Wooden Bar Clamp

 I couldn't find any complete examples of wooden bar clamps that used wooden screws for tightening.  However, I've seen a few examples of modern bar clamps that use steel threads with wooden bars etc.  The project started when I had a piece of partly dried sycamore that I could use to make a screw and some left-over ash and beech pieces. However, both the ash and beech needed to be ripped to size and for this I used my frame rip saw that I had recently made. It was a good opportunity to try the saw and in fact I soon found that the rip blade needed sharpening and the kerf adjusted as it was too wide. The saw then worked well as it cut straight without difficulty.

Screw spindle ready for threading. This was made using a branch of sycamore turned on the pole lathe.

The stock pieces ready for planing. The bar is ash and the arms are dried beech. The tightening spindle has been threaded (1/2 inch). 

My plan is to make a through mortice on the left-hand sliding arm and a through mortice and tenon attaching the right-hand arm to the ash bar. The first stage was to plane the stock to size. The bar was 53 x 23 x 545 mm and the arms 18 x 3 x 5 mm after planing with the hole for the screw 35 mm from the top of the arm. The sizes were mainly determined by the sizes of stock I had available but large enough to provide sufficient strength.

One side of the clamp fitted with the screw spindle threaded (3/4 inch) and the through mortice for moving the arm completed.

The spindle was threaded in the usual way after soaking for 2 days. The through mortice was firstly drilled through with a No 10 auger (drilling from both sides) and then finished by chiselling. Care was needed to ensure a tight fit and to do this the final adjustments to the arm and mortice were done using the joining plane (for the arm) and fine wood file for the mortice. A small chamfer was planed on each corner of the arm. I had considered making the top and bottom of the arm rounded but decided against this as it could jeopardise the fit of the arm. 

Showing the through mortice and tenon on left with dowels through and the moving arm with locators.

I made the mortice and tenon a very tight fit with dowels through and then drilled 5/16 th holes for the oak dowels into the beech arm. I then used these holes to position holes in the ash bar. Care was needed to get the holes in line when drilling with a brace and bit. Final adjustments were made with a round file. 

The end of the screw spindle was fitted with a pressure plate with a gaiter to allow the screw to be turned without the plate turning. This is a similar method to that I used in making the small wooden clamps. Small 6 mm dowels were used in a channel in the screw (as shown below) that was cut in the spindle on the pole lathe. After treating the threads with wax, this seems to be working well.

Details of the gaiter. The two 6 mm dowels are not shown

The finished bar clamp.

Two oak pegs are used to locate the moveable arm on the bar and in addition, a threaded hole was made on the fixed arm as shown. The threaded spindle can be easily removed by pulling out the two dowels in the pressure plate (they are a friction fit and not glued), unscrewing the spindle and then relocating it as needed. 

I am not sure how this can be improved, no doubt I will discover with repeated use! (any ideas will be welcome). I did notice a little movement on the moveable arm when a lot of pressure is applied using the screw even though the arm has no play when the locating pegs are installed. I don't think this will  be a problem as the movement is very small but I have noticed on one design that a small wedge was knocked into the top of the moveable arm to prevent the arm being pushed from the vertical.

Overall, this is a tricky job because of the need to get a strong joint on the fixed arm and tight fit on the sliding arm to the bar. I managed this and was pleased with the fit. I expect the use of a pillow drill would make the process easier but I like my augers and brace too much!!