Wooden Screw Clamp, antique design with wooden screws.

First Attempt.

 I thought it would be interesting to make an antique version of the Dubuque clamp and since I have never made threads on rods, it should prove educational. Below is one example of a clamp:

An example of a wooden threaded clamp.

 This isn't a variable angle clamp and operates in a different way to the Dubuque clamp. The arm nearest the jaw opening has a none-threaded hole on one side nearest the handle with a screw thread on the other arm. The other spindle furthest from the jaw mouth is threaded nearest the handle but the other end is stopped within the arm. As with the Dubuque clamp, the handles are on opposite sides of the clamp. Hence the threads on the two spindles are in the same direction. This also means that loosening the clamp means moving the arms to keep the spindles in place. One way around this is to fit "gaiters" that fit around the spindle in a groove made in the spindle close to the arm, e.g in the above photo these would be in the upper arm. However, the one shown does not have gaiters.

To start, I experimented cutting threads on some 3/4 inch ash dowel, first just using kiln dried dowel and then soaking the ash in mineral oil (Butcher's Block oil) for several days. I used the thread cutter from Axminster tools that is made in Taiwan. The initial cutting gave some intermittent tear-out on the threads as shown. This did not improve much after soaking for up to 3 days so I decided to leave the wood longer in the oil.  

 

My first attempt at cutting a thread on a length of 3/4 inch kiln dried ash dowel.  

In the end I left the dowels in the oil for two weeks but still experienced some tear-out on the threads. I then looked in more detail to the thread cutter.

View into the thread cutter. This shows the "v" blade position at the mouth and the die that the threads then pass though. The position of the cutter can be adjusted "in or out" but it is important that the threads that are cut can travel easily into the die and not bind..ask me how I know?

As far as I can see, there is not much room for adjustment of any kind, e.g. it is not possible to lessen the depth of cut much as the threads need to pass though the metal die. On my first attempt on the oil dowel, I noticed that the blade had been damaged on one of the "v" edges. Luckily I had a spare blade that I used to complete the job. I have since re-sharpened the damaged blade but haven't used it yet. It seems to be pretty soft metal and easily shaped with a diamond sharpener. This also means that the cutter blade will be easily damaged. Anyway, I will report on this later when I have more experience. 

(see footnote on thread cutter experience). 

The dowels that I'd chosen for the spindles fitted neatly into the box of the cutter but I noticed that other dowels bought at the same time did not fit and needed reducing just a little in diameter to get a frictionless and neat fit. The cutting went fairly easily remembering to chamfer the top 1/8 inch of the dowel and also to apply some pressure to get the threader started. May be I was lucky but the cutting went easily without binding. I think it is important to get the dowel the correct size and to know the amount of force needed to turn the threads. If the threader gets very hard or binds, it is no use trying to force it further. Later after doing some further trials it seems that the position of the cutter is pretty crucial so if the cut is not enough, the dowel will bind in the die. If the wood is not fine grained enough or too dry, tear-out will lead to binding in the die and the whole cutter will not work and just strip the wood.

Having made the spindles, I made the arms out of some used beech (oven dried). These were 11 inches long and 2 inches wide (1 inch thick). I drilled holes for the spindles 5 1/2 inches from the pincer jaw and 1 3/8 inch from the end. On the left hand jaw, the holes were 5/8 inch ready for threading and on the right hand jaw the top one was 5/8 inch stopped at a depth of 1 inch and the lower one was 3/4 inch for the straight through part of the spindle. The threads were cut in the beech easily and without any problems.

The spindles were 14 inches long. this allowed 2 inches through each arm, 8 inches for maximum jaw opening and 2 inches for the handle fitting. I made the gaiters from a 6 mm slice of beech about 6 cm long and to the depth of the arms. The grooves in the spindles were made 6 mm wide just inside the arm so that the gaiters were flush with the inside arm surface. The grooves were cut by a combination of sawing, chisel work and filing to a concentric channel. Finally, the gaiters were housed in a housing cut-out chiselled inside of the jaws. The fit was tested, adjusted and then screwed into place.

Finally the handles were cut from some green ash and shaped (about 4 inches long) and a 3/4 inch hole drilled into the centre to a depth of 2 inches to house the end of the spindle.

The final clamp made from beech (arms) and ash (spindles and handles). Some tear-out on the threads but this doesn't seem to effect its use.

Not perfect, but this is my first attempt and it is going to be useful. Next time I will try the following:

1. Try beech for the spindles. This is likely to be closer grained and more amenable to turning threads and hopefully reduce tear-out.

2. Try using greenwood ash.

3. Prepare the spindles better by turning on the lathe to make integral handles and the grooves for the gaiters. 

4. Try making gaiters differently by using two pegs on each side of the spindle but positioned half-way across the arm so they intercept the groove. This looks to be a neater method.

