Why do die grinders skip

Im enlarging some 1/4" holes in the lower inside door portion of a Roadmaster to fit one of my rust proof wands in. all goes fine then several minutes in the die grinder starts bucking. This is nothing new had it many times over the years. I use those endless assortment of carbide end mills of different shapes. In this case started out fine then after a bit the bucking began,. ive tried changing direction and lighter cuts heavier cuts, have a very tight grip of the beast but still wants to skip and bang and rattle all over the place. I dont see any clogging either. Im doing light steel whatever thickness they used on these 96 bodies. It used to happen with thicker material as well though so. Sorry if this is in the wrong place, move me if there is a column for bucking die grinders

It is probably because the edges of the sheet metal hole are impacting the grinding medium on the wheel and bending instead of cutting. Wouldn't a drill be a better tool for enlarging holes in sheet metal.

The cut on the burr contributes to this. I have a bit that has a double cut surface that won’t walk and chatter. The same shape bit with a mostly spiral cut chatters terribly.
Joe

I wonder if air or electric make a difference I would expect a electric tool to have more momentum and not skip as much.
Bill D.

Thanks,

finished it with the air one and it skipped all over but done. I have two electric ones, one a pro tool from a tool and die maker but no speed control then a cheap one I got for one job and it has a speed control but never worked right from new. I likely have some of those cutters that have cutting in both directions. A drill was not a good option there is a 1/4 Slot with a round end, im enlarging the end so say 3/8" on another car i did it with a countersink. Die grinder not as pretty, bouncing around doesnt help.

I think I know what you’re talking about. Does it tend to happen more climb cutting or conventional? I’m guessing this is all done freehand?

yeah free hand always. Have a number of them different angles, this not perfect, door wanting to move away. Sitting on the ground etc. Got enough enlarged to get the wand in rotate it around. I make the wands out of quarter inch brake line then curve them and crimp the end a bit but open enough to make a fan. I dont think it skips the same if you go backwards, it also seemed to start out fine then start bucking. I know this from past stuff just never figured out what exactly causes it. Ive gone slow, ive sped up, ive done very light cuts, ive leaned on it, always seem to end up with it kicking then it wants to bounce around.

Why do die grinders skip?

Because they are happy?

Attachment 397470

Harmonics. Try increasing/decreasing your hand pressure on the tool, the rpm of the tool, the angle of the dangle, etc etc etc. The more, and more often, you change things up, the less time there is for harmonic motions to become harmonic and develop the amplitude to chatter. This chattering is the result of a feedback loop. You want to limit, if not eliminate, the feedback that makes it worsen.

In some ways, it's like driving down a dirt road with a washboard surface: It might be brutal at 40 mph, but get it up over 85 and she smooths out like glass! Reason: The springs/shocks/etc in your suspension can't move up and down that fast, so they float...

Step bit?..............

best I got was going in do some then back off then go in again. Hey Van used work with bands and the thing was why does my amp hum, cause it doesnt know the words.

Its done for now but next time will think about it more, need to drill a piece of wood ouit and organize all the bits. Never used a step bit think that is how they drill them for the rust proof plugs. there is metal behind this very close that is the outside of the door.

The reason for the skipping of the die grinder is because as you go around the hole that you are enlarging, the cutter is going from a conventional cut into a climbing cut.
There is more pressure between the cutter and the doors hole when climb cutting As the cutter enters the climbing cut side of the hole it is grabbed, because the pressure has subsided and the cutter is pulled into the steel of the hole.
The reason it grabs is because you are going around the periphery of the hole 360 degrees and you are climb cutting for 180* and conventional cutting for the other 180*.

Forget what I said about the climb cutting for 180 degrees and conventional cutting for 180 degrees. I was wrong in this case.
Probably the cutter is skipping because as you finish removing some metal when you re going around in a circle the die grinder lurches forward because you are pushing the die grinder in that direction and there is no more metal to hold it back. Thus it begins to climb.
The only way around this is to hold the die grinder in the one hand, and put your other hand over the hand holding the die grinder to steady the grinder and to hold it back as you are cutting to keep it from grabbing, or climb cutting.