Milling mild steel

My Cnc mills aluminium very well I think although I have not mastered finishes yet.

I tried to create a small pocket in Mild steel the other day, with a single flute 6mm endmill. Spindle at 9,000rpm , feedrate 90 mm/pm and depth of cut 0.2mm. Don't know what happened, but it ended up snapping the endmill and making a mess. This is all obviously done wrong.
It was only a practice, but please can someone tell me what rates I should be using for cutting slots in 2.5mm mild steel ? This is not something I am going to be doing very often.

Hi Dudz
Try a look @ these SLOT DRILLS
they are used for producing keyways

9000rpm is far too fast for a 6mm cutter in mild steel. For things to be easy you'd want around 1000-2000rpm, but that's not happening with the spindle you have so just see how low you can set the speed without the spindle tooling.

You'd also be better off using a cutter with more flutes, e.g. 3 or 4. Depending on the spindle speed you can use, you may need to use cutters with a special coating - e.g. the blue ones from cutwell tools.

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Originally Posted by mekanik

Hi Dudz
Try a look @ these SLOT DRILLS
they are used for producing keyways

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Doesn't say if they're HSS or carbide? I'm guessing from the price that they're HSS. Carbide is definitely needed here due to the high spindle speed.

Ah thx. Might be better to use a 4mm 4flute in the blue ones then ? and just do more passes.

Don't do this to me, I am definitely a 20th century machinist. If you tell me you can cut soft wood with your milling machine, I try and persuade you to cut a square peg because I know it isn't going to work. If you tell me you have this magical tool bit that lets you cut mild steel using a woodworking router, I want to see one you did earlier because I don't believe you :hysterical:

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Originally Posted by Robin Hewitt

If you tell me you have this magical tool bit that lets you cut mild steel using a woodworking router, I want to see one you did earlier because I don't believe you :hysterical:

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See here...

I did that with a generic carbide endmill. Admittedly that machine is probably a little stronger than dudz's machine...

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Originally Posted by Jonathan

I did that with a generic carbide endmill.

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Did what? That's a machine build thread (Imagine I could find a bewildered smiley here - grin)

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Originally Posted by Robin Hewitt

Did what? That's a machine build thread (Imagine I could find a bewildered smiley here - grin)

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The last three images in the build log show some parts I cut with that machine from steel.

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Originally Posted by Robin Hewitt

If you tell me you have this magical tool bit that lets you cut mild steel using a woodworking router, I want to see one you did earlier because I don't believe you :hysterical:

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Cutting steel is easy enough with a router provided the machines stiff enough and you use the correct tool for the Job.!
Yes compared to a milling machine it's slow going and your not ripping more scratching away in comparison but most certainly possible and something I've done many times.

Cutwells X5070 Blue Nanograin carbide 4 flute cutters are the magical tool you'll be looking for Robin.!!

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Originally Posted by Jonathan

The last three images in the build log show some parts I cut with that machine from steel.

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Wow, you made a router that was heavier than your milling machine ? This is most excellent.
.
But even so, hand on your heart, would you really recommend it for cutting steel? :hysterical:

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Originally Posted by Robin Hewitt

But even so, hand on your heart, would you really recommend it for cutting steel? :hysterical:

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Well YES.!! . .. Compared to sanding it away with emery paper then I'd certainly recommend it Robin. . . .End of the day it's all relative to the job in hand and the tools available to you.? . . . Certainly better than nothing.

To be honest the same could be said for common milling machine conversions when it comes to cutting or engraving aluminium or 3D work in aluminium.? Compared to a stiff router like Jonathan's new creation then your typical slow running spindle milling machine will be inferior just like routers are for cutting steel.! . . Same principle really.!!
Yes typical Milling machine conversion will cut and engrave Ali and do 3D work in Ali but in comparison it will be much slower due to it's snail pace spindle.!!

Don't knock what you haven't tried.!!

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Originally Posted by JAZZCNC

Cutting steel is easy enough with a router provided the machines stiff enough and you use the correct tool for the Job.!

