Tool holders (for the lathe) gotta be the metal equivalent of wood working clamps: you can’t have enough and when you do have enough, it still isn’t.
I wanted to make a holder for 3/4″ boring bars as the one I have (bought) is 1″ with a reducer sleeve (sorta ick but works well) and doesn’t index bars with a flat. While digging through the stock piles, I found a plate that would make several regular holders.
The first order of business (after squaring the stock – see the previous posts on the fly cutters) was to cut the dovetails. This involves cutting a slot, to depth, then plowing a groove down the center to provide a relief for the dovetail cutter as it really doesn’t like center cutting. I cut this 15 to 20 thou deeper. Ideally I would use a keyway cutter to waste out most of the dovetail but I don’t have one so I went straight to the dovetail cutter. The regular posts were cut as one (and sawn apart after). I think this dovetail cutter isn’t ideal and needs some radial and axial rake, it makes quite a racket and gave me a headache even though I was wearing hearing protection. Notice the different colored chips (and shapes); dark blue and curly when I was really hogging out the slot, silver slivers from the dovetail cutter.
To measure dovetail width, it is best to use dowels/pins in the dovetails and measure between them. Here, I’m using an adjustable parallel to do that (1.080″ with 1/4″ pins for my BXA tool post).
My existing holders are all metric, mine will be all imperial – 3/8″-16 and 3/8″-24. I didn’t have any 3/8″-24 nuts so I just made some (from hex rod) as that was quicker than making a store run. The discs were cut from some rod I knurled.
Next up was the threaded holes. 24 tpi (NF) for height adjustment, 16 tpi (NC) for the set screws. One of the holes is blind and some didn’t have much run out room so I used a spiral flute bottoming tap. These taps eject the chip back (spiral point eject the chip forward) and I was able to power tap everything (started the blind hole under power and then finished with a tap handle).
The bolts in the photo are interesting; I single pointed them from hex stock. Notice the thread goes pretty close to the shoulder and there isn’t a thread relief groove. I did this by running the lathe in reverse so the threading tool moves left to right, allowing me to position it close to the shoulder without worrying about a crash. I used an internal threading bar on the outer back side of the stock.
I threaded some stainless steel rod cut offs for the posts and locktited them in place.
Here is one of the tool holders with a shop made left hand cutter: