302 Dial Gasket Construction

[TelePlay]

The 302 dial gasket can become hard and brittle. NOS or 302 dial gaskets in good condition are hard to find and costly if found. A common replacement is to use a repro gasket on the front side and some sort of washer set up to hold the insert and screw on the backside. Some may even use just a rubber grommet and no gasket. Having everything I needed, I tried to to combine a repro gasket with rubber grommets to construct a "similar to original" replacement gasket.

Using "water thin" superglue (CyanoAcrylate), 3 black rubber grommets and a flat 302 repro gasket (available from a few sources), I worked out the following procedure. It seems involved but it only take about 5 minutes total time per hole.

First prep step is to place the grommet on a #6 gauge solid copper wire. The grommet's tight fit on the wire made it easy to cut one end of the grommet off with an exacto knife (#2A).

Using a common hand held hole punch and a thin piece of card stock, I enlarged the hole in the repro gasket. The card stock placed between the cutting edge and the gasket made it easy to adjust the gasket in the punch, to center the existing hole. The card stock also helps the punch perfectly cut, to cleanly enlarge the original gasket hole (#2B).

With that, I had a cut grommet and an enlarged hole (#2C) to receive the grommet (#2D). The hole punch is just a bit smaller than the grommet OD so the grommet fits snugly into the hole without stretching the gasket.

I then placed the gasket face down on a hard surface and used two toothpicks, while pushing on the grommet with my finger, to make the cut end of the grommet flush with the surface of the gasket (#3B).

I then turned the gasket face up (#3C) and used a needle dipped in the CA to apply the "thin" CA superglue around the grommet/gasket interface (#3D) The thin CA seeps into the space between the grommet and the gasket. I had to buy my "thin" CA online since none of the local hardware or other stores had the water thin version.

After letting it sit for a few hours, I used 400 grit sandpaper on a vibratory tool to sand the CA smooth (#3E). The sandpaper cuts the CA high spots down to the rubber gasket but does not affect the rubber gasket itself thereby leaving a flat glue surface.

The result is a 302 gasket similar to the original gasket (#4).

Overkill? Maybe, but it's easy to do. This method provides a nice mount for the brass inserts and a complete, flat gasket for the dial/shell interface.

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EDIT: After construction installation and removal photos with comments below.

http://www.classicrotaryphones.com/forum/index.php?topic=15516.msg161266#msg161266

[Ktownphoneco]

John  ...  That's ingenious.    Excellent job.    I'll have to try that.    Thanks for sharing the idea.

Jeff Lamb

[cihensley@aol.com]

Excellent innovation.

Chuck

[Jim Stettler]

Harbor freight has a kit with metal grommets and grommet pliers.

http://www.harborfreight.com/grommet-pliers-with-100-grommets-66707.html

I have wondered about using these grommets as replacements on 302 gaskets. I have never tried it and probably never will, but this seemed like a good thread to mention the link.

Jim S.

[HarrySmith]

WOW! Very Cool idea!

[TelePlay]

To follow up on the original post of this topic, after completing the gasket construction I looked at the grommet side with a 30X loupe to see how well the non-glued side was attached. The CA did seep through the joint and each of the 3 grommets was completely sealed to the gasket on the non-glued (grommet) side.

Next test was to install the constructed gasket on a plastic shell (#5A) and to install the brass inserts (#5B & #5C). With the brass inserts in place, it "looked like" a 59A dial gasket was being used.

#5D shows the gasket from the dial side. The ripples in the dial side are due to a shrunk black, possibly soft plastic, shell. The shell was very difficult to remove from the base, had/has a bad odor and the dial was very tight when removing it from the shell.

The gasket was removed from the shell and both sides shown in #6, the dial side (#6B) and the back, grommet side (#6A and #6C). The purpose of this, taking these photos after installation and removal, was to show the grommets were still securely attached to the gasket, the glued grommets were not damaged during the installation and removal process. And, from the photos, I can see two grommets need a bit more sanding.

After the constructed gasket was removed, I placed an original repro gasket in the shell and noticed the holes in the repro gasket did not line up perfectly with the holes in the shell. As such, the grommets centered each hole of the repro gasket on the shrunk shell, now a smaller diameter, causing the gasket to ripple a bit when installed with the grommets. Could also be an issue of the holes in the repro gasket being off a bit, don't know, maybe some of both. Might be able to mark a gasket with the shell holes before construction so that when the holes are enlarged (punched out), the new holes would align better with the shell it would be used with.

[TelePlay]

Having worked on this project for some time now, it becomes apparent as to why WE went with a brass insert and rubber grommeted gasket to isolate the dial from the housing and how those parts work together to do that. I fully agree with the excellent explanation posted by unbeldi in another topic so I am going to post a copy of what he said here, in its entirety, rather than trying to restate the explanation myself:

"I am sure that the purpose of the adapters was to control dial noise. This was a constant struggle until the end of the Bell System by which time even gears in dials were replaced by plastic parts that were more durable and performed more silently than the old all metal dials.

The effect of dial noise can be observed perhaps most impressively in the candlesticks where the mechanical contact of the dial with the base and the shaft to the transmitter is a perfect conductor for sound, one can hear every little gear rattling and any finger nail tapping or scratching on the metal parts which is amplified in the transmitter and transmitted to the receiver.

In the D mount (most 202 telephones) the dial only rests on three elevations around the dial mounting holes, but the dial still makes metal-to-metal contact with the housing which amplifies the clicking. The number 5 dial was somewhat quieter already than the No. 4 dial, but the designers added to the 302 housing these rubber adapters with grommets filling the mounting holes.  To provide better, more rigid support for the dial mounting screws they inserted those brass rivets with which the screws could be fastened tightly, in a way that the dial or the mounting screws made no direct contact with the metal housing at all.  Mounting a dial directly in a 302 housing, metal or plastic, is noticeably louder.

The No. 6 dial was again quieter than its predecessor, but initially all gears were still metal and therefore subject to wear which slowly raised the noise level over time.  Some No. 6 dials later had plastic gears, IIRC, and the other later dials (for 500-series sets and others) were again much quieter."

[TelePlay]

A slight modification to the preparation of the grommet adds about 0.04 inches to the length of the grommet, the part of the grommet which goes through the housing. This is accomplished by grinding off the grommet ring instead of cutting it off. I first tried to free hand the process but that was a bit dicey, unpredictable results. To better control the grinding process, I created the following jig.

First step was to glue four 8-32 nuts to the edge of a piece of 2" x 1 1/2" ABS plastic (#7A) using a short machine screw to hold the nuts in alignment.

I then made a grommet holder using a 4" 8-32 machine screw cutting off the head and attaching that end to a small, round drawer knob (#7B). The grommet fits snugly on the other end of the machine screw.

This jig was clamped to the grinding guide on a very small grinder so that the grommet could be fed from the front of the grinding wheel along the side of the wheel (#7C). This set up allows movement of the grommet past the wheel and in that movement, the grommet ring is ground off the grommet barrel leaving the full length of the grommet intact. Turning the knob advances and retracts the grommet. It is also easy to watch the grinding process making that step easy, quick and results in a flawless ground grommet.

Doing it this way provides two advantages. 1) the part of the grommet that passes through the housing is increased in length by about 0.04 inches, and 2) the side of the barrel where the ring is ground off is rough textured allowing the water thin superglue to more easily get between the gasket edge and the grommet barrel.

Image #8A shows the grommet as receiver and #8B shows the grommet after grinding, the gain in length is about 0.04 inches.

Image #8C shows a ground grommet on the left and a cut off grommet on the right showing the extra length. It also shows the rough barrel on the left end, the ground end which works better for gluing that the polished barrel of the cut off grommet.

Gluing a ground grommet into a gasket hold and gluing as in the process stated above resulted in a very good glue joint with on both sides of the gasket.

[cloyd]

John,
I was thinking along the same lines as your process!  Nice to see that someone has already worked this out.  Instead of buying the reproduction gaskets, I bought left over gasket cut-outs for cheap! online.  I got 32 pieces for $8 including shipping.  I will probably be able to get two out of each remnant.

Could you give me a straight-on image of the repro-gasket with dimensions so I can use it as a pattern?

You gave a source for the grommets, is there a source for "similar to original" brass inserts/rivets/eyelets?  I am thinking fabric and hardware stores, not OPW.

Thank you,
Tina Loyd

[TelePlay]

Installed the dial. Looks like the real thing from the back.

[cloyd]

John,
Very nice work!  I'm going to try that too!
Tina Loyd

[Dan/Panther]

Most craft stores sell thin rubber pads about 6X8" for under a dollar. I think I was able to get 3 from a sheet. I love the rivet touch.
I posted it in the thread about my first restoration. I recall someone saying, in the future some would argue, "I knew they made some without rivets.


D/P

[TelePlay]

Most craft stores sell thin rubber pads about 6X8" for under a dollar. I think I was able to get 3 from a sheet.

How thick are those pads? And what did you use to cut out the gasket? Was that rubber pad easy to cut?

The die cut ones are "perfect" cuts but once installed, can't see them anyway.