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Author Topic: R390A front panel screws  (Read 9432 times)
N3DT
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Posts: 531




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« Reply #15 on: November 23, 2013, 01:55:20 PM »

The OP wanted the screws that go in the front panel into the chassis.  Not the screws that are used to mount the R-390A into a rack.  All the racks I have use # 10-32 machine screws.  There are 8 - 8-32x5/8 and 8 - 6-32x1/2 plus the #6 external tooth washers (actually they're 6-32x7/16, eh and 3 of them mount items on the front panel) that mount the front panel to the chassis.  I'm sure the original #6 washers were formed, but good luck finding them for a decent price.  Doesn't take much to form them, but finding 6 tooth external washers is another adventure.

Actually, there has been a desire for more sets of these screws, so I may get another 100, if anyone is interested let me know.
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KG8LB
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Posts: 237




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« Reply #16 on: December 16, 2013, 11:18:35 AM »

Seems to add some confusion here ?

Have you referred to the depot manual for the mechanical illustration and parts list of the front panel?

 I am referring to the OP's original question "

 

   R390A front panel screws
« on: October 26, 2013, 01:11:33 PM » Quote 

--------------------------------------------------------------------------------

Hi there..

I need information regarding flat head screws on front panel of R390A receiver, what is dimension of these screws?"

"Flat Head Screws " are not "Binding head screws"


It is not profoundly clear whether he is looking for the face plate to chassis fasteners or the face plate to rack fasteners .

I am also referring to your photo showing flat head screws and cupped trim washers using appropriate terminology in an attempt to clarify for others . Formed washers are readily available and  the price difference between them and other quality parts is minimal . T



73!

   
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KG8LB
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Posts: 237




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« Reply #17 on: December 16, 2013, 11:42:24 AM »

The depot manual describes them as " 8-32 x 3/8" binder head screws "

A more complete description would be an SAE (English measure) #8 cup head machine screw with a pitch of 32 threads per inch and the threaded portion being 3/8ths of an inch long. I recall them as Philips head stainless, the depot manual shows a beveled washer under each screw.

Here's a picture of the more common cadmium plated parts:



Stainless would be less bright in color. The depot maintenance manual can be downloaded from a variety of sites free of charge and is very, very complete.

  Just trying to get the nomenclature correct here , no offense intended .

"Cup head machine screw" ?  Your photo shows "flat head machine screws" with cupped trim washers . The cupped lock washers as used on the R-390 series are a different animal but very readily sourced at reasonable (to some) prices .

BTW:
 SAE thread measures are usually expressed in Threads Per Inch numbers while the term  "pitch" is used to express FRACTIONAL or Decimal thread space dimensions . While the terms are both used to sescribe a thread dimension they are not interchangeable without convervion by calculation . The thread "pitch is actually the RECIPROCAL of the Threads Per Inch (or other unit of measure )count . For example :  A 1/4 -20 thread has a .050" pitch .
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N3DT
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Posts: 531




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« Reply #18 on: December 17, 2013, 07:47:41 AM »

All I know is I sent 9A5BDP some 6-32x1/2" (they should really be 9/16") and 8-32x5/8" flat head Phillip stainless machine screws and locks for the front panel to the chassis (not to mount the radio in a rack) and it was what he wanted.  I actually bought another 250 including #6 small pattern nuts, spring locks, flats and sent out the ones I didn't need (for a price) to others on the R-390 mail list that wanted a set of 8.  Everyone seemed happy with them and was able to get a set without spending $20 or more for a small amount.
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KG8LB
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Posts: 237




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« Reply #19 on: December 17, 2013, 09:37:43 AM »

Sure enuff ,

  It was unclear exactly which of the several different type screws on the R-390 faceplate the OP had in mind .

 I was just generally setting some of the improperly used terms straight .
  Flat head and oval head screws fit into a countersunk seating and the appropriate washers are pre- formed to fit that seat . In the US that is usually an 82 degree included angle , some aircraft apps use 100 degree due to material thicknesses.

Again , the pitch is the reciprocal of the Threads Per Inch spec .  A 20 thread per inch thread has a .050" pitch , a 4-40 screw would have a .025" pitch etc. An 8-32 screw is not a 32 pitch .



