Lots of good info on here about threading on a lathe. I bought an indexable type threading insert holder and inserts because I'm too lazy to grind HSS threading bits. However, I haven't seen anything on the depth of cut when threading? I saw a video where they turned the RPM down as low as it would go and took dozens of passes at a few thousandths DOC each pass. That seems pretty tedious, is that a good habit to use? Maybe just while learning?. I'm trying to thread low carbon steel. A36 and 1018. Anywhere from 5/16" to 1". Tom Lipton recommends taking a large DOC for the first pass, but he doesn't mention what it should be. Oh and it's a manual lathe.
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DOC for Thread Cutting
- Thread starter Econdron
- Start date
- Replies 66
- Views 10,539
you don't need to go as slow as it will go, go as fast as you are quick.
first pass? 15 thou or so? as you progress the width of the cut increases obviously which is the basis of larger doc at the beginning.
I've had better luck with very sharp hss at slower speeds
first pass? 15 thou or so? as you progress the width of the cut increases obviously which is the basis of larger doc at the beginning.
I've had better luck with very sharp hss at slower speeds
jrmach
Titanium
- Joined
- Jun 9, 2012
- Location
- Boise,Idaho USA
200 to 300 RPM
Dial in with the compound
.015
then 1/2 of that
then 1/2 of that
etc.
This is ball park for 1018 1/2-20,lots of things will affect the variables,(including your reflexes)practice,practice
Dial in with the compound
.015
then 1/2 of that
then 1/2 of that
etc.
This is ball park for 1018 1/2-20,lots of things will affect the variables,(including your reflexes)practice,practice
oldbikerdude37
Titanium
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- Jun 29, 2010
- Location
- milton freewater oregon
On a big thread 2 TPI take a good bite first pass .100" or more.
Smaller threads 2-4 passes to completion. you dont have to take a dozen passes.
Smaller threads 2-4 passes to completion. you dont have to take a dozen passes.
edwin dirnbeck
Hot Rolled
- Joined
- Oct 24, 2013
- Location
- st,louis mo
Whaaaat 2-4 PASSES ? I have been earning a very good living mostly running a lathe for 50 years in high pressure jobshops .I have NEVER SEEN OR HEARD of anyone single pointing a thread in 2 or 4 passes period. Has anyone else done this? Edwin Dirnbeck
ewlsey
Diamond
- Joined
- Jul 14, 2009
- Location
- Peoria, IL
In CNC land, I start with 20-30% of the thread depth with the first pass. The control then reduces the DOC to keep the chip load the same. I would try to avoid taking a cut less than .002 on a side. I think a 16 TPI thread is about 8 passes on my CNC.
jrmach
Titanium
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- Jun 9, 2012
- Location
- Boise,Idaho USA
Let me think,Today I did 10 pieces 1/2-20 303 SS,,,,,,,,,,,6 passes
Mike C.
Diamond
- Joined
- Nov 25, 2004
- Location
- Birmingham, AL
"I would rather take smaller DOC and get the part done. Then chip the tip off and now its embed in the thread causing me more time then if i just took smaller DOC's. That sucks."
The precise reason I use HSS threading tools. I hate carbide threading inserts.
As for depth of cut, I like to start .010 or so on fine threads (anything under 10tpi) and do 10, 10, 10, 7.5, 7.5, .5, .5, .3, .3 or similar until full thread. You have to juggle depending on thread depth. As for how deep to cut the thread, I found the magic wand right here on this forum, but can't remember the exact topic thread... if you feed with the compound t 29.5 degrees, .75 divided by TPI. Works like a charm.
The precise reason I use HSS threading tools. I hate carbide threading inserts.
As for depth of cut, I like to start .010 or so on fine threads (anything under 10tpi) and do 10, 10, 10, 7.5, 7.5, .5, .5, .3, .3 or similar until full thread. You have to juggle depending on thread depth. As for how deep to cut the thread, I found the magic wand right here on this forum, but can't remember the exact topic thread... if you feed with the compound t 29.5 degrees, .75 divided by TPI. Works like a charm.
Mike C.
Diamond
- Joined
- Nov 25, 2004
- Location
- Birmingham, AL
EPAIII
Diamond
- Joined
- Nov 23, 2003
- Location
- Beaumont, TX, USA
The depth of your starting cut depends on several factors. Thread TPI, size of your lathe, your skill and confidence level, and the material you are cutting.
If you are cutting 4 TPI on a lathe with a 3 or 5 HP motor, then you can take a very big first cut, 0.050", 0.075" or even more. You should know what your lathe and tooling is capable of. If you are cutting 72 TPI on a lathe with a fractional HP motor, then you better start with a lot less: A LOT LESS, 0.005" may be too much.
And the material and your skill level are factored in too. If you are just starting I would try using easy to thread materials like free cutting brass or leaded steel. Start easy so you can get used to the process. Then pick up speed.
