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Thread: HSS vs Cobalt

  1. #1
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    Gentlemen, I do a fair amount of lathe work, consisting of repairs and one off fabrication. I see a lot of interrupted cuts on welded up parts with a lot of mystery materials and I have mostly used Rex M2. My run at carbide was a frustrating experience, I kept chipping them. I picked up a 5% cobalt bit, unknown brand, to see if it was an improvement over the M2. I noticed right away that when grinding it there was more burr on the tool, it seemed softer, and it didn’t seem to last any longer than M2. I am ordering some bits and I see that Enco has some 10% cobalt bits. Do you think I should have seen an improvement with the cobalt and what do you think on the 10% cobalt? I am going to try the 10% anyway but I found the 5% experience to be interesting and I would like to get your thoughts or suggestions.
    Thank you, Mike

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    First what you are calling "cobalt" IS high speed steel. The grades with significant Cobalt ( there are at least 15) are different and not described by percentage of Cobalt. I would consult with Crucible or Sousa Corp. They might have info to help.

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    carbide grades can be very tough and flexible. I think you will find that there's a carbide insert out there that will stand up to interruptions and welds. Try giving sandvik coromant a call. They do so much work in R&D and training, a technician will direct you to a really great insert for your application, I'm sure.

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    I like Cobalt and use it on threading mostly. It is a little tougher than HHS and does ok on interrupted cuts for me. I Use the 10% but it would be a good idea to ask a supplier about what is best.

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    1. Cobalt is usually added to raise the "hot" hardness. They are not necesarily harder, they just maintain hardness at a higher temp. A Rex M42 (8% CO)is not as hard as a M2.

    2. There are shock resistant grades of carbide inserts. If you are using a brazed carbide, a C-5 is more shock resistant than a C-6 (C-2&3 are for cast iron). There is also a difference between USA made and Chinese made carbide.
    JR

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    Email Bill at Carbide Depot with your needs and he'll steer you in the right direction. He responds quickly, prices are good, shipping is fast.

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    I think I see where mf205i is going with his post, I've come up against this problem myself and have found out the following...... maybe a little disjointed but I'll give it a go, please bear with me.

    Weldments can be awkward things,(that's being polite!) balance and the HAZ's being two major factors when considering tooling, a tough grade of carbide would on the face of it be the logical choice, but only if the other parameters can be achieved, mainly enough speed for them to work properly which is ultimately affeced by the rigidity of the workpiece and the capability of the machine to control it.
    The SFM for carbides is say around the 300fpm, and out of balance forces at those speeds can get scary.

    A lot of ''structural'' low carbon and hence commonly welded steels are sticky and don't like being machined, hence the high speed in order to reduce the built up edge problems etc.
    Then added in to that mix you have the HAZ, and at first, interupted cut which is hard on any cutting tool, especially the outer ''skin'' and in the case of stick welding included or uncleaned off slag.

    Think about first principles, the things we learnt at trade school,like minimum tool overhang and please lord NO lantern or American style toolposts!!!! I don't even like the quick chage types as they all seem to over hang the slide more than the good old four way block, allright you gotta shim, but there's one less interface to consider as well............. if you can lock the topslide if it's not being used, and the cross slide once you've set the cut, it all helps.

    So HSS or Cobalt? I'm lucky that over the years I've aqquired sizable stocks (for me) of ''cobalt'' of all sorts of types, and there is a lot of variation, not long ago I bought some Chi' import M42 blanks from J&L, and it's barely any different to our good old standby Eclipse H5

    My fave for heavy duty has got to be Cleveland MOMAX, it's not only tougher, it's harder, try grinding a bit, and stands up well to the sort of punishment weldments dish out.

    If you want something harder look for WKE 45 (probably NOS made I think by Sandvik) then you'll know what hard is and how!

    Tip radius:- the bigger the better, and top rake as small as you can get away with especially in the early stages.

    The method that works best for me is shut the speed down and put the feed up, lots of folk fall in to that trap, especially as we're told speed's everything these days! .050 DOC, .020 feed at 50 rpm, is exacly the same as .050 - .010 at 100rpm.

    Lots of coolant, then for the first cut get as deep as you can to get under the hard skin and general rubbish.
    Tool life won't be high and you could well need a fresh tool before that first cut is done, but after that life gets better...... sometimes you just gotta grit your teeth and sweet talk the lathe through it.

    Sorry if I've rattled on a bit, but I hope this might be of help to you, take care. Sami.

    P.S. Ask if you'd like any further help, or is that jumbled ramblings?

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    Gentlemen, thank you for your input, it has been helpful. I had tried c5 before but it was an import. I will try again, but from a US manufacture. After I made the post I noticed that, in a senior moment, I had substituted HSS for M2 in the title, but I didn’t know how to edit it. Aging Sucks!
    Thanks again, Mike

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    Mike
    Take a look at this site. http://www.imetalindia.com/high-speed-steel.html.
    I'm sure you can find the ASP grades listed there locally in the U.S.
    I used the powdered metallurgy grades on many applications including turning, broaching and gear cutting with a lot of success. If you can coat your tool with Titanium Nitride you'll get even better life and wear resistance.
    Regards

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    mf205i. No problem, ageing sucks?......... no, try to think of it as being more fun

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    I agree with Limy Sami on the speed thing. Dial down the RPMs and use feed rate to determine cuts. Push her till it almost jumps on the first cut. She is gonna bang and she is gonna shake. Like it or not, I prefer an old belt slapper for such work. I also advise a needle scaler be used before you start cutting.

