Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => AmpTools/Tech Tips => Topic started by: PRNDL on June 27, 2009, 09:52:37 am
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By cage screws, I mean those that screw into a cage nut pressed into a chassis.
This happens fairly often - the tip of the screw gets stripped at the very tip - the first or second thread.
Today it was one of the four that hold the chassis in a Crate BV120, but I recall this happening on a bunch of newer amps.
Is there some nut and screw technique taught in a class that I skipped during college?
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Being an old auto mechanic..... don't know what you refer to us in the US, but I learnt a very, very long time ago to start all the screws by hand and leave them loose so you can move parts around easily until all screws arel started, then tighten them up using whatever relevant tool is required, that way no threads strip or cross.
Kosta
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Being an old auto mechanic..... don't know what you refer to us in the US, but I learnt a very, very long time ago to start all the screws by hand and leave them loose so you can move parts around easily until all screws arel started, then tighten them up using whatever relevant tool is required, that way no threads strip or cross.
Kosta
Exactly . I always get the screws started and many times you have to turn them counter clockwise first to get the threads to line up and then one at time until they are all easy to turn by hand then bring then up each a bit at a time until they are all close to tight then x tigthen then . if you feel just a bit of a bind back them out and start over . It's the first few threads that make all the difference in getting them lined up with the nut threads.
At times it does pay to enlarge the holes they go through in the cab so there is no pressure against them and they start much easier .
I had a pignose GV-40 that had these and it was always a difficult thing so I drilled out the holes through the tolex and top cab wood just a bit larger to prevent the pressure against to side of the screws and then they lined up much easier.
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A little WD-40 or machine oil helps too. But I always use my fingers to tighten things first then the proper size screw driver, only use the electric screw driver once everything is ready to go. I learned the hard way how soft the metal parts are these days. Not so in the 50-60's, I noticed things start to change in the quality of the metal itself and the parts. It's cheaper to use soft screws, nuts and bolts and those clips that clip on the chassis for the chassis screws. I use stainless steel screws, bolts, nuts and other parts on my builds now, I have over tightened and broke off enough stuff to learn it pays to spend a little extra for the stainless steel stuff.
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If they are really a problem, I have a selection of taps to run in a little bit to be sure the threads are OK in the nuts.
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Thanks for the suggestions ... I'll have to go back to the old-fashioned method (by hand)!
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Being an old auto mechanic..... don't know what you refer to us in the US, but I learnt a very, very long time ago to start all the screws by hand and leave them loose so you can move parts around easily until all screws arel started, then tighten them up using whatever relevant tool is required, that way no threads strip or cross.
Kosta
Exactly . I always get the screws started and many times you have to turn them counter clockwise first to get the threads to line up and then one at time until they are all easy to turn by hand then bring then up each a bit at a time until they are all close to tight then x tigthen then . if you feel just a bit of a bind back them out and start over . It's the first few threads that make all the difference in getting them lined up with the nut threads.
yep, thats how ya do it.
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Why do cage screws strip at the tip?
Because the tip goes in 1st!!! (If the rear went in first, then it would strip; but then it wouldn't be the rear.)
EDIT: OK maybe once again I'm taking this TOO literally. Yes, it strips because of mis-alignment; then forcing it. Sometimes force results in a proper re-alignment; but you can't count on that.
Here's a neat trick my father taught me to shorten a bolt. Sawing or snipping it often mars the threads. So before you shorten it, thread a nut on first, past the cut-off point; then cut the bolt. Then remove the nut. Unscrewing the nut will heal the damaged threads!
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jjasilli,
that method works extremely well and I've been doing it for years with the only difference being that I grind or file a taper on the tip of the bolt before undoing the nut. By giving it a taper, the bolt locates in the nut much easier.
Kosta
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JJ & Tinkerer are on the right track. I usually use an abrasive blade to cut the screw to the proper length (without the nut). Depending on how precise I want the fit, determines the amount of time I spend putting a taper back on the last two threads, and grinding the lead-in on the final thread. THAT is what fewks up the cage/hurricane nut. Check the business end of the bolt even if you don't cut it- I've seen plenty of bolts and screws with buggered threads straight out of the box, especially if they are imported from a certain communist totalitarian dictatorship (and not labeled as such so I could avoid them altogether)! I don't file usually, I just turn the bolt backwards against the side of the cutoff wheel veeerry keeerfullly :angel (cause if'n youse aint careful and such, the wheel might catch the hut and send it your way at terminal velocity along with shards of the wheel.)
I also run a tap through the hurricane nut (after glueing it in place with PL) because I know if I don't, that will invite some PL to migrate into the threads and cause much wailing and gnashing of teeth.) PL is about the best thing for gluing wood and things to wood. It foams up to fill gaps and hide imperfections in the joinery.