Request for advice regarding the manufacture of an adjustable 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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Hi Everyone,
Ned Simmons from another forum just pointed out that it may be cheaper to machine a flat on the screw, like a standard spring hook shown on page 3114 of the Mcmaster catalog www.mcmaster.com. For example, see image of Mcmaster part # 9634k13. This should allow the screw anchor to clear the hook curvature of the spring.
If I do this, the flat will only be about .0625" thick in order to clear the spring hook. The spring will only have about 40 to 50 pounds on it so as long as a thin flat like that can be machined without problems, it may be a viable option.
Which would be cheaper, machining a slot, or milling a flat like a standard spring anchor and then drilling the hole ? I tend to think Neds suggestion is good, since small end mills are probably weak.
Thanks again guys, John
John2005 wrote:

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Dear John2005:

How long does the screw need to be? They make (shoulderless) set screws with "allen wrench" heads on them... up to 1-1/4" long (in 1/4-28). 1/4"-28 length pkg McMaster# $/pkg 3/4" 25 91385A358 8.78 1" 25 91385A363 10.23 1 1/4" 25 91385A362 11.58
Would that help?
David A. Smith
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Hi David,
Thanks for your reply.
I really have to make the adjustment by rotating the nut and not the screw. I also need a length that is basically like the drawing, i.e., 1.59" to 1.707". I may be able to change this a little, but I think 1.25" will be too short and I won't have enough adjustment.
Thanks again, John
N:dlzc D:aol T:com (dlzc) wrote:

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John2005 wrote:

Drilling is likely to be cheaper than machining. Have you considered using a 10-32 screw with 1/4" head or shoulder and then drilling the hole thru the head (or shoulder). Look at a 10-32 X 1.75" Cap screw for instance.
-jim
-
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Hi everyone,
Thanks for the tips Steve and Jim,
Steve, if you could please email me any specs or sources of supply for the screw you mentioned that would be great. The email in my profile here is in working order if you want to just send it there. I did not know they made a 1/4" hex nut that works on a 10-32 screw, but that will give me more room for a wrench when I make adjustments, and it's a big help to be able to use a smaller wrench in the tight space.
Clever thinking Jim !
I never thought about using the head end of a cap screw to put the hook in. Perhaps I could drill a large enough hole that way, so the curvature of the spring hook will clear the hole. That way I may be able to avoid slotting or machining flats. I will check into that. If the head is big enough for a .145" OD or so hole, it may work well.
Thanks again guys ! John
jim wrote:

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Info on the way....
Steve R.
John2005 wrote:

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Hi everyone,
I just checked into the socket head cap screw, but it looks like the .190" height of the screw is not quite tall enough for a .145" OD hole. It does not leave much material left for the spring to hook on and may be weak. Also, the OD of the head may have to be ground down, since its larger than the .190" threaded portion and will further interfer with the curvature of the spring hook. It was still a good suggestion though Jim.
Thanks for sending the info on the nut Steve, I will check my email. That will help quite a bit with the issues regarding limited space, as I can now use a smaller box end wrench.
Sincerely, John
Steve Rauenbuehler 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
John2005 wrote:

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John -
Since you were originally looking for a .250 screw solution, with an associated nut with .312 flats, and an MS21042-4 nut has .312 flats, could you go back up to that size? That would allow more "meat" around your spring holding feature (hole or slot).
Just an idea...
Steve R.
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Hi Steve,
I think the problem with the nut you recommended is that it is a locknut. I think the resistance to turning that these nuts have would not be desirable in my situation. It may cause the screw to turn with the nut, unless someone holds the other end of the screw with pliers or something. I want the customer to be able to adjust the spring as easy as possible, with just a cheap box end wrench, maybe even a stamped wrench I can send with each product.
If I could find a regular 5/16" hex nut to work with a 1/4-20 or 1/4-28 thread, that would be great. A 10-32 socket head cap screw like the one mentioned in my previous post will also work as long as it is not too hard to machine and drill.
Thanks again, John
Steve Rauenbuehler wrote:

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Dear John2005:

How much adjustment did you need? There are shoulder bolts, that will have a solid 1/4" shaft, a hex key head, and a #10 thread... just not much of it and usually coarse pitch...
McMaster 91259A103 Alloy Steel Standard Shoulder Screw 1/4" Shoulder Dia, 2" Shoulder Length, 10-24 Thrd In stock
Quantity Each 1-4 Each $1.33 5 or more $1.13
Also might consider attaching the spring to a lever, and controlling the lever position with a much simpler screw...
David A. Smith
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Hi everyone,
I found a part # 92196A279 from www.mcmaster.com made from 18-8 stainless that should machine fine, but then on the 2D drawing it says the thread length can vary from 7/8" to fully threaded. I don't know if they mean the thread length can vary that much on that particular part, or from part to part.
I need at least .69" of useable screw thread, so I am afraid I won't be able to use a shoulder screw.
Thanks again, John
N:dlzc D:aol T:com (dlzc) wrote:

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Hi everyone,
I found a Part # 92196A281 from www.mcmaster.com that is made from 18-8 stainless & should work for me. It has a length of 2.5" and the threaded portion can vary anywhere from 7/8" to 2". That will leave me enough room to cut the screw to length, and then use a 1/4" long portion of the non-threaded portion to drill the .098" hole through.
It kills me that the tell you the screw is partially threaded, then the drawing says the thread can vary from 7/8" to fully threaded or 7/8" to 2" thread. That's a big variance if you are working with or in need of the un-threaded portion. I wonder why they are so inconsistent with regards to thread length ?
Anyway, it looks like I have something that will work now.
Thanks again for the feedback guys.
John John2005 wrote:

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John -
Check out a MS21042-3 nut.
#10-32 thread, and only 1/4" hex.
If you can't find specs. let me know, I can send a spec sheet to you....
Steve R.
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