Home Made Indexable Dovetail Cutter

I sat down and thought my way through making one. How I would turn it on the lathe, then how I would fixture it on the mill, and how I would cut it.
In some ways its more of a pain to make than the spring loaded extension compression tapper. Now my thought if maybe misguided on the tapper was I planned to make several of them (and I will) and maybe even sell them (which I probably will not).
For an indexable dovtail cutter I couldn't make one any cheaper (much more really) than an import from somebody like Shars. I could make one that is satisfactory, but so does the outfit who makes the ones with the Shars label. The only real benefit I would get from making one would be the experience and additional skills in my arsenal. Now that does have real value. My experience making the TC tapper showed that if only to myself.
The thing is I run a one man homeshop. It?s a real business. Its my full time job, and it makes a few dollars that I have to pay taxes on at the end of the year. My time is finite. In fact its probably my most valuable resource. I have things I want to make using a reasonably stiff dovetail cutter. I finally decided it was more valuable use of my time to make the parts rather than the tools in this case. I have not paid myself as much per hour as I used to charge as a contractor, but time does add up and have real value. A little over $50 for an indexable dovetail cutter from Shars smokes the time it would take me to make one (1) and realistically I only need one. Well until I wear it out or crash it into a part and break it. Maybe if I needed ten of them all the same...
I like making tools. Its fun and sometimes challenging. I also like making parts. Its fun and since I do more than 90% custom work its always challenging. In this case I'll be making parts not tools.
Of course even thinking my way through the process I learned a couple things. Some I am sure will be painfully obvious to most of you. I may have even known them myself, but not really consciously.
The first thing you have to do when making a dovetail cutter is select an insert. In case you missed it that is THE FIRST thing you need to do. When I was looking up tool and insert prices I noticed sometimes a vendor had the tool, but they were out of stock on the inserts. Of course I had to make sure those were common readily available inserts elsewhere. Most were, but initial searches didn't always show them. I knew I had to have a strong triangle insert.
TNMG is the strongest triangle insert I know of. Unfortunately it has no rake angle. That's set by the tool that holds it. Well that just won't work. If its mounted straight it won't cut because the zero rake will cause the back (bottom) of the insert to rub and break off that extra edge on the other side. If its set at an angle it won't cut a 60 degree dovetail. Something rather less instead. Nope. No good.
TCMT is pretty strong its has some rake angle (7 degrees), and can be mounted square, but depending on the thickness of the insert may only be usable on larger diameter dovetail cutters. The trailing edge could still rub. That's fine I suppose if you are cutting making outside cuts and have a machine powerful enough to provide suitable horsepower at the lower RPM required for a larger diameter cutter.
TDX or TDEX (are they the same thing?) have a 15 degree rake. This allows for small diameter higher RPM (relatively) usage. It has good clearance. It will not rub unless you go out of your way to plan a tool with poor geometry. Its also not as strong maybe as TCMT and like TCMT has half as many cutting edges as TNMG. Ok, for smaller or lower power machines it (or something very similar) may be the best option.
The difficulty of planning the tool itself. It depends on what you are going to cut. For something like a lathe tool holder its not all that important. Really. If its close it will lock up, and the adjusting screw sets the height. I have seen lathe tool holders made by welding two round rods to the back of a block. Its not pretty, but in a pinch it works. For a live (is that the right term) sliding dovetail it might be a little more important that both sides mate up well. This means making your dovetail cutter well. It will work best if the cutting edge is EXACTLY on the center line of the tool. This goes back to insert choice. You need to choose an insert and plan around its thickness. The reality is if you are pretty close it will probably work ok, but pretty close is affected by variance of the inserts as well. If you have done much research on inserts you will find they have tolerances they are supposed to fall within a range. If you are at the edge of the acceptable tolerance for your tool, and the insert is at the edge of its tolerance range you may have a measurable out of tolerance for your finished dovetail.
Ok, if you have read this far it should be painfully obvious I am NOT a tool and die maker. Its might also be apparent I spent some time thinking about this.
Along with reading and looking at manufacturer and distributor information I also watched a number of YouTube videos of various guys. One was, "I just picked a insert I had that didn't fit any of my tools," and another was "I'm just making a single insert tool so the exact depth and position isn't that important." One clearly did not properly support (in my opinion the unused edges of the insert. CRINGE! In my early YouTube video watching some of those comments were taken at face value, but I've learn from watching YouTube videos you have to watch a minimum of five and preferably ten different videos on the same subject. Then apply your brain and see what actually makes sense. A fellow named Randy Richards "RR in the Shop" seemed to do the nicest job, and several people where clearly trying to copy him in their videos. The more honest ones said so. There were even videos where people just showed a Randy Richards dovetail cutter cutting (testing) a dovetail.
Then there is the nuance of multiple flutes. One flute is very doable for anybody who takes the time to learn how to do it properly and defines reasonable tolerances for themselves. The basic preparatory lathe work is unchanged, The secondary flutes all have to match and you have to be able to repeat positioning of the insert accurately for every flute. Maybe it doesn't matter so much for a fast heavy roughing pass (do you even do fast heavy roughing with a tool like this), but for a semi finish pass and certainly for a finish pass you are likely to have only one insert doing all the cutting unless you have been amazing in your tool design, setup, and execution.
My conclusion. I spent more time learning how to make an indexable dovetail cutter than its equal value to buy several of them retail.
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