Controlling width of heated zone

[Eddie D]

Newbie question:  I have some 1/2' round bar (mild steel), that I want to bend in several places.  I have a used, commercial coal forge with a recessed fire pot and clinker breaker.  My question is if there is a way, to limit the heated area (length) in the bar to only a couple of inches?  I notice that I have trouble keeping the bends tight when too much of the bar is heated.  Is it possible to reduce the width of the heat zone with fire bricks or other restrictions?  I hope my terminology was clear enough to explain my problem.  Thanks for any suggestions you can provide. 

Eddie D

[Buzzkill]

Since you are using mild steel it might be easier to cool the areas you don't want to bend by pouring water on those areas after removing the bar from the fire. 

[Frosty]

Welcome aboard Eddie, glad to have you. If you'll put your general location in the header you might be surprised how many Iforge members live within visiting distance.

I'm more of a gas forge guy and localizing heat in a gas forge is a serious exercise in thermal shields and cooling the parts of the stock you want to stay put. If you only need a couple bends in a bar you can slip a piece of pipe to the beginning of the bend and hold the other side in a vise. Yo can make very precise bends this way. Making more than two in one bar can become problematical though.

A torch is the perfect tool though. There's a good reason a blacksmith name of Hobart invented the oxy acetylene torch you know.

Frosty The Lucky.

[ThomasPowers]

I tend to use a postvise and piece of pipe when I need to localize bends.  Order of work does start becoming important as I tell my students "The first rule of bending steel is that it has to be completed in one go *OR* it has to fit back in the forge to heat it for the next go."  (the last is more important with a propane forge...)

[Eddie D]

Thanks guys for the great tips.  It's amazing how the complex becomes understandable when knowledgeable people get involved.  I'm anxious to try both the pipe bending, and localized cooling techniques...in fact I'll probably try them today.  To address Frosty's comment, I live in the hills of east central Oklahoma, and I'd welcome the chance to meet and learn from any fellow blacksmiths in the area.  And to borrow part of Thomas' "handle", I guess I'm the "apprentice curmudgeon". Thanks again for your input!

Eddie D

[Frank Turley]

Another route to go is the time honored use of a bending fork coupled with the use of a bending wrench. The fork can be as simple as a bent U shape of round stock, the distance between legs just a teense wider than the hot stock it receives. It can be clamped in the vise, open end upward. The wrench can be two similar legs welded or forged to a handling length, same distance between legs. The hot piece is "trapped" horizontally between the fork and the wrench placement, can only bend in that place.

[arftist]

Quench the bar leaving just the part you need hot unquenched. Just don't spend too long or you lose all the heat.

This is why I like a deep quench tub

(I use a barrel)

[Eddie D]

Follow Up...

This morning was a little cooler here in Eastern Oklahoma, so I went down to the shop to try out the various bending methods suggested here.  I had already made a several bending jigs (both fixed and adjustable), I haven't made a bending fork yet, but it's on my to-do list.  I'm still hampered by my clumsiness using the tongs.  I'm so slow that some of the multi-stage solutions just don't work very well for me... i.e. selective quenching.   I'm sure that will improve with experience.  What worked best for me was the suggestion to use a pipe.  I used the pipe in conjunction with my bending jig, and by sliding the pipe up to the bend point, got excellent, very clean, repeatable bends.

This exercise did however point out another problem.  What is the best way to mark the bend locations on the steel?  I tried soapstone, felt marker, and even using a punch to mark the spot...none of them worked very well....remember I have old eyes, so I need something that is very visible.

Thanks again for your help!

Eddie D

[swedefiddle]

Good Morning Eddie

Welcome to our world. To create a shape or design, make a soapstone design on a piece of scrap-plate/sheet metal. Opps, I went too far or not far enough, but that looks good anyway....

I welded a pin (round stock) to a scrap of angle bar (x2), with a couple inches sticking up above the Flat. You can put them in a vise and adjust the gap between, or, drop another piece over one pin to make a different radius (doesn't have to fit tight). Your mind is the limitation, don't create "the Box". There is no wrong way, whatever works!!

