Making lathe QC tool post tool holder without dovetail tool?

ErichKeane

Making scrap at ludicrous speed.
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Hi all-
I have an Aloris BXA tool post on my lathe (kind with center 'button' that pushes out to tension). I want a dial indicator holder, but I don't have a dovetail cutter. I don't see myself getting one anytime soon (nothing else on my projects list uses one), so I had an idea to simply cut the dovetails with a normal endmill and a sin-bar.

Obviously there would be a depression in the flat, but I'm thinking that if I can keep it away from the center 'button' part that I'd be alright.

So my question is, is there something obvious I'm missing here? Will this not work for some obvious reason? Cutting out of some sort of aluminum drop I got at a local store if that changes the answer.
 
A dial indicator does not need a robust setup, so your idea will probably work just fine for that use. It would probably give up some rigidity with tooling that would work it harder, but might be OK. 60 degree dovetail cutters are not cheap, but they do have many other uses besides tool post dovetails. The insertable single insert type will last much longer than a solid HSS multi flute type, they are resharpenable, but not easily or cheap. Randy Richard makes a really nice dovetail cutter and sells them himself. I have one and it works great. I do not know how much he currently charges for one. Here is a video where Randy shows how he makes them, in case you want to make your own:
 
A dial indicator does not need a robust setup, so your idea will probably work just fine for that use. It would probably give up some rigidity with tooling that would work it harder, but might be OK. 60 degree dovetail cutters are not cheap, but they do have many other uses besides tool post dovetails. The insertable single insert type will last much longer than a solid HSS multi flute type, they are resharpenable, but not easily or cheap. Randy Richard makes a really nice dovetail cutter and sells them himself. I have one and it works great. I do not know how much he currently charges for one. Here is a video where Randy shows how he makes them, in case you want to make your own:

Ooh, interesting! I DO have a bunch of cheapish carbide inserts, so perhaps I can run one of those instead! I DID just pick up an 1 1/4" steel drop from a local supplier, so this might be a fun project 'first' :)
 
Cut the notch square oversize and add a triangle piece to it.
 
You can make a pair of dovetails by cutting or milling two pieces of steel plate at 60 degrees, then bolt them to the body of your holder. Of course, they have to be spaced to match the Aloris. I have seen a description of this approach showing a real-life example but I can't find the web site now (sorry about that). Hopefully someone else will come up with the link.
 
Ooh, interesting! I DO have a bunch of cheapish carbide inserts, so perhaps I can run one of those instead! I DID just pick up an 1 1/4" steel drop from a local supplier, so this might be a fun project 'first' :)
The dovetail cutter is cutting small radii, and therefor needs inserts with a large relief angle behind the cutting edge to clear the radii. Randy uses TiN coated TPGB321 inserts and they work very nicely on steel, and are easy to find. Typical turning inserts will not work, not enough clearance, they will rub.
 
I ended up not having any inserts that would work, so I decided to try my original plan with a 3/8" endmill.

Sadly, I accidentially tried to copy from 2 different existing tool holders (1 Accusize, 1 Aloris), so I ended up cutting it too large slighty by getting the largest of both dimensions!

It works perfect on 1 of my 2 tool-post locations, but is too loose to lock up on the other. I left plenty of material (since I screw up often :)) so I'll likely reface it and start again tomorrow!
 
Sadly, I accidentially tried to copy from 2 different existing tool holders (1 Accusize, 1 Aloris), so I ended up cutting it too large slighty by getting the largest of both dimensions!
It is extremely easy to go from undersize to oversize when cutting dovetails to fit a QCTP. You REALLY have to sneak up on it. It is better if you make a plug gage that fits the OEM tool holders well, and then use it to test the one you are making. The depth of the dovetail also needs to be spot on. You can measure the dovetail spacing by using a couple dowel pins that seat somewhere in the center of the dovetails, and also on the register on the flat inside, then measure the pins carefully and accurately for height and spacing. There is little wiggle room, especially if you want the QQCTP handle to tighten to the same clock position with all of your tool holders.
 
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Sadly, I accidentially tried to copy from 2 different existing tool holders (1 Accusize, 1 Aloris), so I ended up cutting it too large slighty by getting the largest of both dimensions!
It is extremely easy to go from undersize to oversize when cutting dovetails to fit a QCTP. You REALLY have to sneak up on it. It is better if you make a plug gage that fits the OEM tool holders well, and then use it to test the one you are making. The depth of the dovetail also needs to be spot on. You can measure the dovetail spacing by using a couple dowel pins that seat somewhere in the center of the dovetails, and also on the register on the flat inside, then measure the pins carefully and accurately for height and spacing. There is little wiggle room, especially if you want the QQCTP handle to tighten to the same clock position with all of your tool holders.

Edit: Double post again. I did nothing to cause it.
 
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