# any reason not to use carbide insert bits?



## SE18 (Feb 7, 2014)

So far, I've been using HSS bits for turning, facing, threading on my SB9A (1942) with pretty good success. I've always been told not to use carbide bits b/c SB lathes don't spin fast enough and to only use carbide on cast iron, not other types of steel. I don't have special fast pulleys on my SB so it's pretty much factory speed.

Can anyone comment.

The reason I ask is I did acquire some carbon bits and thought to do some boring with one this weekend but just wanted to check here first.

Thanks


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## Halligan142 (Feb 7, 2014)

It's not that a SB can't "handle" carbide bits it's more that you can't take full advantage of the speed/feed gain you get over HSS.  The other issue although not so much if you're using inserts is that carbide can't be sharpened on a regular grinding wheel.  You need to use a diamond wheel or at least a green wheel.  Another drawback of carbide is that they will chip if abused and don't particularly like interrupted cuts, but it can be done.  I've also found, at least for me that carbide is a bit more finicky with the finish.  I can get a decent finish through a broad range of speeds/feeds with the same HSS bit, but I find an equivalent carbide bit to have a bit of a narrower range.  Again this could be just me.  Oh and those Chinese made cheap carbide bits are garbage.  You need a decent grade by a decent manufacturer.  The last thing is just cost.  If you have them already there is no reason why you can't use them.  Give them a shot and experiment.  Just like everything else there is a bit of a learning curve and you only find out by trying.


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## SE18 (Feb 7, 2014)

thanks! I have to bore to a very close tolerance so it wasn't good to hear you were not getting a smooth finish. I'll be sure not to do any interrupted cuts. I'll try to come back here and report my results! I don't intend, btw to rely on them. 99% of the time I'll stick to my HSS.

But I guess they might be better for some extremely hard alloy?


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## Bill C. (Feb 7, 2014)

Halligan142 said:


> It's not that a SB can't "handle" carbide bits it's more that you can't take full advantage of the speed/feed gain you get over HSS.  The other issue although not so much if you're using inserts is that carbide can't be sharpened on a regular grinding wheel.  You need to use a diamond wheel or at least a green wheel.  Another drawback of carbide is that they will chip if abused and don't particularly like interrupted cuts, but it can be done.  I've also found, at least for me that carbide is a bit more finicky with the finish.  I can get a decent finish through a broad range of speeds/feeds with the same HSS bit, but I find an equivalent carbide bit to have a bit of a narrower range.  Again this could be just me.  Oh and those Chinese made cheap carbide bits are garbage.  You need a decent grade by a decent manufacturer.  The last thing is just cost.  If you have them already there is no reason why you can't use them.  Give them a shot and experiment.  Just like everything else there is a bit of a learning curve and you only find out by trying.



True about the special grinding wheel. Inserted carbide was a edge between the cutting face and the chip breaker and I think they have small radius on their faces. I used them on large lathes with a lot of horsepower.

Anyone use cemented carbide on their SB?  I like cemented carbide because they can be sharpen like HHS with the right wheel.


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## Ray C (Feb 7, 2014)

SE18 said:


> So far, I've been using HSS bits for turning, facing, threading on my SB9A (1942) with pretty good success. I've always been told not to use carbide bits b/c SB lathes don't spin fast enough and to only use carbide on cast iron, not other types of steel. I don't have special fast pulleys on my SB so it's pretty much factory speed.
> 
> Can anyone comment.
> 
> ...



How big of a hole bore are you working with and what material are you working with?  If I'm not mistaken a SB9 has a top RPM of about 1000 -is that about right?  That's plenty fast for most things.  A SB9 is a stout machine and as long as your piece has a big enough diameter to reach the proper cutting SFM rates, you'll be fine.  Use this formula: MinimumDiameter =  9 x SMF/MaximumRPM.

For steel with a typical SMF of 125 the smallest diameter you can work on is in the ballpark of 1.125" (give or take a little).

For carbide cutters, I always use the rough formula of:  RPM = 9 x SFM / diameter.  Some folks tweak the formula a little bit and use 8.0, 8.5 or 9.5 as a multiplier.  -All a matter of preference of what kind of finish you're looking for...

You might want to practice on some test pieces first.  Carbide is a different animal than HSS.  For most metals, carbide wants a minimum DoC of about 8 thou.  With your SB9, I'd probably keep the maximum cut to 15 thou (roughly, maybe more).  I don't use the brazed bits too much but, that's a different conversation...

