Shopsmith Forums

That was a very interesting video, John. I’ve studied chuck drawings before and understood the general idea, but watching that physical cut-away chuck being operated definitely improved my understanding.

As for the three-hole tightening sequence, I’m in JPG’s camp. The first time I heard that advice, I went and tested it on my own Jacobs chuck. If I used just one hole and tightened it as much as I could with the key, I had previously thought that I was finished. But lo and behold, when I moved the chuck key to the next hole, I could tighten it a little bit more. And then when I moved it to the third hole, I could tighten it just a tiny bit more. After the third hole, any further attempts didn’t move the sleeve.

So why is that? After thinking about it for a while, I think it comes down to friction. So the following probably isn’t material to bearing-type chucks, and it certainly wouldn’t apply to keyless chucks.

The thing is, when you tighten a keyed chuck, the key isn’t applying a pure torque to the chuck sleeve. Instead, it’s applying a linear force to it, that’s roughly tangent to the sleeve. So you get torque on the sleeve, but you also get a large linear force that presses the sleeve tightly against the chuck body. And friction from that force will oppose the rotation of the sleeve.

So why does the three-hole technique allow you to get it tighter? My theory is that the sliding tolerances between the sleeve and the chuck body allow the sleeve to cock just a fuzz, and possibly the split nut and jaws as well. But when you move the key on to a different hole, the direction of that tangential force changes, things cock just a bit differently, and you so can get a little more rotation of the sleeve, without applying greater force.

As a thought experiment, if you tightened a chuck with three keys and equal force simultaneously, the linear forces would cancel, and you’d get a pure torque on the chuck, without the friction from an offset linear force. That would be ideal. But tightening from each hole progressively gets you closer to that ideal result.

Well, how come when you 'go around the three holes the sleeve rotates a little more that diminishes each time.

I TOTALLY disagree with the second statement re keyless chucks. They simply do not grip as tightly as a properly tightened keyed chuck.

I consider keyless chucks to be acceptable for flatted shanks only.

How many of have experienced the drill bit slipping and having the shank getting boogered up?

Correct tightening prevents that.


Old Wives tale? Pay attention to the voices of informed experience.





Maybe I have never encountered a GOOD keyless chuck. Lord knows I have encountered crappy keyed chucks.

I couldn't bring myself to watch the entire video. Is there a time point in the video where he discusses why a keyed chuck doesn't need to be snugged up on all 3 holes? I only have anecdotal experience, but would have to agree with Dennis and JPG here. I can feel in my hands when the 2nd location is tightened, but on the 3rd hole I can't perceive it moving more though it could still be moving. Of course, just because the key is turning a little in the 2nd position doesn't necessarily mean the internals are moving necessarily, e.g. it could just be tightening the outer collar while the internals are already tight.

RFGuy wrote: ↑Wed Jan 27, 2021 9:19 am ...Is there a time point in the video where he discusses why a keyed chuck doesn't need to be snugged up on all 3 holes? ...

No. He never discusses it. The three hole sequence is how I learned as a kid. I know it works, don't necessarily know why but I like Dennis' logic. I worked in metals back then, which I think results in greater torque at the jaw/bit interface, and have no doubt that it is getting tighter internally as you sequence through.

- David

If you do not detect movement at the second/third hole, you likely are not applying sufficient torque to the key.

There is no question that increased movement of tapered parts will impart greater force normal to the taper. i.e. more squeeze from the split collar creates greater holding force on the shank.

Friction is at work both when tightening and when holding. The ball bearing versions reduce one source of friction(sleeve to body).

Those who do not believe all this are like those who dis SS!

I find I only ever do two holes on the shopsmith chucks I have. I got the two holes from both HS shop and my training at a machine shop. SOP.

I think a lot of the three hole advice came from older less precise chucks. I have an old hand drill and that one really needs the three hole to work right, well to be honest that is even a little weak and a forth hole(repeat of one of the holes) is needed for metal drilling. I guess I could, make that should have replaced it years ago but I don't really use the drill very often. Besides it would be some effort to find a correct replacement.

At least the battery drills I have all use the key-less design and work very well. I have not sprung for the shopsmith version and don't think I will unless they have a half off sale..... then someone let me know and I'll get one to test.

Ed

The Shopsmith keyless chuck is really nice and I do prefer it over keyed chucks. Bits can and do come loose in it occasionally but it is not a regular thing for mine. I am sure I just didn't turn it enough when it does happen. I have a special order Rohm chuck that I put on my cordless drill and it is fantastic. NEVER has the Rohm keyless chuck ever come loose on me. For the Shopsmith keyless chuck it really is hard to justify unless it is on sale and you really, really want it. Coincidentally it is on sale right now. Be warned though that the Shopsmith keyless chuck weighs a ton which is the only real negative I see for it besides price. With a dedicated drill press, the weight would be less of a concern. My original keyed chuck from Shopsmith is now on a morse taper and dedicated for lathe use.

I ask myself why would the manufacturer incorporate the three holes for the key if only one would be needed. I assume adding those other two adds cost to the chuck.

WHY three holes!

Reduces the need to manually rotate so as to gain access to a hole.

Space is available for the holes between the three jaws.

And IMO lastly so as to provide a tightening force for each of the three jaws.(actually I think three position to each apply force to two jaws at a time).

Regardless rotate around until no further improvement.

JPG wrote: ↑Wed Jan 27, 2021 8:21 pm WHY three holes!

Reduces the need to manually rotate so as to gain access to a hole.

Space is available for the holes between the three jaws.

And IMO lastly so as to provide a tightening force for each of the three jaws.(actually I think three position to each apply force to two jaws at a time).

Regardless rotate around until no further improvement.

That is exactly why I think three holes. Does that not contradict your reason for using all three holes?

I am sorry, I just don't understand this. The rotational force on the sleeve rotates the internal nut that is threaded to the jaws. Everything moves together. Please explain from a mechanical engineering point how it makes a difference by using different holes.
Buckeye has a theory that may be relevant but does it really make a difference at the end of the day?

It seems to me it is like using an open end wrench on a nut and saying you have to put the wrench on all 3 pairs of flats to get the nut tight.