You guys are great!  Thank you for all the great information.  I was having no luck finding anything out with my searches.
If I ever start my own platen replacing business, you all get free ones!
(Probably wouldn't hold my breath on that though, if I were you...)

SoucekFan wrote:

Uwe wrote:

Regardless, not only would using an inexpensive digital caliper on your existing platen give you that information, it would also be a far more reliable measurement.

I do use a digital caliper, but when possible I like to double check against the original factory specs to compare, as some platens may have changed a touch over time due to age, refurbishing, and other factors.

Just out of curiosity, does anyone have any guestimates as to how much a platen might shrink?
Also, as a word of caution to using the Typewriter database's platen specs, I have found a couple to be grossly wrong so definitely go with the other poster's advice that your own caliper measurement is probably the best measurement to go with.  

For example, I am sending off my Remington Noiseless 7 platen to jj short so I have measured it at 37.76mm diameter with my calipers.  The serial number is "H90871" which makes it a 1947 model year.  According to the TWDB, "All portables up to 1949: 1.38" (35.1mm)."  So my platen would have had to grow about 2.6mm -- there seems to be some bad data in there somewhere.   It's a great resource, but definitely keep your brain engaged as it is obviously not always correct.

About the only published platen measurement I have found so far and trust is/are the ones in the TM37-305 War Dept. Technical Manual for Typewriter Maintenance from November 1944.  I use that for my Royal KMM when it says the the "size of a Royal platen is 1.486" diameter" (37.744mm).  My old/current one measures 37.68mm, so I figure it makes sense to me that the old one could have shrunk 0.06mm.  This manual can be found at Maritime.org and is in three pdf files.  It has specs and EXTREMELY detailed maintenance instructions for the most common old ww2 standard size typewriters (Royal, Remington, Woodstock, Underwood, Smith Corona(?) (or whatever it was called then...brain fart).  

Speaking of maintenance manuals, why the heck is this the only one I seem to be able to find?  No problem finding owners' manuals, of course, but I wish there were more scanned in pdfs out there of the actual maintenance manuals that, say, and Olivetti repairman at the factory would have had.

 

Just for information - A 'regular' platen is one with the same density of rubber all the way through.  A 'cushion' platen often has a smaller diameter core than standard, with two concentric rubber sleeves.  The inner one is a much softer rubber than the outer one.  The idea is that the inner one 'cushions' the blow from the typeface.

Uwe wrote:

The database is a fantastic aid, and it's constantly being updated as new data is unearthed, but as you pointed out there are no guarantees that the information is 100 percent correct. I view the database as a combination of best guess speculation and a compilation of all the reference sources currently available to the typewriter collector community. The database tables are fairly reliable, but I would really caution against using information found within the individual galleries created by the so-called "typewriter hunters". Some of them contain fantastically incorrect information, especially when it comes to model names. Even some of the official database conventions for listing model names are incorrect, so it's worth doing a little extra research and verifying information as much as possible if you want your own records to be correct.

I don't know enough about the composition of vintage (or modern) rubber to comment on its ability to shrink. I would think that if any material were to shrink a significant amount that it would crack or show other signs of decomposition, but that's just speculation on my part.

With regard to your Remington platen, I see an error in your logic that actually comes up fairly often here. Most collectors seem to assume that their machines are completely original, absolutely unaltered and representative of the day it was made. You're comparing database platen data to your own measured specs, and because they differ, you're assuming that the database is incorrect. It's very possible that you're right, but how do you know that your platen is original to begin with, that its specs are those of one originally fitted to the machine? It's very possible that your platen was replaced several times over the typewriter's lifespan, and maybe a previous owner had - for some reason - something different installed.

The other factor to consider is that you're comparing measurements for stock/standard platens without taking into account that there were a number of specialty platens available that might have had other dimensions. I think some of these optional platens might be mentioned in the database, but I know of a couple that had a different diameter because they were made to be used with multiple carbons. I'm looking at an ad right now from a platen company that sold resurfaced platens and offered "regular" and "cushioned" replacements; most likely they only differed in the type of rubber used, but it does highlight that there was more than one platen available for a particular model, and that with variations of platens there might also have been variations in their sizing, which of course is important to the proper function of the typewriter. 

I only mentioned using calipers on your existing platen instead of relying on database measurements in my previous post because at least you know that measurement is going to work with your machine.

Fascinating!  Had no idea...