Woody's Workshop – Page 44 – Keeping the Grey Matter active

March 21, 2019February 25, 2021

A Mini Vacuum Clamping Table for PCB Engraving

You know only too well how I keep on going on about FlatCam and milling printed circuit boards on the Tormach PCNC440.

You will also have read about my preoccupation with trying to hold the PCB material flat to avoid variations in milling depth.

I have got it to a reasonably repeatable process using mechanical clamping but you know when a perfectionist starts something it has to be as good as possible …. step forward the Vacuum Clamping Table.

The thinking for this followed on from the Rosebud Grate experiments on my live steam locomotive. The grate consisted of a matrix of larger holes on the underside of the grate leading to a small bore hole on the top side of the grate. The theory as I understand it was that the reduction in size creates a Venturi type effect and boosts the air stream into the fire. I wondered therefore if I reversed the air flow i.e. sucked the air from the large hole into the small hole whether this would be beneficial in providing a boost of the suction. It is a bit tenuous I must admit and I can’t point to lots of science to back this up, but certainly worth a play.

First stop was Fusion 360 and a two part plate was designed. This consisted of a top and bottom part. The bottom part is 15mm cast aluminium with a milled trough and the top plate is 10mm cast aluminium with 6.8mm holes (no science – this is tapping size for M8 that was already in a Tormach collet) on the top side that reduce down to 1.3mm holes (ditto also already in a collet) as breakthrough holes on the bottom surface. Around the edges are M6 screw holes to clamp the two plates together and also M8 mounting holes to fasten the plate to the tooling plate on the Tormach. I didn’t quite think the suction connection fully. After I had worked out the total area of the 1.3mm holes I realised that to accommodate this I needed a 16mm diameter hole for the air inlet. This was not going to be possible to mount on the 25mm overall edge of the plate. The solution was to 3D print a connecting pipe and mount this on the top surface. This adapts to the vacuum cleaner pipe being used as the suction source. The 3D printed adapter did not provide a good seal to the top plate so I had to fit a rubber gasket on it. The parts were all put together as shown below.

Finished vacuum plate on test in the bench vice

Close up view of the 6.8mm blind holes leading to 1.3mm through holes

To my amazement it seems to work !

There does not seem to be leakage on the joint between the two plates and the vacuum pipe adapter with the rubber gasket seems to seal alright. If I put a large piece of PCB material over all the holes it is very difficult to move it. Single sided board is naturally bowed in the manufacturing lamination process and I can see it visibly jump flat when I turn on the vacuum. If the PCB is smaller than the total area of suction holes it does not seem to matter about covering over the ‘non-used’ holes to maintain the grip.

Proof will be when I try to run a board.

The milling process will not have major sideways pressure as the depth of milling is quite small so it should be fine. Clearly I can’t go drilling the component mounting holes in the PCB material with this holding technique but I can spot drill them to say 1mm depth and then finish them by hand having got a guide hole to start me off.

But all this will have to wait as the X axis limit switch has come apart on the Tormach and a spare has been ordered and is on its way.

UPDATE Feb 2021 – Flatcam and milling pcbs 2021 pdf download

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March 8, 2019March 13, 2019

A Bit off Piste – An eventful flight to Toulouse

This has nothing to do with model engineering but thought you might find it amusing/interesting.

Following my wife having spotted some low cost tickets to Toulouse from London Gatwick, we decided to make a quick trip to France to check out that all at our house was OK. The flight bookings were with a well known budget airline that has orange corporate colours.

We checked in OK and the flight pulled away from the stand dead on time but 5 minutes later we were back where we started from. As the Captain said ‘one of his shortest flights’. Apparently a critical sensor in the port engine had gone AWOL. Technicians were called and we sat for 2 hours on the plane while they analysed and fixed the problem.

Off we went once again but having missed our takeoff slot we were now at the back of the taxi queue. Finally we were sat at the end of the runway and the brakes were released …. only for pandemonium to break out in the cabin. The crew started rushing round and shouting to stay in our seats. The take off was aborted and we sat mid runway. Within minutes the plane was surrounded by all manner of fire appliances.

Apparently a passenger’s lithium power tank had burst into flames. I guess his or her laptop or phone’s battery had died while we were waiting for the sensor to be fixed and while topping up from the power tank the charging current surge had upset things. The crew had been quick to put the offending article in a fire proof box.

After blocking the runway for 6 minutes, we were escorted off the runway by the fire crew vehicles to a quiet area of the airfield. A team of fireman boarded the plane and took away the offending article.

While 6 minutes does not seem long there would have been a lot of landings and takeoffs blocked. Had we been airborne when the smoke appeared we could have been sliding down escape slides and the weather outside would not have made that much fun.

Because there had been an incident the airline procedure required that the crew had to be changed so they could be debriefed. We were therefore now faced the delay while a new crew was found. Further to this an offer was made that anyone wanting to leave the flight could do so (they didn’t ask for ‘any passengers of a nervous or superstitious disposition’). A number of passengers decided this was the best option. This meant a baggage crew had to be found to find their bags in the hold. So we had a baggage crew and a flight crew to wait for.

When the new crew arrived they had to search the cabin to match bags to passengers to ensure nothing owned by the departing passengers had been left behind (suspicious or otherwise).

After a total delay of 5 hours (still sitting in our allocated seats), we finally got airborne for Toulouse.

I won’t extend your boredom by telling you about the hire car shambles on our arrival.

We think we might think twice about flying to Toulouse another time but I have to say all credit to the flight crew, the technicians and the fire services for their swift and professional actions.

