Is it worth replacing the rubber on my typewriter platen?

One of the most asked questions from our clients will always be, is it worth replacing the rubber layer on the platen of my typewriter? 
The Short Answer will be: Yes, its is worth replacing the old rubber on your typewriter platen if you heavily type & regularly use your machine.
My Yes is always based on new rubber layer and not pointless shrink tube. 
Old VS new typewriter platen
First, What is a typewriter platen?
The Typewriter platen is the cylindrical black roller on a the typewriter carriage against which the paper is held and where the key arms strike to print impressions on. 
One of the most important parts of a typewriter is its platen & it needs to be taken care as times passes by to get the best of your typewriter and keep your prints at their best. 
Historically, as far as I know and experienced, platens have been made from different kinds of materials such as Metal (The Noiseless company used it), Cork (Was common in the 40 & 50s during the war) , or Rubber (Most common). Internally, it is made of Metal or wooden cylinders on the inside with two metal cogs on each side. 
Second question to ask , how could hard rubber on my platen damage the typewriter? 
Other than the louder than usual clacking sound on the hard platen, your typewriter key arms, or key slugs, are in risk of damage, dent or getting worn heads and this will cause prints to be less sharp, misaligned or even totally out of line. 
On the same hand, another issue that you might have already had is the holes on your paper when you type and that is purely because of a hard platen that doesn't give any chance of distribution of key strike power of contact when it hits the paper surface. 
One less common issue caused by hard platens & mainly extremely hard ones is slipping of the paper while performing the line spacing mechanism. Yes, if your line spacing leaves the 1st letter of the line misaligned, it’s because the platen is causing the paper to slip rather than being properly held in place after the line spacing.
Worn platen surfaces.
worn typewriter platen
damaged typewriter platen
dented rubber on typewriter platen
cracked rubber on typewriter platen
How to revive a hard platen?
That is a wide project to tackle and if you look up on the internet on how to do restore your platen, lots of suggested ways, tricks and sometimes uninformed tips can be found but I will try to summarize what we do at Mr and Mrs Vintage Typewriters. 
Basically, & not all typewriters, we put a small amount of mineral spirits and rub it to clean with a rough cloth. Then, we might reapply any kind of rubber treatment spray that will add some freshness to the rubber surface. 
Everything else is done with old platens is a waste of time & will cause more damage & be eventually fruitless. 
Two techniques we tried but will not accept to use are smoothing  the surface with sanding paper or adding a layer of shrink tube to the platen by using a heat gun. To simplify our refusal to use these procedures, sanding the surface will cause an uneven surface which is the least you need on a typewriter platen and slipping papers and the adding shrink tube will add to the diameter of the platen and rollers causing more pressure on the key arms and not to forget, on certain models, the carriage might be less smooth to advance due to a potential friction between the shrink tubed platen and other typewriter parts. 
The best was will always be replacing the rubber on the platen and that should be done by professionals only that know what kind of rubber to add, what sort of thickness and make sure that it is all even from all sides to avoid any misalignments on the surface. Everything else is not right and will be more of a harm. 
On the other hand, we should talk about the typewriter rollers. but before that, what are rollers needed for? 
Rollers are responsible to apply pressure on the inserted paper and then the platen and contribute to the paper evenly rolling up and down while using the carriage knobs. Rollers are essential and cannot be left unrestored as this will lead to hardness, flattening, or leaving marks on the paper if deteriorating as they age or if exposed to heat.
To recover the typewriter rubber rollers, removing original rubber and replacing it with shrink tube is the best and most cost-efficient solution and that is coming from years of experience. I do not feel it is important to pay a lot of money to add a new rubber layer if you are able to use shrink tube process and make sure that the rollers thickness is the same as the originally fitted one. But, If you rather replacing with a new rubber that is still fine.
Restored Rollers at our Workshop
Worn vs new typewriter rubber rollers
Small recovered typewriter platen rollers
Thick Rollers will cause paper to tear and hard to adjust while thin rollers will cause paper to slip and never grip to the platen at any time and might even move while typing. Therefore, the best diameter is always the closest to the original one and whatever feels right for your typing needs. 
