question about acme pins

[bbb]

i didnt want to side track the thread about the radial and 3/8x10 pin
but whats the difference among acme pins and non acme pins with the same numbers
also why did acme NOT become the standard?
thanks for your replies
p.s.i had a josswest that i couldnt get on my ob shafts to fit untill i found out it had an acme pin and had to get it specially tapped

 

[KJ Cues]

Here's an ACME thread. It has no business being in a cue though that's just my opinion.
It was designed for moving loads, not connecting a cue.
Why didn't it become the standard? Because it's a lousy pin for the application.

HTHs, KJ

 

[Paul Dayton]

KJ is right. It is fine on machinery where it will do the job it was meant to do.

 

[SCCues]

i didnt want to side track the thread about the radial and 3/8x10 pin
but whats the difference among acme pins and non acme pins with the same numbers
also why did acme NOT become the standard?
thanks for your replies
p.s.i had a josswest that i couldnt get on my ob shafts to fit untill i found out it had an acme pin and had to get it specially tapped

I should have read the rules before I posted this reply. Sorry.......

James

 

[SCCues]

Here's an ACME thread. It has no business being in a cue though that's just my opinion.
It was designed for moving loads, not connecting a cue.
Why didn't it become the standard? Because it's a lousy pin for the application.

HTHs, KJ

View attachment 318664

I should have read the rules before I posted this reply. Sorry.......

James

 

[cueman]

Acme threads are stronger at the top and weaker at the bottom. They are also harder to tap into wood cleanly. So there is no real advantage since the pluses are met with equal minuses. There have been a few cuemakers that used acme threads successfully. But if it was really the best I would think more cuemakers would have went to them years ago.

 

[pdcue]

Here's an ACME thread. It has no business being in a cue though that's just my opinion.
It was designed for moving loads, not connecting a cue.
Why didn't it become the standard? Because it's a lousy pin for the application.

HTHs, KJ

View attachment 318664

Exactly... but exactly the same is true of Radial pins.

So why do so many people want them - can it be just better bull$htt
in the marketing?

Consider this - they invented a new name to mask the fact it is a
ball screw and not a connector.

Dale

 

[Renegade_56]

Exactly... but exactly the same is true of Radial pins.

So why do so many people want them - can it be just better bull$htt
in the marketing?

Consider this - they invented a new name to mask the fact it is a
ball screw and not a connector.

Dale

To take Dales post a bit further, acme screws are workhorses for pulling and pushing, not tightening. Same is true with Radial (ballscrew threads found in most CNC precision machinery) and is actually designed for use with a loaded pressure on the actual following part that is usually loaded all the way around with precision ball bearings that creates very precise motion, but generally if you torque them in the application they were designed for you likely over travelled your machine tool. If you used them for a pool cue joint you worked harder than you needed to for a lessor result.

Neither can work as well as a 3/8-10.

 

[3kushn]

To take Dales post a bit further, acme screws are workhorses for pulling and pushing, not tightening. Same is true with Radial (ballscrew threads found in most CNC precision machinery) and is actually designed for use with a loaded pressure on the actual following part that is usually loaded all the way around with precision ball bearings that creates very precise motion, but generally if you torque them in the application they were designed for you likely over travelled your machine tool. If you used them for a pool cue joint you worked harder than you needed to for a lessor result.

Neither can work as well as a 3/8-10.

Just trying to learn here. I'm a tooling and torque nerd.

I agree with the acme thread comments but why is 3/8-10 better than standard 3/8-16? Is it because you're going into wood? I can understand if that's the case, but is it better for some reason if going into a metal insert? If so, why? After all 3/8-24 can create a higher clamp load. Of course it will probably be harder to unscrew and longer time to get screwed.

 

[fERrELZ]

Just trying to learn here. I'm a tooling and torque nerd.

I agree with the acme thread comments but why is 3/8-10 better than standard 3/8-16? Is it because you're going into wood? I can understand if that's the case, but is it better for some reason if going into a metal insert? If so, why? After all 3/8-24 can create a higher clamp load. Of course it will probably be harder to unscrew and longer time to get screwed.

3/8-10 will screw together faster for a given length of pin.

You absolutely will not create a higher clamp load with a finer thread. Research it. The clamp load is a function of diameter, materials and coefficient of friction.

Finer pitch threads are less likely to back off due to vibration. Whether that matters in a cue is arguable.

 

[RBC]

Although I fully realize that the Radial pin design came directly from the ball screws commonly used in today's automated equipment, I find it hard to make comparisons between those actual ball screws and the Radial pin used in pool cues.