   The proper star type lockwashers for flat head screws are usually  thinner than standard star lockwashers .http://www.marshallshardware.com/products/productList.aspx?uid=2-301-452-312

Binding head screws are a different item altogether but most military rack applications use binding head screws rather than countersunk , flathead screws and countersunk trim washers . When countersunk screws are used for faceplates , an OVAL head screw is often preferred . The oval head screw is similar to the countersunk flathead screw but it has a rounded off top surface rather than the flat .

  Many, very many rack applications do indeed use 8-32  screws .

 Length call out for both types of screws is the grip length . Countersunk screws are actually very close to overall length called out as the threaded portion is actually shortened by the head thickness . Binding head screws length is the actual the length below the head .

  

Also worthy to note that Stainless screws are generally not as strong in tensile as their carbon steel counterparts . Probably of little concern for radio faceplates but in other applications the stainless may not hold up as well as the carbon steel fasteners .
Vy best 73 to you , Gary
« Last Edit: December 17, 2013, 10:05:34 AM by KG8LB » Logged
N3DT
Member

Posts: 531




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« Reply #20 on: December 18, 2013, 03:21:02 PM »

Those counter sunk washers are over $16/100, otherwise the prices are competitive, almost.  Plus they didn't have any small pattern nuts that I could find and the shipping was rather expensive.  I think I did OK for the 250 of both screws, flats, washers and nuts for about $32.  I doubt that anyone is going to worry about the washers not being counter sunk.  At least no one has complained yet.  Just saying.
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AA4HA
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Posts: 1434




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« Reply #21 on: December 18, 2013, 03:33:12 PM »

The R-39x series radios use the front panel hardware to hold lots of mechanically important things in place. Unlike some other radios where the front panel is just a piece of dressing for the radio on the R39x it is an critical mechanical component. There are screws in strange places and the difficult ones to find are counter-sunk into the front panel.

Going into R-39x repairs you need to deal with things like Bristol-Spline screws, gear clamps, and a very complicated mechanical gear-train since the radio is reluctance tuned and there are cams, sliders, rails and slugs going every-which way.

One nice thing is there aren't any lightweight components like dial strings. The frequency readout is actually an odometer display and when the radio is properly aligned and linear it is darned accurate.

The design is all Collins but it has been made by about a dozen different suppliers, including a short run by a cosmetics company (crazy). It is all modular with decks and those green captive screws everywhere. Quite the mechanical marvel.
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Ms. Tisha Hayes, AA4HA
Lookout Mountain, Alabama
KG8LB
Member

Posts: 237




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« Reply #22 on: December 19, 2013, 05:10:58 AM »

Those counter sunk washers are over $16/100, otherwise the prices are competitive, almost.  Plus they didn't have any small pattern nuts that I could find and the shipping was rather expensive.  I think I did OK for the 250 of both screws, flats, washers and nuts for about $32.  I doubt that anyone is going to worry about the washers not being counter sunk.  At least no one has complained yet.  Just saying.

   That site was offered as a source for the graphics to illustrate the different types of lockwashers and their proper nomencalture .
 It was not offered as a low cost supplier . However , for convenience sake it may be an excellent source . One thing for certain , using the proper names and dimensional references is the first step to getting the right parts .  You can often find very high quality domestic made hardware on eBay for very low prices , small pattern nuts as well . I recently bought 1000 US made 4-40 plated steel , small pattern hex nuts for $5 .  The pre-formed countersunk washers are always a perfect fit and concentric . They fit and look excellent .  When forced to form flat star washers , I use a seperate fixture to pre-form them . This helps eliminate any chance of marring that freshly finished panel by using the "form in place" methods .

   Some restorers are also particular about getting not only the correct part but quality parts as well . Once again the reminder that Stainless fasteners generally are not as strong as the plated , carbon steel as originally used in many military applications . When strength matters , carbon steel has the edge .
« Last Edit: December 19, 2013, 05:15:26 AM by KG8LB » Logged
KG8LB
Member

Posts: 237




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« Reply #23 on: December 19, 2013, 05:22:28 AM »

The R-39x series radios use the front panel hardware to hold lots of mechanically important things in place. Unlike some other radios where the front panel is just a piece of dressing for the radio on the R39x it is an critical mechanical component. There are screws in strange places and the difficult ones to find are counter-sunk into the front panel.


    I agree 100% . This is why I like to use the exact type hardware and materials as original spec . Some may argue well that something else is "good enough " That is up to them of course . In the meantime many radio techs have restored gear to operation by simply replacing "good enough " with "better" (OEM spec) . Wink
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