#4 The first year at the School of Jewellery.... (Part 2: Making a Mini Clock - The Main Plates)
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Now that the cube had been made it was possible to move on to more horology based making projects.
This project is split into 3 parts that span across the first 2 years of the course. The first parts include making plates, arbors, collets, pillars, screws, washers and nuts using a combination of hand and machine made techniques. The remaining part in the second year covers the machining of an escapement including the escape wheel and the pallets. Once finished, the mini clock will not work as such but it will contain a working escapement- the main goal of these modules is that participating students can machine to fine tolerances whilst also learning the basics of clock anatomy and clockmaking skills. Furthermore, it gives useful hands on experience with working with lathes and drills.
Having a plan, as with most things, is crucial to the success of this project. Certain processes have to be done in a certain order otherwise the component parts will not work effectively together and issues with alignment amongst others will occur. Without accurate datum surfaces there was a risk that all edges and holes could be positioned wrongly so I created a diagram with all of the necessary dimensions to refer to (see below).
We were supplied with 2 roughly cut lengths of 3mm thick brass plate, some different diameters of both round brass and silver steel bars and some hexagonal brass bar.
(Above) The brass plate before flatting
As the plates were going to be pinned together, the surfaces needed to be flatted with abrasive paper and any manufacturing inconsistencies removed. The rougher finish from the flatting helps to prevent the plates from sliding once pinned together and allows for more accurate drilling. The plates are pinned together so that when drilling and filing the two plates are exactly the same and should line up perfectly.
Before pinning, the plates need to be centre marked and drilled to accept the rivet wire. I used Dykem blue marking fluid on the outside of the plates, then marked the vertical and horizontal centre lines with a vernier caliper. The blue fluid is useful as it makes the markings very visible without scoring the brass itself- it can be purchased here. Safety precautions have to be followed when using this fluid as it is toxic in nature so I wear nitrile gloves when applying it and only use it in a well ventilated area! I securely taped the plates together, then clamped them in the pillar drill. I utilised a 1mm drill bit that I modified for brass by reducing the rake angle to 0 degrees. The drilling action used was a delicate touch, slowly nibbling away at the material then retracting every so often to remove debris. This action helps to cut an accurate round hole, and prevents scoring of the hole by waste swarf. Once completed, I inserted a small section of 1mm silver steel wire which was then hammered with a ball pein hammer to form a mushroom type rivet on each side of the plates.
(Above) Dykem and marking out
(Above) Hole for rivets
(Above) Riveted plates with silver steel wire
From the guidance received by my tutor, I started by filing one of the longer sides of the plates- this would act as my initial datum point for the whole project. When filing I used the straight edge of an engineer's square to check for trueness. Once I had achieved a perfectly flat edge I could start marking out the other edges from this. Filing was again used for the other edges and these were regularly checked with an engineer's square against the datum edge. I intentionally left the plates slightly wider (0.1mm) than the specification dimensions to allow for finishing which will be covered later on in the project. The plates required a step cut in the bottom for feet- I marked this out then cut down the sides with a piercing saw. Then using a cut 4 file with a safe edge, I filed the step out and finished it off with needle files.
(Above) Filing the 'step' feet
Next, I marked the position of the holes, and centre punched each. Six holes were to be drilled in total- four 4mm holes for the pillars, and two 1mm holes for the centre arbor and pallet arbors. Before drilling, I securely clamped the plates to a piece of MDF board on the pillar drill bed then spot drilled each centre punch mark to provide an accurate guide for the drill bit. I started drilling with a 1mm drill for pilot holes (with backed off rake for use with brass), then worked my way up to the final drill size. I chose to do it this way to prevent warping of the hole from large debris getting stuck.
The drill bits that I use are made by Dormer and the quality is very good. If working with different metals such as brass and steel it is worth having 2 sets of bits as the rake angle of one set will have to be modified to be able to cut through brass effectively and safely. The set I have comes with 51 bits in a plastic storage box/rack and can be bought here.
(Above) The plates are complete - prior to separation
All of the holes were now drilled and the outer profile of the plates completed so the rivets were removed, and voila! Two identical plates had been made!
Next time I will move on to how I made the pillars, nuts and screws that hold the plates together!
Best wishes,
Chris