Accompanying the just completed rule holder is a scribing block. The scribe is adjusted to fit in the appropriate measurement slot in the rule and locked in place. The scribe is then used to mark the workpiece at the fixed height when both scribing block and part are sitting on a flat surface. A picture of the block from the plans included in the Hemingway kit is seen below.
After squaring the block and reducing it to size the radii need to be cut. All three are 3/4" radius cuts. Line boring on the South Bend lathe will be used to make the three cuts. I've used this method successfully before and hope to repeat that success with the scribing block.
The boring bar and part were set up in the lathe to make the cutout. The boring tool was sharpened with a diamond stone and set to 1 1/8" from the back of the bar giving a 3/4" radius. The vertical milling attachment was put in place and with a 1/16" brass shim the top edge of the block was set on center. A large block of steel was set on top of the proto-scribing block and the screws clamped down. A front and a back view of the setup are shown below. The shot from the back shows the part after a few passes with the cutting tool.
Not far into the cutting I realized boring would take all day at 0.010" per slow pass. The part was removed, marked out for a 45° cut across the corner, and hacksawed, removing half of the material in ten minutes (as seen below). The part was returned to the vise and boring commenced in earnest. Over halfway through the boring became very loud and the finish went to hell. Boring was stopped and the tool was discovered to have lost its tip as seen below. The tool was removed, sharpened on the grinder and returned to complete the cutout.
The boring was continued for some time before the vibration and horrible finish again reared its head. The tool was once again completely dulled. It must not be hardened is my guess. In any event the cutout was close to being finished so the block was moved to the vise and the cutout was completed with a half round file in short order. The first photo below shows the awful finish and the second the filed finish.
It is Juneteenth and working in the shop was my plan for celebration at least until five, when it will be time for a toast to the emancipation of US slaves. There are two other round grooves in the part, so an effort was made to harden the cutting tool. It was heated to cherry red after grinding a new cutting profile, then it was quenched in oil. The part was sharpened on a diamond stone. After just a few passes the cutting edge was completely gone!?!? After deciding to skip these two features, the part was set up in a four jaw chuck with the previously marked out hole location centered. The body was drilled with a center drill and then up to 11/32" through. I don't have an 11/32" reamer as called for in the plans, so the drilled hole will have to suffice. The hole was opened to 3/8" for 11/32" per the plans.
Before completing the block the cotters were made. A 3/8" blank was prepared about 2" long. The was held in the chuck and faced. the end was reduced to 0.190" for 3/8" and threaded with a 10-32 die. Beyond the reduced section a further 21/32" was reduced to 11/32". This was inserted into the bottom of the hole in the block. A bit of finagling was required to get this to fit all the way in. With a 3/8" washer topped by a #10 washer and a 10-32 nut the part was tightened in the hole. The block was held on the milling table and drilled through with a B drill followed by a 1/4" reamer. The ends of the hole in the block were deburred.
After removal the collet blank was put in the lathe chuck and the screw was removed. The resulting shaft was drilled with a #28 drill (to eventually fit a 6-40 screw.) The plan calls for a 5/32-40 screw, which is not something I have acces to with my set of taps and dies. The 11/32" reduced section was extended by 1/32". The hole was deburred. A 0.040" wide parting blade was used to part off the upper collet in the center of the depression made by the previous drilling. The lower collet was then parted off leaving a 1/16" wide section of 3/8" rod. Both collets were deburred and fit perfectly in the scribing block with the drilled depressions aligning with the 1/4" hole in the block.
The bottom of the scriber block was painted with layout fluid and a box was marked with the B&S height gage 5/32" in from the end. This is seen in the first photo below. The block was held in the mill vise with a 3/4" round of aluminum clamped below the reduced end. The pocket was milled with a new 3/16" end mill and the milling went smoothly. The setup and the finished product after a bit of filing are seen below.
The final task to complete on the scribing block itself is the slot. The block was set up in the mill vise with the spindle centered (by eye) on the 3/8" hole through the block. The saw was lowered so the saw was centered at 1/2" below the edge of the block as in the photo below. The cutting blade was advanced very slowly, 1/8", after making contact to produce the slot as shown in the second photo below.
The saw was clearly cutting only on one section of the blade as evidenced by chip buildup. The slitting saw holder was remade by extending the length of the stem and reducing it to 0.375" to fit in the standard mill collet. This part was held by the stem in a collet in the South Bend lathe, where the opposite face was remade concentric with the stem. A test on an aluminum strip was not very clear whether the slitting saw holder was improved.