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I'm not going to argue because you'll just get cross (Why is there no :sad: smiley? Even I could draw a freakin' sad smiley)

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Originally Posted by Robin Hewitt

I'm not going to argue because you'll just get cross (Why is there no :sad: smiley? Even I could draw a freakin' sad smiley)

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Unless your calling Jonathan and me lier's then to me Nothing to Argue about.!!. . . . You said it can't be done, Jonathan showed you proof it could and I'm telling you I've done it many times and pointed you to the tools to do it. . . Nuff said.!!

Anyway back on topic.!!

Dudz the X5070 4 flute will cut steel ok but can't give you any help on DOC or Feeds really has your machine will be the determining factor here.
Trial and error will be needed to find the sweet spot for your machine.

Well that was all amusing first thing on a morning....

Thanks Jazz. Its def not something I need to do all the time. I don't really care if it takes 3hrs rather than 5 mins.

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Originally Posted by JAZZCNC

Unless your calling Jonathan and me lier's then to me Nothing to Argue about.!!. . .

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Blimey, where did that come from? I know you aren't used to people disagreeing with you, but getting cross doesn't mean you are right.

You are suggesting this chap buys an expensive tool bit, tries to wind it sideways through a lump of steel and hopefully discovers some miraculous "sweet spot" from the start so it doesn't break?

I wish him luck.

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Originally Posted by Robin Hewitt

Wow, you made a router that was heavier than your milling machine ?

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Milling machine is 167kg, router is 225kg and will be more when filled with sand, so yes. More importantly it's also stiffer than the milling machine in at least one axis and has the same amount of backlash as your milling machine :)

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Originally Posted by Robin Hewitt

But even so, hand on your heart, would you really recommend it for cutting steel? :hysterical:

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It depends on the situation. I would recommend it to Sasha (whose machine it is), because that's all he's got and can't get a reasonable size milling machine in his house. However if you're cutting a lot of steel then clearly using a lower speed spindle would be the way forward.

I won one of the fancy blue tools on eBay cheaply a while ago but I've not tried it yet as it seems like it would be just too easy to break. In dudz's situation I would try using cheap 1/8" carbide cutters as the small diameter makes the high spindle speed more reasonable (6000rpm should be OK) plus you can break a fair few finding the sweet spot before you've spent as much as the 'X5070' costs.

On a related topic, if you've got one of the Chinese water cooled spindles it's possible to get a bit more torque out of it at low speed. All you have to do is alter the V/f curve parameters in the VFD to raise the voltage slightly at low speed. This increases the flux and thus the torque output available, however you can only gain a little due to saturation. The no-load losses at low speed will increase dramatically (e.g. 10x more) so only raise the voltage a little bit at a time, and keep an eye on the no load current. Clearly this means your water cooling system must be good. You can gain a useful amount of torque from doing this, but do be very careful as it's probably an easy way to burn out the spindle if you're not careful.

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Originally Posted by Jonathan

stiffer than the milling machine in at least one axis and has the same amount of backlash as your milling machine :)

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In that case, you deserve to succeed. It is a lot of effort for a few microns but once you have it, there is no going back :congratulatory:

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Originally Posted by Robin Hewitt

Blimey, where did that come from? I know you aren't used to people disagreeing with you, but getting cross doesn't mean you are right.

You are suggesting this chap buys an expensive tool bit, tries to wind it sideways through a lump of steel and hopefully discovers some miraculous "sweet spot" from the start so it doesn't break?

I wish him luck.

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Ok first I wasn't remotely cross and honestly don't give a flying toss if people agree or disagree with me.!!. . . I know what I know and pass it on when asked or think it can help.!!

Personally I would rather someone recommend to me cutter they have successfully used rather than work my way thru several cutters trying to find one that does the job.

I'll ask you this.!!. . . . If you cut a new unknown to you material on your milling machine even with a cutter you know or have been advised works on that material by a trusted source would you go wading into a lump of steel.?? . . . . No you would take it easy and find the sweet spot.? . . . .You wouldn't waste time and money testing with cheap cutters has you've been told a specific cutter can handle the job.

