EEVblog Electronics Community Forum
Electronics => Repair => Topic started by: TerraHertz on October 05, 2018, 12:11:33 am
-
This is a request for information.
Currently I'm attempting to restore an old Documation TM200 IBM punch card reader. The rubber pinch rollers had degraded to sticky goo, and there's no chance of finding original replacements. So I need to 're-manufacture' them - form new rubber rims on the original aluminum hubs.
I've posted details of this restoration in progress here: http://everist.org/NobLog/20180922_data_in_holes.htm#tm200 (http://everist.org/NobLog/20180922_data_in_holes.htm#tm200)
I recall someone mentioning to me years ago, that they knew of a place in Australia that can re-form rubber pinch rollers for old tape machines and such. But I can't find anything about it.
There's http://www.terrysrubberrollers.com/ (http://www.terrysrubberrollers.com/) in the US. But since I need to do four identical rollers, that's too expensive for me.
Plus I also have a couple of data tape machines, that could do with new rollers too.
I'm mostly interested in learning how to do this myself.
I have a lathe and can easily make a mold jig to form new rollers on these hubs.
I'm looking for suggestions, ideas & resources on materials and process, to form new rollers.
These are idler pinch rollers, that press the paper punch cards against metal driven rollers, so I don't think the surface grip is going to be too critical. The main points will be lasting adhesion to the metal hubs, concentricity, correct diameter and rubber flex, and stability of the material, ie not turning to goo again.
Btw, if anyone has a service manual (with schematics) for a Documation TM200 punch card reader, please let me know.
-
I rebuilt a number of conveyor rollers with a castable urethane rubber. I applied it to the roller in the lathe under low rpm (the stuff has the consistency of medium mud) and let it turn until set. After it was fully cured I cut it down with a very sharp tool.
That was one of the Devcon Flexane compounds. I think it would work well for the pinch roller application.
-
Two part silicone mold making rubber may be the best choice if you can center the hub and make a proper sized outer mold ring.
Self-fusing silicone tape may work; I once made a temporary fix to conveyor drive roller with this tape that lasted over a year. After it has fused to itself it can be carefully sanded to remove high spots; it may take a few trial runs. It may work for a proof of concept or to find the correct diameter.
Non reinforced rubber tubing is available in many sizes, if you are lucky, you may find something that can be stretched over the hub and glued that provides the correct OD.
Many wheelchairs use a very thick walled rubber tube for tires about 22mm OD with about a 6mm ID; if you can find someone that fixes wheelchairs they probably would give you a piece that is too short to use.
Machinable polyurethane is available; I don’t know how it holds up over time.
-
It might be worth asking on http://www.tapeheads.net/ (http://www.tapeheads.net/)
Lots of people there who repair and restore old tape decks.
-
How big is the roller / rubber. Maybe Projector Recorder Belt Company or Stock Drive Products has a suitable replacement for the rubber.
I have cast rollers using HTPB with a curative and dioctyl adipate (or baby oil) as a plasticizer and castor oil as a cross linker. This is the binder used in solid rocket propellant...
-
Something else I should have mentioned: a couple of the rollers are fixed to the same shaft, and bear on the card edges. So if the rollers are not exactly the same they'll make the card twist. This is the main reason I'm only considering casting in a mold.
Also see the pics - the hubs are designed to key into molded material. I think the transport speed will be quite high, so the rubber needs to be well bonded. Oh, and there has to be a hole for an allen key. Easily molded, not so easy other ways.
Winding on tape, gluing on bits of tube, and cutting down rough rubber shapes, don't appeal.
The dimensions:
Stainless steel driven rollers: 25.25mm dia. Hmm, I wonder if they were once 25.4 (1"), but wore down?
Rubber roller hubs: 14.2mm OD, 9.5mm (3/8") thick.
'Measured guess' at final rubber roller size: 26.8mm OD. But it's a bit awkward and error-prone to measure, plus I don't yet know if these are supposed to press on the steel rollers a little, a lot, or have a slight gap. I'd guess no gap, or the rubber rollers would halt, then have to spin up as a card arrives. I have some 'similar machine' manuals to read, which might say. And still hoping for a correct manual. Anyway, something between 25.0 to 27.0 mm OD.
I should be able to work out the ideal OD of the steel rollers, since the cards have a fixed spacing of hole columns, and the drive shaft has a toothed sensor wheel generating the sample clock pulses. Worst case I can make new stainless steel rollers too.
As for what materials to use to cast the rollers... I was hoping to do actual rubber. I guess I need to learn about vulcanizing. It can't be too hard, if car tire retread places can do it.
Asking at tapeheads AND tire making places, next.