The next part is the spindle. A 2" length of 1/4" steel rod was held in a collet in the South Bend lathe. The end was faced and turned down to 0.138" for a length of 0.281". The end was chamfered and threaded 6-40. The part was removed from the collet and about 1/4" was cut off with a hacksaw. After returning the part to the collet the newly cut end was faced to a length of 1 11/32". 11/32" was then reduced to 0.187" (hoping for a press fit). The end was chamfered to complete the part seen below.
The post came next and is made from a 2" length of 3/8" round mild steel. The bar was held in a collet with about 1/2" exposed. It was reduced to 0.138" for 3/8" and threaded 6-40. After exposing 3/4" more stock it was reduced to the same diameter for a further 5/8". Again a bit more was pulled out of the collet and 1/4" was reduced to 1/4". The part was turned around in a 1/4" collet and the unfinished end was faced to length. This not quite finished stepped screw is seen below.
The post was held in the mill vise by the 3/8" end. The end was located and the vise moved 3/32" in. The spindle was centered over the part and after beginning the hole with a center drill the hole was drilled 3/16" deep with a 1/16" drill. A short length of 1/16" steel rod was cut off with pliers and inserted into the just drilled hole with a drop of Loctite. The photo below shows the completed post.
Nuts were up next. The spindle nut is made from 5/8" round steel stock. A piece was cut off at slightly over 1/2" and chucked in the Sherline lathe, where it was faced. It was then center drilled, drilled #33, and tapped 6-40. The last 7/32" was reduced to 1/4" and a decorative groove was added. The hole was tapped a little deeper using the vise. The opposite end was faced to length and the corner chamfered. With my knurling tool the part could not be knurled as the area to be knurled was too close to the chuck jaws. Consequently, 1/4" rod was held in the chuck and one end reduced to 0.138" and threaded 6-40 with the tailstock die holder. The proto-nut was screwed onto the mandrel and the knurling went well. Both ends of the knurl were heavily chamfered resulting in the finished nut seen below.
The nut for the post is identical except it starts with 3/4" stock. Consequently, the same process was followed as for the spindle nut resulting in the post nut seen below. The knurl is not as deep as the previous, but went as far as I felt comfortable pushing it for fear of breaking the mandrel screw. The second photo below shows the set of parts for the scribing block with three remaining, a washer, the scribing arm, and the scribe.
The washer was made with minimal effort. Starting with 3/8" round steel, it was faced, center drilled, drilled 3/16", chamfered, parted off at 1/16", and photographed.
The scriber arm was made from a 1 1/8" length of 1/4" X 1/2" piece of steel. The holes were marked out along with circles for the eventual rounding. A flat for the set screw was also marked on the steel. The holes were drilled with one drilled 3/32" and the other reamed to 3/16". The part was held in the mill vise and the center portion was cut out on both sides. The flat for the set screw was also milled by setting the marked line parallel to the vise jaws and taking light cuts. The photo below shows the crudely shaped arm at this stage.
An hour and twenty minutes of filing and a bit of sanding produced a scriber arm with somewhat round ends. The arm is not a press fit on the spindle, but a sliding fit and will need to be glued in place.
A few adjustments on lengths of post sections and the addition of a quickly made washer were required for the parts to fit correctly and provide sufficient tension to lock the spindle in place. The arm has not been glued to the spindle, but the completed assembly is shown in the two photos below.
A one-armed bandit for lefties!
The last task is making the scriber points. The provided 3/32" round stock was cut into four lengths of 7/8". The lathe head was rotated about 9°. A point was cut on each of the four rods in 0.0025" passes. The cutting was very rough, as expected, even though minimal material was protruding from the chuck. The photo below shows the four rods with their not quite points. The cutting was stopped at this point for fear of breaking the tips off.
The scribes were hardened by placing them on fire brick, heating to cherry red with a propane torch and quenching in oil. The black char was removed with a sanding pad. A 30°-60°-90° triangle was used to align the cordless drill holding the scribe at 30°. With the drill spinning the point was quickly touched against the wheel leaving a 60° included angle point on each. The photo below shows the four scribes now with sharp points.
The points need to be tempered as they are brittle and the points will break off. The usual tempering process is heating the part to about 400° for an hour or to a straw yellow. I didn't want to use the large oven in the kitchen and came up with an alternative, the hot plate with an Altoids tin on top. This is seen below just after turning the hot plate on to 3.5 of five settings or stir fry temperature. Hopefully, this is somewhere near the desired temp. The second photo shows the unhappy Altoids box after six minutes.
After fifteen minutes the basement was becoming quite smelly. So the oven was cooled down and moved to the open garage for an additional forty-five minutes of tempering. After cooling the points were complete, though brown, not straw yellow. The knob and arm on the spindle were glued on using Loctite to complete the scriber block seen below.
The range of the scriber block is 1/8"-1 7/8".