Given a bench grinder which did not work. How to test/fix?
I have not tried to run the grinder. I have removed all attached components, wheels, guards etc and have the electric motor case and wiring intact. I disconnected and tested the switch - OK It has a capacitor (with 2 red conductors) labelled: CBB60....7mF +/- 5% 250 VAC 50/60 Hz E230600 There are 3 conductors exiting from the motor case: Black joins with one of the red from the capacitor Yellow goes to switch Red goes to join with white (from the power cable) and the second red from the capacitor. The cable feed ground (green) was disconnected from the crimp ring screwed into the case and the power cable black goes to the switch. How can I test the motor other than by attaching a new power cord, reconnecting the ground, plugging it in and switching it on? Could the problem be the detached ground or the capacitor or the motor. The catalogue (Princess Auto Power Fist) describes it as a capacitor run induction motor. What does this mean? The motor shaft spins freely by hand with no detected resistance. Grinder specs - Made in China: E237800 cULus listed 10CX 8"...1/2 HP...120V...1.2 no load amps 3560 RPM 3/4" shaft 5/8" wide grinding wheels. I cannot provide more details except, it is bright yellow! Thank you, Jenni.
Re: Given a bench grinder which did not work. How to...
I cleaned all the wiring connectors etc and used a 4-way extension cord with an i/o switch and thermal/arc breaker surge protector thingy. I had a piece of thick cable with a molded three prong plug which I had removed from a dead paper shredder (I think??) and connected the ground to the case (previously not connected) the black to the black and white to the white. I taped the connections and plugged the test cable into the extension thingy with its switch off and plugged it into the wall outlet. Then, with the grinder switch on, I gingerly switched on the extension thingy and the grinder (sans all moving parts) ie just the motor case and spindle (held securely in the B&D workmate) and viola(!) it worked fine and built up to very fast. I switched off the grinder switch and the motor slowed, taking an age to come to rest. Then, I fitted a grinding wheel on the left hand thread end, tightened everything and retested, using the grinder switch to start it and it spun really fast. Soooo, I guess the secure ground is an essential feature of a capacitor induction motor. I checked some old furnace motors that were "maturing" in the basement and they had no capacitor but only 2 wires... I am now trying to remember which parts came off last and put it all back together. I plan to test it each time I put a part back...just in case. I hate it when you fix something on the bench and when rebuilt, it won't work...don't ask about the electric starter on the snowblower..not a happy puppy! Please, pretty please and then some, do tell me if my "fix" is wrong and I could risk all kinds of nastiness. Thanks, Jenni.
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A murphy, A bench grinder must be used with a lot of caution and respect while using this equipment, Check the attached links,instruction and guides, Good luck work safe.
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A grinder that growls when you start it usually means the bearings are worn out or very dry. You can try a little WD40 spray in the bearing area and if that seems to work use some heavier oil to keep it running. It's good to oil the bearings every so often I find.
Buffing takes a lot of power, maybe a lot more than you expected. Bench grinders come in lots of sizes and power levels. If you have a small, or inexpensive, or fractional hp grinder, it simply isn't up to the task. By the way, rpm is also a big factor. A grinder, especially a smaller one, turns at a pretty high rpm. A given hp rating at a high rpm gives less torque than the same hp rating on a different grinder with a lower rpm. On your grinder you might get away with smaller diameter and/or narrower buffing wheels that you use very lightly. Otherwise, your grinder just isn't going to cut it.
Assuming your local tech confirms that your bench grinder tests ok. The problem is probably that the grinder draws too much current for the RCD and is therefore detected as an earth leakage. High amperage devices often do that. Your best bet would be to plug it in to a socket which is on a non-rcd circuit. Maybe you have an RCD on the whole house though?
I would start with returning the grinder and trying a different brand with a lower amperage/wattage rating. If that doesnt work, I would call an electrician to discuss installing a different RCD or running a separate circuit for your power tools.
Yes, the wobble can be fixed. First, remove both wheels and check the shaft bearings/bushings for wear. Make certain the grinder is unplugged and mounted securely. Try moving the shafts up, down side to side; there should be little or no noticeable movement. If there is movement it is a major(time and money) problem. I'm not familiar with what the shafts ride on. It could be, ball bearings(the best-long lasting, least friction, most accurate, but expensive), sealed bearings(almost as good as ball bearings, with many of the same attributes) and bushings(least expensive to produce and fit and cause the most friction. If excessive up,down side to side movement is present a decision must be made as to how much money/time you want to invest. If the shaft exhibit little movement; check if the shaft is running true/straight. Turn the grinder by hand while observing the shaft for bends. If none are seen by eye use a magnetic base micrometer to check run out(deviation from straight). If a micrometer isn't available; bend a short length of wire(coat hanger works nicely) with a small hook on one end and then put a pointer end on the other. Put a screw thought the end with the hook to mount it to the base of the grinder. Then bend the pointed end so it just touches the shaft. Rotate the shaft and notice if the distance changes between the point of the wire and the grinder shaft. Repeat for the other side. A couple of thousands won't hurt. However, any more and the cost effectiveness of tearing the grinder apart straightening the shaft must be considered. The most common cause of grinding wheel wobble is the wheels becoming out of true and/or unbalanced. This is easily cured with a wheel dressiing tool. The tool grinds the wheels in place. By gringing the wheels on the grinder they balance the wheel, true the wheel to the shaft and clean it of imbeded soft materials, aluminum, wood and so forth.
I would take a look at the wheels or wire brush before I went any further. Then I would remove both and just run the grinder to see if still vibrates. But usually one or both of the wheels are out of round.
You should be able to hold the grinding wheel with a pair of leather gloves on your hands and lossen the bolt. Look very carefully at the threads to make sure you are trying to lossen and not tighten. Some are left handed threads on bench grinders.
Goggles or safety glasses need to be worn to protect the operator's eyes from the sparks and metal filings that result. Depending on the workpiece and time of exposure, hearing protection may also be required, the dust produced is also potentially hazardous. The toolrest (or workrest) should be mounted slightly below the center of the grinding wheel with less than 3 mm clearance from the wheel. This prevents the work from jamming between the toolrest and the wheel. Grinding wheels designed for steel should not be used for grinding softer metals, like aluminium. The soft metal gets lodged in the pores of the wheel and expand with the heat of grinding. This can dislodge pieces of the grinding wheel. Wire brushes require particular attention for the safety of the operator and bystanders as the metal wires may become dangerous projectiles as they could bind with the object being brushed and so throw it away with great energy. The machine needs to be securely mounted to a pillar or a bench to be used safely and effectively, often with an emergency stop switch or pedal fitted close by the machine, for use in emergencies.
Grinding is the fastest way to deburr a sharp corner or dress the end of threaded rod or bar stock that's been cut to length. Fit a grinder with a wire wheel, and you have a handy tool for removing rust. Then switch to a buffing wheel and you're ready to polish metal to a mirrorlike sheen. But for most of us, grinders are essential for shaping and sharpening hardened tool steel and high-speed steel.