Not sure this is the right newgroup to ask but what the heck. I am
working on a project where I need to fasten two small objects together
with precise orientation (.5 degrees). The objects will be taken apart
and put together frequently so the fastener cannot be permanent.
Currently I am using a plain screw fastener which I have to calibrate
each time I fasten them together, (by lining up guides on each object).
I desire something more idiot proof and more accurate, I was thinking
maybe a bayonet type mount thats used on camera lens would work, since
they lock in at a fixed position. But maybe I'm thinking too complex,
haven't had any luck searching google because I'm not sure what to
search for, so if someone could give me some ideas where to look that
would be great!

steve

On 20 Jun 2005 13:57:13 -0700, steve wrote:
Not sure this is the right newgroup to ask but what the heck. I am
working on a project where I need to fasten two small objects together
with precise orientation (.5 degrees). The objects will be taken apart
and put together frequently so the fastener cannot be permanent.

How about a V-block setting on a cylinder? Two linear points of
contact, and impossible to misalign unless you screw up very creatively.
Controls both rotational and vertical relationship of the two parts.
If you need precise 3-dimensional placement, make two of 'em at right
angles to each other, and you're locked in.

If that doesn't make sense, please describe the parts for a better
suggestion or description, depending.

Dave Hinz

Yes that makes a lot of sense, simple too! Can this easily be made to
be accurate and not sloppy, I mean, practically speaking, how tight can
I get those V's made on a cylinder? Is there a material of choice for
this application?

On 20 Jun 2005 14:25:13 -0700, steve wrote:
Yes that makes a lot of sense, simple too! Can this easily be made to
be accurate and not sloppy, I mean, practically speaking, how tight can
I get those V's made on a cylinder? Is there a material of choice for
this application?

Steel works great, but v-blocks could be made with a router, a straight
guide, and a chunk of wood if you want. What's your application?

In article 1119301033.308925.119370
@g47g2000cwa.googlegroups.com,
says...
Not sure this is the right newgroup to ask but what the heck. I am
working on a project where I need to fasten two small objects together
with precise orientation (.5 degrees). The objects will be taken apart
and put together frequently so the fastener cannot be permanent.
Currently I am using a plain screw fastener which I have to calibrate
each time I fasten them together, (by lining up guides on each object).
I desire something more idiot proof and more accurate, I was thinking
maybe a bayonet type mount thats used on camera lens would work, since
they lock in at a fixed position. But maybe I'm thinking too complex,
haven't had any luck searching google because I'm not sure what to
search for, so if someone could give me some ideas where to look that
would be great!

steve



The classical solution to eliminate all 6 degrees of
freedom (3 linear, 3 rotational), without redundant
constraints, is one each of a sphere/plane mate,
sphere/cone mate and cylinder/slot mate. Google "kinematic
mount" for more details.

If you already have two surfaces clamped together, and only
need to minimize relative rotation, two pins in a slot is
easy.

If you need accurate linear location as well, think about
two pins in cylindrical holes, or one hole and one slot.
You can loosen up the accuracy required in making the parts
by the judicious use of "diamond pins." For example...
http://www.carrlane.com/Catalog/inde...825071F0B22111
8070C1C513E111D081B0006280B1713050245221E0107070F1 A3C3B2853
56415F

Here's a high-tech solution...
http://www.g2-engineering.com/spherolinder.html

Ned Simmons

I'd simply suggest that the existing screw holding the parts together
be replaced by a tapered pin. Readily removable, yet provides precise,
repeatable positioning.

Or use the existing screw to lock the parts in alignment, and drill a
new hole for the tapered pin, then ream that hole. If the existing
screw holes don't quite line up, then this way is better.

Doug

"Shoulder Screws" have a precisely ground cylindrical shank between the
head and the threads that is very good for locating parts.

Jim Wilkins

In article .com,
wrote:
"Shoulder Screws" have a precisely ground cylindrical shank between the
head and the threads that is very good for locating parts.

But they don't always have the cylindrical part truly concentric
with the threads -- at least based on my experience using two of them to
allow a stack of parts to slide together.

Enjoy,
DoN.

--
Email: | 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 ---

I can see the tapered pin providing alignment, but I would also need to
add some type of fastener to hold the parts together, correct? Or is
this some type of locking pin.

wrote in message
oups.com...
"Shoulder Screws" have a precisely ground cylindrical shank between the
head and the threads that is very good for locating parts.

Jim Wilkins


No, they are *not* good for locating parts. You're at the mercy of the
threads being concentric with the ground body, and that isn't guaranteed.