Ha ha.. I have a small library worth of books on the chemistry and processing of rubber. Found and rescued years ago from an abandoned factory, being demolished. Rescued on principle, not because I had any specific interest in rubber. Maybe I should try looking through them. It's an odd thing. Vandals will ALWAYS smash every piece of glassware in an abandoned lab, but they almost never bother to even touch books. I don't think they can even see them. Maybe think they are some kind of funny looking wall covering.
-
Another material to look at is 3M cold shrink tubing. It is a rubber material that is stretched over a collapsable, spiral wound polyethylene core. You stick the item in the core and pull on the end of the polyethylene. That unwinds the spiral and lets the rubber collapse onto the roller.
I'd forget trying to vulcanize rubber and go with a castable urethane material like HTPB or PBAN.
-
I user to deal with some paper folding machines and a method used on some of the rollers in these was to have a metal or plastic disc on the shaft with a groove in the outside edge, this allowed a soft rubber O ring to be used to provide the friction drive on the paper.
Could a similar method be looked at here, you would need to replace the hubs with new ones(I would be tempted to put a groove near to each outer edge and have the grub screw in between them), these could obviously be made on a lathe if you have access to one or possibly 3D printed.
The advantage of this method is that you only need to replace the O rings in the future.
-
Just an idea.
You might check if the rubber from a hockey puck would be suitable as "donor rubber".
Hockey puck rubber is quite hard.
I used it before to make some oversize rubber bushing for a car suspension where it worked just fine.
You can cut holes into it with a hole saw in a drill press and then grind it to size on the lathe machine.
Good luck, Peter
-
I user to deal with some paper folding machines and a method used on some of the rollers in these was to have a metal or plastic disc on the shaft with a groove in the outside edge, this allowed a soft rubber O ring to be used to provide the friction drive on the paper.
Could a similar method be looked at here, you would need to replace the hubs with new ones(I would be tempted to put a groove near to each outer edge and have the grub screw in between them), these could obviously be made on a lathe if you have access to one or possibly 3D printed.
The advantage of this method is that you only need to replace the O rings in the future.
Hey, thanks, that's a really good idea. I *have* a lathe, and LOTS of O-rings. Cheap in bulk too.
Could also pack the O-rings on with no space between them. They can go on after the grub screw is tightened.
I'm still going to try for molded rubber, since the other tape machines will need flat surface pinch rollers.
But for the card reader, it's an excellent fallback solution.
-
I have a heated-press-type vulcanizer but I don't have any raw rubber. We use it more often as a bakelizer for bakelite (I'm getting low on raw bakelite too... :) ) which is right at the upper end of the temperature range of the apparatus and is really hard on the unit, especially the hydraulic jack, but it is actually intended for making the rubber part of rubber stamps and things like that.
If I had some raw rubber and molds of what you needed, I could easily churn them out. I may have to look into getting some rubber supplies as it sound like a handy thing to be able to do. :)
-
I have had great success with urethane for various projects of this ilk over the years. When I started work, the mechanical engineer on our team showed me that the best way to 'machine' rubber or urethane etc in a lathe was to use a grinding wheel. He had a die grinder and a small wheel that mounted in the tool post. He had sheets of thick urethane which was used as a 'stripper' in press tools.
Skateboard or scooter wheels are a good source of material. I think that urethane can be melted into moulds for a rough shape, but not sure.
Regards, BT
-
I am not that familiar with these rollers as to their materials, however, if you are going to machine (turn) the rubber, it helps to freeze the rubber with cryo before cutting. I have turned rubber before and the freezing helps stiffen it so as to get a clean cut. Also, if these are old parts, Buna rubber was often used back when with different durometer ratings, depending on the hardness and durability needed.
Hope this helps...
-
I think the slip on band or ring option would be a good solution to start with, there is a vast array to choose from and they are easily replaceable, readily available and reasonably cheap. One type is linked below but there are plenty of other types, sizes and materials around in other fields.
These rings can take your things off so be careful where you put them. :o ::)
www.leaderproducts.com.au/products/small-expander-rings (http://www.leaderproducts.com.au/products/small-expander-rings)
-
I think the slip on band or ring option would be a good solution to start with, there is a vast array to choose from and they are easily replaceable, readily available and reasonably cheap. One type is linked below but there are plenty of other types, sizes and materials around in other fields.
These rings can take your things off so be careful where you put them. :o ::)
www.leaderproducts.com.au/products/small-expander-rings (http://www.leaderproducts.com.au/products/small-expander-rings)
They'd be perfect Muttley and plenty stretchable to get onto a flat pulley with ridges on the edges to keep them contained. Generally elastrator rings are a soft rubber too so they should grip pretty good. :clap:
-
I had to make up a roller guide for a particular application and used the torus/ donut shaped ones on hubs I already had, they turned out ideal for the job which needed about twenty of them and they were only a few cents each, a local rural/ farm supplier readily stocked them as well which was handy.
