OK so this is nothing radical but worth adding to the armoury.
I am in the process of making a protective box for my clock bushing tool and the various accessories that are used with it. I had some 9mm MDF board in stock that looked a potential candidate for this. The only problem with a 9mm board thickness is that this didn’t leave much margin for error using standard 6mm dowels and I did not want to use screws or nails to hold my box together.
The solution I came up with was to use 3mm bamboo barbeque sticks as dowel substitutes. These are incredibly strong in sub 25mm lengths.
I did cheat however and did not try fit them in blind holes but instead drilled the mounting holes through to the outside surface. It still looks OK and has resulted in a very strong structure.
Image of the side panel of my home made clock bushing tool protective box. This shows the bamboo barbeque stick dowels bonding into the edge of the 9mm MDF components (the ‘dowels’ can be seen as white dots along the top and bottom edge). The MDF is finished with Yachting Varnish. You can see what a messy painter I am ….
I was presented with a clock that seemed to be low on drive power and it was proving difficult to diagnose where the fault lay. I remembered seeing articles by both William Smith and John Wilding about a device that could give a relative measure of the drive power from the fusee. There is also a brief mention of this in Donald de Carle’s – Practical Clock Repairing.
This will be difficult to describe but in essence it is an adjustable balancing rod that is mounted on the fusee winding square. The movement’s centre wheel and second wheel are left in place but the escapement is removed. The rod has a sliding weight that can be adjusted to counter the drive power from the spring through the fusee chain to the fusee itself. By winding the fusee one step at a time and resetting and noting the counter weight position it is possible to derive a graph of fusee turns against drive power. Here is a pictorial view of the device and below that a picture of my version.
A sketch of the principle of the balance rod for fusee drive checkingMy version of the balance rod. The winding socket is interchangeable for different fusee square sizes.
William Smith suggested making the mass of the sliding weight equal to 1lb and measuring the weight position in inches from the balance centre to the centre of the weight. This results in a graph of drive in lbs/inches.
In practice the balance point is a little subjective to set. You need to move the weight back and forth such that the rod remains horizontally balanced against the drive from the fusee square. Once a balance point is achieved the distance from the moveable weight centre to the winding axis centre is recorded.
On this particular clock I plotted the results of the each turn of the full wind range of the fusee and the balance distance seemed to be reasonably repeatable and overall fairly flat. This suggested that perhaps there was not an individual fusee positional problem but something that was common mode across the range of the winding. To me this indicated that the drive transfer through the centre wheel and the second wheel was potentially the issue.
Checking the arbors against the plate pivots did not reveal a great deal of wear but on dismantling and checking more closely one of the centre wheel pivots had a worn curved profile. I re-made the pivot and re-bushed the plate and reassembled the movement. On re-running the test with the rod I found I had gained an extra 1″ movement of the balance weight along the rod. This suggested that more power was now being transmitted to the train, that is the train was not presenting such a high resistance to motion and more power was being created to drive the clock.
This appeared to solve the problem with the clock having a much stronger beat. This result is indicative of the value of this simple tool.
William Smith also suggests that the balance rod is useful as a temporary drive source. Suppose you have a clock stripped down and want to quickly check the train. Without fitting the barrel and fusee chain, the balance rod and balance weight can be mounted on the fusee square to provide quite a few minutes of drive to quickly exercise the train without having to undertake a full movement rebuild.
I had a recent request to machine some panels in 3mm thick ACM. This has a polyethylene core sandwiched and bonded between two thin sheets of aluminium. The sizes of the various panels requested could not be easily accommodated on my Tormach PCNC440 CNC mill so I had to dust off my CNCEST 3040T baby router. Five out of the six panels would fit inside the 3040 working footprint but the sixth required me to revert to a two setup movement of the workpiece in the Y axis. My write up of this stepping process for oversize objects can be read here.
The CNCEST 3040 has a maximum spindle speed of 10k RPM and is controlled using Mach3 with all the frustrations that brings to the party plus manual tool changes etc etc.
I received DXF drawings of the panels and these were imported into Fusion where they were simply extruded to 3mm before processing in Fusion Manufacturing. Each CAM operation was exported as a separate function into Mach3 regardless of tool changes. This gave me step by step control.
