cnc mill broaching

[Monkeys Uncle]

Not a machinist so be gentle with me.
I have a Bridgeport Series 1 with a Centroid retrofit. Love the machine and use it extensively but never had this requirement.
I use Bridgeport software for most of my parts, Intercon for thread milling and boring.
I need to broach a 3/16" wide keyway in a 1" dia hole that is 3/4" deep.
This is the wheel on a scale steam locomotive, material is cast iron.
My biggest question is about locking the spindle and having it move with the motor stopped.
Any suggestions are appreciated.

[Dan M]

As far as locking the spindle I've seen that question answered before but don't remember what thread. I'm sure one of the more experienced mill user's will be able to help you out with locking out the spindle. I seem to remember that question being asked and answered before, but I don't remember what brand the mill was or if that would matter.


Here's a company with some good videos along with tooling if you haven't already checked it out.

https://www.cncbroachtools.com

[agsweeney1972]

Not a machinist so be gentle with me.
I have a Bridgeport Series 1 with a Centroid retrofit. Love the machine and use it extensively but never had this requirement.
I use Bridgeport software for most of my parts, Intercon for thread milling and boring.
I need to broach a 3/16" wide keyway in a 1" dia hole that is 3/4" deep.
This is the wheel on a scale steam locomotive, material is cast iron.
My biggest question is about locking the spindle and having it move with the motor stopped.
Any suggestions are appreciated.

Does your retrofit have a pneumatic spindle brake installed? If so put the head in low gear and with the brake on it shouldn't move at all.

[Monkeys Uncle]

Have a pneumatic brake. Problem is I can't figure out how to get the spindle to cycle without starting the motor, which also causes the brake to release.

[cncsnw]

What do you mean by "get the spindle to cycle"?

Do you want it to turn, or do you want it to stay put?

[Monkeys Uncle]

Want to broach so spindle can't rotate. Can't figure out how to program so the motor does not run and the spindle is not allowed to rotate but Z axis will feed up and down.
Any program I write that has a Z axis feed will only operate with the brake released and motor running.

[cnc_smith]

Want to broach so spindle can't rotate. Can't figure out how to program so the motor does not run and the spindle is not allowed to rotate but Z axis will feed up and down.
Any program I write that has a Z axis feed will only operate with the brake released and motor running.

Are you using Intercon to create you program or are you using the Bridgeport software to create your g-code program? If you are using the Intercon program you can have the tool called with a M5 in it. If you are using Bridgeport software to create your g-code program is the post creating the problem? Please post a copy of the program you are using.

[toolmaker101]

I would rough the key with an endmill first. It will make an u shape but this will take most of the stock out and make it easier oh the machine.

[Monkeys Uncle]

Thanks for the responses. I gave up on both intercon and the bridgeport software. It's been a looong time but I got out the G and M code sheet and wrote it out. I bought this CNC almost 30 years ago and when purchased had to write everything on my ex-wife's pc then terminal it into the machine. Brings back memories, both good and bad.
Got the broach working as required, will e-mill out the slot as suggested before broaching.

[9wdragline]

I would mill it also unless you have one of those vertical shaping heads for your Bridgeport. Perhaps make a key that has one round side to match the radii of the end mil and the other square. Why does the key have to be partially though the bore? You didn't mention if it was a blind hole.
Another method is to use one of these:

https://www.keyseaters.com/index.html


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