I was hoping to get some safety advice for a project.  Being a small machine shop, we usually try to avoid heating up work pieces. We signed up for a job to make some large J-Bolts. We have turned the threads and are ready to attempt the bend. The bar is 4340 annealed 2" DIA and the radius on the bend is 1 -9/16".  Length is approximately 40in. Any advice, cautions, or recommendations would be greatly appreciated. My main concern is safety. We are going to practice moving from the forge to the fixture cold before going hot, but I have no idea how a diameter this large is going to behave.

My other concern is providing enough heat. We are using my home built forge. I am still in the learning process of getting to tuned properly but I can get metal to a bright orange.

The picture below show the sample bolt we received and the machined bar for our first attempt.

Thank  you for your time,

Don

 

 

How tight are you tolerances on the part and how many do you have to make? I’ve got an idea in my head, but those two factors make a big difference.

David

(pm me, if you want to talk about my thoughts later tonight.)

If you can get it hot enough to bend

then 2” stock is big enough that I think it should retain heat really well, moving between the forge and the bending fixture,

are these gonna be load bearing?

Twistedwillow - These are not load bearing. They hold down a lid for a large melting vessel. The head of the J bolt rides on a bar as a pivot point for a lid as a pair.

David - We are making a total of 6. Going to try the first one and see if lengths are good. The drawing the customer provided is so old we can make out the dimensions of the mating piece. I would think the main concern is making sure we have the 180 degree bend. We can always throw it in the mill and clean the inside radius if need.

Making a bend like that in 2" stock will take a considerable amount of force even when the steel is hot especially something like 4340.  What machinery do you have on hand to do this?  If you are going to attempt it with muscle power, you will need an immoveable fixture, a lever for mechanical advantage and several strong men.  You may also need a large rosebud type heating tip to keep things hot.  Years ago I worked in a shop that would hot bend stock of similar sizes but never that tight a radius. We did it with a fixture, muscle and large bending forks.  If the piece you were given is already cut to length you have no leverage.  If I had to do something like that, I would make the bend on long piece of stock and then cut to length.  I think a machine like a bulldozer (not the CAT type) with a proper jig could do that job.

Current plan is take a welding table outside and anchor bolt it to the ground. We will then weld the fixture to the table. We are going to place another pin on a fork truck and use that to move the bar around. We have a skid steer and larger flat bed trucks as well.

We were actually worried about the bar sagging once we place it in the fixture. Doesn't sound like that needs to be a major concern.

Sagging isn’t going to be a problem unless it’s really long. A typical bending die will be a stud that matches the ID of the bend with a second stud that is just a fraction larger than the stock (it dose expand hot). You need a bit of extra tail to make your bend, I’d you leave it short it won’t hook over the stud right. 
I would use a port-a-power or 2 ton come-along and a cheater on the threaded end. Solid yellow heat is what you need, but the thicker the bar the longer it takes to heat the center, adjust your forge to just hotter than what you want. It’s hard to burn big stock but it can happen wile your trying to get the center hot. Think perfectly toasted marshmallow. Foster on the outside and gooey on the inside, not burnt and cold.  
I have straitened 2” bail spikes. It’s impressive.

I have no additional bending advice to offer, but I would add that since this is not a load-bearing application, don't bother with any additional heat treatment once you've made the bend. That would include quenching! Just make the bend and set the bolt aside to air cool.

To true, we don’t need a two inch “J” shaped anvil!. Remember black is hot. 

I use my post vice, buried 3' into the ground and large bending forks with a 2"+ opening and a matching scrolling jig. I make these out of large grader blade. Use a cheater on the forks and get your material to a good yellow heat. Heres some pics with dimensions. The scrolling wrench is the first I ever made 30+ years ago and has no problem bending large stock to the day. Make the openings a little larger than the width of your stock. This will enable you to do tight radius'. With a good set of adjustable roller stands, one man can do the job with no sag. The bottom pic shows the thickness. I make "J" bolts like this in one heat in my coal forge.

Note:  you only need to heat the section being bent to forging temps; but a lower overall temp can help prevent "self quenching"  where the larger mass of cold metal can pull heat out fast enough to cause issues.     I would definitely think about using a hydraulic press.  Or a immoveable fixture and a LOT of cheater with several beefy workers pushing.  

Heres a pic to demonstrate. The truss is 4'x10'.  The "pickets" are composite scrolls each made of 3 pieces forged from 3\4"x3" on my 25# lil giant, edge bent with the above tools and the final fit was using my rounding hammers. Its as close of a pic of my work to show what can be done. Sorry, but I don't have pics of some of the other heavy iron I've done.

Make sure that you take a longer heat than necessary in order to have a good reserve to do your bend, altho as TW said above, with this size stock, you have plenty of heat to do the job.

Thomas's post made me think, so I want to add a note here. There is one more factor that may make it easier to understand how to deal with heavy iron. 

We all understand what a handling length is. It means we forge the end of the bar and the extra length keeps us away from the heat. It also applies in another way. Large material has a large mass and the handling length on 2" round or 3/4"x3" is what takes the place of "several beefy figures", a cheater from hades, or a hydraulic press. With my post vice set deep, adjustable stands to hold the weight, the mass of the handling length, you can bend and control most any weight of steel. 

With the work in the forks and the scrolling wrench in place, I pull the handling length until I see scale begin to pop. Then I pull the fork and can tweak the heavy steel however I want. 

Hope this helps.

When I was working 2.5" sq stock, we welded a piece of 1" to one end to not need tongs.  Perhaps you can see it in my avatar picture.

 

What you used to heat that stock Thomas power was it kinda  gas forge?

 

Blown Propane  Ribbon Burner and at over 7000' altitude it heated a LARGE forge to welding heat---had another smith accidentally weld their piece to mine in the forge when they were repositioning it. (Had to sledge it off!)

As they are probably using a lathe to thread it is easier to thread first. Easier to make a thread on cheater. 

Big iron is always a trip to work. Great Pic! And thats a "handling length" in good hands.

 

Success!

This forum has been an amazing resource. I'm just beginning my blacksmithing journey and this is the first time I really brought my forge up to temperature. Two guys on a cheater bar and wrapped around with minimal effort.

The only issue we have is the radius came out about an 1/8th in larger than what we wanted. We have five more to do and are planning to make the pin smaller to help tighten it up.

HOORAY!!

Outstanding! Now buy a 40# ruble sledge and tell your helpers that your going to forge anchor chain! Lol

NIce

Awesome!!

We knew You could do it, We were just waiting till You found out.

Good Morning,

Close it up the last little bit, under control, in a press.

Neil