View Full Version : Need Some Help-Exam Table
02-18-2012, 07:50 AM
I have to fashion a release handle for broken medical exam tables in my office.
No replacement part is available. It is the release handle that allows the table back to be lowered or raised when it rotational force is applied to it.
It is made of plastic (hence the problem). I would like to make it out of aluminum.
It is basically a handle set 90* from the rod it rotates. The control rod it attaches to is 5/16 steel hex bar. That bar rotates under spring pressure to allow for the table top to drop.
What I'm looking for is some type of female tubular connector that has a 5/16 hex opening and is at least 1/2" deep. I would prefer aluminum. I may use a few old Chinese crapo 1/4" drive 5/16 sockets and weld a piece of steel to them, and then add a threaded hole with an Allen set screw.
Can anyone figure out what type if there is any readily available Aluminum or Steel part that would accept a 5/16" hex rod into it other than a socket wrench?
02-18-2012, 08:04 AM
Pics of the part:
Holes like that are commonly done with a broach. I've done holes like that by simply pressing progressively larger key stock thru the nearest size drilled thru drilled hole. You could later either plug the hole with a screw, cap or weld it shut.
Alum is soft enough you can pretty much drive a hard steel hex straight into a drilled hole and "form" the shape. You'd need to either do this prior to finishing operations so you remove any damaged areas, or make sure you protect the surface with something to prevent marks.
last option is the simplest. Drill an over sized blind round hole, coat your hex stock with release agent, and fill the hole with epoxy to create the "final" shape. Devcon sells metal filled epoxies just for things like this. the epoxy is a bit thicker and takes more abuse than straight resin alone. We used this trick to fix handles on any number of older X-ray equipment when I worked with the installer.
I found some picts I did as a demo for some one else for doing a square hole rather than a hex one in 1/2" thick alum. You could do the same thing with an arbor press rather than a hammer and punch.
1/2" thick alum 5/16 square stock. I didn't even bother to grind the square. That would make it easier to center but for this it ddn't matter.
1: drill hole
2: place on anvil and locate punch
3: drive thru flip and drive punch back out.
Darn close to a 3/8" carige bolt. I wish I could have found some 3/8" square, but the 5/16" was on the mill table so thats what you get.
02-18-2012, 08:41 AM
Thank you Doug. I tried JB weld already. It lasted about a month. So you're saying to drill a 1/4" hole it a piece of aluminum and pound a piece of 5/16" hex steel through it?
What about tigging a piece of aluminum tubing around steel hex and then pounding it off?
Do you know of any prefab 5/16 hex female piece?
For that demo I simply found the closest drill to the only available square stock I had on hand. If you look close you can just see the round part in the center of the flat square in the finish pict. Easiest way would be to take your key stock and try and pass it thru a drill gage, and find the drill size closest to the smallest size. I'd measure across the flats and use that as the bare minimum size. the bigger the hole, the easier it will be to drive the hex thru, but the less engagement you will have, hence the greater the chance it will "strip" under use. I'd probably shoot for something with between 50-70% engagement at a minimum, and maybe do a "test" run to see how the material reacts. If you are working with blank stock and then machining, it's a bit easier because you can use more brute force.
With a real broach, the "cuts" get progressively larger on each "tooth". You can do the same sort of thing by simply driving larger and larger hex stock thru the same hole until you reach final size. A set would give you a "range" of cutters.
Hex stock can be found as loose material, but a hex allen wrench would work if nothing else. I'd simply buy either a single wrench ( if you can find one) or a cheap set, and cut the one you need.
Edit: I can't think off the top of my head for any prefab hex pieces, but I bet if you hunt McMAster Carr, Graingers, or MSC's books, you can probably find some designed to joint two pieces of hex stock together. My bet is they are steel however. You might find something listed under "knobs" or "handles" with a hex hole as well in those books. Last thought would be to simply hunt for an item you can use as a sacrificial "donor" and cut out the piece you need. Tough part is finding a materiel that would be compatible for joining
02-18-2012, 06:13 PM
I made one out of aluminum by drilling a 5/16 hole in it, then pounding an allen key through it.
The steel one was much easier. I welded a socket to a piece of .125 steel.
I blew through one part of the socket.
02-18-2012, 06:15 PM
02-18-2012, 06:27 PM
02-18-2012, 06:32 PM
Damn! Those would work perfectly. Will order a bunch. Thanks.
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