end mills, how many flutes?

[pgrbffParticipant @pgrbff]

What benefits would a 4 flute 1/2″ end mill provide over a 2 flute, I understand you can plunge cut with a 2 flute but can’t with a 4.

Is it a question of finish? Would a 4 provide a better finish on Aluminium?

[pgrbffParticipant @pgrbff]

[David Southwell ARPSParticipant @davidsouthwellarps]

Posted by pgrbff on 21/08/2011 14:44:12:

What benefits would a 4 flute 1/2″ end mill provide over a 2 flute, I understand you can plunge cut with a 2 flute but can’t with a 4.

Is it a question of finish? Would a 4 provide a better finish on Aluminium?

DAVID: With aluminium I was advised, many years ago, to use high speed steel rather than High Carbon unless using aluminium with a lot of silicon in it. You also need more side & top rake. It is these factors I believe to be most important with aluminum. I have always used five teeth for aluminium. But maybe there are better methods.

[pgrbffParticipant @pgrbff]

So more flutes = better finish?

[Clive HartlandParticipant @clivehartland94829]

This all depends on what you are cutting, side cutting or slots.

Two flutes will cut just fine but if cutting slots then it will sometimes cut oversize. With four or more flutes the cuts are balanced on both sides of the cut and it does give a better finish.

most cutters now have 3deg. clearance on the cutting lip so they are adequate for most materiels.

Carbon steel endmills must be a rarity now as with CNC grinding High Speed steel is the norm.

Carbide endmills with 3 flutes give a very good finish but unless you are into production scales then not worth it.

Stick to high Speed steel cutters with 4 flutes and hold 2 flute cutters if you want to plunge cut.

 

Clive

[JasonBModerator @jasonb]

As you say they can also be used to drill flat bottomed holes. The 4 flutes can be had with a centre cutting end to enable them to be used for drilling or plunge cuts but most need to be fed in from the edge of the work and the more flutes can give a finer finish.

 

You probably wont see many carbon steel milling cutters for sale so HSS will be fine, the ones from Hong Kong that I linked to in one of your other threads work well and the FC-3 type disposable cutters are reasonable value for money, these are mostly flute and will end cut.

 

All the milling on this engine was done with a mix of the HK and FC-3 cutters so no real need to start spending on aluminium specific cutters when they will do fine.

 

Do use some cutting fluid – parafin or WD40 makes a lot of difference

 

As for 5 flute cutters again you are unlikely to find these on anything much below 25mm dia. So as said above 4 flute or FC-3 for most things will be OK

 

J

Edited By JasonB on 21/08/2011 16:31:24

Edited By JasonB on 21/08/2011 16:55:02

[David Southwell ARPSParticipant @davidsouthwellarps]

There you have it – fairly consensual. I make my own cutters so my 5 flute for your smaller size may be a bit OTT for your purpose.

 

My experience is that with aluminium I get a better finish with 5 as against 4 flute cutters but I would agree with the implication from JasonB that it is more important as the cutter size increases. I find the best front clearance between 5.5 & 6 degrees and top rake between 40 & 50 so the cutting edge angle is 46 to 55 or thereabouts. However I am sure JasonB’s mix will work just as well.David

 

[Jim GuthrieParticipant @jimguthrie82658]

Posted by Clive Hartland on 21/08/2011 16:18:05:

This all depends on what you are cutting, side cutting or slots.

Two flutes will cut just fine but if cutting slots then it will sometimes cut oversize. With four or more flutes the cuts are balanced on both sides of the cut and it does give a better finish.

I always understood that two flute cutters were more accurate in cut width when cutting slots.

 

Jim.

[David Southwell ARPSParticipant @davidsouthwellarps]

Posted by Jim Guthrie on 21/08/2011 18:55:16:

Posted by Clive Hartland on 21/08/2011 16:18:05:

This all depends on what you are cutting, side cutting or slots.

Two flutes will cut just fine but if cutting slots then it will sometimes cut oversize. With four or more flutes the cuts are balanced on both sides of the cut and it does give a better finish.

I always understood that two flute cutters were more accurate in cut width when cutting slots.

 

DAVID: I agree in certain circumstances – I would not use a five flute for slotting .( or anything above a two flute) if there was even the slightest amount of  slack in the vice  or if your had any doubts about the precision of your machine or if the available power was on the low side. Anything above two flute puts more stress on the equipment.

Edited By David Southwell ARPS on 21/08/2011 20:12:27

[Clive HartlandParticipant @clivehartland94829]

Perhaps I drive them too hard, I now use a smaller dia. cutter first and then follow with the right size so problem solved.

I have a selection of 3 flute carbide cutters and they have slow helix flutes and I find these superior to the HSS cutters for most of what I do as they will cut much tougher steel than the HSS cutters.

They cost more and are because of the three flutes harder to re-grind but I have made collets with special markings for use on the Worden which does a good job on them with the diamond wheel.

 

Clive

[Steve WithnellParticipant @stevewithnell34426]

So are my three flute, centre cutting cutters end mills or slot drills?