-
From my memory of watching these machines in operation I think your guess of zero to negative clearance on the rollers is correct. I am pretty sure the rollers were rolling whether a card was present or not. Still leaves a lot of guess work on appropriate pressure.
I would question the desire to go with rubber. While a rubber replacement will undoubtedly last as long as you need it to, you are just setting up the next goo replacement job. And rubber has such a wide range of tack and durometer that you won't really be helping much in duplicating original performance.
One concern about using the O-ring idea is that the relatively thin layer means that slight variations in card stock thickness (due to humidity or even QC issues) will make bigger changes in pressure than the thicker section of the original. May not be a real issue, but something to think about.
Just a curiosity question. Do you have a source of the cards to run through this thing? While these things used to everywhere a quick Google showed only a few being sold at collector prices. Typical asking prices were 5-10 cards for $10 US. I have no idea if there are any takers. If so, and you have a box or two of cards stashed somewhere you might be able to fund a whole lot of fun projects.
-
I think the slip on band or ring option would be a good solution to start with, there is a vast array to choose from and they are easily replaceable, readily available and reasonably cheap. One type is linked below but there are plenty of other types, sizes and materials around in other fields.
These rings can take your things off so be careful where you put them. :o ::)
www.leaderproducts.com.au/products/small-expander-rings (http://www.leaderproducts.com.au/products/small-expander-rings)
Biting off sheep's testicles come to mind... :-DD
-
I had the same problem with a small EPSON printer. At the suggestion of someone on the Internet I used surgical latex tubing (silicone tubing works as well). It's absolutely inexpensive and works a treat. You can find it in many ID and OD configurations and in many colors including black.
-
I have to admit to being strongly biased against urethane anything. Too many times I've seen urethane decay into toxic, highly corrosive messes, even worse than rubber. It's great while it's new, not so much after a few decades.
Rubber can be OK if it's properly vulcanized (eg tires) but that's a chemistry adventure. Also interesting to see some youtubers have no idea whatsoever what 'vulcanizing' means.
Silicone rubber varieties seem to be very stable, so I'm interested in seeing what's available in 2-part silicone, for molding. Like I said, machining a mold is no problem, and I also have vacuum pump(s) for bubble removal from a mix.
Another possibility is rollers from old office machines. I have accumulated a large shopping bag full of mixed rollers from stripping street-tossed machines. Didn't think there was much chance of finding something size-suitable and silicone rubber, but was surprised when I looked through the bag.
See pic. Found one just about perfect, so long as I can cleanly cut it into sections for the 4 rollers. Would need to make new hubs, with lips to prevent sideways creep.
But of course that's a one-off. I'm still going to try for a generic, repeatable solution that works for any future pinch roller needs.
Edit to add:
drussell, do you know of any instruction texts on heated press vulcanizing?
BurningTantalum & tpowell1830, yeah, machining rubber. I had figured some kind of high speed abrasive or die-grinder setup might work. I did know of liquid nitrogen freezing, and do have a large dewar. Otoh I try to avoid anything with high consumables cost, which this would have. Still maybe...
It would probably work with silicone rubber too.
An amusing variation: http://everist.org/NobLog/20170321_machining_pool_noodle.htm (http://everist.org/NobLog/20170321_machining_pool_noodle.htm)
Anyway I'm going to try molding first.
Muttley... oh god, no. If I used those, every time I look at the card reader an image of gangrenous testicles would come to mind. Besides, latex is used because it rapidly decays.
CatalinaWOW, yah, if I try this I'd go for fat O-rings, to get enough compression range. Also cheap O-rings have pretty crappy durability, so maybe Viton Fluoroelastomer, or neoprene.
As for cards, someone on cctalk has been generous, so I have a smallish stack on the way here. Plus I have an IBM 026 card punch (still to restore) and a couple of boxes of blank cards. But still looking for more. Both new and punched. A several inch thick stack of punched cards with known data content (as a file) would be ideal.
Ha, someone I'm corresponding with says he recently threw out some boxes of punched cards. I'll mention your "prices were 5-10 cards for $10 US", see if he will kick himself even more.
-
I have used silicone molding material for several purposes. My source was MPK enterprises (web site is hobbysilicone.com) though there should be similar sources in Australia. The one I have used most of is their "Extra Firm 135". Once fully cured its durometer seems about right for roller duty, but it does take several days to reach this. Tack also seems appropriate. I have only been using it for a few years so can't really speak to life, but so far so good.
