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Friday, 14 May 2021

The woodenclocks weight drive - Alternative designs.

 Wooden clocks are driven, in the main by a single drive weight hung from a cord wrapped around the Drum, and it is this type of drive that we are going to look at in this article.

In the first clock, I ever built I used a piece of granite with a hook screwed into the top, it worked well but did not sit well with the traditional image of a clock. For a long time, my plans just included a simple Brass weight which looked the part but, to be honest, wasn't necessarily very easy for woodworkers to construct, so began a series of designs using fabricated parts and some proprietary items.

Design 1 uses a Plastic Tube with wooden endcaps and a threaded rod with nuts at the top and bottom to hold the whole together. I wanted the weight to be attached to the cord simply but a screw-in hook was not going to work with the threaded rod sticking out the top of the weight. This led to the design shown below that uses a Bowline knot on the end of the cord and a wooden hoop holding the nut inside.

With this Tubular construction, the weight is added to the Tube before it is fully assembled. My favourite weight type is of course Lead as it is the densest material that you can practically use and it comes either as Lead shot or as cylindrical weights of the type generally used for Sash type windows.

An alternative to Lead is to use Ball bearings, if bought in the form of 'Catapult shot' they will be much cheaper.

I struggled for a while to find the correct type of Knot to use to hook up the weight to the clock. The problem was that all the knots I was trying would slip until I came across the Bowline knot which is shown here, a bit more complicated to tie but once done it works a treat with no slippage.

Design 2 simplifies the design so that the construction can use a simple hook to connect to the cord hanging from the Drum.

The same weight type can be used as in the previous design but the construction is slightly different in that the top and bottom end plugs are screwed to the Tube around the periphery as shown above.
To make this design even more flexible you can cut a large hole in the Top End plug so that Lead shot can be poured in or out to adjust the weight.

I have the tube shown with a Brass colouring in the above illustrations, you can achieve this by spraying the colour to the inside of the tube before assembly or wrap a self-adhesive Gold film around the outside to achieve the effect.

Design 3 goes for a really simple solution using a standard bottle to hold either Lead shot or Ball bearings or even water depending on your weight requirements.

The illustration above shows how this works using a 500 ml bottle with a Ø28 mm neck, the Hanger showed here cut from plywood sits over the neck and beneath the Cap and the Loop in the Cord formed using the Bowline Knot slips over the bottleneck and then around and to the front of the hanger to engage in the two notches. This simple attachment allows the bottle to be hung on the cord simply and neatly.

I have used this little part numerous times when building prototypes as it allows for the easiest way to adjust the weight to get the clock running regularly without overloading it and putting too much strain on the parts.

Design 4 uses a similar approach with cans, if you own a 3D printer then you can print this Cap adapter to be fitted to the top of a can so that you can use it as a weight on your clock. Click here for a link to the STL file

Design 5 uses a very simple brass weight which consists of a section of Ø24mm brass bar with a length calculated to give you the weight that you need. In the end, I liked this solution best as it was so simple and the small diameter bar give extra clearance from the pendulum Bob which is necessary for some of the clock designs.

To attach the weight to the cord, form a loop at the end of the cord using a Bowline knot and then push the loop in the short hole at the end of the weight. Fit the short weight pin through the cross hole and through the loop and then let the cord take the weight.

The calculation for the length of the bar is as follows:-

Length L = Weight W/π x Radius r ²  x 8.5   where 8.5 is the density of Brass in grams per cubic centre meter.

L = 500/π x 1.2²x 8.5 =12.9 cms ( I rounded it up to 13.5cm to allow for the hole drilled in the top.

Design 6 This is a variation of Design 2 where a single Pulley is incorporate to double the running time. The cord is passed beneath a Pully fixed to the top of the weight and the end anchored to the hook fixed into the clock frame. The only disadvantage to this is that you have to double the size of the weight as half of the weight is effectively lost as it goes into pulling on the Clocks framework.

Monday, 21 September 2020

A design for a Minute engine

 I have tried on several occasions to design a wooden clock with a Swiss Lever Escapement, but so far none has been really successful. The problem is that the lever requires a Balance wheel and Spring for it to work and I can not get a wooden spring to work successfully. 

