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This article was published in the August 2011 (#32) edition of Woodturning Design.
If
Split Sleeve Drive Center as a 6 page pdf
Split Sleeve Drive
Center
Introduction
I read in the June 2010 issue of the AAW Journal an article by Matt Lewis about making your own lathe drive centers from Jacobs Chuck mandrels. This got me thinking about making interchangeable drive centers using a Split Sleeve Drill Driver. A Split Sleeve Drill Driver, shown in Fig01, serves to adapt a drill (and only one size drill) to a Morse Taper—it’s sort of a zero tolerance collet. They’re available from any Industrial Supplier such as MSC. As the Split Sleeve is pushed into the Morse Taper it closes down to clamp onto whatever is inserted into it, assuming that something is the right diameter. As you can easily change the insert, you can buy one Split Sleeve Drill Driver and make any number of inserts using any proper size round stock you can buy, scrounge, or make.
Fig01. The Split Sleeve Drill Driver. The slot lets the Driver compress and hold the drill. The wider opening in the middle of the slot lets you wedge or pry out obstinate drills (or inserts).
This article will show how to make drive centers using a Split Sleeve Drill Driver in a variety of shapes and sizes either by hand turning the stock or using various metal cutters mounted in a drill chuck. Split Sleeve Drill Drivers are limited in size according to the Morse Taper size, as obviously, the drill inserted must be smaller than the Morse Taper less the thickness of the driver walls. For MT2 drivers, the maximum size is 35/64” —I decided ½” was a more sensible size to use as rod stock of that size is more common.
First a one piece 1/2” center will be made using a modified V-bit and then modifications for serrated teeth and size will be shown. For those who don’t like turning metal by hand or want interchangeable center points, then methods using drill chuck mounted cutters will be shown. Then the article will show how to make drive mandrels for various uses.
One piece Center
The basic 1/2” safety drive center is made from 1/2” stock. Oil hardening drill rod is probably the best choice, especially if you want to harden it, but you can start with any steel that is the right size. Begin by cutting the steel about 1-1/2” long. As the whole idea is interchangeable centers, you might as well do a handful while you’re at it. I used a cut-off saw, as in Fig02, because if does a square cut which saves time later. Clean up and square, if needed, both ends of each insert on a bench grinder.
Fig02. Cutting insert blanks. The cut-off saw makes nice right angle cuts.
Hand turning steel on a wood lathe can be a daunting experience, even with cobalt steel bits and a long handle because of the greater forces involved. There are a couple of things that will significantly lessen the stress. The first is moving the tool rest very close to the turning—put the cobalt bit on the rest, not the bit holder. The other is limiting the contact area of the cutting tool, as the force is proportional to the width of the tool actually engaged. You can’t just use a thinner tool, however, as it must be strong and rigid. The best solution I’ve found for that is to grind a small flat area at the tip of a V shaped bit and cutting mostly with the tip. Begin with ¼” cobalt steel bit and grind one end to a V shape using a standard scraper sharpening angle. Then, using the same angle, grind a small flat, about 1/16” across, at the tip of the V as in Fig03. The cobalt bit is then held in some kind of shaft (a 3/8” hole in a ¾” shaft with a set screw will do—I used a Stewart System hollowing tool). The tool rest height should be set so that the cutting tip is at the center of the work when the handle is held straight across (parallel to the floor). Don’t be timid with the tool, as if no shaving is produced you’re only dulling the tool and making heat. With only the small tip engaged and the lathe running at a slow speed, you should be able to produce a shaving without sweating or causing your lathe to shake and protest.
Fig03. The Truncated V-Bit. Only the small flat at the tip engages the steel, making hand turning of steel much easier.
Shove one of your steel inserts as far as it will do into the mouth of the Split Sleeve Drill Driver, and then insert the Drill Driver into the Morse Taper in your lathe headstock. Make sure the Morse Taper is inserted firmly—you can use your tailstock center to push it in. Set the tool rest across the face of the insert and close to it—less than ½”. Turn on the lathe at a slow speed (my lathe doesn’t have a readout, but let’s say less than 500 rpm) and begin to shape the insert. The cutting sequence is optional but it’s reasonable to start making a hollow about half way between the center and the rim and then widening the hollow as in Fig04. Preserve the very center and shape it to a point. You can use the longer side of the V for this. Cut back the rim until you have to point projection you want, and deepen the hollow if necessary. The completed center is shown in Fig05.
Fig04. Shaping the tip of an insert with the Truncated V-Bit.
Fig05. The shaped one piece drive.
If you want a little more drive (say you can’t use much tailstock pressure) you can add teeth with a triangular file. Engage your indexing system or otherwise hold the insert fixed. Hold the file so that the upper flat is parallel to the lathe, mostly straight across the lathe with the axis of the file pointing a little down and a little towards the tailstock so you don’t file the center pin. File a notch, rotate the lathe a bit and repeat until you’ve gone all the way around. The resulting toothed drive is shown in Fig07.
Fig06. Filing teeth on a drive insert to give a little more traction.
Fig07. A completed toothed drive insert in the Split Sleeve Drive.
