A WOODTURNER'S ROSE ENGINE
by
Geoff O'Loughlin
For about three centuries the rose engine has attracted turners
having both a mechanical bent and sufficient funds to afford one of
those beautifully engineered machines of steel, brass and mahogany
such as those built by Holtzapffel. In ‘Woodturning’ issues 65 and 66
for July and August 1998 I described a ‘Poor man’s rose engine’ with
an easily built bed and headstock made largely of wood. Several
readers asked for clarification of the procedures used to cut the
intricate patterns shown at the start of each article, so I will
describe these in more detail.
The main feature of a rose engine which distinguishes it from an ornamental turning lathe is the headstock which is rockable and houses a spindle which can slide in its bearings, both these movements being regulated by cams or ‘rosettes’. Even if only the ‘pumping’ action of the sliding spindle is used, quite intricate patterns can be cut. Also, for much rose engine work a tool rest and tailstock are not required.
Photo 1 shows the rose engine set up for cutting patterns using the pumping action only. From L to R : Handwheel, Headstock, Eccentric chuck, Eccentric cutter held in a Sawbench spindle and clamped in a Cross slide vice, Motor.
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Photo 1. The rose engine and accessories. |
The bed is a platform made from any convenient material such as an offcut from a kitchen bench or a piece of MDF. It must be firm and stable, with a grid of holes through which accessories may be bolted on, and with 4 inch legs to allow for access below. Mine measures 31 in. x 18 in. x 1 1/2 in.
The headstock is 9 in. in length x 3 in. across, and 7 in from the bed to the centre height of the spindle. It was laminated from jarrah, the two end pieces each having a 60 degree V cut into the top before assembling. The steel spindle is held in these V grooves by wooden capping pieces which are bolted down lightly on threaded rods glued into holes in the uprights. When lubricated, jarrah makes an excellent bearing surface, but any hardwood should do. The spindle, of one inch Whitworth threaded rod has been turned smooth in places so that it can slide easily in the grooves. The headstock is held to the bed by a coachbolt.
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Photo 2. Rosette and rubber. |
While turning the hand wheel slowly, the sliding or "pumping" action of the spring loaded spindle is controlled by undulations on the face of a perspex or wooden cam or "rosette" as it is rotated against a fixed follower or "rubber" of steel. (Photo 2).
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Photo 3. Cutting a rosette. |
Also required is a cross slide vice as used on drill presses. The vice is mounted on an MDF base so that it may be clamped in any position on the bed. A small saw bench spindle having a drill chuck at one end to hold the cutter and a pulley at the other, is clamped in the jaws of the vice. (Photo 1).
Photo 3 shows how a rosette is made. With a 4 in. disc of 1 in. thick jarrah clamped on the headstock spindle and held stationary by the indexing system, a rotating fly cutter is moved forward to carve valleys in end grain on the face of the rosette at the desired number of indexed positions. An indexing disc of metal or plastic with 60 holes suits many ornamental turning purposes, being divisible by 2,3,4,5,6,10,12, 15, and 20.
The power for all the rotating cutters is a 1/4 HP motor bolted to a base which rests on a mat of non-skid material. The belt is 1/8 in. diam polyurethane, round in section.
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. Photo 4. Cutting a design using the eccentric chuck. |
An eccentric indexed chuck (Photo 4.) must be made, and a simple way is to:
1. Fix a disc of craft wood to a face plate.
2. Construct a chuck by gluing thin slats of wood, such as ice cream sticks held temporarily on sticky tape, around the side of a 3/4 in. plywood disc of 4 in. diameter. Fit an adjustable hose clamp over the slats for tightening the chuck.
3. Fix the chuck to a larger indexing disc of Perspex having 10 evenly spaced holes and backed by a disc of 1/4 in. plywood.
4. Insert a piece of 3/8 in. metal rod centrally to protrude 3/8 in. from the base. Drill a series of 3/8 in. holes in the face plate to accept the rod and locate the chuck eccentrically, ranging from 1 in. to 2 in. from the centre.
5. Fit an indexing rod of strong spring wire, which also serves to hold the chuck against the face plate. A second piece of wire non pointed, pressing against the other side provides even pressure to hold the chuck firmly against the face plate.
An eccentric cutter is required.
The cutters, made from a power hack saw or "Brobo" saw blade were shaped with a cutting off wheel on a saw bench before sharpening. Although held firmly when the bolts are tightened, a cutter could possibly snap if pushed too hard, so I always use a safety shield. My cutter rotates at 4000 RPM and the radius of cut was 1 ¼ in.
OPERATION: Prepare a disc of wood, or of perspex with the paper backing left on, and glue it to an MDF disc which fits snugly in the chuck and tighten~the hose clamp. Attach the chuck in the offset location on the face plate as in photo 4 Find the centre of rotation. I use a block of wood to hold a pencil in a horizontal hole at centre height while rotating the hand wheel. Position the vice so that the cutter will carve a crescent shape near the centre of rotation when it is moved forward. Clamp the base to the bed in that position.
While the hand wheel is slowly rotated the rubber rides over the hills and valleys of the rosette and the work moves in and out against the rotating cutter. As each hill of the rosette passes over the rubber a fresh cut is made, the pattern building in complexity until the handwheel has completed one revolution. The chuck holding the work is then rotated to the next indexed position when the cutting process is repeated at the new centre of rotation. This is continued until cutting has been completed at each of the 10 indexed positions. In photo 4 a craftwood disc painted white has been decorated using only 5 indexed positions.
Designs may be cut in various woods, but perspex is particularly suitable as with side lighting the intricacy and three dimensional nature of the cuts is emphasised, especially when viewed through the uncut side against a dark background.
