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Loose 302 Ringer Mount - Rubber Grommets Missing

Started by TelePlay, April 21, 2012, 12:32:52 AM

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cihensley@aol.com

O rings just tighten the ringer assembly. The problem of the deteriorated shoulder grommets underneath the ringer is not solved. The bell will not ring properly. The real solution is to drill out the old rivets and replace the grommets. Grommets of the right sized and tubular rivets that closely approximate the originals are available from McMaster-Carr.

Chuck

TelePlay

#16
Quote from: cihensley@aol.com on January 05, 2013, 07:57:10 PM
O rings just tighten the ringer assembly. The problem of the deteriorated shoulder grommets underneath the ringer is not solved. The bell will not ring properly. The real solution is to drill out the old rivets and replace the grommets.

Chuck, in my fix, without drilling out the rivets, I pushed 2 flat rubber washers through the plate holes down each rivet so that they were below the the ringer assembly plate between the ringer plate and the base plate. I then used half of a grommet around the rivet above the ringer assembly plate to sandwich the ringer assembly plate between the half grommet on top and the 2 rubber washers below the ringer assembly plate. By studying the way WE punched the holes in the ringer plate, it seemed reasonably correct, but not perfect, to use flat washers with holes large enough to fit under the plate punched downward toward the base plate and the half grommet to fill the depression left in the top of the ringer assembly plate under the rivet head. It's a two piece fix rather than one grommet as WE first built the phone but the washers and half grommet are very, very tight (I had to use a "C" clamp to compress the two flat washers under the ringer assembly toward the base plate to give me just enough room to get the half grommets around and under the rivet head). Trying to put a grommet in the plate with the rivets in place is an impossible task so I went with the two below one above fix to get it very close to original without drilling out the rivets.

cihensley@aol.com

TelePlay:

Sound like that works. It is better than just using an O ring alone to tighten the ringer base.

Chuck

Dennis Markham

The time I used just the O-ring it worked great for me.  Maybe not the best fix, but it did the job on that particular problem.

TelePlay

It's been a few years since I posted this fix

http://www.classicrotaryphones.com/forum/index.php?topic=6853.msg78533#msg78533

and haven't had the need to install new grommets since then. But, when my painted 302 arrived, the box rattled. Not the phone, the ringer mount. Original grommets totally gone. Good thing I remembered where I posted this technique.

Went to my local Ace Hardware store to find 0.25" throat/bore/hole rubber grommets that were 9/16" outside diameter. The only two numbers that count. A bit pricey at $0.33 each or $1.00 to redo the three rivet mount.

Put a grommet on a Phillips drill bit in my electric drill and used an exacto knife to cut the barrel out leaving the ends which look like half an "O" ring. Put one half with the round side up over the rivet head and pushed it through the metal mount bracket so it would be under the mount bracket. Did that for all three rivets. Then used a "C" clamp to compress the bracket toward the base and slipped the other half over the river head with the flat side up. The part where the grommet barrel was cut off is hidden under the rivet head. Released the clamp and had a tight, solid insulated mount, again.

Hadn't done this 3 years but from cutting the grommet to releasing the clamps, it took about 15 minutes. This really is a nice fix. Looks like the original build.

TelePlay

I added a second annotated image to my post above with an explanation paragraph titled "EDIT" just above the images.

     http://www.classicrotaryphones.com/forum/index.php?topic=6853.msg78533#msg78533

showing what the ringer mounts looks like when removed and why I ended up using two 1/16" thick 1/2" diameter with a 1/4" hole in them between the mounting plate and the 302 base.

It also shows the indentation on the top of the ringer plate which centers the plate on each river when a grommet ring is place round side down (toward the plate) leaving the cut flat side of the grommet to sit nicely on the under side of the rivet head.

That protrusion on the bottom of the plate is why I found using a washer cut in half and slid in from each side would not work over the long run. The protrusion would force the cut washer apart and the pieces could possible fall out leaving the mount once again loose.

TelePlay

#21
Quote from: TelePlay on May 27, 2017, 05:18:05 PM
. . . I ended up using two 1/16" thick 1/2" diameter with a 1/4" hole in them between the mounting plate and the 302 base.

The grommets I used are still available from McMaster Carr, their part number 9600K24, at $7.19 for a pack of 100 - a lifetime supply.

https://www.mcmaster.com/catalog/127/4142

The flange is 1/2" in diameter, the center hole is 1/4" and with an overall thickness of 3/16" for 1/16" thick metal, that means each flange when cut off if 1/16" in thickness.

This 1/16" flange thickness is the important dimension in that if thicker, one won't be able to get the two flanges in place and if thinner, the mount won't be tight.

These might be found in a hardware store in much smaller quantities. The important dimensions are a flange diameter of 1/2" or 9/16", the inside diameter of 1/4" or 3/16" and the flange thickness of 1/16"

NOTE:  The grommet cross section in the first image is general in nature, not to scale of the 9600K24 grommet.

Babybearjs

I've got the grommets covered, what about the new bolt to hold it in... where can you find a short, flat top screw or bolt to replace the rivet? or do you use a new rivet and flat washer?
John

tubaman

Quote from: Babybearjs on September 13, 2021, 09:38:52 PM
I've got the grommets covered, what about the new bolt to hold it in... where can you find a short, flat top screw or bolt to replace the rivet? or do you use a new rivet and flat washer?

