Thursday, 17 January 2013

Garter carriage blues

My usually reliable workhorse garter carriages have been playing me up.  After taking a very deep breath and abandoning any thought of actually knitting something, I tried to narrow down the problems in a systematic way.

Internet searching yielded a service manual here and an excellent set of hints and tips here, but nothing seemed to be relevant to  the health issues of my particular GCs.  I checked the needles, magnets and brushes, all seemed fine on both the GCs and the main bed.  I tried different yarns and tensions.  I tried the same card using fairisle.  All of this led to the solution of a few minor niggles (and beautifully cleaned machines!), but I was left with three intractable problems so I called in reinforcements.

Problem one (KG88) solved: the wrong needles were being selected

Himself is never truly happy without a screwdriver in hand, so he was quick to suggest a strip down of one of the knitting machines, which is a KH 881.  We set up a row of yoghourt pots to hold the  bits and removed the plastic cover for the card reader and the built-in knitleader, so it was possible to see the whole length of the needles.  The problem was immediately obvious.  Although they looked fine from in front one, just one, was bent at the back end.  I must have replaced this sometime in the past and not noticed it was bent.  While the selection mechanism for the main bed was apparently able to cope, the GC could not.  Problem solved.  A new needle was an easy repair, but the thing had to be reassembled.  Too many little screws!

Problem two KG 88II not solved: the GC would not turn at the left-hand end of the row

One garter carriage was now working properly.  Unfortunately, this was the KG88, which does not cast on.  The KG 88II was still sick.  We partially dismantled it and found a botched previous repair, but tidying this up had no effect.  It had to be the pawl, or 'feed change plate' as it is called.  The service manual simply said 'replace the feed change plate' but that isn't an option these days, so we had to try a repair.  Although it was (so far!) unsuccessful, I have documented what we did in case anyone finds it useful.

Figure 1
We had the idea that the springs inside the reversing pawls might be 'tired'.  The way the garter carriage chunters along impulsively, we hypothesised that the pawl might jump the first out-of-work needle, if the spring were not strong enough.  Figure 1 shows our attempts to determine the weight needed to push down the pawl against the spring.  An old baby bottle with millilitre (ml) graduations along the side was suspended from the pawl.  The bottle weighed 30gms and as each ml of water was injected into the bottle, it added 1gm to the weight acting against the spring.  In the 'good' garter carriage the weights were 50gms on the left-turn pawl (the one on the right) and 80gms on the right-turn pawl (the one on the left).  The weights in the case of KG88II were significantly less: 40gms on the right-turn pawl and less than 30gms on the left-turn pawl!

Figure 2
Now what are the chances of being able to replace the entire pawl?  It just so happened that we had a spare pawl and so any experiment to improve the performance of the spring could be piloted on this one.  So, we decided to remove the plastic part to expose the spring.  This is held in place with a pin that is very like the pins that hold a bicycle chain together, but only a lot smaller.  In the case of a bicycle chain it is possible to buy a pusher tool, but in this case, we were on our own.  The tools that we used were: a small centre-punch, a small nut and a small hammer.  The nut shown in figure 2 is perhaps a little larger than it should be.  The objective is to punch through the pin without distorting the steel frame beneath it.
Figure 3

The component parts are shown in figure 3.  The spring can just be seen on the extreme right

Figure 4
Figure 4 shows that the spring has two bends.  A small-nose pliers was placed below the lower fold and that part of the spring was held firmly while the spring above the fold was pushed gently upward.  The process was repeated at the second bend, so that the final position of the spring was much higher than before the exercise was started.

Figure 5
Reassembly required putting the plastic in place over the spring, lining up the holes and inserting the pin.  This is made easier by using the centre-punch as a 'drift'.  As the pin was hammered in, it displaced the centre-punch (Figure 5)

Once the pawl was reassembled and inserted into KG88II the force required to displace the spring was measured and found to be 100gms.  The garter carriage was then set in operation and the left-turn pawl worked perfectly for a while before failing once again.  So our next step will be to re-test the springs.

Someone also pointed out to us that there was originally a spiral spring connecting the two pawls.  The 'good' GC has never had one in my ownership, so I'm not sure if this is important, but it is probably worth fitting one anyway.  Who knows?

An oddity:  Since I wrote the above I've noticed that the problem never happens on 'ordinary' rib, just while knitting patterns ...

Problem solved!  See post of 25th Nov 2013

Problem three (KG 95) not attempted: the row count-down and stop button were non-functional

Never one to learn from experience, I bought a third GC to work with my my lovely new KH 965i.  It went back to the seller because it would not count down properly and the red stop button was non-functional. We could have attempted a repair, but chickened out and bought a KG93 which, I'm relieved to say, works perfectly.

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