Bobo Theatre

Contents

introduction

standards

list of supplies

details of supplies

make frames

make towers

front rail connections using barrel hinges

bottom rail

track rail

back rail

dressing

assembling

final adjustment

Addendum, Velcro catches

1   introduction

A simple design of a glove puppet theatre for children is given, appropriate for a minimally skilled carpenter.

One or two children manipulate standing erect behind an almost opaque back cloth.

If all materials are purchased then the cost is about £ 60 UK (writing in 2001). With all materials present and this design fully understood, the labour required is about 10 hours.

The theatre comprises a demountable structure dressed in cloth. The two illustrations right show this.

Two collapsing rectangular frames are joined to make a tower. Such a tower is provided at right and left. Three horizontal pieces, called rails, join the towers into an integrated structure and carry the drapes.

Key dimensions are given in the table here. Proscenium is the hole through which an audience sees the stage space.

structure

theatre dressed

2   standards

If you are using this to construct a theatre then please read and understand all of the document before you start work. Every detail is here for a reason.

I use the theatrical convention for right and left, which is as seen from the back of the stage looking towards the audience. This is sometimes called stage right ( or left ) and at other times is assumed.

References to top, bottom, above, below, back and front are made with the component in use.

The theatre was designed to metric standards. I give near Imperial equivalents in square brackets which have not been tested together.

Language is U.K. english.

I apologise in advance for any errors. Please check that parts fit.

The order of this is as you might manufacture. I made the prototype, testing and improving as I went. You may rearrange the process order.

If you keep your browser with graphics turned off, then please turn graphics on. It is essential. The good news is that graphics files total less than 20 kBytes.

3   list of supplies

These materials are required :

• wood, 18 x 34 mm, 14 m [ 0.7 x 1.34 ins, 46 ft ], I call this frame stock
• butt hinges that are shorter than the width of the frame stock, 20
• magnet catches that are shorter than the width of the frame stock, 9

• wood, 20 x 45 mm, 1.5 m [ 0.8 x 1.8 ins, 5 ft ], I call this track stock
• wood, 12 x 30 mm x 2.7 m [ 0.5 x 1.2 ins x 9 ft ], I call this thin stock
• curtain track with string pull, 1.5 m [ 5 ft ]

• barrel hinges, 4 sets with nuts and 8 washers
• wood screws for hinges, 80
• wood screws for magnet catches, 16
• wood or metal screws with washers and nuts to secure curtain track, 10
• countersunk plusdriv wood and chipboard screws, 4.0 x 40 mm [ 0.16 x 1.6 ins ] , 6
• epoxy resin, as Araldite
• your chosen finish, I used brushing wax

• Velcro ribbon pair, 16 mm x 1 m [ 0.6 ins x 3 ft ]
• double sided Sellotape for the Velcro
• fabric for facing, 0.8 x 2.1 m [ 32 x 83 ins ]
• curtain, 2 pieces 500 x 500 mm [ 20 x 20 ins ]
• rufflette tape
• 12 curtain hooks
• black gauze, 1400 x 500 mm [ 80 x 20 ins ]
• black bias binding, 200 mm [ 8 ins ]

butt hinge across
frame stock

magnet catch across
frame stock

barrel hinge

4   details of supplies

All the wood lengths given above are tight. Add your own contingency reserves.

The nominally 18 x 34 mm frame stock is sold by my local diy superstore, it measures17.75 x 32.5 mm. They also have small butt hinges and barrel hinges.

For the thin stock I used “half inch plywood” which is 12.4 mm [ 0.5 ins ] thick. This was cut to width then cracks within had to be plugged with like matchsticks and epoxy.

Over a radius of 4 km in South London I found small magnet catches only at : G & S City Market, Elephant and Castle Shopping Centre, these were packaged as DIY PAC DP628 MINI MAGNETIC CATCH. Overall length is 31.5 mm [ 1.24 ins ]. These must be elsewhere. Until someone produces a better idea these are essential.