Ray


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## Rbeckett (Feb 8, 2014)

There is no real reason not to use carbide when the job calls for it.  Most smaller lathes lack the HP and speed to really capitalize on the use of carbide, but is you lathe is still fairly tight and you don't already have a chatter issue, then by all means give it a try.  I would steer away from making the giant depth of cuts some carbides are noted for because that requires massive HP and a very robust machine to deaden the vibration, but for a lathe the size of yours you should be able to get some use and good results from an occasional foray into carbide land...

Bob


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## george wilson (Feb 8, 2014)

I have a 16" lathe,and still use HSS most of the time. Actually,my lathe will run only at half speed. It would only go down to 60 RPM,which is TOO FAST for the size of work this lathe can do. It will swing 24" in the gap. My lathe at work would do 11 RPM,which is a lot better.

I made an intermediate pulley for my lathe,which halves the speed so I can get 30 RPM. So,my large lathe won't really run fast enough to use carbide's potential,anyway.

Anyhow,I only ever use carbide when doing something like taking a facing cut across my 16" face plate(which I always do on a factory new faceplate,because they seldom run exactly true.)








 I might use carbide when taking a LONG cut on a steel bar. HSS can poop out halfway along a real long cut. Then,you lose the perfect surface from having to change the cutter.

HSS makes a smoother cut than carbide,and is easily made into special shapes. I use HSS all the time on my Hardinge HLVH lathe,which swings 11",and 18" between centers. I can make a cut with HSS on that lathe so smooth it does not need further dressing.


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## David Kirtley (Feb 8, 2014)

I switch back and forth. I look at the finish I am getting and how it is cutting. I don't have a permanent setup for grinding so it is easier for me to just grab something else. Metals are not just some homogenous mass that is the same throughout the piece or from piece to piece. You sometimes get some parts that just don't cooperate. Too gummy. Too hard. 

I was turning some W1 the other day and the A.R. Warner HSS inserts just left an awful finish. Grabbed a carbide insert tool and it was happy. Sometimes it goes the other way.


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## Ray C (Feb 8, 2014)

David Kirtley said:


> I switch back and forth. I look at the finish I am getting and how it is cutting. I don't have a permanent setup for grinding so it is easier for me to just grab something else. Metals are not just some homogenous mass that is the same throughout the piece or from piece to piece. You sometimes get some parts that just don't cooperate. Too gummy. Too hard.
> 
> I was turning some W1 the other day and the A.R. Warner HSS inserts just left an awful finish. Grabbed a carbide insert tool and it was happy. Sometimes it goes the other way.




There's a lot of truth in what David says here...  There is a lot of variability when dealing with random pieces of metal and sometimes they just don't seem to cooperate.

 For a long time, I was baffled by this but, I do believe these are the underlying reasons...

 A typical piece of hot rolled or cold rolled has many different layers of surface tensions and varying degrees of hardness.  The hardest parts are near surface.  Not only do you need to change lathe RPM as the diameter gets smaller, the hardness of the metal is decreasing too.  Soft steel does not cut as clean and crisp as slightly hardened steel...

When I'm working on something important, I take the time to fully normalize and completely condition the metal to a known state.  Then, and only then do I get predictable results -regardless if I'm using HSS or carbide.  The cutter you use is important... Knowing the condition of the metal you're cutting is a hundred times more important!


Ray


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## SE18 (Feb 8, 2014)

thanks for the info. I found out that I actually didn't need to do any boring, as all the end mill shanks I have fit my fabricated shop smith holder on drill to mill conversion (long story I won't bore you with). But anyway, I'll copy this info for later usage. I suspect Ray has a good oven for normalizing stuff.


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## markknx (Feb 9, 2014)

Ray I suspected the hardness in layers because whith some cr & hr steel it will cut cleen in the first few passes then you can't get a good finish at all. Thanks you cleard that up for me.


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## Ray C (Feb 9, 2014)

markknx said:


> Ray I suspected the hardness in layers because whith some cr & hr steel it will cut cleen in the first few passes then you can't get a good finish at all. Thanks you cleard that up for me.



Yep, that's very likely what's going on there...  The outer surface (not inclusive of the hard scaly, rusty part -which is no-man's land) is the hardest and it tends to cut a little cleaner than soft gummy metal.  Also, when you're working with small rods of only an inch or so in diameter, it only takes a couple passes before it's time to increase RPM to keep the cutting SFM at the desired rate.  So now you see that two things are going-on at the same time.  And add to that that most folks don't know what kind of metal they're working with much less if it's HR or CR or, if it's already been cut down once before in it's lifetime...  That's why getting a good cut is hard to do when you're first starting-out in this game.  It's not your imagination after all...


