Milling machine - cutting speeds and feed rates

[LandyManLuke]

Hi all,

The Bridgeport is getting to a point where it's usable, I've been doing some research in to cutting speeds and feed rates. Numbers on the internet seem to vary massively.

Can anyone point me to trustworthy figures, or give me an idea based on experience?

I'm using HSS tooling on mild steel for practice. Numbers for aluminium would also be useful.

Thanks,

Luke

[pete3000]

a good read is here http://www.amazon.co.uk/Milling-Complete-Course-Workshop-Practice/dp/1854862324/ref=sr_1_1?s=books&ie=UTF8&qid=1359454673&sr=1-1

his lathe work a complete course is worth a go through also. I don't have anything as big as a bridgeport, but speeds similar to lathework i.e mild steel 6mm cutter 1200rpm, 12mm 600rpm and so on.

Ally and brass can be up to double i.e 12mm 1200rpm.

You can't plunge 4 face end mills and i only ever take a pass along the side upto a 1/3 of the cutter dia and depth only a 1/4 of diameter ie 1.5 mm deep and 2mm in. Feed rates by experiment 1-2mm per sec and build up until the machine complains or you dull your cutters through heat/fracture.

Coolant is important to stop the hss tooling from overheating, as you will dull your cutters quickly with heat especially if swarf builds up.

Carbide is more forgiving of heat but doesn't like interrupted cuts.

[mickeyw]

Hmmmm, I'd struggle to quote figures, I always go with what 'feels' right (from a good deal of experience).

Luke I can't remember if your mill has a geared head or variable speed, that kinda influences RPM choice rather a bit.

I haven't used carbide in years, partly because I have HSS and it does what I need without spending extra £££ on tips etc, but also I don't have need to cut tough tool steels very often.

As Pete3000 says, coolant is important. I bought a 5 litre can of soluble on the bay a couple of years ago. Correct dilution rate is important - too weak and everything goes red very quickly, not to mention inadequate cutter lubrication, too strong and it can take all the paint off the machine that you've been lovingly tarting up

Miller Hexol FR9 is the coolant I am using.

I just had a quick search for 'HSS cutter speeds and feeds', and there were plenty of results to choose from. Try narrowing the search to HSS slot drill or HSS end mill for better results too.

[LandyManLuke]

Thanks for the replies gents,

I just had a quick search for 'HSS cutter speeds and feeds', and there were plenty of results to choose from.

That's been my problem

To put it another way;

- I don't have lubrication sorted yet, on the to-do list. It sounds like this is important and I need to get it sorted - I've only done a few practice cuts so far.

- The Bridgeport has a Model J head (stepped V pulleys) but I've replaced the original motor with an IEC frame motor and inverter, so I can have pretty much any speed I'd like.

- On carrying out tests cuts, the vertical part of the cut looks like it has been 'ripped', rather than cut smoothly. I have read a bit about conventional and climb cutting, but the results don't look too different at the moment.

My plan is to elminate variables one at a time and learn as I go. I should have a working lubricant system within a few weeks and I picked up an optical tacho so I know what the spindle's doing.

thanks,

Luke

[nickwilliams]

The 'workshop' series books are OK for home type projects, but this is the real deal for connoisseurs. Tool porn of the highest class in my view!

You may struggle to get good results using carbide cutters on a Bridgeport. Carbide responds well to lots of grunt and fairly brutal feed rates, but you need a machine with the rigidity and power to back it up.

PM me your e-mail address and I'll see if I can find you a table of feed speeds when I get back to the UK - got to dash now my plane is about to leave!

Nick.

[mickeyw]

Right, if you are using HSS, wait until you have the coolant working. You won't get good result on steel without it, and you'll knacker your cutters at the same time!

For aluminium paraffin can be a good cutting fluid, but generally use the machine's coolant for cutter lubrication, cooling and chip removal.

With steel, don't climb cut. Climbing offers advantages when cutting plastics with very high spindle speeds and carbide cutters, but that doesn't sound like what you need.

What type of cutter are you using? And how are you using it? I don't mean to be rude, but do you understand the differences between slot drills and end mills, and their intended applications?

[LandyManLuke]

What type of cutter are you using? And how are you using it? I don't mean to be rude, but do you understand the differences between slot drills and end mills, and their intended applications?

Not rude at all, I've been doing lots of reading, all new to me. I'll get the coolant system up and running sooner rather than later.

Point taken on not climb cutting.

I've been using (2 flute) slot drills in situations where I need (choose) to plunge cut in to the work piece, and (4 flute) end mills when working in from an edge. I believe this is correct?

Luke

[mickeyw]

I've been using (2 flute) slot drills in situations where I need (choose) to plunge cut in to the work piece, and (4 flute) end mills when working in from an edge. I believe this is correct?

Luke

Correct.

If you are seriously impatient to get cutting before the suds pump is sorted, buy some cutting fluid and pour it into a bean can and apply with a paint brush CAREFULLY. This will lube the cutter and brush swarf away, not so good for coolant though.

