Workshop Wednesdays - Fluting Jig for Spindle Work archive

Wednesday 20 May 2015

Anthony Bailey shows us how to build a jig for successfully machining decoration on spindle work

Gallery

While it can be easy enough to turn legs, columns and other spindle forms, applying decorative fluting lengthwise is another matter and this is where the router, which is typically more of a general woodworking tool, can play its part. To do this requires the making of a special jig and it needs to be versatile and adjustable enough to do more than one job. The version shown here fits a flat bed lathe with a slot in the middle, but it would be possible to create a version that will fit on a twin-rod model as well. The jig will also need to be sized to fit your capacity lathe and the length of work you intend to do.

Equipment used

Piece of 18mm ply

Crosswise ply offcuts

Spiked T-nuts

G-cramp

Router trammel

Long, thin piece of MDF

6.4mm straight cutter

Large diameter Forstner bit

A piece of 19mm ply

Spirit level

A piece of 9mm birch ply

Portable saw

Guiderail

STEP 1

This is the bare turned spindle I will be experimenting on. Getting the router cutter to reach it may be limited by the square top section as it rotates to machine each flute. The jig needs to be able to tilt to match the slope of this and any subsequent legs and columns

STEP 2

The first job is to measure the gap in the bed so a piece of 18mm ply can be cut to be a good fit in the gap; this will locate the U-shaped box jig firmly in place

STEP 3

The next step is to check the width clearance needed for a typical piece that will need fluting. You must allow for the corners, as it will be rotated each time to create successive flutes

STEP 4

You are now able to work out the dimensions of the U-shaped box. Take the length between centres, the height which you feel should be slightly above the centreline and the clearance width. Carefully mark out each component on some 18mm birch ply and cut out with a portable saw and guiderail

STEP 5

Drill the base of the U-shaped box and screw exactly to the middle of the strip, which will sit in the lathe bed gap. Mark both pieces to ensure they locate accurately

STEP 6

It is best to not take any chances, so fit the base in place and check the centreline at both the headstock and tailstock ends; this way you know that the flutes will be parallel to the turning

STEP 7

Now the sides can be screwed to the base. They must be perpendicular so the sides are accurately positioned. The width clearance in the box should match your earlier measurement

STEP 8

Screw some crosswise ply offcuts into the box from underneath; these will hold the box firmly on the lathe bed

STEP 9

The basic box jig should look something like this. At the headstock end the index plate is located behind the chuck and will be essential for accurate positioning of the flutes

STEP 10

Drill four holes 25mm down from the top edge and 120mm in from the ends of the box on both sides - these should be the same 8mm diameter as some spiked T-nuts. Squeeze the T-nuts into the holes from the inside using a good old-fashioned G-cramp

STEP 11

The T-nuts have to sit completely flat on the ply surface so the bolts will be perpendicular when screwed into them

STEP 12

You need two identical movable pieces of 19mm ply to create the running surface for the router. In fact, they must raise and lower at both ends to take account of different size turnings. In order to do this, you need a router trammel. Mark the router's mounting hole positions on a thin, long piece of MDF

STEP 13

Once you have drilled the mounting holes, the router can then be fitted on with the correct diameter machine screws and a 6.4mm straight cutter plunged through it. Next, remove the router and using the cutter hole as a centre, guide a large diameter Forstner bit to drill a bigger hole; this will ensure you have good vision of the machining area

STEP 14

Use the router to drill a hole at the other end of the trammel, which corresponds to the distance between the T-nuts on the U-shaped box. Matching length marks make it possible to mark an arc limit at the end because the intention is to create short arc slots; this will allow each side piece to move up and down at both ends to match the slope of the turning. Here I am using the trammel to machine the first arc. At the other end, it is pivoting on a 6mm bolt in a hole drilled in the ply underneath

STEP 15

Here you can see the arc as it is machined - the centre hole in the trammel makes it possible to start and stop at the pencil lines, which denote the limit of the arc

STEP 16

The bolt at the other is held in the ply using a nut just below the MDF trammel. This bows the trammel slightly at this end but

is insignificant to the resulting cut

STEP 17

Creating the second arc by pivoting is a slight problem because there is no longer a single hole but a freshly machined slot. Carefully tighten the same bolt with a washer and nut in the middle of the arc, as denoted by the pencil centreline

