Monday, November 26, 2012

Symmetrical Alignment Method

Symmetrical Alignment method, is a method for marking and drilling holes so two plates align, and they can be rotated in relation to each other and still align.
Where did the need for this method come from? – I was constructing a Lantern Chuck and needed to make two plates which would be rotated in the lathe, and I was concerned about needing to ensure the alignment of the two plates when screwing the parts together. Typically I would try for a good fit, but mark the two parts to ensure the same assembly orientation in case there were any errors in drilling or marking out. I reasoned this practise would not be beneficial for something which was to be rotated, since my typical method for marking the orientation was to dock matching corners off, or use one fixing bolt as a larger size – both which had the potential to influence the balance of the final device.

Drill press is vertical and holes are shake free fit on pins or bolts of the same nominal size.
Clamping is firm, but non-distorting

In reference to the drawings, the two plates are "Back Plate" and "Front Plate", with three holes to be placed in each plate. The two centre holes are labelled "BC" and "FC" - for the Back Centre, and Front Centre respectively. The other two holes per plate are labelled as "B1", "B2", "F1", and "F2" as a means of showing how they are drilled in the method. (refer Sk. 1)

The plates are marked with the longitudinal axis, and the centre holes (BC & FC), and one hole in F (F1) are punched for drilling. Holes "BC" and "FC" are drilled to match a bolt which will serve to join them together for the marking/drilling - In the case I'm describing I used a 6mm bolt and nut. Hole "F1" is also drilled at a size to match the required task - 5mm in the real world case I'm describing since it is the tapping size for M6x1 threads. Sk. 2 shows the two plates with the centre holes and F1 drilled.

The two plates are laid together and joined with a bolt or pin through the centre holes (Shown as a solid RED sectioned bolt in holes BC and FC in Sk 3). Then the hole F1 is lined up over the longitudinal line for B1 as shown in Sk. 3. A clamp is used to stop the plates moving in relation to each other.

With the plates clamped, a drill is used to drill through F1 to create hole B1. Since I used a 5mm drill to drill F1, I used a 5mm drill to create hole B1 and effectively used hole F1 as a drill guide. – the result is shown in Sk. 4

Once the hole B1 is drilled, the clamp can be removed, and the plates rotated relative to each other – in Sk. 5 I’ve shown the “Front Plate” being rotated about the central bolt which joins it to the “Back Plate”

The top plate is rotated until the visible hole (F1) lines up with the marks for the bottom hole (B2) and then the plates are clamped together again. This orientation is shown in Sk. 6

With the two plates joined at the centre, and clamped in position, the Hole F1 acts as a drill guide for the drilling of hole B2 as shown in Sk. 7. As noted in Sk. 7, the previously drilled hole (B1) is hidden by the undrilled portion of the “Front Plate”

Once the hole at B2 has been drilled by using F1 as a drill guide, you can either leave them clamped, or slip a close fitting bolt or pin through the holes as shown in Sk. 8 as a sectioned BLUE pin.

Irrespective of how the two plates are joined together (clamped or two pins), the whole assembly should then be turned upside down so the top plate is at the bottom, and vice versa – this is illustrated in Sk. 9 and clearly shows how the previously drilled hole B1 is now visible to use as a drilling guide for the hole at F2

Sk. 10 shows the resulting hole at F2 was drilled using B1 as a drill guide.

Sk. 11 is the result and culmination of the “symmetrical alignment method”. Each plate has the three holes drilled, and can be placed with a shaft through BC and FC and have F1 line up with either B1 or B2, similarly with F2 lining up with either b2 or B1 – this means a part will fit either way, and compensates for any minor errors in marking out.

This information is offered as additional information to support the article which was written for MEW (Model Engineers Workshop) for the Lantern Chuck article.

I suppose I should apologise for the dearth of articles lately - things are being worked on, jsut not as quickly as I'd like, and time for writing the articles is becomings scarce again.

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