The diamond-faced grinding wheel is peculiar.. the non-flared, straight cup-type body appears to be some synthetic material with no abrasive material, and the face of cup appears to be a thin ring of abrasive-embedded material bonded to the body.
The radial edge around the face is relieved with a small V-groove (may have been original, or formed by a previous owner, don't know), and the thickness at the outer edge of the abrasive ring on the face appears to be about .025" thick.
The surface of the cutting face is very slightly conical, in that the center extends outward more than the edge at the periphery of the body (maybe wear from use or original). Laying a straightedge across the cutting face of the wheel, it looks like a lathe facing cut performed with a badly-fitting carriage where the cut isn't perpendicular to the spindle centerline, so the center is high.
The Wheel dimensions are 2-1/4" dia. x 1-1/4" width x 1/2" hole, and the thickness of the wheel at the hole is ~3/16". The cutting face width is ~1/2", making the recess/counterbore 1-14" dia. The existing wheel has no markings, but I found an online vendor selling a similar diamond wheel (for $330!) and I looked around for the numbers which were visible in their picture, which lead me to a diamond wheel supplier.
Continental Diamond Tool
appears to be the supplier for the online seller. The wheel numbers are NCDT400R100BQ 1/16, which translated means 30% Nickel coated diamond, 400 grit, 100 (high) concentration, resin bond, and 1/16" depth of diamond. The 1/16" thin diamond/resin "washer" is bonded to a plastic core which makes up the body of the straight cupped wheel. The Continental website has some very good technical info regarding diamond and CBN wheels.
The wheel speed is reduced from the 10k RPM Hermes (Bodine type) 1/15 HP universal motor. The spindle pulley is ~1-21/32" and the motor pulley is ~1-5/32".
A slightly larger diameter grinding wheel could be utilized (but not with the existing wheel guard), a new guard would be fairly easy to fabricate/machine from heavy-wall tubing. It appears that changing the wheel diameter will affect the cutter tip indexing locations when using regular abrasive wheels for HSS, as it would change the contact point of the cutter to the wheel's OD. I can't think of a better way to describe this affect/change, but if a 2" dia wheel were used (instead of 2.25") the cutter would contact the wheel at a point further below the wheel axis centerline.
The small collets are the 2B style (overall length a little over 2"), which is similar in appearance to a miniature version of a 3C style, and the dimensions are found in a Hardinge catalog listed as 2B Becker:
The drawtube of the Hermes grinder has a 7/16-26 RH thread, which mates with the 2B collet's internal thread. The thru-hole of the drawtube is a little over 5/16" dia, so that establishes a limitation there for long workpieces.
The thin, flat drive belt is approx 18"x5/16.
There is a threaded hole at the top of the grinding wheel spindle housing where a conical-point set screw is fitted, which positions/secures an internal part (maybe just a bearing spacer), and although there doesn't seem to be any oil in the closed spindle cavity, the screw may also be a lubrication port.. I haven't seen the bearing types to see if they're shielded or open.
The electrical cord is 2-conductor,so it may be worthwhile to change the cord to a 3-wire earth grounded cord. FWIW, dust residues from aluminum oxide wheels and HSS cutters are conductive. The On/Off switch is located on the back end of the motor case.
Some basic operating steps/tips are found here: