First cuts with the lathe

[Chris12Participant @chris12]

I finally received today the metal I ordered couple of weeks ago (thanks Evri for loosing the first parcel.. 🙄)

 

Cutting in steel was a complete disaster. I tried using the leadscrew feed, tightened everything I could, checked my tool angles, etc but no, no success. My guess is that the stock protrudes too much and should be supported by a center. Will try that tomorrow.

 

I was a bit more lucky with brass. Using the leadscrew feed (via half but) gave an acceptable result.

 

It is quite hard to manually feed at a constant rate without any stop.

 

But was fun nonetheless!

 

[PeteParticipant @pete41194]

My own rule of thumb for material stick out past the chuck is an absolute maximum of 3 times it’s diameter Chris. Even after about 2 times for length, I’d probably still use a live center. Although the expected depth of cut also is part of it. Deeper depths of cut needs tail stock support sooner. What alloy of steel is that? Are you 100% sure your cutting tool tip was on the lathe center line?

Then there’s part rpm. In general for most steels and with high speed cutting tools, that’s around 100 feet per minute maximum. Maybe 300-500 feet per minute with carbide. Measure your parts O.D. multiply by 4 as a round number, that’s your part circumference plus a bit. Divide that into what percentage of a foot or it’s metric equivalent is for your part, Use that 100 feet per minute or it’s metric equivalent, divide that by your percentage of that foot / metric for your maximum allowable rpm on the part. Although I prefer dropping that by around 15% – 20% because the cutting tool edges last quite a bit longer.

Power feed or even hand rate is also important. Under power I look for at least .002″ of feed or higher per part revolution. But that’s not completely possible with very tiny parts. Going too slow will cause the tools to rub and not cut well. And any rubbing quickly dulls the tool cutting edge. Feeding too slow isn’t linear and may not produce the best surface finish over a higher feed rate.

The hand crank on the hand wheels is mostly for large, quick and non cutting moves. Try using one hand on the outside of the hand wheels outer diameter and go far enough to then start to use your second hand to maintain that same feed rate. You then go hand over hand, or on smaller hand wheels use your fingers on each hand to do the same. Some steel alloys and especially some stainless will easily work harden in a literal instant. If the tool isn’t being fed into the work and actually cutting, it has to be withdrawn as quickly as possible. In less than a second if you can do it. The exact same is equally true even when drilling. It’s the heat produced while cutting or with abrasive materials that destroys cutting tools including carbide or even diamond tipped tools which you’ll probably never use. All materials have maximum limits for just how fast they can be machined without destroying the cutting tool edges. That’s a law of physics and can’t be broken with any chance of success.

Industrial recommendations for maximum tool and part rpms usually assume extremely rigid machines and flood coolant is available. Since we don’t have it and our machines are far lighter, any of those recommendations need to be reduced, sometimes by quite a bit. With industrial machining, time is money. Tool life is less important for them than maximum part production speed. Our needs are usually the reverse of that, cutting edge life and cost is far more important for us.

Learn to pay attention to the color of your chips when cutting steel. With high speed steel cutting tools, NO color change at all to even a very light yellow. The tool will still continue to cut at that color, but tool life will be reduced. With carbide, at most a light to medium blue color AFTER the chip leaves the cutting tool and not as the chip is being formed. Dark blue to purple is common on some Youtube videos, but that’s usually with much heavier lathes. And while impressive looking, it still reduces cutting edge life by quite a bit. The dark blue or purple colored chip guys never seem to mention that. With the correct cutting tool angles for the material being cut, the majority of the developed cutting heat should come off in the chip and very little created in the work piece itself. And dull tools always create much more heat. That should be enough to get you started.

[JasonBModerator @jasonb]

Post a photo of the cutting tool in the toolpost that you used on the steel, looks like it had quite a rounded end which is not ideal.

As for handfeeding use TWO hands on the rim of the wheel turning with one while you reposition the othet then turn with that while you reposition the first. The crank handle is not what you want to use for a good finish.

[Howard LewisParticipant @howardlewis46836]

Are you a newcomer to the hobby?

If so, i would advocate buying at least one book on lathework. It will answer many questions before you even ask them. I can make some suggestions if you want.

Pete has covered most points, but a few more questions.

Since it has cut brass satisfactorily, something has changed.

Presumably, you were using a High Speed Steel knife tool?

Was it sharp and properly ground?

The clearance angles (both vertical and horizontal) should be about ten degrees. Don’t go beyond that, or it will weaken the cutting edge, and reduce the area of metal to conduct away the heat generated by the cutting process.

The tool should be mounted so that the cutting edge is on the centreline. If it isn’t it will not cut properly, and leave a pop when you face the end of a bar.

