[slashmaster]

I was just trying to trim the top of a firewood splitting wedge with a 4 flute 3/4" HSS endmill. I believe I was doing something like 400-500 rpm and every once in a while I would see a little spark. Does that mean too much rpm?

[SCzEngrgGroup]

I was just trying to trim the top of a firewood splitting wedge with a 4 flute 3/4" HSS endmill. I believe I was doing something like 400-500 rpm and every once in a while I would see a little spark. Does that mean too much rpm?

That means you hit something very hard. The metal is probably not the best, and inconsistent. Probably won't be much left of that endmill by the time you're done. Some kind of grinder or sander would work better. I've sharpened blades from a wood chipper using a disc sander - worked really well.

[MattTheNoob]

In either case, watch your heat buildup if you are trying to maintain the temper of the steel. If you see the little "rainbow" colors next to your cut or grind, then you are changing the temper of the steel.

[kweierbach]

when you get sparks like that the sharp edge is gone and you have a very ragged edge left. To machine something like this I would use a carbide tool at those rpm's

[slashmaster]

when you get sparks like that the sharp edge is gone and you have a very ragged edge left. To machine something like this I would use a carbide tool at those rpm's

How many rpm should I run a 3/4" HSS through steel then? Anyone know an online chart?

[hoss2006]

How many rpm should I run a 3/4" HSS through steel then? Anyone know an online chart?

calcs and charts here, 400-500 rpm is good.
Hoss

[escott76]

How many rpm should I run a 3/4" HSS through steel then? Anyone know an online chart?

You are missing key information, like what specifically kind of steel. I know you have talked about (for some reason) cutting a fireplace wedge. This is harder steel, so you have to adjust for that. As others have said, carbide is a better bet, you are going to kill an HSS tool quickly doing what you are doing. Just because a chart says "steel" doesn't mean it applies to everything that is a combo of iron and carbon, you have to adjust for specific material.

[hoss2006]

Slash, If you're thinking it may be hardened, since you asked how to check hardness in your other thread,
the files mentioned could tell you and you'd need to move to the left on the cobalt chart and drop the rpm even lower.
Hoss

[USMCPOP]

Trimming the top of a hardened splitting wedge for what ???