Imperial Machine Screws and Taps and Dies

The Imperial system used in the USA is pretty screwy. I'm finding one aspect of the system particularly hard to deal with. I would like to make some threaded studs. A rod with threads at each end.

The problem I am finding is that rod stock is available in fractional inch increments. Standard screw diameters are generally written in decimal inch and don't correspond to even fractional inches. As far as I can tell the only screw sizes that match up with available rod stock in fractional inches are a #5 screw at 1/8" and a 1/4" or #12 screw. I don't believe I've ever seen a #5 screw in person.  They are rarely used. #4, #6, #8 #10 are much more common. I guess I could start using #5 screws but I'd much rather find rod stock that matches #4 and #6, #8 and #10 screws.

Any ideas?

Use millimetric!  8)

JS

Going metric isn't always an option. Retrofits, etc. 

I noticed Switchcraft specifies #5 screws for XLRs. I've never seen one. 

Going metric for this is an option but I don't want to. I can't be the only one who wants to buy rod stock for a #4 NC thread. McMaster has #4 threaded studs but no rod stock.

I've tried to standardize the fasteners I use. Buying all the stuff I need adds up fast. Fasteners, taps, dies, drills, end mills, ect. I settled on using the imperial system because the variety available here is much better than metric. I don't want to mix metric for just a couple of things. Too confusing.

Does it have to be blank rod or can you use all thread?

Grainger has 4-40 all thread rod in many lengths. I'm sure lots of places will have it as well.

gemini86 said:

Does it have to be blank rod or can you use all thread?

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I'm looking for rod stock for #4, #6,#8 and #10 screws.

Ok, maybe I miss understood. I thought you were trying to find rod stock to thread both ends, but now I see that you never said that's what you were doing.

Gold said:

gemini86 said:

Does it have to be blank rod or can you use all thread?

Click to expand...

I'm looking for rod stock for #4, #6,#8 and #10 screws.

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You will need to take next larger size fractional stock and then turn it on a lathe. The rod diameters that small are PITA to work with because of flexing, so you will need to use whether box tool, or follower rest.

Best, M

Marik said:

You will need to take next larger size fractional stock and then turn it on a lathe.

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That's what I feared. I did a lot of looking around and came up empty. I don't have a metal working lathe. I have one that cuts into lacquer disks but it won't work for this   I don't think I want to get into turning right now. I generally have little use for it. My next metalworking challenge is learning to engrave. I have the Taig micro mill. I bet the Taig micro lathe would be great for this.

According to this:

https://en.wikipedia.org/wiki/Bar_stock#Drill_rod

...there seems to be a variety of sizes in small decimal steps.

Brian Roth said:

https://en.wikipedia.org/wiki/Bar_stock#Drill_rod

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Bingo! McMaster carries drill rod. Yay!

I guess one aspect would be the alloy used for the rods.  Some alloys are much more brittle than others, but all that is above my pay grade.

Also, I wonder about rusting properties unless the rod is plated after the threads are cut.  I guess some sort of stainless steel would get around that problem.

McMaster carries drill rod in a few different different types of tool steel. I think you are supposed to harden the steel after you have finished making the part. I have never hardened anything (no jokes please). I've seen the metal worker who used to be in  my building harden some parts he made for me. He used a torch to heat the steel until it was cherry red. Then he cooled it by plunging it into oil. I guess I should read up on that.

Gold said:

McMaster carries drill rod in a few different different types of tool steel. I think you are supposed to harden the steel after you have finished making the part. I have never hardened anything (no jokes please). I've seen the metal worker who used to be in  my building harden some parts he made for me. He used a torch to heat the steel until it was cherry red. Then he cooled it by plunging it into oil. I guess I should read up on that.

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IIRC there was another step where the steel to be hardened was coated with a powder that chemically reacts with the surface atoms. Quenching it in a pail of water to cool it quickly sets the hardness.

I don't recall ever doing this to threaded parts. More for metal on metal bearing surfaces or the like. But do your own research. My recollection is from being an underage worker in a machine shop decades ago..  8)

JR

JohnRoberts said:

IIRC there was another step where the steel to be hardened was coated with a powder that chemically reacts with the surface atoms. Quenching it in a pail of water to cool it quickly sets the hardness.

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McMaster has this document that outlines the process for different types of too steel. http://www.mcmaster.com/#9018kac/=nc21h4

Gold said:

JohnRoberts said:

IIRC there was another step where the steel to be hardened was coated with a powder that chemically reacts with the surface atoms. Quenching it in a pail of water to cool it quickly sets the hardness.

Click to expand...

McMaster has this document that outlines the process for different types of too steel. http://www.mcmaster.com/#9018kac/=nc21h4

Click to expand...

Yup, I was thinking of "case hardening" where you add carbon to the surface of low carbon steel to make just the surface harder, without making the rest of the part brittle.

http://en.wikipedia.org/wiki/Case_hardening

It is slowly coming back to me and IIRC we might have done this for some lathe cutting tools to extend life. But like I said this was a very long time ago and I was a young puke at the time. 

JR

Used motor oil is often used to case harden. It's messy and dangerous.

gemini86 said:

Used motor oil is often used to case harden. It's messy and dangerous.

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Yup, any carbon rich media which coincidentally can catch fire. I seem to recall some white powder but don't have any idea what that was.

JR

I wonder if it was some kind of silicon, which is also very hard.

Edit: Google says that crystalline powders are often used in case hardening.