Panel clock bezel (technical) question

On the site of MSP (Precision Aerospace Manufacturing):
http://www.msp-aviation.com/

Standard ARINC Avionics cases:
http://www.msp-aviation.com/products...ics_cases.aspx are shown.

When going to the ARINC 408A Instrument Bezels the dimensions, (we all need) , are shown.
The numeric dimensions are in the parts list there:
http://www.msp-aviation.com/charts/bezels1.htm then to the pdf

The most common Boeing clocks dim,dimensions are:

MSP Inc. P/N ARINC 408 SPEC. 68002-3 3ATI-S

A...........B.......C........D.......E.......F........G.......H.......R
± .010 ± .010 ± .005 ± .005 REF. REF. ± .010 ± .010 ± .010
3.260 3.175 2.812 3.010 .453 .428 3.970 3.885 .731 inch

Who can help me with the some questions:

Is it NOT a square but an rectangle ?
A and B are NOT equal and E and F are NOT equal too.

Has it something to do with the clamping mechanism ?
Are the dimensions in the clamped state others than in the not mounted state ?

What's the difference between diameter C and D, the dashed and the solid line circle ?
In fact same question for H and G: not equal.

And hopefully simple:

.125R means I presume a radius of that edge of 1/8 inch, BUT what does "16pl" mean ?

Thanks in advance !

Hessel

Hi Hessel,

It means 16 places i.e.the 0.125 radius appears in 16 places.

Meridian

Hello again Hessel,

I've now had a closer look at the drawing and it certainly is confusing.

However it looks as though A, G and E are the dimensions for the outer profile and B, H and F are the dimensions for the inner profile.
This means that there is a 0.0425 step all round.

C is the diameter of the hole and D is the diameter of the counter-bore.

There is still some information missing as the profile below the counter-bore is not defined.

Meridian

Hi Meridian,

Probably a small progress in (in)sight.

Again at the MSP site (link above):
At the Product page:
http://www.msp-aviation.com/products.aspx
At the Avionic clamps:
http://www.msp-aviation.com/products...cs_clamps.aspx
At the ARINC spec. 408 square clamps 1 " deep pagë:
http://www.msp-aviation.com/products...08_1_inch.aspx

There are more or less **two dimensions for the same length ....**

I heard from another builder that the dimensions of the clamp (of course) change when the clamp is fastened around the instrument. So probably also the places of the screws !?

This explains probably the bigger"and "smaller" dimensions in the number-tables.

Of course builders have to use the "smaller" dimensions, to simulate the instrument, mounted in the panel. In that case the distances

**between the screws on the four corners** of an "clock-like-panel-instrument" are:

3,060 inches (77.724 mm's).

Thanks for your help, if newer insights come up, please let me know.

Hessel

Hi,
My family used to own the MSP product line. We sold the product line in 2002. Using the same 65 year old company , we started a new product line called "avionics mounts" in 2007. www.avionicsmounts.com

The question you appear to be asking about the bezel dimensions is due to the fact that the bezel does have a lip around it that is larger then the case size. The case dimensions would apply to the rear size of the bezel to mate with the case. Most of the other dimensions apply to the front of the bezel, as there are two contours around the front so that is why there are confusing dimensional call outs there.
If you are looking for the mounting hole information and cutout size for the 3ATI instrument, ARINC 408 (A) calls out 3.060 hole to hole, and 3.210 opening (side to side and top to bottom) and 3.920 across the corners.

Hope this helps. If you need further info, shoot me an email.

Regards,
Dean Johnson
Avionics Mounts Inc.

Hi Dean,

Thanks for your help.
Some aspects still not fully clear.
Will send you a private message here via the forum.

Hessel Oosten

Hi Hessel,

The cutout (3.210) is slightly larger then the instrument housing. (3.175) ARINC designed the cutouts that way to accommodate the tolerances built into the manufacturing of the housings. This is also so the instrument can be easily inserted through the panel without scraping up the sides of the housing. The outer edge of the bezel, (3.260) is slightly larger then the cutout. This makes the bezel act as a positive stop when it hits the panel. ARINC did this to avoid having problems with the instrument sliding all the way through the panel, falling out, and jamming the flight controls.

I am going to Email you some accurate drawings that come from the ARINC 408 (A) standard. The instrument you are referring to is considered a 3ATI.

Regards,
Dean Johnson
Avionics Mounts Inc.

Dean,

Studying !
Nearly there.

Will be back.

Hessel