On another topic, many wonder how we assess a  typewriter platen & decide if it needs to be replaced or simply recovered. 
As a start, and goes without saying, all pre 1920 typewriters with original platens and mainly special designs will not need to be recovered as we prefer these to keep their original platens as it adds to value as we prefer these to be sold as collectors items and less likely to be used to type on. So, we will not, for example, be changing the rubber on a Hammond typewriter unless client insisted. They will definitely be worn or cracked but its important to preserve the patina on these platens and the discolouration will always add to character. 
Visual inspection is sometimes enough to tell how bad a typewriter platen is. For example, cracks, holes, and surely there might be always dents or misaligned surfaces on the platen that anyone can easily detect. 
Another way to test will be by simply feeding a paper and trying to type. If the letters start punching through the paper, your platens is surely hard enough and will need to be changed. On the same hand, if your paper did not feed at all, it means the rollers need to be changed or rubber replaced or your platen is already flattened at the side of the rollers and will need to all of its rubber to be replaced. 
Now, how to professionally examine the rubber hardness on your platen? 
The Durometer Shore A instrument to measure the hardness of rubber is the best way to exactly rate the hardness of the typewriter platen. 
For the last three years, it delivered the accurate hardness of our platens and helped us decide on what platens needs to be changed and which ones can be safely typed on without guessing. 
A new rubber layer on a typewriter platen will be from 88 to 92 Shore A. 
Any typewriter platen with rubber hardness from 93-97 Shore A, if passed the visual inspection, should be fine and can be typed on for sure & usually these will survive as not all typewriter manufactures back in the day used the best quality rubber on the platens causing the condition of many to deteriorate as time passed by. From experience, Hermes typewriters should always be treated with a new rubber layer as they have always been easily cracked, marked and hard to type on. 
So, when is it time to change the rubber on a typewriter platen? 
When using a Durometer Shore A and hardness is 97+ Shore A, I believe its time to invest in a new rubber layer on your typewriter platen. Usually the platen might pass the visual inspection but the Durometer will confirm hardness and even if the typewriter was never used before, the rubber might have lost its smoothness due to the unsuitable medium it was stored in. 
Using the Durometer Shore A to check rubber hardness. 
  • Picture below showing the hardness of rubber on an old typewriter platen. measurement is 100 and that is hard rubber which is harmful for the typewriter. 
measurement of hardness of rubber on a typewriter platen using Durometer Shore A
  • Picture below showing a new platen being checked. measurement shows 88.5 Shore A on a Durometer that is suitable to be used on typewriter platens. 
 measurement of hardness of new rubber on a typewriter platen using Durometer Shore A
You can find a Durometer Shore A on Amazon or eBay, digital or manual, when we personally prefer the digital as its more accurate. 
To replace the hard rubber on your typewriter platen, please feel free to contact us or check our special page about typewriters  platen restoration as we have been successfully supplying the UK and All Europe with refurbished and renewed rubber since 2018.
Finally, I hope this blog about typewriter platens was helpful as I tried to simplify the terms and maybe help everyone decide if it is the right time for a change of rubber on your platen or not!!.
With Gratitude, 
Mr and Mrs Vintage Typewriter ltd. 
 new typewriter platen recovery


Walid Saad

Thank you for your reference to the hardness meter. This is a good article. I am restoring an old typewriter for very young children to be amazed about but do not care about regular use. The mineral spirits and spray rubber cement ideas look good, if temprorary, for that. I do think you might call some engineers at a real paper handling company (e.g., Heidelberg in Heidelberg) to get the physics on why a rubber roller works by the physics. The smoothness is probably not a direct cause, but it will have to do with the surface microstructure of paper and rubber combining a rigid polymer ‘cellulose’ with zero Gaussian Curvature with a flexible polymer that remembers its shape, like Rubber. Once the flexible polymer ceases to give, the paper loses its hold on the roller. The smoothness just extends the surface area for the hold. Thanks for a nice article. Companies like Heidelberg can build machines that can move most any paper at high acceleration to a few microns of accuracy over many meters between printing stages using exactly these principles of molecular physics.

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