What would you call this
John Husvar
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
Lloyd E. Sponenburgh
626989.073...@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
Jim Wilkins
> ...
> 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
Does that captivate the bolt when the seat is removed?
jsw
J. Clarke
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
Pete C.
#2 is the likely reason, especially if the seat part is a somewhat loose
fit.
Pete C.
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.
John Husvar
<8def15da-730f-4334...@u26g2000yqu.googlegroups.com>,
Jim Wilkins <kb1...@gmail.com> wrote:
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.
cavelamb
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...
--
Richard Lamb
John Husvar
"J. Clarke" <jclarke...@cox.net> wrote:
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.
Offends my sense of aesthetics, it does. :)
Dave__67
> In article
> <8def15da-730f-4334-b017-4be05eb1d...@u26g2000yqu.googlegroups.com>,
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
Jim Wilkins
> ...
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
Denis G.
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?
Tim Wescott
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.
sta...@prolynx.com
>
> - 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.
Stan
DoN. Nichols
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: <dnic...@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 ---
Califbill
wires. Also saves the cost of a through tube.
"John Husvar" <jhu...@sbcglobal.net> wrote in message
news:jhusvar-626989...@news.eternal-september.org...