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Camlock spindle - what is supposed to happen?


Feb 24, 2004
Napa, CA
I have a new D1-6 camlock spindle in my lathe. I was under the impression that a chuck was supposed to pull onto the taper to center it, but that the chuck would bottom against the face of the spindle. That is how it worked on my old lathe with a D1-4. Is that how it is supposed to happen, or is it just supposed to wedge on the taper?

When I put two different chucks on it, applying maybe 15 ft lbs to the locks, there is still a .001 or .0015 gap between the back of the chuck and the face of the spindle. The runout repeatability seems poor, which is sort of what I expect under the circumstances. Am I being too wimpy with the cam locks? How much torque should be expected to pull the chuck in? On my D1-4, it didn't seem to take that much, but it was smaller and perhaps worn in.

Also I don't have a proper key for the D1-6, the key seems like an odd size. I am about to make one up. Should it have a 6" handle? 12"? 3 foot breaker bar :rolleyes5: ?
Can email the scans on the D type noses and chuck backs from ASA B5.9. A thorough study of dimensions and tolerances might give you what you are looking for.

If interested, PM me with email address.

Yes the flat face of the camlock should come tight against the flat face of the spindle. I'm not sure how much torque, I do mine up as tight as I would tighten the chuck jaws themselves. A D1-6 wrench would probably have an 8 to 10" long T handle.

If you cannot pull the chuck tight then polish the chuck taper a little bit. You'll have to chuck the backplate up temporarily to do the polishing, of course. FWIW, I never like to polish inside of a bore with my fingertip supporting the emery cloth. I figure its not possible to get even pressure all the way to the edge or to the back of the hole with something as squishy as a fingertip backing. So use a wrap of emery cloth wrapped around a rod. If you saw cut the rod lengthwise with a hand hack, the resulting slot is about right to insert a strip of cloth in and commence wrapping around the rod. Two or three turns will suffice, and you can keep it wrapped on the rod with a finger on top of the cloth.

Start with the part stopped and place the emery wrapped rod within the taper and cock it up and down until you can feel it settle into place, making full length contact with the taper. Then run the backplate 200 to 300 rpm or so (with the studs removed!) and carefully polish the taper, whilst trying to master the settling of the rod firmly against the taper.

It is best to polish with a strip about 1/2 to 2/3 of the width of the taper, so that you can move the strip lengthwise a little bit to even out the grain of the polish and to view that you are making contact completely across the taper as you polish. If you apply a bit of oil, it will help you track how you hold the cloth and whether you are polishing evenly. Most likely, you do not really wish to alter the machined angle of the taper, just make it a bit smoother/larger.
You got good info from John and Hu but Do Not polish on the spindle nose. If you take too much off of the chuck you can face it off but if you take any off of the spindle you can't put it back.
Thanks for the suggestions so far. How common is it to need to do this sort of fitting?

If the two chucks that I have don't fit, then that implies the spindle is a little big? I don't have good equipment to measure it

I appreciate what you are saying Ralph, but it would be pretty easy to take a fine hard stone and take ever-so-little off the spindle taper. On the other hand I just spent a pretty penny on it, hate to wreck it now. I suppose you could face the spindle too? That would be one of those nail-biters for me...
A .001" gap isn't much. Try going round a couple of times with the wrench, then smack the chuck firmly with a dead blow plastic hammer to see if it will settle on the rest of the way. Most all of my camlocks will not just fall off the taper when the cams are released, I smack them to jar them loose. But I don't have to drive mine on, either.

I don't say it is wrong to alter the spindle taper, but its more likely to have been gauged properly by the factory than would the comparatively inexpensive camlock backplates.
It seems possible that one or more of your pins are not adjusted to the proper length for the cams to properly pull them in. There should be marks on the spindle and cam indicating where the cam is supposed to be when tightened if the pin length is correct. From what I have read, adjustment is commonly needed when a new chuck is fitted.

Don Young
I am aware of the need to adjust the pins.

According to the spec, the taper is just a bit over 7 degrees, so 0.001 pull in is only about two tenths in radius. I am going to try polishing a bit and see what happens. I already tried a few taps with a plastic hammer, not much difference.
I had a 4 jaw that was not even close and had to recut the taper and face. When I was through it was still a bit too snug so I polished the taper with some 400 grit by rolling it on a strip of carpet with my thumb on the wet or dry grit inside the taper. It's still a little tight but I like to put a film of good EP grease on the nose before I mount the chuck, I seems to help it slide up tight.
When I bought my lathe(D1-4), the 3 jaw fit perfectly, but you'd have to hammer the 4 jaw off the spindle. It was too tight.

Before doing anything, I blued the spindle taper, and chuck mating surface.

First, I only blued the chuck, then determined where on the spindle the blue was transferring. Indicating binding by the transfer of ink to the spindle.

I then removed the bluing from the chuck, and blued the spindle taper to verify what I thought I was seeing. This time around I got the opposite effect of transferring ink to the chuck, as well as a visual of the ink removed from the spindle taper. This confirmed my thoughts. The taper in the chuck needed to be smoogied. (I would not, even at that time when I knew relatively nothing about fits, begin to think about messing with the taper on the spindle)

I do all my hand fitups on parts with ink. It's a great visual that eliminates the guesswork. The layout ink works better than a Sharpie.
I'd say that probably about 90% of the parts I make have to fit a worn companion/mating part. In most cases it's impossible to machine the worn area due to the size of the machine. I go oversize, then use ink to smoogie finoogie the large bore/flat surface etc to accept the new part. Blue Dykem is the best thing since sliced bread.
The chuck *should* need a tap to come loose on a D taper. The taper should seat while there is still a small gap on the face, maybe .001" or thereabouts. The cams then draw the face up tight. Every camlock I've ever used that wasn't beat to hell needed a tap with a dead blow to remove the chuck.
The operative word was "hammer", not tap. It was pretty doggone tight. Now it'll come off with a good smack from the heel of your hand, or a tap with a small plastic head hammer.

I remember looking at various discussions at the time. The consensus was that a "perfect" fit was unattainable. A slight interference fit was held to be the norm.

Being as the chuck is made of semi steel(mostly cast iron IIRC), it's my feeling that the chuck will wear before the spindle will. Dunno. I have no idea what the friction coefficient is between the two materials. After about 4-5yrs the fit hasn't changed, so it must be a fairly good one.

I seem to remember one discussion that went as far as talking about yield, and plastic deformation, in relation to just how tight the fit could be. That seemed to be carrying it a bit far, but it was interesting. I tend to think of yield in terms of structural components, not machine components. Might be the same, I just never really thought about it..........and if I do, it's mostly about the stress it takes to cause something to bend, or fail. I guess the only thing I can relate to, is the danger of making a shrink fit too tight...........it just causes the surrounding material to yield, or possibly the part itself. I'd think a pin would have less tendency to yield than the surrounding bore. Steel is stronger in compression. Hence the ability of a column to carry an exceptional load, up to the point of buckling.