HP 97 clutch repair methods compared



#2

I'm reading up on the clutch problem since my card reader was a bit noisy after replacing the drive wheel rubber.

Although a fair tug was needed to pull the clutch off the motor shaft when I first did it to check the condition of the clutch, I now find it comes off quite easily. So, the question is what to do about it.

There seem to be 4 methods in earlier posts, listed below. Clearly, for either of the first 2 to be considered the original clutch material must be in good condition and just slipping a bit, like mine.

1. Superglue between the motor shaft and the original clutch material. (various people have suggested this)

2. A small bit of cling-wrap between the motor shaft and the original clutch material. (Rafa, Spain)

3. Replacing the original clutch, aluminum sleeve and all, with a piece of insulation pulled off of a solid conductor electrical wire. (Bernd Schmeling)

4. Removing the original clutch material from the worm gear shaft and the aluminum sleeve and replacing it with ordinary household silicone adhesive. (described in detail by Johnny Nestor)

Method one is clearly the easiest, but it has been criticized for fears of serious damage under some circumstances if no slippage at all is allowed. Method 2 seems tedious and perhaps not durable. I worry about method 3 because the aluminum sleeve is omitted; if it's not needed I wonder why HP put it there. I like method 4 because I believe that's pretty much what HP did in the first place, i.e., molded the two shafts together with a rubbery material inside a metal sleeve to provide lateral rigidity. However, it sounds very messy and I wonder how hard it is to get perfect centering (or good enough).

So, with that background here's my question: If the clutch material should not be bonded to the motor shaft in method 1, why is it OK to do so in method 4? In both cases the bulk of the clutch material will provide the wanted vibration isolation.

Comments?


#3

First off, something I found out in the past is that it is not a "clutch", which implies that it should slip if there is a card jam (it should not), but that it is an elastomeric coupling that provides a certain degree of vibration dampening. As such, it should idealy be bonded permanently to both the worm gear and the motor shaft.

The method that I use is to use wire insulation that has on OD that permits the metal sleeve to fit over it to retain its shape and ensure a tight fit on the motor shaft. For good measure, I also place a tiny drop of Superglue on the motor shaft before sliding the coupling over it. Since I use only one piece of insulation, its ID is a tight fit on the motor shaft, and I bore it out on the worm gear end to permit it to fit.

Edited: 18 Apr 2010, 3:56 p.m.


#4

Quote:
First off, something I found out in the past is that it is not a "clutch", which implies that it should slip if there is a card jam (it should not), but that it is an elastomeric coupling that provides a certain degree of vibration dampening. As such, it should idealy be bonded permanently to both the worm gear and the motor shaft.

That's what I think too.

Quote:
The method that I use is to use wire insulation that has on OD that permits the metal sleeve to fit over it to retain its shape and ensure a tight fit on the motor shaft. For good measure, I also place a tiny drop of Superglue on the motor shaft before sliding the coupling over it.

If the original clutch material looks to be in pretty good condition, i.e., not at all gooey, wouldn't it do to simply put Superglue on the motor shaft?

Thanks.

Ed


#5

Quote:
If the original clutch material looks to be in pretty good condition, i.e., not at all gooey, wouldn't it do to simply put Superglue on the motor shaft?

That material may seem to be in good condition, but it will have deteriorated badly over time and should not be reused. In my experience, it does not become gooey, but rather it becomes dry and loses its elasticity, and it will just shear and crumble. I strongly advise against trying to reuse it.

#6

Michael,
My measurements show that the motor shaft is 0.037". Solid wire gauge #19 is 0.036. From posts to the forum I've read that the ID of the sleeve is 3/32 = 0.094". I went to a major electronics store today hoping to find #19 with OD of something close to 0.094" and found nothing. Do you remember what you used?

I did find that SmallParts.com lists a Tygon micro bore PVC tubing with ID 0.030" OD 0.090" Have you tried that?

Ed


#7

Ed,

The wire insulation that I used is unmarked, but it has an OD of approximately 2.4mm (0.0945") and the ID of the stranded wire bundle is approximately 1.0mm (0.0394"). I used this particular wire simply because it was lying around and was the only wire I could find that would work. The Tygon tubing might be too tight a fit on the motor shaft; PVC is not very stretchy, but you might be able to hot bore it with a heated nail, which is the way I enlarge the bore on the worm gear side.

Michael


Edited: 19 Apr 2010, 11:21 p.m.


#8

Opps... you're right, the PVC is the hard stuff. Too stiff, I would think, even if I could make it fit.

Ed

#9

I have used #4, Johnny Nestor's method quite a few times with excellent success. It sounds messy and difficult, but it is very easy.


#10

That's encouraging, Dan. I might as well give it a try since I can always clean it up and try something else if it doesn't work for me. How do you keep the silicone from getting all over the motor?

Ed


#11

After you fill in the little cylinder, wipe off the sides and the ends (and your fingers) of any excess. Set the worm gear in the cylinder then slide onto the motor and make sure the axle engages with the gear.

Some silicone will be pushed out of both ends but not as much as you'd think. I use a toothpick and a cotton swab to clean off any excess. If you push down on it and it seems too much is coming out the bottom, just raise it up a bit and wipe it off, then press down again. Center the cylinder. Then set it upright overnight.

It helps a lot to have a strong magnifier or loupe on your head, and lots of light. ;)


#12

After reparing the clutch using the silicone sealant fill method I find that the shaft is not quite long enough to fully engage in its hole in the frame. See:
Shaft fit.

When I did the repair I made sure the motor shaft bottomed out on in the hole in the worm shaft, as suggested in Nestor's write-up. See:

Repaired clutch.

What am I missing?

Ed

Edited: 3 May 2010, 12:41 p.m.


#13

I dug through my notes and photos. I have never seen a case where it didn't engage the frame enough, though there is quite a bit of variability in just how far it goes into the hole.

When I press the worm gear on to the motor shaft there is always some air in the hole in the axle so that it rebounds some. I never try to work it down any further.

-- Dan


#14

Thanks, Dan. I am away from home right now, but later I will try pulling it apart, digging all the silecone out and starting over. While apart, I will experiment with it a bit before putting the new silicone in.

Ed

#15

You missed one version: The coupler can be replaced by appropriate shrinking tube, as well.


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