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Harold Hall

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Earlier, I referred to accuracy being the fourth consideration. The holes in the small jig above were placed using the mill's micrometer dials not so much that accuracy was crucial but at such a small size even an error of only 0.2mm off centre,  if marked out manually, would be visually very apparent on such a narrow item, being just 3mm wide. Some larger components would also need their holes accurately placing, say if setting out gear centres, but for others marking out the holes in the jig by the rule, scriber and square method would be adequate.

 

Bushes.

If the quantity and size of the holes to be drilled is considered to warrant it, then hardened bushes should be fitted to the jig, Sk. 4 shows the normal form though they can be made without the head. Making these is straight forward with silver steel being the obvious choice of material to be used in the home workshop. The sketch shows the shank having two diameters, the smaller being a close sliding fit in the hole in the jig enables the bush to start in line with the hole. The top 1/3 rd of the shank should though be a tight fit in the top plates but not so tight that it distorts the plate which could be particularly a problem if the jig is quite narrow. Having made the bush they require to be hardened.

 

Hardening and Tempering

Those who are experienced in hardening and tempering steel components will need no help, others though should see my pages detailing the method.  

 

Three drilling jigs

Earlier, I stated that drilling jigs could be used for a very wide range of tasks and that as a result it could only cover the subject generally. However, to encourage the viewer to consider their use more often I will finish briefly with three actual examples, two quite common and the other very special.

 

Without doubt, no other workshop task has produced more designs for a drilling jig than the task of cross drilling a shaft or collar, illustrating that in most cases there is not just one design for the job. The methods also show that designs can range from the very simple to the quite complex. Photograph 11 shows a very adaptable jig that can be used either on the lathe top slide, Photograph 12, or, with it having a flat back it c an be used on the drilling machine. Construction of this is shown elsewhere on the site.

Metalworking

Workshop Processes

Cross Drilling Jig
Cross Drilling Jig, using
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11

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12