The one real difference that separates them is the fact that the ball nut is absent with the use of the Radial pin. Let's face it, the ball nut and ball screw work as a team to provide the very low friction, high load capacity, and zero backlash which is what makes them so good at what they do. The fact that the Radial pin, when used in a pool cue, does not have the ball nut changes everything. It now has friction all over the place so it can provide clamping force and have the friction to stay in place. A ball nut and screw could never do that because of the very low friction.

I have been privileged to have a good conversation about the Radial pin with Paul Costain, it's creator. I believe what he was after was a joint screw that would be easy for most cue makers to use and would give very good centering and alignment. The Radial fills that card completely. The female side is easy to make accurately with a tap, and the fit between the pin and the tapped hole has a tremendous amount of surface area and lines things up extremely well. Pretty much anyone with the simplest of equipment can successfully install them with great results.

The only issue I see with them is that they often come loose while playing. I believe this to be caused by poor face contact between the cue and the shaft. At least in the cases I've seen a simple facing of both sides fixes it right up. I think if he had gone with a shorter pitch (more threads per inch) this would be far less of an issue. But, then again, that would make the thread radius smaller which is the strong point of the Radial pin to start with.

Anyway, it's a good pin.


Royce Bunnell
www.obcues.com

 

[pdcue]

Just trying to learn here. I'm a tooling and torque nerd.

I agree with the acme thread comments but why is 3/8-10 better than standard 3/8-16? Is it because you're going into wood? I can understand if that's the case, but is it better for some reason if going into a metal insert? If so, why? After all 3/8-24 can create a higher clamp load. Of course it will probably be harder to unscrew and longer time to get screwed.

IIUC - it is because it threads directly into wood. Recently the trend has
been to use a phenolic "insert" due to the fact that a pin over time
eats away the threads in the shaft. This can be a real problem if the
cue is not screwed together tightly enuff.

 

[Renegade_56]

Just trying to learn here. I'm a tooling and torque nerd.

I agree with the acme thread comments but why is 3/8-10 better than standard 3/8-16? Is it because you're going into wood?

Yup, the threads have more mass though both the pitch diameter and the root diameter and so are less likely to strip out over time,

 

[pdcue]

Although I fully realize that the Radial pin design came directly from the ball screws commonly used in today's automated equipment, I find it hard to make comparisons between those actual ball screws and the Radial pin used in pool cues.

The one real difference that separates them is the fact that the ball nut is absent with the use of the Radial pin. Let's face it, the ball nut and ball screw work as a team to provide the very low friction, high load capacity, and zero backlash which is what makes them so good at what they do. The fact that the Radial pin, when used in a pool cue, does not have the ball nut changes everything. It now has friction all over the place so it can provide clamping force and have the friction to stay in place. A ball nut and screw could never do that because of the very low friction.

I have been privileged to have a good conversation about the Radial pin with Paul Costain, it's creator. I believe what he was after was a joint screw that would be easy for most cue makers to use and would give very good centering and alignment. The Radial fills that card completely. The female side is easy to make accurately with a tap, and the fit between the pin and the tapped hole has a tremendous amount of surface area and lines things up extremely well. Pretty much anyone with the simplest of equipment can successfully install them with great results.

The only issue I see with them is that they often come loose while playing. I believe this to be caused by poor face contact between the cue and the shaft. At least in the cases I've seen a simple facing of both sides fixes it right up. I think if he had gone with a shorter pitch (more threads per inch) this would be far less of an issue. But, then again, that would make the thread radius smaller which is the strong point of the Radial pin to start with.

Anyway, it's a good pin.


Royce Bunnell
www.obcues.com

If there is so much clamping force and friction, why do they back off
under load - as in 'come loose when you play pool with the cue'.

It seems to me you the can't have both at the same time.

The alignment issue is also a non-starter for me. How can it be a problem
to get the pin centered and straight unless you are building cues using
a hand drill? I've done a few on a wood lathe just for fun.

Dale

 

[fERrELZ]

Although I fully realize that the Radial pin design came directly from the ball screws commonly used in today's automated equipment, I find it hard to make comparisons between those actual ball screws and the Radial pin used in pool cues.

The one real difference that separates them is the fact that the ball nut is absent with the use of the Radial pin. Let's face it, the ball nut and ball screw work as a team to provide the very low friction, high load capacity, and zero backlash which is what makes them so good at what they do. The fact that the Radial pin, when used in a pool cue, does not have the ball nut changes everything. It now has friction all over the place so it can provide clamping force and have the friction to stay in place. A ball nut and screw could never do that because of the very low friction.

I have been privileged to have a good conversation about the Radial pin with Paul Costain, it's creator. I believe what he was after was a joint screw that would be easy for most cue makers to use and would give very good centering and alignment. The Radial fills that card completely. The female side is easy to make accurately with a tap, and the fit between the pin and the tapped hole has a tremendous amount of surface area and lines things up extremely well. Pretty much anyone with the simplest of equipment can successfully install them with great results.

