Slotting/Broaching Long Blind Keyways

[aal806]

I am new to this so please have some patients.

We're currently using a slotter with HSS to machine internal blind keyways in our products. Dimensions vary; Lengths from a few inches to 18.5", widths from .375" to 1.500", and depths from .300" to .375".
I have been researching how to get this done with carbide inserted tooling on a CNC vertical mill, but have hit a wall. Tooling vendors that I have reached out to will not touch it because of the tolerances needing help. Mainly the width +.001" / -.000".
Personally, I think the tolerance is ridiculous. But that is what engineering calls for.

We use undersized HSS to slowly walk our way to the specified width. Tooling vendors seem to suggest on size tooling, but this makes me nervous.

Any help with tooling or educating me about on size tooling would be very much appreciated.

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[Jim Dawson]

I assume your goal is to automate what is now a pretty much manual process?

Typically internal keyways are cut with on-size tooling. -0.000/+0.001 seems about right on the smaller sizes, but maybe a bit tight on the larger sizes. A blind hole adds another layer of complication to the mix, but you must have that well under control.

I really don't think a VMC is the best tool for the job. While it could be made to work with the right tooling, finding one with about 40 inches of Z clearance might be a little difficult, at least until you get into some really big machines. What might work well as a base machine is a small metal planer (moving table) or perhaps a huge shaper (moving ram), maybe 1930-50's vintage. Then add some CNC functionality to it. As much as I hate hydraulics, a hydraulic ram might make the most sense for this application.

Using carbide insert tooling shouldn't really be a problem, it would just require the proper insert and holder geometry. You would most likely need to build your own tool holder for the insert. I would think any just about any rectangular insert would work. A SNMG 431 insert might work for most of your work.