Milling mild steel

[WandrinAndy]

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

[JAZZCNC]

We'll have to do it another time.

Hugs

Robin

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

[AdCNC]

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.

[JAZZCNC]

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.

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.!!

[CharlesJenkinson]

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.

[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

[magicniner]

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.

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

[CharlesJenkinson]

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

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.

[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, 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

[Neale]

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.