Another kit from Hemmingway Kits. This one was to make a boring head for the milling machine. A kit was purchased with an MT2 arbor. The kit would require the machining of a dovetail slideway, so a 60 degree milling cutter was ordered.
This page is not intended to plagiarise the Hemmingway design (by Mr G.H. Thomas), but rather to add some images to the work instructions given in the kit.
The kit from Hemmingway came with some useful notes, drawings, and the materials/fixings required. There were also suggested machining steps illustrated for some of the more complicated parts.
The sliding member was machined first. The starting blank was not quite square on the cut faces, so the 4-jaw chuck was used to get all the faces at 90°.
The blank part marked out for the adjuster hole which was then centred in the 4-jaw chuck....
......and then drilled to size right through.
The milling machine was used to cut the lower.......
....and upper shoulders, as well as reducing the part to final width. Without moving the vice....
.....a 60° dovetail cutter was used to cut the angled shoulders on the parts.
The sliding member was turned in the vice to be drilled and reamed for the gripping bushes which would hold the boring cutter.
The underside was sawn, milled and filed to create an under-cut.
Then the tapped hole was counter-drilled, on the drill press, before....
...the excess material either side of the nut was machined away.....
...and then the nut was rounded with a file.
The chamfer on the underside of the sliding member was machined with light cuts on the mill.
The Housing. The cut ends of the housing block were squared off in the 4-jaw chuck and then the screw hole was drilled and counter-bored to the drawing.
The mill was used to cut a slot through to the drilled hole and to rough out the shoulders for the dovetail.
The dovetail cutter was used to create the dovetail to the drawing. Light finishing cuts were used on all the working surfaces to ensure parallelism, and minimal tool deflection
A test fit with the sliding member showed a gap where the dovetails met. The problem seemed to be that the corner on the sliding member was sharper than the one in the housing.
This was remedied by filing the point off the sliding member as shown above, to get the working surfaces to meet.
The result would be a fractional offset to the threaded nut, but this could be compensated for with the front plate positioning.
Before removing the part from the mill, the housing was used to hold the gib strip for edge machining, in accordance with the instructions.
The housing was rotated in the vice for drilling and tapping of the gib strip screws, and also adding detents in the gib strip using the set-up shown above.
Then the 4-jaw chuck was used to machine the threaded hole for mounting arbor and skim the top face to final profile to ensure it was perpendicular to the hole.
The cosmetic shoulders on the housing were added on the milling machine, using the set-up shown above.
The adjuster thread was machined between centres and then thread cut to match the sliding member.
A split collet was machined from brass to hold the adjuster thread so that the detail on the end could be machined.
The adjuster nut was centre-drilled, drilled and threaded on the lathe.
The lathe chuck was moved to the milling vice for cross-drilling......
....before returning to the lathe for finishing and parting off.
The end plate was prepared by drilling the centre hole and the two mounting holes.
With the housing, sliding member, threaded rod and nut assembled, the position of the two mounting holes was then transfer drilled to the housing.
The adjuster knob was made by knurling a piece of steel bar and then drilling, and tapping the internal thread, before cross-drilling on the milling machine.
The locking screw was made by knurling a piece of steel bar and then cutting an external thread, before parting off the bar stock.
The brass collet clamps were turned to the plans, including the flange which would be used to hold then secure for the drilling operation* for the boring bar.
The universal MT-02 arbor was put in the lathe headstock and a thread was machined to match the housing.
The whole boring head was now assembled onto the arbor. The marked position for the boring bar was set to run true by winding the adjuster screw.
The position of the sliding member was locked with the gib screws and locking screw and then the end plate and adjuster screw were removed.
* The hole for the boring bar was now drilled and reamed to 3/8". This operation would also cut the required notches in the brass collets.
This photo shows a check fit of the boring bar in the sliding member collets.
The flanges were then machined off both collets, to allow them to pull into the sliding member hole, to clamp the boring bar.
This photo shows the brass collects re-fitted without their flanges.
The back profile of the dial was machined first......
....before fixing it to an arbor to have the conical face machined.
With no dividing head, a paper sketch of the dial division was fixed to the rear of the lathe headstock and a height stand set up as an indicator.
Without changing the top slide angle, a piece of a silver steel was ground to a sharp point and mounted in the tool post.
Markings were scratched on the dial facing using the top slide handle. Two turns for the small division and three for the long ones.
The dial was cleaned up with a file and then some abrasive cloth.
A centre punch mark was added to the front plate, as an indicator.
The finished tool
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