In the first part of the Cut Knurling Tool write-up the spindles, spindle housings, bearings, and nuts were made. This second part of the write-up focuses first on making the tool's holder arm.
The holder arm will be modified so it can be held in the recently completed South Bend four way tool post. The slots in this tool post are 2 3/4" X 9/16" X 3/8". The shaft of the holder, held on the compound is designed with a 5/8" square cross section. This implies only one modification needs to be made, one side of the tool holder arm needs to fit in the four way tool post. The height of the shaft on one side will be reduced to < 9/16", while the depth of this extension will be 0.375".
Two features of this holder arm will be a challenge for me. (At least I hope only two!) The end of the holder has the female side of a dovetail. The holder also has a slot cut completely through from top to bottom that extends for over an inch, from the bottom of the dovetail, into the shaft. The plans show a 1/32" slot to lock the dovetail, when the knurls are set at the correct height. (The discussion of the construction indicates that a 1/16" slitting saw was used to cut the slot and it was completed with a hacksaw, my hacksaw blades are 0.04" thick.)
Some steel was located that should fit the bill, but is not ideal. I am guessing it is cold rolled as it doesn't have the scale of hot rolled. The steel is a 1 5/8" diameter rod, 4" in length. The length is not an issue as the shaft can be shortened a bit to fit the rod. The round shape implies a lot of material removal is needed. Turning this round stock into a 1" square bar is the first order of business and will be done with the South Bend lathe.
The bar was faced on both ends. It was held in the four jaw chuck after reversing two opposing jaws. The exposed side was faced in increments of 0.010", removing about 0.28". (An attempt to increase cut depth to 0.015" led to too much vibration.) The bar was then flipped in the chuck so the opposite face of the bar was exposed. The new flat was set on the chuck jaws as I don't have skinny enough parallels. It was tapped flat with a mallet and then faced like the opposite side. This produced the bar, whose end is seen in the fourth photo below. This bar is about 1.1" from flat to flat.
The last two sides were cut this morning using the same setup in the lathe. The final dimensions are 1.07" X 1.07" X 3.96". The part was deburred and readied for fly cutting to its final 1" square size.
The newly made four way tool post performed flawlessly during the entire cutting process. Even with all of the intermittent cutting and the resultant pounding the tool post remained rock solid. Also impressed with the resilience of the HSS inserts from A R Warner!
The part was brought inside and mounted vertically to an angle plate on the Sherline mill. Verticality was insured with a square and light shining through the gap. The top was faced with a fly cutter, The part was flipped over and mounted on parallels. The opposite end was similarly faced with the fly cutter, seen below.
The part was then turned on its side and mounted to the angle plate while sitting on an adjustable parallel. The fly cutter was removing too little material in a pass, so was replaced with a two insert mill. The block of steel is seen below after one pass of the cutter.
The finish is not the best from either tool. Burnishing is supposed to provide a mirror finish. Hmmm! Maybe another tool project? Amazon sells a burnishing tool for the lathe, the MachEl, which would easily fit the South Bend. I have been unable to find an inexpensive burnishing tool for the mill.
The block was finished on all four sides with the two insert cutter. As much as 0.010" was removed in one pass and more might have been possible. The final finish was best with 0.005" or less and slow feed. The final dimensions of the block are 0.997" X 0.997" X 3.945". the faces are parallel to within 0.001" from end to end. The angles between faces are 90° as determined with a square backed by a light. Only the last 1/2" remains 1" X 1". The rest will be reduced to 5/8" X 5/8" and one side further machined to fit the four way tool post. All of that the focus of future work.
The next step is cutting the dovetail, something I have little experience doing. The article goes into great detail on cutting this dovetail and how to measure it. So I begin with some level of confidence. The first task is roughing out the slot. The end of the steel blank was painted with Dykem™ blue and marked for the two dovetail sides, 0.277" in. The block of steel was held with two machinists clamps on an angle plate. The side was located and the spindle was moved in so spindle center was 0.188" beyond the scratched line. A 3/8" four flute end mill was used. The slot was cut in 0.020" increments with cutting fluid. It went reasonably well except for exiting the slot. Tremendous chatter would ensue as the end mill exited unless the feed rate was slowed substantially, about as slow as I can turn the dial. The two photos below show the milling setup and the completed slot. The ding in the back wall from a particularly bad exit can be seen in both photos.
