New threading tool

JSH

Active Member
#21
Almost a year since the last post, but I will dig it up any way.

I was gifted a 5/16 set a while back. I decided to give it a try. Went to do some 7/8-14 threads. The holder drags on the part and burnishes the threads. Worked good but could not get proper depth. Swapped out tools and tried to pick up the thread, that did not turn out as I planned,lol.

Do I just go to a bigger holder to get the depth or is there a different insert?
Keith spoke of certain specific inserts above. Can you elaborate or direct me to the definition of such.
Jeff
 

Pistolero

Well-Known Member
#22
In my limited experience, the inserts are specific to the holder, and the insert is
rated for a particular range of thread pitches.

This is the one I use, and it is rated for from 8 TPI to 48 TPI. It should cover what you need.

https://www.shars.com/products/inde...rtial-profile-ag60-carbide-threading-insert-1

The holders are marked for various inserts - this one is an AG60 type and the holder is:

https://www.shars.com/5-8-x-5-8-rh-indexable-cutting-tool-universal-external-threading-toolholder-1

But, I was put off by the cost of the individual holders until I ran into this deal.

https://www.shars.com/1-2-indexable-carbide-turning-tool-set-1

For about twice what ONE holder costs you get a set of seven with one insert each and wrenches.

Hope this helps.

Oh, and when you figure out what insert you want, eBay direct from China has way, WAY better
prices, like one tenth the cost per insert, shipping included.

Bill
 
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JSH

Active Member
#23
I have been using allindustrial for a while. $75 and over free shipping. Got about a dozen QCTH now.

I was just fooling around yesterday. Had been a while since I had used power feed or threaded anything. I got all set up to thread, but it just didn't seem right, but what the heck maybe it is just me. So I start cutting threads. Good gravy, what the heck is going on? Forgot to change the one on the banjo under the cover, loosen a bolt, pivot and tighten back up.
I went ahead and cut them just for the heck of it, it's going slowwww,lol. Looked like threads for a scope tube.

Got it figured out and cut with the HSS bit. Came out ok, but I couldn't find a fish tail, got a half dozen. Squared up against the chuck, close but not perfect. Good lesson though.
I played long enough to fill up a five gallon bucket with aluminum curls.
Lucked into a fair bit of round stock from a buddy, aluminum,brass,12L14,drill rod all odds and ends, some 20' sticks I had to cut in half to get in my truck. Amazing what a six pack of craft beer can get a guy.

The Sheldon is a fine piece of iron Bill. The back gears are not as noisey as some new lathes that guys think are quite.
Jeff
 

Pistolero

Well-Known Member
#24
I am glad you are enjoying that lathe, Jeff. It did a lot of good work for me, and
has never been abused. I know all three owners, all single person owner/operator
situations. The first two were for making money, the last one, me - just for fun.

If you made that many chips, you probably learned a lot,too. Yes, the back gears
are straight cut, so make a bit of "reverse gear" type of noise, but not too bad. Overall,
a good older machine.

Bill
 
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Ian

Well-Known Member
#26
Basically, yes. "Feed rate" of the carriage vs. spindle speed, that is. The ratio of the gears connecting the spindle to the apron leadscrew locks in the pitch, can be run at any appropriate speed.
 
#27
LATERAL feed rate, relative to spindle rotation rate, yes. Inward feed is
manual, you make multiple passes, cuttting the thread a bit deeper each
pass, unlike a tap or die. Each time you re-engage the thread, you
must use an indicating device built into the lathe to reengage the lateral feed
at just the right time to re-cut the same thread location.

It probably sounds more complex than it is. You can learn to thread in about
15 minutes of instruction, assuming you already are up to speed on the basic
controls of the lathe for turning.

Bill
 
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#28
Oh so what I'm seeing in the video is the carriage moving not the part (?)
Is there a set of formulas for different thread pitches or is it relative to the lathe you are using? ( & the dia of the part)
 
#29
The thread pitch is set by gearing between the lathe spindle and the carriage
feed mechanism. Older lathes required manually installing the correct gears
between two shafts. More modern lathes have a 'quick change gearbox' an a
chart of which positions to select for a pair of selectors for each desired pitch.