STEP 18

Bolt the two movable side pieces onto the outside faces of the U-shaped box. Next, screw a piece of 19mm ply across the top of both at each end. At the headstock end, fit a wider piece with a cutout in the middle so it will fit around the chuck. If the lathe is sitting level, use a spirit level to check the movable assembly is also sitting level at each end

STEP 19

Now cut a piece of 9mm birch ply and drill and fit to the router base, then glue a small fillet underneath on each side. This router carriage must slide smoothly along the top of the box from end to end. It is best to do this while the glue is still wet, which will ensure a good fit with no waggle

STEP 20

The final assembly should look like this. Note how it consists of three parts: the fixed U-shaped box, the movable guide assembly and on top of that, the sliding router carriage

STEP 21

Here you can see a close-up view of the carriage sitting on the guide assembly. If necessary, you can lightly wax the meeting surfaces; this will give a smooth sliding action, although I didn't find it necessary

STEP 22

Each fluting job will be different. In this case, the fluting needs to stop slightly short of the long flat section. Use screws in the end blocks, which will limit router travel. This one is at the headstock end

STEP 23

At the tailstock end the screw is hardly extended at all as the stop block will already be sitting over the leg end

STEP 24

There are a variety of possible cutters you can use, which are available from all good cutter brands. However, some will work better than others and you need to choose the right sizes. Too big a diameter and the cuts will overlap at the narrow end of a taper. I have started by using corebox and V-cutters as they are easy to work with but there are curved profiles too. I decided to reverse the index plate as it was unmarked and then used a felt-tip pen to mark 20 evenly spaced holes to register on

STEP 25

Rest the cutter on the job and set the depth stop to give a modest cut depth to start with. Once you have done a pass and checked the depth, you can set it deeper if necessary. To defurr the cut, you can run the cutter back in the other direction, which will clean up the cut, then move to the next registration position and repeat the process, etc.

STEP 26

Here you can see the first completed leg in softwood, which was made using a small diameter corebox cutter. Now it's time to experiment with some other cutter profiles and see what you can produce


Woodworkers Institute

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Diagrams Click an image to enlarge

Handy Hints

1. Birch ply is the best jig-making material there is. It is clean looking, stable, reliable and available in a wide variety of thicknesses. Standard Far Eastern ply is often of variable quality, depending on which grade you buy and it does not look, well, jig like. It is not nearly so pleasing on the eye or as solid and dependable in the core structure. 18mm ply is best for rigid structures like this jig but a selection of thinner boards is also useful - 9mm, for example, is rigid enough to carry the weight of a router without reducing cut depth unduly. One of the most useful thicknesses when you need it, such as creating the curved stands for turned items as previously seen in Woodturning, is 1.5mm birch ply. Very thin but tough and flexible, it is perfect for laying up in several curved layers glued together
2. In terms of hardware, most of us keep a collection of nuts and bolts and washers for repairs and jig making in the workshop. I have a case each of coarse metric nuts, bolts and washers and, in addition, our local independent DIY superstore has every variety of fixing I could wish for. If you need knobs, T-nuts and other specialised fittings, companies such as Trend and Axminster can supply them. It is always worth keeping a selection in stock - you never know when you might need them
3. There are plenty of router cutter brands that have suitable cutters for router lathe work in their ranges. Wealden Tool Company Trend, Titman Axminster and CMT to name but a few. The trick is to find cutters that are the right diameter and the right profile. Whatever diameter of turning you intend creating, you need to work out in advance how many flutes you can machine successfully. To make the trial one in this article, I needed to have 20 equally spaced registration holes so the same number of flutes would be showing in-line with each flat face at the top of the leg. This narrowed down my cutter choice as did the diameter at each end as the cutter flutes would start to overlap at the bottom of the leg. The cutter manufacturers website should show each profile with its dimensions from which you can work out which size and type to buy
4. In terms of indexing, I have used a proprietary indexing jig, which is convenient and reliable especially if you already do indexing work on the lathe. However, it would be possible to make up your own plate if you have light engineering skills. It needs to be accurately bored and have a perfectly circular shape for balance when running, if you are doing turning. The advantage of making your own is that you can decide what index spacing you actually need. For router lathe work, you need less rather than more index positions, so you can create spacings that may not be available on a ready-made one. You will obviously need a rigid but adjustable indexing pin arm to lock into each hole; this could consist of a standard metric bolt, for example