Keyway "broaching" on CNC lathe with no M19 / spindle lock?

[Crowne]

I've got a few hundred delrin parts with a 5/8" bore that need an 1/8" keyway. My new-to-me Cobra 42 doesn't seem to support spindle orientation (M19) or a spindle lock.

I assume that, without a lock, it would be a bad idea to try and broach (really, shaping) the keyways on the machine using one of those carbide insert tools which you feed in and out to shape the keyway?

I could make a rudimentary spindle lock myself, though having to place it on and off every part wouldn't be ideal.

Any suggestions?

 

[dandrummerman21]

I have done broaching in a bt40 mill that does have M19 to "lock" the spindle, but the "lock" is at the motor, and the spindle is belt driven, so there's a bit of give in either direction if you try to rotate it by hand.

Doing mid 30's RC 4130 3/16" wide, I had no issue with the little bit of give.

I doubt you have a gearbox else I would say put it in low.

How easy is it to rotate by hand? Does S0 lock it in place at all?

Seat of my pants says to give it a try. Else take it to the arbor press while it's running. Might get away with a single stroke with a push broach?

 

[Booze Daily]

I did similar in UHMW. No spindle lock and the parts came out fine.
Give it a try.

 

[706jim]

The trick here is the material. Hard to do anything wrong with Delrin so I suspect there is no need for a spindle lock.

 

[Crowne]

Alright! Seems like it's worth trying and seeing how it behaves. Thanks everyone.

 

[Crowne]

To report back on this, I was able to broach successfully without the spindle lock. I am taking 0.0015" each pass, and the spindle stays solidly put. It works really well, the only difficulty was chip management with the ID groove I need to do to provide relief for the broaching tool.

 

[sinha]

What was done to keep the spindle "locked?"

 

[angelw]

What was done to keep the spindle "locked?"

I suspect nothing. If the cutting edge of the tool is made parallel to the X Axis, the cutting force applied to the workpiece is Axial, with no tendency to rotate the part and the chuck. I've cut many keyways in this manner and have many clients that have also.

Regards,

Bill

 

[Crowne]

That's right, nothing keeps the spindle locked except the static friction of the spindle bearings.
As Bill noted, the cutting forces are axial and balanced, so there is no tendency for rotation.
Of course, if my spindle could lock, I would do it, but it's not necessary, at least not in Delrin as I am doing.

 

[sinha]

So, there are no vibration issues, not even in harder materials?

 

[rjwalker1973]

So, there are no vibration issues, not even in harder materials?

I have done like the OP in Plastics and 6061, but never tried a harder material like Monel or Hastelloy. Be interesting to know if anyone else had tried harder materials and how it came out.

 

[EmGo]

I have done like the OP in Plastics and 6061, but never tried a harder material like Monel or Hastelloy.

I've seen a pretty cool little shaper attachment for live tool turrets, but the cobra doesn't have that

 

[Garwood]

My Hardinge SP42 has a big spindle brake. A Cobra 42 does not?

 

[EmGo]

My Hardinge SP42 has a big spindle brake. A Cobra 42 does not?

I don't think so, ran one for a few days once, it was the entry-level Hardinge, kind of plain-jane.

 

[Houndogforever]

Hell my conquest 42 from 1989 has a disk brake on the head.
I put a 8mm key way in a 30mm bore of 4140.

Can you reach in and rotate your chuck at any time? I have a setting on mine that lets me choose either free state, or locked in position.

 

[fmari --MariTool-]

Most mill spindles even when locked do not isolate load from the spindle bearings. Broaching will flatten the balls or rollers in the spindle bearings in short time.

This is why all multitasking spindles have an elaborate spindle clamp that isolate the spindle bearings when in turning mode. Broaching delrin I am sure will not be an issue, but any steels will be asking for trouble.

Im not saying dont do it, just saying to be aware of the damage you will be doing to your bearings.

 

[Crowne]

Most mill spindles even when locked do not isolate load from the spindle bearings. Broaching will flatten the balls or rollers in the spindle bearings in short time.

Frank, you're right of course about mill spindles, but lathe spindles have correspondingly larger bearings, so I figure it wouldn't be an issue in that case?

 

[sinha]

Most bearings are designed only for radial loads.
Some can also take axial loads.
I am not aware what type of bearings are used with lathe spindles.

 

[gregormarwick]

Typical arrangement on a lathe is a big cylindrical roller bearing first behind the spindle nose, with some arrangement of angular contacts behind it to take thrust, and another cylindrical roller at the rear end of the spindle. Some high speed lathe spindles might forego the first cylindrical roller and use only angular contacts, but I'd expect those to be uncommon.

Broaching in a lathe is basically a non-issue - enough of it is done every minute of every day around the world that we'd know if it was causing mechanical failures. I have done a lot of it in lathes and in multitask machines without any issues. To be honest, I expect that it is harder on the ballscrew and slides than it is on the spindle, but I don't have any evidence to back that up.

I've never tried it in a mill though, mainly because I don't trust the spindle orient.

 

[EmGo]

I've never tried it in a mill though, mainly because I don't trust the spindle orient.

Oldwrench used to use his haas as a slotter. I never thought that was a good idea but he said he did it for years with no ill effects.