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kenc
02-25-2005, 03:58 PM
A question for you metalurgists. When buying (say) a dovetail cutter, what advantage does the cobalt option give over TiN or straight HSS?
If I am prepared to cut fairly slowly and to brush on adequate lube, would I get any better longevity out of TiN or Cobalt steel tooling over HSS?
I am not looking for a cutter that survives HEAT any better than HSS necessarily, just looking for something that stays sharp longer when cutting unhardened O1.

Ken

sidneyt
02-25-2005, 05:58 PM
I'm not a metallurgist. Cobalt is added to HSS to increase its red hardness. It does not, however, increase its toughness compared to M2 HSS. For this reason it is slightly more prone to chipping. Unless you need the greater red hardness capability of cobalt you are probably better off sticking with M2.

3 Phase Lightbulb
02-25-2005, 06:10 PM
Funny thing is, I think Cobalt has a lower melting tempature than mild steel... Well, that's what the metal melting point chart that I was looking at the other day said.. Can anyone verify that Cobalt has a lower melting tempature than mild steel?

-3Ph

dsergison
02-25-2005, 06:28 PM
yeah, it's funny isn't it. like solder. NONE of it's components melts as low as it does. weird.

metalurgy: where the sum of the parts is not = whole http://bbs.homeshopmachinist.net//smile.gif

3 Phase Lightbulb
02-25-2005, 08:18 PM
Also I think Alum Oxide was way up there at the top of the list.. I haven't welded alum yet, but I would think the thicker the alum Oxide coat gets, the harder it would be to weld...

-3Ph

tryp
02-25-2005, 09:29 PM
The difference between a regular M-2 endmill and a cobalt M-42 endmill is the same difference between a regular high speed drill and a cobalt drill. It can be run faster, and will last longer.

precisionworks
02-25-2005, 09:41 PM
Tryp said it well. I never buy HSS anymore, just coblat or solid carbide. One of the best (read cheapest)sources is a seller on eBay:

http://search.ebay.com/_W0QQsofindtypeZ15QQuseridZcindy21cindy21QQfromZR7 QQnojsprZyQQpfidZ0QQsinceZ30QQfsopZ1QQfsooZ1QQfrpp Z50

She sells only Niagara cobalt, & you can usually get brand new end mills, 1" diameter, for $5-$6, less if you need smaller. Cobalt does have a tendency to chip if your part isn't well fixtured, but nothing like solid carbide.

------------------
Barry Milton

sidneyt
02-26-2005, 12:46 PM
"It can be run faster, and will last longer"
It can also break easier if it is a dovetail cutter with little pointy cutter teeth. Dovetail cutters are different from end mills in this regard. Consult Machinery's Handbook on the relative difference between M2 and M42 HSS. If you look up dovetail cutters carried by KBC, Travers and JTS (I could have included others) you will notice that they carry cobalt dovetail cutters, yes, but the Niagara dovetail cutters are only M2. IF you are not running dovetail cutters in a production environment, M2 HSS is probably a better choice and they are also less expensive.

kenc
02-26-2005, 12:49 PM
Thankyou all guys. Looks like I'll stick with HSS.

PSD KEN
02-26-2005, 10:23 PM
HMMM, checked Cindy's site, great deals on shampoo, stainless steel creamer w/flip lid, WOW!

precisionworks
02-27-2005, 12:09 AM
Geez Ken, I buy your books, send ya to school, find the cheap places to buy brand new Niagara Cobalt end mills, and still have to list the URL:

http://stores.ebay.com/Cinderellas-Palace_Niagara-Endmills_W0QQcolZ4QQdirZ1QQftidZ2QQtZkm

Nothing but endmills, endmills, endmills........................

wierdscience
02-27-2005, 12:30 PM
Cobalt so long as it's alloyed and not surface treated is an improvement to HSS.

Tin coating is just that,a coating,once it's gone it's gone and what is left is a regular HSS tool.

Whenever the cobalt option is availible on a tool and the price isn't too much more I buy the cobalt because they do last longer than regular HSS.

kenc
02-27-2005, 12:35 PM
Darin,
I was looking for a backup to the 60 deg dovetail cutter I have. Once I find something useful, I don't like to risk being without one.
Anyway, the cobalt ones are about 2X the cost.
Ken

tryp
02-27-2005, 02:29 PM
Well I still say buy the cobalt cutter, the minor difference in brittleness is nothing compared to the many times over useful life you will get out of it. Just don't let the work spring and keep your setup rigid and you will never break a tooth. You will only realize the benefit however if the cutter will be used regularly and you wear one out once in a while. Which it sounds like you are doing if you need a backup.

Rich Carlstedt
02-27-2005, 10:03 PM
CHIPS are the cause of breakage in the tips of dovetail cutters.
Get them out of there, and the cutters will last longer.
I am totally against compressed air on a mill EXCEPT for this use only.
I have a micro minature air jet which will not throw a chip more than 8 inches. it is put directly behind the cutter to get them out. no broken teeth in over 20 years
don't forget the safety glasses !

Albert J. Hoch
02-28-2005, 01:28 PM
<font face="Verdana, Arial" size="2">Originally posted by dsergison:
yeah, it's funny isn't it. like solder. NONE of it's components melts as low as it does. weird.

metalurgy: where the sum of the parts is not = whole http://bbs.homeshopmachinist.net//smile.gif

</font>

For any alloy there is a mix of its compnents that has the lowest melting temperature called the eutectic point. :-)
Sincerely
Albert J. Hoch Jr.