 

 

Steve

 

PS:  I have an article somewhere explaining why two flute cutters should be used to machine slots and four flute cutters should not be used.  I’ll post it if I can turn it up.

 

Edited By Steve Withnell on 21/08/2011 22:15:09

[Anonymous]

I wouldn’t have thought that the number of flutes would have much affect on the finish, assuming of course that you’re using a constant chip loading. The helix of the flutes may have more of an effect.

 

I have read about slot drills (traditionally two flute) cutting oversize slots, although I’ve never really noticed the problem. Keys are made to fit anyway; I think keysteel is normally supplied slightly oversize.

 

There is supposed to be a theory that cutters with odd numbers of flutes are less prone to chatter. I suspect that within the amateur workshop machine rigidity would be the over-riding factor.

 

On the manual vertical mill I tend to use a mix of HSS and carbide, two, three and four flute, depending upon what comes to hand at the time!

 

On the CNC mill I’ve standardised on 6mm and 10mm three flute uncoated carbide and 12mm three flute HSS rippa mills. Smaller cutters, special forms, different numbers of flutes and special coatings are used as required.

 

The vast majority of cutters I buy these days are centre cutting, whether they be two, three or four flute. I suspect this trend is driven by commercial use of CNC where the same cutter is used for all operations where possible and hence needs to the ability to cut on the sides and end.

 

All things being equal a cutter with more flutes should allow more material to be removed per unit time. However, the gullets (space between the teeth) are smaller and more prone to get jammed with swarf, so as in all things it’s a compromise.

 

Personally I think that three flutes is a good compromise between metal removal, swarf clearance and tool strength. And it’s what my local tool store sells!

 

Regards,

 

Andrew

 

Addendum: Here’s my take on Steve’s question. I think the distinction between end mills and slot drills is becoming blurred, and traditional endmills are dying out. For carbide cutters I use Garr, as they are stocked by the local tool shop. In their catalogue they only list endmills. I had a quick flick through the 90 odd pages of endmills, 2, 3 and four flute, and as far as I can see they are all centre cutting.

 

Edited By Andrew Johnston on 21/08/2011 22:23:30

[David Clark 13Participant @davidclark13]

Hi Steve

If you are cutting on the end, they are end mills.

If cutting on the sides they are end mills.

 

Slot drills usually cut on the ends and sides.

They are designed to cut 1/2 to 1 thou undersize as long as you don’t force them.

They are ideal for cutting keyways but if cutting a keyway to a depth, you need a new slot drill for each depth you are cutting or you might get a stepped keyway.

 

I never cut a through slot to width in one go.

I usually drill the ends out slightly undersize, no need to centre drill.

Plunge a size slot drill at each end and then mill an undersize slot.

I then mill to width with a smaller end mill or slot drill taking out one side at a time.

Takes slightly longer but gives perfect results, dead to size and with a perfectly formed radius at both ends without keyholing.

regards David

 

 

[John Stevenson 1Participant @johnstevenson1]

For soft material like aluminium you want as few teeth as possible in the cut and as much clearance as possible to get rid of chips, you can now buy single flute plunge cutting end mills / slot drills etc for aluminium.

 

Let me try to expain about end mills and slot drills. Many people have their own description of these but I’m afraid no one is right any longer – even me !!!
First off lets go back in history and see what we had. There were 4 flute end mills and 2 flute end mills. Some could plunge some couldn’t. Confused? well you will be.
The two flute ones were called slot drills in the UK and were ground with one cutting edge over centre so they can plunge cut vertically down and then traverse, hence the name.
The 4 flute end mills usually had a hole in the centre for clearance when grinding and so can only cut on the sides of the tool. Trying to plunge with one of these will leave a central pip that will break the cutter when you try to traverse.
Now when we got towards the end of the 20th century things started changing. We had better methods of producing cutters with fancy 5 and 6 axis CNC grinders. We started to see 3 flute cutters getting popular as a compromise between rapid metal removal and chip clearance. We also started to get the 3 and 4 flute cutters with one lip ground over centre like the two flute in the picture. This means that these can also plunge.
To cap it all the manufacturers put paid to any standards by calling their cutters all sorts of different names. Where a 4 flute cutter was called an end mill it can now be centre cutting and be called a 4 flute slot drill.

If you look in any cutter catalogue nowadays you will find that they call a certain type of cutter by one name on one page and another manufacturer calls it by a different name on another page!

The manufacturers have moved the goalposts. The cutter descriptions we all grew up with in Chapmans and Moultreich has gone out the window with the advent of grinding techniques.

 

I took a 20mm solid carbide 4 flute end mill [ non centre cutting ] in for regrind last month and when it came back it was 4 flute over centre slot cutting cutter. What do I call this now?

 

The main thing to look for when buying cutters is the number of flutes you require and whether they are centre cutting or not.

 

I can see the time when the old 4 flute centre pipped type will become obsolete as most cutters are ground up from blank material nowdays.
I had a load of cam track slots to do the other week at 7.2mm wide. I had a choice of doing two passes with an undersized cutter or having a cutter ground down to 7.2mm

I decided to go with the special cutter and asked the local T&C grinders to supply and regrind an 8mm cutter down. Instead they just ground the new cutter straight onto a 8mm solid blank, 3 flute centre cutting. It was on the machine for all of 3 minutes.

 

The reason you don’t use a 4 flute for cutting slots is that when two teeth are opposite in the cut they are both cutting equal but as soon as it revolves 1/4 of a turn one tooth is at the head of the slot but it’s opposite mate in in fresh air.

 

This causes the cutter to pivot on the tooth at the head of the slot and cause one of the two teeth in the cut to push over to one side and so make a larger cut.

 

This doesn’t happen with 2 or 3 flute cutters and there is never this 90 degree offset between teeth.

 

John S.

[jomacParticipant @jomac]

JasonB, cool looking engine, and nice machining, What is it.??? size etc etc, how did you make the cams.

David how do you make your end mills, a short answer now, and an article in the ME, or MEW. would be great to peruse.

John Holloway

[pgrbffParticipant @pgrbff]

Thank you all for your answers, I feel I am slightly the wiser. I have some knowledge as I am a regular user of router cutters but I feel this is a lot more complicated. I ordered some 2 flute, but the company has sent me 4 flute, so I have both.

[JasonBModerator @jasonb]

Jomac it’s called a “Hoglet” as in small Harley Davidson and designed by Randall Cox. The drawings were published in issues 11 & 12 of Model Engine Builder, back issues are available.

 

Its 1″ bore 1″ stroke, open crank with twin 4″ bronze flywheels that fit between the two frame plates. You can also make a kick starter for it, all the details are in the drawings. All made from barstock. Will stand about 9″ tall when finished.

 

I have still got the cams to do but they are shown done using the inside-out boring head method which is not too difficult. I’m going to make a couple of cams, one as standard and another which will open the exhaust porst earlier to get a nice throughty tickover and maybe even spit a few flames out.

 

There is a video of one running here and a good build diary here

 

I just do a bit on it now and again when I feel like a change from my Traction Engine.

 

J

[David Southwell ARPSParticipant @davidsouthwellarps]

Posted by jomac on 23/08/2011 14:28:45:

David how do you make your end mills, a short answer now, and an article in the ME, or MEW. would be great to peruse.

DAVID: I keep it simple — if I need a helix cutter I buy it — but I find most jobs do not really justify a manufactured helix and many cutters are not helix in any case. I take some HSS steel cheap from scrap merchants (usually large old HSS drils). Turn them down to whatever diameter I require Create the number of cutting edges I require 2/3/4/5 etc setting them out parallel to one another using my divider. The rest is done using with a heavy duty grinder (a combination of stones are required) but you do need to make yourself a firm accurate holder to get the cutting angles dead right before final honing. If you do not take care you are more inclined to get chatter than with a helix.

My methods are similar to those one shown on:

http://home.iprimus.com.au/stevor/milling_cutters.htm

and I now use the formulae shown on that site (with a few mods depending upon the material) rather than my original (and somewhat haphazard) if it looks right it will sometimes work method!

 

Old High tensile bolts are another useful source of suitable material although usually carbon steel it does the job.

 

 

[David Southwell ARPSParticipant @davidsouthwellarps]

Just better mention the site I gave does not actually show an end mill version very well — but I think you can deduce the approach from what is visible. It is just a matter of grinding the end of the cutter to the shape you require. I think I have my dimensions chart in digital form somewhere – if I can find it I will post it.

Edited By David Southwell ARPS on 23/08/2011 19:32:02

Edited By David Southwell ARPS on 23/08/2011 19:32:20

[Sub MandrelParticipant @submandrel]

A two flute cutter can never have more than one flute cutting at a time. With more than two cutters the number of flutes cutting changes as the tool rotates, meaning the forces on the cutter change iregularly (e.g. the load on one flute jumps as another flute leaves the work). That is why two flutes or a single edged cutter are theoretically best for cutting to a size.

 

If you think VERY carefully about 3-flutes cutting a full width slot, you’ll realise that the loads are pretty well balanced but those of a 4-flute go up and down like a yo-yo.

 

As we all know, in practice things neve quite work out like the theory

 

Neil

[David Southwell ARPSParticipant @davidsouthwellarps]

I very much agree with

 

STUBB who said:

” loads are pretty well balanced but those of a 4-flute go up and down like a yo-yo”

 

that is why I start with an assumption that even number is unlikely to work well- – however it depends upon what you are cutting , the size & shape of cutter, the speed and the load. That is a lot of variables. There is, IMHO, no perfect solution and no absolute rules. There is nothing to beat “suck it and see”!

[Anonymous]

Posted by Stub Mandrel on 24/08/2011 21:39:42:

A two flute cutter can never have more than one flute cutting at a time.

 

Straight plunge cut?

 

Regards,

 

Andrew

 

PS: In theory, theory and practice are the same, but in practice theory and practice are completely different.

[Author]

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