Wadkin Resurrection: Back Miter Fence (II)

For Part I of this Wadkin saw revamp sub-project, click here.

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When working on an irregular object, like this rough back miter fence casting, I would like to think that I could find an initial fixturing position and then generate perfect surfaces, one after another, from that starting point. That hasn’t worked so far quite like I might have hoped. Instead what I find is that I get better results by fixing an initial position as best I can, taking light skims off of a face and then an adjacent face, and this in turn allows the piece to better register to the initial face and base of the vise, and eventually subsequent passes on those surfaces, once I circle back around to them, gradually draws the part into a good geometric form with adjacent faces being 90˚ to one another. The key point being, I suppose, don’t bite off more than you can chew and proceed with a certain degree of caution and an abundance of observation. No different than joinery work really.

Here I’m taking a skim off of the inner edge of the base of the casting:

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I’ve changed cutters after a reader comment in a previous post mentioning a fly cutter. While I don’t have a dedicated fly cutter, I do have a Mesa Tool accessory boring bar with coated insert for my Criterion Boring head which works superbly as a fly cutter:

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I dare say that cutter gives exceptionally clean results, much better than the previously-used router bit(s). The boring head normally is a tool used for precisely fly-cutting the perimeter of a hole – i.e., the cut is in a sideways direction proceeding downwards. In machining work, it is not considered accurate to simply drill a hole if precision is desired, rather, one drills a hole undersized, then uses a boring bar to skim it to the desired dimension. The Criterion boring head is one of the standard in the field, though by no means not the only quality boring head made. Mine is the medium-sized one, and is adjustable on a 0.001″ (diameter) basis. In using it as a fly cutter though, there is no need to adjust anything but the depth of cut.

Here I’m decking the underside of the pivot boss portion of the casting to a preliminary depth relative to the base plane of the casting:

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A couple of recent improvements to my mill I might mention in passing. One is a mounted proper machine lamp:

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You can see in behind it the original wire for the lamp which would have come with the machine from the factory, now long-gone. Fortunately, the spacing pattern on the lamp mounting was very close to the original lamp mounting holes, so I was able to simply bolt it on without any messing around.

The other improvement is a cast aluminum Newall DRO mounting arm I found on Ebay for cheap ($45):

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Previously the DRO was clamped to a plywood frame on the machine table, and was in the way half the time. I was able to mount the swing arm to the machine column using a lifting hook hole so no hole drilling was required.

After working my way around the back miter fence casting, I am on to final clean-up on the base:

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One more light skim got a clean surface there. Then it was on to decking the underside of the sweep arm portion, taking it to the target height dimension relative to the base:

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In the interim I also took a very light skim off of the front miter casting to make sure the mounting bolt boss on that casting was clean and flat, and also cleaned up the upper surface of the sweep arm portion. You’ll see the cleaned surfaces in a picture further down this page.

Now decking the pivot boss to final height:

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Critical surfaces now nearly done, given the clamped position for the part I could take the opportunity to work on tidying up the casting otherwise. I put a 0.75″ (19mm) 4-flute spiral end mill in the collet holder, turned the rotary table 17.5˚, and started in on machining the angled side face of the casting:

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Done, about 12 passes later, with a pass or three now afterward to clean off the end of the casting:

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Very happy with that result overall.

With the same tool now cleaning off the other end of the casting:

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The casting is removed from the vise and flipped, so that the final height of the pivot boss can be machined:

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Then the upper portion of the sweep arm, not a critical surface, is decked to leave a finished thickness for the arm of 0.75″:

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A little additional support on the far end of the sweep kept the part from deflecting in the cut.

It looks like it will fit well to the front miter fence:

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You can see above that there is a rebated upper edge yet to be cleaned up on the inside face of the back miter fence. That rebated edge is for mounting an extension bar with stops, however I have found the stops on the  extension bar on the front miter fence work rather poorly, so I have hesitated to mill this feature in to the back miter fence casting. but, the aim is to make the piece more or less stock, so…

…I executed the cut:

Last passes were to clean up the fence face:

The next step will be to machine the pivot bolt mounting hole and the elongated curved fixing bolt slot. Both of these tasks should be straightforward enough with the rotary table, but I think I will need to get a hold of a smaller boring bar as the finished hole dimension is 0.75″.

All for this round – thanks for swinging by on your busy day.