Hardwood drilling automation

Are the dimensions of the drill tool Imperial or metric?
The illustration of the machine shows the spindle motors with collet chucks, needed for the more accurate tool centering required for slot milling, rather than Jacobs chucks typically put on a drill spindle. Router spindles run at much higher spindle speed than is normal for drilling. They work with carbide tools that withstand much higher temperature, and they will fry steel drills. Also, drill spindles are much less expensive than router spindles since they don't need super precision high speed bearings capable of handling radial as well as axial cutting force. Router spindles are usually run on high frequency power and don't cool themselves well at lower spindle speed.
I don't know if the length of the workpieces will vary. The illustration shows the positioning and tool movement both using the same track. Automated drill spindles frequently have the tool movement built in and can be positioned on less expensive ways that don't need to be hardened and ground for precision accuracy and durability.
What's your estimate of the production volume?

deemoss said:

I need tο drill stepped holes in hardwood that are as co-axial as possible. Since I want to avoid work holding repositioning as much as possible, I came up with the following automation.

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Excellent build design. Your design insures the drills are coaxial, therefore the holes will be coaxial.
Repositioning the workpiece does nothing more than add more error and effort into the process.

deemoss said:

My problem is estimating the spindle requirements, considering the custom, stepped, bit (see picture). Will a cheap 2.2kw (3hp) 24rpm spindle OK? Do I even need a spindle with a VFD or a fixed-speed motor would do the job cheaper?

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Yes a collet system is a very good choice for both accuracy and tool retention. A fixed length spindle also is much more accurate than any spindle which is required to extend and retract.

I question your stated "24RPM", is that a typo? Seems extremally slow for your given drill size.

While a fixed speed motor may work, the surface speed difference, in the drill diameter to the counterbore diameter, may make choosing the best RPM an exercise in frustration. A variable speed motor would give you the opportunity to "fine tune" and dial in your speed to fit conditions. You could even program a faster RPM for the drill and then slow the RPM once the counterbore diameter enters the workpiece.
If chip evacuation is an issue a change in RPM may cure that or adding a peck cycle would be another option.

Other than that IMHO, you have done an excellent job.

note As to my qualifications; I spent a career in a tool and die shop where our sole "product" was to design and build one of a kind, custom machinery, for a wide variety of industries. From simple fixtures, to muti-station fully automation machining, drilling, assembly and packaging equipment.