The variety of designs or "carvings" which can be made on a rose engine is infinite, as there are so many variables, changing any of which will affect the outcome. They include:
!. The number and shape of the valleys cut in the rosette.
2. The radius and depth of cuts.
3. The angle of approach to the work which determines whether you cut circular or crescent shaped grooves.
4. The distance of the cutter from the centre of rotation, and whether above or below it.
5. The number of indexed positions on the chuck base.
Much of the pleasure lies in experimenting, usually with quite unexpected results. The following examples illustrate just a few of the possibilities. All were made using a ten hole indexing disc around the chuck:
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Photo 5 This is a 5 in. disc of MDF on which were glued myrtle and maple veneers with a sheet of blue epoxy resin between them. |
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Design in Perspex. Photo 6. This was cut in a perspex disc of 7 in. diam. The thickness is not critical but the thicker the better. The rosette had 10 valleys. |
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Photo 7. Another design in Perspex.
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Rose engines also have rockable headstocks. This can be achieved by supporting the headstock on two cone shaped metal points, one protruding under each end of the headstock and seated in undersized holes in the bed. I recently unearthed some old Peugeot push rods which have a ball. at one end and .a socket at the other, and couldn't resist utilizing their ends as rocking points which work beautifully, (Fig. 1).
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Figure 1. Section through headstock to show rocking points and wooden bearings for spindle. |
Rubber bands are excellent for holding the headstock down on its rocking points, as the required tension is easily obtained.
The rocking movement is regulated by a cam which is clamped on the spindle between the bearings The "rocking" cam or rosette may be made as earlier described except that the valleys are cut on the edge instead of on the face of a Perspex disc. Alternatively, a cam of whatever shape you would like to reproduce can be cut from Perspex or from M.D.F. It may be square, five sided oval or whatever you fancy. The cam is kept in contact with a wooden "rubber" of jarrah by rubber bands as shown.
For oval turning,(see photo 8.)
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Photo 8. Rose engine set up for oval turning. Lto R: Hand wheel, oval perspex cam (red) and rubber, oval shape turned from Huon pine by router bit in spindle (pale blue). |
TURNING THE BOX WALL.
Fit an oval cam on the shaft and tighten the lock nuts. Attach the work to the faceplate. Using a quarter inch parallel sided router bit, driven either by the spindle (Photo 8 )at about 6000 RPM or in a router and clamped in the cross slide vice, shape the outside of the vertical box wall while rotating the work slowly with the hand wheel. Shape the inside similarly, first cutting a step into which a base may be fitted. Remove the box wall by parting it off with the router bit.
SHAPING THE BASE AND LID.
Prepare a piece of wood for the base and fix it with double sided sticky tape to a support of M.D.F. on the face plate. Cut out an oval shape with the router bit to fit neatly into the step cut in the wall, and glue it in position. Cut out a lid of wood or of Perspex in the same way, with a stepped edge to locate it in the top of the wall.
ORNAMENTATION OF THE LID.
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Photo 9. Oval box of jarrah with lignum vitae insert. | |
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Photo 10. Oval box of jarrah burl with perspex lid. | |
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Photo 11. The perspex lid. |
If the lid is of wood the top may be decorated with a "barleycorn" pattern of overlapping circles (Photo 9).As the difference in length between the .long and the short axes of the cam remain the same, larger turnings become more circular, while toward the centre the cuts approach a figure of 8 as seen.
If the lid is made in Perspex (Photos 10 and 11.) it is preferable to embellish the under side as the cut facets appear more three dimensional and sparkling when viewed through the uncut side. The barleycorn pattern consists of a series of evenly spaced overlapping circular grooves cut with an eccentric "cutting frame" held in the cross slide vice. The central design of the Perspex lid was cut using a 12 valley rosette on the headstock spindle in pumping mode while the headstock was bolted down. After cutting an inner pattern of 12 crescent shaped cuts during one revolution of the hand wheel, the eccentric cutter was moved further out and in line with the headstock so that 12 circular cuts were made. A final series of circular cuts was superimposed a little further out.
AN INDEXING METHOD FOR EQUAL DIVISION OF AN ELLIPSE.
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Photo 12. Using a band saw loop of 120 teeth for indexing. |
If a normal indexing disc is used to locate the overlapping circles of a barleycorn pattern on an oval shape, the spacing will be uneven, being tighter at the sides than at the ends. A simple way to overcome this is to use for indexing, a loop of bandsaw blade having the desired number of teeth, and fixed around an oval piece of M.D.F. as in photo 12. The overlapping join can be soldered or pop rivetted.
The indexing oval although larger, should have the same proportions as those of the cam. The oval shape for the cam was drawn with a pencil guided by a loose loop of cotton thread around two nails and then cut out on a band saw.
Cut the MDF slightly oversize, then sand it down until the blade is a good fit. Glue it in position with the teeth overhanging the edge and drill out a centre hole to fit the headstock spindle. The indexing arm (Photo 12.) which is hinged and tensioned by rubber bands, carries a piece of brass plate on which a tooth rests for each indexed position.
OTHER SHAPES.
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Photo 13. Five sided bowl in black heart sassafras. | |
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Photo 14. Huon pine pedestal dish. | |
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Photo 15. Oval shaped goblet in walnut. |
Photo 13 shows a bowl shaped by a router held in the cross slide vice while the headstock rocked against a five sided cam.
The Huon pine pedestal dish of photo 14 was formed by guiding the movement of the router with the cross slide vice while the headstock was rocking against a square cam and the headstock spindle pumping on a 12 valley rosette. As the diameter is reduced the four corners of the base and pillar become more pointed.
The walnut oval goblet of photo 15 was also produced using the router and the oval rocking cam, but for the pumping action a cam having two gently sloping valleys was responsible for the raised ends of the goblet.
