Case hardening time

[Mark Elliott]

I am about ready to pack harden some screw mills.   To my mind,  I don't need much depth on the case,  just enough to hold an edge.   Do you think a hour at 1475F should be sufficient?   Wouldn't that also be sufficient for most lock parts (except the frizzen, of course)?   

[jerrywh]

Mark. What is a screw mill ? What kind of steel did you make them out of ?  When I make small tools I make them out of a grade 8 bolt. Then just harden and temper them.

[smart dog]

Hi Mark,
I suggest 90 minutes at higher temp like 1550-1600.  However, I don't know what steel you are using.  I use 1475 when color casing a component but higher temp when I am just concerned about wear.

dave

[Mark Elliott]

Thanks Dave.    I upped the temp to 1600 and will hold it there at least 90 minutes.   That should be a pretty thick case that I can sharpen a number of times.  

I am using 1018.  

Jerry,  A screw mill is used to make screws by hand.   I have made sets of three.   One cuts the shaft to the outside of the finished threads, one cuts the slightly smaller diameter on which the threads will be swaged by screw plate, and the last cuts the head.  

You start with a rod (I am using 1/4" 12L14) at least as thick as the the head.   One end of the rod is forged square to fit in a brace.   The other end is forged and filed like a pencil point.   You insert the pointy end into the mill and turn the rod with the brace.  In sort order, you end up with a screw blank that just needs to be threaded and then cut off the rod.   

I have made my mills simple, from 3/4" rounds, with flats filed on opposite sides to fit vertically in the top of a vise.   The original ones had a tab welded on the bottom so that it clamped in the vise horizontally instead of vertically, like mine.  I figured it was a reasonable modification for simplicity of fabrication.   I figured some gunsmith somewhere did that as I have seen all manner of rough forged tools that came out of back woods shops.  

It is all part of my 18th century tool kit to make a lock just like they do down at Colonial Williamsburg.   I thought that I might do some demonstrations at Dixons and the likes.  

[JCKelly]

You will get the most uniform hardening, and best hardness, if you quench in cool salt water.
A 10% mix would be 13 ounces of table salt in a gallon of water

A fellow I met who had worked in very, very rural mideastern areas just told them to use enough salt dissolved in the water to float a potato.

Salt water is what Nicholson file quenched their 1095 files in. Way, way back when they actually made files in the USA

The salt helps keep from having steam blankets form on the part. Steam forms and collapses. The steam part does not cool very well. So hardening can be non uniform, leading to distortion. Cracking in extreme cases.

[jerrywh]

 Mark.
  I thought that is what you were doing but weren't sure we had the same terminology. I never went as far as to make those old type screws . Must be fun.

[Mark Elliott]

Success!

I finished case hardening my screw mills and used them to make my first all handmade screw in less than an hour.   It isn't the best screw in the world, but it will get better.   I needed to do a better job pointing the rod and keeping it perpendicular to the mill.   

Here is a pic of the screw with a tapped hole the screw fits along with the screw mills, tap drill, tap and screw plate used to make them.   I made all those tools except the screw plate.   The screw plate is an original 18th century English screw plate.   It was unused when I got it.  It still had its temper color on it.   

[Mark Elliott]

You will get the most uniform hardening, and best hardness, if you quench in cool salt water.
A 10% mix would be 13 ounces of table salt in a gallon of water

A fellow I met who had worked in very, very rural mideastern areas just told them to use enough salt dissolved in the water to float a potato.

Salt water is what Nicholson file quenched their 1095 files in. Way, way back when they actually made files in the USA

The salt helps keep from having steam blankets form on the part. Steam forms and collapses. The steam part does not cool very well. So hardening can be non uniform, leading to distortion. Cracking in extreme cases.

I have always quenched 1095 using quench oil.   I will have to try brine sometime.   If it was good enough for my files,  it should be good enough for everything else I make.   

[FDR]

Success!

I finished case hardening my screw mills and used them to make my first all handmade screw in less than an hour.   It isn't the best screw in the world, but it will get better.   I needed to do a better job pointing the rod and keeping it perpendicular to the mill.   

Here is a pic of the screw with a tapped hole the screw fits along with the screw mills, tap drill, tap and screw plate used to make them.   I made all those tools except the screw plate.   The screw plate is an original 18th century English screw plate.   It was unused when I got it.  It still had its temper color on it.   

That is so cool!  Thanks for showing the pictures.

Fred

[okieboy]

 Mark, just curious why you mane the tools out of 1018 and then case hardened instead of using a steel that hardens, like 4140 or O1 tool steel? Historical correctness?

[JCKelly]

Mark Elliott - 1095 does not get quite as hard when quenched in oil as it does when water or brine quenched.

If you are making springs you do NOT want the metal to get too hard. A temperature controlled furnace is ideal, but usually us basement types temper by one or the other half-A-- recipie. I would suggest log on to Dixie, and buy the one Kit Ravenshear booklet they still have, on V-springs. 

For cutting tools, yes, quench in salt water. Those you do want to be hard.

Okieboy - 4140 will not get hard enough to be a decent steel cutting tool. O1 is appropriate, though. The "O" means "oil hardening"

[rich pierce]

Mark, I just love the work you're doing.  Inspires me.

[jerrywh]

 Like Kelly said --- 4140 is not a good tool steel for cutting tools. The last 2 numbers is the carbon content. 40 is pretty low.

[Mark Elliott]

Mark, just curious why you mane the tools out of 1018 and then case hardened instead of using a steel that hardens, like 4140 or O1 tool steel? Historical correctness?

It is cheaper, easier to acquire, and easier to work and more like the original wrought iron from which the original most likely would have been made.    I do use 1095 and W-1 drill rod for some tools and parts.   I use the w-1 drill rod for drills and taps as well as wipers.   I use w-1 instead of o-1 because it is less likely to air harden when forging small/thin parts.    I have had problems forging small parts from o-1.   Actually,  I have had problems forging large parts from o-1.   W-1 is just more forgiving.  

[Mark Elliott]

Mark Elliott - 1095 does not get quite as hard when quenched in oil as it does when water or brine quenched.

If you are making springs you do NOT want the metal to get too hard. A temperature controlled furnace is ideal, but usually us basement types temper by one or the other half-A-- recipie. I would suggest log on to Dixie, and buy the one Kit Ravenshear booklet they still have, on V-springs. 

For cutting tools, yes, quench in salt water. Those you do want to be hard.

Okieboy - 4140 will not get hard enough to be a decent steel cutting tool. O1 is appropriate, though. The "O" means "oil hardening"

I was originally using 1095/1085 for springs.  So, that is where I got the oil quench.   So,  I should still use oil for springs and brine for cutting tools with 1095?   

[44-henry]

I would be concerned with cracking using a brine quench with 1095. Though others might disagree unless you have a good temperature controlled furnace, or a very good way of holding your temps steady for extended periods of time it would be better to stick with lower carbon steels such as 1075/80. Both of these are more forgiving for simple heat treat methods. As for casehardening tooling I have made a lot of end miils, reamers, and lathe bits from casehardened mild steel with very good results. It is a great way to make inexpensive tooling for limited use applications, though with the way that your tools are designed to work it should last for a long while. Nice work.