Chipload for two flute slot drill in mild steel

[LeonM]

Hello

I am cutting some 2mm mild steel panels using a 4mm HSS slot drill (these are quite large sheets, they tend to flex hence the need to carefully control the feed) I am a little suspicious of the recommended feed rate recommended by the manufacturer - their website seems to list a default tooth load of 0.05mm per rev (.002 inch) for all their tools and materials.

I am running about 3200 rpm at the moment with shallow (0.5mm) cuts and a feed rate of 80mm per minute. Is this ballpark? Or should I trust their figures and cut at 250-350mm per minute? I suspect I would have to go quite shallow to stop the tool deflecting at the higher feed.

Thanks for any comments.

[davereagan]

Can you use a solid carbide endmill? Your surface speed at 3200 rpm is 40 Meters per minute. You could go 100-150 M/minute with coated solid carbide. How many flutes do you have? 80mm per minute is crawling even with 2 flutes. A chipload of .03mm is safe with such a light depth of cut. That would give you 192mm/minute with a 2 flute cutter at 3200 rpm. Hang as little of the tool out of the holder as necessary.

[DareBee]

If you are slotting through, it is best to get it through and cut in one shot.

Chipload specs are good BUT they need to be reduced WHEN tool is long, tool holder is wimpy, spindle is wimpy, set-up is poor (less than ideal), etc

We can't possibly recommend an exact solution due to too many factors that we need to see first hand.

IMO Never use HSS cutters under 3/8" dia. Carbide has gotten so cheap it will pay for itself many times over. Over 3/8 price of carbide really jumps + HSS cutters of that size are getting enough mass that the deflection is now acceptable. (have you noticed how incredibly far sideways that 4mm cutter deflects? Terrible)
Get a better material set-up.

[LeonM]

Thanks for the replies. I have been reluctant to try carbide due to the flex in the material - I am cutting a hole 350x350mm from a 900mm square panel. I am clamping the material with a square chunk of plate 300x300mm that fits inside the cutout. The material outside the hole is only clamped down at the edges, so it is a less than perfect setup. The only way I can think to make it more rigid would be to have plates that cover most of the work except the narrow zone that I am going to slot but this would be a bit of work (we are cutting holes in door panels for electrical cabinets - the panels are precoated so milling is the only real option that does not damage the powdercoating).

I did try slotting in a single pass but as you predicted the deflection is pretty scary - about 0.5mm depth looks comfortable before the mill bends too much.

I might try the .03mm that dave suggests - if I got to 190mm per minute with reasonble tool life I would be very happy.

Thanks again

[tgeng]

could you not sent job out to a laser cutter and save yourself the problem.

[LeonM]

Unfortunately we can't laser cut the panels - they are already powder coated when we get them and the laser will damage the powder coating (the filters we fit to the holes do not really have a bezel to hide the edge so it has to be neat, we used to jigsaw then file...) plus the panels get scratched and damaged if we send them out.

We looked at punching them in a single operation but we would need a 100 ton press plus a handful of dies for the different sizes.

[DareBee]

WATERJET

[LeonM]

Just out of curiosity how much would you expect to pay to get a 350x350mm hole cut by waterjet in a sheet of mild steel? We had some quotes to have 10 squares of rubber (about the same size) cut into small strips and the quote came back at $1700 so we have never really considered it again.

[DareBee]

That is ludicrous.
Thin rubber can be difficult and usually requires sacrificial sheets top and bottom (and maybe a couple of bricks).
Lets say rubber material plus 2 sheets (same size) of 16 gauge = $40
Waterjet cutting (minimum charge) of $120
Equals $160 plus shipping costs.

Your steel cutting would be under a minimum charge as well (for one).

Back to the milling - use carbide cutters - no valid argument can be made not to do so.

[LeonM]

Thanks Darebee - I agree the quotes were crazy. I assumed they spend a lot of their time charging for specialised work like exotic ceramics and try and charge every one the same.

I will order some carbide cutters in this size and give it a go - I was initially reluctant due to the vibration of the sheets and was expecting them to crack but for $20 it is worth a try.

We really want to cut them in house - we have the machine already and we only need to do say one every night to keep up - our main business is actually wiring the cabinets and we can only wire one every few days so the milling only needs to match this. It certainly is not the fastest but as long as it is convenient and we can get a few panels cut from each milling bit we will be happy. We have about 100 to cut in total over the next couple of months.

Regards