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HSS v Carbide Tipped Tools

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Dave Harris15/12/2010 22:28:51
28 forum posts
I have purchased and used some carbide tipped tools sold by a number of the ME suppliers who regularly advertise in the ME and MEW. I have to say that I have never been happy with the finish I get from these tools . At the ME exhibition I asked for assistance on the SMEE stand and was advised that for a belt driven lathe with a top speed of less than 2000rpm it was not adviseable to use tipped tools as they require far higher speeds than available for most ME lathes and also more power ,because they need to take deeper cuts to work correctly than most model making lathes can cope with, as most have relatively low power motors, and that I should use HSS cutting tools and learn how to sharpen them correctly. The answer I got seems quite logical, but if so, then why is the Model Engineering world being 'flooded' with these apparently unsuitable cutting tools?
ady15/12/2010 22:46:38
612 forum posts
50 photos
Just experiment.
 
Carbide is an amazing material, which can also be used with negative rake(or is it positive) and is extremely strong if you don't make it too sharp.
A stiff lathe gets the best out of carbide, you just "shove it in there".
 
HSS is easier to use and is far easier to achieve a good finish, but sometimes a tuff job needs carbide, carbide is also great for heavy roughing and boring.
 
So you need both types of tool because both are great at what they do best.
Don't chuck any away, you'll need them all eventually.
 
Carbide is also best in a hugely repetitive production style environment, where after 500 units you swap out the old tooltip and plug in a new one which is specifically for that job.
 
My most useful carbide tool  is the parting tool which has roughed down an incredible number of heat hardened guffy offcuts, and while not very sharp now, is extremely strong and has saved me a huge amount of HSS hassles.

Edited By ady on 15/12/2010 22:49:27

ady15/12/2010 22:50:30
612 forum posts
50 photos
What kind of lathe have you got?
Dave Harris15/12/2010 23:02:23
28 forum posts
I am using a WARCO 918 lathe
ady15/12/2010 23:19:12
612 forum posts
50 photos
Looks no' bad.
 

 
 
For better stiffness you could knock up a turret/big toolpost for bolting directly onto the cross slide.
Or even easier, a nice chunky flat steel plate on the cross slide with the 4-way toolpost slapped on top.
 
...I think you may notice a slight difference...
 
I only ever use my compound for tapers, they're not very stiff things and are really only any good for light cuts IMO.
 
I've noticed that the swarf is quite a lovely shade of blue with carbide, and with boring jobs the bore can turn a deep blue as the chips build up.

Edited By ady on 15/12/2010 23:25:10

Andrew Johnston15/12/2010 23:24:53
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7061 forum posts
719 photos
Traditionally carbide tooling has been recommended within the ME community for jobs such as turning iron castings. Here the 'skin' may be hard, or have sand embedded in it. A carbide tool will handle this, whereas a HSS tool will blunt quickly.
 
However, to get the best out of industrial style indexible carbide tooling you need to run at fairly high speeds and feedrates. Generally the required rpm is within the range offered by ME type lathes. But the high speeds and high feedrates imply a high rate of metal removal, which in turn implies a lot of horsepower; which may not be in the range offered by ME lathes.
 
Carbide inserts are relatively blunt compared to HSS tooling and rely on adiabatic shear bands (google it) to achieve a good cutting performance. At the shear band the metal is very hot (often red heat). To achieve this requires a lot of power.
 
In essence the problem is probably not lack of rpm, but possibly lack of power.
 