The end mill was replaced with a 60° dovetail cutter. The bottom was cut to depth first with the dovetail cutter somewhat centered in the slot. The angle was cut on one side. Measurement was challenging. My micrometer did not fit in the slot even without the pin in place, so calipers were utilized. Only the tip of the calipers fit in the slot, so they had to be held at an angle to give an almost repeatable reading. The angle was cut to the appropriate depth and the cutting was repeated on the opposite side of the slot, in 0.005" increments with cutting fluid. The second angle was also cut until measurement over a pin showed I was close to the desired measurement. Putting pins in both sides of the finished dovetail allowed measurement with the aid of an adjustable parallel. The measurement was spot on target, 0.283"!
With the holder still clamped vertically the hole in the dovetail was drilled. The spindle was located according to the plans. The hole was spot drilled, drilled and reamed to 0.188" to a 1/2" depth. The first photo below shows the new hole. The holder was then moved to the vise where it was held on a 1/8" support and the angle plate was used as a stop. Before milling the sides a second hole was drilled 0.875" deep with a #3 drill followed by opening the first 1/2" to 1/4". The bottom of the hole was tapped 1/4"-28.
Milling began yesterday on the four sides to reduce them to 0.625" from their current 1" dimensions. After some experimentation yesterday using a new and very sharp 3/8" two flute end mill, removing 0.075" X 0.020" seems to be a comfortable rate of material removal. This morning I will explore upping the width of cut to 0.1". There are a lot of passes to be made. The milling stops short of the head of the holder. This will be cleaned out at the end using a ball end mill for a rounded transition between the head and the handle. The first photo below shows the progress after three passes the last two with 0.150" wide cut, still at 0.020" deep. The remainder of milling will wait until this afternoon when the spouse is out. About 0.040" shy of completion the new height of this handle was checked. One end was 0.015" thinner than the other. The steel was transferred to parallels as seen in the second photo.
The steel now sitting flatter had about 0.010" removed to make the faces parallel. Another 0.025" was removed in one set of passes across the block. 0.150 X 0.025" is an acceptable cut. The block at this stage is seen below. It is approximately 0.015" too thick, the last bit will be removed by fly cutting, leaving a better finish.
After a break for a class, Kumiko Box Making, the milling was continued. The second side was milled to a depth of 0.170" in passes 0.025" deep as above. The completed two sides are shown below. It is beginning to look a lot like a tool. The modification for fitting my 4-way tool post will be made after cutting it to rough size. Two long corners will be removed on one side leaving a ridge fitting the tool post's slot.
The next two faces should be a bit quicker as the block is now 0.657" wide, so five passes will suffice. The first of the last two faces was cut with the part set on a 3/16" thick brass cutoff. The part after three faces have been rough cut is shown below. After deburring the part was flipped and set on parallels for the last series of cuts.
Focus returned to holder arm cleanup with a ball end mill. This end mill was used to create the filet in the corner. First, the side of the cutter was used to remove most of the waste. The end mill was then advanced both sideways and vertically, 0.005" in both directions. This was repeated two more times creating the filet and dropping the height in the corner by 0.015".
Final work on the sides consisted of removing the last 0.015" with a 3/4" two flute cutter leaving a decent finish and acceptable matches between the filets and the finished faces.
Before slitting the holder arm needs to fit the four way tool post, which has a 9/16" high slot. 1/16" needs to be removed from both top and bottom faces of the holder, approximately 3/8" wide on the side opposite the to be drilled slot. This material removal does not need to run the full length of the holder arm and will be stopped about 1/2" shy of the larger end with the dovetail.
The holder arm was carefully marked for milling two opposite faces to fit the four way tool post. After clamping it on parallels material was removed with a four flute end mill, the full width desired, 0.375". The last pass was 0.003" deep and left a nice finish. The first side is seen below. The part was flipped over and the opposite face cut. Both sides had a little over 1/16" removed for a length of 2.75" from the end. The second photo shows the completed milling.
Cutting the slot for clamping the dovetail is the final operation on the holder arm. The holder arm was returned to the milling vise and set so the new shoulders sat on the vise top. A 0.054" slitting saw was lowered to just touch the top of the dovetailed part of the holder arm. This location was set to zero on the DRO and the saw lowered 0.375". The saw was then moved to just touch the dovetailed end of the part and this location also set to zero. The cut will be 1 1/4" long as measured from this last location. A few passes were made with the saw and cutting went well, though a bit noisy, so the bulk of the work will be done when the house is empty. The photo below shows the setup and the beginning of the slot.
The slot was initially cut from the end of the holder arm in passes that were 0.015" deep. Once the end of the holder arm reached the mandrel cutting moved to the sides. These cuts went only partway into the sides about 1/4" from full depth, though a significant amount of material was left in the center, first photo below. This steel was removed with a hacksaw. After some cleanup the completed part is seen below in the second photo.