The magnets are used in pairs of the same magnetic polarity. One more magnet than is used is required to ensure that enough pairs are available.

To be sure you understand the requirement, the hinge and the magnet catch are drawn lying across the width of the wood, right.

Also right is drawn a barrel hinge. In one local shop these are called pin hinges.

20 x 45 mm is a standard size from the woodyard. See section 9 for discussion about the width.

Woodyards also have a wide range of small wood forms for the thin stock. The dimensions are not critical.

None of the wood sizes are critical, but any variation brings consequences.

The curtain track is the common domestic track that comprises a plastic extrusion 30 mm high, with a pulley box at each end. This provides two grooves, the upper groove is for attachment, the lower groove is the track for runners.

The Velcro is to be attached to wood using double sided Sellotape. You may have access to self adhesive Velcro, which is probably preferable.

My choice of finish is light tan brushing wax, I had some left over. It is easy to repair, quick to be ready and looks good. Plan how you will apply your choice of finish under or round the attached Velcro and other appended bits.

Study the fabric requirement and obtain your choice. Four panels dress the front. Mine were plain. The theatre looks dull when standing idle, during a performance it is excellent as the dark colour enhances the stage.

Black gauze is the back cloth, manipulators look through this to see what they are doing. It should look dark, transmitting about 10 % of the light or less. Manipulators' eyes adapt to it.

The curtain can look splendid because it is never a distraction from the action.

5   make frames

The structure is based upon a single design of folding rectangular frame. Four frames are required with small adaptions for different purposes. The frames are identified as : right side, right dorsal, left side and left dorsal. The structure has two backbones.

The special features of each of these frames are given by this table :

Two towers will be made for each side by joining with screws the side and dorsal frames. This is described in the next section.

The frame is a trapezoid using frame stock and the butt hinges, as shown right. The frame is 1000 mm [ 39.4 ins ] high to its top principal surface by 350 mm [ 13.8 ins ] wide. The E piece at the bottom is 20 mm [ 0.8 ins ] above the floor, vertical pieces A, C and D provide feet.

Cut these lengths of the frame stock :

side, dorsal
and closed frames

Sections 7, 8 and 9 explain how the front rails will be mounted. You could drill the B pieces to receive the barrel hinge pins. I suggest that you do this work later for simplicity.

Assemble two of each of the frames, as shown above right.

To make each frame fit four hinges to the pieces F. Do this with the wood at right angles to and touching a surface to ensure proper set of the hinge. Then fit three of the flanges to the verticals. The last flange of each frame has to be at the bottom of pieces A and D, marked in position with the frame collapsed, to ensure that it will collapse without stress.

It is a challenge to keep the hinges at right angles.

Pieces F become hinged struts that stabilise each trapezoid at a rectangle. This strut attaches at its loose end with two magnet catches. The struts are hinged to the pieces A and D, as drawn right.

To move the strut to and from its active position the frame, as a trapezoid, must swing past 90 º. The pieces E must be shaped by cutting or sanding 5 º off their ends. Their effective lengths must not be changed. I sanded after assembly.

Each strut is held in the active position by two magnet catches, one on the strut and one on each piece B or C. The magnet catches have to be paired with the same magnetic polarity. The best way to match the magnets is to test each with a compass, as drawn right. When you find a pair put them together face to face, head to toe.

Two similarly marked magnets attract each other because they are used facing each other with one inverted.

One magnet catch holding the normal catch plate is not strong enough to carry the load when the frame is carried. So the two magnets are necessary.