Regards,
 
Andrew
Ian S C16/12/2010 02:54:09
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7468 forum posts
230 photos
I find that I use a high speed, and feed, and a slightly shallower cut than with HSS.My lathe is a 1326 belt head Taiwanese one with a 1.5hp motor. The time I have problems is if I take too deep a cut, and the tool digs in,the belt slips, turn off lathe, more often than not chipped tool, would be better with geared head because the hp is OK.
I'll see if I canfind the article in ME worth looking at.  Ian S C
KWIL16/12/2010 09:07:55
3681 forum posts
70 photos
3/4 HP on a Myford Super 7 is more than enough to work these tips properly, the real problem is that "traditionally" MEs pussyfoot about taking light cuts! When the swarf blues on cutting it is running well. Obviously with 3HP on the Harrison it is not any problem at all. At all times the tool must be set at the corrrect height, whereas with HSS you can get away with it (to the detriment of the edge and finish)
Hugh Gilhespie16/12/2010 09:34:30
130 forum posts
45 photos
I am a recent convert to the SumitomoTitanium Carbide tips. I don't know if these suffer from adiabatic shear bands or any other dread disease but by 'eck, they give a cracking good finish, at least to my very untutored eye. According to the chap who sells them see here , unlike tungsten carbide they work well with light cuts so avoiding the power problem. I use them on a 1.5 HP Boxford and they certainly do the business.
 
Regards
 
Hugh
ady16/12/2010 10:48:42
612 forum posts
50 photos
I have little power on my Drummond, it's still not set up right and only has a direct belt drive.
 
I find that job stiffness is far far more important and light cuts with a decent finish are easy peasy as long as the tool has a reasonable edge.
 
The material flies off at a quite amazing rate and unlike with hss no resharpening is needed after a certain period because carbide degrades so slowly.
 
I also do a lot of rear post work because the geometrics are more favourable, carbide can chip relatively easily if it gets pulled into the work.
Using a rear post approach, it only squeaks if things aren't quite right.

A carbide tipped dead centre also makes an excellent drill spotting tool if you "half centre"the very tip.

Edited By ady on 16/12/2010 11:05:25

Douglas Johnston16/12/2010 11:46:09
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814 forum posts
36 photos
Sumitomo T12A grade tips are a pleasure to use if you get the ones with positive rake. I too had mixed results with carbide tips in the past with the surface finish being a bit hit and miss.
                  It seems to come down to the quality of the cutting edge, with a ground finish being far superior, along with the positive rake. I picked up some tips a while ago which were designed for cutting aluminium and were very sharp and had a high positive rake. These tips produced a superb finish on aluminium as you would expect but they also gave a super finish on steel and I use them for finishing cuts on steel (including stainless 303 )
                  I think the answer is to use any old carbide for roughing but change to a better tip for finishing. Ebay can be a very good place to pick up tips ( I really should not be saying this so just don't be bidding against me!) having picked up some amazing bargains over the years.
Doug
chris stephens16/12/2010 12:23:47
1049 forum posts
1 photos
To echo Hugh's point, very few carbide tip manufactures aim their product at the home market, most are made for big heavy industrial uses. Sumitomo do however make tips that can be used on even the meanest of machines. Even here though there are pitfalls, best not to be too cavalier when using them as they are quite brittle. Once you learn how not to chip the tip, they do last very well.
One must be wary of generalisations, not all tips are bad for home users and not all Sumitomo tips are good for them either. It is a question of getting the right tip for your application. 
Too many see carbide tips as a way of bypassing the learn to sharpen HSS route, this is a mistake. As is "it's good enough for industry so I must need them too." Perhaps an analogy would be, 40 ton Artics (the majority of tips) are used in the transport industry, but a Mini (HSS or the right Sumitomo or comparable tip) is better for commuting. Both vehicles are for use on the road(machining) but best not to pick the wrong one when popping down to the shop, whether it be retail or work.
If you do want to by-pass the learn to sharpen your own HSS, there are Tangential tools. These are the easiest tools imaginable to sharpen and can give an outstanding finish to the work.
 