(Too high and it will rub rather than cut, too low and the clearance angles will seem to be excessive)

The bar appears to be about 10 mm diameter, and the length protruding from the chuck should not be excess, , as already said, only few diameters of the work, or it will flex and cause all sorts of problems.

The depth of cut should not be excessive. The operator manual for a mini lathe advises that a roughing cut should not exceed 0.010″ (0.25 mm)Bearing mind the low power of the brushed motor fitted to older mini lathes, this is quite conservative.

For finishing, the feed rate should be about 0.002″ (0.050 mm) per rev, certainly not more than 0.004″/rev.

Learning to rotate a handwheel slowly and steadily is one the techniques that needs to be learned very early on.

Assuming that the material is mild steel, the speed should not exceed 900 rpm.

Because i am too lazy to change belts, too often, most of my work is done at no more than 600 rpm

HTH

Howard

[John HaineParticipant @johnhaine32865]

What sort of steel did you buy and from whom? Lots of steel stock is intended for construction and machineability is not a requirement. If you are starting out it’s better to buy specifically free cutting steel.

[John Haine]

On John Haine Said:

What sort of steel did you buy and from whom? Lots of steel stock is intended for construction and machineability is not a requirement. If you are starting out it’s better to buy specifically free cutting steel.

+1 What is the provenance of the steel and brass?

The finish on the steel is really awful but is nothing to do with stick out. I’d agree with John and suggest it is at least partly the material.

The finish on the brass is poor too and there is a spiral where the tool has been wound back to the starting point. That implies the setup isn’t very rigid, or there is something wrong with the tool. If the issue was stick out then the depth of the spiral would get deeper further out from the chuck. The depth seems quite consistent so stick out is not the issue.

It would help to see the bigger picture, ie, the whole lathe and setup plus details of the tooling.

Julie

[Chris12Participant @chris12]

Thanks all for the feedbacks, really appreciated.

 

As said, this was my first attempt, so I most probably did many things wrong.

 

The stock is EN1A, bought specially as it is a free cutting steel. Both the steel and the brass come from RapidMetal.

For feeding, I either used the feed (from the half nut) or manually fed it, turning the handle very carefully and trying to be as regular as possible.

I will post a picture of the tool tonight. But I really think my stock was protruding too much. Will try again tonight with either less stock out of the chuck or with a dead center.

[Dave SParticipant @daves59043]

Looks like cold drawn, which can be a bugger to cut nicely even if in a ‘free cutting’ alloy

[noel shelleyParticipant @noelshelley55608]

The digging and tearing put me in the mind the tool could be below centre, blunt, to deeper cut or the material is not for turning. Once you know or have some idea you will know which may be the cause. Buy some material you know will work eg free cutting steel and have a go. The book, Lathe work – a complete course, No 34 in the workshop series is a good start at about £8. It will get you started on the how’s and why’s.. If your bar ls 3/4″ (20mm ) Then run the lathe at about 500 rpm. Set centre height by offering the top of the cutter to the tailstock centre first then using a bit of short (1″) scrap with only 1/2″ stick out, face the end and see that it’s correct, To low will leave a pip, to high will try to push the pip off, adjust as necessary. Beer can Etc makes good shim to effect adjustment.  Good Luck. Noel.

[SillyOldDufferModerator @sillyoldduffer]

Don’t panic Chris!  This sort of result is a common beginner experience.  The lathe is designed to cut metal, including steel, but the operator has to get several ducks in a row!   For example:

• Suitable metal – many alloys do not machine well.  (EN1A should be OK)
• Correct cutter, sharp, and positioned at centre height (note advice above about rubbing causing rapid blunting, heavy handed is also bad – chattering etc.)
• Cutter and workpiece held rigidly:  minimise overhang, snug up gibs, lock unused slides, support with centres etc.
• RPM, Feed-rate and depth-of-cut balanced to match the cutter, material and machine.  I start with RPM = 10000/diameter, which is ball-park correct for HSS cutting mild-steel.
• Lubricate if the cutter is HSS

Next pictures result from me deliberately doing everything wrong to vibrate my lathe in an experiment!  The pipe doesn’t machine well because the steel tends to smear and tear, the work is grossly over extended and unsupported, and I used a carbide roughing cutter set  too low and run at the wrong rpm, feed-rate and depth-of-cut.  No lubrication, and I moved the saddle manually, not power traverse:

Result, appalling noise, and the pipe suffered a horrible mix of cutting, digging in, and unwanted burnishing:

I suspect Chris has accidentally hit similar issues is milder form!  A couple of things not quite right, easily done.  If photos and details are provided, the team will spot problems.  They’re often easily corrected.

