Milling speeds

Hi I am about to machine gun metal castings and I am wondering what would be a recommended speed or RPM on the mill. If anyone knows of a chart for machining different types of metal I would be great full if I could down load it. Thank you John

There's an app for iPad or phone, android too, called FSWizard.

The free version of the FSWizard app only gives you three choices of material: a Hot rolled steel, an alloy steel and an aluminium. You need to pay almost £50 for the Pro version if you want the full range of materials it covers. An internet search will almost certainly be quicker and cheaper.

There is an interesting paper with a great deal of info on the properties, and machining of copper/brass alloys here:

**LINK**

Put this app in your head: RPM = 4 x CS divided by diameter

Cutting speed (CS) for steel is about 100 feet/min. For brass and aluminium you can double that, ie 200.

So your RPM would equal 4 x 200 divided by the diameter of teh cutter, in inches.

So for a 1" diameter cutter, RPM equals 800 divided by 1 = 800rpm.

For a half inch diameter cutter, RPM = 800/0.5 = 1600 rpm.

and so on.

If your gun metal castings have a hard skin, you might want to cut those rpm in half just to be safe.

These figures are for HSS cutters. Double the rpm for carbide cutters.

Edited By Hopper on 18/07/2017 09:22:04

what happens though if I mill at much lower speeds ?

The cutter won't work so well, you'll need to feed slower. I've discovered over time to both turn and mill quite a lot faster than when I started. Cutting depends on shearing action at the tool edge, and I once read that this depends on the metal getting very hot and softening right at the point of shear. If the tool is going too slow this is not so effective and the tool will have a higher loading. For example, I find that when getting a poor finish on steel or ali often it improves matters to run the tool faster not slower. Milling aluminium, I find that the tendency for the metal to build up on the tool edge is significantly less when running the tool fast. And also, when running faster, the inevitable vibration produced by an intermittent cut of a milling cutter is better damped by the machines mass when it is at a higher frequency.

+1 on that : my beginner mistake as well. Cutters run too slow wear out faster too, the combination of slow speed and light pressure results in rubbing rather than cutting, which blunts the edge.

But beware of the opposite beginner mistake, which is to cut harder and faster than a hobby machine can cope with. This can cause poor finish as well as burnt out electronics, broken gears and snapped shear pins. Beware of overdoing it If you're an impatient he-man!

There's a nice balance to this that I'm still struggling to attain. I imagine that good machinists read clues like noise, chip size, chip colour, and resistance to get best results. More like a playing musical instrument than swinging a sledge hammer, or is that fanciful?

Dave

Edited By SillyOldDuffer on 18/07/2017 12:18:44

FYI... apart from Google & all of the above responses here is a quick ref. table from Presto's pocket book...




George.

Edited By mechman48 on 18/07/2017 21:48:21

Hi Mechman

That looks like a useful table, but if I save it and blow it up to a reasonable size it is very blurred and I can't read it. Am I doing it wrong?

I don't think so Duncan, I get the same result as you. The JPG is just 514 x 480 pixels and compressed a bit too much for my old eyes to be able to read it. A higher resolution photo would be appreciated.

Thor

Latest version of the Presto "councellor" can be found here, milling speeds about 3/4 the way down. Pages for 2 and 4 flute, HSS and 8% cobalt, metric and imp diameters etc

One other thing with gun metal, all your fancy cutting speed calcs won't be any use if your cutters are not sharp. GM being relatively soft does not respond well to blunt cutters.

Edited By JasonB on 19/07/2017 07:57:39

Jason tried your link for 'Presto councillor' ... ?



after a few seconds another page tries to open up ' set up ' ... some music link?

... anyone else having link probs?

George

Not sure whats up there but it opens OK for me.

Failing that it is the bottom of the list of downloads

.... Still getting blank page from your other link... will try again later

Geo.

George

Works for me, may be your browser settings

(Although I have the Presto book anyway    )

Edited By David Standing 1 on 19/07/2017 10:33:35

I have a very similar booklet called Atorn Databank from Monks and Crane. It has identical pages for a lot of the information in it.It is at least pre 2010 but has no publication date in it.

Martin C

Thanks Jason, just downloaded the Presto "councellor".

Thor

Jason, got it ! had to open IE to view it ,wouldn't view in Win Edge for some reason also checked that I had the latest Adobe pdf reader, I do, anyhow downloaded & saved to my files, thanks for the links. Also editing my 'albums' & in the process of removing some pics somehow managed to remove all the pics in my 'miscellaneous album' tut, tut, 

George.

Edited By mechman48 on 19/07/2017 15:29:25

Hi John,

I came across sheet of cutting speeds for various materials some time ago,not sure where I downloaded it from,but it seems to cover everything.. I would be happy to post you a copy if you like.