There is a lot of science involved. Basically it is how the material being cut reacts with the cutting edge of the tool. If you compare the same material with different cutting edge profiles it will give you some idea. Tool manufacturers such as Sandvik have numerous solutions and in production machines it may take numerous trials with a particular machine to get to an optimum tool life. You can search online and find many articles on the science behind it all. With small hobby machines and a single type of tool for everything much is trial and error, what works for doesn’t for another.

"Hence Mr Wheelers question if you saw it in time."

The mysterious disappearing post! I wondered about that as it vanished almost in front of my eyes, without trace!

Sense and sensibilities ensuring inclusivity and diversity I guess?

fpm is directly scalable from a Sherline to a Holbrook but that is where the similarity and theory end and why cutting speeds and feeds are recommended and not compulsory, dependant on tool material and geometry, machine rigidity, the way the work is held etc. The chances of getting a consensus on the OP question is about as likely on here as agreement on which lathe is best.

Paul.

On a small hobby machine it's often suck it and see

If you do a big piece cutting can be not very good on the outside and improves as you whittle it down

Not so easy to see subtle differences on a larger powerful machine because it compensates for more issues

On the other hand a unimat sl shows you everything, a unimat is great for showing you good tool grinding angles since you have almost no stiffness

Edited By Ady1 on 01/08/2020 08:02:59

Suck it and see also applies in industry. For example a lot of high temperature alloys can be machined but since very few businesses use them there is not real "knowledge". So manufacturing engineers have to find cutting speeds. The easiest way is to put a piece in a lathe………

JA

Try Sparey,s book, still good after all this time.

Simple Direct No bull.

Mr Wheeler, I thought it was incisive and excellent advice-but it disappeared.

I also thought it was good advice although very much straight to the point, a very similar comment has been made but not in such a direct manner.

Emgee

Chris Tick Tock,

I hope you did not think I was being smart or rude with my reply, this was not my intention.

The reason I mentioned Sparey,s book is because, like you, I had little or no idea regarding cutting speeds/materials ect, but this book explains it all in plain terms. If it is now out of print, more,s the pity, since it,s a goldmine of information for beginners [like me ] No doubt there are many other good book available, I just never felt the need to look any further than this one since it seems to cover almost everything.

No doubt others here will advise you on the subject but the speeds given by Sparey are ;

Stainless Steel 50ft per min

Carbon Steel 60

Cast Iron,, Mild Steel Wrought Iron 80 ft per min

Brass 200

Aluminium and its Alloys 300.

To calculate revs Cutting speed divided by quarter of work diameter= r-p-m

Sorry if I sounded like a Smart-Arse, that is far from the case, I can assure you !

One thing that doesn't seem to have been mentioned is the maximum speed. The cutting edge will get hot, and the higher the speed the hotter it will get. At some speed it will get too hot and will go soft, so it will lose its edge very quickly. This can be quite noticeable, I found when boring cylinders on the Myford that there is quite a small speed difference between the cutting edge going blunt quickly and cutting all day. That was with HSS, cutting a good grade of cast iron (no hard spots) but much the same applies with carbide although the maximum speed will be higher. The heat at the cutting edge will depend on the material, for instance stainless steel is a poor conductor so will tend to get the edge hotter, while brass will conduct the heat away better, allowing a higher cutting speed.

The quality of the edge matters a lot too, thinking mainly of HSS. A really sharp edge will stay sharp longer and give a better finish. This is where a diamond hone is nice.

John