Up until now I have had no problems in single point threading. However, the coarsest thread I have done is probably 12tpi.
I am currently trying to cut a 6tpi thread and I am not winning
I have a old change gear lathe with a 2tpi leadscrew. I set up the gears for 6tpi and verified it by taking a .001" cut and measuring the 'scratch' with a thread gauge. However, as I advance the compound (set to 29*) on successive passes, the thread just re-cuts itself. After several passes, the major diameter is reduced and there isn't much depth to the thread, despite decent chips coming off. Regardless, the thread still measures 6tpi.
Initially I didn't use the threading dial, as the thread I am cutting is divisible by the leadscrew pitch (I never use it on even number threads) but I tried using it and the problem remained - despite using the same mark on the dial (it takes ages for it to come around!). I engaged the half nuts about an inch before the cut to ensure any backlash had been taken up.
I ground a 60* bit out of a 1/2" blank and checked it against a gauge before honing the cutting edge. I ground 10* relief angles on both sides and left the top flat. I am wondering if I need more side relief, given the helix angle of a 6tpi thread? I don't really know/understand the whole geometry of the tool/helix angle but thought it may be something I should consider.
I didn't take pictures, as I was somewhat disgusted and thought it better to walk away, counting to 10...
I am currently trying to cut a 6tpi thread and I am not winning
I have a old change gear lathe with a 2tpi leadscrew. I set up the gears for 6tpi and verified it by taking a .001" cut and measuring the 'scratch' with a thread gauge. However, as I advance the compound (set to 29*) on successive passes, the thread just re-cuts itself. After several passes, the major diameter is reduced and there isn't much depth to the thread, despite decent chips coming off. Regardless, the thread still measures 6tpi.
Initially I didn't use the threading dial, as the thread I am cutting is divisible by the leadscrew pitch (I never use it on even number threads) but I tried using it and the problem remained - despite using the same mark on the dial (it takes ages for it to come around!). I engaged the half nuts about an inch before the cut to ensure any backlash had been taken up.
I ground a 60* bit out of a 1/2" blank and checked it against a gauge before honing the cutting edge. I ground 10* relief angles on both sides and left the top flat. I am wondering if I need more side relief, given the helix angle of a 6tpi thread? I don't really know/understand the whole geometry of the tool/helix angle but thought it may be something I should consider.
I didn't take pictures, as I was somewhat disgusted and thought it better to walk away, counting to 10...
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