I developed Clock 29 as a 3D printed clock a couple of years ago and this used a plastic spring but in association with a gravity escapement, so as a development project, the design of the Minute engine is to look at some of the variables that would need to be resolved for a clock utilising a Swiss lever movement to function

Typical Swiss Lever Escapement

Using the arrangement of the parts in the illustration above, which is standard for a typical Swiss lever escapement, the next decision to make was the type of drive train to use and what the power source would be. The power source was straight forward as I wanted a small compact design so it would have to be a steel clock spring that would allow the engine to run for several hours. 
From this point it the design of the gear train would hinge on the requirement to have as an output an Indicator Hand that would revolve once every minute. Initial testing of the oscillating frequency of the Balance wheel and spring suggested a gear pairing of around 10:1 for the first stage and then followed by a 64:1 would give a relatively simple 3 stage gear train with 10:1, 8:1, 8:1 using three large wheels with 64 teeth and two pinions with 8 Teeth and 1 Pinion with six teeth.

Gear train

This is the arrangement of gears that I finally settled on leaving only the connection to the Spring used to power the device and a frame to hold it all together.

The two images above show the completed Minute Engine and how the drive power is fed to the gears through the back frame.
The Engine, as designed here will run for around 4 hours on a complete wind is accurate to around 1 minute per hour. To improve on that accuracy more development will be needed on the Spring and the Balance wheel. The design of the balance wheel includes the provision for the fitting of up to 12 Ø4 diameter steel ball bearings around the periphery and in this case, I adjusted the number used to just 2 balls, 1 positioned at the 12 o'clock position and one positioned at the bottom in the 6 o'clock position.
This ran to within 45secs per hour, accuracy wise this was as good as I could achieve with this current arrangement
To improve the accuracy further, work is needed on the Balance Spring to speed up the running slightly to get to a more reasonable 10 seconds/hour which for a plastic 3D printed clock is probably as good as you could ever expect.

It was never my intention to create an actual clock from this exercise, only to use it as a means develop a working Swiss Lever Escapement and then use that as the engine to drive a complete 3D design for making by 3D printing. As a consequence of this, I inadvertently made it rather difficult to incorporate the Minute hand and Dial that would be essential to gauge the accuracy of the running clock, the subsequent compromise was the introduction of a Minute hand at the back of the gears and a short section of Dial mounted on the Back Frame, not ideal but I was able to use it to measure the accuracy of the running clock.

Building the prototype

Should you wish to make your own you can download the STL files from any of the sites listed below.

I would start with the main gears and make sure that the 3D prints are clean with no strings or bumps that could prevent the smooth running of the gear train.

You may have to drill the holes in the frames to size so all the holes indicated as being a Tight fit should be Ø3 mm diameter and the holes designated as loose should be Ø2.2 mm. Now mount the gears onto the shafts to the dimensions indicated above and lightly oil the shafts to ensure smooth running.

There are 5 pins to be fitted to the frame as shown above before attempting to fit and of the gear sub-assemblies, these will all be a tight fit in the frame. Again lightly oil the shafts prior to fitting the gears to them.

Start by fitting the 3 large 64 toothed gears and the small 6 toothed gear into the front frame.

The spring I used in this engine is a Loose Loop Triflex Clock Spring 6mm wide x 0.4mm thick x 1000 mm long, purchased from Cousins UK part number. The ends will have to be modified as shown above by heating the ends to red heat and allowing to cool slowly. This will soften the ends and enable them to be reworked so that they can fit onto the Cas and drive printed parts.

With the spring-loaded into its case and the drive component fitted into the centre of the spring, offer up the Spring case and slide the drive over the end of the shaft and push it home. You may have to slowly rotate the Spring Case Anti-clockwise to get the sprockets on the drive to engage and allow the assembly to be pushed right home flush with the back case.

Now for the tricky bit, whilst holding the spring case in place fit the Retaining ring over the Spring case, whilst swapping fingers so you never let go of the spring case, and then having got the retaining ring fully over the Spring case make sure the window in the side is near the bottom rotate the ring clockwise to the stop to finally have the spring locked in place. The last step is to fit the Sprig loaded Pawl to the bottom of the ratchet using the two pins on the frame beneath the spring. To fit the spring locate the left hand hole over the left hand pin and squeeze together the other ends so that the very end of the Pawl pokes through the window in the Spring Retainer and engages the Ratchet.

