Messages

Thank you.  I misunderstood the use of the template.  The derivation of the template is much easier to see, once it is realized that it is for pivot rather than roll. 

When one considers roll as opposed to pivot, the math seems much more complicated.  One is trying to have a certain angle at the edge.  This angle is measured in the plane perpendicular to the edge.  For a curved edge, it is the plane perpendicular to the tangent to the edge.  Even without taking into account movement back on the wheel with a curved edge, effectively a shortening of the blade projection, things seem rather difficult to calculate (at least for me).  Do you know if this has been worked out?

There does seem one advantage to sharpening with roll alone as opposed to some variable combination of roll and pivot, at least for knives with shallow curves.  That is repeatability.  For example, when one watches Wootz (Vadim) sharpen, which is always a pleasure, his body is positioned above the blade, his hands are positioned on and control both sides of the blade, and he has a very precise motion like a practiced golf swing.  He is, of course, not only taking several passes with one stone or grit, but also using multiple grits at precise settings.  Unless the angle is repeatable in the curved portions, this will not make much sense.  For most purposes, it will not be so important if the edge varies from, say, 12 dps to 15 dps along the blade, more that the angle at a given place along the blade is constant from one pass or step to the next.

Once one moves from hard wheels to paper or felt, the compressibility, or even runout of the wheel,  may make up for small differences, but this will be at the risk of rounding the edge.

On 10/27/2015  JAN presented a setting template for clamping the knife jig along the blade so that as the blade is lifted (airplane roll, not yaw) the change in angle to the wheel tends to zero out the change in angle from contacting the wheel further back toward the support.  Is there a development or presentation of the math for this.  I would be most interested to see how this done.  Thanks.

I might add that what I really suggest is machining the plastic, PEX, bushing ID after it is pressed into the wheel.  An alignment mark is made to be sure the bushing has not rotated relative to the wheel.  Then the whole assembly is placed on the drill press table and the ID hole reamed to size turning the reamer by hand, not under power.  I had a great deal of trouble getting felt wheels on my Tormek T8 and paper wheels on my Baldor 3/4 shaft buffer to run without wobble.  When I ordered a third, 200 grit, CBN wheel for the TORMEK, it would not fit, even trying to remove any burrs with a fine file, etc.  Finally, I obtained a 12 mm adjustable reamer, and in moments that fit problem was solved.  A bit later, it occurred to me that the reamer could be used as described to fine tune the felt wheels to the T8 shaft, which immediately stopped wheel wobble and obviated the need for a pair of spherical washers.  Then, I ordered a reamer covering the 3/4" diameter of my buffer and fine tuned the paper wheels on the Baldor buffer.  This immediately stopped wobble and again obviated the need for spherical washers.  These days adjustable reamers are not prohibitively expensive.  The 12 mm was about $12.00 and the 3/4" about $20.00.  When you are dealing with $300.00 CBN wheels, $75.00 felt wheels, and $50.00 paper wheels, being able to do a proper job fitting them to the machines seems well worth the expense.

I realize this is an old topic.  A metal custom bushing is not really needed to mount, for example, a felt wheel on the 12 mm shaft of the Tormek (T8).   If you will get a piece of 1/2" PEX pipe, best is a straight piece, not from a roll, you will find that the O.D. is almost exactly 5/8" and the I.D. is almost exactly 12 mm.  If you take out plastic reducer bushings from the wheel to get to 5/8" I.D.and insert a piece of PEX of correct length, you will have a suitable bushing for little expense.  Also, with a 1" thick felt wheel, if you get standard 12 mm (stainless) washers one inside the wheel toward the motor, and 4 on the outside of the wheel, it will clamp the wheel.  If your wheel thickness places the outside washer on the small threaded part of the shaft, simply glue two washers with a bit of epoxy so that the outside washer is concentric with the shaft before clamping.  There is a further advantage of a plastic PEX bushing.  It is critical that the bore hole be exactly perpendicular to the plane of the wheel, otherwise there is wobble.  The PEX is very easy to machine.  With an adjustable 6 blade reamer set to correct size and a drill press, used unpowered, it is easy to trim the PEX ID to exact diameter and perpendicularity.