Request for advice regarding manufacture of a spring anchor

Hi everyone,
I have uploaded a small 19KB .GIF file to rapidshare showing a drawing of a simple adjustable spring anchor I am making from a 10-32 screw.
Here is the download link...
http://rapidshare.de/files/24739574/Spring_Adjustment_Screw.gif.html
Regarding the drawing, an extension spring hook goes through the .098" hole, and the other end of the screw gets a hex nut that can be no larger than 5/16" flat to flat, such as part # 90760A411 from www.mcmaster.com. Due to space limitations, the hex nut must be adjusted with a box end wrench.
The .359" to .390" OD spring ( similar to the #80583 www.centuryspring.com) uses .08" diameter wire, but the problem I ran into is that the hole is not really large enough for the spring, due to the curvature of the hook.
Can a machinist cost effectively just make a .098" wide slot in the screw, about .145" to .155" long, instead of a .098" OD hole?
I know slots are generally easy to do, but since it is so small, I wanted to get some feedback. If the slot can be made cost effectively, It will work well with the spring.
If the slot cannot be made cost effectively, then I must use a larger screw that will allow for a hole of about .145" OD. A 1/4-20 or 1/4-28 screw would work great, but I could not find a nut that is 5/16" flat to flat max, and that has a 1/4-20 or 1/4-28 thread.
I did find a 1/4-32 nut (part # 91862A516) from www.mcmaster.com, which is only 5/16" flat to flat, but then I can't seem to find a screw for it. Mcmaster also sells a 1/4-40 nut that would work, but same problem, I cannot find a screw.
I would appreciate any feedback anyone can provide. Hopefully, just creating a slot in the 10-32 screw is viable and cost effective.
Thanks for your help. John
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Shouldn't be too bad to just slot out that hole with a 1/16 (.0625) two flute endmill. Drill the hole first. These EMs are easy to break, get a few extra for seed.
Karl
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Hi Karl,
Thanks for your feedback.
Maybe I will just go with the slot method then. I would appreciate any further feedback from any other machinists or anyone that may have had some experience with small slots.
I just don't want to change the design, send the DWG off for quotes, and then have the machinist say it can't be done or is too expensive for the product.
I was not sure if they had end mills quite that small, or if there would be a problem with breakage, but it should not be too expensive to stock up on extra end mills as long as the breakage is kept to reasonable levels.
Thanks again, John
Karl Townsend wrote:

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snipped-for-privacy@yahoo.com says...

I think it would be less expensive to mill flats on the anchor where the hole goes thru, like an off the shelf anchor - see McMaster p.3114. This will reduce the size of the hole needed to clear the curvature of the hook.
Ned Simmons
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Hi Ned,
Good thinking ! Thanks for the tip.
In AutoCAD, It looks like I will have to machine the flat so that it's about .0625" thick, in order to accomodate the size spring I am using. Will that be enough material left, i.e., it won't chip away during machining will it ? The spring should only have 40 to 50 pounds maximum on it.
I would appreciate feedback from any other machinists, regarding which method is cheapest, i.e, cutting the slot, or milling the flat and drilling the hole.
Thanks again everyone,
John
Ned Simmons wrote:

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snipped-for-privacy@yahoo.com says...

Look here to see if there's anything that'll work (or is easily modified) before you start making something you can get off the shelf.
<http://www.misumiamerica.com/SearchResults.aspx?ProductValue=spring % 20anchor>
For example... http://www.misumiamerica.com/PDFViewer.aspx?Metric lse&PageW5
Ned Simmons
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On 2 Jul 2006 08:49:56 -0700, "John2005"

=================You may want to consider making your own 1/4-32 rod and nuts.
see https://www.brownells.com/aspx/ns/store/ProductDetail.aspx?p 074&title=FRACTIONAL+CARBON+TAPS+%26+DIES
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Take a look at M5 nuts and threaded rod-nuts are 8mm across, should be close enough to 5/16". Agree with others, just grind flats instead of machining slots
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After rereading the entire post, metric isn't going to make any difference...
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John2005 wrote:

