The Cambridge Turning Trials

[Anonymous]

Here are the first of my results on surface finish versus turning speed and coolant. In this first post I will reiterate my results for EN3B, so that all the results are in one thread. I’ll put the different materials in their own posts, so that we don’t end up with very long posts. I haven’t posted pictures of my latest tests as I don’t think my photography is good enough for the pictures to add anything. All the materials used were sourced from professional metal stockists, so they should be the grade they claim to be; although harsh experience has shown that the same nominal grade from different suppliers can vary widely.

 

Disclaimer: I don’t claim that these results are definitive, there are too many variables for that! However, they may be useful as a starting point and to dispel some myths.

 

Unless otherwise stated the common factors for all tests are:

 

Lathe: Harrison M300

Coolant: Biokool14 soluble oil, from Hallett Oils

Depth of cut: 40 thou, 80 thou off the diameter

Feed: 4 thou per rev

Tip: Korloy CCMT positive rake insert with 0.4mm radius, grade N3120

 

For completeness, here are my results using EN3B, a steel that I have always found to be a bit of pig (or should that be badger) on which to get a decent finish:

 

Material: 1.375″ diameter steel EN3B

The four trials were:

 

Trial 1: 260rpm (94fpm), no coolant

Trial 2: 260rpm (94fpm), coolant

Trial 3: 1200rpm (432fpm), coolant

Trial 4: 1200rpm (432fpm), no coolant

 

General appearance:

 

Trial 1: Surface is rough and inconsistent axially, if wiped with a paper towel it picks up fibres

Trial 2: Looks and feels slightly smoother and is more even axially than 1

Trial 3: Smoother and more shiny than 1 & 2, but is inconsistent axially

Trial 4: Surface feels smoother than 3, is very uniform axially and shiny

 

Under a magnifying glass:

 

Trial 1: Surface is dull, torn and uneven

Trial 2: Surface is dull and torn, but not as uneven as 1

Trial 3: Surface is slightly torn, but is also slightly burnished

Trial 4: Surface is much more highly burnished than 3

 

Swarf:

 

Trial 1: Came off in small, cold, uneven pieces, generally a few mm long

Trial 2: Came off in small, cold, uneven pieces, generally a few mm long

Trial 3: Came off in long cold curls

Trial 4: Came off in pretty dark blue long curls; longest piece was over a metre

Measurement of Surface Roughness (Ra), taken axially at three points around the periphery (all in micrometres):

 

Trial 1: 6.01 6.75 6.30 Average=6.35

Trial 2: 4.97 4.52 4.16 Average=4.55

Trial 3: 2.72 2.62 3.05 Average=2.80

Trial 4: 2.12 2.45 2.76 Average=2.44

 

So, for me, using carbide at high speed without coolant, gives the best finish and appearance.

 

As an additonal test I tried a fine cut, 2 thou off the diameter, at 1200rpm and 4 thou per rev, no coolant. Measured difference before and after was 2.1 thou, and the finish was good, but slightly uneven axially. So, while it is perfectly possible to take fine cuts on EN3B it is not necessarily a good thing to sneak up on dimension from a surface finish point of view.

 

Regards,

 

Andrew

 

Note: I’m not measuring to a tenth of a thou (!) just interpolating the readings on the 1″-2″ micrometer to get the resolution.

[Anonymous]

Introductory Post – EN3B

[Anonymous]

Here are the turning trial results for stainless steel.

 

Material: Stainless steel 1.25″ diameter, grade 303 free machining

 

Trial 1: 180rpm (59fpm), no coolant

Trial 2: 180rpm (59fpm), coolant

Trial 3: 800rpm (262fpm), coolant

Trial 4: 800rpm (262fpm), no coolant

 

General Appearance:

Trial 1: Surface is rough and torn, picks up fibres when wiped with a paper towel

Trial 2: Smooth finish and uniform

Trial 3: Smooth finish and uniform

Trial 4: Smooth finish, but slightly less uniform that 3

Under a magnifying glass:

 

Trial 1: Surface is dull, torn and uneven

Trial 2: Surface is smooth, little or no tearing

Trial 3: Surface is smooth, no tearing

Trial 4: Surface is smooth, no tearing, but slightly uneven axially

 

Swarf:

 

Trial 1: Long tight coils, several feet long

Trial 2: Short coils, about 1″

Trial 3: Short pieces, not coiled

Trial 4: Short pieces, not coiled, light yellow colour

 

Surface roughness (Ra µm):

 

Trial 1: 5.07 3.52 3.84 Average=4.14

Trial 2: 1.83 1.80 1.72 Average=1.78

Trial 3: 1.97 1.86 2.12 Average=1.98

Trial 4: 2.06 2.06 2.30 Average=2.14

Small depth of cut test 2 thou off diameter, 800rpm, 4 thou per rev, with coolant:

 

Difference before and after, 2.1 thou, excellent finish, as good as the best of four trials above.

