Turning cutting speed for Al

[GSRocket]

Guys, what would be the right speed to turn 90mm Aluminium round bar.
I'm setting up a new pulley system for my lathe.
Thanks

[jack620]

Good question. When I first got my lathe I made a table of RPM vs diameter for most of the common metals and plastics. There were huge variations in recommended cutting speed between the different information sources.

It is hugely dependent on the power of the lathe, DoC, feed rate and tool material. Here's a few figures for 90mm aluminium with HSS tooling:

Machinery's Handbook: HT (eg 6061): 550-640RPM
Hercus Textbook of Turning: FC: 640-1060RPM, HT:320-640RPM

I'm still a babe in the woods when it comes to turning, so I start with the slowest speed in the literature and go from there. Interestingly, for many metals the Hercus ToT recommends the highest speeds. Sometimes MUCH higher.

Chris

[Michael G]

I use the formula* RPM=9000/d.
That's for normal (mild steel). For thermoplastics, brass and Al I multiply by 3 (copper & bronze x2, free cutting steel x1.5, higher carbon steels and CI x0.5)
That assumes HSS. For carbide, multiply by at least 3.

For 90mm Al, RPM = 9000/90 = 100rpm (steel)
3x100rpm = 300rpm (Al)

As Chris said, that's a starting point. Faster and you can overheat (destroy) your cutting edge; too slow and finish may suffer (and you will get bored)

Michael

*The full version is RPM=(300x cutting speed(m/min))/d. A typical cutting speed for steel is around 30m/min, so I use that and then adjust the result. However, the full formula is occasionally handy when faced with a cutting combination you don't know a mutliplier for - exotic tipped tools for example.

[morrisman]

I've found the free machining grade is very forgiving and the speeds are not critical

These pages are from the Action aluminuim catalogue , the branch in Greens road Dandenong

[fittermachinist]

hey mate,

at work the other day i was facing aluminium at 1600rpm with a reasonable cutting speed and turning down the outside on holding the job on a manderal between centres at 1200

which gave a good finish

[pipeclay]

You need to give more information so as the person asking the question can relate it to what they want to do.
Its no good telling what you did if there is nothing to judge it by.

[rusty steel]

Hello GSRocket,
Just between you and me, I have never learned formulae for cutting speeds. :- I would probably set the speed at 250 -300 rpm for that diameter. I use HSS tools and motor oil thinned out with diesel to assist cutting, and it would spray everywhere if the speed was much higher (I have a couple of pieces of cardboard which I use to stop the oil getting on the floor). Unless you are using Free Machining Al. it could weld to the tool if the speed is too high.
Russell

[jack620]

Methylated spirits is also a good coolant for Al. I put it in a squeeze bottle and squirt it on. It evaporates and leaves no residue. You need a nozzle with a small orifice otherwise you end up wasting a lot.

[Ueee]

Metho? Thats a new one for me, i always use kero.....

As for formula, if you work in imp the formula is CS/(dia/4) where CS is your cutting speed in feet per min. I cut mild at 100fpm, other material i use the try it and see approach a lot.

[GSRocket]

Thanks guys. Appreciate your responses.
I was already thinking of a bottom speed of 300 RPM but I might make it a bit
slower in case I want to spin something a little larger.
I noticed the guys at a fabrication shop close by who seem to specialise
in rather beautifully made things in Al and stainless, use metho in a squirt bottle
when using a jigsaw to cut Al plate (fairly thin plate, about 3mm I would guestimate)

[rusty steel]

I didn't realise you were asking about the slowest speed available on your lathe.
I think the slowest speed available on most lathes (except for electronically controlled ones) would be about 30-50 RPM. When thread cutting, I would not like it much higher. :C Russell

[GSRocket]

I didn't realise you were asking about the slowest speed available on your lathe.
I think the slowest speed available on most lathes (except for electronically controlled ones) would be about 30-50 RPM. When thread cutting, I would not like it much higher. :C Russell
My lathe has no thread cutting capabilities. It's actually an old pre WWII pattern makers lathes with a flat bed.
Technically it's probably only a wood working lathe. Its only got a 1" shaft so steel cutting or any heavy cutting is probably not advisable.
It originally came with a 3 speed pulley system with twin belts.
I'm reworking the whole drive system.

[morrisman]

I didn't realise you were asking about the slowest speed available on your lathe.
I think the slowest speed available on most lathes (except for electronically controlled ones) would be about 30-50 RPM. When thread cutting, I would not like it much higher. :C Russell

The slowest speed on the Hendey gearbox is 18 RPM . But with the 6 to 1 reduction headstock fitted , that brings it down to 3 RPM :o

All of that data is for a 60 hz 4 pole motor. The factory RPM data is thrown away when a VFD is fitted as I have done . MIKE

[MuellerNick]

Surface speed for HSS would be 40 ... 80 m/minute, for carbide 200 ... 400 m/minute.
With a pulley, I'd start at the lower end, because they tend to vibrate/resonate.

