Milling mild steel

[Robin Hewitt]

I'll just try and sneak in a quick reply before Jazz arrives (ooer missus smiley)
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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

[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 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

[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.

[Robin Hewitt]

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

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

[JAZZCNC]

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. .

[magicniner]

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

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

[Robin Hewitt]

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

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