Conclusion: Contrary to popular opinion stainless steel is easy-peasy, provided you don’t turn slowly without coolant! Best is slow speed with coolant, although high speed with coolant isn’t far behind. It is possible to take fine cuts and still retain a good finish. Personally I’ll probably stick to high speed, for the time saving, and take a slighly worse finish.

 

Caveat: I don’t know what the error on my surface roughness gauge is, but I’m guessing +/-10%? Remember that a difference of 0.2 in the readings is 200nm, about 8 millionths of an inch, even a gnats wotsit is huge in comparison.

 

Regards,

 

Andrew

[Anonymous]

Here are the turning trial results for brass. I’ve never seen it recommended to turn brass with coolant, and have never done so, so I didn’t include coolant in this trial.

 

Material: Brass 1.375″ diameter, grade CZ121

 

Trial 1: 800rpm (288fpm), no coolant

Trial 2: 1700rpm (612fpm), no coolant

 

General Appearance:

 

Trial 1: Uneven surface, axially inconsistent

Trial 2: Even surface

Under a magnifying glass:

 

Trial 1: Regular fine radial pattern, repeating consistent with the size of the chips

Trial 2: Smooth surface, no discernable radial pattern

 

Swarf:

 

In all cases the swarf came off as a stream of fine particles, and got everywhere!

Surface Roughness (Ra µm):

 

Trial 1: 3.56 3.66 3.55 Average=3.59

Trial 2: 2.61 2.41 2.41 Average=2.48

Fine cut test, details as before, at 1700rpm, 4 thou feed, and no coolant.

 

Difference before and after 1.9 thou, slightly uneven finish, not as good as trial 2.

 

Conclusion: As expected brass is pretty straightforward; the finish does seem to be better at higher speeds. A fine depth of cut does degrade the finish.

 

Regards,

 

Andrew

[Anonymous]

More results, this time for EN1A.

 

Material: EN1A, 1.25″ diameter, free cutting, but not leaded

 

Trial 1: 370rpm (121fpm), no coolant

Trial 2: 370rpm (121fpm), coolant

Trial 3: 1200rpm (393fpm), coolant

Trial 4: 1200rpm (393fpm), no coolant

 

General Appearance:

 

Trial 1: Uneven finish, torn, picks up fibres when wiped with a paper towel

Trial 2: Smooth and even finish

Trial 3: Smooth and even finish

Trial 4: Smooth and even finish

Under a magnifying glass:

 

Trial 1: Surface uneven and torn

Trial 2: Surface looks uniform and smooth

Trial 3: Surface looks uniform and smooth, some burnishing

Trial 4: Surface looks uniform and smooth, surface is burnished

 

Swarf:

 

In all cases the swarf came off in small (few millimetre) pieces.

 

Surface Roughness (Ra µm);

 

Trial 1: 5.85 5.35 4.87 Average=5.36

Trial 2: 2.86 2.83 2.65 Average=2.78

Trial 3: 2.46 2.47 2.36 Average=2.43

Trial 4: 2.24 1.94 2.15 Average=2.11

 

Fine cut trial, 2 thou off the diameter, 4 thou/rev feed, 1200rpm, no coolant. Difference before and after, 2.0 thou, slightly uneven finish axially.

 

Conclusion: Not surprisingly very similar results to EN3B, but a better finish overall, as one might expect, as it is sold as free-cutting.

 

Regards,

 

Andrew

[Anonymous]

Final set of results, for aluminium alloy. The recommended turning speed for HSS is 500fpm, for carbide it is an eye-watering 1800fpm. My lathe doesn’t go that fast! The 500fpm equates to about 1700rpm, and the lathe is pretty noisy at that speed. I’m not going to annoy the neighbours on a Bank holiday Sunday by running at the top speed of 2500rpm. So the tests for aluminium are at one speed only, with and without coolant.

