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Bench Grinder

WARNING: Grinders are Dangerous.
Grinding wheels can break apart while turning at high speeds.
Always use appropriate eye, breathing & clothing protection.
Read, understand & follow all of the manufacturer's instructions.
Dust from grinding tool bits is dangerous if inhaled.

Stock bench grinders can be modified to make them more useful for tool bit grinding & general shop use. Often, a grinding wheel has a 1" hole but is used on a ½" shaft and is usually adapted using concentric plastic spacer rings. I took a 1.000" aluminum dowel, centered it in the Jet 4-jaw, faced it, centered drilled, then drilled a 31/64" hole. Chamfer the opening & then use a well-lubricated 0.500" reamer at the lowest RPM. When the reamer is all the way through, stop turning the part & then withdraw to keep a tight tolerance. I use ¾" wide wheels so I cut-off the spacer length slightly bigger but not interfering with clamping action of the washers & left-hand nut. I found some nicely machined clamping washers from another arbor I had in my grinding accessories. The spacer is a tight fit to both the wheel & the grinder shaft. The wheel is now held more precisely in the grinder. II use both a star dresser & a carborundum dressing stick which makes the surface smooth & flat.

Aluminum shaft spacer for grinding wheel (1.000" OD,  0.500" ID & about ~0.75" long).
Note: left-hand nut & thread on the left side of the grinder.

The next mod was the tool rest. Most grinders have inadequate rests & mine was no different. I replaced it with the Veritas tool rest. It is a great improvement over the OEM rest.  It has a wide range of adjustment. Its best feature is the ½" x ½" channel on the tool rest platform that is used to guide jigs. There are several jigs available but custom jigs may be fabricated to suit any need. Shown is a jig that allows me to precisely grind tool bits at 60º for threading. The rest mounts onto the bench. They recommend using ¼ x 20 carriage bolts but I tapped holes into the grinder mounting plate & used ¼ x 20 socket head cap screws & nylon washers. Note the ½" x ½" channel to guide jigs. The rest's center hole is for (Veritas) pivoting jigs. The locking handles can be pulled & rotated to any detent position.

WARNING: DO NOT remove the shroud that covers the wheel.

 
Top & bottom view of a jig used to grind tool bits for threading.
It is rotated 180º to grind both angles. The guide bar is ½" x ½" x 2"
I now use the diamond grinder with its miter.

Measuring total indicated run out (TIR) of the chuck using a dowel pin.

One of the most useful modifications I have ever made was to mount a drill chuck onto the (right side) shaft of the grinder. The arbor adapters are available at motor supply/repair shops in a variety of shaft/chuck thread sizes. A taper-mounted chuck is not recommended since sideway forces could make it come loose. The arbors usually have only two ¼-28 set screws. I drilled & tapped three more set screws (as referenced from the center, pre-existing set screw); one every 90º. I use US made set screws. This set screw arrangement allows adjusting the run out in the same manner as a 4-jaw chuck. Any chuck can be used. Pictured is a Jacob's medium-duty 5/64" to ½" chuck. This example is mounted onto a ½-20 threaded arbor. One could use a keyless chuck (not recommended) but keyed chucks grip so much tighter. I hack sawed the shaft threads off to place more motor shaft into the arbor. Use the drill chuck on the right side of the grinder since most accessories (arbors, sanding drums, etc.) are made for that turning direction. I use a full-face visor for eye protection. The reflexive tape is for use with a laser tachometer.

This grinder & its mounting plate were moved off the bench to make way for the carbide grinder.
It is now on a free-standing, cast-iron pedestal having rubber feet.
A drill-bit sharpener can be used with the grinder.

Pedestal foot detail.

½ hp, 3400 RPM, 100 lb. grinder for carbide with a 220 grit Norton diamond wheel (right side).
Motor can rotate in either CCW or CW direction. An adjustable miter is included.
Quickly & accurately grinds carbide tool bits & hardened steel.
The cup has a valve & allows coolant to be dripped onto the part while grinding.
The large, cast-iron pans under each wheel catch the debris/liquid.
Because of the pans, I did not mount the grinder onto a sub-plate.

The 220 grit makes a nice smooth finish but it removed metal too slowly.
Mounted a more aggressive 100 grit diamond wheel on the left side making a good combination with the 220 grit wheel.
I can now remove a lot of metal fast with the 100 grit then finish off with the 220 grit.
Diamond wheels do not need (messy) dressing & last a very long time.