Things that go bang in the shopIf you cut, grind, weld, or generally beat on metal, odds are you've had something happen that really got your attention-one of those sudden, unexpected wake-up calls that reminded you to put on your safety glasses or not weld in your shorts. We recently had such an incident.
We were happily grinding away on a newly constructed creation when this reinforced grinding wheel let go-and it let go with a vengeance. Our shop has 16-foot walls and the peak of the roof is somewhat higher, yet a chunk of the exploding grinding stone was still able to put a hole in the metal roof! Look closely at the photo above and you'll see the puncture between the skylights.
As with most near disasters, we were our own worst enemy. We make it a habit to disconnect the hose from any air tools when they're not in use for a variety of reasons, not the least of which is that it keeps us from tripping over the hose and bouncing an expensive tool off the floor. Another practice we adhere to is throwing the wheel away when a grinder with a rigid disc is dropped, no matter how old it is, and installing a new one. But, somehow we violated not one but both of our self-imposed rules; after getting tangled in the hose, pulling the grinder off the workbench, and then watching it hit the deck, we got sidetracked and forgot to change the disc. But, after hearing a chunk of the fractured disc whiz by our ears and seeing the hole it put in the roof, we suddenly remembered. The moral to the story is: No act of stupidity goes unpunished.
The truth is, common sense is the best protection against hurting yourself, but here are a few things to keep in mind when using a grinder of any type:
1. Wear safety glasses or a face shield.2. Wear long leather gloves to protect hands and forearms.3. Wear hearing protection.4. Position the grinder so sparks and grit thrown off will not hit you, anyone else,or end up some place inappropriate (like inside an engine being assembled).5. Make sure the material being ground is well secured.6. Never grind flammable materials or combustible gases in the area.7. Replace the grinding disc when it becomes worn to half its original diameter.8. Make sure the abrasive stone/disc has the proper rpm rating for the grinder used and is replaced if damaged.9. Position yourself so as not to be in the line of flight if a grinding disc does come apart.10. Cover painted surfaces and especially any glass (grinding debris will make a mess of windows) if there are any cars near your working area.
When 12-Volts is six too manyQ.I've been a subscriber since '79 and I'm still working on the same project! I have a question on gauges in my '31 Chevy. How can I use these six-volt gauges with 12-volts? Add resistance in some configuration, in line, shunt to ground, capacitor across the meter movement, what? I have saved all my issues, so maybe you can tell me of a past article I can look up. Great column and a great magazine.Robert DowdallOsterville, MA
A.It's nice to hear from someone who has been working on a project for as long as some of ours have been around, but let's get to the point.
First off, not all instruments recognize voltage. An amp meter is a good example; it only recognizes the amount of current passing through it. However, keep in mind that capacity can be an issue. Most early examples were only capable of handling 30 to 40 amps-anything more than that will cause the gauge to fail. Note the 30-0-03 or 50-0-50 on the face of the meter and don't exceed it.
The simplest way to reduce 12-volts to six on gauges that are voltage sensitive is with a resister. However, according to Ohm's Law, a resistor reduces voltage by an amount proportional to the value of the resistor times the current flow through the resistor-the formula is: V (voltage) = I (current) x R (resistance). But the problem is that most electrical gauges use senders that vary in resistance to make the needle on the gauge deflect. In other words, a gas gauge may draw more current when the tank is full than it does when it's empty because the sender varies the resistance in the circuit. More current through the gauge makes the needle move to the full mark; as the gas level drops, the float on the sender moves, thus changing the resistance of the sender. More resistance means less current flow through the gauge, so the needle moves away from the full mark. If a resistor is added to the supply side of the gauge, the voltage provided would vary as the sender changes the resistance in the circuit, and that will result in inaccurate readings.