PDA

View Full Version : Socket hex cap screw confusion...



lakeside53
01-27-2010, 11:12 PM
I have a South Bend (skinner) 6 inch 4 jaw chuck. I just put a new backing plate on it and one of the cap screw vanished..:mad: . So.. heck, I'll just buy another.

Well... It take 5/16-18 x 1 3/4. easy.. but... it the new one won't fit. The head is larger on the new caps screws than the original.

The new screw takes a 1/4 hex and has a 15/32 (0.468) diameter head.. yep - standard.

The old screw takes a 3/16 hex and has a 0.430 diameter head...

I can't find any reference to this reduced head size on McMaster.. and my local suppler has no idea where to get them.

ideas? other than boring out the chuck, grinding down the head 30 thou...., or finding the missing screw..

vpt
01-27-2010, 11:32 PM
Find the screw, it couldn't have gone far. Using a flashlight helps immensely!

Black_Moons
01-27-2010, 11:37 PM
grind the head, its not a precision job, use stationary belt sander or something and with some test fits it will be done to amazeing accuracy in seconds.. or stick it on the lathe and try and turn it with some carbide.

joeby
01-27-2010, 11:57 PM
I seem to remember there being a change in the standard dimensions for socket head capscrews. I believe the Machinery's Handbook, at least some of the older ones, had both listed.

Kevin

whitis
01-28-2010, 12:15 AM
0.429 to 0.4375 was the head size for a 5/16 hex socket cap screw in ASA B18.3-1947. That changed around 1960. Might look for someone who carries "1936 series" parts.
http://www.engineersedge.com/wwwboard/posts/4762.html

One source that may carry 1936 series:
http://www.midwestsocket.com/

If you are really desperate, you can get oddbal fasteners made, but it may cost you.
http://www.chicagonutandbolt.com/services.html
Though this might be a standard special order item - i.e. they are setup to make it but don't stock it. Like these folks:
http://www.dysoncorp.com/boltsandscrews.html
http://www.nssocketscrews.com/index.php/html/standard/socket-cap-head

But you can fix the new part faster than you can probably find the obsolete part. New Screw may be about HRC 39-45. Less than carbide, HSS, hardened carbon steel, or a good file. 0.430 still leaves a lot of material around a 1/4" hex socket. So turn it down or if you can't use the chuck or a collet, put it in a drill press or other rotating spindle and hit it with a file.

dfw5914
01-28-2010, 12:21 AM
My 12th edition MH (1945) lists max head dia as .4375 and socket width as .2187 (7/32). Just buy all new screws and grind the heads as required. Or modify the chuck to accept modern hardware.

Machinist-Guide
01-28-2010, 01:07 AM
I seem to remember there being a change in the standard dimensions for socket head capscrews. I believe the Machinery's Handbook, at least some of the older ones, had both listed.

Kevin


Yep they changed these screws in the 60's I was a small kid at the time but I remember my dad telling me about it when I started in the trade in the 70's

lakeside53
01-28-2010, 01:38 AM
Find the screw, it couldn't have gone far. Using a flashlight helps immensely!


lol... not "dropped" - just put down somewhere... but, you have no idea... :D

I resorted to my "guarranteed to find everything lost" method - clean up. Hours later, no joy...:mad:

Oh.. it will turn up sometime.

lakeside53
01-28-2010, 01:41 AM
Change of standard - interesting. I learn something every day.

I bet I'm going to have problems with my B&S surface grinder.. need to keep those old bolts separate,

ERBenoit
01-28-2010, 06:26 PM
Oh.. it will turn up sometime.

And then you'll wonder what it was ever for. At least that's what happens on ocassion when I find "lost" things. :)

Rich Carlstedt
01-28-2010, 06:43 PM
Yes, Socket Head Cap Screws (SHCS) were revised in 1962.
the Allen keys used were increased in size to increase torque transfer and reduce stripping the key (wrench).
Head sizes were also changed.
As soon as you see two Cap screw, and one had a bigger wrench opening, you know its a newer one.
One of the additional reasons for the change was improved Metallurgy and industry standardization. Cap Screws made to this standard are the finest in the world.

Lakeside.
Be careful on our B & S Grinder.
On my old # 2, B & S I found odd threads, like 1/4-22.
Some say they were really # 14-22 ( .242 OD) ( which is still odd

Rich

ulav8r
01-28-2010, 07:20 PM
Find the old one, the easy way. Ask your wife to help you find it. She will quickly find it in an easy to find location. She will then delight in telling you how blind and dumb you are. It will make her day.