The cutter I recommended is made to be run at high speed cutting dry It's the correct tool for this exact situation. I've used them and know they work with the same spindle Dudz is using.
If I had the same machine with same spindle I'd tell him the cutting conditions I use but I don't, so I can't. So next best is to advise careful approach regards DOC and Feed which is mostly dependent on machine stiffness and spindle power so what's the problem here.?. . . . That's a sensible approach to me given the situation.!

Certainly better suggestion than saying don't bother it can't be done because it's not a milling machine.!!. . . Jezzz if we listened to crap like that DIY CNC would never have happened.!!

Come on Robin Get real Man and stop the snobbish elite-ism that only milling machines can cut steel.!! . . . Yes they cut it easier and deeper but still can be done by other machines with correct tooling and care.!

Now chill buddy.!!. . . I am.!!.:thumsup:

Hi Jazz

I'd love to stop and chat but I have too much to do today. We'll have to do it another time.

Hugs

Robin

If we are about to do a group hug, please may I be wedged between the two most buxom ladies? :excitement::joker:

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Originally Posted by Robin Hewitt

We'll have to do it another time.

Hugs

Robin

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Yes I couldn't find the Hugs Smiley has well Robin but I'm not clever enough to think about spelling it. . . Lol

interesting convo chaps. :-) ive just watched a vid Jonathan's doing test cuts in aluminium on the second pass you can here what i class as pretty bad resonance of the cutter, that alone is mainly down to the rigidity and mass of the machine, now i to have use them blue coated cutters on jobs in the past, they are "OK" as chinese and korean cutters go but there are better out there but at a cost, personally for me using a router of any sort to cut steel is asking bit, especially when spindle plays a big role in the quality, and time it takes to machine a job in steel. i would convert a mill to cnc for use on steel any day and not rely on a cutter to be the saving grace. i can't see any router thats been made on this forum that could hold to a few microns. My machine at work does that but that way 6.5 ton.

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Originally Posted by AdCNC

i would convert a mill to cnc for use on steel any day and not rely on a cutter to be the saving grace. i can't see any router thats been made on this forum that could hold to a few microns. My machine at work does that but that way 6.5 ton.

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You Bloody trouble causer starting this back up again. . .Lol

I agree 100% Addy but that doesn't mean router can't cut steel like was suggested they just don't do it as good or quick. For the Odd time you need to cut mild steel with a router then provided it's of good strength it's possible and can get jobs done, Yes not High accuracy Jobs but still profiles etc then it works.

Many moons ago the Windows Guru's said controlling a CNC machine with Windows was imposible So Art fennerty proved them wrong. . . . . . Never say never.!!

I landed on the calculation of specific cutting force (SCF) whilst researching the other day. I get the feeling that fiddling around with some of the parameters in the SCF equation via the use of fancier cutting tools like the blue nanograin, and speeds/feeds and DOC appropriate to routers, that the actual cutting force comes down, for cutting materials like steel. And this is what makes cutting harder materials possible on a router versus the traditional milling machine, i.e. It's a different process.

I'll just try and sneak in a quick reply before Jazz arrives (ooer missus smiley)
- blank line inserted here -
You can't slow the spindle so you have to use tiny tooling to get some semblance of the right ft/min, then you work out the feed rate for a credible chip thickness and it is stupidly fast, so you reduce the depth of cut to reduce the horsepower which has to go down the spindly little tool to reach the tip, find the DOC is less than the backlash on your Z axis, realise it is impossible and something has to change. What you really need to do is cut the rpm but that puts you back to square one :hysterical:

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Originally Posted by dudz

My Cnc mills aluminium very well I think although I have not mastered finishes yet.