OR

Craftily empty the washing up liquid bottle and fill that with suds and squirt at the cutter as required, provides better lubrication than the above and is less dangerous

Having said that, it depends how precious SWMBO is about the fairy bottle, and whether she finds out where it went

[potato head]

Check the spindle for end float and run out as well. That could be part of the issue.

[Phil Hancock]

4 S

D

Was the formula we were tought, S being the cutting speed in feet per minute & D being the job/cutter diameter in inches.

Mild steel 80ft/min, cast iron 60ft/min.bronze 80ft/min,

[B reg 90]

Google HSS milling speeds. You can find tables that will give you a starting point.

Coolant - get your system set up. Worst case some kind of weed killer spray bottle would do - pump it up and you have 5 minutes of coolant spray?

Milling in my experience is all about planing the job. Leave a bit on the job to do a finer finishing cut to get a better finish. Make sure the job is ridgidly clamped to the bed. Understand how you will finish it before you start it.

It's hard work getting from a machine laned in your garage to a machine you can use productively. Also £££ in tooling and misc other stuff. The coolant will make you wince on it's own.

Adrian

[B reg 90]

Other coolant suggestion - coke bottle - use a scribe to punch a small hole in top. Fill with coolant. You can squirt where needed.

[vulcan bomber]

With steel, don't climb cut. Climbing offers advantages when cutting plastics with very high spindle speeds and carbide cutters, but that doesn't sound like what you need.

Erm, climb milling is fine on just about all materials, the ONLY issue you get from climb milling with any tool, wether its a 6mm slot drill or a 6inch, carbide insert face cutter with 20 flutes is snatching, caused by the back lash in the tables screws. Big machines such as the big cinncinati at work has a contraption on it to send the back lash the other way and allow you to climb mill with the locks slack. Climb milling tends to give better finishes and longer cutter life.

To the OP, i'm affaid that theres no hard and fast rules to feeds and speeds however if your using decent quality high speed tooling then you want quite a deep cut, with low rpms and low feed rates. Also make sure the quill is not hanging out the machine and make sure its locked up.

You will find rippa cutters alot better for removing material before using standard slot drills and end mills for finishing.

You will also find that the more flutes on a cutter the more chance of vibration, i tend to use slot drilos for alot of milling work, even outside profiles.

If your getting vibration then lower rpm. Same for drills, they require low rpm and high feed rates, if they vibrate and snatch just nip the lock on the quill a tad.

If you can, use collets direct to the spindle, autolocks move the cutting forces a long way from the spindle bearings creating vibration.

You'll notice i have mensioned vibration alot... Its the biggest killer of tools after running tools too fastamd burning them out.

[vulcan bomber]

You can't plunge 4 face end mills

Carbide is more forgiving of heat but doesn't like interrupted cuts.

You can plunge with a end mill. Standard endmils however dont cut on the centre so you have to drill a pilot hole as it were. An end mill or slot drill will give a good, consistant hole size as well.

And erm, Carbide is fine with intermitant cutting, its a milling cutter, EVERY cut it takes is intermitant.

[sean f]

If your getting vibration then lower rpm. Same for drills, they require low rpm and high feed rates, if they vibrate and snatch just nip the lock on the quill a tad.

If you can, use collets direct to the spindle, autolocks move the cutting forces a long way from the spindle bearings creating vibration.

You'll notice i have mensioned vibration alot... Its the biggest killer of tools after running tools too fastamd burning them out.

I am surprised that to reduce vibration you lower rpm (I am not saying its is wrong for milling as that is not my area).

I optimise big drills for a living and generally it it starts vibrating it is often as it is trying to take to much in one cut, standard response is to increase rpm and reduce rate, then less depth of cut per rev. I admit this is for drilling rock but I would have thought the same principle would hole with the proviso that to much rpm will generate heat and burn things out. Our drill bits often cost over 100,000 and it can cost over 1,000,000 to change one out so we try not to break things, excess vibration kills them, the sensor packages behind can run into several million, current one would be over 3 million, the vibration kills them as well. Mind you weather is stopping thing now, rolling around in 10 m waves due to rise to 12m by midnight.

[vulcan bomber]

If you drop the rpm then the feed per tooth increases putting more pressure into the cutting face edge of the tool and also reduces the force that the cut is taken on at so the cutter doesnt bounce.

The longer the tool the worse it gets....

And the most expensive drill we have is a 40mm Udrill, or cub drill. Using it is very much the opposite of normal jobber drill.

[ejparrott]

Dave is right, 99% of the time we climb mill, even on the bridgeport clone.

Cutting long thin shafts can be fun for vibration, you need to adjust the speed up and down to stop it vibrating as you go.

We use up to 65mm spade drills on our machines.

[vulcan bomber]

Cutting long thin shafts can be fun for vibration, you need to adjust the speed up and down to stop it vibrating as you go.

You not got any steadies down your place?

[ejparrott]

Can't always use a steady

[vulcan bomber]

Going on from what Ed's said about long thin stuff, (I hate milling and turning stuff like that) What he's descriing is harmonic vibration, and thats a pig to stop. Biiiiig cutters, have there cutting teeth spaced at slightly different intervals to reduce harmonic vibration.