# Threading tool helix angle



## Martin22250 (May 7, 2017)

I'm new to the hobby, and grind my own hss tools for my lathe work. I grind my threading tool with no helix angle, maybe that's the wrong term?  Just a 60 degree angle, I've read and seen you tube videos of helix angle grinds on the tools. I haven’t did less than 16 tpi yet on my lathe and my threading seems to work fine, just curious how many hobbyists are grinding helix angles on their tools.


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## Karl_T (May 7, 2017)

Do you mean bottom rake angle?

I put ten degrees on the left, zero on the right.  For left hand threads, do just the opposite.


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## Martin22250 (May 7, 2017)

I guess that's what I'm talking about, I thought it was called helix angle, that's why I'm asking cause doing a fine thread compared to a course thread would change the grind angle. I haven't put any angle on my tool and it seems to work fine just curious if I should be doing it


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## Karl_T (May 7, 2017)

Ya, I'm not sure of the term either. Might be called a relief angle.

At any rate, the thread is at an angle on the part, I'd call that the helix angle, and the tool should not rub on it. Ten degree would be way more than ever needed.


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## 4GSR (May 7, 2017)

I haven't ground a threading tool in many years with the inserted tooling I use now days.  About 7 to 10 degrees is about right, generally did this on both sides.  That way if I had to cut a left hand lead thread, I didn't have to grind another cutter.  The only time you have to worry about heliex angle having an effect on threading is cutting multi-start threads and very coarse threads on smaller diameters.  Such as 3/4" 5 Acme or similar.  Ken


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## tertiaryjim (May 8, 2017)

Martin It's helix angle plus relief angle for the leading edge of the tool.
Relief depends on the material and is usually 4 to 6 deg. Can be less for hard materials or more for soft materials
if you want to check the charts.
Helix angle "increases" as the number of threads per unit, metric or inch, "decreases".
I use a total clearance that will allow me to thread 40 to 12 TPI on most pre-made tools but when it comes to 
special projects or very coarse threads like acme I make a tool by the formulas for that one.
Over time you'll build a lot of threading and special tools so they will be on the shelf when you need em.
I find it easyer to do the math and then grind a number of tools with the same setup so there's sharp ones in the 
box ready to go.


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## mikey (May 8, 2017)

[QUOTE="Martin22250, post: 484403, member: 44966"... just curious how many hobbyists are grinding helix angles on their tools.[/QUOTE]

I don't grind a helix angle on my threading tools and haven't had a problem.


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## Tozguy (May 8, 2017)

I grind enough relief on the side of the tool to account for the helix angle plus some. It is good to be aware of the helix angle of the thread being cut in case it becomes a factor.


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## epanzella (May 8, 2017)

I cut enough relief on both sides to thread either way. I have not yet needed to thread anything less than 13TPI. So there's that.


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## Wreck™Wreck (May 10, 2017)

The helix angle changes with diameter, roughly a right angle triangle.
The adjacent side is the circumference, the opposite side is the lead, the adjacent/hypotenuse angle is the helix angle.


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## mikey (May 10, 2017)

Wreck™Wreck said:


> The helix angle changes with diameter, roughly a right angle triangle.
> The adjacent side is the circumference, the opposite side is the lead, the adjacent/hypotenuse angle is the helix angle.



So, Wreck, do you think trying to grind a HSS tool to accommodate the helix angle has value? Have you done this or even heard of it being done in your shop? 

You do remember HSS tooling, right? It tends to be sort of shiny and squarish-looking and you don't screw anything onto it ...


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## Wreck™Wreck (May 10, 2017)

mikey said:


> So, Wreck, do you think trying to grind a HSS tool to accommodate the helix angle has value? Have you done this or even heard of it being done in your shop?
> 
> You do remember HSS tooling, right? It tends to be sort of shiny and squarish-looking and you don't screw anything onto it ...