chriStephens 
David Colwill16/12/2010 12:48:44
782 forum posts
40 photos
   I started using carbide about 5 years ago when I got some DCMT toolholders with a second hand Emco CNC. These are the smaller 07 size. I too had problems adapting but decided to persevere. I do quite a bit of work in plastics and aluminium, so I started buying the correct grade of tip which makes a huge difference. This lead  me to buying other grades for cast iron and stainless which again offer improvements when used on the appropriate material and of course tip radius (finer for finishing).  I am fortunate that I get paid for 85% of my work so I can buy these tips at my customers expense hence what may appear to be a costly experiment. It is worth pointing out that companies like Cutwel will allow you to buy a box of ten tips but mix the grades (eg 4 general purpose, 4 aluminium and 2 cast iron) also if you can buy toolholders which take the same tips then this reduces the expense.
   I was originally using a Warco BH600 and could achieve good results on most materials I have now replaced this with a much heavier and more rigid machine which has improved things even further.
   The suggestion by Douglas to use an aluminium grade insert for fine finishing on steel certainly works as I have used it myself with fantastic results but be warned these tips are very delicate and will not stand much abuse.
Dave
 
Jens Eirik Skogstad16/12/2010 18:57:01
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400 forum posts
22 photos
Better to use both HSS and Carbide in home workshop. The carbide tipped tools has some limited range: With the HSS tool, you can grind the HSS tool to a form who you want to make and form the material as you want who are impossible with the carbide tool.
PekkaNF16/12/2010 20:05:04
96 forum posts
12 photos
My (very limited) experience shows following:
* HSS is more forgiving. When usinc carbide you better do homework first, cutting speed and feed can be critical
* HSS benefits of emulsion or any kind of cutting fluid. Excluding cast iron, any liuquid and any quantity and quality is better than nothing.  For carbide, you don't need any cooling (compressed air would be great sometimes to remove swarf) most of the time, intermitent or marginal cooling/cutting fluid sems to do more harm than good. Been there done that and you may get away with it with all too low cutting speed, but when you approach any useful value and squirt liquid on hot bit....guess what goes brittle.
* HSS is easy to sharpen and gives you very big control ovet, but you produce sparks when sharppening them (this is no-go for me for now).
* With carbide you may need to go down to 0.4 or 0.2 mm radius and that is britle with manual machine. You pretty much need machine feed - little hesitation with manual feed and that edge may still looks perfect, but it does not cut way you like it and even worse- ot does not cut diameter you read dial in for a next cut.......
 
IMHO HSS is more forgiving in the home workshop and if you can sharpen it, it gives best flexibility. On the other hand: with carbide you can do things that will put smile on your face if you machine and setup has enough grunt and you dare to start with "table" values. They are NOT -however to do odds and ends at whim. Also decent tool holders and few boxes of bits will set you back seriously. Cheap holders and no name no standard bits are not that great start really.
 
I will use both and I have to figure out how to sharpen HSS in a safe and contolled manner, without putting garage to a fire risk.
 
I'd say: Use both, but do the home work, bits are not cheap!
 
PekkaNF
Dave Harris16/12/2010 22:51:45
28 forum posts
Gentlemen,
 
   Thanks for the explanations and suggestions. I have already modified the topslide on my 918 to a four point mount instead of the original two point mount sytem used. Following the above posts and my experience so far I think some HSS tools are the way to go for me as it is difficult to obtain quality tips and as already pointed out the tipped tools realy need to be run at much higher speeds than I have available to me and also need to take deep cuts which I do not have the motor power available to do. It  just seems a pity that the 'model engineering trade' do not supply enough information and advice regarding the use of these tools, given that many new model engineers will not have the knowledge demonstrated in the replies to my question. Again many thanks for your responses.
 
Regards   Dave Harris
Terryd16/12/2010 23:49:24
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1946 forum posts
179 photos
Hi Dave,
 
Can I say that you've made the right decision in my opinion. I've used HSS tooling since my apprentice days, far too many moons ago to mention. I've even used plain high carbon tool steel to make cutting tools before many exotic tool steels were available and have had great success over the years. 
 
There is nothing wrong with using HSS unless you wish to turn exotic alloys and then you will probably turn to Carbide in one form or another,  However I have known many model engineers who never touch tnat alien stuff and make some exceptional models.
 