The next part the author refers to as the head and is the most complex part of the tool. A block of steel was cut from stock with the horizontal band saw. It was then faced on three sides in the South Bend lathe to give a block that is somewhat square. The block at this point is 1.08" X 1.20" X 1.51". The block will be accurately squared up in the mill and all sides finish cut to produce a 0.875" X 1.094" X 1.375" block of steel.
An update on the ordered knurling wheels (purchased in Part 1 of this series) is in order. Turns out after much communication with Accu-Trac, they corrected my mistake. The first knurls ordered are DP 128, which is almost identical to the second set, which are 40 TPI. I blame it on my eyes, but the brain probably is responsible for most of the error.
The milling continued ad infinitum. The two flute end mill eventually dulled. An attempt to sharpen it with diamond stones helped some, but the same size four flute end mill was better, though could cut only about 0.015" deep for the 0.150" passes. A lot of passes later and the block was measured. A two insert cutter was used to produce an improved finish and bring the block to size, though the finish was disappointing. Consequently, the block was sanded from 150 to 600 grit, removing most, but not all, of the grooves from the milling.
This is a very complex part with features on all six sides. Therefore the sides were marked T,Bt,F,Bk,L, and R to help me avoid mistakes. The front face has the protruding spindles and the dovetail in on the right face. The next step is drilling two holes into the top of the head, one 3/16", 0.4" ⊥ and one 3/8", 1.325" ⊥. Before marking out the locations a decision was made to select a corner for all measurements as opposed to measuring from the nearest side as in the plans. My block is not spot on dimensionally. The selected corner is the front, right, top corner, which was heavily Sharpied.
The locations for these two holes was marked with the height gauge, the head sitting on a 1-2-3 block.
The nascent head was held in the vise on the milling table and the datum corner was located. The table was moved to put the 3/16" hole location on center. It was center drilled, drilled, and reamed to a depth of 0.4". This hole will open to a slot on the face of the dovetail that is yet to be milled.
The mill is not large enough to handle my 3/8" reamer with the part in the vise, so the head was moved to the four jaw chuck in the lathe. One jaw had to be reversed to get the next hole location aligned with a tailstock center. The hole was center drilled, drilled in steps, and reamed to 3/8". The holes were lightly chamfered by hand. The head with two holes is shown below along with the lathe drilling setup.
Time to fess up. If you look carefully at the second photo above, you will see the glaring error. The large hole is too close to the dovetail side of the part (facing the camera). Yes, the part needs to be remade. This was done this early August morning. The part was cut with the bandsaw closer to size, about 1/8" in each dimension. The excess was removed on the lathe leaving about 0.01" in each direction.
The block was set up in the mill. My angle block is not tall enough to get the fly cutter down to the work. (The riser block is installed in the mill.) Using a fixture set, two 1-2-3 blocks were clamped together at right angles to produce a larger angle plate, which was clamped to the milling table with strap clamps. The Sherline milling collet was used as a spacer, because it fit and the two ends are parallel. Using a 3" C-clamp the new block was clamped to the top 1-2-3 block with an aluminum spacer to avoid marring the work and a piece of cardboard in the back to avoid marring the 1-2-3 block. Two quick passes with the just sharpened fly cutter gave a nice finish. Repeating this on the other five sides provided a second block for the tool's head.
The holes were drilled and reamed in the correct locations. The block was then set up in the milling vise and the corner was removed with an end mill 0.15" X 0.055". The dovetail cutter was used to make the first dovetail side, first cutting to the exact depth, 0.156", and then cutting to the correct width, 0.062" from the edge. The first photo shows the correctly located holes and the second the first of the two dovetail cuts.
The second dovetail was cut on the back of the part as it was held in the vise. After getting within about 0.02" the handle was tried for fit. After each 0.005" was shaved off with the dovetail cutter, the handle was again tested. The first photo below shows the handle just barely able to wiggle on the end. After a cut of 0.002" the dovetails could be mated, a tight but smooth fit. The second photo shows the fitted dovetail joint. I'm one happy camper!
This article's description of how to cut dovetails is outstanding. Michael Ward deserves kudos for his excellent tutorial.
The slot was cut before removing the part from the vise. Its location was determined relative to two sides. It was easily cut with a 3/16" end mill in 0.015" passes to 0.219" deep. The slot was then widened evenly on both sides to 0.215". The slot is seen in the first photo and the second shows the mated parts. The slot and drilled hole will house the tool's height adjustment mechanism.
At this point the article jumps to making a variety of smaller parts, with a return to the head in the future. This write-up continues in Cut Knurling Tool 3.