As long as the bottom of the tool clears the flank of the thread then all is good, recently had to grind a bevel on the bottom of Acme internal inserts to clear the helix angle on 1 1/2-4  internal threads.
Yes I am quite aware of what HSS tooling is as the occasional form tool must be ground.

I see no advantage to grinding a tool edge at a more acute angle then required this just makes it weaker, keep the angles to the minimum.

Edit: PVC may be turned using very sharp tools with high angles in my experience. Did 20 parts 2 weeks ago in a polyester round material with the Trademarked name Tecapet and the chips were a mess, could not get them to break. 
https://www.ensinger-inc.com/products.cfm?page=product&product=tecapet+pet


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## mikey (May 10, 2017)

Wreck™Wreck said:


> As long as the bottom of the tool clears the flank of the thread then all is good, recently had to grind a bevel on the bottom of Acme internal inserts to clear the helix angle on 1 1/2-4  internal threads.
> Yes I am quite aware of what HSS tooling is as the occasional form tool must be ground.



Okay, thanks, that's what I thought as well.

You do know I was messing with you, right?


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## Wreck™Wreck (May 11, 2017)

mikey said:


> You do know I was messing with you, right?



Indeed I do.

Have to make 5 parts today with 7/16-12 threads for a Customers antique furniture restoration project, I will just have to wing it and see if it sticks.
There is no thread data available that I can find using the usual sources.


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## Rustrp (May 11, 2017)

Wreck™Wreck said:


> The helix angle changes with diameter, roughly a right angle triangle.
> The adjacent side is the circumference, the opposite side is the lead, the adjacent/hypotenuse angle is the helix angle.


Just about the time I think I have this thing lassoed someone changes things up. My understanding is the angle increases as the TPI decreases and this would be true on standard bolts and threads we use daily, so the larger the diameter, the greater the angle, but a 1 1/2" dia. with a fine thread (I'll say 20 tpi) would have a Helix angle much less than the standard 1 1/2" UNF.  I'm just looking for clarity when you commented on diameter. 

To throw something additional into the mix; How does the compound angle play into this? If the tool is ground to 60° and the compound is set at 29° for right hand or 31° for a left hand thread, how does the helix angle come into play if I'm advancing my compound for the depth of cut?


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## benmychree (May 11, 2017)

Wreck™Wreck said:


> Indeed I do.
> 
> Have to make 5 parts today with 7/16-12 threads for a Customers antique furniture restoration project, I will just have to wing it and see if it sticks.
> There is no thread data available that I can find using the usual sources.


No data available?  Machinery's handbook is a resource for such info, they have a section for threads of a certain pitch, such as 12 in many different diameters.


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## benmychree (May 11, 2017)

Another cure for this "problem" besides inserts, which tend to be expensive and easily chipped and broken is the threading tools made by Aloris, which bolt to the front face of the holder and are adjustable for helix angle and are sharpened ONLY on the top surface; they are made in several ranges of pitch (with more or less flat on the root portion of the tool, and also in several pitches of Acme thread and can be reground on the root portion for in between pitches.  I have used them for many years; they may not be cheap, but they last many years.  Also they may be reversed in their holder and used for cutting upside down with reverse lathe rotation; this is sometimes desirable when cutting a thread against a shoulder.


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## Dinosaur Engineer (May 11, 2017)

The only time the thread helix angle becomes an issue is when cutting really coarse threads or multi-start threads.  The cheapest easy way to get around this problem is to grind the HSS tool from round stock and then to turn the tool to the helix angle.  The 60 deg point angle is affected to a very small degree but for most applications this effect on the angle is insignificant.


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## benmychree (May 11, 2017)

Dinosaur Engineer said:


> The only time the thread helix angle becomes an issue is when cutting really coarse threads or multi-start threads.  The cheapest easy way to get around this problem is to grind the HSS tool from round stock and then to turn the tool to the helix angle.  The 60 deg point angle is affected to a very small degree but for most applications this effect on the angle is insignificant.


