Calling All Collets

When you need “toolroom” precision or are machining delicate parts or materials on the lathe, using collets can be the best approach. The most common lathe collets are Hardinge 5C (foreground, left and right), which go up to 1-1/8 inch. Smaller bench-mounted lathes and hobby lathes typically use a miniature version of 5C collets, designated 3C (foreground center and back row). 3C collets go up to 9/16 inch.

Most metal lathes come with a three-jaw chuck for a good reason: They are the best option for general-purpose work. They accommodate the widest possible range of diameters and the rapid scrolling mechanism allows work to move at an efficient pace. The downside to a three-jaw chuck is that it can’t match the precision of collets or the versatility of an independent four-jaw chuck. This isn’t to say you can’t produce precision work using a three-jaw chuck—you can—as long as you work within the limitations inherent to the design.

Three-jaw chucks are susceptible to both runout (top) and wobble (bottom).

Runout is the primary reason three-jaw chucks lose to collets when it comes to precision. Runout is the off-axis error that is exhibited during rotation. Wobble can also be an issue with three-jaw chucks. The most common cause of wobble is a stray piece of metal getting pinched between the workpiece and one or more of the chuck jaws. That’s an easy fix: Clean the jaws. But the culprit could also be a damaged jaw. A chuck that has lived a particularly hard life may have one or more jaws that have become bell-mouthed (wider at the tip than at the back). This can be fixed by regrinding the grip faces of the jaws (as a matched set), but that’s a topic for another day.

Before and after adding the washer to conceal the missing paint scuffs left by the previous hardware. (Photos: Paul Dye)

Wobble can also occur when you’re trying to grip a very short segment of the workpiece with the tips of the chuck jaws. Wobble of that type can usually be eliminated by repositioning and retightening the work in the chuck or by using the tapping method described in my July 2022 column, “Cogswell’s Molds.”

Another potential issue with three-jaw chucks is that they are big and bulky, which can make them less than suitable for small or delicate parts. Which brings us to the subject of this project: using collets instead of the three-jaw chuck to make a set of decorative washers for the glareshield on Paul Dye’s SubSonex jet.

Note there’s no angle dimension for the chamfer. The angle was made by setting the cutter to the approximate angle and then turning off the material to the setback line (0.045 inch).
In order to use the 9/16-inch 3C collet, the ends of three short pieces of 3/4-inch Delrin rod were turned down to 0.563 inch using the three-jaw chuck (left). Like many small bench lathes, the chuck on my lathe is fixed to the spindle with three screws (right).
The components of the 3C collet system: the handwheel (A) for tightening and loosening the drawbar (D) to the collet (F). A spacer (B) provides hand clearance between the spindle adapter sleeve (C) and the back of the lathe. An adapter (E) fits in the spindle to convert the MT3 spindle taper to the C3 collet taper. The collet system for my lathe was purchased from

Paul had originally used buttonhead screws (thread size 8-32) on the glareshield. Buttonheads were a good choice. They combine a low profile with a relatively large face. But after a few times removing the glareshield for various tweaks, and despite the fact that they only needed to be moderately tight, the two screws closest to the canopy (one on each side) were stripping out due to the shallow socket and sharp angle, which required the use of a ball driver. In the end, Paul changed all the buttonhead screws to socket head cap screws (SHCS). This solved the problem of the heads stripping out, but presented a minor (but annoying nonetheless) issue of bare metal showing where the paint had worn off from the old screws. You can’t have that on a show-quality airplane!

Truing the outside diameter and truing the face (left). Using a ¼-inch end mill in the tailstock Jacobs chuck to rough size the counterbore for the screw head (right).
With the lathe running at slow speed, a caliper was used to scribe the chamfer setback (left). An ACME thread tool was set up at an angle, then slowly fed into the work to turn the chamfer to the scribe line (right).
A small boring bar was used to enlarge the counterbore from 0.250 to 0.265 inch (left). After drilling, the through hole was tapped 8-32 (right) and then the washer was parted off to length (not shown).
Using a screw to hold the washer, the part was reversed in the chuck (left) and then the back side of the through hole was carefully chamfered to remove the burr from parting off (right).
The finished washer set, ready for installation. The threads are barely perceptible, but there is enough engagement to feed the washer onto the screw and have it stay there.
The glareshield of Paul Dye’s SubSonex jet. For details about building the SubSonex, see “Turbine Temptation” (November 2019 through May 2020).

Short of respraying the glareshield or using flat washers, which Paul did not want to do, we conjured up the idea of making decorative washers to conceal the missing paint and dress up the look of the screws. The material we selected was black Delrin, a tough, easy-to-machine DuPont plastic that’s similar to nylon. Unlike a basic flat washer, these were made with a close-fitting counterbore and a beveled face and they are threaded so they stay married to the screws when removed. (Anyone who has ever spent the better part of a day trying to find a small washer among an array of wiring harnesses will agree: That is a good feature.)

That’s it for now. Time to get back in the shop and make some chips!


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