HSS Lathe Tool Angles for Small Lathes

[James AParticipant @jamesalford67616]

I am sure that I found this information somewhere on this forum, but cannot relocate it.

I have found a whole range of sites suggesting angles for tool bits for lathe tools, but many of these relate to large, solid machines. I seem to recall that different angles are recommended for flimsier lathes (Flexispeed).

What angles do people find are best on a light machine for cutting steel, brass or aluminium?

Thank you.

James.

[James AParticipant @jamesalford67616]

[Steve WithnellParticipant @stevewithnell34426]

Hmmm Not an expert at this, and I've always used the typical forms, not really thought how they might change on a small lathe or had any particular problems. One thing about small lathes is that they are used to cut much smaller components and that means that the cutting edges do need to be kept super sharp.

There has been some debate about carbide inserts, which can have a (in comparison with a sharp HSS edge) large radius, because they are manufactured for larger production machines.

I'm really interested in what the more experienced have to say on the topic.

Steve

[Clive HartlandParticipant @clivehartland94829]

Engineers grind tools to suit application, in general James allow 10 Deg. front clearance and 12 Deg.top rake.. I see no reason to have special angles for smaller lathes apart from the fact that smaller section tooling is a bit flimsier. The angles I have quoted for steel bur for Alu increase the top rake to 20 Deg.

Round nose tools use the same front clearance all round the tool, this way you can cut both ways. With experience you will soon get the best angles for the materiel you are cutting.

Regarding tipped tooling, I have said before that you should use them on a powerful rigid machine. They actually do not Cut, but shear the metal and in consequence require more power and a higher speed,.Speed increase of at least 150% over HSS tooling.

There are many references to tool angles in machinery books and a little research will soon find what you want but in any case they are general references and sometimes you need to go outside recommendations.

Clive

[Gas_mantle.Participant @gas_mantle]

Hi,

I'm glad you asked this question as I'm planning to grind my own tools for the first time and will be interested to see the responses you get.

I came across these 2 videos yesterday that seemed helpful to people with smaller machines (ignore the first 30 secs where he talks about the weather !)

**LINK**

**LINK**

Peter

[BazyleParticipant @bazyle]

10 degrees fo reverything simplifies life until you get a fancy T&C grinder. You can then perhaps make a 9 degree honing guide that lets you make a very slight touch up to only the tip not trying to remove a lot of metal and not rounding it over by trying to do it freehand.

[HopperParticipant @hopper]

LH Sparey's book "The Amateur's Lathe" has an excellent section on grinding toolbits for modelmaking sized lathes. He recommends using a "knife" tool with quite a bit more side and top rake than you would normally use on a bigger lathe, and no back rake. From memory, the included angle between the top face and the leading cutting face should be 55 degrees. Once I stopped grinding my toolbits like I was used to at work on bigger lathes and followed Sparey's advice, I found my chattery old 1937 small lathe could take a .100" deep cut without dramas.

Brass takes less of an angle. For aluminium, the same tool as steel can be used. In all cases, finishing the sharpening by hand on an oil stone helps.

If you are a beginner, I would recommend Sparey's book as a great starting point.

[Roger WoollettParticipant @rogerwoollett53105]

I have a small (Cowells) lathe and use 1/4inch HSS tooling. I don't think rake angles need to be so much different from standard – perhaps a bit greater for steel. What I do find important is to keep the cutting edge really sharp. I use diamond laps to keep tools sharp. Use them little and often.

Roger

[MuzzerParticipant @muzzer]

My first lathe (Portass model S) was bought from an old boy in Birkenhead who was an avid model engineer (Steve Farmer, any one?) – and a full time lifelong lathe operator. He spent almost every waking minute in a workshop of some form and his locos were pretty impressive – one of those guys who would build it up in the front lounge and then remove the window to get it out. His back yard was completely filled with his shed / workshop.

