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Unread 08-07-2018, 12:31 PM
risho900 risho900 is offline
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Socket Head Screws

Just wondering where these are used other than shaft collars. Also, what are the most common sizes and lengths a teams should have?
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Unread 08-07-2018, 12:37 PM
risho900 risho900 is offline
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Re: Socket Head Screws

Oh just remembered they're also used in gearboxes. So in addition to apart from shaft collars, where else are they used?
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Unread 08-07-2018, 12:39 PM
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Re: Socket Head Screws

For us... everywhere. 1/4-20 and 10-32's mostly, but 8-32, 6-32, and 4-40 have their uses on the smaller side, as does 5/16-18 on the larger. For lengths... anywhere from 1/2" to 3.5" depending on the application. We stock many sizes of each, which lets us use the proper length for whatever we're doing. We do use flat heads at times, but unless you need that sort of clearance, it's not worth the work. Button heads can also be useful, falling between socket head and flat head in terms of profile. We use buttons for anything that sticks down towards the carpet on the bottom of the robot, or on the bottom of mechanisms that could touch the carpet - it's much safer from a "snag" perspective than a socket head.
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Unread 08-07-2018, 12:43 PM
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Re: Socket Head Screws

Personally, I have used them pretty much anywhere and everywhere. They’re screws, and often it’s easier and more space efficient to design with them than hex head screws.

That would include assembly of custom parts, assembly of COTS parts, sometimes as a pivot or shaft when a shoulder screw is a problem. Another good use is shaft retention, though often a button head makes more sense.

Is there a reason why you’re asking about where they’re used?
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Unread 08-07-2018, 12:46 PM
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Re: Socket Head Screws

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Originally Posted by Jon Stratis View Post
For us... everywhere.
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Unread 08-07-2018, 12:47 PM
risho900 risho900 is offline
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Re: Socket Head Screws

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Originally Posted by cadandcookies View Post
Personally, I have used them pretty much anywhere and everywhere. They’re screws, and often it’s easier and more space efficient to design with them than hex head screws.

That would include assembly of custom parts, assembly of COTS parts, sometimes as a pivot or shaft when a shoulder screw is a problem. Another good use is shaft retention, though often a button head makes more sense.

Is there a reason why you’re asking about where they’re used?
It's because I'm trying to figure out what screws I need to buy. My team is investing in more hex head tools like ratchet kits so I'm probably gonna by hex head for main use but for things like shaft collars and gearboxes I want to buy socket head but I'm not sure what sizes and lengths for those. Also, adding on, what about set screw sizes and lengths?
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Unread 08-07-2018, 12:54 PM
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Re: Socket Head Screws

We used a mix of metric and SAE, and I highly suggest you don't do that.

My experience in the workplace is all metric fasteners and Inch units (It's weird but it works well). So That's what I tried to do for my team, which lead to much confusion.

Get 1/4-20, all shapes an sizes,
8-32 and 10-32 are also very common,
Higher loads and bigger interfaces you can go all the way up to 1/2-13 or 5/16-18.

Also, don't forget rivets. They held together ~60% of our robot and are nice for tough to reach places (in terms of getting wrenches in tight places)
We used aluminum and steel 3/16" and 1/8" rivets. Aluminum for light loads, steel for higher loads.
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Unread 08-07-2018, 01:01 PM
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Re: Socket Head Screws

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Originally Posted by risho900 View Post
It's because I'm trying to figure out what screws I need to buy. My team is investing in more hex head tools like ratchet kits so I'm probably gonna by hex head for main use but for things like shaft collars and gearboxes I want to buy socket head but I'm not sure what sizes and lengths for those. Also, adding on, what about set screw sizes and lengths?

It would be a good idea to purchase flat washers to put under the heads of the socket cap screws, especially the larger ones such as #10 and 1/4-20. The surface area of the heads is smaller than for other styles (hex head, pan head or button head). When used to fasten softer materials like aluminum or plastic in higher stress applications, I have seen many instances where the heads start "pulling through" the material. A flat washer will spread the forces over a larger area and minimize this.
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Unread 08-07-2018, 01:44 PM
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Re: Socket Head Screws

Quote:
Originally Posted by risho900 View Post
It's because I'm trying to figure out what screws I need to buy. My team is investing in more hex head tools like ratchet kits so I'm probably gonna by hex head for main use but for things like shaft collars and gearboxes I want to buy socket head but I'm not sure what sizes and lengths for those. Also, adding on, what about set screw sizes and lengths?
Generally speaking, a basic set of allen wrenches are going to cost less than a set of wrenches. Using hex head for your bolts means you need two wrenches to put in a single bolt - the head and the nut. If they're both ratchets, that can lead to some confusion - which one do you flip around when it doesn't work? Using a socket head lets you stick an allen wrench on one side and a wrench on the other. The wrench may be racheted, but then the allen wrench won't be, letting you know which one to flip if you're going the wrong way.