Start by fitting the Escape wheel to the end of the shaft that contains the 6 tooth gear on the other side of the frame, this should be a tight fit on the shaft. Follow this by sliding on the Lever and adding one of the endstops to retain it in place, this to be a loose fit on the shaft.
The Spring shown here in purple should be fitted along with the Spacer shown in blue to the back of the Balance wheel and orientated to the Balance wheel using the short pin. The outside end of the spring has a boss that should be fitted onto the short pin in the Frame and held in place with another Endstop.
Now fit the two ball bearings to the Top and Bottom positions on the balance wheel and finally fit the Balance wheel to its shaft securing with another Endstop. This Balance wheel / Spring sub-assembly should be a loose fit on the shaft.

That's it the Minute engine is complete and should run for a good 4 hours between winds.

Parts and materials required

1 - I used ABS for all of the parts and printed all the parts with 0.2 layer thickness and 50% fill, the exception to that was all of the smallest parts printed solid.

2 - The Mainspring was a Loose Loop Triflex Clock Spring 6mm wide x 0.4mm thick x 1000 mm long, purchased from Cousins UK Part number 6401000LL. Hopefully, the description is enough for you to source the same spring locally.

3 - All the shafts were made from Ø2 diameter Silver Steel or Drill Rod as it is termed in the US. A 300mm or 12" length should be sufficient.

4 - A couple of Ball bearings to weight the Balance wheel Ø4 mm diameter or Ø3/16"

5 - You can use this JPG files for the Dial insert that runs in an arc around the top of the back frame.

6 - STL files for you to build your own Minute Engine can be downloaded here.

7 - If you use Solidworks you can download the Spiral spring file here

Thursday, 14 February 2019

A chart for discovering Woodenclocks features.

There was a time, not so long ago that I could remember the details of all my clocks, but sadly there are now so many that it becomes progressively more difficult to do that. So if I am having trouble remembering details of all the clocks I realised that it must be twice as hard for you to make choices of the clock you want to make for yourself.
With this in mind, I have put together a chart that tries to list all the relevant information about each one to make your choice a little easier.
The chart is actually a PDF file that was created in Excel with each clock listed down the first column and the relevant feature information in the following columns.

Notes on the chart.

The first column, Made From indicates the material that the clock was designed to be made from, the great majority are designed to be made from hardwood and an earlier post on that topic gives you some help choosing the most suitable for your clock.
The choice, of course, is not limited to just wood, you can construct these clocks from metal or plastic as well, and many people have already done this, but wood is the most popular choice, after all, it is a wooden clocks website. There are some exceptions to this, and these are the 5 clocks designed and intended to be made using 3D Printing. These clocks are not supplied with DXF files for CNC machining but use STL files instead for use with a 3D printer. These were originally intended for use as prototypes for me when developing the clock designs, but have proved to be popular so they are now included in the portfolio of clocks.

Third column Units indicates whether the clocks were designed in mm or inches, all clocks from Clock 9 onwards are dual dimensioned in both mm and inches.

The fourth column indicates the degree of difficulty in building the clock. This is usually down to how complicated certain parts or assemblies are actually to make If a clock can be made entirely using the CNC machine and hand tools then it is easy. Even Easy clocks are not really simple, clocks to work continuously and accurately still take a lot of time and patience on your part so be prepared for a challenge.

With the Intermediate category, we have clocks that are a little more complex and will have bearings and ground steel shafts to provide more precision in the clock. You may also need to find some slightly more difficult assembly operations that need to be carried out.

When you get to the Hard clocks it's just more of everything that the others have and you probably need some better equipment like a lathe and pedestal drill.

There are a couple of Very hard clocks that both have a quite complicated build requirement and lots of fine adjusting to get the clocks to run and keep running.

The Longest Part column gives you some indication of the size of the finished clock, in each case, it will be the length of the Back frame of the clocks.

The Pendulum Length column gives you an indication of how fast the clock will tick, a length of 990 mm will do a tick-tock in 2 seconds, and a 250 mm length will do it in 1 second. So the shorter the pendulum the faster the rate. An earlier article on the subject of Pendulums explains this in more detail, see link below.

The Weight needed to run the clock continuously will vary dependent on the quality of the build, the more friction in the working gears the more weight you will need. My clocks being prototypes are generally speaking a little rough around the edges because of the change that gets made to the parts to get them to work in the first place. So you may well find that your clocks will need less weight to keep the clock running, you can only find this by experimentation.