For example, what sort of cutter, and how was set it to height?  Other gotchas: starting out, I bought a set of brazed carbide cutters that were vile: found much later these are often sold unsharpened, and need to be touched up on a green-wheeled grinder – no-one told me that!   And if you go with carbide inserts, my preferred cutters, the sharp type industry recommend for non-ferrous metals do a good job on steel at hobby metal removal rates.   Some insert shapes absolutely require a heavy rigid industrial machine, high-rpm, with a powerful motor!

There’s a fair bit to learn.

I wonder if this experience has affected Chris’s views on milling on his small lathe?  It should, at least temporarily!  I suggest first step is to get the lathe working as a lathe. Once that’s conquered, look at milling again.  If turning steel is a struggle, then milling with a vertical slide will be even more difficult!   Take it one step at a time.

Dave

 

 

[Mike HurleyParticipant @mikehurley60381]

<p style=”text-align: left;”>As the old saying goes – So little time, so much to learn.</p>
Even after years cutting metal, I still got some right old rough finishes occasionally! The thing to do is learn by finding out why: go back to basics every time. It will be one of the common factors concisely documented by others above.

Half the pleasure in this hobby is about solving problems and the sense of achievement when resolved

Just don’t get disheartened! Everyone on this forum has been there sometime!

Mike

 

 

[noel shelleyParticipant @noelshelley55608]

Your a brave man Dave to do that ! Noel.

[Chris12Participant @chris12]

Thanks Dave, Noel and all for your feedbacks, very kind of you !

To answer some questions/points :

– I have books. Many books ! Been thinking about doing model engineering for 2 years now, so been reading/watching a lot about it.

– I’m not disheartened! I used to do woodworking until not so long ago, and I remember the first box I made (still have it, still using it). But it is an abomination. Compared to the latest piece of furniture I made, you can see the evolution. I know this is the same here, there is some learning curve. And that’s part of the charm.

That being said, it’s nice to have some feedbacks about what is being done wrongly, helps to improve quickly.

 

Not thinking too much about the milling side right now, I think I need to focus on using the lathe properly before thinking about milling !

Some carbide tools were provided with the machine, but they dont inspire me confidence. Gave them a quick try and I think I will stick to hss.

Here are some pics of one of the tool I’ve been using on steel : (I think the angles are okayish, but the cutting corner looks a bit dodgy..)

 

[Howard LewisParticipant @howardlewis46836]

All newbies need to learn the basics, so that they become more competent as they gain experience.

Hopefully, the steel IS free cutting mild steel.

Avoid rebar like the plague, never intended for machining, so VERY difficult to machine for a decent finish

There is a lot to learn, all at once, so commence with the MINIMUM of of variables.

Having ground the tool and set it on centre height, so do not have more than three diameters length sticking out of the chuck (Incidentally, a Self Centering, 3 jaw chuck is MOST unlikely to hold work absolutely concentric. , 0.003″ (0.075 mm) run out is a good one).

As an Apprentice, the first two things that I learned were that putting on a cut removed twice as much as expected (the other side coming round and being cut) and how to rotate a handwheel slowly and steadily to achieve a steady feed.

Where are you located? Some face to face tuition will help you.

Part of the learning curve is to sharpen the tool correctly and to set it on centre height, and then to learn by cutting metal, at finding the depths of cut and feed rates to provide a good surface finish.

Using power feed might give the finish that you want, but removes the lesson of learning how to handle the controls.

For a start just stick to ABSOLUTE basics, set a low cutting speed, learn how depth of cut, and feed  rate affect surface finish. Buy and read “Basic Lathework” by Stan Bray (45 in the Workshop Practice Series) or Lathework, A Complete Course” by Harold Hall (34 in the WPS)

Stan Bray was the founding editor of Model Engineer’s Workshop, and was succeeded by Harold Hall, so they both know what they were about.

A knife tool, although sharp and set at centre height will still produce a very slightly rough finish.  A minute rounding of the nose will improve matters, but learn to walk before even trying to jog, let alone run or sprint.

Since the tool is moving along a rotating workpiece, the cut will actually be a spiral. A slow feed per rev will GENERATE a very fine spiral, a rapid feed will produce an obvious spiral.

The depth of cut will determine how obvious the spiral is.

As you learn the basics, on one machine, you will also become familiar with the characteristics of that particular machine. A supposedly identical machine might behave slightly differently, for a variety of reasons.

Until you have gained experience, you are going to have difficulty in working to fine limits, so don’t expect air tight fits! (Some of us, even with years of experience have difficulty from time to time!)