This job would be a classic example of how tools are built-----with the use
of dowel pins, either straight, or diamond, as Ned alluded. If exact
orientation is desired, pins can be installed such that the parts will come
together in only one way----and held together by screws of one's choosing.
Tapered pins would be a PITA in this instance, for they don't always release
without a struggle. Dowel pins, properly applied, do, and have the
potential to locate within tenths of a thousandth.

Need more info? Feel free to ask. I worked for years as a tool maker.

Harold

"steve" wrote in news:1119301033.308925.119370
@g47g2000cwa.googlegroups.com:

Not sure this is the right newgroup to ask but what the heck. I am
working on a project where I need to fasten two small objects together
with precise orientation (.5 degrees). The objects will be taken apart
and put together frequently so the fastener cannot be permanent.
Currently I am using a plain screw fastener which I have to calibrate
each time I fasten them together, (by lining up guides on each object).
I desire something more idiot proof and more accurate, I was thinking
maybe a bayonet type mount thats used on camera lens would work, since
they lock in at a fixed position. But maybe I'm thinking too complex,
haven't had any luck searching google because I'm not sure what to
search for, so if someone could give me some ideas where to look that
would be great!

steve


Something similar to a carriage bolt, but with ground flats would work
also. If you want only one orientation, make it D shaped.



--
Anthony

You can't 'idiot proof' anything....every time you try, they just make
better idiots.

Remove sp to reply via email

http://www.machines-cnc.net:81/

A taper pin is self-locking. That means the taper is shallow enough so
that when you bang it in with a hammer or press it in with an arbor
press (or a drill press, for small pins), it won't come out.

Small Parts (www.smallparts.com) and MSC (www.mscdirect.com) sell them.
You need a tapered reamer to make the mating hole. A "taper pin
reamer", not a "repairman's tapered reamer".

Doug

steve wrote:
working on a project where I need to fasten two small objects together
with precise orientation (.5 degrees). The objects will be taken apart
and put together frequently so the fastener cannot be permanent.

Two precision pins (cheap) separated by 1" on flat mating surfaces with
a screw about half way between them. Drill the two holes for the pins
in one operation and slightly undersize. Ream on set to press fit size
and the other set to snug sliding fit. The objects slide together and
the screw merely holds them. It is quite easy to get considerably
better than .5 degree this way.

Ted

The ones I used were close enough that they didn't bind badly in holed
drilled and tapped for the thread and bored and reamed above that for
the shank. The arrangement would have been better if the shoulder
screws threaded into a floating nut plate but it was a blind hole in
the top of a dovetail slide.

I made a successful jig to drill precisely spaced dowel pin holes in
the top jaws for a Microcentric lathe chuck by turning down 3 disks on
a freshly turned stub mandrel that fit snugly in the disk's reamed
center holes. The disks were all shaved down until any one would just
fit between the other two which were resting on the chuck's locating
pins.

To drill the top jaws I located the first dowel pin hole to the mill's
accuracy, put a pin and disk in it, chucked another dowel pin with the
second disk on it, then moved the table until the third disk would
slide between the other two. Lock the table, recheck fit, drill and
ream. All 3 top jaws fit onto the chuck with finger pressure.

Jim Wilkins

"steve" wrote in message
oups.com...
Not sure this is the right newgroup to ask but what the heck. I am
working on a project where I need to fasten two small objects together
with precise orientation (.5 degrees). The objects will be taken apart
and put together frequently so the fastener cannot be permanent.

As others have suggested, dowel pins are specifically made for this
appliction.

However, you need to consider who will be assembling/disassembling the
product in question, and whether they're capable of taking the appropriate
care required to not bugger the dowel/hole fit.

While a pair of dowels will allow repeatability within a couple
ten-thousandths of an inch, there is a significant risk that an untrained
operator will incorrectly assemble the joint and (typically) use the dowel
to "shear" its mating hole due to the dowel entering on an angle. Once this
has occured, the hole will require rework to function correctly.

There are ways to minimize the risk. Having the appropirate hole size is
important (precision slide fit as opposed to a light press fit), using a
relieved dowel pin, using one standard pin and one diamond pin, using
hardened bushings instead of soft reamed holes, etc. You pretty much need to
have lubrication every time the dowel is assembled into the hole as the fit
is virtually completely intolerant of corrosion or excessive friction.

The bottom line is that dowels are used extensivly in the tooling industry
and would probably do an excellent job for very little cost in your
application.

HTH.

Regards,

Robin

"Robin S." wrote in message
. ..

"steve" wrote in message
oups.com...
Not sure this is the right newgroup to ask but what the heck. I am
working on a project where I need to fasten two small objects together
with precise orientation (.5 degrees). The objects will be taken apart
and put together frequently so the fastener cannot be permanent.

As others have suggested, dowel pins are specifically made for this
appliction.

