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Harold Hall

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Cross Drilling Jig, lathe only project, Harold Hall

I do not make out to be an expert on cross drilling jigs but do know there have been many designs for carrying out what appears, though falsely, a simple operation. Having made and used this item in this article, Photograph 1, I can confirm that it performs the task with considerable ease and to a high standard that must make it amongst the best available.

 

Body

This is the main item and is made from a cast iron casting that machined well. The taper, necessary when making castings, makes securely holding the part for machining, a task that must be approached with care. The casting is largest at the base and smaller at the top, the top and bottom surfaces being nominally parallel.

 

To securely hold the part in the four jaw for machining the top face first, place small pads of soft copper a short way up the chuck's jaws, making sure that the casting is gripped over a wider area, not just the lower edge, see Sk. 1. However, before fitting into the chuck, using the coarse wheel of the off hand grinder, make a substantial chamfer, say 2 mm, around all edges. This prevents the lathe tool having to break through the outer faces that may have hard spots present,  especially important if HSS tooling.

 

Having machined the top, Photograph 2, reverse and refit the casting with the now machined top held cleanly against the chucks face and machine the base. We now have two parallel faces that  will begin to make holding it more secure. There is though a problem that  can be overlooked.

Metalworking

Workshop Projects

I do realise that non UK viewers may find the transport costs for the casting that makes up this kit prohibitive, as a result, making this project a non starter. However, I would though suggest that the project is worth studying as some of the methods, and the principle behind the design, may be of interest. For those interested, details of the castings can be found on the "Hemingway Kits" web site. Also, whilst the casting is the best approach, for those for whom transport costs rule this out then the design can be adapted to be made from a block of bright mild steel.

This project is aimed predominantly at the workshop owner who uses the lathe for milling. However, the item being made should be of interest to the viewer who's workshop contains a milling machine.

 

The photographs that were taken when the jig was first made are no longer available. Because of this, the photographs that follow have all been taken with the parts that have already been made and finished.  

 

Do take note of this fact when studying them for each  task being illustrated as some will show latter operations also completed.

Cross Drilling Jig
Cross Drilling Jig, making

All pictures can be clicked on to provide a larger view

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 1

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 2

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Drawings