Grinding the tools is not a particularly black art or difficult.  There are a few standard angles for rake and clearance and I was taught to make a fair approximation in a relatively short time.  If you're not sure I suggest you make a simple adjustable table for your grinder and use a few templates (card) to set the angles as you grind them. The tables supplied with most tool grinders are c**p and not adjustable enough or sturdy enough.  Also change the wheels for good quality ones, it's worth it.  You can find suitable profiles for basic turning tools in hundreds of text books and on the internet, it's not a secret.
 
One suggestion is to hone the cutting edges, I use a carborundum slip stone but modernisers use fine diamond hones.  Hoe regularly to keep a fine edge.  You can test your tool by using it like a Stanley knife and try to cut paper. it works with a properly sharpened one.  One thing not often mentioned is a 'Built Up Edge'  this happens when turning or otherwise cutting softer, more tenacious materials such as mild steels, copper and some aluminiums to mention a few,  especially when not using cutting oils.  A small quantity of material can weld itself to the cutting edge and needs removing by honing , just watch out for it.
 
Terry

Edited By Terryd on 16/12/2010 23:58:51

Ian S C17/12/2010 10:11:39
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7468 forum posts
230 photos
If you must use carbide tools, I find that I only ever use the low ratio speeds on my lathe, that gives me a maximum speed of 500rpm, a depth of cut of .030" , maybe a little more is quite all right with me, perhaps a bit slow, but any paid work I do is by the job, not by the hour.  You have to give the tip a wee touch up before going for the last thou or so, HSS is by far the better at this stage.
  A local engineering shop that makes and repairs hydralic cylinders etc has gone back to HSS after using carbide for a year or so, their lathe is a fairly large Dean Smith & Grace, Its proberbly pre WW2, and was not rigid enough for carbide tools. Ian S C
Dave Harris17/12/2010 20:24:23
28 forum posts
Terry and Ian
 
Thanks for the additional comments. I have located a book which has information regarding sharpening HSS tools. As soon as I can clear away some work in the Garage workshop that 'er indoors' wants done I will be able to set up the grinder with new wheels and start to learn how to grind HSS tools. As a 'new' model engineer but recently retired pen pusher I am happy to learn and experiment and have to admit that the reference books from the first half of the 20th century make more sense to me than some of the modern ones(must be my age!)
 
Once again, many thanks to all of you for the responses, there is plenty for me to muse over and try out.    Seasons Greetings to you all!
Versaboss17/12/2010 21:26:13
512 forum posts
77 photos

Hi gents,

in this thread I found 2 things which I think have not been discussed adequately.

The first.: nobody asked what the OP (Mr. Harris) meant with his 'carbide tipped tools'. Possibly the ones with brazed on tips and not the indexable chips? I too think that the former are almost good for nothing, except maybe roughing out some cast iron chunk. I had once a couple which were (diamond) ground to a mirror shine and very sharp. That was another story, but over time I managed to damage them too and had lost the access to that grinding service.

And the second: I found it strange that some postings gave the impression that with carbide (inserts) you have to take deep cuts and need a lot of power.

One of the jobs I have to do is the following: on a stainless hex screw, M5 and with a shaft length of 14 mm, the thread is turned down to a dia. of 3.5 mm and then a 60 deg. point turned on the end. The screw is held by the head in a collet and sticks out the full length. The turning down of the dia. is done with HSS, mainly because it has to be a 45 deg. form tool. Cutting oil and a very fine feed, iirc < 0.05 mm per turn.

Now for the point I use one of these 35 deg vee chips (VCxx), 1200 rpm and wiggling the top-slide to and fro almost as fast as I can, while the left hand gives a little jerk to the cross-slide of between 0,1 and 0,2 mm. For the last pass often 0.03 mm or even smaller, and slower. If I don't pay attention the point gets so sharp it can prick a finger easily. The swarf looks loke woman's hair...

I have no problem in taking fine cuts wit carbide inserts, but you need one for finishing and not a 'rougher'.

Greetings,

Hansrudolf

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