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2011년 7월 23일 토요일

카메라 수리 tips - 나사들

카메라 수리 tips - 나사들






What do you do if you break a screw? Usually the main problem is in removing the threaded shaft of the screw from the mechanism plate, camera body, or other part into which the screw fits. If there's a portion of the screw thread extending above the part, you may be able to cut a screw slot. Use a screw-slotting file to cut a screw slot in the broken end of the screw thread. You can then use a screwdriver to remove the threaded shaft. But quite often the screw thread is flush with the part.

First, try "tickling" out the screw thread. Push your closed tweezers against the outer circumference of the screw thread and push the screw thread in a counterclockwise direction (clockwise for a left-hand thread). Continue trying to push the screw thread in the unscrewing direction a little at a time. When there's a sufficient portion of the screw thread extending from the part, you can grab the screw thread with your needle-nose pliers. Then continue turning the screw thread until you can remove it from the part.

If the screw thread is too tight, the tickling technique won't work. You may then have to drill out the screw thread. But that's dangerous. The screw thread may be harder than the mechanism plate, camera body, or other part.Often the screw is steel and it goes into a brass part. Most drill bits cut in the screw-tightening direction. So, as you attempt to drill out the thread, you're actually tightening the screw. Fortunately, you can get special drill bits that cut in the opposite direction that loosens the screw. When you turn the drill in the loosening direction, you'll often find that the drill bit grabs the screw thread. The drill then unscrews the thread rather than actually drilling it out. You can get the special drill bits from Fargo Enterprises (left-hand drill bits).

Here's another concern you'll sometimes encounter regarding screws, which is locating (or shoulder) screws. A locating screw has a shoulder, a section without screw threads that passes into a hole in the part held by that screw. The shoulder serves to precisely position the part being held, perhaps a mechanism plate where the position is critical. Some of the screws holding the part may be locating screws while others are regular screws. If you know in advance which screws are locating screws, remove those screws last. Why? Tightening the other screws tends to shift the part against the shoulders of the locating screws. The locating screws may then be very tight; they'll be easier to remove after you take out the other screws. But replace the locating screws first. The locating screws then serve their purpose to properly position the part.

OTHER THREADED PARTS

1. Threaded parts, such as retaining rings and lens barrels, may not want to start properly. Be very careful to avoid cross-threading the parts, the finer the screw threads, the more easily you can cross-thread the parts. Here’s one   reassembly tip that usually works: start by turning the threaded part in the opposite direction (the direction for unscrewing the part) while applying slight downward pressure. For example, suppose you need to turn a part in a clockwise direction to screw it ont  o another part. Start by turning the part in a counterclockwise direction. When you hear (or feel) a slight “click,” you’ve found the starting thread. Now turn the threaded part in the proper direction (clockwise in our example).

2. Most threaded parts have right-hand threads you turn the screw, retaining ring, etc. in a counterclockwise direction to remove it and in a clockwise direction to install in. But be on the lookout for left-hand threads. If a part won’t unscrew by turning it counterclockwise, you may have to turn it clockwise for removal. Left-hand threads may be used in cases where the normal operation of the part may cause it to unscrew. For example, you turn the wind lever in a counterclockwise direction to cock the shutter that’s the direction that may unscrew a right-hand thread. It’s therefore not unusual to use left-hand threads around the wind mechanism, such as the cap screw that holds the wind lever. Try to avoid using excessive pressure when removing a threaded part if you’re turning the part in the wrong direction, you may break a screw or strip screw threads. With antiques and even with modern cameras that are a few years old, you can’t always get replacement parts.

3. If a ring has two slots or two holes spaced 180°apart, it's most likely a threaded retaining ring. Here you should have a spanner wrench like the one        pictured at the right. Spanner wrenches come with straight tips for slots and pointed tips for holes; the spanner wrench shown at the right accepts interchangeable tips.
For example, in folding cameras a retaining ring usually holds the shutter to the lens standard. You can reach the retaining ring by collapsing the bellows (storage position) and opening the camera back as in the photo at the left. In this example, use a spanner wrench with straight tips to unscrew the retaining ring. The illustration below of the front of the Miranda shows a situation where you want the pointed tips unscrewing the retaining screw that holds the self-timer cocking lever.
It's sometimes difficult to reach a retaining ring that holds a shutter. There's not much room when you're working through the back of the focal-plane aperture. However, you can reposition the tips in the versatile spanner shown above; this flexibility allows you to reach and unscrew most retaining rings. In illustration Abelow right, we've flipped the tips 180° from the illustration above; a spring-loaded ball locks the tips in place. Or you can tilt the tips as shown in illustration B below to change the angle to reach the particular retaining ring within the limited space for the spanner. Careful: Since the tips in B are no longer locked firmly in place, be very careful to avoid slipping. If you slip, the spanner-wrench tip could scratch the retaining ring or, worse yet, the rear lens element.

www.in-fotech.com

(2007.10.05)

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