Having more than one diameter drive can be very useful. The smaller the diameter drive the smaller you can work at the headstock without hitting it. The larger the drive the less chatter and vibration problems you’ll have. There is no single optimum size, as the best size depends on what you’re trying to turn, how long it is, and what wood you’re using. So make several sizes.
To make a smaller size drive, mount a new insert in the Split Sleeve Driver and mount it firmly in the lathe. You can use the tailstock to prevent it from vibrating out while you’re reducing the diameter if you like. The quickest way to reduce the diameter is with the Truncated V-bit. Bring the tool rest up very close and adjust the height so the cutting tip is at lathe center. Turn the lathe on at a slow speed and start cutting as in Fig08. You may find it easier to swing the back of the handle rather than slide the bit along. Continue until the insert is the diameter you want. You can make the length of the reduced diameter nose to suit your application, but 3/8” to ½” is a good place to start.
Fig08. Reducing the diameter of an insert with the Truncated V-Bit.
If you’re intimidated by hand turning steel you may wish to use a file to reduce the diameter. When you order your Split Sleeve Drill Driver, have a look on the Industrial Supplier web site at files. There are many more choices there than at your local hardware store. You’ll find that a large coarse bastard file, either square or triangular, will remove stock a lot faster than the fine and by now probably dull file you’ve got lying about the shop. Get the tool rest out of the way, and turn the lathe on at a slow speed. You’ll still need to stroke with the file, but the lathe will do most of the work. If it feels like the file is trying to kick back at you then slow the lathe done some more. Continue until you have the diameter you want. Then cut the nose as before.
Fig09. Reducing the diameter of an insert with a coarse square file.
If you want a larger drive center select a ½” hex head bolt with an untheaded shaft at the head. Cut the bolt about 1-1/4” below the head. Clean up the cut end and insert the bolt into the split sleeve driver. Bolts are not made to precise dimensions and it may be a little undersize. If the bolt turns in the sleeve even when pushed in all the way, but doesn’t rattle, you can salvage it by grinding bevels on the end of the bolt as in Fig20. Form the point and hollow as before. A standard ½” hex head bolt will yield a ¾” drive center, which is probably as big as a center with a ½” shaft should be.
Separate Pin
Using a separate pin has some advantages. It’s easier to make long pins separately and you can avoid hand turning steel if that proves difficult for you. Begin by mounting a steel insert in the Split Sleeve Driver and mount the Driver in your lathe. If you want to reduce the diameter of the insert do that first. Select the material for the center pin. Small drill rod (about 1/8”) would be an excellent choice. I didn’t have any so I used a merely good finishing nail.
It’s important to have the center pin really in the center of the insert, so mount a combined drill and countersink in your drill chuck. The combined drill and countersink is short and rigid, so it won’t deflect and produce an off-center hole. Turn on the lathe at a slow speed and drill in far enough to start a hole as in Fig10.
Fig10. Starting a well centered hole with a combination drill & countersink.
Select a drill the exact size (or maybe a tiny bit smaller) of your center pin material. Substitute the selected drill bit for the combined drill and countersink in your drill chuck. Using a slow speed, drill in ¾” to 1” as in Fig11. Retract the drill to clear swarf from the drill if necessary as a clogged drill often deflects. You can form the hollow using a countersink or large drill. The countersink is fine for small centers, but the usual 60 degree countersink leaves a lot of unsupported center pin in large (3/4”) centers. Mount the drill or countersink in the drill chuck and form the hollow as in Fig12.
Fig11. Drilling the insert for a separate point.
Fig12. Using a countersink to form the cup.
It’s possible to make the center pin adjustable by drilling and tapping a radial hole for a set screw. The problem with adjustable center pins is that they tend to readjust themselves and do it at the worst possible time. Since it’s so easy to make multiple inserts, I suggest you used a fixed length pin. You can leave the pin long at this time unless you want a very short pin, in which case you’ll have to put a point on it before inserting it. Scuff up the part of the rod that will be inserted with sandpaper. Put a piece of masking tape on a convenient surface and put a drop of CA glue on the tape. Roll the end of the rod in the CA glue and quickly insert it in the drilled hole in the drive center. Tap the rod down until it bottoms out, or drive it into place with your tailstock. The result is shown in Fig13. Cut off the rod at the length you want with cutters or a hacksaw. Then turn the lathe on at a slow speed and use a file to shape the rod to a point. The result is shown in Fig14.
Fig13. After gluing a pin in place.
Fig14. After sizing and shaping the pin.
Removable Pin
If you want the ability to have more than one pin length but don’t want to deal with slippage you can make multiple pins for a single center. You will need a #1, 1” taper dowel pin and the matching reamer. You can get the taper pins (100 in a box) and a reamer from an Industrial Supplier. You may be able to find single taper dowel pins and a well stocked hardware store. Prepare an insert for the Split Sleeve Center. Begin by measuring the diameter of the taper pin at the small end. Select a drill that matches, or is slightly smaller, than this diameter, and mount it in your drill chuck. Drill all the way through the insert as in Fig15. Remove the drill bit from the drill chuck and mount the taper pin reamer. Begin by making the longest pin you want—you can cut additional pins shorter. You can use a drill sizer to estimate how far to ream by finding a hole that lets the taper pin insert far enough and then gently inserting the reamer into that hole and marking with tape. With the lathe at a slow speed advance the reamer into the drilled hole a little ways as in Fig16, then retract the reamer, turn off the lathe, and try the fit of your taper pin. If it doesn’t go in far enough, turn on the lathe and advance the reamer a little bit more and try the fit again as in Fig17. If it doesn’t take several iterations you’re not being cautious enough, as if you ream too far you’ll have to start all over with a new insert.
