Typewriter Talk / On the subject of platen rubber

**Posted by tricnomistal** 30-6-2017 20:49:28

Hi everyone,

I didn't know whether to post this here or in the repair area, since I see it as related to, but not necessarily all about, repair.

Anyways, I have a question that I realized today is, at least for me, problematic. I've never had the pleasure of handling a well-cared for typewriter, having never lived close to a sizable number of collectors or ready access to them. The ones I've purchased were dug up from people's basement or pulled from people's barns. And so, all of the ones I've owned and handled had--what felt like to me --rock hard platens. But I imagine that there is a balance: too soft of a platen would also be undesirable.

So, I have a conundrum. Having never felt a platen with the proper rubber elasticity, when I'm trying to refresh or refurbish my hardened platens, I don't have a point of reference to compare them to. So now, in my roundabout way, I've come to my question: Does anyone know of a good item for comparison to give me an idea for how hard/soft a good platen should be?

I'm sure there's more of these questions that I'll stumble across in time.

Thanks!

**Posted by DRH** 01-7-2017 08:13:07

From what I understand, you want to look for three things when it comes to the condition of the platen: 1) it should have a smooth, dark appearance, and not have a dusty white look to it. 2) If you run your finger across, it should have a 'grippy' feel. 3) you should be able to sink your thumbnail into the rubber and it should slowly spring back.

I've had various degrees of success with rubber rejuvenator. But they will, on the surface, restore the original appearance and the 'grippy' feel. It just depends what condition the rubber is in when you get the machine.

But in general, rubber is manufactured in a wide scale of hardnesses by what is called the Durometer scale, or Shore scale (jeopardy question, anyone?)
Shore 20A = Rubber Band
Shore 40A = Pencil Eraser
Shore 60A = Car Tire Tread
Shore 70A = Running Shoe Sole
Shore 80A = Leather Belt
Shore 100A = Shopping Cart Wheel

If you are looking for something to compare a platen to, I would look for something in the 60A to 70A range. Hope that helps

**Posted by tricnomistal** 01-7-2017 11:46:42

Perfect! Thanks for that info. I didn't know about that hardness scale. Interesting.

**Posted by SoucekFan** 01-7-2017 11:47:15

DRH wrote:
If you are looking for something to compare a platen to, I would look for something in the 60A to 70A range. Hope that helps

From an earlier post on the subject: "A general purpose platen would originally be rated in the 90-92 range."

**Posted by tricnomistal** 01-7-2017 15:11:19

SoucekFan wrote:
DRH wrote:
If you are looking for something to compare a platen to, I would look for something in the 60A to 70A range. Hope that helps
From an earlier post on the subject: "A general purpose platen would originally be rated in the 90-92 range."

Hmm if that's the case, then I original assumption about platen softness was on the soft side.

**Posted by Tea Typer** 01-7-2017 15:43:58

What is the consequence of having a too soft platen?

**Posted by SoucekFan** 01-7-2017 16:05:35

I think it would be strange to encounter a platen on a vintage machine that was too soft. I occasionally run across a machine with a platen that is comparable (by touch) in softness to newer rubber, but the vast majority are harder than ideal.

**Posted by tricnomistal** 01-7-2017 16:13:54

SoucekFan wrote:
I think it would be strange to encounter a platen on a vintage machine that was too soft. I occasionally run across a machine with a platen that is comparable (by touch) in softness to newer rubber, but the vast majority are harder than ideal.

I suspect that that would indeed be very unusual to find. But the question of what the issue with a too-soft platen is is still interesting to me. For example, what if I was refurbishing a platen, as I've seen lots of others do, and I choose rubber that's too soft? If I had to guess I'd imagine the type might not be as distinct.

**Posted by SoucekFan** 01-7-2017 16:22:04

Tea Typer wrote:
What is the consequence of having a too soft platen?

If it was too soft, the impressions would be blurred. I have not encountered this, myself.

**Posted by SoucekFan** 01-7-2017 16:41:35

tricnomistal wrote:
For example, what if I was refurbishing a platen, as I've seen lots of others do, and I choose rubber that's too soft? If I had to guess I'd imagine the type might not be as distinct.

I strongly recommend not trying to do it yourself. It requires a great deal of experience, knowledge, and expensive equipment to do it properly.