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Harold Hall

Workshop Processes

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With four sides now finished the two remaining faces were machined with the casting mounted directly onto the machine table (well almost), Photograph 6. I said, well almost, as it is essential that the machined face is fully in contact with the fixed post rather than the unmachined face below being against the machine table. Even so, not only does the surface being machined need to be at 90° to the end face but also 90° to the long face. This being the reason for the second post seen in the photograph. The procedure therefore was to hold the vee block firmly against both posts as it was being secured.

 

However, this process is only valid providing the post's upright faces are accurately at 90° to the machine table. If you wish to adopt another method then using an accurate vice would be a suitable alternative but you will still have to be cautious how you position the workpiece to achieve both 90° angles. With the fifth face now surfaced the final one was machined with a similar set up but this time with the lower face firmly against the machine table, the second post was of course not necessary this time.

 

The next stage was to machine the vee and to make it easy to set the width of this reasonably central I covered the top with marking blue and scribed a line on each face as a reference for the eventual width of the vee. For positioning the casting I placed a shallow vee block in the base of the vice so as to set the part accurately to 45° enabling  it to be positioned with ease and then machined the first side, Photograph 7.  Later, I would be adding a small groove in the base of the vee so was able to stop machining just short of the second side as the groove would remove any unmachined surface. With the first side machined I turned the casting and machined the second side in the same way.

 

The groove in the base of the vee was made with the block again being held in the vice thereby completing it except for the tapped holes that are used for fixing it to the base, more about that later.

 

Accuracy

Whilst the eight faces were now complete it seemed appropriate to check them for accuracy though the level of accuracy considered necessary is for the user to decide, in any case this is not expected to be a precision item. I first checked the six sides to see if they were at 90° to their neighbouring faces, then,with that done, I placed a round bar in the vee and stood the assembly on the surface plate and checked that the bar was horizontal using a dial indicator, finding a difference of less than 0.05mm which I deemed to be acceptable. Next I clamped the bar to the block and stood it on its side doing that from both edges to check that it was central, Photograph 8.

Vee Angle Plate, Machining
Vee Angle Plate, Machining
Vee Angle Plate, Checking
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 6

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 7

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 8