Why so many socket head cap screws?

[SmoggyTurnip]

Seems like 90% of the machining projects i look at use socket head cap screws. They are also used on most lathes that I see, and on tool holders etc. On my lathe the carage lock screws are socket head cap screws and they are always filling up with swarff making it hard to get a hex wrench in there. It is easier to strip the socket head on a socket head cap screw than it is on a Robinson head and a normal Hex head doesn' get filled up with dirt. I had to replace the screw on my screwless vise and on several of my quick change tool holders for this very reason. I replaced them with normal hex Heads. So why are they so popular?

 

[LCT]

Seems like 90% of the machining projects i look at use socket head cap screws. They are also used on most lathes that I see, and on tool holders etc. On my lathe the carage lock screws are socket head cap screws and they are always filling up with swarff making it hard to get a hex wrench in there. It is easier to strip the socket head on a socket head cap screw than it is on a Robinson head and a normal Hex head doesn' get filled up with dirt. I had to replace the screw on my screwless vise and on several of my quick change tool holders for this very reason. I replaced them with normal hex Heads. So why are they so popular?

We use them in injection molds because they can be counterbored in the plate so they don't stick up past the surface. The heads don't take up as much room as a hex head either.

 

[cfellows]

I use them in model work because they are cheaper and easier to obtain than hex heads in the small, numbered sizes such as 2-56, 4-40, 6-32, etc. Also, allen wrenches are more prevalent than sockets and wrenches in these small sizes.

Chuck

 

[Mcgyver]

because they are so easily recessed - you never see them proud of the surface.

I don't put them on models though as most things i make are representative of an era or type of machine that didn't use them. going hex or better yet studs on a model is an easy way to improve the look with zero additional skill or chips required....unless you a masochist and make your own . i hear you on the cost Chuck, but I take forever to build so it doesn't add up to much.

 

[Jadecy]

I don't know if this is still the case but cap screws used to be grade 8 by default. Some of the smaller hex head bolts found at the hardware store seem like they are made out of cheese. I also like the look of them.

 

[nemt]

One very important reason to use cilindersockethead screws, is that they need less space compared to a hexagon head. Specially when using the wrench to tighten them on a hex bolt needs a lot more space then a socket head screw. And if you use the good grade, for bolt as for the key, you don't have to expect trouble!
I myself prefer sockethead screws for models as well for other engineering problems.

Nemt

 

[PolskiFran]

I tried locating some 6-32 hex head screws when I was building my Upshur gas engine. I couldn't find any locally or in the standard supply catalogs so I decided to try my hand at making a few. I tried to follow the dimensions of a heavy head 5/16-18 bolt as a guide. These are common on the old gas engines. I started with making 8 pcs. to end up with 5 good ones, I needed 4pcs for the engine. After 2 nights of turning, threading and hex milling to fit my nut driver, I replaced the socket head screws with the hex heads. I snapped one head off with the nut driver. The screw was replaced with the spare and it really looked good. After about a year of running at shows I had to disassemble the engine for a cleaning. I found that two of the screws had snapped during operation. I went back to the allen cap screws and have had no trouble.

A few factors could have caused failure.
1) Using 1018 CRS for material was probably a bad choice for such a small screw
2)Having cut threads instead of rolled threads reduced the strength.
3) Milling the hex probably put some stress in the screw even before it was installed.

I will use allen screws where there going to be any amount of force. The purchased screws are stronger than anything I can make easily.

Hope this helps,
Frank

 

[Bogstandard]

We are very lucky in the UK, hex headed bolts are fairly easy to come by, so it is just not necessary to make your own.

If I make a 'period' model, I tend to use hex head with a lot of stud/nut work, just because that was how it used to be done on such engines.

If it is a model I have designed and made, I tend to use cap screws, but hide or recess the heads as much as possible, because to me they tend to look ugly.

One thing I can't stand to see is philips head domed screws on a finished model. I use them during the build to save having any damage to the final screws, but swap them out when the engine comes to completion.

John

 

[Stan]

Both socket head and hex head bolts are relatively modern inventions. When making models of anything made a hundred or more years ago, the standard was square head bolts with square nuts.
North American manufacturers tended to make their own fasteners with no standard size. In fact, as their punches and dies wore, the size changed. They solved both of these problems by supplying a set of wrenches with each machine. Even early automobiles came with wrenches to fit their particular size of fastener.

 

[SmoggyTurnip]

North American manufacturers tended to make their own fasteners with no standard size. In fact, as their punches and dies wore, the size changed. They solved both of these problems by supplying a set of wrenches with each machine. Even early automobiles came with wrenches to fit their particular size of fastener.

lol - This must be what they are doing in China now because my milling machine and my lathe both came with a 17mm wrench, But the one for the lathe is too small for the nuts on the milling machine. Both wrenches are stamped with the number 17 and look identical.
Each wrench fits the machine that it came with but not the other.

 

[Stan]

Smoggy: You may be right on what I have just called Chinese metric. I have both SnapOn and Chinese combination wrenches and frequently neither will fit. I also have a box of 10-32 socket head capscrews that neither metric or inch wrench will fit.

 

[rickharris]

Historical interlude:

Joseph Whitworth is the man to blame (or not) Born 1803 he took an early interest in engineering and eventually gained employment with Henry Maudslay (the father of the screw cutting lathe). He became a casting expert and was responsible for the development of much modern casting and surfacing technology.

The development that is most applicable here is he identified a lack of standardisation in engineering - each manufacturer made their own standard thread/nut/bolt spanner etc as said - this made life very hard.

When he was asked to develop armaments for the British military he developed a standard for threading - the Whitworth standard. This prevailed in the UK, with other "standard" threads such as British Standard Fine (BSF) and British Standard Cycle (BSC) until metrication - and in some areas still prevails today especially in softer metals such as Aluminium.

BUT Whitworth identified and documented the initial standard which was widely accepted. This and his other development made him a very wealthy man. He set up a trust before he dies and charged the trustees to spend his money supporting technical education which they still do to this very day.