Shopsmith Forums

All that I was referring to regarding keyed chucks WAS referring specifically to a Jacobs chuck or similar brands.

Now for the three hole/three jaw relevance.

The sleeve which the geared key rotates has a small amount of play due to the necessity for clearance.

That cocking of the sleeve caused by the single 'point' application of torque will cause the sleeve to not bear against the three jaws equally. The sleeve is threaded as are the jaws.

By tightening at all three hole locations, the pressure against all three jaw threads will be more equalized. I am sure you realize that there are also tolerances at play here.

The jaws are tapered and slide in a correspondingly tapered hole. The threads merely push the jaws into the narrower part of the taper. That sliding tapered motion is what moves the jaws closer to the center.

If the three jaws are not equidistant from the center the drill will potentially wobble and the holding pressure will not be equal on all three jaws.

Do realize the surface area of the jaws against the bit is very small. It is only by exerting substantial pressure of each jaw against the bit that the bit will not slip. If one jaw is spaced further from the center than the other two, only the two will apply that force. That allows the bit to shift towards the more distant jaw and that decreases the pressure of both the closer jaws.

Again this is somewhat academic if only wood boring with small bits is relevant. Only when larger id bits or metal drilling is involved will slipping bits occur due to NOT going all the way around.

The bottom line is, if it tightens more at each successive hole, then it is doing something useful.

Now if one is not exerting sufficient force with the key to cause movement of the sleeve, then it is moot.

Personally I go into gorilla mode when tightening bits with round shanks.

I’ve also found that sequential tightening using all three holes results in a better grip on the bit. I have a set of Forstner bits with round shafts, and if I don’t tighten sequentially, the bits are much more likely to slip. Ditto for my circle cutter, which I always use with speed reducer, cranked down to 100 RPM — that’s a whole lotta torque on tap. Like JPG, for that tool I keep sequencing until the key just doesn’t move anymore.

Why does it make a difference? I don’t know for sure, but I have a theory. When the key drives the gears on the sleeve, it’s applying both a torque and a side-load to the sleeve (unlike a keyless chuck, to which your hand will apply an almost pure torque). That side load presses the sleeve against the chuck body, generating a friction force that opposes the sleeve rotation. To the extent that this causes “binding” of the sleeve, moving on to a different key hole changes the direction of the side loading. It stands to reason that this would relieve the binding, and allow the chuck to tighten a bit more. At least that’s what it feels like to me.

Well in the machine shop where I worked the sop was two holes not three.

The other thing I should mention that everything that was 1/2" and larger were not chucked in three jaw chucks. We had only a couple of the machines that were drill presses in the sense of drill presses you are likely think of as drill presses. Most were monsters with multiple heads and bits with coolant flowing through them. Or high speed spindles running at speeds you associate with routers or faster. Even the chucks on the other drill presses were a lot higher quality then most of you have ever used.

Anyway I do believe that the chucks we have for our shopsmiths can be tighten with just two holes I see no problem with people using all three or even making a second pass around to be sure.

Shops now use bits with non round shanks, three flats is common and they are even finding there way in to home shops with hex shanks and the like. If you are having issues with bits slipping this might be another thing for you to look into.

I had some early hand chucks and found them lacking but most of the battery drills now come standard that way and the ones I'm using now I trust so progress has been made. Even the new 5/8" shopsmith sells is one of these and while I don't own one I have to assume that it works well too.

I don't think one hole is enough and I think two works well but again if you want to use 3 holes then do so. Each to their own.

Ed

I second the sinking table or rising headstock ideas, especially If you're putting a fair amount of force on the quill feed. The movement's an easy thing to miss unless you're looking for it.

There's a happy medium in setting the table and headstock locks: tight enough to hold but not too tight. I'm never sure I'm hitting it.

Thanks for all the help. It turns out that the problem is a sinking table.

As I said in the original post, I tested and eliminated that theory. But when none of the other suggestions fixed my problem, I went back to it. I realized that I had switched to a small bit and scrap pine to run that test. When I reran it with a forstner bit and a piece of oak, the table sank. (Then I realized that I could have just leaned on the table with a bit of weight and discovered the same thing. But I like to complicate things.)

So on to the next problem when I get back to the shop later this week. I suppose I could use the telescoping legs to give the table extra support. But that would be a hassle and I need to get to the root of the problem. I'll look through the manual and see if there is a way to adjust the lock on the carriage. Maybe I'll need to replace the wedges that push against the way tubes??

"89 vintage" what? 500 or later. Only the later are adjustable/subject to getting 'loose'.

JPG wrote:"89 vintage" what? 500 or later. Only the later are adjustable/subject to getting 'loose'.

It started life as a 510.

Eugenius wrote:

JPG wrote:"89 vintage" what? 500 or later. Only the later are adjustable/subject to getting 'loose'.

It started life as a 510.

Then there is a nut on the back end of the shaft that moves the wedges when the lever is 'tightened'. Adjust the nut for greater clamping force(a little goes a long way).