Bottlehead Forum
General Category => General Discussion => Topic started by: Doc B. on June 07, 2016, 01:20:25 PM
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I used to post tips based upon recent repairs that had come across the bench. As I am temporarily doing the repairs that come in, I thought I might resurrect this for a bit. Today's topic
SCREWING
Based upon several of the repairs that have come in lately it occurs to me that we have emphasized soldering skills so much that builders have abandoned any knowledge acquired of how a nut and screw work. A screw and nut are called fasteners. That is because they are intended to fasten things together. This is done by putting the nut on the screw thread and then tightening the nut snugly. Now, while most folks seem to comprehend the first part, there seems to be a general lack of knowledge of how to do the second part. The trick is in actually tightening the nut. Grab the nut with pliers or the proper size socket and tighten the screw into it. It's a pretty miraculous thing that happens when you do. Instead of the screw and nut simply being a wobbly hanger which falls apart in shipping, when the nut is tightened the screw and nut actually FASTEN the part to the chassis and stay that way.
In the best cases all that will happen if you don't tighten down your hardware is you will see me posting this kind of rant after I have tightened 15 or 20 loose screws on your amp. In the worst case you will be getting an email with a photo from me because your plate choke and output transformer fell off in shipping and broke your base, made a big gouge in the process, scraped your meticulous paint job and ripped out the connecting wires.
So please take a little extra time and pride in your work and tighten those nuts down as you go. You don't have to Herc them until they snap the screw, but make sure they are snug enough against the lock washer that the amp can't shake apart on a UPS truck ride across the country.
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... or dropping four feet off the conveyor belt to a concrete floor while being loading into said UPS truck...
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I had a friend call over to replace a rear differential that was making a clunking noise. I only had to drive the car 20 feet to know what i was hearing was not a differential but a wheel about to fall off. Tightened up the wheel nuts and voila, no more noise.
When he asked "what should i have torqued them up to" i could only reply "enough so they don't fall off foot pounds"
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There is German word for that, goodntighten ;)
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Next rant -
The rubber feet supplied with the wood bases are not optional. They are there to create an opening for airflow under the chassis. In some cases parts will fail if the base sits directly on the shelf with no space for air circulation.
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<rant>
Over the years I have worked for a number of companies building machinery for manufacturing industry, so they are all either out-and-out special purpose one-offs or at least built to order. All of these are "hand-built" but unfortunately this often appears to be "without the aid of tools". It seems that just as soon as you have a technician working for you who understands the function of a fastener then he (almost universally) retires and you are left with an apprentice who doesn't even appreciate the importance of turning up in the morning, never mind actually doing the job properly. Loose fasteners have been the bane of my life for the last 40 years...
It isn't just amp kits, Doc.
</rant>
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As to tightening... I'm always worried about OVERtightening. Put the speaker binding posts on the Stereomour today and felt like I could just keep turning that wrench. It's tight, sure. But when is it the right tight?
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As for tightening...hold the screw/bolt, turn the nut. This causes the lock washer to bite the nut and the surface so it can do its job...lock the two together.
Get a set of nut drivers! I can't think of anything on these kits that requires a wrench.
It's tight when the nut doesn't want to turn and the parts being held won't move. It's easy to break or strip the threads on these small screws. The best way to learn is to break some.
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There's always torque wrenches 8)
Dave