Old mill, no through spindle coolant, coolant not reaching inserts - U drill

Hello,

Using old Maho MH600E mill and trying to drill holes (22 mm diameter) into 20 mm steel (low carbon steel, S355 european) plate. Drilling with U drill that's meant to have through spindle cooling, but the old Maho doesn't have through spindle coolant, so i am having trouble with keeping the inserts cool.

Chips are wrapping around the drill and they form like a fan or a barrier that won't let any coolant reach the tool.

I've been trying to mess with speeds and feeds to get the chip to break but nothing yet. Old soviet union era machinist said that it's normal chip for that type of steel and that i'm probably not getting the chip to break without through spindle coolant anyway.

I tried to remove the chip after every hole and then cool the insert and then drill the hole but it takes a long time and i still broke one of the inserts. Cutting speed 220 m/min, 3180 rpm, feed rate 159 mm/min, 0,05 mm/revolution. These are the insert manufacturer's recommended parameters. What would you change to get the chip to break?

I'm pretty new to CNC machining. Any advice on what to do? Apologies for any grammar errors.

Thanks

Morderesh said:

I'm pretty new to CNC machining. Any advice on what to do? Apologies for any grammar errors.

Thanks

Click to expand...

No need to apologize, your English is better than my Estonian.

You should look into getting a coolant inducing toolholder like this: Hi-Jet Holder Side Lock Type | BIG KAISER

Many vendors offer similar devices, so search for what's best for your needs and availability/cost.

You may need to hand load the holder, as well as managing the coolant connection. For long runs this isn't an issue, but could be if using a lot of different tools. But an advantage is that you could dedicate a higher pressure pump just to this tool, making it more effective for drilling.

Usually carbide inserts like to be run hot or fully cooled, having thermal cycling in your cut can damage them and lead to premature failure. So you may be getting failures due to the way you're currently drilling, not just due to mechanical stress only.

Good luck, let us know if you find a good solution.

I machine a lot of S355 and use insert drills all the time, usually with through coolant, but sometimes without.

S355 comes in a lot of grades/conditions that all behave a little different. However, generally it is soft and gummy and doesn't break chips easily with a u-drill. A higher surface speed than recommended and a lower feed is the usual solution.

1 - 2x diameter is usually fine without through coolant, 3x and deeper is when it gets problematic. Drilling through 20mm plate should be perfectly possible without through coolant.

Your cutting data is pretty close to what I would use and would expect to work, but it depends on the drill. eg. Sandvik 880 with GM geometry inserts needs about 180m/min to break a chip while Tungaloy TDX needs 250m/min or more (numbers off the top of my head).

Tell us what specific drill and inserts you are using, also a picture of the chips.

You should have no problem drilling 20mm deep without through coolant. Try increasing feed to make a heavier chip. Or maybe get a different insert or drill. I recently used a Sandvik 870 drill to do a very similar job in the mill without through coolant and it worked great.

If all else fails and you cant get chips to break, you can program in some tiny dwells every few mm just long enough to get chips to break. Don't peck it with carbide, chips get in the way when going back in and crack the inserts.

I would 2nd what Miland recommended. I've used them drilling 304 and they work great.