How do I know a cutter is still sharp?

Yeeaap. That endmill is hosed. Put on one of my brand new endmills (3/8 shank 1/2 normal 4-flute), went through it like butter.

Kinda disappointing for $30, but then again I was abusing it. I'll save up for a nice endmill. Annnd also try to use endmills properly. I touched up the flycutter and managed to get it to take off 14 thou in one pass, although that's probably the limit. It cut nicely at 10 thou.

I'm also aware that I can't expect huge amounts of materials to come off, but there is a difference between a finishing pass and "mass removal" - that's more what I was asking about. I only have a hacksaw for steel, though kinda seems like I need to also save up for a porta-band. :)


Thanks everyone!
 
End mills can be reground to be sharp again, but the diameter will be smaller than originally, which is not an issue with most work. The shanks are also useful for making cutters, center points, and other tools for the shop. Don't throw it away...
 
I'm a little late to the game here but, in mild steel, I generally expect to get about 90 to 120 minutes out of a HSS end mill, cobalt roughers maybe a bit more. Solid carbide endmills can last a few hours under perfect conditions. It is better to run a rougher full depth if your machine will take the load.

For your machine, using smaller end mills, spinning faster, and increasing the feed rate might be a more efficient material removal strategy. Rather than buy expensive endmills, for utility work buy the less expensive ones from ebay something like this https://www.ebay.com/itm/5X-HSS-CNC...057.m570.l1313.TR12.TRC2.A0.H0.Xend+mill.TRS0
 
What RPM were you running with the rougher? With a 3/8" endmill cutting mild steel, I would typically use around 900 RPM. I ate a lot of endmills before I learned about proper cutting speeds.
 
If you watch ebay carefully you can sometimes score a fistful of good endmills, like from an estate sale. For 30$ I scored about 300$ worth of great ones, many brand new. There's a bit of luck involved, but it's a good way to tool up, especially in the beginning when you are on a tight budget, and if you zork a couple, no big loss
mark
 
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@Hawkeye it was around 1200rpm I think - my mill doesn't have an RPM thingy. Just a 0-2500rpm dial. It's on my list to buy a handheld RPM gauge (the one that works with reflective strips) so I can be more accurate.

@JimDawson Thanks, I'll check those out. Having a lifespan measured in minutes is bananas, I had zero clue it was that short. Definitely makes me re-think the prep work phase. I think a good set of files is in my future...

@markba633csi Estate sales are kind of a no-go for me, usually require a lot of time that sits either in work or family slots, but good point. I used to get stuff from garage sales, but it's uncommon to find machining things there.
 
Bob Korves said:
End mills can be reground to be sharp again, but the diameter will be smaller than originally, which is not an issue with most work.
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If only .01" to .015" of the end mill is being used, I would just have the end geometry reground.

One thing that I do with end mills in that condition is too lightly grind or stone a small bevel on the cutter tips. This can be a "by eye" operation. They work well for roughing operations.

When inspecting end mills for wear, I look for a glint of reflected light from the cutting edge. Any glint means a worn end mill.
 
I meant specifically Ebay for the estate sale thingy, but yes it takes time to watch and bid
 
I did some more work squaring stuff up last night. I have come to terms with my flycutter. Pretty sure with some more work to the geometry and sharpening it can take a bit more of a cut, so this will become my go-to "remove material off a large flat surface" tool. I experimented with using endmills sides instead of tips (how come not called a sidemill? :) ) and got some really nice surface finishes.

My simple brain is realizing more and more how utterly critical speeds and feeds are for proper cutting. So I am putting my projects on hold to get my power feed done, plus ordering that RPM meter, plus finishing up my DRO install.

Thanks again, everyone!
 
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