Hello and welcome back to my blog. Today’s post continues a series in which I’m building a butler’s desk of American black walnut, in this post I will detail the process in which I make a stay for the fold down desk of brass using machine tools and files.
A stay is used to prevent damage to the desk top by way of accidental over extension without the supporting drawer extended. The stay will be made of three components; a hinged tab located on the inside of the desk, a slotted stop on the inside of the cabinet and a linkage which connects the two when the desk is opened.
I’ve searched high and low for a ready made stay, and while some options do exist I found faults with all of them, many of which looked so promising that I actually purchased and tested them ou
So, instead I set out to make my own, a process which begun by ordering sized chunks of 360 brass. 360 brass is very similar to 385 architectural brass (also known as architectural bronze) but made a little more easily machinable which also translates to a better finish off the machine.
Along with this batch of brass I decided to finally upgrade my collection of files, I ordered precision files from McMaster-Carr. I received Nicholson Swiss-made files that cut beautifully. My aging collection of junk files finally made their way to the trash.
The work began by first prepping the brass to rough dimension, flattening and squaring the faces of each piece. This process is critical as the machine will use these faces as reference. I also applied a basic layout, in ink, to prevent obvious errors.
With the brass now prepped, the next step is to setup the machine. I’m using a vise to hold the brass so the vise jaws must be aligned parallel to the travel of the machine. This will ensure that the resulting cut will also be parallel. I use a dial indicator on a stand with a magnet base to check against the face of the vise.
Next, after placing the brass in the vise I must ensure that the surface to be machined is running parallel along it’s top surface. I do that in much the same way, traveling the ways to check for runout. I ensure that it is accurate within .001″ along the length of the brass.
Next, I begin my first cut. I only have a few cutters for the milling machine, so I am using a large six flute end mill which will produces a quality surface finish.
After the inside corner is cut I can use that as a reference for the four cuts to follow. This creates the basic cutout for a tab which will be installed onto the interior desk face.
The next machine operation for this tab is to drill the center hole which will house a shouldered screw. The shouldered screw is a ‘friction-resistant’ screw, also made of 360 brass and to very tight tolerance. The screw is intended for laboratory equipment, but it will do well here.
Now that the rough cutout is complete, the next step is to refine the tab, a process I do by hand. First, I clipped the corners off with a hand saw and then filed the edge to a smooth radius. This is where the precision files come in to play, they allow a smooth surface finish.
Next, a consistent finish is applied by sanding with blocks and paper, and finally the outside corners are chamfered with the files.
The resulting piece is nearly complete but not quite, the anchor points are next to be cut, so back to the machine shop for those to be accurately drilled and chamfered.
Round two at the machine shop:
This time I scribed marks with a knife to cut down on time spent locating my bit. I’m cutting the part that will act as a receiver for the bar linkage, first making the slot.
Then cutting away to reveal the profile.
A nice benefit of building my own hardware is that I can build in offsets rather than working around preset offsets or working with sloppy tolerances to account for offsets. This will become more apparent once the parts are mortised into the case, but I accounted for the .040″ gap around the door by offsetting the slot in this receiver from the mounting plate by that same .040″. I did so in order to allow the bar to travel through it’s range of motion unhindered and without the need to account for change in angle in multiple directions.
The next step was to deck the bar linkage then drill and tap for the #10-32 shouldered screw.
After all of the machine work is complete, I return to the woodshop with parts in hand ready to begin filing.
The first step is to round the top of the linkage, install the machine screw and file the back of the screw flush.
Next I file the inside of the receiver until the corners are square. I also want the inside to slope downward at the bottom and up at the top to allow additional travel of the linkage bar.
Finally everything is filed, finished to 220 and chamfered at the corners. I will leave most of the hardware unfinished until it is test-fitted to the case, but I could not resist finishing at least one item.
I have assembled the linkage so that the complete stop can be seen.
The linkage bar will have a button installed into it, however, I must first install the linkage into the case and align everything correctly, after that is completed I can set the length exactly and put the machine screw stop in where it should reside.
I hope you have enjoyed this post, a brief aside from woodwork but all together critical for cabinetmaking, I look forward to your comments.