For each frame when the rectangle is complete, fit the strut :

• take a pair of similar magnets
• mount one of these on the piece B or C, depending on frame type. The magnet requires 10 mm [ 0.4 ins ] clearance when the frame is collapsed, as drawn above.
• put a hinge on the strut so that it will lie flat when collapsed.
• mark where to mount this with 10 mm [ 0.4 ins ] clearance from the magnet, again as above.
• offer the strut and mark the loose end to fit as drawn right.
• cut and mount the strut then fit the magnet.
• adjust the magnets so that frame stands vertically

In effect the struts are active at flatter than 45 º so that the other magnet swings past the strut for stowage.

Eight of the butt hinges are mounted on end grain. This does not work without help. After manufacture dissassemble from the end grain and put epoxy resin adhesive into the screw holes, then reassemble.

The following paragraphs show how the holder for the back rail is be provided. The back rail is parallel to the two front rails, and the side and dorsal frames are at right angles to each other. So the angle off perpendicular that the back rail crosses the dorsal frame is the same as the angle of the front two rails. Section 7 sets the angle at 20 º. You can change this.

You may prefer to provide the back rail holder when the front rails are in place adjusting the angle of the slot to match the angle of the front rails.

testing a magnet

strut

Cut a chip off the top of the pieces D. The angle of cut is 20 º. The two cuts are to mirror image each other. This is shown right.

The cut enters half the width of the D piece. The bottom of the cut is to align with the top of the adjacent piece E.

The wood remaining from the cut forms the side of the holder for the back rail.

Lay a piece of the thin stock at an angle of 20 º from rectangular across the frame stock. Mark the thin stock at the frame stock edges.

Cut two pieces of thin stock to the lozenge shape so marked. These will provide the second side for the back rail holder. Offer the lozenge shapes to form the back rail holder, you may care to cut the unused side to be square with the frame, and chamfer. Screw and glue the lozenges to the top of the dorsal frames leaving a comfortable space for the back rail.

Velcro hook pieces are adhered to the top of the side frames to hang the side panels. Where to fit these is described in section 11 on fitting the drapes.

section of back rail and
its holder at right

6   make towers

The towers are identified as stage right and stage left. Assemble using their frame pairs.

The join of the towers must align the two corners of the B and C pieces so that the rail mountings will work accurately. Clamp the pieces together on a bench top. Three countersunk 40 mm [ 1.6 ins ] woodscrews are used for each tower.

The stage right tower is shown in plan, part cutaway. Letters identify the wood piece id.

The left tower is a mirror image of the right tower.

You will find that the towers stand securely.

Adjust the magnet positions to see the towers standing vertically.

With frames collapsed a tower has an L section. The two towers nest neatly.

right tower
made of two frames

7   front rail connections using barrel hinges

This section is a practical description how to attach the front rails, specifically described in sections 8 and 9. The technique gives direct control to you because your supplies are different to mine.

A barrel hinge comprises two parts : a barrel and a pin.

The front rails attach to the frames. The rails are at an angle of 20 º to the side frames. This looks attractive and is stable. A different angle may be used, but all four connections and the back rail mounting must be at the same angle.

Each attachment is made by fitting the pin to the B piece in the corner of the tower. The barrel is fitted to the rail. Mounting a rail drops two barrels on pins.

My barrel hinges required 6 mm [ 1 / 4 in ] holes in the B pieces and the rails. Because of the process described here the barrel hinges must fit tightly into their holes. They were fitted with a washer. They are secured with a nut without a washer.

On the B pieces flat bottomed countersunk holes of 11 mm [ 7 / 16 ins ] diameter are necessary for the nut. The depth of this has to be controlled, too deep and there is no access to drive the nut. You may need to create access.

To the right is a plan section through the B and C pieces as joined together in a tower.

Pins must align one above the other. Corresponding pins must be at the same height.

The corners of the frame are sanded to provide a flat bearing surface for the rails. This sanding is the adjustment for angle with freedom to assemble the rail.

I use the term 'sanding', but depending on you frame stock dimensions you may choose to cut first.

It is necessary to discover where is the vertical centre line for holes in the B pieces. A procedure follows.