Steve gave me loads of really helpful knowledge and advice when I was getting going in my early to mid teens, for which I have always been very grateful. One really helpful tip was how to grind a special HSS cutter for a lightweight (not very rigid) machine like the Portass by running a groove along the edge of the bit using the corner of the grinding wheel. Basically it generated a lot of top rake without weakening the tool, probably about 20-30 degrees. In other words, you could probably use the same angles as you would for aluminium. Sure enough, I was able to take reasonably sizeable roughing cuts (it's all relative) and also nice fine finishing cuts (fine fluffy shavings).

If you were using an indexable tool on a lightweight machine, the polished CCGT inserts which are designed for primarily aluminium would be very suitable. They are described as suitable for finishing cuts in steel as well as for general machining of light alloys. Being polished, they are razor sharp. Obviously they aren't designed for brutally heavy cuts in steel but by definition that's off the cards here anyway.

Murray

[John CParticipant @johnc47954]

May I suggest using a tangential toolholder? There are lots of posts out in internetshire about this device, but it removes a lot of the mystery and magic of toolgrinding. I use holders from the Antipodean advertiser to the right of these posts – no connection, just a satisfied UK customer.

Edited By John C on 09/08/2015 14:31:31

[MuzzerParticipant @muzzer]

I think the discussion is more focussed on the rake angles, particularly the top rake. That isn't really a function of the toolholder and you would still benefit from bigger top rake whichever way you choose to go – tangential, horizontal HSS or insert. Also, as I said in my last post, the polished inserts have a pretty sharp edge so may be quite suited to small machines.

[Neil WyattModerator @neilwyatt]

I would say +1 for the CCGT inserts Murray has mentioned. I use these: http://www.jbcuttingtools.com

I have a mini-lathe, although it is modded with a half-horse 3-phase motor it is no moire rigid than a standard machine. Over the last few days I have been making some little gear spindles from some 1/2" no-name stainless steel of a rather tough nature. I've been using about 870rpm and a depth of cut of 1.5mm (60 thou) with the CCGT insert and it shows no signs of giving up.

They are more fussy on small cuts, but you can shave off half a thou if you need to.

On aluminium the sky is the limit and the finish is perfect

I use CCMT for steel.

Note that both of these tools have a geometry with sharp cutting edges and positive rake and quite small corners – much as you would grind an HSS tool so you get similar performac

Neil

[James AParticipant @jamesalford67616]

Thank you for all of this advice and the suggestions, which are exactly whatI was looking for.

Regards,

James.

[Douglas JohnstonParticipant @douglasjohnston98463]

About a year ago , in a moment of madness, I put a low bid on ebay for 50 polished inserts for aluminium. To my surprise I won the inserts and set to work making a few holders. These inserts were used for aluminium for a while giving superb results and I subsequently bought some different shapes, of the same type, from the supplier.

I then started to use the inserts on steel and was amazed at the surface finish they produced and their durability. I even used them on some hard heat treated steel and they performed perfectly.

The inserts have high positive rake and are very sharp and perform very well on my small lathe (Myford Speed 10 ).

The ebay supplier was 'engineering-r-us' but they don't seem to have any listings at the moment. The only problem was they sold the inserts in lots of 50, but with a few lucky bids I now have a lifetime supply (make that two lifetimes ) at a cost per insert of about £1.

Doug

[AjohnwParticipant @ajohnw51620]

The inserts mentioned are sometimes called raked tips. I don't use the square one as they are a bit of a pain when shoulders in work have to be faced so I use these

The rad is small so when a shoulder is faced it can usually simply be plunged in a bit to leave a square shoulder. They can also cut in all directions. This one is listed for finishing stainless and works well on all materials. I also have some micro polished ones specifically for aluminium. They are 11mm tips. The holder is one from the cheap 10mm sets sold on ebay. Only problem with that is all of the other shapes that come with them and in some cases changing the screws to torx types. I buy my tips from APT Carbide as I find the prices are good. I have bought of ebay in the past but concluded that some were used and not new so I don't any more. I have seen buckets of tips at used machine tool dealers in the past and even been invited to examine them with a magnifying glass. They get taken of production machines before they are really worn out

There is no real simple answer to angles on HSS lathe tooling. One of the most important factors is finish. I polish mine up with a slip stone. I also usually use the stone to add a small rad to the tool as in general large rads are bad news for normal turning. Rad's distort the metal as it comes off which tends to result in more tearing. For finishing the rad only needs to be large compared with feed that is used.

