Monday, January 9, 2017

Modified Surface Grinder Attachment

I posted my surface grinder attachment that I built for my 2x72 belt grinder a few months back.  It had a couple of problems that I wanted to address, so I decided this past weekend to make some modifications. Here's what the attachment looks like now.

If you recall from my previous post on this tool, I had used a heavy-duty draw slide with a welder's magnet attached for the sliding part of the surface grinder.  It worked fairly well but the flex and wobble of that set up did not hold very tight tolerances.  Although it was much better than surface grinding by hand, my tolerances were still at 2 to 3 thou off.  The modification began with replacing the slide mechanism with a linear guide that is designed for CNC machines.  These guides are very accurate and slide freely on a tack filled with ball bearings.

I added a cross support under the guide at the point load of the wheel on the attachment to stiffen it up and increase its accuracy, removing any flex of the guide track.  For the new table I added six nyodium magnet strips into milled slots in an aluminum block to create the mounting surface for the blades. The table is only 6" long, so this will be limited to folder blades, but since folders is what I do, it should work just fine.  I also added some aluminum blocks with rubber bumpers at the top and bottom of the track to keep the table from sliding off the guide.

Finally, I turned a wooden knob and added it to the adjustment screw for comfort and better control. The whole thing got a coat of grey paint to match my grinder for looks and protection from rust.  I still need to add some kind of a handle to the table to be able to slide it up and down easier, but I ran out of time.  It shouldn't be a big deal to add one this next weekend.

I took the time to grind down the table so that it would be parallel with the contact wheel.  I then put it through its paces.  I grabbed a scrap piece of steel, purposefully ground it all out of shape and gave it a run on the newly modified attachment.  It worked absolutely perfect!  After proving that it would work on the scrap piece of metal, I grabbed the hardened blade that I had on my bench for the Guardian folder that I started some time ago and mounted it up.  I took the surface finish up to 600 grit and took the blade over to my bench to test the thickness.  From tip to tang, there was only about a 0.5 thou variation.  I'm not sure the kind of tolerances are built into a standard surface grinder since I've never used one, but I can certainly live with 0.0005.  This should help me to significantly raise the bar on the fit and finish of my future knives.  I look forward to using it more.

I hope this inspires other knife makers to try something similar in their shops.  Thanks for stopping by the Robinson Edge.

-  Brandant Robinson


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