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Nice that you are ahead of me on the hot knife idea.

Even nicer that you are way ahead of me on the safety aspects

:)

For that use a dremel with cut off circular bits. It should be easy. It should be easy to do with a file as well, but time consuming

In this case I would have used a flat head soldering iron, it can make precise cuts \ holes very easily. I have a separate one for this kind of jobs or small plastic welding.

If you use the grinder at low speeds, be careful not to press too hard to speed up the job. Extra torque will just loosen the steel shank (happened to me a few times) and ruin the bit.

At high speeds; just as in a dental drill; the cut at each rotation is extremely small (hence low load), it is just the very high speed which eats through the material fast.

A sharp wood chisel (1/2" or 1/4") should do the job, as long as you have a vice in which you can hold the plastic part. Don't hammer with a mallet, as that might crack the part. Instead, hold the chisel and apply firm pressure to cut wafers out of the material to be removed. Be patient. If you don't have chisels, get some 1" wide saw blade pieces from junk shops, and have a workshop grind them down for you.

The stone grinder cone will just melt the plastic and leave it there, instead of removing it. If you have a high speed rotary tool like Dremel, you can use a milling cutter.

Brilliant idea! Never thought of the ubiquitous chisel! I have one but that’s a 2 inch I had bought for some woodwork. Let me see if I can source a ¼” chisel from somewhere.

Problem with chisels are, sharpening. I’ve only sharpened it once when I had a carpenter working at my apartment complex. He did it on his sharpening bench. How do we sharpen them otherwise? Say, at home?

Visit a hardware shop and ask for a sharpening stone. Even today, most of the carpenters use this including myself at home.

Put some water droplets on the stone and rub the chisel and would be a good exercise for your arms too :).

Else, a workshop fellow with a grinding machine should help but then he needs to be very careful in ensuring that he isn't sharpening it way too much that the metal is super think at the edge good enough to break.

A sharpening stone is the best solution. The tricky part is holding the chisel steady at the correct angle during grinding.

I double-grind the edge of my wood-chisels.
* First I hold it at 15deg (approx) to get a neat rectangle at the chisel's end with the rough side of the stone (it has 2 different grades in one), with a clean sharp edge (no waviness). Long, slow firm strokes - I keep the stone in a shallow plastic box in water
* Once every few minutes, I reverse the blade, hold it flat and remove the burr that develops on the opposite side. Appearance of the burr is a sign that you are getting a sharp edge; if not, keep grinding
* After that, it is a couple of minutes with the smoother side of the stone with the chisel held at 30deg. This produces a bevel at the edge - a mm or so wide - which enables the chisel to hold sharpness longer!

All the carpenters I have used in Bangalore sharpen their chisels on a planed wood piece with stone powder. They carry a stone which looks like clumps of coarse river sand, pink in color. They powder small pieces with a hammer and use the powder. Never liked their method, which I assume is centuries old. Most of these carpenters can't get a joint right the first time. Their least count is 1 soot / nool / dara / whatever (~3.x mm), and they can't work to millimeter specs. :mad:

Do that ONLY when the edge has become a rounded blunt edge. Otherwise, a person at a workshop grinding machine will do more harm than good to the edge. Metal working tools are fine with those grinding wheels, since they are heat treated afterwards. Also, their cutting edge will not cut paper like butter - which is the standard to test sharpness of wood working chisels. Some grinders have a slow speed setting, which should be used with wood working chisels, and frequent dipping in water to keep the edge cool.

Best is the guy who has a wheel powered grinder behind his cycle seat, and goes around calling "chakku chhuriyan tez karalo" (much like what Jaya Bhaduri sang in Zanjeer :)). They have a better feel for it. They also carry pieces of 1" wide saw blades to craft custom knives out of.

Bought a RC Helicopter for my son and within a day or two, the battery in the copter went kaput. Thinking of replacing it. Its a Li-Poly 250mAh 3.7v
Should I source the same spec battery or the mAh can be on the higher side. On eBay, I could see batteries with 300-350mAh 3.7v. Can these be used?

And for my earlier requests on removing crayon marks in the wall was accomplished by our pidilite made stainoff sponge. It was available in Hypercity, Rs.50 a piece. But the life of it is very minimal. I could just rub off the marks which were half a ft long, not more than that. Need to source more to clean my walls.

Yes you can use them. No problem. Charging time will be longer thats all. As long as the battery fits in the slot properly, you should be fine.

Charging time would be longer as well as the battery backup if i am not wrong? So the copter works only with 3.7v and the mAh can be any.

Yes backup will also be longer.

Yes you can use any capacity battery as long as its 3.7V.

Option 1) Get an End Mill. A cheap HSS one is good enough for plastic. Hold in dremel and slice away the plastic.

Option 2) Get a cheap soldering iron. Use it to melt and cut and shape the plastic as per your requirements.

Normally the plastic melts (assuming thermoplastics rather than thermosets) and clogs up the grinding wheel. Like trying to grind aluminium.

Use a coarse burr.

Regards
Sutripta

I usually use diamond coated discs on a mandrel with my dremel clone. Works very well on plastics and acrylics.

Like this one: