Author Topic: Small milling cutters  (Read 3326 times)

Offline DavidA

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Small milling cutters
« on: January 23, 2016, 06:53:47 AM »
I'm used to using large industrial milling machines, but  when it comes to my small tabletop machine I am a bit wary.

What would the group suggest as a reasonable speed (rpm) to run a 10mm HSS two flute cutter when cutting bright mild steel ?

I believe this material to be to EN3 spec. Non leaded.

Dave.

Offline philf

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Re: Small milling cutters
« Reply #1 on: January 23, 2016, 06:59:59 AM »
I'm used to using large industrial milling machines, but  when it comes to my small tabletop machine I am a bit wary.

What would the group suggest as a reasonable speed (rpm) to run a 10mm HSS two flute cutter when cutting bright mild steel ?

I believe this material to be to EN3 spec. Non leaded.

Dave.

Hi Dave,

According to FSWizard 1,640 rpm:

http://zero-divide.net/index.php?page=fswizard

Phil.
Phil Fern
Location: Marple, Cheshire

Offline DavidA

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Re: Small milling cutters
« Reply #2 on: January 23, 2016, 11:21:04 AM »
Phil,

Thanks for that, and the link.

I looks as if you used 'very soft steel' as an input.

I suspect this stuff is a bit tougher, so I tried 'structural steels <0.5% Carbon.

I believe it is C15, or there about.

Gives me an rpm of 1380.

I guess the best thing to do is call in the steel supplier and ask them for the spec.

All I'm making at the moment is 'T' slot nuts. The machine does appear to be making hard work of it. There again, it is only a Micro Mill.

Dave.

Offline Pete W.

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Re: Small milling cutters
« Reply #3 on: January 23, 2016, 01:51:10 PM »
I might be hallucinating but I seem to remember someone quoting a rule of thumb for rate of metal removal (e.g. cubic inches per minute) versus horsepower (or Watts) at the tool.  Maybe you're running out of horsepower? 
Best regards,

Pete W.

If you can keep your head when all about you are losing theirs, you haven't seen the latest change-note!

Offline DavidA

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Re: Small milling cutters
« Reply #4 on: January 23, 2016, 02:22:09 PM »
Pete,

A possibility, but in this case I doubt it.

I'm only cutting 3mm wide and 0.5 mm deep.

Having watched Stefan Gotteswinter's video where he does a comparison between HSS and Carbide cutters

https://www.youtube.com/watch?v=MOEkoSvA30A

 I don't think I should really have a problem.

Dave.
« Last Edit: January 23, 2016, 03:38:13 PM by DavidA »

Offline Fergus OMore

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Re: Small milling cutters
« Reply #5 on: January 23, 2016, 04:13:54 PM »

My thoughts are that you are probably not using the correct cutter.

If you are using a 'slot drill' slot drill, you might try an end mill.

I've just been trying to sort out the goodies which came with my little Myford ML10 and found that whoever had owned the lathe used the faceplate and a single point  tool  to mill.

My suggestions might be wrong, however.

Cheers


Norman

Offline DavidA

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Re: Small milling cutters
« Reply #6 on: January 23, 2016, 04:45:10 PM »
Norman,

You may be right, I am using a slot drill.

I admit that I didn't expect it to make a difference.
I always thought that the only real difference was that you could plunge with a slot drill, but not with an end mill, but it is certainly worth giving an end mill a try.

Dave.

Offline DavidA

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Re: Small milling cutters
« Reply #7 on: January 24, 2016, 12:51:32 PM »
I managed to finish the 'T' nuts.  It would appear that the main problem was that |I was being too gentle on the feeds and speeds.

I upped the speed to something around 1350 rpm (hard to tell, no markings; A cheapo tacho is on it's way) and fed it quite aggressively and this seemed to work.

It was a new cutter when I started, and towards the end the vibration was starting to tell me that the edge was going.

On removal, the very tips of the cutter were showing signs of wear, but the rest of the edge was ok. no apparent wear on the flutes. So really it needs sharpening before any further use.
The conclusion I come to is that it doesn't matter if it is an end mill or a slot drill as only the very tips do any cutting in normal milling.

 And that when cutting anything tougher than leaded steel it may be worth getting a carbide.

Dave.

Offline seadog

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Re: Small milling cutters
« Reply #8 on: January 24, 2016, 01:26:44 PM »
You can't plunge with all end mills, some are not centre cutting.

Offline DavidA

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Re: Small milling cutters
« Reply #9 on: January 24, 2016, 01:46:07 PM »
Seadog,

Yes, I know.

See my response (#6 above) to Norman.

Dave.

Offline philf

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Re: Small milling cutters
« Reply #10 on: January 24, 2016, 02:05:55 PM »

On removal, the very tips of the cutter were showing signs of wear, but the rest of the edge was ok. no apparent wear on the flutes. So really it needs sharpening before any further use.

Dave.

Dave,

If you haven't got a tool and cutter grinder just take the corners off on a bench grinder. A 45 degree (ish) chamfer with about 5 degrees clearance will give your cutter a new lease of life.

Phil.
Phil Fern
Location: Marple, Cheshire

Offline DavidA

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Re: Small milling cutters
« Reply #11 on: January 24, 2016, 03:11:56 PM »
Phil,

That would be one way to go; thanks for the idea.

But as this is a very low power machine I really aught to aim for a nice crisp edge with minimal contact area.

I could take the cutters down to my old work and get them touched up.

As I am gradually 'rationalizing' my numerous time consuming pursuits (aka hobbies) and starting to get my machining into some kind of order, I have a cutter grinder pretty close to the top of my wish list.
Meanwhile I may have a go at H Hall's grinding rest.

Dave.

Offline DavidA

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Re: Small milling cutters
« Reply #12 on: January 29, 2016, 02:16:56 PM »
Phil,

Going back to the original reason for me creating this thread.

I just received my copy of 'Milling:a complete guide' by Harold Hall.

I think that all of the items he covers in the book have also been presented in Model Engineer's Workshop; but I reasoned that it would be more convenient to have all this stuff in one place.
The items covered and the techniques used are very interesting,

But what immediately struck me was the speeds he uses.

He is recommending free cutting mild steel for his projects. But running a 12mm HSS cutter at 500 rpm.

Agreed, he does indicate  that there is some leeway in this, but 500 rpm is less than half the recommended speed.

I do tend to wonder if many people have taken this advice too literally and wonder, as I did, why they were having problems milling with small cutters.

Dave.

Offline chipenter

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Re: Small milling cutters
« Reply #13 on: January 29, 2016, 03:38:57 PM »
At lower speeds less heat is generated and the cutting edge lasts longer , and you don't need to use coolant .
Jeff

Offline DavidA

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Re: Small milling cutters
« Reply #14 on: January 29, 2016, 04:28:24 PM »
Jeff,

I appreciate the above points.

However, it would perhaps be a good idea to point out to the reader that the speeds used are not the same as the ones to be found in standard tables.

After all, the book is entitled 'MILLING; a complete course'.

Dave.

Offline sparky961

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Re: Small milling cutters
« Reply #15 on: January 29, 2016, 04:42:53 PM »
Everyone eventually accrues a collection of "rules of thumb". Some lead to argument but that doesn't matter if it works for you.

One that I picked up years ago was 0.500" = 500 RPM. This is a good starting point for milling and drilling mild steel with HSS.  Since RPM to diameter is linear you can easily do the math in your head for others. Double the diameter, half the speed. Half the diameter, twice the speed... etc. You quickly learn to look and listen and watch and adjust accordingly. Oh, and for carbide I typically double or triple the RPM.

Running slower will, for the most part, take longer and make the cutter last longer. Tool books will usually give production speeds that get the job done quickly at the cost of quickly wearing tooling.

On a manual machine I mill and drill stainless much slower than suggested. I get excellent results.

Best way to learn is to get some sharp HSS cutters tharent too expensive. Start with book values and adjust both ways to see what happens.

Offline chipenter

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Re: Small milling cutters
« Reply #16 on: January 29, 2016, 05:23:55 PM »
I should also add that I use a rubber puffer for small cutters , cutting it's own chips will knock the edge off if not cleared .
Jeff