Machining a job that is outside a milling machine’s table travel using Fusion 360

Introduction

This write up is not for the purists with years of experience but is an explanation of how I thought through how to machine something over size that would not fit into my Tormach PCNC440 milling footprint as a single operation.  Hopefully it might help others to grasp the process.

The challenge began when a local turret clock expert came to me and asked if I could machine a new Hour and Minute Hand for a clock he was working on.   The Hour Hand was around 14” long and the Minute Hand some 18” long.   

Here is the Fusion 360 view of the minute Hand.

clock minute hand milled in three steps

Clearly these lengths were way outside the 440 table X movement (10”) so a plan was needed.  There then followed a lot of staring into the distance at mealtimes and also at bedtime accompanied by vocal “hmmm”s as I tried to mentally visualise what was needed.  This idiosyncrasy is something my wife has come to terms with over the years…..

My conclusion from this mental preparation was that I needed to be able to accurately step the stock across the tooling table and then take two or three bites at the profile machining.  

What follows would almost certainly benefit from a video but sadly I am not set up for this. 

Click the link below to download the PDF document.

Milling an oversize object

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A Spanner in the Works – or simply a Stick

From previous posts you will be aware of my involvement maintaining the local church clock.   Over the past months my colleague and I have been nibbling away at various little problemettes with the movement and things are now looking quite good.   For the past two weeks it has run sweetly and maintained +/-1 second over that period.

Then last night it stopped.

This morning we wandered round to see what the problem might be.  The first thing we do on arrival is look at the front dial to see at what time it had stopped.   This time it had stopped at around 10.35 last night. We climbed the tower and inspected the movement.   

There did not seem anything obviously wrong so we decided to swing the pendulum and get it working again. We had arrived at just before 10am and our inspection took us over the hour and the front the dial was showing 10.35.  Because we were now ‘within the hour’ it was acceptable to wind the hands back to the correct time which was now just after 10am.   

I pulled out the motion work locking pin and began to move the hands (which were now independent of the movement) in a backwards direction to set the time. Except the hands would not move backwards.   There was resistance.  Something bad had happened to the motion work.   

We checked the mechanism to both the front and rear dial but there was nothing obviously wrong but the hands refused to go backwards under light pressure and I did not want to force anything at this stage.

We went outside again and this time checked the front and now also the rear dial and this is what we saw : –

church clock with stick jamming the mechanism

Our feathered friends had built a nest on the belfry window ledge and a stick had fallen from the nest and jammed itself in the dial.   The odds of this happening must be pretty thin.

A careful waggle of the hands back and forth broke the stick free and we then reset the time and hopefully all will now be well.

The interesting observation was that the stick was only brushing the hand in the forward direction but in reverse it was pushing against it.    The forward resistance was still sufficient to reflect back through the motion work into the main mechanism to stop the escapement and therefore the clock.

Another bit of knowledge gained.

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The Gravity of the Village Clock

Some time ago I made mention of getting involved with the running of the village clock.   There was an added incentive as this was a Cooke of York movement dating back to 1869.  Anything associated with the  City of York is always of high interest as it was my birth place.  That is except the soccer team but I try not to get drawn into that discussion.

Back to the clock.  Myself and a colleague in the village have been working on the clock to bring it back to time.  We were getting pretty close.   Then it stopped.   Despite a few restarts it refused to run for any length of time.

We rolled up our sleeves and gave it a thorough visual inspection.   We were just about to leave it for the day when we spotted that the pins on the pin wheel on the gravity escapement arbor seemed very tight to the arbor supporting bracket.   Closer inspection revealed one pin of the five seemed to be slightly at an angle.  Even closer inspection showed a visible witness mark on the bracket where the pin or pins were rubbing on the bracket.   There was no mechanism to centre the arbor away from the bracket.   

We decided to remove the arbor complete with pin wheel, fly etc.   This was fairly straightforward.  A single screw at the opposite end to the escapement arms could be unfastened and the arbour came free.  Except it wasn’t that easy to unscrew as the screwdriver slot was very narrow.

Having got the arbor assembly back to my workshop I discovered two of the pins were lose, one of them to the point of falling out.   It seemed to have been held in place from coming out any further by the support bracket.   

I marked and numbered the escapement legs and removed each pin in turn, shortened each by 0.5mm, degreased the threads on each pin and its associated mounting hole and then refitted each one with a dab of Loctite to hold them in place. 

Spinning the arbor in my hand I could now see that all pins looked parallel and the length was much more consistent.  Hopefully the pins will now comfortably clear the mounting bracket.

The gravity escapement arbor showing the five escapement legs and the five pins that needed shortening

To make refitting easier I made a small hand tool to fit the slot on the mounting screw and used a hacksaw blade as a pseudo screwdriver blade to more easily turn and tighten the screw.

Since refitting the arbor the clock was running slightly slowly so we removed a penny from the weight tray and it now seems pretty much spot on.