With 90 mm diameter, that would be 140 ... 280 RPM or 700 ... 1400 RPM.

If you are using a form tool that cuts the full profile, you might have to go way down with RPM because of the cutting length.


Nick

[jack620]

Rocket,
I found these notes on turning pulleys a while ago. I've never made one myself, so I don't know how good the notes are. Also Tubal Cain (mrpete222) on You Tube has a 3 part series of videos on turing a pulley. Here is Part 1:

MACHINE SHOP TIPS #65 Lathe Project Pulley Part 1 of 3 tubalcain - YouTube

Chris

[GSRocket]

Thanks Jack.
Although I'm not going to turn up the pulleys, those videos are very helpful for what I want to make.
I'm going to use the original cast iron pulleys which are 3 speed and there are 6 grooves to each pulley.
I'll add a second set of pulleys (like a drill press) to get the speed down low.
These pulleys will get made by a retired lathe man down the road, but rather than have twin V belts which take up a lot of shaft space..
have the pulleys made to take a flat belt with 7 ribs, the same profile that serpentine belts in cars have.
I'm yet to check out if I can get very short ribbed belts.

[Old Croc]

Thanks guys. I noticed the guys at a fabrication shop close by who seem to specialise in rather beautifully made things in Al and stainless, use metho in a squirt bottle when using a jigsaw to cut Al plate (fairly thin plate, about 3mm I would guestimate)
To me it would seem the boys that are using metho and a jigsaw are close to visiting their maker. :no:Why the hell would you use a bottle of highly explosive alcohol and a powertool with sparking brushes in the motor. Kero is a much safer alternative, but even it can produce explosive vapour,
rgds,
Crocy

[jack620]

Since when is metho highly explosive?

[BobL]

Since when is metho highly explosive?

metho itself is not explosive but an air metho vapour mixture is. It has a LEL (Lower explosive level of 3% and UEL of about 20% which means it has wide range of conditions under which the vapour will explode.
Metho has a NFPA rating of 1B (same as petrol) which is only one down from the most explosive stuff rated at 1A like acetylene.

Some useful info on flammability here: http://en.wikipedia.org/wiki/Flammability_limit

Kero is rated at 2 but has a higher flash point , 38ºC versus 12ºC for metho.

[MuellerNick]

There is one single good use for WD40: Cutting aluminium. Here, it works.
As it contains a lot of petroleum, pure and cheap petroleum is even better.

I prefer coolant (water-oil-mixture).


Nick

[BobL]

When using something volatile and potentially explosive one needs to be very careful of this stuff and provide very strong exhausting capabilities. This stuff rises and accumulates along ceilings and one may not notice the levels that have built up - one flashover and the whole building catches fire.

[jhovel]

...As it contains a lot of petroleum, pure and cheap petroleum is even better....
Nick

Nick, the English translation for the German word "Petroleum" is Kerosine or Kero, as BobL as Old Croc mentioned.

The word "petroleum" in English is a generic term for crude oil and in some circles all hydrocarbons.

(The German word for "Metho" or "methylated spirits" or "methanol" is "Spiritus" or "Methylalkohol").

Cheers,
Joe (Jupp)

[MuellerNick]

Nick, the English translation for the German word "Petroleum" is Kerosine or Kero, as BobL as Old Croc mentioned.


I knew that there are differences, but the stupid dictionary said "petroleum". OK, kerosine.

Gas, gasoline, petrol. Different meanings in different English-speaking countries. :((


Nick

[GSRocket]

There was absolutely no chance of an explosion or accumulation.
The guy was out in the open with a nice breeze blowing.
Perhaps there was a slight chance of fire but the guy is a real craftsman
so I'd say he'd been doing it for a long time.

[jack620]

Nick,
I might give the WD40 a try. It's cheap and doesn't smell as bad as kero.

Bob,
thanks for the info. To put those numbers into some perspective, I guess we would need to know if the 3-20% explosive level range is achievable in a workshop situation. If it is, I'll ditch the metho. If not, then the numbers are academic. If it is, at what ambient temperature? Is it the flashpoint of 12C? It was warmer than that in the workshop when I was turning Aluminium last week and the pile of swarf was still wet with metho the next day, so there wasn't much evaporation occurring.

Cheers,
Chris

[BobL]

Bob,
thanks for the info. To put those numbers into some perspective, I guess we would need to know if the 3-20% explosive level range is achievable in a workshop situation. If it is, I'll ditch the metho. If not, then the numbers are academic. If it is, at what ambient temperature? Is it the flashpoint of 12C? It was warmer than that in the workshop when I was turning Aluminium last week and the pile of swarf was still wet with metho the next day, so there wasn't much evaporation occurring.

12ºC is the temperature at which sufficient meths can start to evaporate to form an explosive mix. in a 6 x 4 x 3 m shed around 2L of meths would have to evaporate to make a 3% mix. At that level you would really smell it. If you had a 100 cfm exhaust fan running (in theory) you would have to be evaporating around 5 L/hour to generate a 3% mix. In practice and to provide for safety margins I would shoot for a max of 2L/hour. Better still I would run something like a 500 cfm fan so that would completely eliminate the problem.

