HP 97 card reader clutch shaft repair



#8

The first time I reassembled my clutch (using the silicone sealant repair method) I seated the worm shaft firmly against the end of the motor shaft. When I mounted it in the frame I noticed the tip of the worm clutch only barely engages its pivot hole in the frame. I have dissambled it, planning on pushing the work shaft not quite as far onto the motor shaft, making it engage the pivot hole by perhaps 0.025" more.

However, I'm now thinking maybe this is not necessary. I've noticed that there is about 0.010-0.015" endplay in the motor shaft, and since the motor turns counter-clockwise and the worm has a Right Hand thread the shaft assembly will be driven forward, pushing the tip deeper into the pivot hole.

Any thoughts on this?

Ed


#9

I have never done the repair this way as I favour the insulation method.

Remember that there is a ball bearing at the tip end of the worm gear. This will cause end shake if it is missing, it is tiny!

Some questions:

How do you centre the shaft with the silicon method. The wobble of an off centred system would cause a lot of vibration. After all this is a dampening couple and not a clutch.

I take it you have not swapped parts from another calculator system as for example, the HP 42 card reader assembly (looks identical) is not the same length as the HP 65 system:

HP-65 		drive roller axle: 	8.32mm
HP-41C drive roller axle: 8.23mm
HP-65 worm gear length: 14.43mm
HP-41C worm gear length: 14.36mm

As far as end shake goes, all my systems have been very close to a tight fit and the bearing acts as it should. That is there has been no endshake. Having said that, other then vibration I don't see a problem with some other than noise.

Cheers, Geoff


#10

Quote:
I have never done the repair this way as I favour the insulation method.

I pursued the insulation method for a while but abandoned it because I couldn't find a suitable piece of insulation. It seems to me that a size that gives a good fit on the motor will be too tight on the worm shaft. Also, I wanted to fit the aluminum sleeve over it, but that would leave a very thin wall over the worm shaft.

Quote:

Remember that there is a ball bearing at the tip end of the worm gear. This will cause end shake if it is missing, it is tiny!


I've noticed that. On mine it seems to be peened in on the opposite side of the frame so did not fall out.
Quote:

How do you centre the shaft with the silicon method. The wobble of an off centred system would cause a lot of vibration. After all this is a dampening couple and not a clutch.


When I did it the first time I followed advice given in previous posts by others: let it harded a few minutes then push it around a bit till it looks OK. All this is done with the motor vertical with the shaft up.

This time I am going to try to put the motor/worm shaft assembly into the frame after the silicone has hardened a bit. I think this will allow better centering, at least for the worm shaft, since it will be in its pivot hole at one end and on the motor shaft at the other. The only thing that can be off center is the sleeve, and that can be minimized by pushing it around a bit with a small screwdriver to get the gap between the sleeve in the frame hole even all around. Also, I will be able to get a better axial fit.

At this point I am very encouraged by the silicone method. It is really not very difficult. My desktop bench vice makes it a lot easier. For example, the frame can be held in any position you want while fiddling with the motor and worm gear. Also, I squeeze the silicone directly into the sleeve using the smallest possible cut on the silicone nozzle. Not messy at all that way.

Quote:

I take it you have not swapped parts from another calculator system as for example, the HP 42 card reader assembly (looks identical) is not the same length as the HP 65 system:


Nope. So far, I've found everything I've lost. Even that tiny nylon washer! (BTW, what's it for?)

Quote:
As far as end shake goes, all my systems have been very close to a tight fit and the bearing acts as it should. That is there has been no endshake. Having said that, other then vibration I don't see a problem with some other than noise.

So maybe the bearings in my motor are worn out?

Thanks for your help. I'm in no hurry with this project so it may be a while, but I'll report back with lots of photos when I'm finished.

Ed

Edited: 15 May 2010, 7:13 p.m.


#11

Hello Ed

Quote:
I pursued the insulation method for a while but abandoned it because I couldn't find a suitable piece of insulation. It seems to me that a size that gives a good fit on the motor will be too tight on the worm shaft. Also, I wanted to fit the aluminum sleeve over it, but that would leave a very thin wall over the worm shaft.

Thats why I use the double insulation method:

Diassemble:

Fabricate new couple with two insulations; narrow and wider inner diameters:

Reassemble:

Quote:
I've noticed that. On mine it seems to be peened in on the opposite side of the frame so did not fall out.

Some are and some are not, probably due to some plastic frame deterioration. I have had them fall out and resorted to epoxing them back.

Quote:
So maybe the bearings in my motor are worn out?

Could be, how much end shake when you pull and push on the axle. They can be pushed to hard in their internal mounts, for example, when trying to fit a to tight new couple and sleeve into place.

Cheers, Geoff

Edited: 16 May 2010, 3:50 a.m.


#12

Quote:
Could be, how much end shake when you pull and push on the axle. They can be pushed to hard in their internal mounts, for example, when trying to fit a to tight new couple and sleeve into place.


When I gently pull the shaft out as far as it will go and holding feeler gauges up next to it I judge it to be 0.010" endplay.

I'm going to try to make the worm shaft extend far enough so as to give about 0.030" pivot engagement when the motor shaft endplay is taken out towards the motor. Thus when the motor is on it will engage 0.040".

Edited: 17 May 2010, 5:58 p.m.

#13

I believe I've seen your photos before. My problem was I couldn't find a wire with insulation like your white piece. It seems that its ID would have to be nice tight fit over the worm shaft, while at the same time it would have to be not so small that it wouldn't slip over the red one. In addition, the OD would have to slip into teh aluminum sleeve. I spent a lot of time looking over the wire selection at a local, well stocked electronics store with no luck. That's when I began looking at the silicone approach, although your insulation method looks easier.

Ed

Edited: 18 May 2010, 1:05 p.m.


#14

Dead IPod head set insulation ;-) The thick part before it splits.

Cheers, Geoff

Recycle, recycle, recycle


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