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Harold Hall

Workshop Projects

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Drawings

When making the arms initially omit holes C and then assemble together with the arm spacers and secure by riveting and filing flush the ends of the arm spacers (6). Next place the cross bar (11) between the two arms, clamp and drill the 10mm hole through all three, ideally, drill and ream. Small holes could though initially be drilled in the three parts enabling them to be aligned using a pin making it easy to position the parts for clamping.  

 

Follow this, with the cross bar between the two arms, by measuring the width across these and make the hinge pins (4) just larger, say + 0.02 to + 0.04mm. I have included the third pin as a spacer as that is the way I have made mine and it worked well, more about that later. However, the reader may like to omit this and place a nut behind the countersunk plate to secure the screw, then another nut inside to support the second plate with a third nut on the outside. The two can then be used to adjust the space at the outer end of the side plates. In retrospect, I think perhaps this is the best method.

 

At this stage I assembled the parts and found that there was still a little movement at the ends of the arms, though very much less than previously. This was not that surprising as any clearance between the hinge pin (4) and the cross bar (11) would be multiplied by a factor of about 7 to 1. I decided therefore to take out the clearance between the two parts by securing the hinge pin with a screw (H3). This improving the situation considerably. To avoid the screw sliding the hinge pin sideways as it started to grip, causing one of the side arms to become stiff, or even locked, I placed a small ball of very fine copper wire between the screw and the pin.

 

With the tool reassembled I then put it to use producing a diamond knurl on a piece of 20mm diameter steel, 230M07, maybe leaded, but it was only a scrap so was not marked. Photograph 3 shows the setup and Photograph 4 the result, as can be seen this is good. It is a pity that I did not carry out the same test prior to carrying out the changes but my opinion is that it was an improvement, it was certainly more satisfying to use.

 

This prompted me to measure the movement at the end of the arm,  Photograph 5. Applying a firm pressure with a finger, the result was about 0.0005” (imperial dimension as I was using an imperial gauge as the photograph shows). Using a very firm pressure the deflection was still only just above 0.001” and some of that may be due to other factors. I declared the repair a sizeable success!

Two Wheel Knurling Tool, Side Supported
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 3

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 4

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 5