The only issue I see with them is that they often come loose while playing. I believe this to be caused by poor face contact between the cue and the shaft. At least in the cases I've seen a simple facing of both sides fixes it right up. I think if he had gone with a shorter pitch (more threads per inch) this would be far less of an issue. But, then again, that would make the thread radius smaller which is the strong point of the Radial pin to start with.

Anyway, it's a good pin.


Royce Bunnell
www.obcues.com

A few things:

The radial is supposedly better because it relies on the minor diameter of the pin to align the cue. In any way, shape or form, relying on the minor diameter of the screw to align anything is a horrible idea.

The cue comes loose because the pitch of the threads is too large. End of story. Facing may help, but if it does it is unlikely it is due to more contact area. Friction force is independent of contact area. If facing is helping, it is likely because the surfaces are either cleaner or rougher.

Radial pins may be sufficient or passable, they are not good. Cues don't take much for a pin to be passable or sufficient.

Let's just be honest...any bastard pin is only a marketing gimmick for the unwashed masses to drool over. Snake oil, nothing more.

There was only one reason to ever move away from the 5/16-18 imperial standard thread: The ability to cut threads directly into wood. That's it. No other valid reason exists...unless you want to argue going to a smaller pin which would actually allow a higher clamp force if torque remains the same.

Good luck.

 

[RBC]

If there is so much clamping force and friction, why do they back off
under load - as in 'come loose when you play pool with the cue'.

It seems to me you the can't have both at the same time.

The alignment issue is also a non-starter for me. How can it be a problem
to get the pin centered and straight unless you are building cues using
a hand drill? I've done a few on a wood lathe just for fun.

Dale

Dale

What I was trying to say is that the Radial pin has much more friction and clamping force than a ball screw and ball nut, not more than other joint pins.

I have pretty much always found that if a cue is coming loose while someone is playing that facing both the butt and shaft joint faces takes care of the problem. I don't really think that it actually loosens while under the load of the impact, but more than likely as the cue flexes. My belief is that refacing the joint adds more clamped area so the problem goes away.

As for centering, I too can put a joint pin and threaded hole in the center. My Hardinge super precision CNC lathe can position to something like 5 decimal places and uses collets with less than .0004" runout. But putting the parts in the center doesn't cut it all by itself. If there is any play in the pin to insert fit, then when you joint is tightened up, it will tweak ever so slightly to one side. I've always been fascinated by this as I thought the taper of the thread would create somewhat of a "cone on a cone" and would center perfectly. I can only guess that the friction of the faces coming together causes the small gap between the pin and insert to be shifted off to one side. In any case, if I build a cue with an exact diameter and the pin in the center, and do the same with a shaft, they will not be exactly concentric when you screw them together. Sure, they are close enough for many, and you can easily sand the to to fit perfectly, but that doesn't work for me. I build hundreds of cues, meaning butts, and thousands of shafts all independent of each other. They must fit concentrically when any shaft goes on any butt. The easiest way I have found to achieve this is through the use of carbide mandrels in the sanding and finishing process. The Radial pin, because it doesn't have as much play or clearance will align much closer than the typical 14 thread pin into an insert so most cue makers find it easier to get their parts concentric. We do very well with the standard 3/8-10 joint pin. But, not everyone has the same equipment that we do.

We don't use the Radial, but I still think it's a good joint pin. Having said that, I don't think the joint pins make as much of a difference in how a cue plays as some folks seem to think.

Well, I'm off to dinner, but I'll be back tomorrow. I enjoy these discussions. I've learned many things from your posts, and I'm sure that will continue.

Have a good night!

Royce

 

[3kushn]

3/8-10 will screw together faster for a given length of pin.

You absolutely will not create a higher clamp load with a finer thread. Research it. The clamp load is a function of diameter, materials and coefficient of friction.

Finer pitch threads are less likely to back off due to vibration. Whether that matters in a cue is arguable.

That's strange. I have 2 questions.

Why is there not a higher clamp load on fine pitch vs course when recommended torque is higher and the "Tension" induced in the finer pitch screw is also higher.

From the Holo-Krome Technical Manual for Socket Head Cap Screws Grade 12.9(The first manual on file I got my fingers on)

3/8 UNRC Recommended torque is 740 in/lbs producing a tension of 8620 pounds of tension in the screw.

3/8 UNRF Recommended torque is 845 in/lbs producing a tension of 9,770pounds of tension.

I'm guessing that tension translates in some degree to clamp load. Is that wrong?

Can you also tell me how "coefficient of friction" plays a role in clamp load?

Sorry for the hijack. I get it that course is quicker and adequate for this application. Just worried since my business life revolves around properly installing bolts and controlling torque, that I may be full of crap on this topic.

