength. And the "test" pull you did seems to prove me wrong.
What I should have said was that I didn't think yours was as strong as a military tow bar.
That's not to say yours isn't plenty strong enough.
Eric
CBVET

No offense taken .

I welcome questions because if someone sees something wrong with it I want them to speak up. I may try and argue ( consturctively) with you a little but safety is the main concern.

And no, I don't think it is as strong as the military bar either as far as the ring is concerned. There ain't no telling what that thing would hold.

I'm going to try and get a price nailed down tomorrow.

James, Your welcome to borrow it but I don't know how I'd get it to you.

 

[MilitaryRestoration]

round tube is much stronger than square. also dead lift weight is different than impact weight and shock weight... You are dealing with two complete different types of forces. You may be able to lift 40000lbs of dead weight but at impact may only hold 30000olbs. Working for a steel company for many years and cousin a masters degree in engineering i've learned a few things... just my ... be careful, too many people being sued now days

not to mention each time you start and stop with a pintle style hitch you are technically wearing down and very minimal damaging the hitch and receiver due to the slack, which in then equals metal fatigue. especially with something out of flat bar metal so to speak, as 'halftrack' was getting at. I've seen the newer style reinforced tow bars broken under normal use, in this case a 5ton 818 pulling a 5ton 813, 818 slammed on brakes and the forces found the weak point, in this case the tubing of the towbar... but again my just watching out for you and others

 

[colomil]

Wow the accident that busted that towbar must have hurt somebody!

I will have to disagree on the round vs square strength argument. In simple tension, they are the same strength (given the same cross sectional area). Round tube is much stronger for twisting forces (like driveshafts) and square tube is stronger for bending/cantilever as long as the forces are parallel to the the Y axis (this puts the top of the cross section in axial tension, the bottom in axial compression and the sides in Y axis compression. A round tube under the same load will flatten out and bend under the yield load of the square tube.

I would certainly consider going with a purpose built lunette as this will see some serious abuse. You might also consider using 2.5"x 0.25 seamless square tube (A36 would work, A400 or 4130 would be better) so you could slide some 2" square tube inside for added strength. When towing light stuff like CUCVs, the 2" square tube inserts could be removed to make the bar lighter and easier to work with. When pulling big stuff, put the inserts back in.

Anyway, I hope you do start building them, or at least putting together plans.

 

[halftrack]

I'm not and engineer but I have a suttle comment.

Wouldn't round 4130 tubing be better than square tube?

Not trying to put down anyones work here just and only a question.

Any engineers out there???????????

4130 is what all the old tubular aircraft frames were made of.

I understand that it is a challenge to weld but strong as he!! when completed.

Jim

The reason I brought up the "tear out" factor is because I am an engineer (mechanical, but not a licensed P.E.) and I see this done all the time at construction sites and its a big "no no". They (consrtuction workers) are always looking for improvised "hooks" and try making them out of plate steel. When you start using plate for lift loads you need to start considering the "grain pattern" of the plate which can only be seen under microsope. Plate steel has a tendency to "tear or rip" along the grain pattern which is formed
during the rolling manufacturing process of the plate. Its not he actual "lifting of pulling loads" that breaks or causes steel to fail. It is often the "shock" loads that do them in I can only imagine that a towbar will be seeing a lot of shock loads.

As mentioned in the above post, they make pre-made lunettes that are forged and ready to be welded on your particular application.

 

[m16ty]

Thanks to everyone with all the advice.

I was going with the plate to try and keep the cost down but after reading the post I may go with a factory made ring.

I'm still waiting on my water-jet guy for pricing and after that I should be able to nail down a price.

 

[m16ty]

Still researching on the design.

Talked to a guy today that I've known for a long time that owns a small forging factory. He told me he had a contract at one time to make the towbar forgings for the Military. He had to send the dies back when he lost the contract but thinks he still has the specs and prints filed away somewhere ( he's looking for them). He said to make some now he would need to make atleast 500-600 to pay to get the dies made.

He also used to make tow shackels and thinks he can get the dies to reproduce them. Said he's had several Military contracts over the years. I'm going to talk to him some more and see what I can find out.

 

[Lonesome715]

For that price we can just continue to get them other places.

 

[m16ty]

For that price we can just continue to get them other places.

Oh, I agree.

I'm still going with the plans to cut the ring out of steel. The current plan is to make the ring out of 3/4" and add a 3/8" ring slightly smaller than the 3/4" to add to the top and bottom to make a total of 1 1/2" thick (for strength) and give a more rounded edge. The price as of right now is looking like in the $350 range. I'm going to build another prototype with the improvements and a better fit and finnish before I commit to selling them.

If I decide to make them to sell they are going to have a label on them that says " for off road use only" to cover my butt. Use them however you see fit though.

 

[jrou111]

For $300-350 Definately!
For $350-400 Maybe

 

[Lonesome715]

For $300-350 Definately!
For $350-400 Maybe

Agreed.

 

[m16ty]

Well I've finally made some progress on my towbar manufacuring. I've built another prototype with waterjet cut pieces and a beefed up lunette. The lunette is made from 3/4" plate and renforced with two 3/8" rings which gives a total thickness of 1 1/2".

I've already invested several dollars in R&D and prototypes. Before I get any deaper into this project I need to find out how much interest there is. Price is going to be $350 per set. They will be painted OD and stinciled "for off road use only" to cover my butt. Do with them what you wish .

I also have a M715 and CUCV so I could make feet for those if anyone is interested.

Any takers?

 

[powerhouseduece]

Looks good! I only have a small question for you that might have been over looked.

Are you MIG welding them togher? I only ask because I have done it, and took class's on welding and learned that MIG welds are prone to cracking under this type of load over a very short time. This is why 90% of the time that everything in our chemical plant is Stick welded togher. It is more willing to "flex and give" where a mig weld would crack and brake.


Personally, IMO, since you working with thick metal to start with I would use a E6010 root pass first. Than just go over it with some E7024 "jet rod". That will get the weld DEEP into the metal and wiil have a little give and you will be good to go!

Also, to tell you the truth, Stick welding can be faster, and less troublesome than even a heavy duty mig welder. but that's just my $.02 for what its worth.

 

[m16ty]

All welds are welded with stick.

 

[powerhouseduece]

All welds are welded with stick.

Just checking

The weld police has struck!

 

[SCSG-G4]

I'll pass the word to the local fellows who do not frequent SteelSoldiers and see who is interested at $350.

 

[brianrbull]

What Rod are you using? I prefer 7018 myself . The 6010,6013 rods are ok for farm repairs but not so good for full penetration welds.

 

[m16ty]

root pass with 6010 (which is a deep penetrating rod) and cap with 7018. You're right about 6013 though. 6013 is mainly used to weld thin stuff.