Just take time to learn, and learn from your mistakes

Howard

[JasonBModerator @jasonb]

Most likely that cutter

 

The area I have marked around the edge in pink does not really look like it has been ground or if it has it is flat and that is why it cut the brass better. Try grinding again so that the main area goes right out to the external edges

The very top edge of the rounded corner is also blunt (green)

 

[bernard towersParticipant @bernardtowers37738]

The cutting edge of your tool is non existent I suggest that you grind back the front edge to achieve a sharp edge and the side angle if necessary then stone the ground edges then wipe the stone round the front left corner a couple of times to create a small radius as mentioned above by Howard. Best of luck.

[Howard LewisParticipant @howardlewis46836]

That tool is not sharp! Which will contribute to be your problems

It is not sharp on any edge.

Read your books for what they say about tool grinding.

Regrind it until both faces have sharp edges, set it on centre height, and then try with a cut of say 0.005″ (0.0127 mm) with a slow feed rate. Things may well improve.

Try to find someone near you who who is experienced and is willing to provide some face to face tuition. You will be surprised mat the wrinkles that become visible on the way!

Keep us updated on your progress

Howard

[noel shelleyParticipant @noelshelley55608]

Not much point in me saying much, the others have said it ! I’m surprised you got it to cut at all ! Re grind it to a sharp edge on both top edges, try to maintain the angles/clearance (don’t worry about a slight rounding on the vertical edge yet) Re set and try again. It should now cut all be it that the finish may not be perfect. A gentle stoning on the front vertical corner whilst keeping the angle will improve the finish. Good luck. Noel.

[jamesp1Participant @jamesp1]

Cutter? Surely lathes have tools and toolbits and milling machines have cutters? The difference being cutters rotate while tools and toolbits remain stationary? (Not sure where that leaves shapers though?)

[Howard LewisParticipant @howardlewis46836]

Cutter? Surely lathes have tools and toolbits and milling machines have cutters? The difference being cutters rotate while tools and toolbits remain stationary? (Not sure where that leaves shapers though?)

While most of us are trying help a newbie, can the above please be moved to pedants corner.

[Nigel Graham 2Participant @nigelgraham2]

Another book by Harold Hall that you may already know of, is Tool & Cutter Sharpening (No. 38 in the Workshop series).

It walks you through making simple to moderately elaborate accessories that turn the ordinary offhand-grinder (usually supplied with a very rough-&-ready rest) into a basic but very useful tool-grinder for HSS lathe tools.

A tip on using the oil-stone to put that tiny radius on the very corner of the tool: rest the tool on a suitable surface such as the bench (not the lathe or its stand!) and rub the stone up towards the edge. Same principle as sharpening any edge tools. The rounding will often show as a bright line because its surface is slightly smoother than that from the grinder.

Apart from the better finish as Noel has pointed out, machine components are normally finish-turned with a tiny root radius in grooves and shoulders, to reduce stress concentration.

[Chris12Participant @chris12]

Thanks all for your advices. So i re-grinded the tool, and this time didnt round the edge as i did previously. Just used an oil stone to remove the burrs.

 

The results are promising ! (sorry the pics arent great. need to get some light at the lathe). The finish is still not great, but at least it is somewhat smooth.

 

Something i would like to get clarified : in many of the books, they advise to slightly round the edge, or put a radius. Should that radius be put only on the vertical edge ?

 

 

 

[Wink HackmanParticipant @winkhackman25989]

Give the carbide insert tooling a try – I use this tool 90% of the time:

https://jbcuttingtools.com/shop/ols/products/ccmt09-turning-and-facing-lathe-tool-right-hand-ccm-trn-and-fcn1

You can use the CCGT ground and polished inserts on both steel and softer metals, and the finish is excellent.  I only ever use HSS now if I need to make a form tool or something very small where I can’t use an insert.  Another benefit is that you don’t need to check tool centre height and re-shim after sharpening the tool. Just change the insert and carry on.

[Charles LamontParticipant @charleslamont71117]

You can put a radius, something like 1mm, on the vertical edge between the front and side faces.

The edge of the top face should be dead sharp all round.

Your chips seem to be blue, which means the spindle is running too fast for an HSS tool.

For cutting mild steel with an HSS tool, you need some cutting lubricant.

[RobCoxParticipant @robcox]

Hi Chris12,

Your last paragraph above has hit the nail firmly on the head! Yes, the vertical edge is the one that you round off. It makes the pointy tip stronger by getting rid of the sharp delicate bit on the end. The cutting edges, the two near horizontal ones, should be sharp enough that were you to run your finger over them they’d stand a good chance of cutting you.

I can recommend a youtube video by ThisOldTony in which he starts with an unsharpened toolbit and shows why each of the grinds is done and tries it out each step of the way.

If you’ve been woodworking, cutting metal has similarities except the forces are greater so the tool angles are less acute for strength. Your metalworking lathe tool should be able to cut wood, albeit without leaving the nice surface finish you’re familiar with.

Rob

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