 

[conetip]

3/8-10 will screw together faster for a given length of pin.

You absolutely will not create a higher clamp load with a finer thread. Research it. The clamp load is a function of diameter, materials and coefficient of friction.

Finer pitch threads are less likely to back off due to vibration. Whether that matters in a cue is arguable.

I am not sure where you got the info on clamp load to thread pitch.
But the finer pitch does give a higher clamp load for any given bolt size.
The finer pitch has a greater area for the bolt to yield , so a M12x1 bolt of the same tensile rating material. has a higher clamping capability than the M12x1.75 , but for the very same torque being applied, the 2 examples will have a very similar clamping pressure. This is because the torque is a result of friction from both that of thead and that of the head of the bolt/screw.
Clamping force can only be achieved by materials yielding ,usually within the elastic limit of the materials.
In a lot of calculations they ignore thread pitch in the formulae, but for a more precise calculations they do take into account thread pitch and thread form.
There can be combinations that negate the general rules, like washers under the screw heads, or lubricants either on the thread or on the clamping surfaces, or when a yielding washer is used between the components. The fine thread as stated will resist coming loose when subject to vibration, but in some situations, a fine thread can tighten under certain conditions and also cause a failure like a coarse thread coming loose can cause a failure.

With cues, the wood is the weakest part of the equation and the joint face materials effects the torque when assembling a cue.

Neil

 

[fERrELZ]

I am not sure where you got the info on clamp load to thread pitch.
But the finer pitch does give a higher clamp load for any given bolt size.
The finer pitch has a greater area for the bolt to yield , so a M12x1 bolt of the same tensile rating material. has a higher clamping capability than the M12x1.75 , but for the very same torque being applied, the 2 examples will have a very similar clamping pressure. This is because the torque is a result of friction from both that of thead and that of the head of the bolt/screw.
Clamping force can only be achieved by materials yielding ,usually within the elastic limit of the materials.
In a lot of calculations they ignore thread pitch in the formulae, but for a more precise calculations they do take into account thread pitch and thread form.
There can be combinations that negate the general rules, like washers under the screw heads, or lubricants either on the thread or on the clamping surfaces, or when a yielding washer is used between the components. The fine thread as stated will resist coming loose when subject to vibration, but in some situations, a fine thread can tighten under certain conditions and also cause a failure like a coarse thread coming loose can cause a failure.

With cues, the wood is the weakest part of the equation and the joint face materials effects the torque when assembling a cue.

Neil

Yes, I left out the part about the same torque being applied, thank-you for catching my inadvertent mistake. This is obviously the case in a cuestick since one only uses his hands to tighten the cue and will tighten every cue to basically the same torque.

That said, your wording that a fine thread will 'give' a higher clamp force is misleading. The finer thread will allow a higher clamp force Before Failure, achieved by applying a higher torque.

Thread pitch means very little in the calculation until the pitches compared are vastly different.

 

[fERrELZ]

That's strange. I have 2 questions.

Why is there not a higher clamp load on fine pitch vs course when recommended torque is higher and the "Tension" induced in the finer pitch screw is also higher.

From the Holo-Krome Technical Manual for Socket Head Cap Screws Grade 12.9(The first manual on file I got my fingers on)

3/8 UNRC Recommended torque is 740 in/lbs producing a tension of 8620 pounds of tension in the screw.

3/8 UNRF Recommended torque is 845 in/lbs producing a tension of 9,770pounds of tension.

I'm guessing that tension translates in some degree to clamp load. Is that wrong?

Can you also tell me how "coefficient of friction" plays a role in clamp load?

Sorry for the hijack. I get it that course is quicker and adequate for this application. Just worried since my business life revolves around properly installing bolts and controlling torque, that I may be full of crap on this topic.

Your information is good, but per Conetip, I left out the important proviso that the same torque is being applied in the situation at hand (tightening cues by hand).

Tension is pretty directly related to clamp load.

As Conetip mentions, the compression of the faces causes clamp load. What he skimmed over is that the compression forces are also translated into sliding friction, thus for a lower friction interface, the torque applied will result in higher clamp loads (and more compression of the surfaces).

I think you have a fine understanding of properly installing bolts and controlling torque. The fact that we are dealing with cues and tool-less tightening kind of switches things backwards. You likely deal with installing fasteners that are engineered to supply the correct clamp load (i.e. flanged plumbing, iron beams). These fasteners are chosen such that the clamp load and the friction between the joined members resists the slipping of the two members and no shear force is applied to the fastener (most fasteners are very poor at resisting shear loads). In the cuestick world, we start with a torque (the amount that a person can be reliably expected to apply with his hands) and end up with a screw selected by being the largest that will work.