Intro: EZ-Adjust Bench Grinder Table
Easy to adjust to grind at different angles, and designed for stiffness, this scheme works pretty well to fix my major complaints with the normal bench grinders. Features include an easily locked angle adjustment dial, a totally disassociated crossfeed, and a structure incorporating a T-beam table to reduce deflection.
This project cost me about 60$; 25$ for a used bench grinder, 26$ for steel and screws, and 10$ to get the parts welded. (I had a lot of left over 1/2" rod, but that 60$ price tag does not include the wood for the base.)
Step 1: Material List
As far as big machines go, you'll need a mill and a welder.
The tool list, continued... and a 3/8" and a #7 drill bit (or whatever you like using for a 1/4-20 threaded hole), a 1/4-20 tap, a woodworking clamp, a hand held drill, a lathe, a whetstone, a circular saw, a file or wood rasp, a hot glue gun, and a Dremel.
The material list.... about 18" of 2x8, about 10" of 2x4, about 17" of 2x1/8" steel, about 40" of 1" angle iron, about 3" of 3/8"x1/8" steel, some sheet metal 4" square, two short 1/4-20 screws, two 1/4-20 thumbscrews, one 1/4-20 wingnut, one 1/4-20 nut, five (5) washers, two wood screws, some wood glue, some hot glue, a couple carriage bolts, and 2" of 1/4-20 threaded rod.
Step 2: Design and Machining
We'll start with design and machining.
Because your bench grinder will be a different size than mine, you'll need to size the table length and 2x4 height.
Table length between the pivot shafts must be at least the overall width of your bench grinder, plus 1.5 inch: Wt = Wbg + 1.5" (+). It must be at least this long, or the bench grinder will not fit between the 2x4 uprights, but it should not be too long; while the table is one of the stiffer parts between the workpiece and the grinding wheel in the current setup, that would change fairly quickly if you started to stretch it towards 30" OAL. (This dimension is 17" for this grinder. See sketch.)
2x8 length for the base (which determines the distance between the outside faces of the uprights, and thus the table support arms) should be, at most, 1.75" longer than the length of the length of the table between the pivot shafts: bW = Wt + 1.75 (+0/-0.125). It must not be longer than this, or the table's pivot shafts will not be able to reach their bearings, the 0.5" holes in the table support arms, so, depending upon the accuracy to which you can build the wooden base, you might plan to have this dimension be a little smaller than this maximum - perhaps by 0.0625". (This dimension is 18.75" for this grinder)
2x4 length for the uprights, which determines the height of the table relative to the wheels, should be 0.25" more than the height of the center of the grinding wheel from the 2x8 base, when the bench grinder is clamped to the base with the carriage bolts. (This dimension is 5.375" for his grinder)
The slots on the table support arms and thumb-screw holes on the rails are designed to allow table placements from 2" to 10" from wheel center. The high end of this range is intended to allow the grinding of convex radii on workpieces clamped to the table, with the angle adjustment unlocked. Because this range is so wide, the exact placement of the uprights on the base in the front-to-back direction is not critical.
The distance between the 1/4" holes on the angle lock hold-down (only picture in this step) is 2".
The diameter of the angle dial is about 3.5".
Once you've figured out these things, you can machine the metal and wooden bits. See the sketches. Some notes:
* You'll probably have to enlarge the 0.5" bearing holes in the table support arm just a hair. I used a Dremel.
* You'll want to smooth the adjustment slot in the table support arm. I draw-filed it.
* All small holes in the rails, table pivot shafts, and support arms are drilled #7 and threaded 1/4"-20... if you want. Go ahead and use something else.
*The sketch included is for the "left" table support arm. The right rail is it's mirror image. You'll note that there's no need to drill and tap the two 1/4-20 holes in the actual left table support arm... and in the actual grinder, you can omit them.
*The sketch included is for the left rail. The right rail is it's mirror image.
*There's a shallow recess at the ends of the table pivot shafts. This is to make it so that the clamping force of the screws is applied to the outside of the shaft, where it it can resist the highest torque. This is not precision machining, so feel free to try this with a large endmill in your mill, or with a Dremel, or whatever.
*You'll note that the corner of the rail is ground off. This is to prevent the table support arm from riding on the corner, rather than the flats, of the rails... the exact dimension is not important (three digits for irony).
*Lap the clamping surface of the angle lock hold-down. This makes it smoother, reducing the wear-and-tear to the angle indicating dial.
*For the angle dial, after laying out with a protractor and ruler, engrave it to make the markings. My sheet metal already had paint on it, so that came out really nice, but use whatever you have.
Step 3: Welding
Weld the table up as shown in the sketch. The pattern is designed for ease of welding, with the intended sequence of operations:
1) Placing angle iron hanging over the edge of your table, as if protecting the edge, place the pivot shafts on the table and lined up with the edge of the angle iron. Weld the posts on.
2) Flip that over, and put it on a short riser which is a bit narrower than the length of the table, or the corner of your table, and stitch on the 2"x0.125" piece of steel. Try to make the bottom surface of the two - which will form the top of the table, once you flip it over into the use orientation - continuous.
Screw the short pieces of 1/4" threaded rod into the threaded holes in the right table support arm, back weld them, and grind the bearing surface (where you just backwelded) flat. If you have a TIG, go ahead and make that weld autogeneous. If you have a capacitive discharge stud welder.... you know what design changes to make, maybe: the placement of those studs should be within a couple hundredths to reduce play in the angle-locking mechanism.
Step 4: Base Assembly
Apply some wood glue to the end of the 2x4 upright and glue it to the 2x8 base. Keep it in place with a wood screw while the glue dries.
Once the glue dries, file off the outside edge of the uprights, so that the rails sit on them firmly.
Lining up the front surfaces of the rails with fronts of the uprights, trace through the threaded holes in the rails to mark their location. Drill shallow holes, perhaps 1/2" deep by 3/8" diameter, under where the holes were, to allow the thumbscrews to be put through those threaded holes.
Clean the rails up so that glue will stick, and glue them to the uprights with your favorite adhesive. I preheated the rails on the stove and used hot glue.
Hold the rails in place while the glue cools/dries/cures. If you clamp in the manner that I did, make sure that you clamp gently.
I then glued some squares of rubber conveyor belt material to the bottom of the base.
Step 5: Assembly & Self-grind & Zeroing
Assemble everything. The picture should make it pretty straight-forwards.
Note that, due to the depression in the end of the pivot shaft, the washer is required.
Once that's done, hold the table roughly level, and adjust the cross-feed so that it just touches the grinding wheel. Tighten the cross-feed thumbscrews, turn the grinder on, and slowly let the table down. A reasonable place to stop is at about 60 degrees - much more, and you'll start compromising the stiffness of the table quite a bit.
To zero, make a mark on the back of the upright at a height 0.125" below the center of the grinding wheel. Set the angle dial to 0 degrees and lock it in place. Set a ruler on the table, loosen the screw which holds the angle dial to the table pivot post, adjust the table position until the ruler lines up with the zeroing mark, and tighten the angle dial-pivot post screw.