They're 8mm Socket Head Machine Screws with a section of threads ground off to the minor diameter, leaving about 5-6mm of thread at the tip and about 10mm at the head end. The threads engage at both the tip and head ends.
They're used on the front seat mounts of a Sunrise Medical Rhythm power wheelchair with a certain seating system.
I can see *how* they work. They engages threads on both sides of a square tube. What I can't see is: Why do it that way, considering it only prevents the seat frame rising up off the mount? Seems like any old bolt would do. Or if one were a *really* anal Engineer*, a shoulder bolt.
John Husvar <jhus...@sbcglobal.net> fired this volley in news:jhusvar- 626989.07371728062...@news.eternal-september.org:
> I can see *how* they work. They engages threads on both sides of a > square tube. What I can't see is: Why do it that way, considering it > only prevents the seat frame rising up off the mount? Seems like any old > bolt would do. Or if one were a *really* anal Engineer*, a shoulder
bolt.
There are a couple of good reasons to do it that way:
1) if the "pin" is under any significant strain, a threaded body will create stress risers that may cause it to fatique in the stressed area
2) if the item bearing on that smooth section is banging around any, it will bung up the threads, making it difficult to remove the fastener in the future. (A tube bushing around the bolt would help prevent that, but is probably more cost and work to implement than the turned-down bolt body).
On Jun 28, 7:37 am, John Husvar <jhus...@sbcglobal.net> wrote:
> ... > They're 8mm Socket Head Machine Screws with a section of threads ground > off to the minor diameter, leaving about 5-6mm of thread at the tip and > about 10mm at the head end. The threads engage at both the tip and head > ends.
> They're used on the front seat mounts of a Sunrise Medical Rhythm power > wheelchair with a certain seating system....
Does that captivate the bolt when the seat is removed?
> John Husvar<jhus...@sbcglobal.net> fired this volley in news:jhusvar- > 626989.07371728062...@news.eternal-september.org:
>> I can see *how* they work. They engages threads on both sides of a >> square tube. What I can't see is: Why do it that way, considering it >> only prevents the seat frame rising up off the mount? Seems like any > old >> bolt would do. Or if one were a *really* anal Engineer*, a shoulder > bolt.
> There are a couple of good reasons to do it that way:
> 1) if the "pin" is under any significant strain, a threaded body will > create stress risers that may cause it to fatique in the stressed area
> 2) if the item bearing on that smooth section is banging around any, it > will bung up the threads, making it difficult to remove the fastener in > the future. (A tube bushing around the bolt would help prevent that, but > is probably more cost and work to implement than the turned-down bolt > body).
One other benefit of the threaded design, assuming that both walls of the tube are tapped, is that the bolt tightens without crushing the tube.
> John Husvar <jhus...@sbcglobal.net> fired this volley in news:jhusvar- > 626989.07371728062...@news.eternal-september.org:
> > I can see *how* they work. They engages threads on both sides of a > > square tube. What I can't see is: Why do it that way, considering it > > only prevents the seat frame rising up off the mount? Seems like any > old > > bolt would do. Or if one were a *really* anal Engineer*, a shoulder > bolt.
> There are a couple of good reasons to do it that way:
> 1) if the "pin" is under any significant strain, a threaded body will > create stress risers that may cause it to fatique in the stressed area
> 2) if the item bearing on that smooth section is banging around any, it > will bung up the threads, making it difficult to remove the fastener in > the future. (A tube bushing around the bolt would help prevent that, but > is probably more cost and work to implement than the turned-down bolt > body).
> LLoyd
#2 is the likely reason, especially if the seat part is a somewhat loose fit.
> On 6/28/2010 7:55 AM, Lloyd E. Sponenburgh wrote: > > John Husvar<jhus...@sbcglobal.net> fired this volley in news:jhusvar- > > 626989.07371728062...@news.eternal-september.org:
> >> I can see *how* they work. They engages threads on both sides of a > >> square tube. What I can't see is: Why do it that way, considering it > >> only prevents the seat frame rising up off the mount? Seems like any > > old > >> bolt would do. Or if one were a *really* anal Engineer*, a shoulder > > bolt.
> > There are a couple of good reasons to do it that way:
> > 1) if the "pin" is under any significant strain, a threaded body will > > create stress risers that may cause it to fatique in the stressed area
> > 2) if the item bearing on that smooth section is banging around any, it > > will bung up the threads, making it difficult to remove the fastener in > > the future. (A tube bushing around the bolt would help prevent that, but > > is probably more cost and work to implement than the turned-down bolt > > body).
> One other benefit of the threaded design, assuming that both walls of > the tube are tapped, is that the bolt tightens without crushing the tube.
Yes, however that is a function of having both sides of the tube tapped and has nothing to do with having an unthreaded section in the middle of the bolt.