I have seen this done on tools from the now defunct Mare Island Navy Yard machine shops; they had a special  tool holder that was used with a lantern type tool post to hold the round tools.


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## Wreck™Wreck (May 11, 2017)

benmychree said:


> No data available?  Machinery's handbook is a resource for such info, they have a section for threads of a certain pitch, such as 12 in many different diameters.


Yes, I own a MH, the shop where I am currently employed has 3 different editions and none contain this data even in the special threads section.
The sample is likely well over 100 years old and somewhat damaged too boot, the parts were delivered today if they do not bounce it will be a miracle, I also have no idea what they do as usual.


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## T Bredehoft (May 11, 2017)

Early in my apprenticeship I made a block to hold a 3/8 HHS tool for grinding (on a surface grinder) a 60º threading tool. It had built into it 7º relief under each side of the cutting surface. This was to clear the flank of the cut thread. My toolmaker (mentor)  had instructed me to study the Handbook to determine the angles.  I do not remember how I arrived at the 7º angle, but it never failed me. I still have the block, but no longer have access to a surface grinder.


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## Tozguy (May 11, 2017)

Rustrp said:


> Just about the time I think I have this thing lassoed someone changes things up. My understanding is the angle increases as the TPI decreases and this would be true on standard bolts and threads we use daily, so the larger the diameter, the greater the angle, but a 1 1/2" dia. with a fine thread (I'll say 20 tpi) would have a Helix angle much less than the standard 1 1/2" UNF.  I'm just looking for clarity when you commented on diameter.



To my mind the helix angle increases as TPI decreases for a given diameter. 
But for a given TPI the helix angle decreases as diameter increases.


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## benmychree (May 11, 2017)

Wreck™Wreck said:


> Yes, I own a MH, the shop where I am currently employed has 3 different editions and none contain this data even in the special threads section.
> The sample is likely well over 100 years old and somewhat damaged too boot, the parts were delivered today if they do not bounce it will be a miracle, I also have no idea what they do as usual.


I stand corrected; MH does not list a pitch diameter for this small of a screw with 12 pitch, however one could go by the table of thread depth  (.07217" ) for a sharp V thread tool; turn a small neck on the part to diameter minus twice the depth and thread until the point of the tool touches the necked diameter.


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## Wreck™Wreck (May 11, 2017)

Rustrp said:


> Just about the time I think I have this thing lassoed someone changes things up. My understanding is the angle increases as the TPI decreases and this would be true on standard bolts and threads we use daily, so the larger the diameter, the greater the angle, but a 1 1/2" dia. with a fine thread (I'll say 20 tpi) would have a Helix angle much less than the standard 1 1/2" UNF.  I'm just looking for clarity when you commented on diameter.
> 
> To throw something additional into the mix; How does the compound angle play into this? If the tool is ground to 60° and the compound is set at 29° for right hand or 31° for a left hand thread, how does the helix angle come into play if I'm advancing my compound for the depth of cut?


The angle of the compound on a lathe is meaningless for this conversation and its use is not required when threading regardless of what UTube how-to videos will tell you.
A thread is an inclined plane like a ramp or roof, helix angle is a function of lead and circumference therefore a 3/8"-16 thread has a far more acute helix angle then a 3"-16 thread as seen here with 4 TPI threads.
As mentioned above this will likely only become a problem with very course or trapezoidal threads


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## Rustrp (May 11, 2017)

Wreck™Wreck said:


> The angle of the compound on a lathe is meaningless for this conversation and its use is not required when threading regardless of what UTube how-to videos will tell you.
> A thread is an inclined plane like a ramp or roof, helix angle is a function of lead and circumference therefore a 3/8"-16 thread has a far more acute helix angle then a 3"-16 thread as seen here with 4 TPI threads.
> As mentioned above this will likely only become a problem with very course or trapezoidal threads


