Taper thread turning

Hi group, I want to make a 1" BSPT taper pipe thread tap. Okay I can
cut the pitch on my lathe okay and that would be fine for a straight
thread but is there any way of cutting a tapered thread without a
taper turning attachment?
Thanks in advance.
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There are two ways. 1) Offset the tailstock by the desired amount of taper and turn "normally". 2) Set the compound at the desired taper angle and make "x" movements with it.
Bob Swinney
Reply to
Robert Swinney
"is there any way of cutting a tapered thread without a taper turning attachment?"
" Set the compound at the desired taper angle and make "x" movements with it."
Thats am impressive sounding tactic Bob. Id enjoy watching it done.
Reply to
That procedure is used for omnidirectional variable pitch threading. You have to cut the full thread depth in a single pass.
It might be possible on a CNC lathe or a chucker with power feed available to the compound.
Best Regards Tom.
Reply to
Oooppps! Thanks Tom. I shoulda engaged brain before hitting keyboard. I was referring to taper turning not *taper thread turning*. Sorry.
Bob Swinney
Reply to
Robert Swinney
In my youth I saw such a setup using a drive from the end of the lead screw that ran through gears above the bed to tailstock height. A long drive shaft with universal joints and a sliding joint in the middle put drive to where the compound handle had been removed. It was a special setup put on one lathe and used for the single machining operation. Randy
Reply to
Randy Zimmerman
You can chase the tapered thread by running between centers and offsetting the tailstock such that you get ¾" taper per foot. On short items that isn't much of a problem, but it can be challenging to get enough movement of the tailstock on longer items.
Your only other options if you don't have a CNC would be to use a rapid threading attachment, or a tracer. A special stylus is required for threading when using the tracer.
Reply to
Harold & Susan Vordos
I haven't tried it, so I'm not sure if it's effective or practical, but it's been mentioned here before that a tap of the same thread pitch (even if it's not the same diameter or tapered) can be used like a form cutter.
If the tap were held at an angle to the lathe's center axis to match the desired taper(and supported to keep from snapping), then the correct feed would move the side of the tap into the workpiece as it advances toward the headstock.
If you had the appropriate cutters from the threading die, this probably/might've already occurred to you. Probably would be difficult with a wimpy lathe though.
WB ...............
Reply to
Wild Bill
Hmm ... I don't think that he is going to be cutting threads with the compound, unless there is some interesting linkage to the hand crank. :-)
As for the offset -- it would be pretty close, but it would introduce some slight error into the thread pitch, as you would be cutting the length on the angle instead of parallel to the axis of the pipe. The error would probably be little enough to not be a problem, as the angle is fairly shallow and the length of the thread is fairly short.
But -- really, other than the taper turning attachment, perhaps a pipe threading die would be the other way to get a perfect thread -- or close enough, at least.
Enjoy, DoN.
Reply to
DoN. Nichols
A tap? Why not just spring for the tap and be done with it. This is kind of like making your own twist drills.
Reply to
Roger Shoaf
Because it's not a normal tap but part of a special threading set up and will have a hole right through the centre and a hole through the driving shank to drive it. Thanks everyone for the ideas. I dont have CNC, a tap or die of the correct pitch, no way could I use the compound so it's the tail stock idea or buying a tap and getting the holes spark eroded.
Reply to
Buy a commercial tap and edm the holes you need with a sinker edm. If you are in the UK (well it is BSP !) I'll do it for you.
Bromley, Kent, UK
Reply to
Andrew Mawson
Thanks for the offer but I am 12,000 miles away in sunny Australia enjoying beautiful summer days. Short sleaved shirts and shorts are the order of the day so you will understand that I want to stay away from the freezing northern hemisphere at the moment. As a matter of interest how much would it cost?
Reply to
While I haven't made a tapered tap, I have made a tap <
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\Making_a_tap.txt> and I have made a tapered thread. The thread application was a on-of so I wasn't particularly concerned about how long it took.
I always thread away from the headstock as that let's me just run off the end of the work piece. I use the usual compound at 29.5 degrees for advancing the cut and zero the cross feed so I can make a cut, move the cutter out of the way, run back to the starting point, re-set the cross feed, advance the cut and make another pass.
For the pipe thread, I simply started half a turn further out on each pass and advanced the cut by the calculated amount (e.g. 0.0015" for a 20tpi thread). On completion I dressed the thread very lightly with a triangular file and put the piece in service. No leaks.
Reply to
Ted Edwards
I have drilled holes in taps using a carbide drill, sounds like the best way is to buy the tap and drill holes in it. WhAt size tap and what size holes?
Reply to
Nick Hull

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