All tap holes injure maple trees.
Extensive research into spile-hole damage (with an eye to reducing it, and preserving productivity) is precisely what has driven the downsizing of spiles. Few producers (essentially no serious ones) use even the 7/16 size currently. The area of damaged wood (which cannot produce sap in the future, until the tree has overgrown it with adequate thickness of new wood to support a new spile hole) is significantly less with a smaller hole, and the amount of sap collected is substantially the same regardless of hole size.
In this particular study, comparing 5/16 and 7/16 spiles, the 5/16 spile had only 59% of the damaged area as the 7/16 spile (for gravity - i.e. bucket or bag collection, as opposed to under vacuum where it was generally less, but not as much less.)
More recent research also indicates that using a new (washing, boiling, alcohol or even autoclaving do not suffice - new) spile each year increases sap yields, as there is some type of EXTREMELY persistent biofilm that resist all the mentioned treatments and lead to the tree blocking off the hole early. As such, purchasing a 10-pack of modern small spiles and using, then discarding, one each year for 10 years would be both kinder to your tree and more productive for your sap collection than using your hand-carved spile.
Mentioned in this page (as unpublished and personal communication - I have also had the above specifics that don't work confirmed in personal communication with Dr. Perkins, who stated that they had, in fact tried all of them without success):
Also, don't overdrill the depth, for the same reason:
This shows a nice visual of a taphole and a section of tree above the taphole (taphole damage extends above and below the actual taphole for some distance)
This image from northernwoodlands.org shows a board with a visible taphole and several visible stains (the tapered dark areas.) You can see that a good deal of new white wood has grown over the two stains to the left of the hole as the tree continued to grow. Even the stain with the hole has been grown over, but it was some years (and tree-growth rings) later than the other two. As a general guide, you never want to tap directly above or below a visible old tap hole.