1544034753314.png

The lower two levers are moved laterally to select the thread pitch. The chart is right above the selectors. Pull out the
black knob, move handle down, then laterally to correct position, then back up, release knob and a pin pops into
one of the holes to lock it in place.

A pic is worth 1,000 words. 24 TPI is with the left hand lever in C, right hand lever in 6.

This is a Grizzly factory pic of my lathe. The leadscrew which actually drives the carriage laterally
is the third horizontal shiny rod from the bottom on the right edge of the photo, with the threads.

Bill
 
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Brad

Administrator
Staff member
#31
Jim, the video is a bit deceptive because the camera is mounted to the carriage. That means the camera is in the same position relative to the tool at all times. This makes it appear that the turning stock is moving laterally.
If I mounted the camera on the large bed it would be far more clear.

When I got my large I figured threading was a black art I might attempt after 6 months of more. I was threading in under a month.

Threading is a simple process really. Mostly a matter of looking the desired thread pitch up on the chart for the lathe and selecting the proper gears by the appropriate method for that machine. My lathe can cut far more thread pitches than the chart shows. I can easily get a 27 TPI for Star punches even though it is show nowhere in the documentation for the lathe.

The simplest way I can describe it is that the headstock gearing regulates the relationship between linear motion of the carriage for each rotation of the spindle. If it moves 1 inch for every 14 rotations you get a 14 TPI thread.

Once you see the process live it becomes very simple.
 
#32
Ian,
Thank You
COOL BEANS! I enjoyed it like it was "Netflix" I just love to learn about this stuff!
Many years ago I had a job in a factory I was a spot welder. I used to spend 2/3's of my lunch hour in their machine shop every day. Never got to do anything except design some of my copper welding dies and watch them as they ran them. But I loved looking over their shoulders.
Now; So Little Time yet so much to learn! I appreciate it
 
#34
Mr Pete has some classes set up on flash drive. I got one last year, and still watch it over and over.
I looked around here about some vocational night class refresher courses, nothing. He is a good teacher.
 

Ian

Well-Known Member
#38
One extra about Tubalcain's video, he hinted at but did not fully discuss thread fit. He used a nut for demonstration purposes, and si ce we are often making one-off things that only have to fit one other, that can be ok.....but making threads to fall within the tolerance of a certain class of fit is more of a challenge. For example, threading a rifle muzzle for a standard fit class so it will accept any commercial muzzle device. The usual method of measuring outside threads employs pitch wires, a chart, and C-clamp micrometer. That way, KeithB (who probably owns and uses an expensive but much faster thread micrometer) can make 7/8x14 die blanks that will fit your press, my press, or anyone else's with the correct amount of clearance. Having a way to measure thread pitch accurately, before removing the part from the lathe and losing all the timing and alignment, is crucial. Joe Pie has a good video on using pitch wires, together with a small rant about never relying on a production nut as a thread standard.
 

KeithB

Resident Half Fast Machinist
#39
We have two thread mikes, a 0-1" and a 1"-2", along with one set of interchangeable anvils. Both are SPI and as I recall were a around $100 each. Probably a little expensive for a hobbyist but again, time is money and spending five minutes to diddle around with thread wires and look in a table to determine parameters every time we need to measure a screw is too much under production circumstances. We do use thread wires the few times we cut any thread over 2", which has been exactly twice in the last ten years.

Threads are interesting in that once a thread form (shape, as in 60* V or 29* ACME) and thread pitch (the distance from a point on one thread to the same point measured axially to the next thread) is specified everything else can easily be calculated. Doesn't matter if the screw size is 4" in diameter or 1" in diameter, if it has 16 threads per inch the thread size is (virtually) identical.

One of the sweet features of a CNC lathe is that any thread pitch can be cut, the pitch is simply specified as a feed rate in whichever canned threading cycle you choose to use. Want a different pitch? Just change the numbers, not the gears. One of the major costs in making mechanical lathes is the cost of the precision gearset needed for universal thread cutting. A CNC lathe uses sensors on the carriage and spindle and a computer program to read the code and drive the motors. Far cheaper than 24-36 precision cut gears in a complex gearcase.

Our Haas lathe even has a canned cycle to cut tapered threads such as those on pipe. WIth CNC it's all numbers...