Hairline Cracks in Tongs

[GoodThing Factory]

just finishing up my first pair of v-bit tongs and they ended up with w few hairline cracks which seem to have shown up in up expected places. hoping to get some thoughts on what caused them and how to avoid in the future. 

i started w 10" of 5/8 square stock hot rolled mild steel .... purchased from speedy metals so pretty confident the material is as advertised. i dont have a power hammer so the reins were drawn out by hand. used a hot chisel and square stock to forge the bits. 

any thoughts would be apprecsiated. 

thanks

 

 

 

[Crazy Ivan]

Leaving sharp corners on the finished piece makes stress points. On the jaw the crack starts in the corner created from splitting the V and it looks like the edge is sharp as well. Quenching may have added to the stress (if you quenched them) and working too cold will also increase stress. Then there's always the possibility of the steel being a bad batch (though definitely not common). That's why steel comes with heat #s from the mill so if there is a problem down the line they know which batch it was. Idk if this helps. I'm just speculating without knowing how many heats you took, if you burnt the steel, if you worked it too cold, what type of feul you use in your forge etc. 

[Frosty]

I don't have anything to add to what Ivan said, it looks like worked too cold and cold shuts are high on my probability list too.

Next time forget starting the Vs with a chisel and just go straight to the square stock. Maybe mark the lines for  the Vs with a piece of welding wire, all you need is a little track for the corner of the sq. stock to socket into.

When it falls to medium orange go back to the fire.

Those are my thoughts and nobody who's seen them thinks I make high end tongs.

Frosty The Lucky.

[GoodThing Factory]

3 hours ago, Crazy Ivan said:

Leaving sharp corners on the finished piece makes stress points. On the jaw the crack starts in the corner created from splitting the V and it looks like the edge is sharp as well

thanks for the feedback ivan - which edges are you referring to as being sharp? when i started the v the bit was squared, are you saying rounding the edges a bit would put less stress on the steel when splitting? 

also, as a beginner i dont work that fast so it takes me more heats than someone with experience to get the bit right. certainly more than 5 but prob less than 10 working with the chisel on the v - does that sound like an excessive amount?

 

[Crazy Ivan]

The edges of the jaw before you split the V is what I mean by corners. If they are a sharp 90 degrees that makes a stress riser where a crack is more likely to form. You dont need to "round" them, but take a second and lightly knock them back with your hammer or file them back (before you split). Also, at 2nd glance I saw the crack starting at the center of your split as well. This pretty much has me convinced it is a combination of sharp edges and quenching judging from how far back the crack ran. 1stly on that, I would suggest after you split your V, take a blunt chisel (I use a masonry chisel which is ground to a radius instead of being sharp) and go back into the V to fuller the bottom of the cut. Are you using a cold chisel to split by any chance?

[GoodThing Factory]

thanks ... i see what you mean. i am using a hot chisel but i definitely did chisel down to the lowest point and then opened the split a bit by angling the chisel a bit right and left. only after i got the split going did i fuller using 5/8 stock - if i'm understanding you ... i should have used a radiused fuller to open the v and forge down to the desired depth rather than the chisel? 

re quenching ... i quenched in oil rather than water under the assumption that quenching in water is more likely to cause a crack  - is that accurate?  

 

[Crazy Ivan]

Yes, and yes. So it sounds like if you keep the corners "soft" and fuller the V to finish it you may have better luck. Also, don't quench hot. Only at a black heat if you are in a hurry. I also see some grind marks that are from a hard disk grinder? You shouldn't need to use that. Work things flat and square at the anvil and any touch up should be able to be done with a file or flap wheel. Those deep hard disk marks are also potential stress risers. 

[GoodThing Factory]

with all my detailed description totally forgot to mention that the first attempt to rivet bound up the tongs ... so i did quench hot in water in an effort to get them moving but they were solidly locked up so i cut off the head with a cut off wheel - the marks you're seeing -  i did also clean up the hole w drill press and filed away excess material. maybe that quench was the culprit? 

anyway really appreciate your time and advice. 

thanks!

 

 

[Crazy Ivan]

Ya that quench may have done it. Also, if your rivet is too tight, that's fine. Just put the rivet unsupported over the hardy or pritchel hole (whichever it fits over best without the head touching) and hit the other rivet head. Think of it as upsetting the steel. You are upsetting the rivet head into itself which makes its height lower which gives the tongs more room to swivel. Make sense?

[ThomasPowers]

You might ask them if it was "hot rolled Mild" or hot rolled A-36 sold as mild.  Most of the dealers I'be been buying from use the two interchangeably; but they are not where heat and water come into play!

[GoodThing Factory]

56 minutes ago, Crazy Ivan said:

Also, if your rivet is too tight, that's fine. Just put the rivet unsupported over the hardy or pritchel hole (whichever it fits over best without the head touching) and hit the other rivet head

yes, makes sense - clever work around. i assume you do this at a cooler temp like dull red or black and want to make sure the shoulder is supported by the anvil or block? 

32 minutes ago, ThomasPowers said:

"hot rolled Mild" or hot rolled A-36 sold as mild

thanks ... i ordered and used what the company lists as a36 hot rolled mild steel. would cold rolled 1018 or a higher carbon steel have been a better choice for tongs? any thoughts would be great. 

[ThomasPowers]

Well I like tongs made from alloys that can't be quenched; (except for my Titanium ones), like 5160 or 4140.  You can make the tongs lighter and still have the strength and "flex".

 However if you are hot working steel then 1020 or 1018 will be less fussy to work with and not as sensitive to being quenched as A-36 tends to be. Since I came into the craft through bladesmithing I often don't have any water in the shop at all---save for my drinking water.  I normalize when I want to cool or just toss a finished piece on the floor out of the way.  Only when I'm doing a project where I will need to localize heat using water do I fill my quench bucket and I tend to dump it on the mesquite tree to the west of my shop when I'm done needing it.  I have seen a blade leap out of the tongs, fly through the air, bounce off a wall and hit a 1" slit in a covered water bucket and destroy itself.

A-36 is not as forging friendly as real mild but is now commonly sold as "mild" so I thought I'd ask.  It is what we generally use nowadays as it's the cheapest and many of us smiths are all about the cheap!

[Crazy Ivan]

50 minutes ago, GoodThing Factory said:

yes, makes sense - clever work around. i assume you do this at a cooler temp like dull red or black and want to make sure the shoulder is supported by the anvil or block? 

 

Exactly. 

[ForgeMan32]

You may try making them a little thicker on the next go around. And definitely when splitting that V work the metal hot. Your slitting chisel or whatever you opened it up with will suck the heat out of thin stock like that very quick. When your done forging they always say to put it back in the fire to relieve stress from prior forging. Normalizing.  Looks like your definitely on the right track