In article <8def15da-730f-4334-b017-4be05eb1d...@u26g2000yqu.googlegroups.com>, Jim Wilkins <kb1...@gmail.com> wrote:
> On Jun 28, 7:37 am, John Husvar <jhus...@sbcglobal.net> wrote: > > ... > > They're 8mm Socket Head Machine Screws with a section of threads ground > > off to the minor diameter, leaving about 5-6mm of thread at the tip and > > about 10mm at the head end. The threads engage at both the tip and head > > ends.
> > They're used on the front seat mounts of a Sunrise Medical Rhythm power > > wheelchair with a certain seating system....
> Does that captivate the bolt when the seat is removed?
> jsw
No, it must be completely removed to tilt or remove the seating system. The bolt has to unscrew from both ends first, then the far end male thread. has to engage the near end female threads and unscrew through them to be removed.
Pete C. wrote: > "J. Clarke" wrote: >> On 6/28/2010 7:55 AM, Lloyd E. Sponenburgh wrote: >>> John Husvar<jhus...@sbcglobal.net> fired this volley in news:jhusvar- >>> 626989.07371728062...@news.eternal-september.org:
>>>> I can see *how* they work. They engages threads on both sides of a >>>> square tube. What I can't see is: Why do it that way, considering it >>>> only prevents the seat frame rising up off the mount? Seems like any >>> old >>>> bolt would do. Or if one were a *really* anal Engineer*, a shoulder >>> bolt.
>>> There are a couple of good reasons to do it that way:
>>> 1) if the "pin" is under any significant strain, a threaded body will >>> create stress risers that may cause it to fatique in the stressed area
>>> 2) if the item bearing on that smooth section is banging around any, it >>> will bung up the threads, making it difficult to remove the fastener in >>> the future. (A tube bushing around the bolt would help prevent that, but >>> is probably more cost and work to implement than the turned-down bolt >>> body). >> One other benefit of the threaded design, assuming that both walls of >> the tube are tapped, is that the bolt tightens without crushing the tube.
> Yes, however that is a function of having both sides of the tube tapped > and has nothing to do with having an unthreaded section in the middle of > the bolt.
Might it be that this allows both sides to engage threads without having to screw all the way through? Certainly a labor savor - if somewhat expensive...
> On 6/28/2010 7:55 AM, Lloyd E. Sponenburgh wrote: > > John Husvar<jhus...@sbcglobal.net> fired this volley in news:jhusvar- > > 626989.07371728062...@news.eternal-september.org:
> >> I can see *how* they work. They engages threads on both sides of a > >> square tube. What I can't see is: Why do it that way, considering it > >> only prevents the seat frame rising up off the mount? Seems like any > > old > >> bolt would do. Or if one were a *really* anal Engineer*, a shoulder > > bolt.
> > There are a couple of good reasons to do it that way:
> > 1) if the "pin" is under any significant strain, a threaded body will > > create stress risers that may cause it to fatique in the stressed area
> > 2) if the item bearing on that smooth section is banging around any, it > > will bung up the threads, making it difficult to remove the fastener in > > the future. (A tube bushing around the bolt would help prevent that, but > > is probably more cost and work to implement than the turned-down bolt > > body).
> One other benefit of the threaded design, assuming that both walls of > the tube are tapped, is that the bolt tightens without crushing the tube.
> > LLoyd
I can understand all the reasons presented. It's just that the things are so crudely made and that the male threads so often get munged so it's difficult to completely remove the bolts.
The bolt bodies aren't even turned down. They're ground down, apparently by a chimpanzee suffering from Parkinson's Disease -- or at least from Essential Tremor.
Somehow just doesn't seem right on a $20,000+ power wheelchair.
> In article > <8def15da-730f-4334-b017-4be05eb1d...@u26g2000yqu.googlegroups.com>, > Jim Wilkins <kb1...@gmail.com> wrote:
> > On Jun 28, 7:37 am, John Husvar <jhus...@sbcglobal.net> wrote: > > > ... > > > They're 8mm Socket Head Machine Screws with a section of threads ground > > > off to the minor diameter, leaving about 5-6mm of thread at the tip and > > > about 10mm at the head end. The threads engage at both the tip and head > > > ends.
> > > They're used on the front seat mounts of a Sunrise Medical Rhythm power > > > wheelchair with a certain seating system....
> > Does that captivate the bolt when the seat is removed?
> > jsw
> No, it must be completely removed to tilt or remove the seating system. > The bolt has to unscrew from both ends first, then the far end male > thread. has to engage the near end female threads and unscrew through > them to be removed.
Maybe it's safety thing- bolt loosens up, but does not fall out since it can't re-start the threads (in the 2nd portion).
On Jun 28, 9:54 am, cavelamb <cavel...@earthlink.net> wrote:
> ...
Sometimes if you backtrack a design rationale it leads to a bright, inventive newbie engineer who doesn't understand manufacturing yet. I introduced one very talented engineer to Pemnuts and another to spring- loaded ball plungers. It seems they don't learn the subtleties of sheet metal in school. I picked up some from ham radio and aircraft fabrication books and others from catalogs.
