I purchased a 1/8x28 BSP split die, around 25.3mm in diameter, and it would not fit in my existing tailstock die holder V1.
My V1 holder was made to fit my cheap metric set of unsplit dies, all of which are around 24.8mm diameter.
So, I was forced to make a new holder (known as the V2 in this neck of the woods).

After using the V1 for a while I learnt that a tailstock die holder needs a tommy bar, because threading can become hard on anything above M6.
I also learnt that if the holder has a bigger diameter then it is easier to turn by hand, because of the extra leverage (moments about a point).
I also paid attention and made a good job on the set screws, so I could properly adjust split dies.

I did not intend documenting the build, so there are a lot of missing pictures in the sequence.


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↓ I started out with a lump of 50mm mild steel, cut to size in the bandsaw.
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↓ I did this job in the Myford ML7, which suddenly feels pretty small when you put large diameters in the chuck.
Because of the size of the metal bar, I used a slow speed to start with, and plenty of support from a centre in the tailstock.
When I had removed a large amount of metal, I felt more confident and upped the speed.
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↓ I turned one end down to smaller diameters, to reduce the weight of the tool, and also to make it a more comfortable fit in the lathe chuck.
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↓ I turned the piece around, to start on the end that will hold the die.
I aimed to leave the diameter on the business end as wide as possible, to give more leverage when turning by hand.
I do not have pictures of most of the build.
While working on the die end of the holder, I kept the work in the chuck the whole time.
I drilled a 12mm hole all the way through, and then reamed it to 1/2inch. I chose 1/2inch because I had some bar in that size; which saves a lot of hassle. It is far smoother than I could turn it!
I used a boring bar and made the recess to suit the diameter of the die.
I knurled the work, using a scissors type knurling tool, and dressed the edges using a file while the work was rotating in the lathe.
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↓ I removed the chuck (keeping the work in the chuck), and mounted the chuck in the rotary table on the milling machine.
I used the rotary table to index the holes for the set screws. I drilled and tapped each hole to M4.
I also drilled and reamed an 8mm hole for the tommy bar.
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↓ I used a center drill and created a chamfer to tidy up the holes.
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↓ Here is the 1/2inch bar that fits into the chuck in the tailstock, and the 8mm tommy bar.
The 8mm bar is from a printer, which saves a lot of hassle, as it is far smoother than I could turn!
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↓ Here are the set screws. I used M4 Hex head screws, and dressed the ends in the lathe.
The screw that goes in the split is pointed, to give fine adjustment when opening and closing the die
The other screws are a bit more rounded.
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↓ The scissor type knurling tool is easy to use and does a good job for me.
I position the tool so that the knurls are close to the end of the job, and are just fractionally hanging off the end of the work.
I adjust the knurling tool and cross slide, so that the knurls are at the top and bottom of the work. I then tighten the clamping screw by hand so that the knurls are grabbing the work. I then back out the cross slide, so the knurls become loose again as they come off of top and bottom dead center. I tighten the clamping screw up a little bit, maybe one or two turns. I screw in the cross slide again, so the knurls are back in position and are now clamping the work very firmly indeed.
I start the lathe and feed the apron by hand using the apron wheel. When coming back, or going over the knurl again, the knurling wheels fall into, and follow, the previous tracks.
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↓ Here is the tool in action, cutting a 1/8x28 BSP thread (around 9mm), on a part for my homemade ML7 oilers.
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↓ A good chamfer makes for an easy start.
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↓ I struggled a little, cutting a thread at around 9mm diameter, and my hand hurt after a while.
On steel, I found it easier to do the thread in 3 passes; starting off with a loose die and tightening the die up on subsequent passes.
I later redone the part in brass, because it was easier to work with, and I could cut the threads in one pass.
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