 

Material: Aluminium alloy, 30mm diameter, grade 6082T6 – tempered and artificially age hardened, ie, precipitation hardening

 

I used a different tip here; a high positive rake and polished tip from Greenwood Tools, advertised as specifically for light alloys. One of the main problems in machining light alloys is BUE, built up edges. The material softens and forms an edge on the tip, which mars the finish, before it breaks away and another edge forms, and so on. I have never suffered from this using these tips, and I normally turn light alloy dry, so they do seem to work. These tips have a radius of 0.2mm, so I halved the feedrate to 2 thou/rev for these tests.

 

Trial 1: 1700rpm (526fpm), coolant

Trial 2: 1700rpm (526fpm), no coolant

 

General Appearance:

 

Trial 1: smooth and even finish

Trial 2: smooth and even finish, but not as bright as 1 – I think this was caused by the swarf bunching up, getting trapped, and rubbing on the workpiece

Under a magnifying glass:

 

Trial 1: Surface smooth and even

Trial 2: Surface smooth and even, but with a faint helical pattern in places; caused by trapped swarf?

Swarf:

 

Trial 1: Long tight curls

Trial 2: Some tight curls, some messy balls of swarf, all mixed up

Surface Roughness (Ra µm):

 

Trial 1: 1.12 1.12 1.16 Average=1.13

Trial 2: 1.21 1.16 1.16 Average=1.18

 

Fine cut, 2 thou on diameter, 1700rpm, 2 thou/rev, with coolant. Difference on diameter before and after was 2.0 thou. Surface finish looked excellent, so I measured it as:

 

1.12 1.11 1.14 Average=1.12

 

Conclusions: No real surprise, aluminium alloy turns beautifully at high speeds and gives a good finish. Coolant doesn’t really affect the finish, but it might affect the swarf production, which in turn may affect the finish due to trapped swarf. However, I expect I’ll stick to cutting dry, as the speeds involved tend to result in washing the workshop with coolant.

 

Regards,

 

Andrew

[Anonymous]

Here are the final set of test results (stand up the boy who said hooray). It was suggested to me a while ago, on this forum, that high positive rake polished tips could be used to get a good finish on materials when using fine cuts (I’m embarrassed to say that I cannot recall who made the suggestion).

 

All tests were done with the afore mentioned tip from Greenwood Tools taking 2 thou off the diameter and at a feedrate of 2 thou/rev. All the materials are as listed in the previous posts. After each test I made a subjective assessment of the finish and measured the Ra values. Here are the results:

 

Brass CZ121 1700rpm, no coolant

 

Excellent surface finish, completely uniform

 

Ra values: 1.15 1.27 1.32 Average=1.25

 

EN3B 1200rpm, no coolant

 

Uneven finish axially

Ra values: 1.81 1.92 1.95 Average=1.89

 

EN1A 1200rpm, no coolant

 

Smooth finish, but slightly uneven axially

 

Ra values: 1.70 1.67 1.75 Average=1.71

 

Stainless Steel 303 800rpm, no coolant (I forgot to turn it on!)

 

Excellent finish, completely uniform

 

Ra values: 1.61 1.86 1.72 Average=1.73

 

Aluminium Alloy 6082T6 1700rpm, coolant

 

Excellent finish, completely uniform

 

Ra values: 1.12 1.11 1.14 Average=1.12

So, the polished tips do give an excellent finish, but not apparently on low carbon steels, at least not visually. It may be that the finer finishes are partly due to the slower feedrate.

 

Ho hum, there’s a point when experiments have to stop and the real work begins. So tomorrow in the workshop I’m actually going to make parts for my traction engines.

 

Regards,

 

Andrew

[nick morrisonParticipant @nickmorrison17107]

Congratulations, this is very interesting and useful, please extend and continue the

 

‘Cambridge trials’. regards Nick

[Nicholas FarrParticipant @nicholasfarr14254]

Hi Andrew, very interesting, and a very good presentation of your results, very easy to follow the individual trials.

 

Regards Nick

 

 

[Anonymous]

Thanks, I’m glad the results have been of some use. They have certainly made me think! At some point I expect I’ll try the Sumitomo tips from Arc, as they seem to be reasonably priced and come recommended.

 

I would also hope to add the results of extra tests as interest and time permits. The next test will be on EN8, as this is pertinent to another thread.