On speeds, the big problem is not cutting the thread, you can thread as fast as any other cut. It is stopping at the end of the thread without running into some other feature of the part. The time honored method on a manual lathe is to have one hand on the cross feed knob and the other on the lever for the half nuts. When you SEE that you are about to reach the end of the thread, you simultaneously disengage the half nut and QUICKLY back the cutting tool out far enough to clear the OD. I usually back out approximately one turn. This assumes that you have a functioning threading dial. If not, then you have to stop the spindle, but it will coast a bit so timing is even more critical. Some lathes have automatic cutoff devices to end threading. I actually have a manual crank handle that I can attach to the back end of the spindle so I can go very slow on some critical threading operations. It allows me to stop exactly where I want to and to do so at exactly the same spot on each successive pass.
As you may surmise from the previous paragraph, the faster the spindle speed, the more difficult the timing will be. This is why many recommend slow speeds for threading. If you have a wide clearance area at the end of thread, you can crank up the spindle speed and threading will go a lot faster. Of course, practice makes perfect and after a lot of threading experience you can use faster speeds.
In a production situation there are other ways to cut an accurate thread quickly, like a die head on a tail stock turret. Or CNC, of course.
If you are cutting 4 TPI on a lathe with a 3 or 5 HP motor, then you can take a very big first cut, 0.050", 0.075" or even more. You should know what your lathe and tooling is capable of. If you are cutting 72 TPI on a lathe with a fractional HP motor, then you better start with a lot less: A LOT LESS, 0.005" may be too much.
And the material and your skill level are factored in too. If you are just starting I would try using easy to thread materials like free cutting brass or leaded steel. Start easy so you can get used to the process. Then pick up speed.
On speeds, the big problem is not cutting the thread, you can thread as fast as any other cut. It is stopping at the end of the thread without running into some other feature of the part. The time honored method on a manual lathe is to have one hand on the cross feed knob and the other on the lever for the half nuts. When you SEE that you are about to reach the end of the thread, you simultaneously disengage the half nut and QUICKLY back the cutting tool out far enough to clear the OD. I usually back out approximately one turn. This assumes that you have a functioning threading dial. If not, then you have to stop the spindle, but it will coast a bit so timing is even more critical. Some lathes have automatic cutoff devices to end threading. I actually have a manual crank handle that I can attach to the back end of the spindle so I can go very slow on some critical threading operations. It allows me to stop exactly where I want to and to do so at exactly the same spot on each successive pass.
As you may surmise from the previous paragraph, the faster the spindle speed, the more difficult the timing will be. This is why many recommend slow speeds for threading. If you have a wide clearance area at the end of thread, you can crank up the spindle speed and threading will go a lot faster. Of course, practice makes perfect and after a lot of threading experience you can use faster speeds.
In a production situation there are other ways to cut an accurate thread quickly, like a die head on a tail stock turret. Or CNC, of course.
jrmach
Titanium
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- Jun 9, 2012
- Location
- Boise,Idaho USA
You and my half nut would have a very short acquaintance.It would grind in submission rather that engage and go with the flow at those rpm's.
Why?
I would run it faster if it went any faster. My machines are tools. They make money. They get oiled and maintained. The lathe I cut said threads on is 63 years old and the leadscrew and half nuts look like new and drop right in at 275 leadscrew RPM.
jumpinjimmy447
Aluminum
- Joined
- Mar 18, 2013
- Location
- galt California
No I shure havent ?
jrmach
Titanium
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- Jun 9, 2012
- Location
- Boise,Idaho USA
Garwood does it in 2 passes at 1100 RPM,,,
oldbikerdude37
Titanium
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- Jun 29, 2010
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- milton freewater oregon
16 TPI is a pretty fine thread and not very deep, no need to go light and slow.
Hell yes, fuck around all day making passes is a waste of time if you are doing the same thread over and over, we dont get paid by the miles of carriage travel.
Tool wear is a factor to wear off the end .002" or the end .020" that is 10 times the tool life.
The times I go slow is when the shaft is 16 feet long and even then I will clamp a makeshift headstock side steady rest to a forklift so I can get RPM up to speed for carbide.
RPM will get some decent finish that does not look like a Chinese lag bold. Smooth side are better for gauging.
I thread closer to the way you do, make lots of smoke!
Guess I never went to musheenist school. Just some HS shop where I got to cut threads with a hand ground HSS bit at creeper speeds. Running a shop for profit, I don't understand the slow and easy concept. I've watched several friends thread at 1500+ RPM and that sure makes a lot more sense to me. They run shops, they make chips for profit and use the machines as they were intended. Trying to run carbide at HSS speeds is kinda dumb no? Especially when you're working with stainless. If you rub the death out of the shit taking eeny weeny passes it's a bitch. If you put your man pants on and make a real chip the stuff doesn't work harden. Take a finish pass or two and you're done.
With the RPM's cranked it's soooo much easier to get a nice, consistent thread.
With the RPM's cranked it's soooo much easier to get a nice, consistent thread.
Toms Wheels
Titanium
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- Dec 30, 2005
- Location
- Jersey Shore
I like the huge chunk of HSS that bolts to the tool holder on a QCTP. No profile to grind just a touchup on the top surface and its sharp again. Robust, unlike carbide with manual threading when you take a slightly deeper cut, leading to broken tip.
Looks like this ( unable to load photo)Aloris calls it a Threading blade, works great.
Looks like this ( unable to load photo)Aloris calls it a Threading blade, works great.