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Microset Clock Timing Instrument Upgrade

Mumford Microset Clock and Watch Timer

Some while ago I bought a Microset Timer from Bryan Mumford.   This is a lovely device that allows you to monitor all manner of parameters on clocks and watches.   It has an acoustic sensor to listen to the beat of the clock or watch and an optical sensor that creates and detects a beam of light that is chopped by the pendulum.   From these simple accessories all manner of diagnostics can be done on the clock under inspection.   If you want to know more I suggest you log into Bryan’s site.   Bryan also has some videos which you can find on YouTube.   You might also want to download and read a pdf collection of articles written by Chris McKay in the Horological Journal about using the Microset to fault find on Turret Clocks.

Microset Timer from Mumford Micro Systems

The Local Church Clock

If you are a regular reader of this blog you will know that I have got involved with the local church clock which is a Cooke of York movement.   I have been working with a fellow engineer in the village to try to bring the clock to time and we are slowly getting there.   Our last major breakthrough was finding the fly was lose on the gravity escapement arbor.   Since tightening the fly the clock has been much more reliable.

There is a weight tray on the pendulum which has an assortment of coins in it where someone historically has been fine tuning the pendulum swing. Because the clock has been running fast by a few seconds per day we have been slowly removing the coins one by one to bring it closer to time.   I think it is now at a point where we need to monitor it long term with the Microset.

Microset Upgrades

Bryan offers an upgrade to the Microset that allows a temperature sensor to be added to the recorded information.   There will almost certainly be temperature changes in the clock tower so it seemed like a good idea to upgrade with the temperature option.   This was ordered and duly arrived from Bryan and is now fitted.   There is also an upgrade to allow the Microset to record data into internal storage in the Microset rather than depending on having a PC connected.   I would be more comfortable leaving just the Microset in the church pendulum cupboard rather than my portable PC so I also ordered this upgrade.

It took me about an hour to do both upgrades on the Microset.   The memory upgrade involves a chip change inside the device and the temperature monitor needs an additional 3.5mm jack socket fitting and wiring to accept the new temperature sensor.   Neither is a difficult task but clearly need to be done carefully so as not to do any damage to the Microset.   Bryan’s instructions are well written and illustrated.

Since the upgrade I have been running the Microset on the bench with a Smith’s clock movement.  (It is actually the one I stripped down, cleaned and rebuilt on my ‘Clocks 1’ course at the BHI).   The new Microset facilities seem to work well and as expected.

Microset optical sensor monitoring a Smith’s clock mechanism

A New Sensor Needed – 1st Attempt

To implement measurements on the church clock the supplied optical sensor as shown in the picture above is not totally ideal.   It has a very narrow gap between the transmit light source and the receiver detector diode which on a turret clock is not  easy to use.   

It is possible to get round this my fitting a cocktail stick or similar to the pendulum bob and using this to break the beam but it is a bit messy. I had picked up a bag of laser diodes and detectors at a local ‘ham’ radio junk sale and I decided these might form the basis of a new sensor which might be more useful to a large pendulum assembly.   Bryan is a really helpful guy and although he does offer a larger laser sensor he was more than happy to help me with the required electronic interface to the Microset.  The one proviso is that the amount of current drained from the Microset 5V power supply must be kept below 30mA.

I set to and made the most elegant and over engineered solution for my laser sensor.   This is shown below.   The black mountings were designed in Fusion 360 and 3D printed on the Sindoh 3DWOX.

First ‘elegant’ laser detector for Microset timing instrument

The spacing between the emitter and detector is adjustable by sliding the transmitter along the steel rods.   The power to the laser is also carried down the steel rods.   A small DTC transistor provides the interface to the Microset and the 5V supply provided by the Microset is dropped via two diodes to power the laser.    It works really well ….. but … when I went round to the church to install it I realised I should have checked one or two things first.    The rating nut at the bottom end of the pendulum (used to make course adjustments to the pendulum length) was almost touching the floor of the pendulum cupboard.   My wonderfully elegant laser detector would not fit under the pendulum to monitor the swing.  A serious re-think was needed. The gap was so narrow that at best I will only be able to get a piece of 16 SWG aluminium sheet or PCB underneath the rating nut.

A New Sensor Needed – 2nd Attempt

I did say I had a bag of laser diodes and detectors so a new version would be possible and I could then save the posh one for more public facing activity.

As mentioned above I decided to use PCB as the base board.   This is shown below.

Mk11 Laser Detector Specific to local church clock with little clearance from rating nut to floor

This has the advantage that I can use the copper surface to mill tracking into it to aid the wiring.   The downside is that it is quite flexible and therefore possibly not stable enough to keep the laser aligned with the detector diode.    To resolve this I soldered strips of nickel silver (could have been more PCB) either side of the centre line as shown but leaving a gap for the pendulum swing.

I designed a common holder for the laser and detector diode in Fusion 360 and 3D printed two of these on the Sindoh 3DWOX.

The finished detector assembly still had a tendency to flex so I stuck some old pieces of credit card on the lower surface, one at each end before the mount and a large piece in the middle.   This seemed to cure the problem without adding significantly to the base thickness.

Microset Display

When plugged into the Microset all seemed to work well.   Here is a typical PC display of the Microset data.

Microset Data Display showing the data from a Smiths clock mechanism and also the green line showing the temperature

I now need to get it installed in the church tower.

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