 

Regards,

 

Andrew

[mgjParticipant @mgj]

Yes thanks. It would seem that there is a lot of variation!

[chris stephensParticipant @chrisstephens63393]

Hi Guys,

I am sure that the tips that Arc sell are marvellous things but they are not necessarily the best for “our” use. If you want a really good tip for a very fine finishing cut, wel,l up to a mm or so, T1200A cermet is the material to go for. The only chap that I know sells to these to the hobby market is the guy who advertises in the comics. I have not bought from him, but I did from his predecessor. I believe that he still supplies instructions for there best use, follow them closely if you don’t want to chip the tip!

To sum up, Sumitomo make hundreds of tips but not all of them are for us. Don’t be disappointed and buy the right ones first time, as first impressions tend to last!

 

http://www.carterprecisiontools.co.uk/index.html , is offered for information but I have not had any dealings with them and am not connected in any way.

christephens

[Hugh GilhespieParticipant @hughgilhespie56163]

Hi, Just to say that I have dealt with Carter Precision Tools several times and it is a superb service. Highly recommended.

 

Regards, Hugh

[HasBeanParticipant @hasbean]

Gents,

I have used the predecessor to Sumitomo T1200A (T12A) and found it gave a superb finish but, as mentioned, care is required as they did chip easily.

I now use Mitsubishi NX2525 which is also a cermet which appears to be just that little bit tougher, recommended to me by, and available from, Greenwood Tools.

 

Regards,

 

Paul

[Anonymous]

It’s what you’ve been waiting for; the turning trial results for EN8! Not surprisingly in many ways it was similar to EN1A and EN3B, but in other ways was sufficiently different to be interesting.

 

First, turning trials as before, same insert from Korloy, 40 thou depth of cut, 4 thou/rev feed.

 

Material: EN8, 1.625″ diameter

 

Trial1: 260rpm (111fpm), no coolant

Trial2: 260rpm (111fpm), coolant

Trial3: 800rpm (340fpm), coolant

Trial4: 800rpm (340fpm), no coolant

General Appearance:

 

Trial1: Uniform finish but slightly rough, picks up fibres from a paper towel

Trial2: Uniform finish, feels smoother than 1

Trial3: Uniform finish, feels smooth, but picks up fibres from a paper towel

Trial4: Uniform finish, feels smooth

Under a Magnifying Glass:

 

Trial1: Surface is slightly torn

Trial2: Dull but not torn

Trial3: Dull but not apparently torn

Trial4: Uniform, not torn, slightly shiny

 

Swarf:

 

In all cases the swarf came off as a short (5mm) tightly curled helix; at higher speeds it was hotter!

Surface Roughness (Ra µm):

 

Trial1: 5.73 5.36 5.90 Average=5.66

Trial2: 3.95 4.02 3.52 Average=3.83

Trial3: 3.06 3.36 3.06 Average=3.16

Trial4: 3.27 3.20 2.66 Average=3.04

 

So similar to previous steels, but with two major differences. The turned surface was always very uniform axially and radially, even when slightly torn. Secondly the higher speeds didn’t give as great an improvement as might be expected from previous results.

 

So, do another trial, same conditions as trial 4, except at 1200rpm (511pm). Like night and day! The finish is now almost a mirror finish, easily the best of the low carbon steels seen so far. The surface is smooth, but with slight radial grooves under the magnifying glass.

 

Surface Roughness (Ra µm)

 

1.55 1.76 1.62 Average=1.64

 

I’m gobsmacked at the difference in finish between 800rpm and 1200rpm.

 

Finally the fine depth of cut trial, insert from Greenwood Tools as before, 1200rpm, 2 thou/rev feed and no coolant.

 

The finish is smooth and uniform but not as good as for the deeper depth of cut. Under the magnifying glass the surface is smooth and uniform.

 

Surface Roughness (Ra µm)

 

1.92 1.96 1.86 Average=1.91

So there we have it, similar to EN1A and EN3B, but different too.

 

Regards,

 

Andrew

[Anonymous]

Here are some more tests, this time using the Mitsubishi NX2525 tips from Greenwood Tools, with a 0.2mm corner radius. These tests are specifically looking at the finish obtained with small depth of cut. Speeds for each material were those found to give the best finish in the above tests. Common for each test are the following:

 

After a 5 thou depth of cut to ensure concentricity of the part, a test cut of 1 thou depth, 2thou off the diameter. In all cases feed was 2 thou/rev.