The next column lists the Run Time, it is based on my experience with the building of the prototypes and can only be used as a guide, there are a lot of factors that can affect the running time, not least of which is the height of the clock above the floor, or more precisely how far the main weight will drop from fully wound to when it hits the floor. For the times listed in this column, I had the clocks mounted so that the centre of the dial was 1500 mm above floor level if your clock is mounted at 1650 mm then you will increase the running time by 10%. There are several ways to increase the run time, you can add a simple Pulley arrangement to double the run time but this will also require you to double the weight. The letter P adjacent to the run time in this column indicates that this clock was designed with a pulley built into it. There are other ways to increase run time, one is to reduce the diameter of the Drum so that less cord is let out with each rotation of the drum, but again this doubles the weight.

The final column Escapement tells you what type of Escapement is used to control the ticking of the clock, the simplest and most common escapement is called The Graham named after its inventor, this is a dead beat type escapement that halts the rotation of the Escape wheel at each Tick and Tock, a simple design that works really well but not the most efficient design because of the friction involved. The Gravity Escapement overcomes most of the areas of friction experienced in the Dead beat design, the design used on these clocks which I call the Woodenclocks Gravity Escapement was design specifically for use on these woodenclocks it is a more complex escapement but it does result in more efficient clock design. The Verge and Folio is one of the very first designs to be used in the very early clocks, it is visually quite interesting but not very accurate. Then there is the Grasshopper a very elegant design invented by John Harrison back in the 18th century, it is actually quite hard to get it going, needs a fair amount of tinkering. Finally, the Flying Pendulum is definitely one of a kind wonderful to watch it working but not very accurate.


Wood for Wooden clocks

Simple Pendulum

Thursday, 8 February 2018

How to cut Clock Frames on a smaller CNC table.- Part 2

In the previous post I looked at 4 ways to in which you could cut profiles that were longer than the working area of your CNC machines table.
This time I shall look at a single method that can be used to simplify the operation using the Cut2D software from Vetric

To start this we need fill out the Job Setup Dialogue in the top left hand corner of the screen, the blank size and thickness to be used , along with the Z datum and the XY Datum which importantly should be set in the bottom left corner of the blank, the red dot marking the spot.

Next we load the DXF file and centre it in the blank using the F9 key after highlighting all of the parts. Now draw on a horizontal line across the centre of the blank and draw on two holes near the ends of the that line as shown, and a further two holes on the bottom edge of the blank vertically aligned with the first two holes. The first two holes are the index holes in the blank and the bottom two are the location pin holes to be drilled in the spoil board on the table.

Having completed that we can generate the first tool path to drill the holes in the Spoil board, I have used a Ø3mm cutter for this, same as is used for all the other cuts. These two holes will be used later to fit location pins into when the blank has to be moved. Save this tool path and generate its gcode so that you can drill the holes in the Spoil Board later.

Now we can  generate the next tool path to cut the two holes on the centre line using the same cutter.

The tool path for all the holes is generated next, followed by the tool path for the outside profile cuts.

So far the tool path generation has followed the normal path, and at this stage you would be ready to generate the gcode for the rest of the cutter paths. We do however need an extra couple of steps now to generate two separate paths with a vertical displacement of the blank in between.
We do this using the Tool path Tiling Manager as indicated below, this brings up the dialogue box shown on the left. We need to select 'Feed through in Y' under Tile tool paths and the Tile Height to half the blank length. The first tile is shown as the bottom half of the blank and is marked T1, clicking on the Active Tile box  changes it between Tile1 and Tile 2.
You need to keep this Dialogue box open through the next steps.

With both 2D and 3D windows open on screen un-tick the 'Draw tool paths in original position'  and set to Tile 1. Now Tick the bottom 3 tool path box's so that they will be included in the generated gcode and save the tool paths.

The next step is to generate the code for the second tile, click on the Active tile box to change it to 'Tile 2' and also un-tick the 'Drill holes on the centre line ' box in the toolpaths window, as we don't want to cut into the location pin that will be fitted in that position, now save the tool paths.

The final step is to actually cut out the Backframe on the CNC machine, so step 1 is to cut out your blank and place it on the spoil board with the bottom edge of the board near the bottom of the table, mark the bottom left-hand corner of the board onto the table and then set up the Datum XY on the machine itself by moving the cutter to that location and zeroing it. Move the blank out of the way and Zero the Z height to the table top and load the gcode for drilling the two holes into the table, now cut the two holes.
With that preparation complete return the blank to the top of the spoil board and fix in position with the bottom left hand corner on the Datum XY mark and fix in position, zero the Z height to the top of the Blank if necessary .
Now load the tool paths for Tile 1 and cut the holes and profiles.
With that complete release the blank, fit two dowels into the two holes drilled into the spoil board and locate the blank over them and fix the blank down in its new position, load the tool path for tile 2 and complete all the cuts.
Thats it your done and hopefully have a perfect Backframe completed.

Thursday, 1 February 2018

How to cut Clock Frames on a smaller CNC table.

For several years I worked with a CNC machine that had a small 400mm x 250mm working area, not anymore, now I have a Stepcraft 600 with 600mm x 400mm working area and life is so much easier.
It did, however, make me realise that during all the times I struggled to cut those clock frames I had found a number of different ways to get around the problem so this article will describe 4 of those ways.
None of these is really simple and all require that you are able to use CAD software to manipulate the files, the first two can be done on 2D CAD using the DXF files whilst the last two require the use of 3D CAD to work with the STP or IGS files.

Method 1 - Vertical displacement of the Blank.

The first step is to download the DXF files and load it into your CAD software.

Once loaded you will need to draw a large rectangle around the Clock Frame and centre the frame within it, this represents the size of the actual wood blank you will be cutting the Frame from. Next draw in the two holes on the horizontal centre line of the blank shown above ringed in purple. 
Now draw two rectangles to form two virtual blanks, these join over the centre line of the actual blank. Now draw in the second pair of holes at the bottom shown here as half holes as the fall on the edge of the blank and will be drilled into the Baseboard only. 
The second pair of holes needs to be vertically aligned with the pair in the middle of the Blank, the size of the holes is up to you to suit whatever location pins you have to hand, and spaced widely apart. 

When the Virtual blanks and the holes have been added then you can save the virtual Blanks as two separate DXF files, as shown above, these are then ready to be loaded into your Cam software to generate the gcode. The blanks should be the same size as each other so that when you bring them into the CAM software you can make XY Datum position at the bottom left-hand corner of the blank.

The next step is to create a drilling operation to place the 2 bottom holes into your baseboard, then create another drilling operation for drilling the top holes in the top of the virtual Blank of the bottom section (green above). 
This preparatory work completed you can carry on and prepare all the cutting steps for both the virtual blanks.
The next step requires you to load the actual blank onto the CNC machine and place the bottom left-hand edge on the XY Datum, then clamp the blank in place and proceed with the cutting. 
When the cutting of the bottom section is complete you can fit two location dowels in the holes you previously drilled in the baseboard and then locate the holes drilled into to centre of the blank over the dowels, clamp down and complete the cutting operations on the top of the frame.

Method 2 - Radial displacement of the Blank.

The procedure for this method is pretty much the same as the Offset method but instead of moving the blank vertically between cuts we swivel the whole thing around 180 °.

This time load the DXF files into your CAD software and create the large outer rectangle that represents the actual blank and then the 3 location pin holes on the centre line. The centre hole is on the vertical centre of the blank and the two outer holes equally spaced each side. When completed the virtual blanks can again be saved as separate DXF files to be used in the CAM software.

The same procedure as before drill the 3 holes into the baseboard, making the Datum XY on the bottom left-hand corner of where the blank will fit, then load the blank with the bottom left-hand corner of the blank on the Datum XY, clamp in place and complete the drilling and cutting operations for the bottom section.
Now remove the blank from the baseboard, fit the 3 location pins and refit the blank rotated 180° and complete the cutting.

Method 3 - Make frame in multiple sections.

These next two methods require the manipulation of the 3D CAD files to cut the IGS or STP files into segments and then generating the DXF files from those new parts.
The files are loaded into your 3D software and then cut into 3 parts using a Z shape spline or surface to generate a Half Lap joint on the ends of the parts.

After the 3D model has been cut into the sections these sections are used to Generate new DXF files that can be used in the CAM software to generate the gcode for cutting the parts.

Method 4 - Simple split with Biscuit.

In the 3D  model cut out a pocket in the back of the frame between two holes and then cut the frame into two halves, see below.

After the 3D model has been cut into the sections these sections are used to Generate new DXF files that can be used in the CAM software to generate the gcode for cutting the parts.
With this method, it is also possible to make the changes in the 2D files by drawing the pocket and the split lines onto the 2D drawings files and creating two new DXF files that are used to generate the gcode.

Sources of 2D and 3D software

If you need 2D/3D CAD software you can try these sources

Autodesk Fusion 360  2D/3D CAD  free versions available.

