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Hymek First Aid

Posted by D869 , in class 35 23 February 2015 · 746 views

I'm hopeful that the Hymek (which you may recall had failed prior to Warley) is now on the mend.

In our previous installment, I'd got hold of some spare worm wheels from BR Lines and installed them in the loco but this had not cured the uneven running which I still thought was caused by the wormwheel skipping on the worm (hence the trashed original wormwheel)

We have AbRail coming up on Saturday, so I finally got back around to looking at the problem... with visions of needing to make new worm shaft bearings or some such nasty job.

Further investigations and testing with just one wormwheel installed at a time confirmed that the wormwheel mesh was indeed the issue. On one bogie it was intermittent (hence the jerkiness). On the other bogie the motor was free to spin with no drive imparted to the bogie at all.

Now there is some play in the worm shaft bearings but I could not believe that this was enough to cause the problem. With the thing stripped down and laid on its side I checked out the worm mesh... and realised the cause of the problem.

To cut a long story short, the phosphor bronze strips that pick up power from the bogies had too much 'spring' in them, probably a misguided attempt on my part to ensure good pickup from the bogies. This meant that the weight of the loco was being carried on these strips and that the bogies were being pushed to the bottom of the travel allowed by the pivots.

The fix was to bend the strips much more carefully so that they still contacted the bogie pickups but without enough 'spring' to carry the weight of the loco. Roughly speaking they need to be fairly level in the chassis when the bogies are removed. With this setup the loco weight is taken by the top surface of the bogie pivot, so the bogies sit as high as possible in the body and the worm mesh is as tight as the pivots will permit. The photo shows one pair of the adjusted strips.

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There still seems to be some audible 'chatter' so perhaps I might check out the mesh more closely. Filing the pivot tops would close up the mesh but would not be reversible if I get it wrong, so I think I'll probably leave things alone for now.

The other slight problem in November was that one half of the chassis block had snapped in two. Remember this?

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Solution? Mill out a slot in the chassis, make some threaded holes and fit a metal 'splint'? Err... no. :no:

Here is my precision engineering fix for this :sungum: ...

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MinerChris
Feb 27 2015 02:52

Seems like sound engineering principles...
 
7214525854_733237dd83_n.jpgEngineering flowchart: Does it Move? WD40 vs. Duct Tape (original artist unknown) by dullhunk, on Flickr

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queensquare
Feb 27 2015 09:54

Splendid, my kind of engineering solution there Andy!

 

Jerry

Cheers folks. Glad we're on the same wavelength.

 

Regards, Andy

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richbrummitt
Mar 02 2015 13:28

I assume that there is not space to fit a ty-rap for a belt and braces approach.

I assume that there is not space to fit a ty-rap for a belt and braces approach.


Not inside the body I fear.

Do you think I should put a couple around the outside to be on the safe side?
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richbrummitt
Mar 16 2015 14:10

Not inside the body I fear.

Do you think I should put a couple around the outside to be on the safe side?

 

Yes. Maybe some of that tape that they place around derelict buildings warning not to enter the unsafe structure too, just to be sure.

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A blog about my own modelling projects (as distinct from the St Ruth group layout) - centered around BR WR circa 1968-1972 and my own minimum space 2mm Scale 2FS layout 'South Yard'

 

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