If you do start looking at speeds and feeds don't regard them as gospel. They are even available for tool steel cutters not just various grades of HSS and carbides. What they really are is limits intended to maximise metal removal rates and give "reasonable" tool life. They are not magic. People may find that a better finish is obtained using heavier cuts / faster feeds but this has nothing to do with the cutter it's down to limitations of the machine that is being used. This does assume the cutter has been set up correctly. Oddly some carbide tip manufacturers specify very very slightly above centre but it's safer to stick to on centre to very very slightly under it.

John

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[KWILParticipant @kwil]

So there you are, consensus is that you can use tipped tools on small lathes. You do not have to use HSS unless that is your own particular choice.

[James AParticipant @jamesalford67616]

I have never been sure: are these tips carbide or HSS?

[Anonymous]

Posted by James Alford on 10/08/2015 13:42:16:
I have never been sure: are these tips carbide or HSS?

Sintered carbide and then coated if required – those specifically for aluminium tend to be made from finer particles and the faces are polished to minimise BUE.

Andrew

[chris stephensParticipant @chrisstephens63393]

Hi KWil,

Of course you can but, and it is a big but, they have to be the right ones. To a lot of newbies a carbide insert is just a carbide insert, without realising that there are a myriad of different types often with very specific purposes. Anybody buying a load of industry surplus tips hoping they have solved all their problems is surely in for a disappointment.

Buying tips from, say, JB you are pretty certain to get the right purpose you have asked for, but if you ever look in an insert catalogue looking for tips, watch your step as you have entered a minefield. The general majority of tips are for industry, where the money is, not with the penny pinching old farts, sorry, cost conscious old farts, in model engineering (myself included)

chriStephens

[KWILParticipant @kwil]

Quite agree Chris, as always caveat emptor applies

[AjohnwParticipant @ajohnw51620]

These carbide tips follow similar rules to other cutter materials. That's basically the wedge angle of the cutting edge form by any top rake and side rake and ir's orientation when cutting.

Perhaps the simplest example is typical brazed tip carbide cutters. It can be difficult to get any other than ones suitable for use on cast iron where there may also be interrupted cuts. Due to this both rakes are low to provide a strong cutting ege. They can be used on any material though and have been by many people. They just aren't optimum in terms of metal removal rates.

The raked tips add rake by moulding the op of them to provide it and even if intended for specific metals can be used for other materials. This one for instance intended for aluminium but also suitable for finishing stainless steel. These also work well on brass and copper. There home page shows how metals and tip types are grouped together.

**LINK**

Why finishing ? It isn't suitable for taking heavy cuts but how many HP do machines have when that needs considering? Big machining centres will take rather large cuts. In some cases HP's are going to be beyond what can be run on a household electric cooker/shower feed let alone a 3 pin plug.

Then there is this type, basically a stainless steel cutting type also suitable for general use

**LINK**

APT usually sell in 10's but they also sell some in 2's for hobby use so it doesn't cost much to try them.

I should add a whoops. I've been fitting 11mm tips to the cheap 3/8" sets. I think that they should be fitted with the 9mm. The 11mm tend to be undersized and the 9 over. I have bought 2 of the correct holders for them recently but as usual they are for left hand bar turning and facing. The only way of getting the arrangement I posted a photo of is to buy a set or making one. I intend to do that with 1/2 square gauge or key steel if I can find some at some point.

The tips that come with the sets are usable as well. I suspect they are GP, jack of all trades.

John

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[VicParticipant @vic]

I've just bought some round inserts to try on a wood turning Lathe. I wasn't expecting them to be that sharp in spite of another buyer saying he uses them on wood to good effect. When they arrived this morning I was pleasantly surprised at how sharp they are, I'm expecting them to work quite well.

[James AParticipant @jamesalford67616]

Thank you all for the follow up replies.