Meanwhile I did a couple of experiments. The first was using a log of  ash (probably a few months old after felling) and turning small section it on my pole lathe to 3/4 inch diameter (19.05 mm). I checked the diameter with a vernier so it was a snug fit and then passed it through top section of the thread cutter (i.e. unscrewed the top of the cutter and checked that the dowel passed through easily but not too loose). Also I had a section of ash thread I'd cut when I first got the cutter and used this to position the blade in the cutter by screwing it through the tool and checking the fit. 

Piece of greenwood ash dowel (3/4 inch diameter) and handle made on my pole lathe.

I then dipped this is some Butcher's oil for 10 minutes and used the cutter to make threads. I applied pressure to start with and had a few crunching sounds but then it turned smoothly producing a thread of wood shavings from the cutter. This didn't happen with the dried ash used to make the screw clamp as described above. I then coated this with some boiled linseed oil and left to dry. At this stage the thread went smoothly (not overly tight and a snug fit) through a nut I'd previously made from dried beech. 

Dowel after threading.

Close-up view of the threads cut on the greenwood ash.

The other experiment was using a piece of kiln dried beech that had been stored for some years in my unheated workshop. I rounded this with a drawing knife and turned to 3/4 inch on my pole lathe. Again I checked the fit through the cutter box and made adjustments on the lathe so the fit was snug and not too tight. I then immersed this in Butcher's block oil for two days.

Kiln dried beech dowel (3/4 inch diameter) and handle turned on my pole lathe.

 

After threads cut on the beech spindle

Close - up of beech spindle threads.

The thread cutting was successful and went without any problems. 

(see footnote on thread cutter experience). 

Second Attempt

I tried another wooden clamp, this time using some waste beech and the spindle shown above together with another spindle made in the same way. The advantage of making them on a pole lathe is that the handles can be turned on the end of the dowel and also the grooves in the spindles to hold the gaiters can be positioned easily. Hence the spindles can be remounted on the lathe at any point when making the clamp.

The clamp is smaller (6 1/2 inch mouth and 8 1/2 inch arms) but similar in design to the one I made above apart from the method of holding spindles in place. The gaiters were basically rods either side sliding in the grooves in the spindles. I drilled the holes for the rods in the arms before I drilled the holes for the spindles and then checked the positions for the grooves in the spindles before turning them on the pole lathe. The rods were 1/4 inch square, the grooves just over 1/4 inch wide so the mortices were squared with a 1/4 inch chisel.

Finished clamp showing the positions of the four gaiters on the left-hand side.

I did make some mistakes. One of the holes for the spindle was not aligned correctly. As these are hand drilled it would have been better to drill through both arms clamped together, so lesson learned. The other mistake was to make the mortices for rods for the stopped mortice closer to the inside rather than in the centre of the arm to give more clearance of the gaiter from the end of the spindle. The end of the stopped spindle was 15.1 mm diameter as determined by the internal diameter of the 3/4 inch cutting box and with a 1/4 inch rod, the groove was 8.7 mm diameter so not a lot of room to spare.

I treated the wood with linseed oil and the threads with wax (applied the wax and then threaded it through to remove any excess wax). I had to enlarge the stopped hole a little because of the misalignment making it stiff to turn but the clamp works well now it has been used a few time. 

Comparing the two, I would say the beech spindle clamp has tighter threads and there is less movement. Both are easy to use. I think the "peg method" of gaiters is better and more robust in use but is more difficult to make. Anyway, each time I make one I learn something new !!

Third attempt.

I made a third attempt this time using beech spindles and handles and using oak dowels for the gaiters. The jaw opening was 11 cm and the total length was 23 cm. I used thinner wood for the arms, about 1 by 1 inch and made the handles out of a 1 by 1 inch beech off-cuts, about 3 inches long. I planed the arms to size and made 3/4 inch threads in one arm (at the centre and one about 1 inch from the end). The other arm is more complicated as it involves positioning gaiters to hold the spindles. I did this by marking the centres of the main holes using the first arm to get the exact position. I then marked the arm to show the position of the spindle edges, i.e. the top stopped spindle would be 15.1 mm diameter and the lower spindle 3/4 inch diameter. I centred the 5/16 th inch (6 mm) holes for the gaiters on the outer edges of the spindle and drilled from both sides. This gave a 3 mm channel in the spindles to allow the gaiter to hold the spindle in place. I then drilled the main holes, i.e. 15 mm and 3/4 inch for the spindles, intercepting the holes for the gaiters.

 I then mounted the beech dowels (8 inches long) on the pole lathe; these had been soaked in oil for 24 hours, and I sanded them to the correct diameter as they were supplied slightly over-size. The top spindle was to be threaded from stopped side, i.e not the handle side, so the spindle was reduced to 15.1 mm diameter on the pole lathe for the last 25 mm and then marked in the arm to locate the channel for the gaiter. This channel was then turned on the lathe and the depth checked against the arm. 

Likewise, the lower spindle was reduced to fit through the threader box top and the gaiter channel on the handle side marked using the arm and then turned, again checking the depth using the arm. On both spindles 1 1/2 inches of 3/4 inch dowel was allowed to fit into the beech handles.

The threads were then cut as described before taking care to keep their appropriate length. The arms were then chamfered as needed and the oak dowels for the gaiters inserted and checked for movement and the channels adjusted as needed. When finally constructed the gaiters were a tight fit but in addition a blob of glue was applied to each side before inserting and when dry, the dowels were chiselled to fit the arms.

The third clamp made from kiln dried beech and oak dowels for the gaiters. 

The clamp with dowels for the gaiters looks better and is easier to make. However, there is still a problem centred on making the gaiters. The gaiter on the stopped side is a smaller diameter (9 mm) as determined by the threader but seems fine and is not subject to shear. However, the gaiter on the handle side of the spindle closest to the jaw opening (13 mm diameter) is subject to sheer stress as the handle is tightened. Unfortunately I had made one of the gaiter holes too close to the centre of the spindle and so a deeper channel had to be turned that compromised the spindles strength. It hasn't sheared the spindle at the channel yet but fear it may well do so in use. To address this in the future I will take more care to position the gaiter holes relative to the spindle centreline and also move the centre for the gaiter dowels 1 mm outside the spindle edges giving channel depths of 2 mm (rather than 3 mm) and diameters of the spindles at the gaiters of 11 mm and 15 mm. Hopefully this will give more strength when tightening the jaws.

Final Attempt!!

Since writing this I have made two more similar clamps. In fact the one just described did shear as the channel for the gaiter was too deep. I made a new threaded spindle and this time omitted the the gaiter. Hence there was only a gaiter on the spindle on the stopped side. This worked fine and so in future I will only use gaiters on the spindle on the stopped side, i.e. on the spindle furthest from the jaw.

Spindle for the stopped side. The end diameter going into the arm is 15 mm and the channel about 6 mm wide and 2 mm deep (cut on the pole lathe). The spindle does not go completely through the arm and the threads only go as far as the inside surface of the arm. Two 8 mm oak dowels hold the spindle in place.

On the two further clamps I used beech dowels (adjusted to the correct diameter) that had been soaked in oil for two days, kiln-dried beech arms, 8 mm oak dowels for gaiters and dowelling the handles, and I turned four inch long ash handles on the pole lathe. In fact turning the handles from green wood is the most time consuming part of the project. The diameter of the handles was adjusted to allow the clamp to sit flat on a bench as sometimes it is necessary to clamp the clamp to the bench!

I guess this is the final version of a clamp with 8 inch arms and jaw opening of 6 inches that seems to fit the bill. It has been treated with linseed oil.

Beech arms, ash spindles and sycamore handles.  I found ash more difficult to thread even after 2 days soaking in oil,

Some notes as I make more clamps: 

1. The single gaiter works well but needs careful measurements to get right. I allow 2 mm overlap and I drill from each side.

2. Better to make handles the same diameter (or slightly less) than the arm depth so the clamp can sit flat on the bench.

3. It is essential to adjust the diameter of the spindle dowel so it fits through the thread- turning tool comfortably.

Based on this I made two more clamps. The holes in the non-threaded arm were enlarged slightly to compensate for minor misalignment of the screws and ease the turning when clamping, i.e. they should not be a tight fit especially when drilling by hand without a drill press.

Both of these have beech arms but the upper one has ash screws and handles.  Both the screws and the handles were turned on the pole lathe. One has 9 inch arms and the other, 10 inch arms. This seems to be a good design and both work freely.

Foot note on experience with using the thread cutter.

 

Since writing the above I have used the small thread cutter a lot and have come across one major problem apart from the fragility of the blades. I found that the cutter blade came out of alignment with the screw threads because of either movement of the barrel of the metal screw thread and also partly by wear of the beech base where the blade sits. This led to the effective threads per inch changing very slightly during cutting and causing the thread to bind when screwed into the "nut". to remedy this I removed the metal barrel (carefully punched it out using a wooden dowel) and reinserting with araldite adhesive being careful to adjust the position to seat the blade correctly. The rear of the beech seat for the blade was worn a little and so a small strip of brass was inserted at the rear to raise the blade as needed. Another strip was inserted nearer the blade tip to raise it a little. After several attempts to get the right position and adjustment, I compared the screws with those that had been cut when the thread cutter was new.

This shows the blade cutting when in good order. The wood was hazel cleaved from a tree trunk felled last winter (now late May) and rounded on the pole lathe and left for a week before finally rounding and getting to a diameter suitable for the thread cutter. The important thing here is the depth of the cutter adjusted by looking at successful threads and so that the blade is cutting right to the external surface of the dowel producing a deep thread without tear-out at the top of the thread, 

I did find the green hazel and sycamore available locally also gave clean cuts. Basically, cleaving green and doing some initial shaping with a drawknife and then on the pole lathe so that the section for threading is about 1 inch diameter. This was then left to dry for a week or more and then finally shaped on the pole lathe before threading.