> They're 8mm Socket Head Machine Screws with a section of threads ground > off to the minor diameter, leaving about 5-6mm of thread at the tip and > about 10mm at the head end. The threads engage at both the tip and head > ends.
> They're used on the front seat mounts of a Sunrise Medical Rhythm power > wheelchair with a certain seating system.
> I can see *how* they work. They engages threads on both sides of a > square tube. What I can't see is: Why do it that way, considering it > only prevents the seat frame rising up off the mount? Seems like any old > bolt would do. Or if one were a *really* anal Engineer*, a shoulder bolt.
> *WARNING: Possible redundancy
Maybe it's an option for a strap or hanger that's not used on this wheelchair. Could a strap or cable pass through the tubing if it's open on both sides?
> On Jun 28, 9:54 am, cavelamb<cavel...@earthlink.net> wrote: >> ...
> Sometimes if you backtrack a design rationale it leads to a bright, > inventive newbie engineer who doesn't understand manufacturing yet. I > introduced one very talented engineer to Pemnuts and another to spring- > loaded ball plungers. It seems they don't learn the subtleties of > sheet metal in school. I picked up some from ham radio and aircraft > fabrication books and others from catalogs.
> jsw
School teaches you the Science of Engineering, but the Art has to come from somewhere else.
Whenever I was tasked with helping to hire engineers fresh from school, I always gave points to someone who did something real before or outside of normal college coursework. Those are the folks that hit the ground running.
> On Jun 28, 9:53 am, John Husvar <jhus...@sbcglobal.net> wrote:
> > In article > > <8def15da-730f-4334-b017-4be05eb1d...@u26g2000yqu.googlegroups.com>, > > Jim Wilkins <kb1...@gmail.com> wrote:
> > > On Jun 28, 7:37 am, John Husvar <jhus...@sbcglobal.net> wrote: > > > > ... > > > > They're 8mm Socket Head Machine Screws with a section of threads ground > > > > off to the minor diameter, leaving about 5-6mm of thread at the tip and > > > > about 10mm at the head end. The threads engage at both the tip and head > > > > ends.
> > > > They're used on the front seat mounts of a Sunrise Medical Rhythm power > > > > wheelchair with a certain seating system....
> > > Does that captivate the bolt when the seat is removed?
> > > jsw
> > No, it must be completely removed to tilt or remove the seating system. > > The bolt has to unscrew from both ends first, then the far end male > > thread. has to engage the near end female threads and unscrew through > > them to be removed.
> Maybe it's safety thing- bolt loosens up, but does not fall out since > it can't re-start the threads (in the 2nd portion).
> Dave- Hide quoted text -
> - Show quoted text -
This is probably the answer, if there is one. I run into "captive" bolts all the time on take-down guns, but usually only the tip is threaded, the rest is relieved to the head. Kind of dumb to require - both- sides of the tube be in time to get the fastener in. Somebody got carried away with their CAD installation, probably. Then the guys actually making the thing figured out what they had to do to put it together. Do you supposed they had to order extra-length taps? And what keeps them from just using a regular bolt with a nylock nut instead? Tapping has got to be a whole lot more expensive than just drilling a clear hole through.
On 2010-06-28, John Husvar <jhus...@sbcglobal.net> wrote:
> besides a masturbate of Engineering, that is?
> They're 8mm Socket Head Machine Screws with a section of threads ground > off to the minor diameter, leaving about 5-6mm of thread at the tip and > about 10mm at the head end. The threads engage at both the tip and head > ends.
> They're used on the front seat mounts of a Sunrise Medical Rhythm power > wheelchair with a certain seating system.
> I can see *how* they work. They engages threads on both sides of a > square tube. What I can't see is: Why do it that way, considering it > only prevents the seat frame rising up off the mount? Seems like any old > bolt would do. Or if one were a *really* anal Engineer*, a shoulder bolt.
I think that the reduced diameter keeps the seat from bashing the threads so much that it is difficult to remove the screw at some future time. (They probably just put in a plain screw at first, and learned that they needed to fix it somehow later. :-)
It could have been turned down past the part under the head -- except that the hole on the other side was already tapped, instead of the reduced diameter needed for the smooth minor diameter.
Enjoy, DoN.
-- Email: <dnich...@d-and-d.com> | Voice (all times): (703) 938-4564 (too) near Washington D.C. | http://www.d-and-d.com/dnichols/DoN.html --- Black Holes are where God is dividing by zero ---
> They're 8mm Socket Head Machine Screws with a section of threads ground > off to the minor diameter, leaving about 5-6mm of thread at the tip and > about 10mm at the head end. The threads engage at both the tip and head > ends.
> They're used on the front seat mounts of a Sunrise Medical Rhythm power > wheelchair with a certain seating system.
> I can see *how* they work. They engages threads on both sides of a > square tube. What I can't see is: Why do it that way, considering it > only prevents the seat frame rising up off the mount? Seems like any old > bolt would do. Or if one were a *really* anal Engineer*, a shoulder bolt.