[AjohnwParticipant @ajohnw51620]

In terms of hss tool angles this might help. A tool that will work well on any material. All of the angles are more or less the same except that there is little back rake. There is no point in being precise. It's the easiest tool to grind – bar turning and is often ground with less rake than this one.

It's on a 3/8" toolbit. Reflections and bits make it look a little odd in places. It's sharp and straight sided. The rad is straight as well and has been stoned on. All of the surfaces around the cutting edge have been polished with a stone. The finish of the tool is important as it will be transferred to the work and in the case of aluminium poor finish will generate more friction melting it and causing it to stick to the tool unless the cutting speed is bought well down. I periodically run the stone around the tool while it's in the lathe to keep it sharp. Some turners always do this before taking the final cut.

It would take a huge post to go through everything so just the basics. Actually I don't think that is possible anyway. A better idea is to grasp the principles and try various things out

Rads on tools distort the material more than a straight edge as it's being cut so for normal turning small is best. It just needs to be large compared with the feed. This may not be the case with extremely large rads and rather shallow depths of cut. It can be interesting to try this by turning using a parting off tool at a modest angle to the work angled in the direction of the cut. A lot depends on how tight the machine generally is.

The top and side rake form a wedge. The top rake will tend to pull the tool into the work. The side rake resists this tendency. On materials such as aluminium it's possible to increase these angles a lot and balance them so that very little effort is needed to take much larger cuts than a machine can normally take. The best balance is when the side rake has reached a point where the tool almost self feeds. Top rake to experience this is of the order of 30 degrees. Side – gradually increase it until this happens.

The catch with trying to do this on all materials is that having lots of side clearance weakens the cutting edge and on brass for instance the same tool might even self feed. On cast iron it might even chip and will wear more rapidly due to the very acute angle at the cutting edge. For various reasons including heating in use harder materials need reduced wedge angles and rakes. Just to complicate things more acute angles cut more easily which can reduce tearing. Slow speeds can help with that problem as well at times and get rid of boring bar chatter.

Back rake simply helps guide the swarf away from the work.

Front clearance is needed to prevent rubbing. If the tool happens to be above centre for some reason more is needed especially on small diameter work. This is why tools should generally be set a touch below centre – the centre height of the work may vary along the bed. The tail stock might be a touch low etc. Boring is the other way round plus the bars will bend a touch.

The other factor is heating effects. People might not think that their tools don't get hot but the problem is right at the tip of the cutting edge not the whole tool. If sharpened correctly they will cut paper. They have a very fine edge. Heat conduction rates from the edge drops off as the wedge gets sharper. It's even possible to weaken HSS when the tool is being ground. Any sign of tempering colours appearing is bad news.There are different grades of HSS. M42 for instance is reckoned to have better red heat strength than others. It's very easy to wreck some grades this way. Less so as the cobalt content goes up. 5% cobalt / HSSE is often used for any sort of metal cutting tool for this reason – to help maintain the cutting edge not the whole tool.

Tool bits needn't be large. During training I mostly used 5/16 HSS on machines that were easily capable of removing 1/2in of 4 to 5in dia mild steel along with a very heavy feed. A 3/4" or bigger super weld tool would be used for that sort of thing. In the normal range up to a 0.150" cut or so 5/16 bit were fine except for one aspect. The holders applied something like 15 degrees of back rake – grinding that on the tool would weaken it and also make grinding them more difficult. Generally when steel is provided for some job 0.150" cuts aren't needed. On a large machine to get the best out of them this is the sort of amount of excess material that is needed. A large machine in very good condition may need a cut of at least 0.040" in order to take all of the play out of it so that a consistent finish can be obtained. Materials don't have consistent hardness. Some machines would need more than that. The general idea is to use similar sized cuts to clean up and finally size a part. Some of those cuts would be used to determine exactly how much material is actually removed and the cuts adjusted accordingly. I once bought a sort of slightly larger super adept, similar thing but a smaller than a zyto. The cut need on that to get a decent finish was around 0.050", 0.1" off the diameter. It had a 1/2hp motor. That was in mild steel. It might be more or less on brass or aluminium etc. The machine went in the bin, crap head stock bearings and no way to fix them.

John

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