BXA toolholder, why dog point screws?

[Bill D]

I have several BXA tool holders. I notice the cheap, made in China, ones have dog point set screws to hold the tooling into the slots. the USA made ones tend to use flat ended screws. Is there any advantage to the dogpoint screws I am not seeing? They do hold smaller diameter boring bars down and into the slot differently then a flat screw tip. I am not sure which is a better method.
I thought dogpoint screws cost more to buy so I do not see it as saving money.
Bill D

 

[Milland]

They'll take more "smushing" before becoming larger than the minor diameter of the thread, meaning they can be removed even after some damage.

 

[CalG]

The Original just might use hardened screws from unbrako etc.

Hard screws just might not Mush out like the imports ....

Just a thought.

 

[EPAIII]

Inexpensive holder manufacturers may save money by using low grade, unhardened set screws. These can mushroom at the tip, making them irremovable. Ask me how I know.

There are two ways to fight this. One is to use high grade, hardened set screws, which cost more. The other is to use the dog point set screws: the dog point mushrooms and the thread, which is further back does not - at least not right away. I am sure a Chinese manufacturer can buy the dog point set screws at very low prices if they get them in hundreds of thousands.

Buy and use grade 8 or the metric equivalent set screws and you will be OK.

 

[PegroProX440]

It seems like the word dog is used in a few instances in the machining world and I have no idea of the meaning other than the animal. Dog screw, lathe dog, stop dog on a surface grinder. What is a dog?

 

[gregormarwick]

Dog point screws are common on premium holders for cnc lathes, especially VDI tooling.

Rather than cost, it's likely that Chinese manufacturers are emulating that.

 

[Milland]

It seems like the word dog is used in a few instances in the machining world and I have no idea of the meaning other than the animal. Dog screw, lathe dog, stop dog on a surface grinder. What is a dog?

Otherwise know as canids, dogs...

OK, in this context a dog point is a cylindrical tip on the end of the screw, with a diameter smaller than the minor diameter of the thread itself, and of some length (i.e. not very short). I don't know if there's an official standard for the length, but they'll be roughly 50 to 100 percent of the thread OD.

Some examples from McMaster: McMaster-Carr

 

[Nmbmxer]

I got a dozen oversized CXA holders from aliexpress for my home shop and they have dog point set screws. If you put a 1" tool in the 1" slot there are two threads engaged on the set screws, you can't actually tighten the tool in place. But at $20 / holder it's easy to afford a box of high quality flat tip set screws.

 

[henrya]

I’ve replaced all the screws in the budget holders with quality U.S. made screws. Huge improvement for very little money.

 

[Mike1974]

It seems like the word dog is used in a few instances in the machining world and I have no idea of the meaning other than the animal. Dog screw, lathe dog, stop dog on a surface grinder. What is a dog?

Interesting question, I don't know either? I worked at a stamping place that had two roll forms and we called the catch mechanism in the die a "dog" too.

 

[Bill D]

Mushing out the tip makes sense. The full flat end is better for smaller tools that do not fill the slot depth. If I put in a small shank tool the dog point grabs the outer edge of the shank not the top.
I will have to look and see on my oversized holders if they are dog point or not and,how much thread is engaged for full size shanks.
Bill D

 

[M.B. Naegle]

Interesting question, I don't know either? I worked at a stamping place that had two roll forms and we called the catch mechanism in the die a "dog" too.

Dog (engineering) - Wikipedia

So essentially a "Dog" keeps things from moving. Dog point screws I think were originally made to engage a slot or counter-bore of a part on the other side, kinda like an adjustable key. I think the lathe "Dog" gets its name because without it the shaft would spin independently on the centers.

 

[Gordon Heaton]

In machine-tool language, a 'dog' generally refers to a nub, stub or other projection designed to 'catch' or hold some other part, or cause two or more parts to move together without positive fastening between the parts.

 

[dsergison]

Why do you think "generic import manufacturer" consciously decided dog points were better?
Why do you think they put any thought into their hardware selection besides that it fits?
Why do you think you know which hardware type costs them more?
Maybe their uncle has a screw shop just down the road and was already making millions of dog point screws.

What a silly question.

 

[Frank Ford]

I've replaced a number of the cheesy tool holder set screws with regular USA hex cap screws. Is there any reason to use set screws?

 

[M.B. Naegle]

I've replaced a number of the cheesy tool holder set screws with regular USA hex cap screws. Is there any reason to use set screws?

less stuff for chips to tangle into

 

[Gordon Heaton]

. . .is there any reason to use set screws?

Yes. With some designs, the height adjusting thumbwheel would interfere with a hex-head bolt while an allen wrench will still pass the wheel for tightening. Not a factor if all you use are the two outside screws.

 

[EPAIII]

NO.

My design QC tool post. As you can see, I used SHCSs. The stainless ones in this early photo had rounded ends (more below) but they were softer than HSS so they mushroomed. I removed then before they became so big that taking them out would enlarge the tapped holes. The stainless looks nice, but I replaced then with high grade, black oxide cap screws. The cap screws are hardened and work just fine.

On the tips of the screws: I gave it some thought. Cap screws usually come with ends that are the result of the rolling process that produces the threads. Normally nothing is done to them after that so the ends are somewhat irregular. I did not like that as it might move the tool bit as it was being tightened. While a flat, dog point may be the ideal tip, it would be hard to make in my small shop. So I choose a tip that provided contact at a centered point but was somewhat broad. This was a rounded tip with a large radius. I made these tips by first putting a chamfer on the screws and then working them on cloth backed sand paper that was backed up with multiple layers of soft cloth so it had some give. A few dozen strokes while rotating the screw in my hand produced a nice, large radius curve. And the high point was in the center so it did not have much tendency to move the tool bit as the screw was tightened.

The only advantage that I can think of for the set screws is that they take up less space so more holders can be stored in a smaller space. That does not make much difference with my holder design as they are somewhat large anyway. A definite advantage to the SHCSs is that the Allen socket will be larger than that on a set screw of the same thread size so it will last longer with use. I don't know how many set screws I have had to replace because the Allen socket either wore round or that area just split apart.

If you are curious about my shop made, QC tool post, which I believe has significant advantages, you can get the plans here:

Quick Change Tool Post for Lathe - HomemadeTools.net

I've replaced a number of the cheesy tool holder set screws with regular USA hex cap screws. Is there any reason to use set screws?

 

[EPAIII]

I think that cost is always a consideration for the Chinese manufacturers. It is how they beat us out of business. But I was not arguing that cost was the reason for the dog point. I was trying to say that the cost would be about the same for them no matter what tip was on the set screw.

Now, is it a well thought out design choice or are they just copying the better brands? I don't really know. Perhaps I was giving them too much credit. But, for a set screw, the dog point is probably the best choice.

What I was saying is that they purchase/use set screws that are not hardened and this would be a cost saver for them as it is an extra step that does not have to be performed. Time is money, even in China. And this is problematic no matter what the tip shape is.

Dog point screws are common on premium holders for cnc lathes, especially VDI tooling.

Rather than cost, it's likely that Chinese manufacturers are emulating that.

 

[michiganbuck]

They, the ones with a flat nose can apply pressure with not so much chewing the mating part. some times they fit into a slot or recess for a locator... they don't mush and then get stick in a hole/thread.

Qt: [ Is there any reason to use set screws?] just to clear the out surface from having any protrusions..And where needed a double set screw is a locking thread.