[R-390] RF subchassis separation

[Chris Farley]

I was looking through the drawings to see how that shaft is supposed to be pressed/crimped into place.  It appears there may be a drawing missing from the set (SM-D-178900 missing, as referenced to on SM-B-178901), but here is info gleamed from drawings of the shaft, the RF gear train assembly front plate, and the gear train assembly:

The pressed-in portion of the shaft is .219" +.001" -.000" by .040" deep.  That end also has a hole drilled into it, which strangely is shown without specs, aside from being 1/4" deep and tapped at 8-32.  

The hole in that front plate is complicated.  .2187" +.0005" -.0000" hole.  Countersunk at 82° ±3° to .343" on the front, and countersunk at 82° ±3° to .248" on the rear. 

Now I'm no machinist, but that sure seems like it must be a temporary "hold it in place" plan given the approx .0001" press-fitand overlapping tolerances, and then probably flared out from the rear for a more solid fit.  
Question is, why does the shaft drawing show the rear hole to be threaded??  Is there actually the possibility of using a screw to hold that shaft in place?  One is not shown on any of the drawings I have seen thus far.  
BUT if it IS indeed threaded and they aren't messed up from whatever pressing or staking took place, or the ID is such that you COULD drill/tap it, sticking a truss head screw (or a screw with a <shudder> FLAT WASHER) in there would seemingly be a pretty easy fix, assuming there is clearance behind the plate. 

????

Regards,
Chris




________________________________
 From: rbethman <rbethman at comcast.net>
To: r-390 at mailman.qth.net 
Sent: Monday, March 3, 2014 8:40 PM
Subject: Re: [R-390] RF subchassis separation
 

Mark,

I've looked at the post you showed in the pic.

Since it was highly likely a press fit, it can be "staked" to fix it 
back in place.

It won't be a simple task.  I'd seek out someone with machinist skills.  
That would be someone that can help with this.

Application of something very like the metal bonding tube that for the 
life of me that I can't remember right now.

The combination of "staking" and that compound should make it tight once 
more.

By golly!  I think it is JB Weld.  It finally popped into the old noggin 
as I began to sign the end!

Regards,
Bob - N0DGN




On 3/3/2014 8:35 PM, Mark Richards wrote:
> Now finally doing a rebuild of my R-390A.  Gear train has been 
> disassembled, cleaned, and now in the re-assembly process I hit a 
> snag:  there's a post which hosts the Differential Gear Assembly, and 
> it is very loose.  It cannot be screwed down tightly.  I suspect that 
> this post is press-fit into the gear backing plate. As the post is 
> loose, I think this is accounting for the fact that the Differential 
> Gears are not aligning properly with adjacent gears, nor with the 
> front gear cover.  There is considerable mechanical friction when the 
> front plate is attached.
>
> So, my questions:
>
> 1. Can the RF Subchassis be separated from the gear assembly plate and...
> 2. Can the Differential Gear Assembly post be repaired?
>
> A photo of the offending post:
>
>    http://kumichan.net/private/03-03-2014 20-28-04.png
>
>
> I have another complete gear/RF Subchassis that is of dubious 
> electrical condition, but is mechanically sound.  If I can separate 
> gears from chassis, then maybe an option is to swap out the RF 
> Subchassis with the good gear set?
>
>
> /K1MGY

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