Screw together two 150 mm [ 6 in ] pieces of frame stock to an L form test piece, to model the B and C pieces in the tower. Mark the B piece of this.

Mount a barrel on a 80 mm [ 3 in ] length of thin stock. Drill two holes for the barrel. One hole is 15 mm [ 0.6 ins ] below the top of the thin stock for the experiments described here and for work on the bottom fittings. The other puts the top of the barrel in line with the top of the thin stock for work on the track rail fittings. This is the rail test piece.

When sanding it is necessary to remove wood over the height of the rail in contact plus the height of the pin.

Remove wood from the one corner of the L form test piece until the hypoteneuse is at the target angle.

Press the rail test piece onto this corner with the barrel pressing against a washer on the B piece.

Measure from the centre of the barrel to the C piece. Separate the pieces.

You will drill holes for the pins at 1 mm [ 0.04 ins ] less than the measured distance. This provides two flat surfaces for the rails to bear against and positional tolerance for drilling.

Drill a hole in the L form test piece and sand down until the pieces just fit at the target angle. To remove wood from one corner back the sandpaper onto half the length of the block.

Now you should be ready to fit four pins in the towers. If the test failed then you can use the test pieces experimentally to solve the problem.

Barrels are fitted symmetrically about the centre line of the front rails on 760 mm [ 30 ins ] centres.

When all the barrels and pins are fitted and checked they should be removed. Put them back with the screw threads loaded with epoxy resin. These have to be reliable.

barrel hinge fitting
in corner of tower

20 º  test piece

8   bottom rail

When assembled, the bottom rail contributes stability to the structure, it defines the bottom of the proscenium and it supports a drape called the skirt. It must not hinder the curtains.

The bottom rail is thin stock cut to 1240 mm [ 49 ins ].

Round the corners at the ends.

Two barrels are mounted thereon as described in section 7.

The holes for barrel hinges are 15 mm below the top line of the rail.

Holes for the bottom rail supporting pins are in the B pieces at 575 mm [ 22.6 ins ] above the floor. As the B pieces do not touch the floor measure carefully. See section 7.

Four 30 mm [ 1.2 ins ] long pieces of Velcro hooks are adhered to the bottom back of the rail with double sided Sellotape. A piece is used adjacent to each C piece and two equally between.

In action my string pulls locked under the bottom rail. I solved this by chamfering the underside of the bottom rail where it is accessible by a hanging string. Decide which side you will hang the string, and chamfer the rail.

9   track rail

The track rail contributes stability to the structure in use, it carries the curtain track and it carries a drape called the pelmet which masks the top of the curtain and defines the top of the proscenium.

Cut the track extrusion to 1100 mm [ 43.3 ins ]. Dismantle the track to do this.

With its end boxes overall length of the track is 1185 mm [ 33,5 ins ]. The track rail must carry this. I made the rail 1225 mm long to provide end protection to the track. Use track stock.

Round the corners at the ends.

I mounted the track on the rail so that their bottom surfaces align. The runners hang below this. The flat surface of the track fits directly to the back of the rail. The bare wood above the track equals the width of my Velcro.

The track end boxes are proud of the mounting surface of the track by 1.5 mm [ 0.06 ins ]. Cut a 1.5 mm trough in the rail for the boxes to fit into, this is 75 mm [ 3 ins ] wide.

The rail is to be mounted using two barrels at the same centres as the bottom rail, symmetrically about the centre. It would be sensible to drill them together.

The barrel has to be mounted so that the top surface of the barrel is at the same height as the top of the track. Cut the track to allow access for the nut. The track has to be removeable, the barrel hinge is permanently in place.

The pin part of the barrel hinge is to be mounted high in the corner of the towers. Leave enough space for the barrel to enter. Mine is 50 mm [ 1.97 ins ] from the top.

