Wednesday, March 20, 2013

Monty Remon’s Quick Retract Threading Tool

"I did not realize I needed a quick retract threading tool until I found several examples on the net, and then I was only spurred into action when I glanced inside my odds n' sods tin and noticed the configuration of the eccentric bush/pinion shaft from a carriage assy., and a 20tpi bolt! I played with the items for a few minutes and the grey matter started working, this led to the construction on the left in the picture. At this stage in the proceedings I still required a tool bit clamping/stop method and a two(!) lever operating system, things looked a bit messy so I resolved to start again using round tool bits and a split clamping method as per tail stock to simplify things. I slept on this. By the morning another new design was in my head, the lump on the  right in the picture. It is just standard Taig TP size, 5 holes to drill, 2 slots to mill, 3 simple turnings and a bit of tapping and threading. The lever/cam gave me agro but it operates a treat. The round tool bit slides through a brass sleeve let into the tool post and the bit clamping bolt, a location collar is clamped to the end of this using a smaller bolt, the plain portion of this operates in a slot for alignment purposes and the protruding head of this bolt is acted on by the cam/operating lever. The collar location sets the protrusion of the tool bit and the angle of the cut for left or right feeding. A piano wire spring housed in the bottom of the tp spring loads the tool bit collar into the cutting position where it abuts the milled face. The cam controls the timing and amount of retract movement. Sorry no pictures of swarf, just finished components and sequence of operations req'd as I remember.
NOTE. Threading dim (x), I tried 6mm, 3/16 and 1/4" diam., and pitches 20-40, 20 is a bit coarse for clamping and 40 gives a lot of lever movement!
Locate some 1" sq., aluminium stock and turn to tool post length, drill and recess for mounting bolt. Mount tp on the xslide and drill through 1/4" diam., 3/16"" in from front edge (that's the tool bit height sorted). Turn bush from 3/8" brass .8" long , to be a tight fit in the 1/4" post hole with a flange at one end for seating, part off and super glue in place. Mount tp again rotate 90 degs clkws and drill back side across the brass bushing 3/8" diam., 3/8" deep 1/4" in from the edge, then through drill (x)" diam.. Turn the clamping bolt from 3/8"diam., steel, 3/8" long stepped down to (x)"diam, 1.35" LOA., thread last 3/8" with (x)" LH thread. Finish to running fit. Fit bolt and camp in place. Mount tp, turn back 90 degs anticlk to drill through and ream the bush and clamped bolt to 1/8" diam.. Remove the clamping bolt and turn .020" from the steped face to permit clamping action. Rotate tool post 180 degs and mill 3/8"diam., "D" slot .3" deep. mill 3mm horizontal slot 1/4" deep to house the long bolt. Invert the tp and drill the 3/16" spring housing, 3/16" in (in line with the bit hole) and .22" back to break through to the "D" slot. Drill and tap at bottom of hole for a spring retaining grub screw. Turn collar from brass .36" diam., .32 wide and 1/8" bore. Drill and tap 3mm .12" from one edge to accept the collar bolt. Drill 1/16" hole in the bottom of the collar about .07 from the edge to accept the 18g piano wire spring. Grind 3/4 of the spring length to a flat section to give some flex (or obtain thinner wire). The components are now assembled in order to align the cam and lever assy..
The clamping nut was turned from brass 1/2" hex stock to 3/8" diam., for 1/4" and 1/8" left with flats for spanner work, drilled and tapped for (x)" LH thread. The lever was made from a piece of 1/8" brass 2" long with a 3/8" hole to fit the nut boss. The cam could be made from 1/8"x 1/2" brass with a 3/8" hole to fit the nut boss also, the length (peak) of the cam can be measured from the tool post bolt range and then a slope filed to get a smooth action. The critical part of the operation harmonising the cam and lever action, is achieved by fitting a spanner to the locked assy., and slackening off, go another 10degs and bring the cam to contact the bolt head, the cam/lever/nut assy., should be soldered in this position. The working position of the lever on the tp (horizontal locked) can be set by packing washer thickness, max., req'd obviously less than the thread pitch."

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