Wednesday, April 30, 2014

Step #8: Fabricating the fingers for steady rest

I could have rapid prototyped the fingers but it's relatively easy to fabricate them from 3 pieces of 2.25 by .75 square brass bar stock and about ten times less expensive. I started by machining down the width of the bar stock pieces as a touching slip-fit into all three slots. They shouldn't rattle but they should slide easily when it's all done but that means starting just a little snug so your final clean up doesn't leave them too loose. Remember that you'll be removing a bit of material from the sides of the channels as well.

Next step is to reduce them to .375 thick from front to back so that the clamps will have a small amount of travel to clamp the fingers down tight. A few moments at the sander with the miter gauge set correctly and the matching 30 degree angles were on the tips. Leave the blanks long at the top right now as you'll trim them during a later operation.

Time for bluing, marking out of the slots at .25 wide and the correct length (detail drawing included with the kit) and a bit of chain drilling and filing had the slots in no time.
The raw brass bar stock for fingers
Fitting finger's width first, then depth
Scribe finger centers and shape tips

Mark out slot to drill and file (or machine)
Sequence showing chain drilling and filing to square
Having a stable vice makes draw filing flat and square possible 
Lapping to a bright finish through 600 grit after all shaping is complete
Before installing the fingers in the frame, the back and side walls of the finger slots need to be finished. You can use a sanding block and careful checking but if you have a mill you can make quick work of this. Again, remove a very, very small amount here. This part isn't for visuals, it's only for flat so leave some of the raw texture but test for flat and level with each other. You don't want fingers meeting up oddly in the center. This is also when you will tune in your finger fit in the channels.
Sanding block

Carefully flatten finger slots side and backs
Fitting the fingers into the frame and inserting the clamps. Pretty!
Perfect match up of finger tips

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