First threads!

[DavidR8]

@DavidR8, Awesome job! You are making some real progress forward.

The 29.5 degree angle thing gets a lot of rookies on their first time (myself included). I prefer to skip the compound angle and thread with the cross slide only. It saves time and I haven't seen any difference in the quality of cut between the two. Plus it makes it much easier to advance on the diameter directly (skipping the trig for the compound slide). Try it out at some point and make a decision which you like better.

I do almost all my threading with carbide (and turning too!). There is not really a minimum speed limit for carbide, the big difference is the maximum speed you can cut. If you find carbide is not working well for a particular application, you may want to look for a sharper insert with a ground edge. These are often advertised as being for aluminum but they work very well on soft steels and stainless as well. I see it is easy to find the 16ER insert with this edge geometry, although I haven't tried them personally yet.

Soft metals like aluminum, 1018, etc don't like to make pretty threads in my experience. Try picking up some 41L40 and threading on that. You'll be amazed at how professional your work will look.

I usually use the threading tool to create a relief behind the thread I am about to cut (about a thou or two below the full depth of cut). This gives you room to disengage the half nuts.

Thread mics are great and very fast, however you should pick up a cheap set of thread wires and get used to using them. You can use them for any diameter thread and any pitch. They will get you out of a tough spot where you can't use the mic.

Thread tables are my most used chapter of Machinery's Handbook. I use these to copy the major diameter and pitch diameter tolerance range to my notebook before heading to the lathe. I also use this website frequently to calculate the tolerances of threads that aren't in Machinery's Handbook: http://theoreticalmachinist.com/Threads_UnifiedImperial.aspx

Keep up the great work!

Thanks, I'm going to keep at it because this is a skill I want to develop. So definitely open to all information and perspectives.
It's completely mesmerizing to watch the tool make its way along the work, a chip curling off and at the end of it you have a useful part.
Amazing!

 

[SLK001]

The leaded steel cuts very nice (that's what the "L" in the designation means). South Bend used a lot of leaded material for that reason.

As for the 0º vs 29.5º-30º argument, the 30º approach puts less cutting stress on the tool (it only cuts on the leading edge). Less stress usually means a better looking thread. Anyway, I usually clean up my threads with a couple of high speed passes with a triangular file to clean up the flanks of the thread, then a flat mill file to clean up the tops.

I have a 0-1" thread mike that is really, really useful. I plan on getting both a 1"-2" and a 2"-3", but right now, I use wires for those.

 

[DavidR8]

Alrighty folks,
A bit more lathe time tonight.
Having had my fill of CRS I tried some 10L.
Cut off a chunk, faced it off, took .010 off the diameter.

Cut a gutter and blued it up.

Picked 16 TPI as my pitch, put it in back gear and took a scratch pass.

Pretty darn happy with the results.

Buoyed by my success I turned a piece of CRS to the major diameter for 3/8” and repeated the process.

The results speak for themselves.

I am stoked!


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[DavidR8]

The leaded steel cuts very nice (that's what the "L" in the designation means). South Bend used a lot of leaded material for that reason.

As for the 0º vs 29.5º-30º argument, the 30º approach puts less cutting stress on the tool (it only cuts on the leading edge). Less stress usually means a better looking thread. Anyway, I usually clean up my threads with a couple of high speed passes with a triangular file to clean up the flanks of the thread, then a flat mill file to clean up the tops.

I have a 0-1" thread mike that is really, really useful. I plan on getting both a 1"-2" and a 2"-3", but right now, I use wires for those.

I just bought a 0-1” thread mic last night!

I turned some 10L tonight for the second time. What a dream that is compared to CRS!


Sent from my iPhone using Tapatalk

 

[Nigel123]

The leaded steel cuts very nice (that's what the "L" in the designation means). South Bend used a lot of leaded material for that reason.

As for the 0º vs 29.5º-30º argument, the 30º approach puts less cutting stress on the tool (it only cuts on the leading edge). Less stress usually means a better looking thread. Anyway, I usually clean up my threads with a couple of high speed passes with a triangular file to clean up the flanks of the thread, then a flat mill file to clean up the tops.

I have a 0-1" thread mike that is really, really useful. I plan on getting both a 1"-2" and a 2"-3", but right now, I use wires for those.

