Suggestions for making an HP9810/9820 printer platten



#6

I've got an HP9820 in bits on the bench at the moment and one of the faults is that the printer platten has turned to goo.

I've taken the whole thing apart and will clean off the remains of the old rubber. The problem is making a new one.

I've had a couple of ideas :

1) Make a mould and cast a new roller around the existing spindle using one of the 'Devcon' products (which are stated as suitable for rollers)

2) Fit a metal or plastic 'core' around the existing shaft and put a rubber tubing sleeve over that.

Any more suggestions welcome. Any ideas where to get (silicone?) rubber tubing of suitable diameter?

I have a reasonable workshop including a lathe and milling facilities...

Thanks in advance for any help.


#7

You might check you auto parts supplier. They may have vacuum or fuel line in the size you need. It's also possible to use two hoses to get to the size you need. In the US typewriter collectors have their platens redone by Ames at reasonable cost and high quality.

#8

Check my piece in the articles section on repairing the HP9100 printer platen using 3M cold shrink. This material seems to be a perfect solution to the problem.


#9

I've looked at 'Cold Shrink' at Digikey, and read the 3M data sheet.

Am I correct this stuff is fairly thin-walled? The 9820 platten has an overall diameter of about 1/2", the spindle through the middle is about 1/4" diameter (these figures are guesses, whatever you do, don't make one from these dimensions!). And it needs to be flexible enough to allow one part to be forced past it during assembly (a metal core with, say, 1/32" of rubber coating would not work).


#10

No, it is fairly thick. Like .0625 thick unshrunk. The material that I used shrunk down around 50% onto the 9120 0.58" diam platen core to the exact size of the original platen (becoming around 0.115" thick). It is a silicone rubber that is designed to weatherproof high voltage connections. Should be very stable over time. The material is very grippy and has a texture and firmness that are perfect for platens.

Also the material comes in various sizes with a specified shrink range. There is usually a range of it available on Ebay. I would suspect that the final thickness varies as the amount of shrinkage. If you need a little more final diameter you could use a base layer of thin heat shrink, etc. Finding the exact size I used, may require DigiKey if you are in a hurry.

I'm not sure how the 9810 platen differs from the 9120. The 9120 is a stainless core rod. I scraped all the old goo off and cleaned it. You insert the platen core into the center of the cold shrink tube, then unzip the supporting shrink core material. The rubber collapses onto the platen rod as you go and you have a perfectly encased platen.


#11

Quote:
No, it is fairly thick. Like .0625 thick unshrunk. The material that I used shrunk down around 50% onto the 9120 0.58" diam platen core to the exact size of the original platen (becoming around 0.115" thick). It is a silicone rubber that is designed to weatherproof high voltage connections. Should be very stable over time. The material is very grippy and has a texture and firmness that are perfect for platens.

Clearly 'fairly thick' is relative. From memory, I need something about 0.25" thick after shrinking. I am not sure if putting 2 layers on would work well.

Quote:

I'm not sure how the 9810 platen differs from the 9120. The 9120 is a stainless core rod. I scraped all the old goo off and cleaned it. You insert the platen core into the center of the cold shrink tube, then unzip the supporting shrink core material. The rubber collapses onto the platen rod as you go and you have a perfectly encased platen.


I think the main difference is the thickness of the rubber. The 9810/9820 printer platten has a metal rod in the centre (I don't know what metal..). That, of course, I can clean up and use again.

There's a rubber roller moulded onto that that's about 2-3 times the diameter of the rod. That, of course, is what I need to replace.


#12

If you have a 1/4" core and need 1/2" final diam, then you need a rubber coating with a web thickness of 1/8" which is pretty close to what I got with my cold shrink. The 9120 core has a greater starting diameter and the material that I used was at its maximum allowale shrinkage, so I suspect that it puffed up about the maximum amount when it shrunk. To cover a 1/4" diam core you would need to start with a different size material than mine. I don't know what its final thickness would be.

Otherwise, I think you would need to either build a bigger core or shim your old one. If you are lucky mayby two layers would work. Or a layer of something thinner underneath a top layer of cold shrink. At one time I tried some thick heat shrink on a 9120 platen, but it would not shink evenly enough to make a smooth surface.


#13

I am probably being a total idiot...

I can get Cold Shrink in the UK from Farnell. It's not cheap, so I don't want to waste it.

I assume you cut it to length before puting it onto the spindle, but then how do you pull out the core. It implies in the instructions you pull the free end of the core, and it starts collapsing from the end opposite to that where you're pulling (if you see what I mean), but that can't work if you've cut it to length, can it?


#14

The cold shrink core is just a cylinder made of polyethylene. It has a perforated/scored spiral cut along its length. One end of the core is a tail that is fed back into the cylinder. When you pull on the tail, the far end of the core material unzips and unwinds. This allows the cold shrink to collapse. I left about a half inch of cold shrink hanging over the ends of the spindle. After unzipping, I trimmed it to the proper length with a razor. I did it this way since I did not know how much the material shrunk lengthwise as it collapses.

On one piece, I inserted the printer spindle, started collapsing the core, and when I had the spindle fully covered, I stopped collapsing the core and cut the cold shrink. This left the remaining cold shrink on the rest of the uncollapsed core that I then used on a second machine.

