[taiwanluthiers]

I've been milling pre hard 4140 steel. Carbide machines it readily but I also found even with 4 flute end mills, it's dulling the cutting edge (mostly the ends and the corners) rather readily. I have been touching them off with a dremel diamond wheel, it's cheap and it sharpens the cutter to a serviceable edge but every so often I would need to touch off again. Eventually it messes with the geometry but I can still maintain a good cutting edge...

Are there better tools for milling pre hard 4140 steel? It machines with HSS but dulls it even faster, but it still dulls carbide. It doesn't dull the flutes so much but it dulls the ends much faster and that often messes up the machining characteristics when the ends get dull.

[DubMFG]

Its the sort of thing you have to come to expect with milling hardened materials. This is where inserted tools come in very handy, if applicable. Else, find your local grinding house and see what their regrind costs are. Up here in Canuckistan our local vendor charges $7.15 in Canadian Pesos for a 1/4" regrind, and if you buy the tool from them in the first place the first regrind is free.

[taiwanluthiers]

Insert tools are great if I need to surface mill but I already use fly cutters for that. Carbide lathe tool bits are cheap and easy to sharpen. It doesn't help me if I need to mill a 1/4" slot however.. and even those inserts cost a lot, like over 10 dollars per insert.

[DubMFG]

Consumables are what they are: Consumable. Just part of making parts that you have to deal with. I would advise you to do the math: How much is your time dealing with endmills worth against the cost of purchasing new tools/regrind/inserts instead.

[taiwanluthiers]

My time machining isn't worth much, it's a hobby and not a job so there's no cost per hour to deal with. However regrinds are only worth it for larger end mills 1/2" or over...

I reground the ends with a diamond wheel and it works though the edge doesn't seem to last as long as a fresh regrind.

[DubMFG]

Its not just your time machining, its the time that you could be NOT machining that's valuable. If taking the opportunity cost of sharpening your own endmills is worth it, then thats your best bet.

[taiwanluthiers]

Well, I get 10 dollars an hour working, but buying new inserts and end mills cost more than that. Basically unless I'm actually getting paid to machine, any money I spend is basically a cost, not savings.

It takes me about 10 minutes to remove the slightly dull end mill, touch it off on the dremel, and go back to machining.

[engnerdan]

Look for an end mill with a corner radius, they will hold an edge much longer. If you need to end the cut with a square corner then switch to a square corner end mill to finish the cut. I didn't see any description of what flavor end mills you are using.

Check out these end mills if you are not using a Variable Helix/Variable Flute end mill. These things work wonders in pre-hard 4130/4140 and stainless. They will cost a bit more than the cheapest carbide but they last many times longer.

https://www.maritool.com/Cutting-Too...101/index.html

For cheap carbide tools sold locally to me I go with YG-1 typically
https://www.walterhammond.com/storef...x=0&orderQty=1

For cheap import I have used HRC Tools
https://www.hrctools.com/

-Dan

[taiwanluthiers]

thanks for the reply. I never tried variable helix because it is a LOT more expensive than just regular end mills (by a lot I mean a lot, I can get regular end mills at 5 dollars a pop if I look in the right places, though they are typically used or if I'm lucky re-ground). I buy used end mills simply for the fact that I can resharpen it with a diamond wheel, and often the bottom part is the part that makes the biggest difference. I buy used so I don't worry as much if I chip it or something. I hate chipping 30 dollar end mills, and it happens too often sometimes.

I have just been using normal 4 flute end mills. Actually for a bit I have been using 2 flute end mills as well. It works but oftentimes I need to keep the speed high otherwise the cutter will chip in a big way. But at high speeds the chip load is really small, and if I increase the feed rate bad things happen.