I have cut numerous threads without thread gauges using the no of threads divided into 0.75 or 0.742 for the infeed of the compound
I use HSS cutter the threads are smooth no filing needed
Use cutting oil and a couple of spring passes
I use 29.5 degrees as it only cuts mostly on the leading edge
One thing to remember is the backlash in the gear train and always feed in the direction of travel

 

[DavidR8]

@SLK001 newbie question; is it a 60 degree triangular file?

 

[mikey]

The leaded steel cuts very nice (that's what the "L" in the designation means). South Bend used a lot of leaded material for that reason.

As for the 0º vs 29.5º-30º argument, the 30º approach puts less cutting stress on the tool (it only cuts on the leading edge). Less stress usually means a better looking thread. Anyway, I usually clean up my threads with a couple of high speed passes with a triangular file to clean up the flanks of the thread, then a flat mill file to clean up the tops.

I have a 0-1" thread mike that is really, really useful. I plan on getting both a 1"-2" and a 2"-3", but right now, I use wires for those.

Not being argumentative in the least but I just wanted to be sure Dave is clear on this. A 30 degree approach angle will have most of the cutting occurring on the leading edge of the tool because it is a flank infeed BUT the trailing edge rubs at this angle, which can lead to rough threads and chatter. This is why an approach angle between 25 - 29.5 degrees is most often recommended; it eliminates trailing edge contact and produces cleaner threads. It also eliminates the need for passes with a file to clean up the flanks. A file off the top is a common practice but if the threads are cut to the proper pitch diameter with a sharp tool, this is certainly optional. A sharp HSS tool with adequate relief angles to get past any helix angle issues also goes a long way towards eliminating the burrs the file is intended to deal with.

No offense, SLK001. Just needed to clarify things so Dave understands why typical practices are what they are.

 

[DavidR8]

I did a bunch of reading last night and I have a much better understanding of why the 25-29.5 degree approach angle is used.
As I visualized it in my head, a perpendicular approach has both sides of the tool cutting simultaneously. I can imagine that the tool could chatter from side to side as it cuts.

Increasing the angle toward 29.5 degrees is going to decrease the cutting pressure on the right side side of the tool as more and more of the profile is cut by the left side of the tool until the left side of the tool is cutting all of the left side profile and the increasing depth is cutting the right side.
(I'm not explaining what I see in my head very well)

 

[mikey]

Dave, I've posted this chart multiple times on this forum but thought I would do it again because it is an extremely useful chart. It tells you what your blank OD should be to produce the class of fit you want, be it a class 1, 2 or 3A. It also gives you the pertinent pitch diameter so you know what your target range is when you use your thread mic. You won't need all of this data for every thread you make. Most of the time you can cut to fit a nut or female thread you already have, in which case the following formulas will get you close enough.

Estimated thread infeed using cross slide = 0.75/tpi; Alternative formula = Maj dia - Min dia / 2
Estimated thread infeed using compound = 0.75/tpi X 0.866 (which is the Cosine of 30 degrees)

Note that no formula is exact. It is wise to begin checking for fit or pitch diameter before you get to any calculated infeed. I typically start checking at least 0.005" before, or more for a class 3 thread. You do not want to overshoot your final depth of cut.

It is also important to taper your infeed depths of cut. For the first pass, you can go up to about 0.010" deep but for subsequent passes you want to take lighter cuts because more of the tool will be engaged in the cut as you go deeper and cutting forces increase dramtically. For a second pass, 0.005" works, then 0.003-4" for the third pass, then 0.002-3 for the fourth pass and so on.

 

[mikey]

I did a bunch of reading last night and I have a much better understanding of why the 25-29.5 degree approach angle is used.
As I visualized it in my head, a perpendicular approach has both sides of the tool cutting simultaneously. I can imagine that the tool could chatter from side to side as it cuts.

Increasing the angle toward 29.5 degrees is going to decrease the cutting pressure on the right side side of the tool as more and more of the profile is cut by the left side of the tool until the left side of the tool is cutting all of the left side profile and the increasing depth is cutting the right side.
(I'm not explaining what I see in my head very well)

Dave, let me clarify one point. At 29.5 degrees, most of the cutting is done on the leading flank of the tool, while the trailing edge does make contact but it tends to wipe the trailing edge of the thread to produce a better finish there. I said above that 29.5 degrees eliminates contact; it does not, but it greatly reduces it and to beneficial effect.