On 5/18/17 11:16 AM, Tim Shoppa wrote:

The rule of thumb is that if you get 3-5 threads fully engaged that's
good - so at 40 threads/inch, 5 threads is 1/8" Drill the hole a bit
more than 1/4" deep (approx), tap the first 3/16" inch (so you can use a
regular old tap), blow the chips out afterwards, use fasteners that are
the right length.

Is the number of fasteners for mechanical strength, for RF sealing,
thermal transfer, or what? You might be able to get by with fewer
fasteners if you use a conductive elastomer gasket (or even copper foil
tape which deforms when you screw the lid down).

5 fasteners in 5" is spacing them a bit less than an inch apart.
Even in Aluminum, your threads are probably stronger than your fastener.

Threads			Fastener	

Engaged Length 0.125 in Engaged Length
TPI 40 TPI
Diameter 0.112 in Diameter
mean Diam 0.0995 in Root Diam 0.087 mean Diam
Engaged area 0.0391 sq in Area 0.00594 Engaged area
Load 200 lb Load
Shear stress 5,119 psi 33,644 Shear stress
Ultimate strength 42 ksi ultimate 74 Ultimate strength
Shear Strength 24,249 psi proof 55,000 Shear Strength
Safety factor 4.74 Safety factor 1.63 Safety factor

Aluminum			Steel	

On 5/18/17 11:53 AM, jimlux wrote:

Fixing the table formatting

It would be easy to re-design the job for cheaper machining..  Do you
really need to tap the holes?  You might use self taping screws.  Id the
would work then you can do the work yourself with just a hand drill.

OK it you must use machine threads and they must be #4 size try "rivets"
these work like pop rivets but leave a hollow thread insert in the hole
that will take screws.  Takes all of 5 seconds to install a thread hole.

Think again about threading aluminum.  It is not very strong, it would be
easy for an end user to strip the #4 threads.  Better to use the rivet or
other steel thread insert.    Even native nuts  installed with flush rivets
is better

So try self threading screws first them go to threaded inserts, you could
install 100 4-40 inserts in one hour using just hand tools.

On Thu, May 18, 2017 at 9:54 AM, cdelect@juno.com wrote:

--

Chris Albertson
Redondo Beach, California

Yes, generally when something is expensive to manufacture it is because the
designer was not thinking about costs.  A design with 40 size "tiny" thread
holes in just not cost-effective.  A redesign could save hours work.

On Thu, May 18, 2017 at 11:16 AM, Tim Shoppa tshoppa@gmail.com wrote:

--

Chris Albertson
Redondo Beach, California

Or go for thicker wall aluminium tube, oversized endplates and long bolts or threaded rods running the entire length down the outside of the tube so you're clamping both ends in one operation. No tapping required. Simples!

On 19/05/2017, at 6:16 AM, Tim Shoppa wrote:

Why are my eyes watering?

On 19/05/2017, at 5:03 AM, Bob Darlington wrote:

Andy,

Although this is a hydraulic cylinder, this is along the lines of what you
described.

On Thu, May 18, 2017 at 19:18 Andy ZL3AG via time-nuts time-nuts@febo.com
wrote:

--

Ken
WA2LBI

Sent from one of my mobile devices

So the goal is not to attach end plates, that is the solution. The real
goal is a sealed container that can be re-opened.    I suggest a trip to
the plumbing supply store.    Why not just use screw-on end caps

It you need it sealed 4-40 screw are not able to provide any reasonable
clamping force.  The weak link is the aluminum threads.  You need enough
force to deform the gasket material and those little screws are not going
to do it.

If you need a gas tight chamber, look at plumbing parts.  They make
screw-on end caps with both make and female threads.

There is also a system for brazing alumni that work almost as well as
celiac welding and you can do it with a propane lumber's torch.  They sell
the rods at Harbor Freight.

Why not post a specification (enclose with x,y,z inside dimension,
water/gas tight/ ends on one end,....) and ask people for ideas on the
lowest cost way to make that using simple tools.

There are SO MANY solutions, one is double sided, coper clad PCB material.
You can cut it with a wood saw and then solder the panels together to make
a box.  I find that I can solder brass screws to copy PCB material and
make thread posts or studs.

On Thu, May 18, 2017 at 4:13 PM, Andy ZL3AG via time-nuts <
time-nuts@febo.com> wrote:

--

Chris Albertson
Redondo Beach, California

On 5/18/17 2:36 PM, Chris Albertson wrote:

Interestingly enough, for 4-40 hardware, the screws fail before the
aluminum does.  The area of the thread engagement is quite a bit larger
than the cross section of the fastener that is not thread.

For large fasteners, where the thread depth is a smaller fraction of the
fastener diameter, this may not be the case (as anyone who has stripped
the threads on an aluminum cylinder head with a steel sparkplug will
know, in a deep and visceral way).

There are a lot of variables involved. Run the screws in and out of the aluminum a number of times and
the holes will fail first ….There are other gotchas as well.

Bob