The rail has to be cut so that it does not clash with dorsal frames when fitting. This cut is an oblique trough that reaches down to the tops of the barrel and track. The best way to mark this is with the rail fitted in place of the bottom rail. The angle of the cut is the same as the angle of the front rails.

Measured along the rail my trough is 39 mm [ 1.53 ins ] long.

I mounted the track on the rail with 9 of 4 x 25 mm pan head screws. With the track in position I drilled through the mounting groove of the rail. Nuts slip into the groove to meet the screws entering from the front.

Two screws are used on the end outside the cutaway for the barrel mounting. One screw connects the end box and one the track.

You may prefer to use wood screws, entered through holes drilled in the groove. This will probably require more cutting of the groove. You could cut off the top and bottom shroud from the mounting groove of the track extrusion.

A forward arm is provided with the track to overlap the curtains. This is intended for mounting where it clashes with the proscenium sides, so I mounted the forward arm on the back of the bogey using longer screws than supplied. This is functional but the bogey is not designed for this. You must choose what you will do about the arm. I think that it could usefully be shortened.

Five curtain runners are put on each side. This requires six hooks on the curtain.

Four 30 mm [ 1.2 ins ] Velcro hook pieces are adhered to the top back of the rail with double sided Sellotape, as on the bottom rail.

cutaway of track rail
showing track, oblique cut,
screw mounting
Velcro patch and
barrel hinge

You have to address the pull string.

Identify which is the openning and closing string. Centralise the closed bogeys on the string. Cut the openning string leaving about 70 mm [ 3 ins ] hanging. Then open the curtains and cut the closing string to the same length. Then provide your choice of pull knobs. I draw mine right.

Perhaps you don't cut the strings short, but provide a Turk's head.

In use open and close the curtain by pulling the short string.

Pulling too hard on a string swings the far side of the track rail up off its mounting pin. If you are concerned about this then drill a fine hole in the track rail on the outside limb. Thread this with cord tied to a peg that plugs the gap over the track rail to prevent it rising off the pin. The cord must be just long enough.

string pull

10   back rail

The back rail supports the back cloth and assists stability.

Cut 1350 mm [ 53 ins ] length of thin stock.

Round the corners at the ends.

Cut an oblique groove so that it drops into the slot on the top back of the dorsal frames and one third of its height wraps round the frame stock.

You might adapt the length to match your purchased black gauze.

It sits in the holder at the back of the dorsal frame.

Fit 30 mm Velcro hooks pieces on the front of the back rail, the top of the Velcro aligns with the top of the rail. A piece is put at each end of the gauze, Four piece are put adjacent to the dorsal frames, three pieces are distributed equally in the central span.

11   dressing

This table gives the cut sizes for the fabric panels. All are cut rectangular. I allow 20 mm [ 0.8 ins ] for hem at each edge.

Make these panels, tailor to fit.

The side panels attach to the top of the side frames, along the back edge of the wood. The edge of the panel aligns with the join between the side and dorsal frames. The outside of the panels hang out past the edge of the frame by 5 mm [ 0.2 ins ].

Fit three 300 mm lengths of Velcro hooks to the top of each frame. One piece attaches adjacent to the hinge on the frame top. One piece is on the centre line of the panel. The last piece is located so that the both spans from piece to adjacent piece are the same. This permits the two panels to be interchanged.

The pelmet should work at 100 mm [ 4 ins ] seen. You may wish to adjust this. We removed cross fibres to make 15 mm [ 0.6 ins ] of fringe along the bottom.

When closed the curtains are to be used almost straight along the track, there is insufficient room for smooth movement with generous drapes. Make the curtains normally using rufflette tape.

The curtains hang down to 10 mm [ 0.4 ins ] below the top of the bottom rail. This prevents the curtain tangling with the back of the barrel pins. If you can ensure that there is no chance of snagging then a longer curtain would be better.

Fit curtains using six hooks on each side.

You will probably find back cloth that fits. Top and bottom need a hem. It must be tailored round the wood of the dorsal frame. This needs a U cut with square corners to be edged with bias binding.