I used a 12mm thick MDF sacrificial (spoil) backing board to mount the panels. As all the panels were of the same general dimensions this made mounting the panels a repeatable process using a fixed matrix of woodscrews into the MDF. The 12mm depth of the mounting board made the tooling pin reference holes for the Y move much more rigidly fixed and as a result more repeatable to use.
The main problem encountered was that the ACM does not readily adapt to machining with conventional end mill cutters. I tried using my stock 2 flute parts and these would skim on the top aluminium surface while the plastic underneath deformed to the Z axis increasing pressure. Once sufficient pressure was exerted the tool would finally bite into the aluminium and punch through into the plastic with a noticeable ‘clunk’. This played all sorts of havoc with the Z axis height referencing and also lead at one stage to the Z axis stepper coupling working lose.
The solution was to go to a single flute spiral cutter style. These were purchased from APT Tools (UK supplier). Hot knife through butter comes to mind with the result of this change.
The single flute spiral end mill from APT Tooling UK
For straightforward hole cutting I used standard PCB carbide drill bits from Drill Services (UK supplier). These are nice to use as all have a standard 1/8″ shank which makes tool changing a little bit easier.
Once all these frustrations were overcome the process became much more repeatable albeit with one or two curved balls due to Mach3 lock ups. Have you ever enjoyed trying to manually re-reference a half finished job ? …..
The finished largest panel that required a two step movement in Y axis
More accumulated knowledge gained and lots of black plastic swarf (chips) to clean up before it could migrate everywhere into the house.
I have had a few requests for a compendium of all my spreadsheets created over the months and years. This will be a work in progress as new sheets are created and then added. Here are the current contents.
A Bull’s Foot file comes in various formats. In its simplest form it is a small circular filing surface mounted at right angles to a handle. Its common use is for making good after a clock plate has been re-bushed when there is a need to selectively finish the newly inserted bush material to be flush with the plate surface.
The commercially made files sometimes have a curved lower surface or have a periphery ring or bordering parallel strips of metal to ensure that the filing action cannot go deeper than the existing plate surface level. Without this the filing action would lead to unwanted scratching and disfigurement of the plate.
I have got around the commercial geometry by using a homemade flat filing surface with two protective spacing mediums. To get quickly to somewhere near flush I use a piece of 35mm film (5 thou thickness) with a suitable hole punched in it glued or held over the bush. This protects the plate from a wider area of damage caused by my flat homemade Bull’s Foot. There is graphical representation of the concept below. This is a method suggested by William Smith and John Wilding in their various books. If I want to get even closer to the plate surface I have some sticky backed shim material that is 1.2 thou thick that I stick around the bush.
With the commercial items, the bush is filed until flush using an increasing finer grade abrasion on the Bull’s Foot disc. This means having to have a number of different abrasive Bull’s Foot files. These are unusually difficult to source and expensive to accumulate.
My solution to this is to have a few Bull’s foot metal ‘blanks’ to which I mount appropriate circles of different grades of wet and dry paper. The chosen wet and dry is simply held in place on the ‘foot’ with double sided tape.
Homemade Bull’s Foot files and handles
The blanks (no more than 12mm diameter) are made from a disc of 3mm ground flat stock brazed onto a 3mm silver steel shaft. Once brazing is complete the disc is trued in the lathe by gripping the shaft. The shaft is then heated to allow bending at right angles and then mounted in a home made handle.
The handle is around 75mm long and is made from 15mm wooden dowel with a strengthening collar made from a 15mm length of 15mm copper water pipe. The dowel is turned down such that the collar is a push fit and a 3mm pilot hole is drilled in the end face. After preparation the dowel is varnished with the collar in place. These homemade handles get used on other tools around my workshop such as needle files and gravers.
I agree the wet and dry will not last for ever but it is a cost effective and flexible option to a box full of ‘proper but not used very often’ Bull’s Foot files. An alternative to using wet and dry is to Araldite shaped pieces of broken files onto a similar shaft and handle concept. These would last longer but once again more handles would be needed to cover the grades of file needed. The spacer medium would still be required to protect the plate surface.
For those of you more adventurous there is an alternative handheld solution detailed on the Sherline website.