I'm not sure I like the idea of meths saturated swarf laying around. I use Meths when drilling and tapping and turning ally but I do not flood the whole work. I use a pump pack and squirt the meths directly at the cutting site and i never use more than about half a litre in any one day. If it happens that I generate wet swarf as soon as I'm finished I put it in an open drum which contains couple of kg of sawdust and I keep that outside out of the rain. I like the fact that it leaves no mess

[jack620]

in a 6 x 4 x 3 m shed around 2L of meths would have to evaporate to make a 3% mix.

Thanks Bob. My workshop is 9x6x3m. I used less than 500mL of metho, so I guess I was safe. :2tsup:

I'll be more diligent about cleaning up the metho soaked swarf next time. I've got plenty of sawdust in my dust extractor. I'd never thought of using that before.

Cheers.

[BobL]

Thanks Bob. My workshop is 9x6x3m. I used less than 500mL of metho, so I guess I was safe. :2tsup:
That sounds OK. BTW my calculations assumes that the meths vapour spreads evenly through out the shed. If there is no stirring of the air inside the shed there may be local regions where it can go higher than 3%. I would suggest running a fan somewhere to stir up the air.


I'll be more diligent about cleaning up the metho soaked swarf next time. I've got plenty of sawdust in my dust extractor. I'd never thought of using that before.
I do that will all my volatiles and solvents as they evaporate away a bit faster that way. It's also easier to put slightly sticky sawdust into the bin than the sludge left over after cleaning things like paint brushes and car parts.

[GSRocket]

I have accidentally discovered the solution to a possibly explosive
problem with lubricating aluminium,


Neatsfoot oil is used in metalworking industries as a cutting fluid for aluminium. For machining, tapping and drilling aluminium, it is superior to kerosene and other water-based cutting fluids.
You can get it from any hardware store.....Anybody tried it?

[morrisman]

I have accidentally discovered the solution to a possibly explosive
problem with lubricating aluminium,

You can get it from any hardware store.....Anybody tried it?

Pure neatsfoot oil is made from cows feet and bits , its a animal product . Most of the stuff hardware stores sells is not pure, its a made up of a cocktail of stuff that is labelled as neatsfoot oil but it isn't . Some of the books recommend it for thread cutting . Mike

[bwal74]

Hi,

Read this post the other day and interestingly enough I had to turn some alum.

A bit of a story though, the end user ordered 3 ft at 5" Diam, we received 3 metres at 130mm of high grade aircraft aluminium. So I can cut 2 of the required pieces which are approx 25mm thick by 108mm Diam. A lot of left over.

The 3 metre length will explain the first photo.

The other photo's just show what I'm up to. Cut using carbide insert, between 3mm DOC and 0.10mm DOC finish wasn't too bad. Cut Diam down to 107.90mm and that's as far as I got as the diagram is wrong. Hopefully get sorted out by Monday (Poets day today). Cut at 325 rpm and can't remember the feed rate but was pretty slow. Used oil based coolant.

I hadn't used a fixed steady for some time. Scared myself half to death on the first cut as I had the fingers too tight. Sounded terrible.

Cheers Ben

[Bryan]

Sorry Ben, if you can't be bothered rotating your photos I can't be bothered looking at them. :(

[jack620]

So much grumpiness in the world.

Ben, Happy Poets Day! Did you really cut it by hand with a hacksaw?

[QC Inspector]

For those that use iPhones there are a number of free Apps, and some you pay, :rolleyes: for that calculate cutting speeds, feeds etc., for many materials along with other useful machining information.

Pete

[Bryan]

So much grumpiness in the world.

No that was my helpful side. If I was grumpy I would have said nothing.

[bwal74]

So much grumpiness in the world.

Ben, Happy Poets Day! Did you really cut it by hand with a hacksaw?

Hi,

Sorry about the photo's being the wrong way, straight off the phone and posted a couple of hours before going to the hospital for son number 4's grand entrance this morning.

Yep, cut pretty much all of it with the hacksaw (well most of it - used a 125mm grinder around it first). Hoisted it onto the cold saw with the outer jaws removed but still didn't fit and the bandsaw is broken at the moment (not sure if it would cut that thick anyway).

Cheers Ben

[Bryan]

Sorry about the photo's being the wrong way, straight off the phone and posted a couple of hours before going to the hospital for son number 4's grand entrance this morning.

Congratulations. Hope all are well.

[bwal74]

Hi,

Back at work today. Started where I finished off two weeks ago. Drawing wrong, so had to start again (drawing and actual pieces wanted not even close!).
Anyway I used the fixed steady, something I haven't used for sometime, with some problems (noise and workpiece coming loose - nothing happened but scary enough).
Pipeclay gave me some suggestions such as using a live centre and cutting a bearing path for the fixed steady. Really worked a treat, something I totally forgot. A lot less noise and running much smoother. Thanks Pipeclay.

Cheers Ben