Threading tool helix angle

[mikey]

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 ...

 

[Wreck™Wreck]

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

 

[mikey]

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?

 

[Wreck™Wreck]

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.

 

[Rustrp]

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?

 

[benmychree]

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.

 

[benmychree]

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.

 

[Dinosaur Engineer]

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.

 

[benmychree]

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.

 

[Wreck™Wreck]

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.