    I disagree with Sami on another thing. A hardened lantern toolpost is a good thing, if you keep the tool back. Choke up on the cutter bit and shove the toolholder all the way in. Sometimes, I just use a half inch bit in the toolpost and skip a toolholder. I agree that a good stout tool block is a good idea. Mount the cutter as if you are going to beat on it with a sledge hammer. Keep the radius big, the rake angled, and the clearance low.

    Forgive me. I am from the old school and will probably die with an Armstrong toolholder in my hand. I am the fool, at work, that hand grinds specials and form tools. Those of us without full CNC and good sense have to adapt and overcome.

    I agree that Cle-Mo-Max is good, really good. I use it a lot. Chinese mystery metals make poor cutter bits. The cost per cut is darn high with import steels. My old favorite is the "OLD" Latrobe double six. They once made a cutter that would take a pounding and still hold up to slag. Nowadays they have cut back on their recepie. It is still M2. It is just at the lower end of the mix.

    For coolant I tend to use bacon grease for such work. It looks like you are burning, more than cutting. Fortunately the smoke is sweet and the neighborhood pets come a running.

    One way to get really good cutter bits is to get T-15, or M-4 inserts from Arthur R Warner. For lower horsepower machines and nasty interrupted cuts, they sell good the stuff. A high speed positive rake insert in a stout toolholder is hard to beat. Call up www.arwarnerco.com . These people know high speed steel and customer service. For cheapskates like me, they are the place to get the lowest cost per cut. Tell them what you need and they will put it in your hand. I like them because they will supply what you need, not what they have.

    Break out the earplugs and happy cutting.

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    I agree on the lantern toolpost. It greatly depends on how big a toolpost is being used. My 18" L&S with a #2 Armstrong (1 1/4x 5/8") running 3/8 -1/2" tools is PLENTY rigid enough.

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    Mike,

    We make and machine weldments all the time, sometimes with very exotic contamination. Limy Sam is correct with the high feed low speed aproach but I would caution against using more than 8% M42 cobalt content. I bought a box of 10% bits some years ago but don't use them because they seem to take hours to grind to shape.
    I prefer 5% for the very reason that I am grinding very frequently to renew the tool and this is by far the sweetest on the wheel.

    Charles.

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    The larger Lodge & Shipley oldies came with a unique "stair stepped" pressure ring for the Armstrong style tool holder to sit on. This replaced the cupped ring and rocker. The whole ring had to rotate if the tool moved.

    John

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    One way to get really good cutter bits is to get T-15, or M-4 inserts from Arthur R Warner. For lower horsepower machines and nasty interrupted cuts, they sell good the stuff. A high speed positive rake insert in a stout toolholder is hard to beat. Call up www.arwarnerco.com . These people know high speed steel and customer service. For cheapskates like me, they are the place to get the lowest cost per cut. Tell them what you need and they will put it in your hand. I like them because they will supply what you need, not what they have.
    Charlie:

    Thanks for letting us know about Arthur R. Warner Co. After reading your post I decided to see what I could find in HSS inserts to use with all my 1/2" Kennametal insert holders so I called them up.
    I also needed 3/8" shank turning, profiling, threading & boring tooling for two small lathes I have with low center height and to use for fine work on the larger ones. I found everything I needed there. They offer 3/8 & 1/2" kits, individual inserts and a wide variety of HSS replacements for carbide inserts. What a find. I have now added significantly to the quality of my tooling collection.

    Lawrence

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    try t-15 ONCE.i bet you'll never go back. i like it much more
    than m-42 . harder to find, more expensive
    difficult to grind...but
    my fave hss.

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    The most popular material for our rotary broaches here at Slater Tools is M2. However, we also offer the PM4 and T-15, but... our experience has been to try M2 first, and work your way up from there. It seems that each customers machine and personal touch for speeds and feeds makes this a bit too delicate to perfect or recommend the best HSS for any given application.

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    i don't get it i have acquired like 750 pounds of brand new hss end mills drills reamers and stuff and no one seems to want them i cant sell any of them im about ready to scrap them i would think i could sell them for 5 dollars a pound instead of scrap price of 1.30 heck i don't mind using hss its actually still efficient in some instances due to carbide cost these days but i just have so much i couldn't use it all in 20 years.

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    Honestly i just use my normally go to tcmt 110208 running a Kennametal **850 insert, there tuff and have a generous edge prep, that will happily true up stick tig or mig in either normally mild steel (think 60** or A2, A15, A17 tig filler) or do just as well for stainless 316 at that. Will cut happily even at a couple of hundred Rpm on say a 1" shaft (most of what i build up these days is sub 1" complex bits) Will probably go circa 5 thou feed. BUE is only a insert issue in alu with these ones, steel won't cut clean, but they will cut the narliest of welds + any remaining flux. Then switch to a nice insert with better geometry for final finishing. I never find Hss lasts long enough to make it viable in these conditions. Carbide ran with care will happily munch along for damn near forever. Hss just seams to wear the end off!

    At lower speeds, you need to be running less feeds to avoid chipping carbide inserts. A rigid lathe also helps massively, carbide likes a stable cut, can be interrupted at low speed with out issue, but during the cut there must not be chatter, that's what chips inserts in my experience the most.

    Ohh a typical TCMT insert corner is a circa $1 item (this can be a real good use for some of he Ebay older carbide grades as a discount insert source). Hence to me its easier and more productive to use say a corner or even 2 than mess with Hss, all be it your typical corner has next to no real cost apart from time in hss. That said i normally only build up shafts out of down equipment, so times more significant to the customer than costs at this point. By the time i have welded it, straightened it and machined it insert costs are easily sub 5% of the total of the job probably sub 2%.

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    Kennametal KC5010. I have been using this grade for years and I started using it on 17-4 PH Stainless castings with lots of interrupted cuts and welds. This grade is tough and wears out gradually instead of just giving up all at once. Try it...you'll like it!


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