Fig15. Drill through the insert for a dowel pin point.
Fig16. Reaming a matching taper for a dowel pin point.
Fig17. Testing the fit of the taper pin
If you want a tall pin you can file the taper pin to a
point while it is mounted in the insert.
For shorter pins, put a blank insert in the Split Sleeve Driver.
Drill using the same size drill as before entirely through the insert.
Ream less than you did for the actual center.
Mount the dowel pin in the insert, turn the lathe on at a slow speed and
shape the tip with a file. The
result is shown in Fig18. Then
remove the pin (you can do this with a pair of pliers or more elegantly by
knocking it out with a rod smaller than the drilled hole) and remount it in the
center. The result is shown in
Fig19. The center I used for these
photos was made from a ½” bolt and was a little undersized.
I beveled the end of the bolt, as in Fig20, so the
Fig18. Shaping the pin with a short tapered insert.
Fig19. The finished Taper Point Drive Center.
Fig20. If a drive slips, you can bevel the ends slightly. This will engage the recess in the middle of the Split Sleeve Drive and prevent twisting.
Mandrels
You can also use a Split Sleeve Driver to hold mandrels. As the Split Sleeve Drive is vulnerable to vibrating out of the lathe Morse Taper if unrestrained it won’t substitute for a collet chuck, but you can do final trimming/sanding of the end without the tailstock if the heavy work is done with tailstock support.
For light duty mandrels you can use wood dowels. You may need to more accurately size the dowel on the lathe or by driving through a drill gauge or steel bar with a ½” hole. Just insert the dowel into the Split Sleeve and insert the Split Sleeve Drive into your lathe. Bring up the tailstock for support and shape the mandrel to suit your purpose. Fig21 shows a sample wooden mandrel. This one is shaped arbitrarily, as I didn’t have a purpose in mind.
Fig21. A completed wood mandrel.
For heavier duty or more durable mandrels brass would be a better choice. Cut ½” brass rod to the length you need and press firmly into the Driver/Morse Taper. The tailstock is good for this. You may with to retract the tailstock, turn a small dimple for it, and re-engage the tailstock as in Fig22. Then turn the brass to suit your purpose. Brass is much easier to hand turn than steel, but it still requires more care than wood. You can use ordinary HSS turning tools (even a skew) but keep the tool rest as close as possible, turn the speed down, and limit the tool contact area. For instance if you want a cylindrical segment you can do a callipered parting tool cut at each end of the segment, but you may find that a 1/16” parting tool, as in Fig23, chatters a lot less than a 1/8” wide tool and feels friendlier, even if you have to cut more than a tool width to fit your caliper in.
Fig22. Brass rod mounted for shaping into a mandrel.
Fig23. Using a thin parting tool to cut to a measured diameter.
I found that my ½” roughing gouge (reground from a deep spindle gouge) as in Fig24, was the user friendliest tool for stock removal on brass. For final sizing use a file as in Fig25. And if the dimension is critical measure with dial calipers with the lathe turned off.
Fig24. Roughing the brass to diameter with a small roughing gouge. Less tool contact equals less force required.
Fig25. Filing the brass to final dimension.
Fig26 shows a special purpose pen mandrel I made for a single tube pen. Without the extra length of an all-purpose mandrel, and with full tube width support, it is quite solid when turning. The end of the mandrel is turned to fit the brass tube but a half inch or so shorter, and the turned area just to the left of the tube matching area is sized to substitute for a bushing. I left some extra length so that if the bushing area becomes undersized I can simple retune the mandrel by cutting up further. Fig27 shows the brass mandrel set up for use (except the tube is naked for clarity). The tube slips onto the mandrel, and the tailstock holds a bushing in the tailstock end of the tube.
Fig26. The completed brass mandrel.
Fig27. The brass mandrel set-up as a single tube pen drive.
Fig28 shows a Split Sleeve Drill Driver with a collection of inserts. Remember that you can easily suit the inserts to your own needs.
Fig28. The Split Sleeve Drive with a collection of inserts.
Tools
Metal cutting saw
¼” square cobalt steel cutter & holder
Various drill bits
#1 dowel pin reamer
Files
Materials
½” Split Sleeve Drill Driver
½” steel rod and/or
½” wood dowel and/or
½” brass rod
~1/8” steel rod and/or
#1 x 1” taper dowel pin
Author
David Reed Smith is a basement woodturner and compulsive tinker from Hampstead, Maryland. He welcomes comments, complaints and questions via email at David@DavidReedSmith.com. This article, along with more than 50 others, will be available at www.DavidReedSmith.com.