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Card Reader pressure roller diameter?
Message #1 Posted by Ian Phillips on 27 Aug 2011, 3:44 p.m.

I successfully replaced the gummy wheel on my 41CV card reader but got careless and lost the tiny nylon roller that applies pressure to drive the card movement.

I searched the floor and my bench several times fruitlessly so I plan to make a replacement roller as I have a lathe and the means to do it.

I have searched the archives but cannot find a drawing or any sizes so I would be grateful if anyone could tell me the dimensions of the nylon roller please. For simplicity I will put a hole through the roller and run it on a separate spindle.

TIA

Ian

      
Re: Card Reader pressure roller diameter?
Message #2 Posted by allen on 27 Aug 2011, 3:56 p.m.,
in response to message #1 by Ian Phillips

Can you vacuum the floor with a clean bag and then search the bag? That might be faster, if much less entertaining??

I've dropped those rollers before, only to be found through prayer and prostration, chiefly the latter.

      
Re: Card Reader pressure roller diameter?
Message #3 Posted by Michael de Estrada on 27 Aug 2011, 4:21 p.m.,
in response to message #1 by Ian Phillips

I measured one I have with a digital vernier caliper and got the following:

Roller diameter = 2.68mm

Roller length = 2.22mm

Pin diameter = 0.97mm

Edited: 27 Aug 2011, 4:21 p.m.

            
Re: Card Reader pressure roller diameter?
Message #4 Posted by Ian Phillips on 27 Aug 2011, 4:42 p.m.,
in response to message #3 by Michael de Estrada

Thanks for the replies.

As to finding the original part I have mostly given up. I'm pretty sure it did not get to the floor, which is jet black dense short pile carpet so its usually easy to find things on. Its not trapped in my clothing or anywhere on the bench either.

Since I asked the question I have made a roller out of PTFE, I worked out it should be 2.1mm long but I have made it 3.8mm diameter so its probably too large. I'm not sure my loose pin idea will work though because it looks like it will project into the gap under switch 'rocker' and stop it working. I am just going to cut some 1mm ground shafting to length and try it though.

As a matter of interest, are there only two 'switches' actuated by the card insertion? there looks to be three locations but I only found two gold springs and two actuators (one of which hardly has any movement).

Ian

                  
Re: Card Reader pressure roller diameter?
Message #5 Posted by Randy on 27 Aug 2011, 4:59 p.m.,
in response to message #4 by Ian Phillips

There are only two switches, one turns the motor on, the other says the leading edge of the card is over the head.

As for the roller, any non-magnetic material should be fine, brass would be an easy choice to machine. The diameter is not critical but I suspect a few thousands (of an inch) over-sized would be better than under.

Edited: 27 Aug 2011, 4:59 p.m.

      
Re: Card Reader pressure roller diameter?
Message #6 Posted by Dan W on 27 Aug 2011, 6:10 p.m.,
in response to message #1 by Ian Phillips

If this is the same roller in the 65/67/97 card readers, I have a spare I could mail you.

If you want to make your own, be advised the pin/cam on the end is slightly offset so that rotating the roller will change the pressure. I have a good photo of the end showing this offset, from which you could take some measurements, if that would help.

Send me an email if interested in either.

-- Dan

            
Re: Card Reader pressure roller diameter?
Message #7 Posted by Ian Phillips on 28 Aug 2011, 5:47 p.m.,
in response to message #6 by Dan W

Quote:
If this is the same roller in the 65/67/97 card readers, I have a spare I could mail you.

If you want to make your own, be advised the pin/cam on the end is slightly offset so that rotating the roller will change the pressure. I have a good photo of the end showing this offset, from which you could take some measurements, if that would help.

Send me an email if interested in either.

-- Dan

Thanks for the offer, but I have made a PTFE roller that runs on a pin that is a snug fit in the recesses. The card move through cleanly every time but I have not managed to find what is causing the 'Malfunction' or Checksum Error messages since I reassembled it, although it was working fine last time I used it (about 6 years ago!)

Using the card reader with new 'N' cells I sometimes get the 'Low batt' message too. I have an old (single) memory module that I am thinking of using as a temporary connector so that I can measure the battery volts on load or alternatively use a bench PSU to see just how much current is being drawn.

Ian

Ian

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