I understand this part and I'm not going off of YouTube. When you mentioned diameter increase increases helix angle increase it seemed as if you were excluding tpi. When I look at this I am looking at a side view of the thread and using the axis as a reference. I'm sure I will probably never cut a thread where helix angle becomes an issue. My comment regarding the compound was in reference to which cutting edge of the tool is doing the cutting. I'm also looking at this from my reference which is bending sheetmetal. When I'm forming a complicated piece for a hip or valley of a roof, what I'm seeing isn't always what is. 
What I do understand is helix angle is a standard and when we make parts for others it becomes important, especially in larger diameters.


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## benmychree (May 11, 2017)

Wreck™Wreck said:


> The angle of the compound on a lathe is meaningless for this conversation and its use is not required when threading regardless of what UTube how-to videos will tell you.
> A thread is an inclined plane like a ramp or roof, helix angle is a function of lead and circumference therefore a 3/8"-16 thread has a far more acute helix angle then a 3"-16 thread as seen here with 4 TPI threads.
> As mentioned above this will likely only become a problem with very course or trapezoidal threads


I was not using compound depth of cut; the table in MH is about depth of cut (straight in) not the distance the compound is fed inwards; this is why I suggested turning a short neck onto the screw to a size double the amount stated subtracted from the nominal diameter, and feeding in with the compound until the sharp point of the tool hits the turned down portion, the compound only supplying the means of feeding into the cut.  Incidentally, I have never used the 29/31 degree setting for the compound, always setting to 30 degrees off straight in.  I do not know of a single journeyman in my apprenticeship shop who used the one degree difference in threading, and I was taught machine work by a shop teacher who was an apprenticeship instructor at Mare Island Navy yard and had apprenticed there himself.
I do not like chips being generated on both sides of the cut; the interference of each chip with the other can lead to galling


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## Wreck™Wreck (May 11, 2017)

Rustrp said:


> I understand this part and I'm not going off of YouTube. When you mentioned diameter increase increases helix angle increase it seemed as if you were excluding tpi. When I look at this I am looking at a side view of the thread and using the axis as a reference. I'm sure I will probably never cut a thread where helix angle becomes an issue. My comment regarding the compound was in reference to which cutting edge of the tool is doing the cutting. I'm also looking at this from my reference which is bending sheetmetal. When I'm forming a complicated piece for a hip or valley of a roof, what I'm seeing isn't always what is.
> What I do understand is helix angle is a standard and when we make parts for others it becomes important, especially in larger diameters.


The helix angle is dependent on the diameter and lead where it is fixed, it is not STANDARD
I never use TPI when discussing threads with anyone, only lead, they are not always the same.

A 16 TPI  thread is 1 divided by 16 or .0625" lead so one trip around a 1" diameter bar during threading  is 3.141 inches per revolution X  16 times per inch or roughly 50 inches of cut length.

A 2" bar threaded 16 TPI is 2 X Pi X 16 revolutions per inch or 6.2 inches per revolution X 16 per inch = roughly 99", you have traveled the same distance in one plane yet have traveled nearly twice a far in another.


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## benmychree (May 12, 2017)

benmychree said:


> I stand corrected; MH does not list a pitch diameter for this small of a screw with 12 pitch, however one could go by the table of thread depth  (.07217" ) for a sharp V thread tool; turn a small neck on the part to diameter minus twice the depth and thread until the point of the tool touches the necked diameter.


I had a further thought on the 7/16 - 12 thread pitch; as disclosed above, MH does not list this diameter in the 12 pitch series, but what is to stop one from using the pitch diameter from a larger size of the same pitch and deducting the difference in diameter from a larger size thread, such as deducting .1875" from the pitch diameter of  a 5/8-12; .5709 minus .1875 = .3843 PD for a 7/16-12 thread, although, without a calculator at hand, check my subtraction skills!


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