End mill rpm

[Dougie SwanParticipant @dougieswan43463]

Hi

I have blunted more end Mills than I care to remember

I’ve just bought a new 1/2″ dia hss one and wondered if anyone can give me a ballpark figure of the correct spindle rpm for this on En1a steel

Thanks

Dougie

[JasonBModerator @jasonb]

If you took a rule of thumb of 100ft / min cutting speed for steel with HSS that put you at 770rpm.

Depends a bit on the cut as to whether you are flattening the top of a part or milling the side, top you may want to go a bit slower and also reduce the feed a bit depending on stepover..

 

[Ramon WilsonParticipant @ramonwilson3]

Hi, You may find this simple chart of use Dougie. I wrote it out when I first started training and has done me fine ever since

 

You can simplify the formula to an approximation –  Cutting Speed x 4 divided by the diameter of the cutter in inches so your 1/2″ end mill at 100 ft per min would be 800 – just adjust it to suit the conditions/type of steel at the time

Tug

PS I should have said this is for HSS – carbide could be up to 5 times more if the machine is capable

[Gary YeadonParticipant @garyyeadon51936]

Good Evening Dougie – Do you have a copy of Machinery’s Hand book you can refer to?
This shows how to calculate your cutting speed from the formula V=Vopt x Ff x Fd

I can send you copies if needed.

Regard

 

Gary

[duncan webster 1Participant @duncanwebster1]

Make sure you keep the tooth load up, feeding too slow causes the cutter to rub and go blunt very quickly

Tubal Cain Workshop Handbook has useful info

[JasonBModerator @jasonb]

If its HSS coated with something like TiAIN then you can run faster, say 150ft/min plus which is 1200rpm

Here is a 10mm at nearer 180ft/min, 10mm vertical DOC x 0.5mm horizontal DOC.

[Martin ConnellyParticipant @martinconnelly55370]

If you have a table of rpm for drills then the same rpm can be used for mills of equal diameter as well. As Duncan says above not cutting fast enough will quickly overheat and blunt the edges. You should be getting chips coming off as waste, if it is very fine slivers or dust then you are feeding too slowly.

Martin C

[Nigel McBurney 1Participant @nigelmcburney1]

The speed /feeds recomended above ,are correct,but they are based on industrial use,with a good rigid machine and no doubt assume pumped suply of soluble oil, you do not state your machine,a lightweight hobby machine can be a bit light on spindle rigity so try reducing the speed down to 70/80 ft per min with sufficient feed to avoid rubbing,and decent tool lubrication, reducing speed does not harm HSS ,it will increase tool life,the job takes longer ,so what its a hobby not a production line.

[Tony Pratt 1Participant @tonypratt1]

The ‘Little machine shop’ website has a useful speeds/feeds calculator.

Tony

[JasonBModerator @jasonb]

The only downside with reducing cutting speed on a benchtop hobby machine is you loose some grunt from the motor if it’s an electronic variable speed. I tend to favour upping the spindle speed, keep the same modest chip load which therefore needs an increase in feed rate but reduce DOC if rigidity is a problem.

70ft/min on a 1/2″ cutter could be 20 to 25% motor speed so not where it is going to be putting out it’s full potential

[old martParticipant @oldmart]

I am afraid to use HSS endmills on steel and always use solid carbide or shell mills with carbide inserts if appropriate. The HSS are kept for aluminium or the finishing cuts on steel. Not being able to sharpen HSS is the main reason for keeping them for best. Used solid carbides sometimes com up on ebay and I have got some bargains, and reground ones are usually better value for home use especially if they are slightly undersize.

Lubricant of some type should always be used with HSS to prolong the life and slower speeds are safer. Solid carbide always gets max rpm when I use it as manual mills cannot get anywhere near the speed ideal for this type of tooling.

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