As a bonus, consider bolting a 1x1 extrusion onto a robot. You don't want to have the bolt pass all the way through, with the head on one side and the nut on the other, it'll deform the extrusion when over tightened. So instead you drill a nice big clearance hole on one side, so you can slide the bolt in and have the head inside the tube - no deformation, and nicely secured. However, now you can't get your wrench inside the tube to tighten the bolt! Using a socket head, this isn't a problem, as the allen wrench sticks right out that clearance hole you already have.
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Unread 08-07-2018, 02:02 PM
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Re: Socket Head Screws

Even off of robots, I see them everywhere. I just removed ten hard drives from old computers a few hours ago - ~80% of the mounting scres were allen head. Most "crash door" hardware is set and released with a 5/32" allen key (this, not robotics, is why I have one on my key ring).

As Phil and Jon have noted, "cap head" sockets have the smallest heads of headed common threaded fasteners of a given diameter, which can be a blessing when fitting into tight spaces, or a curse when using soft materials. Button head are typically closer to the size of a phillips or flat blade head. Allen requires less contact force for a given torque than either of these.

Also, don't forget set screws! The vast majority of headless screws I've seen have allen sockets. These are great when the head of a screw would get in the way of other motion, or imbalance a rapidly rotating shaft. You find these on shafts, locks, and complex devices like printers and automobiles.
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Unread 08-07-2018, 02:42 PM
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Re: Socket Head Screws

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Originally Posted by GeeTwo View Post
Also, don't forget set screws! ... You find these on shafts
Ugh, set screws are the worst of hub connections. Use a cross pin, hex or spline broach, taper lock, glue, or like anything else if you you care about reliable or significant loads. I speak from (regrettable, professional) experience.
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Unread 08-07-2018, 02:48 PM
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Re: Socket Head Screws

Get an impact driver and a set of hex bits for it too. You'll thank me. Just don't go too hard when you're tightening screws on a tube
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Unread 08-07-2018, 02:56 PM
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Re: Socket Head Screws

My experience is that while it's good to have stock of hardware in hand, until you've been doing it for 20 years, it's not particularly useful in designing and building a custom robot. We spec fasteners by application, and every year we end up buying a substantial amount of hardware that is very particular to that year's robot design. If it we're me, I'd keep the money on-hand and be ready to fire up a McMaster order as soon as I had a robot designed in January.
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Unread 08-08-2018, 12:37 AM
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Re: Socket Head Screws

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Originally Posted by Chadfrom308 View Post
Get an impact driver and a set of hex bits for it too. You'll thank me. Just don't go too hard when you're tightening screws on a tube
I have to disagree - unless your frame is built of steel, refrain from using an impact whenever possible. Hand tighten all fasteners. The quickest way to make your (aluminum tube) frame suspect is to put an impact into the hands of your pit crew. Especially over the course of an event or two. The only way to prevent this is to have stand-offs inside the tube - and that is nothing but a nightmare!

For allen wrenches, we have found these (both in SAE and Metric, long and short) to be life savors. Purchase two sets of each.

And just note - you will never be able to standardize to a small arrangement of fasteners. It has been tried by many teams better than us, and none have really come out clean. The best way to tackle the problem of 'too many tools/fasteners' is to 5S the shop. 5S along with FMEA has made our pit the most effective and efficient I have seen - last season we were down to less than 5 minutes from robot in to robot out.
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Last edited by Chief Hedgehog : 08-08-2018 at 12:48 AM.
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Unread 08-08-2018, 08:23 AM
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Re: Socket Head Screws

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Originally Posted by Chadfrom308 View Post
Get an impact driver and a set of hex bits for it too. You'll thank me. Just don't go too hard when you're tightening screws on a tube

This is an inappropriate tool for those who are untrained and/or inexperienced i.e. students and mentors who don't use them on a daily basis over a long time. It will be very difficult to control with sufficient finesse so that one does not crush tubes and other soft materials and is not necessary for the relatively small fasteners used in FRC. It will make the issue I raised about socket head screws worse. Many of the current Vexpro gearboxes are molded plastic and use socket cap screws. They are particularly vulnerable to being permanently damaged from overtightened screws.
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