Newbie- Trouble milling hot rolled steel on a manual Bridgeport

[Geof]

Originally Posted by panz ....Right now I'm roughing with a 1/2" 4 flute AlTiN roughing endmill. My speed is 1000 RPM ..... ..... I ran with "Universal" synthetic coolant via a spray bottle..... I've chewed through around 6 cu. in. of material tonight and the endmill is in great shape.......

The end mill will be in great shape because you are going so slow. There is nothing wrong with that but if you are paying more for the cutter than you would pay for an uncoated one you are wasting a bit of money. At that speed and with coolant the coating is not doing anything.

[ryansuperbee]

What's up? Hey I was just reading this post and a half inch bit at 1000 RPM is way too fast!!! He needs to slow that down to 400-500 RPM If he did that he would actually be able to increase feedrate. He is work hardening the material at that RPM. The trick with steel is low RPM and high(er) end feedrate. Hope this helps!

[Geof]

Originally Posted by ryansuperbee What's up? Hey I was just reading this post and a half inch bit at 1000 RPM is way too fast!!! He needs to slow that down to 400-500 RPM If he did that he would actually be able to increase feedrate. He is work hardening the material at that RPM. The trick with steel is low RPM and high(er) end feedrate. Hope this helps!

I am sorry but you are wrong in more than one way.

The material under discussion is hot rolled steel, low carbon steel, not an alloy steel and it will not work harden.

The surface feet per minute using carbide on hot rolled steel can be anywhere from 300 to 600 depending on the depth of cut, tool engagement and chip load. Normally for roughing the lower end is appropriate with the higher end used for finishing. With coated carbides much higher sfm can be used but this is not applicable to lightweight machines in most cases.

A 1/2" cutter running at 1000 rpm is only doing 130 sfm.

[mc-motorsports]

Originally Posted by Geof I am sorry but you are wrong in more than one way. The material under discussion is hot rolled steel, low carbon steel, not an alloy steel and it will not work harden. The surface feet per minute using carbide on hot rolled steel can be anywhere from 300 to 600 depending on the depth of cut, tool engagement and chip load. Normally for roughing the lower end is appropriate with the higher end used for finishing. With coated carbides much higher sfm can be used but this is not applicable to lightweight machines in most cases. A 1/2" cutter running at 1000 rpm is only doing 130 sfm.

Yep, what he said...

Any slower is wasting time. Any faster and you start getting too much flex in the spindle and head and or just run out of HP. Not the best production machines, but very versitile, inexpensive, low operating/repair/maintence costs, and can be quite precision when you know what your doing. The Bridgeport knee mill is not to be under-estimated, but should not be compared to a Mori either.

The only time I have ever had a problem with "work hardening" 1018 or 1020 is tapping smaller holes when you use a dull tap drill to make the hole.

MC