-
To repair a pinch roller for an Edge Bander (a machine that affixes the trim to plywood/MDF sheets) I used a piece of automotive hose slipped over the metal hub. The hose's thickness was uniform enough to get the job done without grinding although I'm sure it wasn't as critical as the card reader.
Cheers,
-
I have used silicone molding material for several purposes. My source was MPK enterprises (web site is hobbysilicone.com) though there should be similar sources in Australia. The one I have used most of is their "Extra Firm 135". Once fully cured its durometer seems about right for roller duty, but it does take several days to reach this. Tack also seems appropriate. I have only been using it for a few years so can't really speak to life, but so far so good.
How's this for a coincidence. Google silicone molds sydney. Three come up. One of them I will be driving close by tomorrow anyway. http://www.aldaxstore.com.au/g/9855/contact-us.html (http://www.aldaxstore.com.au/g/9855/contact-us.html)
I pass close by there at least once a week. But didn't know about that place since it's down a side street.
@duak. There are some pretty funny pics of improvised roller fixes here: http://www.terrysrubberrollers.com/mods.html (http://www.terrysrubberrollers.com/mods.html)
Yet more roller fun. My card reader is missing the input hopper weight. (Requred to make the cards feed correctly.) A guy in Sweden with a reader that still has the weight sent me some photos. Ah, more rollers to make. Plastic ones with O-rings
-
@duak. There are some pretty funny pics of improvised roller fixes here: http://www.terrysrubberrollers.com/mods.html (http://www.terrysrubberrollers.com/mods.html)
Improvised rollers don't work with audio. Even small fluctuations in the traction of a tape reflect in the pitch of the sound. It's an unpleasant effect known as wow and flutter. Terry's pinch rollers are therefore worth their price.
For machines that do not need to maintain a precise constant speed however, you can get away with some rubber hose, rubber foot, o-rings, etc.
-
I have an old HP85A computer that the DAT drive's roller had failed. I ended up using two side by side silicone O-rings.
https://youtu.be/fffhkLRajY8?t=348
-
Pinch rollers for analogue video and audio were really quite precisely made items, they had to be, there was no clock to re-sync and the 'data' was 'real time' so there's no way to correct tape transport aberrations which, as someone else pointed out, produces unpleasant side effects so I'm really interested in seeing the results of any attempt to re-cast them.
I reckon it's going to be really difficult to do but I hope to be pleasantly surprised as I've a couple of old tape decks I'd like to get going again.
One idea that does occur to me would be to remove the old rubber then cast the original metal core roller into some hard plastic and machine it down to true it, once that's done it might be possible to sleeve it with silicone rubber or perhaps even 'dip coat' it?
-
I'd be quite interested to understand why it is that some rubber parts seem to stand the test of time OK, while others go hard and others become sticky.
One of my occasional pastimes is restoring audio DAT decks, and when the pinch roller starts to go, the bit error rate creeps up until the rf signal becomes impossible to lock on to and decode properly. The odd thing is that, even though most of the machines I work on are from the mid '90s, a roller from one machine can be in much better condition than another, even when the mechanisms are identical.
-
Rubber or silicone tubing maybe ?
-
MG Chemicals Rubber Renue (https://www.mgchemicals.com/products/cleaning-products-for-electronics/cleaners/specialty-cleaners/rubber-renue-408a-408b) I used in the repair shop use on old pinch rollers and platen rollers. It's a 'must have' if you are working on old cassette decks, reel-reel, turntables, printers etc.
Techs told me to never use it on belts, but MG says it works there. I thought it can make the belts swell.
-
May be different environments. Remember Bob Pease's discovery that air ionizers ate all the rubber seals in his house? So one deck that lived in a smoggy city, or a freshly painted house, or ... dies, while another got better, cleaner air.
-
From a recent discussion I had in a shoe shop it appeared that for some shoes with man made soles there could be significant deterioration of the soles if stored in their boxes, whether worn or not.
I have got a couple of pairs where the soles have gone tacky and one that has developed cracks even out of the box, but at the same time I have noticed that cassette deck and turntable belts do not last as long as I would expect and rubber bands have a very short life expectancy before going brittle.
All this supports the idea that the environment plays a big part in how long we can expect these components to last, I am glad I only use digital systems for recording these days, as I hate to think of the amount of hassle all the drive belts on a multitrack tape deck would cause having to be replaced regularly.
-
From a recent discussion I had in a shoe shop it appeared that for some shoes with man made soles there could be significant deterioration of the soles if stored in their boxes, whether worn or not.
Yep. That happened to me. I thought I was really clever buying a decades worth of shoes I liked when they were cheap and discontinued. After 5 years they just disintegrated on initial wearing. In the literal sense of the word.