On another piece, I cut the shrink and the core and had two pieces to work with. The first piece had the tail of the core still in place and it worked just like a regular cold shrink. On the other piece, I grabbed the far end of the cold shrink core with long hemostats to unzip it. I think the first method worked slightly better.


#15

Thanks for the methods...

Incidentally, I don't think Cold Shrink will be suitable for this machine without some kind of 'core' under it. I took my 9810 apart yesterday -- it still has a good platten -- and measured the diameter. It's 0.85" (much larger than I guessed). The spindle is, indeed, 0.25", which means I need a thickness of 0.3" of 'rubber'.

Need to think some more before ordering anything, it's not exactly cheap!


#16

Tony,

My local ACE Hardware has a number of bushings - both bronze and some kind of plastic like material. Some are both with bronze on the inside and the plastic on the outside. The plastic is hard and appears to be machined rather than cast. Maybe something called deldrin (sp?). Maybe it is possible to find the right size bushing which can be glued (loctite) to your spindle, then a shrink coating applied to the outside.

Or you can just ask a machine shop to make the correct size bushing. It seems to me that such a thing would be cheap and worst case - you would need to have someone with a lathe turn down the outside to the correct diameter. The 0.25" spindle would be a common size and all you have to do is find something close or slightly oversized. The bushing could be hard plastic or aluminum.

FS


#17

Quote:
Tony,

My local ACE Hardware has a number of bushings - both bronze and


We don't have 'ACE Hardware' stores in the UK, but I am sure I
can find soemthing...

Quote:

Or you can just ask a machine shop to make the correct size bushing. It seems to me that such a thing would be cheap and worst case - you would need to have someone with a lathe turn down the outside to the correct diameter. The 0.25" spindle would be a common size and all you have to do is find something close or slightly oversized. The bushing could be hard plastic or aluminum.

FS


That is not a problem. As I said in my first message, I have a lathe (which cost me rather more than any of my HP toys...). I can
quite easily make a 0.5" or whatever sleeve to put over the spindle and Loctite it on

#18

You could make a spindle about 0.65" OD and coat it with the cold shrink or try two layers of the stuff. If you used tw layers you would probably have to buy two different sizes (doubly not cheap). I have seen it on Ebay for cheap (but watch the size).

I think Katie fixed hers with rubber adhesive tape (probably not a long term solution). I might give rubber adhesive tape (not vinyl electrical tape) a try this way: Wrap it with side by side pieces. Sand the end seams down as best you can. Cover with a thin heat shrink and shrink it down.


#19

Here's something that I wrote about doing this repair 6 years ago. It's held up perfectly ever since:

Quote:

I used "Magic Wrap" rubber self-fusing tape bought at Home Depot (the exact same stuff is also sold under the name Wrap n' Seal) to fix the 9810 printer platen. I started by removing all the old rubber from the 1/4" platen shaft (it's rubber all the way down) and cleaning it really well. Then I had a local plastic cutting place make a 2-1/8" cylinder of 3/4" Lucite rod with a 1/4" hole drilled axially through it. (The hole needs to be within 5-10 mils of dead center, I let them do it because I don't have much in the way of machine tools. But I probably could have better job myself using Delrin, not Lucite.)

I forced this onto the shaft and centered (left to right) it (just banged it on, no glue was needed). Then I carefully wrapped the Lucite with the rubber tape doing about a 3/4 width overlap while stretching the tape (you need to do that to make it fuse to itself). This gave a fairly even resulting diameter of .86". The platen needs to be about .82" so I deliberately left .04" to grind down in the process of getting ride of the overlap bumps. The "grinding" was very time consuming: I put the shaft in a drill press for all of this and used #100 sandpaper very slowly and carefully getting rid of the ridges and making the rubber smooth. (Doing this on a lathe would be much better, if you have one.) After it was all smooth and as even as I could make it, I cut off the excess rubber on the ends of the Lucite cylinder and reinstalled it.


I recently noticed that Home Depot now sells a silicone rubber self-fusing tape called "Stretch & Seal" that might give good results too.

-Katie

Edited: 15 Feb 2007, 11:52 a.m. after one or more responses were posted


#20

The diameter of the (good) platten in my 9810 printer (exactly the same mechanism) is 0.85". I've checked this with a micrometer, and I don't believe I am 30 thou out :-). I suspect the exact diameter is not that critical, though.

The is one possible problem. There's a (red) paper guide flap under the platten, the paper feed key presses on an extension of it's pivot spindle (the flap the lifts the printhead off the paper which, in turn, operates a microswitch on the front of the machine to start the drive motor).

The only way to assemble the front section of the printer is to put the flap in upside-down and then turn it through 180 degrees to get it to the right position. Part of the flap has to be forced past the platten. If the platten 'core' is too large a diameter (with, therefore, a thinner rubber sleeve over it), this will not be possible. A quick measurement (ruler, nothing fancy) suggests a clearance between the flap and the platten spindle of 0.25", so you have to be able to reduce the platten diameter at that point by about 0.1 ". The last thing I want to do is make up all the parts and find I can't actually assemble the thing!

#21

Tony,
I repaired a 9810 printer with the help of a friend from the U.S. He made the core roller of a piece of nylon rod and covered it with heat shrink tube. After shrinking this gives a smooth surface with execellent grip. It works without problems for me. I can send you photos if you like.
Achim


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