Mill Plunge Torque

[Damn Yankee]

Happy Holidays, All!

I am looking to motorize the Z-Axis of my Weis VM25-D mill. Instead of just fast Up/Down of the head, I thought it would be nice to size the motor for plunge milling; for now, ignoring how much stress the machine can take. But being a Newb, I am unfamiliar with the forces required for various metals, that is, I am really interested in the forces required for plunging through different metals.

Can an expert give me approximate values of torque required to plunge mill through aluminum, mild steel, and hard steel with a Z-Axis leadscrew of 10 TPI? Alternatively, the force required at the work (in any units) would be great as I could do the conversion.

Hope all are safe and thanks!

John

 

[JimDawson]

A properly sharpened 1/2'' drill requires about 300 lbs of downforce in mild steel at normal feeds and speeds with no pilot hole.

Having said that, plunging with endmill without drilling a pilot hole first is problematic at best, the geometry of an endmill is not correct for drilling holes. If I must plunge with an endmill, I normally drill a pilot hole at least 2/3 the diameter of the endmill. With a pilot hole, the downforce required is much less than a drill of similar size.

There are cases where plunge cutting may make sense. Like a long slot or removing a lot of material from the center of the work. In that case, first drill a pilot hole, plunge with an endmill, then step over about 1/3 the diameter of the endmill and plunge again. Rinse/repeat until you have the removed the material.

You can easily calculate the torque required by using a lever arm and a spring scale. The pinion gear on the quill is most likely about 1'' diameter (if you want real accuracy, pull it out and measure it.) A spring scale attached to the hand lever and a little math will give you a pretty accurate reading of the torque required. An alternate method would be to use an old school beam type torque wrench on the pinion shaft. Once set up, just test some different materials.

 

[Damn Yankee]

A properly sharpened 1/2'' drill requires about 300 lbs of downforce in mild steel at normal feeds and speeds with no pilot hole.

Having said that, plunging with endmill without drilling a pilot hole first is problematic at best, the geometry of an endmill is not correct for drilling holes. If I must plunge with an endmill, I normally drill a pilot hole at least 2/3 the diameter of the endmill. With a pilot hole, the downforce required is much less than a drill of similar size.

There are cases where plunge cutting may make sense. Like a long slot or removing a lot of material from the center of the work. In that case, first drill a pilot hole, plunge with an endmill, then step over about 1/3 the diameter of the endmill and plunge again. Rinse/repeat until you have the removed the material.

You can easily calculate the torque required by using a lever arm and a spring scale. The pinion gear on the quill is most likely about 1'' diameter (if you want real accuracy, pull it out and measure it.) A spring scale attached to the hand lever and a little math will give you a pretty accurate reading of the torque required. An alternate method would be to use an old school beam type torque wrench on the pinion shaft. Once set up, just test some different materials.

Thanks, Jim.

I think I am on the right track. The 1/2" drill = 300lbs gets me in the ballpark!

I guess I missed the part about making a pilot hole first - sorry. Instead of "mill" I should have written "drill" with a drill size included.

Sometimes my mind is ahead of my typing. Usually it is behing everything else...

Thanks,
J