Ray


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## drsorey (Feb 9, 2014)

numbie dumb question?
I really don't use carbide much, but use high speed steel all the time.  Can the material be "normalized" without a special oven?  I don't have the space in my very limited shop for a heat treatment oven, plus I have sawdust all over the place.  

DRSorey


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## David Kirtley (Feb 9, 2014)

Most steels, the slower you let it cool, the softer it gets. Most low tech approach is to build a fire and put the piece in and heat it to the Curie point (where it loses magnetism). Then let it cool as the fire goes out. Preferably packed in something to insulate it like sand or vermiculite. Anything else would be a variation on this.


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## Ray C (Feb 9, 2014)

drsorey said:


> numbie dumb question?
> I really don't use carbide much, but use high speed steel all the time.  Can the material be "normalized" without a special oven?  I don't have the space in my very limited shop for a heat treatment oven, plus I have sawdust all over the place.
> 
> DRSorey



Maybe...  Most (but not all) low to high carbon metal can be "Spheroidized" which will soften the entire piece all the way through.  The procedure is to elevate the part to 750 F and leave it there for about 16 hours then, shut off the oven, leaving the door closed and let it cool naturally to below 300 F.  This will take most of 24 hours to complete. This is one technique to stress relieve and soften most carbon steels and alloys.

The other way is to heat to just above austentizing temperature (bring it to 1600 F) for 30 minutes for each inch of cross section then, let it gradually cool.  This whole process can be done in roughly 10-12 hours.

Either way will get you about the same end result.  The part will be totally soft and need heat treating as per design or desire.

It's a pleasure to work on metal like this though.  Nice and consistent, no surprises.  I also like working on heat treated pieces provided they're not much harder than RC 35.  A real pleasure to work on... Every cut feels and looks the same and the finish is real nice.

Ray


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## Ray C (Feb 10, 2014)

I'd like to update the information about spheroidizing so no one encounters difficulties...

Low to mid carbon steels can be spheroidized with the recipe given in the previous post whereby medium carbon metal should sit in the oven for closer to 20 hours instead of 16.  For high carbon steels,  the temperature will need to be around 1200-1300F and the soak time is 30-24 hours (respectively at those temperatures).

The "slow cook" method of softening metal is more complex because, one must accurately know the initial condition of the metal to determine the proper cooking length.  Anyhow, cooking at 1300F for 24-30 hours is a safe bet for most common carbon steels and it will produce some softening on hardened alloys like 4140.  For tool steels above 1% carbon, the temps and times increase to 1400F and 30 hours minimum.  Some of the esoteric tool steels have full normalizing temperatures up in the 2000-2200 degree range and in those cases, it's actually useful to consider the slow-cook method because it's somewhat hard and expensive to reach those high temps.

Just want to point-out that these are general guidelines for the "slow cook" method for folks not using a calibrated furnace.


Ray




Ray C said:


> Maybe...  Most (but not all) low to high carbon metal can be "Spheroidized" which will soften the entire piece all the way through.  The procedure is to elevate the part to 750 F and leave it there for about 16 hours then, shut off the oven, leaving the door closed and let it cool naturally to below 300 F.  This will take most of 24 hours to complete. This is one technique to stress relieve and soften most carbon steels and alloys.
> 
> The other way is to heat to just above austentizing temperature (bring it to 1600 F) for 30 minutes for each inch of cross section then, let it gradually cool.  This whole process can be done in roughly 10-12 hours.
> 
> ...


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## Dan_S (Feb 10, 2014)

one of the tricks for running carbide insert tooling on a small lathe, is to use inserts designed for finishing inserts. They are designed to make chips with a smaller depth of cut, and slower feeds.

These 2 videos are of my little 8x14 running inserts.

[video=youtube;P1xbg4KKbeU]http://www.youtube.com/watch?v=P1xbg4KKbeU[/video]
360fpm
0.005 in/rev
0.02 doc in hot rolled 4140

[video=youtube;Zu-XGyuvB9g]http://www.youtube.com/watch?v=Zu-XGyuvB9g[/video]
668fpm
0.005 in/rev
0.04 doc in 6061-T6 aluminum

- - - Updated - - -

I forgot the obligatory shot of blue chips.


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