Keep the bottom of the back cloth light and flexible to cause minimum distraction to the manipulators.

Fit Velcro cloth to the panels to match all the hooks mounted on the structure.

12   assembling

After the towers are in place, the rails are most easily fitted in this order :

1. fit the back rail
2. fit the bottom rail
3. fit the track rail

If I had known what I know now I would have put numbers on the rails, small, facing front by the connections.

13   final adjustment

When the structure is complete and assembled it should stand firmly on a level surface. If it rocks you can raise or lower a foot by adjustment of the magnet position.

This was first posted 24 March 2001. The text has been revised to correct errors and improve the explanation until 29 September 2001. Other changes were stylistic.

I will no longer maintain the page. My final thoughts on this are given below as an addendum, 16 April 2002.

Addendum

In use the structure is stable because all lateral thrusts are transmitted through the struts under compression. These primary loads put the magnet catches under compression.

I am disatisfied with the magnet catches. They are very easy to use but they are difficult to find and they are inflexible as a resource.

The magnets have only secondary uses. They hold the frames while being erected, they stop the struts falling sideways and they support the frames when the theatre is carried. The maximum static vertical load at the outer foot is half the weight of a frame, this load is 500 g [ 1.1 lbs ] .

For secure operation I want to carry a 100 % margin, equal to a load of 1 kg [ 2.2 lbs ] at the foot.

Bought catches are no use, they are all fiddly in use and have sharp edges.

At the time I made this I was fixed on a hardware solution. I now realise that simple handmade alternatives are possible. I describe two ideas here.

Both suggestions require a wooden block fitted to the frame upright, where the magnet catch would be fitted. This block has to be vertically as short as possible for the best angle of the strut.

Both the catches described do not include any means of adjustment. The block or the strut can be trimmed to adjust. I would clamp the block in place, adjust, test and then secure. I would not provide a rotatable 270 º spiral block, because little hands would unscrew it.

Velcro catches

The strut could be shaped as drawn right.

The end face of the strut is recessed for the Velcro.

I tried this using my frame stock. I used 11 mm x 32 mm of Velcro. This provided an adequate area for the toe to press against the block.

It is necessary to trim off the sewing borders from the Velcro to get the maximum active area. It is also necessary to adhere the Velcro with epoxy resin.

My test supported 700 g at the foot.

700 g is not enough. But this can be increased by locally widening the strut. With no loss there is space available equal to the thickness of two hinges. If more area of Velcro is required then the strut may be made wider still opening the frame slightly in storage.

To support 1 kg the width of the Velcro should be 16.5 mm. Because the Velcro is on an oblique face this requires an extra thickness of 4 mm. Constuctors can decide just how much Velcro to use and so what extra width is needed.

The sensible approach is to add the width of the two hinges.

Elastic

A length of elastic material may run close to the line of the strut. I draw this showing the elastic material in red.

The tension in the elastic material is to be 1.5 kg [ 3.3 lb ] . The elastic length is 490 mm [ 19.3 ins ] . The extension under load may be as little as 5 %, depending on the material.

The block may be given an oblique face and the strut cut to match so that the strut swings into place with no over movement of the frame.

Suitable elastic material may any one of be synthetic mutifilament, rubber in a braided sheath or a monofilament. This is the same problem solved in trampolines. The difficulty is finding 2 metres.

Attachment at the bottom could be by one or two holes through the horizontal piece, pieces E. The connection can be recessed on the under side.

Attachment at the top is harder because the vertical piece of the dorsal frame is on show and must not be drilled. The solution is to connect to the vertical piece of the side frame, piece B. Perhaps one piece of elastic could be secured to serve both frames.

Because of the hinge spaces the elastic should not interfere with the folding of the frames.

If I was doing it now I think I would try to make it work with Velcro, because that is available. Upholsterers use it.