I tried to create a small pocket in Mild steel the other day, with a single flute 6mm endmill. Spindle at 9,000rpm , feedrate 90 mm/pm and depth of cut 0.2mm. Don't know what happened, but it ended up snapping the endmill and making a mess. This is all obviously done wrong.
It was only a practice, but please can someone tell me what rates I should be using for cutting slots in 2.5mm mild steel ? This is not something I am going to be doing very often.

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Use a 4mm or 6mm coated carbide Slot Drill that's intended for ferrous materials, 3 or 4 flute.
The tooling will be up to the numbers you've quoted, whether it works will be down to your machine, if it's a bit short on rigidity halve your feed rate to start with and creep up on the optimum.
Leaving a finishing allowance and making a finish cut (or two) will help with dimensional accuracy.
Make sure you're squirting a bit of lube on the cut fairly regularly, 75/25 Paraffin/Engine Oil or WD (buy a gallon, not aerosols) work nicely in a plant sprayer. Keeping the cut clear of chips with compressed air will help your tooling and machine to cut more smoothly - industrial machines running these speeds have high pressure flood coolant jets,
Regards,
Nick

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Originally Posted by Robin Hewitt

I'll just try and sneak in a quick reply before Jazz arrives (ooer missus smiley)
- blank line inserted here -
You can't slow the spindle so you have to use tiny tooling to get some semblance of the right ft/min, then you work out the feed rate for a credible chip thickness and it is stupidly fast, so you reduce the depth of cut to reduce the horsepower which has to go down the spindly little tool to reach the tip, find the DOC is less than the backlash on your Z axis, realise it is impossible and something has to change. What you really need to do is cut the rpm but that puts you back to square one :hysterical:

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But its a different square one. I'm not saying I'd expect a shire horse to win the grand national, or vice versa. No one is saying there isn't an ideal.

My first milling operations were carried out on a lathe with a milling cutter in the chuck and an angle plate and single axis slide mounted on the cross slide, it's fiddly and far from ideal but got a lot of small jobs done to the required spec with the only equipment I had.
I progressed to a spindle driven vertical milling attachment which allowed me to use the lathe cross slide as a table, it took quite a lot of work to adapt it to fit my lathe and rigidity wasn't great but it did some good work and was all I could afford at the time.
I'm sure a lot of the work these stop-gap measures allowed me to complete was "Impossible" in the eyes of a man with the ideal machine for the job, the correct machine for your job is the one which you have reasonable access to which can be made to complete the job to a standard you are happy with in a time you can put up with ;-)

- Nick

Ditto - my first "vertical" milling was done in a lathe because that was all I had. I progressed to a built-from-a-part-machined-kit vertical mill which was much better but still very bendy compared to the Bridgeport I used in evening classes. I now have a Chinese vertical mill which is wonderful compared to what went before. But all three machines had something that a typical 2.2kw spindle doesn't have - slow speed. With cutter speeds in the 500-1000rpm range, I could minimise resonance, keep up chip size, etc, without overloading the machine. These water-cooled spindles are great things but they just don't go slowly enough for some things. That's why I have plans to CNC-convert the mill, once the new router is built.

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Originally Posted by magicniner

My first milling operations were carried out on a lathe with a milling cutter in the chuck and an angle plate and single axis slide mounted on the cross slide

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Nil problemo, been there done that, keep the cuts light, fine and dandy.

IMPOSSIBLE is in the eye of the beholder.!!. . . . . If we all took the It's IMPOSSIBLE approach just because the tools we had to hand weren't the ideal then we'd still be living in Caves.!

To be honest I don't care if Nah sayers don't believe it can be done because when I've completed the IMPOSSIBLE I feel . .GOOOOOD. .:yahoo:

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Originally Posted by JAZZCNC

IMPOSSIBLE is in the eye of the beholder.!!.

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I will steal, keep and re-use this most excellent expression ;-)

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Originally Posted by JAZZCNC

If we all took the It's IMPOSSIBLE approach just because the tools we had to hand weren't the ideal then we'd still be living in Caves

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Blimey, where did that come from?
Did someone say, "Impossible"?
(Someone outside Jazz's brain case that is) :hysterical: