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Carbide tool holder

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NormanV:
This is a story of a mod., with a bit of knowledge and a lot to learn. Unfortunately I didn't take any photos of my progress as my camera was broken, but now that I have a new one there will be a shot of the finished item.
I bought a tool holder at an Autojumble (my first, I'll definitely go again). It had a 25mm square shank, my lathe tool holder only takes 16mm. No problem, just pop it in my homemade milling vice on my homemade milling machine. Using a 12mm HSS end mill I tried my first cut ( Huh, I need to get on and finish my Quorn!) I placed an order for a Carbide end mill, this was positive, I live in a holiday area and the seller has a caravan just down the road, so the cutter was delivered next day. I popped it in the mill and off I went. What a difference! Needle sharp splinters of steel were sprayed in all directions. I pushed it further, red hot splinters flew everywhere. Then it stopped, no warning no smoke, no nothing. It just stopped. I was quite worried, the wiring of this machine had stretched me to the limit. Trouble shooting was possibly going to be a step too far. 
Next morning I switched it on and joy oh joy, it worked. It must have been an overload in the speed controller. Although it was now working I was finding that the rate of metal removal was quite slow and I was worried that I would ruin the carbide end mill. Then I had a revelation, I ordered some 1mm thick cutting discs for my angle grinder. They arrived after 2 days, 30 minutes work had the tool holder roughed out and another 30 minutes in the mill had it machined nice and square. Phew, what a palaver! At least next time I will be able to do it more quickly.
I tried it out on a piece of mild steel, rotten finish, it is too late now I'll sort it out in the morning.

Lew_Merrick_PE:
In my experience, a tool holder responsible for poor finish suffers from one (or more) defects.  (1) The foundation for the insert is not flat (usually from being hemstitched with a ball mill).  (2) The periphery locator os a poor fit.  or (3) the clamping arrangement does not hold properly.  I have reached the point where I made the foundation from a piece of CRS bar stock and silver solder the periphery locator in place (usually "sacrificing" an insert to assure alignment).  I have no photos, but I have been making insert toolholders this way since the late-1960's.

Pete.:
Wind your rpm up and take healthy cuts, see if the finish improves.

chipenter:
Is that a cutting incert or the anvill ? I have never seen a TN incert with a flat top like that before .

awemawson:
Norman, as chipenter says, it certainly looks as though you have no insert in the holder, and are cutting with the carbide seat that the insert should locate on.

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