RPM vs material ready reckoner

[jack620]

I started making up a table on Excel with the following info:

material to be cut
diameter of workpiece in 10mm increments up to 100mm
type of cut (roughing, finishing & parting)
RPM

The idea is to enlarge it and stick it to the wall behind the lathe. It would give me a quick reference for setting RPM on the lathe without having to look up a nomogram. I was going to extract the numbers from a nomogram I have in a turning book.

One problem I have run into is that different books list different cutting speeds for a given material. Some figures differ by a factor of 2. Apparently depth of cut and feed rate also affect cutting speed. So I need some data which is relevant to the sort of cuts you would make on a Hercus 260 size lathe.

Before I embark on this, does anyone else have a table like the one I'm proposing?

[pipeclay]

Only off the top of my head,depending on HP,material,DOC,feed,tool type,material size,material length,method of holding,finish required etc.

[jack620]

anyone else?

[pipeclay]

Do you want an idea of speed feed for using the Hercus from a book or from experience.
If from experience it will be a generalisation on a wide range of materials and machines.
another well proven method of working out this cutting performance calculations is SIAS.

[jack620]

I'm not fussed where the info comes from. As I have no experience to fall back on I want a table I can look at and determine, for example, that 2" aluminium needs to be turned at XXX RPM.

I wouldn't call ''Suck It And See'' a method of calculation.

[pipeclay]

See what happens when your tables dont work.

[jack620]

Do you go out of your way to p*ss people off?

I said quite clearly I have no experience to fall back on and I want to make a table to give me a starting point. I wouldn't know whether 25mm MS bar should be turned at 200RPM or 1500RPM without looking in a book. I need a starting figure to work from. One day (hopefully) I won't need to look in a book.

Unless you have some constructive information to provide I respectfully request you go to someone else's thread and annoy them.

[Dave J]

I can fully understand where Pipeclay is coming from with his replies.
It will vary a lot like he said with every bodies different situation. I use HSS mostly and usually go by what I think, if I run too fast in steel I will soon be sharpening it again, so you learn pretty quick.
You should be able to find some online calculators to help you out, but I think most will be for carbide. Other than that some books will have a basic speed and feed range and the grizzly manuals have a small conversion chart in them like this one on page 41, but it is in imperial.
http://cdn0.grizzly.com/manuals/g0709_m.pdf

Dave

[jack620]

Thanks Dave,
That's the sort of info I was after. Your response is an example of why I visit this forum a few times every day. There's a huge amount of knowledge out there for a newby like me and most people are prepared to spend some time sharing that knowledge rather than throwing out wise-cracks.

I'll have a look at the link you posted. I can easily use Excel to convert from imperial to metric.

Cheers

[Bryan]

One problem I have run into is that different books list different cutting speeds for a given material. Some figures differ by a factor of 2. Apparently depth of cut and feed rate also affect cutting speed. So I need some data which is relevant to the sort of cuts you would make on a Hercus 260 size lathe.

Before I embark on this, does anyone else have a table like the one I'm proposing?

No I don't but I have a suggestion. You could start with the more conservative values for your table. They are likely to suit a smaller lathe. As you get a bit more experienced and better at sharpening tools you may want to try pushing one parameter at a time.

I think what Pipeclay is driving at is you can't put enough info in a table for every situation. That may be true but I've done a lot of tabulating and I find it a useful exercise.

[jack620]

Hi Bryan,
My plan is to make the table using "book" figures for cutting speeds and modify the data as required to suit my lathe and level of ability. I figure you've got to have a ballpark figure when you're starting out. As you suggest, I plan to operate at the bottom end of the recommended speed ranges initially. I don't want a chart that covers all possible variables, just something that covers the more common metals and plastics over a range of diameters.

Somebody has PM'd me and kindly offered a PDF copy of a book with some data they think will help me.

[simonl]

Hi Jack,

I too am on a steep learning curve in this caper. Some time ago I did pretty much the same thing as you. Except I produced two tables. One table listed a range of materials from cast iron, steel, carbon steel, stainless, brass, aluminium etc etc, and the cutting speeds in M/min (and ft/min) for HHS and TCT inserts. Most of this info I got from the net.

The other table I have is an excell spread sheet that gives you the required RPM for a given diameter to produce the cutting speed that you have just looked up on the other table. This table was pretty easy to produce because once you put in the equation, you just copied it across all cells for the range of diameters you think you will need. In fact, for certain diameters at either end of the tables, some speeds were not achievable on my machine, but the info is there non the less.

As suggested previously, tables are still no match for hands on experience but it gives me a place to start with for someone like me who is a hack!

Cheers,

Simon

[jack620]

Hi Simon,
Thanks for the feedback. If I PM you my email address would you be kind enough to email me copy of your spreadsheets? Or maybe it's possible to post them here?
Cheers

[simonl]

Hi Jack,

PM me and I will email them to you when I get home in the morning.I'm on night shift at the moment.

Cheers mate,

Simon

[Dave J]

Hi Jack,
I have some charts in some old tafe books that I will post up now on the other computer with the scanner if every things working OK and the kids haven't buggered it up.

Be back shortly.

Dave