Thread: Some basic metal turning questions

For starters what type of tool are you using(HSS or Carbide)

Do you know what type of material you have.

For got to ask what size lathe are you using,what HP have you got.

Blued swarf coming off generally indicates too much heat for whatever reason, depth of cut, feed rate, workpiece speed or combination of any of them.

Assuming you are using HSS cutters the RPM is calculated by

1000 * Surface Speed
-----------------------------
3 * Diameter of work

The surface speed for Mild Steel is around 30 - 45 so for turning 50 mm stock the RPM would be 200 RPM, for 25 mm it would be around 400 RPM etc. If you are using carbide tooling you can triple the RPM.

As for feed rate and depth of cut, this depends on the rigidity of the lathe and it's power - the best approach is to feed the tool manually at first and let the lathe "talk to you". You should be able to feel when the lathe is cutting well and when you are overloading it.

I'm using HHS, and I think the lathe has a 1 HP motor. The lathe is identical to this one:

There are a lot of variables when it comes to turning,if your machine is metric you could try a feed rate of .05 to .1

Depth of cut you could try for roughing any where from 2 to 5 mm.

Usually the HP will determine your DOC,although on a machine like that you would probably choose the finer Feed for the deeper DOC.

Are you using your HSS with a Chip Breaker ground or just Top Rake.

What is your Finish like on your job with the settings you are currently using.

As allready mentioned you could probably run at about 200 RPM but as your Diameter reduces if you want you can increase it.

It is somewhat unusual to be getting a blue swarf when using HSS.

How much time are you getting out of your tool between grinds.

You still didnt say what type of material you are machining,this can also influence the colour of the swarf.

With the coolant you are using is it oil or a solubile cutting oil,If it is solubile and you havent got a coolant pump I would suggest filling an empty 600mil or larger soft drink bottle and use this to squirt on the job.(just punch a small hole in the lid with a nail or scriber and squirt on the cutting edge while machining,if using straight oil and you dont mind the smoke use a small brush and paint your material with it before machining and dab it occasionally as its cutting.)

Originally Posted by Gavin Newman

Blued swarf coming off generally indicates too much heat for whatever reason, depth of cut, feed rate, workpiece speed or combination of any of them.

Only for HSS tools, if you are running carbide dry and the chips are not blue you are not trying hard enough...

But as you say, blue chips when using HSS tools is a big no no, you will blunten the cutting edge quick smart...

Thanks for the advice. I'm even newer to it than you think. I'm turning an old shaft of some machine into a dolly for a machine similar to a jack hammer (it's a pneumatic picket post driver). I don't know what sort of steel it is, but I assume it's of decent quality (is that low carbon?). My main problem is my own lack of patience. I've been cutting at 2mm to 3mm for a while now and it's all going well. But slowwwww to reduce 50mm to 25mm in some parts. I swapped over to a tungsten cutter and I've slowed the whole thing down.

I'm using Rocol cutting oil just swirled across the work piece before each cut. The image shows the basic shape of the dolly, with the shaft being 25mm, the middle collar being 35mm and the lump on the end being 50mm.

What length is your job,are you using a live centre to support the end.
Is your 2/3mm depth of cut or off the diameter.
With the Carbide tooling you should be able to increase the RPM and Feed rate.

Originally Posted by pipeclay

What length is your job,are you using a live centre to support the end.
Is your 2/3mm depth of cut or off the diameter.
With the Carbide tooling you should be able to increase the RPM and Feed rate.

It's 210mm long, I'm using a live centre. Off the cut. Took me a moment to work out what you meant; so I'm cutting 4mm off the diameter. This is the first real job on the lathe for me. I've just been learning and making mistakes on scrap up till now. I'd say the biggest learning curve is the type of tool to use for each task.

Do you have Left and Right hand tools.
Have you finished the job or are you after advice on how to goabout doing it.

Originally Posted by pipeclay

Do you have Left and Right hand tools.
Have you finished the job or are you after advice on how to goabout doing it.

Thanks Pipeclay. I have almost finished. I need to clean it up a bit. I think my main problem was that, for a first job, there was an enormous amount of metal to remove. The swarf would fill a bucket! I made a few mistakes. Again impatience. But it should work all right.

Originally Posted by Rossluck

Thanks for the advice. I'm even newer to it than you think. I'm turning an old shaft of some machine into a dolly for a machine similar to a jack hammer (it's a pneumatic picket post driver). I don't know what sort of steel it is, but I assume it's of decent quality (is that low carbon?). My main problem is my own lack of patience. I've been cutting at 2mm to 3mm for a while now and it's all going well. But slowwwww to reduce 50mm to 25mm in some parts. I swapped over to a tungsten cutter and I've slowed the whole thing down.

I'm using Rocol cutting oil just swirled across the work piece before each cut. The image shows the basic shape of the dolly, with the shaft being 25mm, the middle collar being 35mm and the lump on the end being 50mm.

I assume when you said your cutting oil was "swirled across the work piece" you meant that you ran the tip of the oil bottle along the workpiece while it was spinning leaving a spiral of oil in its wake ... right? I only mention this because as a beginner I did the same thing because my instructor kept telling me to "use oil!"

Eventually I realized that this wastes a lot of oil (I think that happened about the time I started to pay for my own oil, instead of using the school's supply). Since you're just starting out, a quick tip that might save you a few pennies on oil - use a cheap paintbrush! Load the paintbrush with oil, then run it along the spinning workpiece (keep your hands and the brush away from the spinning chuck jaws).

This will apply a nice even coat of oil along the workpiece, and in turn will use less oil. Less gets flung off for one thing. And since the brush gets loaded with oil, you can often use it for 2 or 3 passes before needing to reach for the bottle again.

Just a thought.