 

EN3B: 1200rpm, no coolant

 

Surface finish is inconsistent axially and has a rough feel; looked better after the initial clean-up pass

 

Ra Measurements (µm):

 

2.95 3.32 3.55 Average=3.27

 

EN1A: 1200rpm, no coolant

 

Same as EN3B, surface finish is inconsistent axially; looked better after the initial clean-up pass

 

Ra Measurements (µm):

 

3.15 3.06 3.15 Average=3.12

 

Stainless Steel 303: 800rpm, with coolant

 

Very uniform finish with no tearing visible

 

Ra Measurements (µm):

 

0.95 1.05 1.12 Average=1.04

 

Brass CZ121: 1700rpm, no coolant

 

Slightly uneven finish axially

 

Ra Measurements (µm):

 

3.12 2.97 2.86 Average=2.98

 

Aluminium 6082T6: 1700rpm, no coolant

 

Excellent finish, but some slight axial variation, possibly caused by swarf getting trapped

 

Ra Measurements (µm):

 

0.80 1.21 1.01 Average=1.00

 

EN8: 1200rpm, no coolant

 

Slightly uneven finish, not torn but a series of axial grooves visible under the magnifying glass

 

Ra Measurements (µm):

 

2.70 2.72 2.91 Average=2.78

 

For convenience the Ra finish obtained with a polished positive rake insert above are repeated here:

 

EN3B: 1.89

EN1A: 1.71

Stainless Steel 303: 1.73

Brass CZ121: 1.25

Aluminium 6082T6: 1.12

Discussion: These inserts gave a very good finish on stainless steel, the best seen so far, and marginally better on aluminium, although I expect this to be within the error bounds of the measurement. However, the results for low carbon steels, and surprisingly for brass, were worse than those for a polished insert. All in all a bit of a mixed bag. At some point I will buy some Sumitomo inserts from Carter Precision Tools, but I don’t find the website easy to understand, so it’ll have to wait until I have more time.

 

One thing I am learning from these tests, is that I cannot get a good finish on low carbon steels without using a decent depth of cut. I just need to learn to be confident in my micrometer readings and cross-slide dial, and don’t pussyfoot around with small depths of cut; or just cheat and use the cylindrical grinder.

 

When time allows the next tests will be on annealed silver steel.

 

Regards,

 

Andrew

 

[Steve WithnellParticipant @stevewithnell34426]

EN16T Turning trials from Blackpool

 

Carbide tip 3/4 inch EN16T round bar under test

 

1500 rpm no coolant

 

Following advice went hard at it.

 

Blue turnings stuck to arm and burnt same – must wear long sleeves

Sparks off workpiece – not seen that before

Lathe (5 x 22) not happy at 0.5mm cut

Mirror finish on workpiece

 

Conclusion

 

EN16T should only be used by real men with real lathes and tools, anything associated with rice or pasta won’t make the grade.

 

EN8 will have to do in my ‘shop…

 

Regards

 

 

Steve

 

[Nicholas FarrParticipant @nicholasfarr14254]

Hi Steve, according to the Model Engineers’ Workshop Data Book, that was issued as a collection of cards in the early days, EN16 and EN16M are considered as being poor at ease of machining, it dosen’t list EN16T so I don’t know if it is any different.

 

Regards Nick.

[KWILParticipant @kwil]

EN16T is, as it says Tempered.

[Steve WithnellParticipant @stevewithnell34426]

The piece I have must have been EN16BT – “Bad Tempered”

 

Seriously, I did get an excellent finish, but the skill to deliver that finish “at size” is probably beyond me. You can’t creep up on this stuff. It also tests the rigidity of the machine too.

 

Steve

[Anonymous]

Hi Steve,

 

Thanks for posting the results for EN16T. Oeeeer, I like rice and pasta, so I’d bettter steer clear! In my defence I can at least say that I don’t like, or eat, quiche.

 

It’s interesting that your results seem to reinforce my experiences. In order to get a decent finish on low and medium carbon steels you need to run fast, with a decent depth of cut.

 

I always wear long sleeves when turning for just that reason; my normal fleece has loads of metal embedded in it where the swarf has melted the material. I have seen sparks coming off steel when turning, but only on hot rolled or black steel. I assume that the sparks are actually the mill scale coming off red hot, rather than the swarf itself. Can anybody confirm this?