Neil

 

[gote]

14 hours ago, Eddie D said:

This exercise did however point out another problem.  What is the best way to mark the bend locations on the steel?  I tried soapstone, felt marker, and even using a punch to mark the spot...none of them worked very well....remember I have old eyes, so I need something that is very visible.

It all depends upon what you are doing but sometimes it is possible to us some kind of external marker or stop. If you use a pipe for bending, you can put in a bar inside and somehow fix it so the pipe stops in the right place. You can use a suitable piece of heavy wire fix it to the bench or vise with a couple of C-clamps and bend it so it points to where the end of your stock (or previous bend) should be if the vise grips in the right place.

[SReynolds]

Two common methods I employ include notching with a hack-saw when I can .....  or liquid paper corrective fluid pen. Unless you go into welding heat, it won't burn away. 

[Glenn]

If you nave several bends to make, then a jig and HOT metal makes a repeatable bend.

COLD bending against jigs means you must allow for spring back and other issues. When cold bending and the bend is a little large, due to spring back, take a pencil and relabel the dimensions on the drawings you work from. (grin)

Best way is to make 20 bends and choose the two that match. The rest can be straightened back out and the metal reused. It is al about practice, practice and some more practice. Do not worry cause few get it exactly right the first time. You learn to use jigs, stops for measurements, and leverage to your advantage. 

[DSW]

Notches, chisel marks, punch marks etc can often be felt even if not seen. When using jigs, stops or reference marks on the jig/table can help you with repetitive bends. Your reference mark may not even need to be in the heated area. It might simply be the end of the piece pushed up tight against a stop, or a mark on the stock you align with a specific part of the jig.

[Frosty]

You can also twist wire around your mark but you have to be careful not to get it under the pins, stops, vise jaws, etc. or it will mark the stock under pressure.

Don't make several turns, just one and twist the ends together to hold it in place. Use mechanic wire, bending heat isn't or shouldn't be hot enough to burn the wire off but be careful how much air you give the fire. Wire is thin and WILL burn pretty easily hopefully it's in tight enough contact with the parent stock it won't melt right off.

No, it doesn't always work but iron wire is a common way to connect steel for welding.

Frosty The Lucky.

[Frank Turley]

As to layout, dividers can leg off the proper distance for the bend while the metal is hot. When using fork and wrench, the hot workpiece is "captured" between the near leg of the fork and far leg of the wrench. The distance between the two will give a tight, radiused bend or a larger, radiused bend.

[SReynolds]

Unconventional fire pot. 6" wide x4" . It works like a torch. Almost pinpoint. I have to move it about to heat a long area but I seldom need to heat a long area. 

I understand your plight.  Most fire pots are like 6" wide by 8" or the like. I use one 10x10 but this thing pictured is sweet.

[ThomasPowers]

Trough forges are not unconventional they were common for jobs where they fit the need  Look at the Johnson NG trough forges---enough of them out there I have seen a score on the used market.  Look at some of the charcoal fueled knifemakers forges that used a narrow rectangular fire (though generally they used it lengthwise)

[SReynolds]

Never seen one in all my years.  I thought about employing it both directions.  But lengthwise isn't needed for me. I do some forging with a torch and understand why it works so well in some cases. 

[Eddie D]

All I can say is what a great forum! I got so many good suggestions as a result of my original post. In fact, one of the reasons it's taken a while to get back to the discussion is that I've been experimenting and trying out ideas that were presented here.

Obviously, as a new blacksmith, every operation, every technique, every reaction is something new to study and learn from. One cause and effect leads to yet another cause and effect, and so on. To me, that's part of the challenge and appeal of learning this craft.

With that said, I've attached a picture of a dinner bell and the bending jig I used to make it. The jig and the methodology are based in part on your suggestions. Over the course of building, trying, and modifying the jig, it's gotten a little “cobbled up”...but it works.

I bought a propane torch from Harbor Freight, that lets me control the width of the heated zone. It cost $15 and it heats the ½” bar to cherry red in about 1 1/2 minutes. Should have done that first.

Anyhow thanks again to all who replied with comments and suggestions!

Eddie D

Edited August 1, 2016 by Eddie D