Twenty years ago Bob Marvin wrote comm 180 outlining his method of making wooden bodied reamers for "flute type" instruments.

I have made a modification to the design outlined in comm 180 to allow the use of wooden bodied reamers to be reliably used in smaller instruments such as treble recorders or traversos. However the modification reduces the chip clearance and so reaming is slower. I have outlined the basic approach below, and I apologise for any duplication with comm 180

The main problems with wooden reamers are that there is a high level of friction between the wooden body of the reamer and the bore of the instrument, and that the wooden body of the reamer is not very stiff or strong to resist the friction torque. Obviously the approach to solving this problem is to make the reamer as stiff as possible within the limits of the material, and to reduce the friction and cutting loads as far as possible.

Examining a failed recorder centre joint reamer (made to Bob's design) I noticed that a crack had started at one of the holes drilled in the reamer to accept a fastening screw. This suggests that the holes in the reamer are acting as stress concentrators.

The reamer had also twisted along its length, and had felt very "spongy" during use.

I tried a number of different arrangements and then found that by bonding a metal blade into a substantially circular cross section reamer body you could get close to the strength and stiffness of a plain wooden rod, and as a secondary benefit you had no holes to act as stress concentrators.

Because most of the bore is now filled with the reamer body you need to pare away a little area ahead of the blade to allow the chips to collect.

Generally I have found (as was reported by Bob) that the body diameter needs to be around 0.2mm smaller than the blade dimension.

First cut a length of material allowing a transition section on the front to take the bore from the pilot hole size to the lower size of the reamer, and allowing a 75mm long handle with the bore profile length in between.

If your blank is nice and square in section then you can mount it in a four jaw chuck. The ones with engineering type jaws give a very good support to the blank. If the blank is not very square then use a prong drive, but you will need to be much more careful to avoid the blank whipping, particularly for long centre joint reamers..

Turn the blank 0.2mm under the bore profile at each measurement point. Turn the very end of the transition section to a diameter slightly less than 0.2mm under your pilot hole diameter. I usually do the final sizing with coarse sandpaper, as it is easy to ease the diameter to size and ensure that the profile is not wobbly in between the measurement points. Be careful if using this method as some woods have a marked difference in their radial and tangential hardnesses, and can sand noticeably oval. If this is the case then take the larger dimension and ensure that when you come to slit the reamer you cut along the long axis (or the reamer may bind in the bore).

Remove from the lathe and cut a longitudinal slit with a handsaw. The slit should run for the whole length of the reamer and extend down to the centreline (i.e. you are cutting down halfway)

Pare a small flat along one side of the slit to provide a small chip clearance area ahead of the cutting edge (see diagram above).

Try fit a blade into the slit and grind it away until there is only a small amount to be removed to bring the reamer to size. It is a good idea to rough grind the blade before bonding it into place, as you can cool the blade with water. Once the blade is in place you need to be very careful not to overheat the blade as it can destroy the bond between the blade and the adhesive.

Clean the blade with alcohol and bond it into place. Use plenty of adhesive, allowing it to squeeze out as the blade is inserted. The idea is to completely fill the slot up with metal blade and adhesive to replace the material removed during the slitting operation and return the strength of the reamer to a complete circular cross section. The blade should run for the whole length of the reamer, so that when it is bonded into place all of the reamer is stiffened up by closing the slot. Excess epoxy can be wiped off and remaining residue cleaned off with alcohol.

Allow the adhesive to cure completely. For standard araldite this takes at least 24 hours (48 hours is better). For the "5 minute" epoxies allow at least 1.5 hours!

The blade can be filed or ground to the correct bore profile according to your design. Be careful to grind or file the blade so that the back corner does not rub against the bore (making the ground edge of the blade tangential to the reamer body will do this). Also be careful not to remove too much material or you will have a section of the reamer that will not cut.

I use oak for my reamers. As hard and close grained as you can get. This is just because oak is a cheap and readily available wood with a hard surface and high strength. It is not the nicest of woods to turn, but is adequate if you do the final sizing with abrasive rather than try to get it to size with a turning tool.

Oak is not the easiest of woods to dry, so inspect the surface for checks to make sure your supplier hasn't dried it too fast. Assume that any surface checks travel a substantial distance into the wood and discard that piece and buy a different one. Even if the checks are shallow they can catch the tool and pull a chunk out of the surface rendering the reamer useless. If the wood has any defects at all you can expect the reamer to collapse in use, and all of your hard work will be wasted.

For long reamers 12" hacksaw blades are too short and I use bits of worn out bandsaw blade. However for shorter reamers (e.g. for a four joint flute) then Sandvik "All Hard" HSS hacksaw blades are excellent, producing a long lasting edge.

For slitting down the length of the reamer body I start the cut using a 550mm tensioned mitre saw. Once a kerf is established I use use a normal 22" handsaw with nice coarse teeth (7 tpi or so), so the sawdust will collect in the gullets. Just be careful of your fingers when establishing a kerf!

I use epoxy adhesive to hold the blade in place. Either "5 minute" Devcon, or standard Araldite.

To lubricate the reamer I have found that the best thing to use is talcum powder liberally rubbed in to the back of the reamer on the opposite side to the blade.

You can get cheap talcum powder from supermarkets without any scent, but all of my reamers smell of lavender, as I am using up one of Cath's unwanted Christmas presents!

I have been unsuccessful using either non-drying or drying oils, both when the reamer is soaked in oil and when the excess is wiped away. It works for a bit and then locks solid. However this may be due to the wood I am using for the reamer (Bob and others have recommended oil as a lubricant for wooden reamers).

I ream by hand gripping the blank in a vice and using and gripping the back of the reamer with an adjustable spanner. (I turn the reamer from 1" square section blanks and the handle section is left square).

It is important not to turn the reamer backwards when retracting it or the chips will lock up between the body and the bore.

Keep the reamer sharp! You don't need to raise a burr on the edge to get the reamer cutting but do keep an eye on it and sharpen it if necessary. Discard the reamer when sharpening has made the it cut undersize.

With a reamer with such a shall chip clearance area it can save a lot of time to step-drill the bore after the first pilot hole has been drilled through. Always leave the step-drilling a little short of the point where the drill diameter meets the final bore diameter to allow for slight eccentricity of the step-drilling and wander during reaming. Step-drilling also helps to reduce reamer wander as the reamer starts cutting at more than one place along its body, helping to align the reamer with the pilot hole.

It is important to retract the reamer every couple of turns and brush off the chips using a toothbrush or slip of wood. If you don't then the chips will bind as mentioned above. If you rub the planed surface of the chip clearance area with a soft pencil then it helps to stop the chips sticking.

Clive Catterall