 

Who wants to try EN24?

 

Next time I order from my steel supplier I might get a few lengths of some of the more unusual steels, just to see how they perform.

 

Regards,

 

Andrew

 

On edit: Steve, you’re ideally placed to answer a machining question; what feeds and speeds should we use when turning Blackpool rock?

Edited By Andrew Johnston on 03/07/2011 22:29:14

[Anonymous]

After a bit of a break, I've done another set of trials; this time on silver steel. The silver steel used was 25mm diameter, recently bought in my local professional tool warehouse. There's no direct equivalent in Machinery's Handbook, but I think that the tool steel W1 is a fairly close match; W1 is a high carbon plain steel for water hardening. For W1 the recommended speeds are 100fpm for HSS and 350fpm for uncoated carbide. For these trials I used speeds of 370rpm and 1200rpm. The insert used was a 0.2mm radius insert from Korloy, grade NC3120 for steel. In view of the small nose radius in each case depth of cut was 20 thou and a feed rate of 2 thou/rev. I tried four combinations:

Trial1: 370rpm, no coolant

Trial2: 1200rpm, no coolant

Trial3: 370 rpm, coolant

Trial4: 1200rpm, coolant

 

General Appearance:

 

Trial1: Uniform finish but felt slightly rough

Trial2: Uniform finish, feels smooth

Trial3: Uniform finish, feels smooth, but there was concentric banding every 40 thou

Trial4: Uniform finish, feels smooth, but there was concentric banding every 40 thou

 

Under a Magnifying Glass:

 

Trial1: Surface is slightly torn

Trial2: Smooth and even finish

Trial3: Smooth and even finish, but with banding

Trial4: Smooth and even finish, but with banding

 

Swarf:

 

Generally the swarf came off in long curls. Without coolant the curls were very tight, and at 1200rpm were dark blue in colour. With coolant the curls were much more open.

 

Surface Roughness (Ra µm):

 

Trial1: 2.67 2.51 1.80 Average=2.33

Trial2: 1.80 1.75 1.81 Average=1.79

Trial3: 1.63 1.76 1.63 Average=1.67

Trial4: 1.45 1.63 1.50 Average=1.53

 

Just out of interest I also tried a run at 1200rpm with no coolant and a feedrate of 1 thou/rev. The finish felt very smooth and even, the average roughness was 1.65µm. Slightly worse than with 2 thou/rev, so might as well use the higher feedrate and save time. I was slightly surprised that with such a low feedrate the swarf still came off in long curls.

 

Generally the finish from any of the trials was acceptable, with a slight caveat for Trial 1. I was rather surprised by this, as I started the trials with the memory that silver steel was a bit of a PITA to machine and was prone to tear if the cutting conditions were wrong. Either my memory is playing tricks, or I had a duff batch of silver steel. In practice I think I'll use about 350fpm with no coolant. Although the finish is slightly rougher it is acceptable and doesn't have the very visible banding. I've no idea why the coolant should cause the banding, but it was consistent.

 

In the near future I need to do a batch of hardening in the electric furnace. When I do I'll put a length of the silver steel in and harden it. I'll then have a go at turning it in it's hardened state.

 

Regards,

 

Andrew

Edited By Andrew Johnston on 21/05/2012 21:59:44

[jason udallParticipant @jasonudall57142]

Love this.

Nice to see some original research.

thanks for sharing

[Russell EberhardtParticipant @russelleberhardt48058]

Posted by Andrew Johnston on 21/05/2012 21:58:52:Although the finish is slightly rougher it is acceptable and doesn't have the very visible banding. I've no idea why the coolant should cause the banding, but it was consistent.

Perhaps the banding is there all the time but the finer finish with coolant makes it more visible. I've noticed banding occasionally but it is always at leadscrew pitch. I have also noticed it can appear on an otherwise good finish when polishing after turning.

I' ve always assumed that it is caused by a slight rocking of the saddle on it's ways but stand to be corrected.

Russell.

[KWILParticipant @kwil]

These result concur with my long held view and experience, that if you get the cutting conditions correct with insert tooling, the need for coolant is very much rediced. Colour of the swarf (without coolant) is always a good indication of the near correct conditions.

Thank you Andrew for your ongoing commitment to these trials.

[Author]

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