External Imperial Threading on Import Lathe

This is the 2nd in a 2023 series on threading on an import lathe. This video will cover external imperial threading. Double depth of threads, compound angle, calculating amount of compound advance, etc.
Link To Part 1 - Change Gears • PM-1127 (and other imp...

[@malcolmtill]

An absolutely first class lesson on threading. Thank you.

[@G1951-w1y]

I like your formula. Good point.

[@AmateurRedneckWorkshop]

Well done. Thanks for the video keep on keeping on.

[@johnbarnwell400]

Thank you so much for this lesson ! I have the same lathe you have except mine is not the LB large bore … mine is 1.57 inch bore …this was very helpful as I am just a hobbyist beginner .. .. I’ve always used dies and taps for threads but I really want to be able to cut single point threads .. I also have the PM 728 VT milling machine and have copied your aluminium fixture plate and it has been so handy for work holding .. .. please keep the videos coming ! Your channel is one of my top favorites!

[@melgross]

Just a few of points to add to this fine presentation. The more of the thread you cut (the deeper you go), the more metal you’re taking off, so on a larger thread, you need to take a finer cut as you go. The last cuts should take no more than 0.002”. The thread on both the screw and nut are both flattened. That flat is determined by the size thread. That’s why the diameter of the thread is a bit smaller than the nominal diameter. This is for strength and to give some room between the parts. When you’re threading for yourself, as long as it fits, it’s usually ok. But if you’re making parts for customers, or to be interchangeable with some other part, you really should consult the charts for proper fit. This is usually given as H values - 1, 2, 3, 4, etc. the last bit of info is that the rear of the cutting tool DOES cut. Some people say that cutting at 29.5 degrees has the tool cutting only at the front face. South Bend stated in their manuals that it cuts on the rear as well. A couple of years ago, or so, Joe Pie did an excellent video in which he showed conclusively, that it not only does cut, but why it needs to cut. Worth watching. By the way, if you buy thread cutting insets, be careful what you buy. The are partial thread inserts, and full thread inserts. Check it out.

[@feeseize9569]

Lee I’ve got zero experience single point threading on my mini lathe but I thought you were supposed to turn the threaded area down to the major diameter first. If I’m not mistaken that saves the threading tool from having to dig down as far. Love your channel. Greetings from Wilmington.

[@MrPragmaticLee]

Starting with the nominal value (5/8 in this case) is fine IF you don’t know the minor diameter, but that is why I had to make several extra advances on the compound. Thanks for stopping by.

[@dennythomas8887]

Great method for setting the compound. I'll try that next time. Thanks Lee!

[@erikschoeneborn9479]

Really love how you explain everything so clearly. Very easy to follow. Thank you.

[@lawrencewillard6370]

Been 'rebuiding' an old lathe for a few years. Got it 'close' to be able to get finer work done. Thread cutting was an unknown to me, now it isn't anymore, thanks to you. Appreciate it greatly.

[@davidlloyd6045]

Great video. I do have a question. Will it work if you touch off and set both cross slide and compound both to zero. Then advance the cross slide the .118” double depth and then reset zero. Back off the compound and cut the threads. This way you don’t have to do the math for how much to advance the compound. You would just go to zero.

[@MrPragmaticLee]

As long as you accounted for any backlash in you dials. Thanks for stopping by.

[@2deadlyesh]

Thank you for sharing, im looking to commence building miniature steam engines like my Great Grandad and learning the ropes.

[@kimber1958]

nice demonstration

[@incubatork]

On the material prep page you say you cannot turn as the travel (with lead screw)speed is too fast, Why can you not disengage the half nuts and use either hand feed or the feed shaft for prep work? My lathe is metric and all I need to change is 1 gear to change from metric to imperial and I have only 1 carriage shaft but 2 positions, either feed or half nuts. Also my lathe has no thread dial and its also not an optional extra so at some thread pitches I need to leave the halfnuts engaged and reverse the lathe.

[@billshiff2060]

You are using the obsolete (since 1948) American national thread double depth. You have to be using a cutter that is too sharp to make those numbers work. The double depth for an ASME UNC 11tpi thread is .098 /2 = .049.
That thread will be out of spec and weak.

[@clifeddens1658]

Best yet for threading instructions.