However, you need to consider who will be assembling/disassembling the
product in question, and whether they're capable of taking the appropriate
care required to not bugger the dowel/hole fit.

While a pair of dowels will allow repeatability within a couple
ten-thousandths of an inch, there is a significant risk that an untrained
operator will incorrectly assemble the joint and (typically) use the dowel
to "shear" its mating hole due to the dowel entering on an angle. Once
this
has occured, the hole will require rework to function correctly.

There are ways to minimize the risk. Having the appropirate hole size is
important (precision slide fit as opposed to a light press fit), using a
relieved dowel pin, using one standard pin and one diamond pin...

Holy cow. Does anybody still use diamond pins? That's what they used decades
ago to assemble master jigs and master watch plates, but I thought those
things disappeared.

Did they teach you about watch plates in your tooling classes? That was once
the ultimate expression of the toolmaker's art.

--
Ed Huntress

"Ed Huntress" wrote in message
...
"Robin S." wrote in message
. ..

"steve" wrote in message
oups.com...
Not sure this is the right newgroup to ask but what the heck. I am
working on a project where I need to fasten two small objects together
with precise orientation (.5 degrees). The objects will be taken
apart
and put together frequently so the fastener cannot be permanent.

As others have suggested, dowel pins are specifically made for this
appliction.

However, you need to consider who will be assembling/disassembling the
product in question, and whether they're capable of taking the
appropriate
care required to not bugger the dowel/hole fit.

While a pair of dowels will allow repeatability within a couple
ten-thousandths of an inch, there is a significant risk that an
untrained
operator will incorrectly assemble the joint and (typically) use the
dowel
to "shear" its mating hole due to the dowel entering on an angle. Once
this
has occured, the hole will require rework to function correctly.

There are ways to minimize the risk. Having the appropirate hole size is
important (precision slide fit as opposed to a light press fit), using a
relieved dowel pin, using one standard pin and one diamond pin...

Holy cow. Does anybody still use diamond pins? That's what they used
decades
ago to assemble master jigs and master watch plates, but I thought those
things disappeared.

Did they teach you about watch plates in your tooling classes? That was
once
the ultimate expression of the toolmaker's art.

--
Ed Huntress


It's been a few years (ok, more than 20) since I last built tooling, but I
was still using them at that point in time. I can't imagine not using them
when the situation calls for them. They're the ultimate for fitting more
than one item to the same set of pins.

Harold

The object is a small (2 ounce) electronic orientation sensor and it
needs to know the orientation of it is relative to the object its
attached to.

Robin,
Yes the removal/replacement will be done by the end user, so I can't
use the dowel suggestion (although a cheap and excellent way to do it).
I'm now thinking more of the keyed male/female set (maybe just a simple
square shaped key and hole), slide it in with some type of lock-down
mechanism that doesn't effect the alignment. .5 degrees isn't extremely
precise so maybe this will work. The object is a small (2 ounce)
electronic orientation sensor and it needs to know the orientation of
it is relative to the object its attached to.

steve

(I replied to this message but it didn't show up)

Yes you are right, the dowel method is excellent but I need a method
that's more user friendly, I'm thinking a keyed slot with some type
of locking mechanism, accuracy requirement is not excessive so maybe it
will work. The application is an orientation sensor that needs to be
aligned to the object its measuring the orientation of.

"Ed Huntress" wrote in message
...

Holy cow. Does anybody still use diamond pins? That's what they used
decades
ago to assemble master jigs and master watch plates, but I thought those
things disappeared.

I don't think I've ever seen one personally, other than in jig books.


Did they teach you about watch plates in your tooling classes? That was
once
the ultimate expression of the toolmaker's art.

A "watch plate" doesn't sound familiar.

I'm not sure I'd be interested making a watch plate, if it truly is the
"ultimate expression of the toolmaker's art." I'm in the middle of my
European practical final exam and filing a square hole to an H7 tolerance is
just about enough expression for me....

Regards,

Robin

"steve" wrote in message
oups.com...
Robin,
Yes the removal/replacement will be done by the end user, so I can't
use the dowel suggestion (although a cheap and excellent way to do it).
I'm now thinking more of the keyed male/female set (maybe just a simple
square shaped key and hole), slide it in with some type of lock-down
mechanism that doesn't effect the alignment. .5 degrees isn't extremely
precise so maybe this will work. The object is a small (2 ounce)
electronic orientation sensor and it needs to know the orientation of
it is relative to the object its attached to.

..5° works out to +/-.0043" over one inch. This should be easily achieved
using a free-running keyway.

Let us know how you make out..

Regards,

Robin

The shoulder should go into the mounting piece. That makes the two pieces
exactly right.

--
Why isn't there an Ozone Hole at the NORTH Pole?