If the "hole end" of the threaed rod doesn't have to fit through a 3/16" hole, then:
If you swedged about a 1/4" length of the end of the threaded rod it would get thinner in one direction and wider in the other.
Plus, the flat surface should be easier to start a drill on.
That should let you easily drill a strong "practical size" spring hook hole.
Shouldn't take "rocket surgery" to figger out how to swedge the end of the screw. Anything from a hammer and anvil on up ought to work.
Jeff
--
Jeffry Wisnia
(W1BSV + Brass Rat '57 EE)
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John2005 wrote:

(...)
Floss it! I bet a few passes with a length of this abrasive cord would put the necessary features into those hole openings muy pronto, with less 'stress rising' than that of an oblong hole.
47015A26 Aluminum Oxide Cord, .070" Size, 180 Grit, 50' In stock at $16.44 Each
--Winston
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Hi everyone,
Thanks for the tip on the abrasive cord Winston.
Perhaps a small dremel tool could also work well.
A guy named Jim from the Sci mech engineering forum suggested to use a 10-32 socket head cap screw, and just drill a larger hole in the head of the screw to clear the curvature of the spring. If I can get a .145" OD or so hole in the head, it may be easier to just drill the screw head as opposed to making slots or making flats.
I just thought of one possible drawback as I am writing this, aren't most of those socket head cap screws kind of hard ? Perhaps a carbide drill bit will work.
Thanks again guys, John
Winston wrote:

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Do you have room to use a thumb screw? Already flattened lots of area to drill...
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Socket may not be deep enough to drill that size without hitting the bottom of the socket-bit will wander or break..
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From a reference sheet, head height on a #10 SHCS is .190" max, socket depth is .090"...

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Hi Rick,
I would be drilling the hole through the diameter of the screw head, so the limitation is the .190" head height, since I need about a .145" OD hole to allow clearance for the spring hook. However, the diameter of the socket head is also larger than the .190" screw body, so I will likely need even a larger hole than .145".
I keep comming back to Ned's Idea of just milling a flat and drilling a hole. I guess I will go that route. Swedging or pressing the flat as suggested before may also work well.
I checked some of the stock anchors, but most are not long enough, and the ones that are long enough will probably still need to be cut to length and the hole enlarged. With that in mind, it may be best to just make them from scratch from a .15 cent screw.
Perhaps it won't make a real big difference either way, I just wanted to try to keep things as simple and cheap as possible.
Sincerely, John
Rick wrote:

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Did you look at the thumb screws? Not sure if you have enough room for the heads of them, or if they are cost effective...
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Hi Rick,
I looked at some thumb screws but they were a little too bulky and expensive.
I'm just going to take a 1/4" long portion of the 10-32 screw end, make it flat, and then drill a .098" hole in it. I was able to make the flat .108" thick, and the center of the hole is .128" in from the end of the 10-32 screw.
It's looks like it can hold a 45 pound spring load with no problems.
Thanks again, John
Rick wrote:

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Someone else mentioned forming the flat, a 2-1/2 pound machinist hammer and a small anvil would take one hit......... Make a threaded holder to position it and keep your fingers out of the way.
John2005 wrote:

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Hi everyone,
After thinking about it, I am afraid if I drill a .098" OD hole through the threaded portion of a 10-32 screw, it won't be strong enough because it only leaves .02" on each side of the hole to the minor diameter of the screw. Plus, the threads may be a stress riser.
I found a Part # 91251A353 from www.mcmaster.com that should work well for me. I can cut the head off and use the un-threaded .190" OD portion to drill the .098" OD hole through. However, this screw has a hardness of Rockwell C39 to C45. Can a flat be machined and a hole drilled fairly easily with a carbide cutter and drill ? I just wonder if the screw hardness will be a problem to machine or drill.
I need an overall screw length of about 1.707" and about .69" of usable thread length. I did not see an un-hardened screw that met my dimensional requirements and still had an unthreaded portion I could put the .098" OD hole in.
Please let me know what you guys think.
Thanks again for your help.
Sincerely, John
RoyJ wrote:

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