Rotary broach chuck grip strength

[Bill D]

I plan to do a little rotary broaching on my vertical mill. Never having done any I am not sure what type of collet or chuck to hold the tool holder with. Will a er25 collet be strong enough grip or will the shank slip into the collet Until it bottoms out. I suppose it could be bottomed out before tightening but that prevents the collet from being drawn done into the cone to get tight.
I will assume a drill press will not be able to do a 3/8 hex broach. Would a three jaw chuck in the lathe tailstock be able to take the forces and stay accurate enough? Or is some kind of collet setup needed.
Bill D

 

[Cole2534]

The definitive answer is........maybe.

Material properties, pilot hole size, and tool size/shape/sharpness all come heavily into play, less so but still important is feed rate.

In a pinch I did a 3/8" square (27/64" pilot) in some 1144SP (100ksi yield, RC in low 20's) in a Bridgeport and I feel like I was asking too much of that quill. My CNC mill or lathe do this with ease, but both have pretty good axis thrust in Z.

 

[L Vanice]

You could use an end mill holder to attach the rotary broach to the mill spindle. There is essentially no torque transmission needed, but the axial load might be high, depending, as Cole said. I would prefer solid contact with the shoulder or end of the shank on the rotary broach tool, rather than depending on a collet or chuck to grip the tool shank.

Larry

 

[Cole2534]

You could use an end mill holder to attach the rotary broach to the mill spindle. There is essentially no torque transmission needed, but the axial load might be high, depending, as Cole said. I would prefer solid contact with the shoulder or end of the shank on the rotary broach tool, rather than depending on a collet or chuck to grip the tool shank.

Larry

Forgot to mention that- I run them in solid holders in the mill and solid bushings in the lathe.

 

[guythatbrews]

A backup screw in the collet chuck will impede tightening but a spacer in between thr nut and broach holder won't. Use a spacer and no worries.

3 jaw with bsckstop will work fine as long as it repeats concentricity.

 

[eKretz]

Yeah, use a spacer out against the front of the nut and give it a try. It will take a good amount of force to do that, you'll have to try and see. I'd give the tailstock the better chance of working well.

 

[boslab]

Buy a spare collet in case you spin it out, other than that , why not.
Mark

 

[gbent]

Backup screws in the collet chuck are meant to be snugged up after tightening the chuck.