If my understanding is correct then @TelePlay cut the grommets as described and inserted half underneath and half on top. The original rivets thus stayed in place.
:)

TelePlay

Quote from: Babybearjs on September 13, 2021, 09:38:52 PM
I've got the grommets covered, what about the new bolt to hold it in... where can you find a short, flat top screw or bolt to replace the rivet? or do you use a new rivet and flat washer?

tubaman is correct. The following is to show why.

The 302 ringer mount used a specific counter sunk head semi tubular shoulder rivet. When set, the base plate was bonded to the rivet between the rivet shoulder step and the tenon crimped from the bottom of the 302 base plate. As such, the flat headed counter sunk headed rivet stood in place whether the rubber grommet is intact or missing as shown in this image



Since these rivets were made for WE using WE specifications, I doubt anyone could find a replacement and NOS rivets would be an unusual find. The rivet company I use is Hanson Rivets and this link will take you to their selection of shoulder semi-tubular rivets.

https://www.hansonrivet.com/rivets/shoulder-rivets-3/

To order the best replacement, one would have to take a ringer mounting plate out, drill out the existing rivets, and measure that rivet to try and find a match.

Using a nut and bolt would not be anything close to a restoration/replacement and would if done would require a flat headed bolt, a washer to keep the bold head from pulling through the grommet, a brass or aluminum tube spacer placed over the bolt to get the spacing right and then a nut at the end of the bolt which would be seen from the bottom of the 302 base. Since it is not that hard to get one of the flanges of a grommet through the ringer mount hole to hold the mounting plate up off of the phone's base plate, I see no reason to remove the exiting mounting rivets. Getting the second half around and under the existing rivet head is a simple task.

Attached is a reasonable facsimile cross section drawing of how this mount is constructed (it is not to perfect scale but it is close). The ringer mounting plate is in gold, the 302 base plate in black, the countersunk flat headed semi-tubular rivet in grey and the two (upper and lower) grommet flanges in red. You can see how the step shoulder of the river is sandwiched to the base plate when the semi-tubular tenon is set with the proper rounding tool for hollow rivets (image below - each diameter requires it's own tool) to make the set look original.

Also attached is a rivet sizing sheet from Hanson Rivets showing the different measurements to be taken or made to match a rivet. The numbers in red are estimates or unknown except for the rivet head diameter. The measurements are close enough if one wants to look for a replacement rivet. Hanson does not have them.

This is a unique fix in that I've only run into 3 302s with bad ringer mount grommets in well over 10 years. The problem is, if the original grommets are hard, partially deteriorated or totally missing, the ringer will not sound right.

A simple fix with the flanges from the right sized grommets.


TelePlay

If one really needed to replace the 3 or 4 rivets holding the ringer mount in a 302, such a rivet could be improvised. Looking at the Hanson Rivet section for tubular rivets,

https://www.hansonrivet.com/rivets/tubular-rivets/

no rivet can be found with a 0.50" head and a 0.10" thin tenon. 0.50" rivet heads have about 0.25" tenons. The rivet hole in the 302 base plate is approximately 0.10" of and inch so commercially available tubular rivets with a 0.10" tenon would have a 0.20" head.

The governing rivet dimension is the length of the tubular tenon which is work thickness plus clinch allowance.

In the image below, the green item is the thin fender washer and the blue is a tubular spacer that provides the shoulder for the washer to replicate what a WE rivet would do to hold the 302 ringer mount in place. From the charts, it seems like the head diameter of a tubular rivet is about twice that of the tenon so a 0.10" tenon would have a 0.20" head and that would slip right through a 0.25" ID grommet.

The grommets would be placed into the plate holes (red item), the blue spacer placed in the grommet inside hole, the washer placed on top of the grommet and the rivet placed through the washer and spacer and through the base plate hole.

The blue spacer would have to be cut shorter than the height of the grommet so that when the rivet/washer assembly is set, the spacer would be short enough to allow some compression of the grommet while the washer against the spacer which is against the base will provide a tight mount, will not wiggle on the washer.

The work thickness is actually the length of the blue spacer. The length of the blue spacer will provide tension on the grommet and the head of the rivet, above the washer, should be level with the ringer mounting plate to not interfere with the ringer.

If a new rivet is really needed, a reasonable facsimile can be created like this. Finding the right parts, cutting the spacer length and setting rivet are a lot more work and material intensive than simply cutting the flanges off of a 9/16" or 1/2" grommet and forcing one through the hole and the other under the rivet head, as shown in prior replies.

I can't imagine how a ringer mount rivet would or could be removed during service or even thought of being drilled out to replace the grommets. The WE rivets appear to be a corrosion free metal, possibly aluminum based on the color of the rolled crimp seen on the bottom of the base of a 302, and just don't come out by themselves.

But, if a replacement rivet were needed (and I'm sure these large headed small shoulder/tendon rivets are no longer commercially available), this is how I would go about doing it, and the cost of parts plus time spent finding and configuring the components in my opinion would be excessive.

Maybe one of our life time phone fixers can come up with a better fix to replace rivets, this is just how I would go about doing it. I've only been doing this type of restoration work for a handful of years.