Free CAD CAM software  for free software

Vetric Cut2D   Excellent for  CAM $149 / £110

Monday, 22 August 2016

Using a Balance wheel and Spring to regulate a wooden clock movement.

I had wondered for a while if it would be possible to regulate a wooden clock with a Balance wheel and spring instead of using a Pendulum. I'm not at all sure that it actually offers any advantage other than being far more compact, and that, of course, is where the original designs for this type of regulation originated.
The Lever escapement invented by Thomas Mudge in 1750, has been used in the vast majority of watches since the 19th century, despite its popularity it does have some drawbacks, the main one being that there are several points where friction occurs, so the incorporation of a gravity escapement could help overcome that when used in a wall mounted wooden clock.

To explore the possibilities further, I built a rig combining an existing Woodenclocks Gravity Escapement, with a Balance Wheel and Spring, instead of a  Pendulum used in the original. With some adjustment to the size and stiffness of the spring, the rig started to work.
Now I can start to look at a complete clock design using this concept to ensure that it would actually work in practice.

The action of the escapement is a little difficult to understand just from the video, but the following notes should hep.

 This is the view onto the Backplate of the new clock design with all the main components identified.

 Position 1: The balance wheel has reached its furthest Clockwise position, The Gravity arm has been pushed back by the Impulse Finger and so allowed the Lifting Lever to be released  and dropped down to its stop position ready to engage the next Lifting finger when the movement is reversed.

Position 2: The Gravity arm has now given its impulse to the Impulse Finger on the Balance wheel and the tip of the Gravity Arm is about to push on the trigger.

Position 3: The Gravity arm has now pushed the Trigger to release the Escape wheel, this must happen before the fork on the end of the Lifting Lever reaches Lifting Finger otherwise the mechanism will seize up.

Position 4 The Gravity Arm is now being pushed back by the clockwise rotation of the Escape wheel, the Lifting Finger is causing this by pushing against the fork in the end of the Lifting Lever.

Position 5 As the Gravity Arm is pushed back the Trigger is also moving back to its locking position ready to stop the rotation of the Escape wheel any further. The Balance Wheel has now reached its furthest Anti-clockwise rotation.

Position 6 - The Balance wheel is now free to move back Clockwise again and has nothing else to do until the Impulse Finger reaches the impulse pin to start the cycle over again. 

Monday, 16 November 2015

Cut 2D Inlay toolpaths

In the new desktop version of Cut 2D they have added several additional features to improve its functionality, included in these, is the new Inlay Toolpath commands.
I was interested in this particularly as it was a further way of adding numerals to the clock dials.
To test what it could do and to ensure that my new CNC router was capable I designed a small test piece that is shown below. It is simply 3 separate numerals and a small rectangular plaque with numeral shaped pockets, machined to fit the numerals into.

First step was to set up Cut 2D with a blank size and a thickness, which in this case was 90mm x 90mm x 6.2mm thick, and then load the DXF file and centre it in the blank using F9 function key.

The Inlay Toolpath command, is the new addition to the Toolpath operations menu shown below.
Clicking on the end icon brings up sub menu allowing you to choose which operation you want to do first. The first two choices are for the numeral itself in either a stepped or a straight form, with the second two choices for either a pocket or straight through cut.
One of the main advantages of using the Inlay tool path option is that when a pocket is programmed it takes account of the cutter size being used and adds the appropriate radius to the internal square corner on the numeral, if it didn't do this the numeral would not fit in the pocket without post machining operations.

First select the Pocket option and fill in the details required, including the Pocket allowance box highlighted below. The Pocket allowance is there to give you some clearance between the pocket and the numeral to be fitted into it, it is useful for giving space to fit if there is any post machining finishes to be added, paint or varnish etc.0.25 mm is a good starting Point.

Next select the Straight inlay option and fill in the details required, this time leave the Allowance offset at zero, its probably best to keep all your adjustments for the fit on the pocket. This time you will need to add tabs to hold the numerals in place when you cut through.

Next select the outline for the plaque and choose a normal 2D profile toolpath and fill out the details as you would normally, to cut straight through, again using tabs.

Now select all the tool paths and click on the preview  toolpaths to make sure it is going to cut what you require. Once that's OK the you can click on save toolpaths, now you are ready to machine.

Once that's OK the you can click on save toolpaths, now you are ready to machine. The image below shows the sample I machined and put together.