Postscript : – better to travel hopefully ….. we then had a 3 hour delay on the way home. Weather at Gatwick delayed the flight out to Toulouse. Think we will stick to the ferry next time.

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March 2, 2019March 4, 2021

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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February 22, 2019February 22, 2019

Setting up the timing on a Polly V locomotive

TLC for the Polly V

I have been the owner of a Polly V 5″ gauge locomotive for some time now. It has run OK but I have always had some unexplained happenings with it. Things like being reluctant to start and sounding ‘out of balance’ to use a clock making term. I also admit that while I know the overview of how it works I have never got to grips with Stephenson Valve Gear. I decided that some investigation was needed.

New Piston Rings

A bought a new pair of O rings for the cylinders a few weeks ago and decided it was time to fit these as a first step in an engine health check. This was easier to do than I expected. The end face of each cylinder is held in place with eight hex head screws and when these are removed the end plate can be taken off. The cylinder rod can be disconnected and the piston pushed out of the end sufficiently to swap out the O rings. A liberal coating of silicon grease on the new O ring allows the piston to be gently squeezed back into the cylinder and job done. Having completed this exercise I was feeling a bit more confident.

The Stephenson Link

Out of curiosity I decided to have a look inside the valve chests on top of the cylinders. These were a bit more fiddly to get at as I had to remove some of the chassis work but not a major problem. On the bottom face of each valve chamber are two slots. These slots allow steam in and out / to and from the piston cylinder. The timing block moves back and forth across these openings to alternately allow steam in and out of the piston chamber. The movement of the block is controlled by mechanical linkage and each cylinder is out of phase with the other to balance the drive to the wheels.

Having opened the two chests I noticed that both looked to be set up in a different way and as I rolled the engine up and down on the bench the openings in the bottom face of the chest were not revealed in a synchronised manner. Some investigation was needed.

When I bought the engine I also got a full set of the construction notes supplied with it from which the previous owner assembled it from new. I found these notes difficult to follow which was due to the fact that I was not conversant with the names of the individual parts mentioned. I stuck with it and the first thing that struck me as wrong was the gap at the end of the Stephenson Link was not the same in ‘Forward’ and ‘Reverse’ settings on the quadrant reverser. I had no idea why this was important and no idea of this was an absolute gap size that was needed (an actual measured distance) or just a relative similar size. Clearly it was not either of these and I needed to adjust it.

Much gloom followed as I realised the adjustment for this was behind the side water tank. This would have to come off. This looked fairly straightforward except the injector water feed is coupled into this tank in the cab area. The gland nut holding this is inside the water tank and a real pain to unfasten. The amount of arc that is possible to apply to the nut is very restricted. Eventually I managed to free this and the tank came away to reveal the quadrant rod adjuster. It was then a two minute job to adjust the quadrant rod length to balance up the end gaps on the Stephenson link in Forward and Reverse.

View showing side tank removed and the quadrant rod adjuster

Timing the Valve Gear

Having balanced the Stephenson Link, the next step was to adjust the valve blocks. I put the quadrant reverser at its Centre position and rolled the engine up and down on the bench watching each valve block move. The movement of each block was not symmetrical . In the Centre position the block should only just move a small amount back and forth to just reveal the two port openings in the base of the chamber.

This is easy to adjust by removing the valve actuating link arm screw. After some back and form adjusting I got the blocks to achieve the minimal movement needed about the centre position.

If I now rolled the engine back and forth on the bench in ‘Forward’ or ‘Reverse’ the movement of the blocks increased to reveal the full area of the two ports and with each side of the engine leading in turn. I now had a nice action of the valve blocks alternately opening and closing over the front and back ports with no excessive movement. Things looked much better. I cleaned up the valve chamber lid and fitted a new gasket to each chamber. I put the engine on the rolling road and using compressed air ran the engine up. Wonderful ! It now sounded more balanced and was much happier to start in Forward or Backwards. Here is a pictorial representation of the valve action.

Without the balancing in the Stephenson Link this would not have been possible to achieve.

The Eccentrics

While delving around on the underside I noticed that one of the eccentrics had movement on it and the eccentric arms were sloppy. On the Polly kit the eccentrics are positioned with a grub screw into pre-drilled holes on the axle.

Another major gloom session ensued as it looked at first sight that the boiler would have to come off to work on the eccentric arms. However after playing with positioning of the eccentrics I found I could get the clamping screws out, drop the arms off and so allow tightening of the grub screws. In the process of doing this I found that there were tiny packing pieces between the faces of the eccentric arm halves. Clearly the original owner must have believed the eccentric arms were too tight and had packed them out. I did a trial fit without the packing and the eccentrics ran freely. Perhaps this had been done as a running in adjustment. On completion I did a second run on compressed air with no obvious issues.

Putting it back together

Re-assembling the chassis work was straightforward except replacing the side tank water feed to the injector. The original nut had been mangled by the previous owner so needed replacing. Rather than just fitting another hex nut I made a brass knurled nut. In the confines of the side tank this gave me better grip with my finger ends to tighten the fitting. Once it was finger tight I could use the end of a screwdriver to increment it tighter using the knurling surface to give me purchase.

Replacement knurled nut to fasten the injector water feed into the side tank

Other work

While having grease embedded under my finger nails I did a few other jobs on the engine.

The whistle valve had always leaked steam and I had bought in a new version of this with a stronger spring action. This was fitted along with a new steam valve feeding the injector.

I re-positioned the pressure gauge to be central in the cab rather than off to one side as originally fitted.

I fitted a new set of drain cocks on the cylinders.

Finally I adjusted the cylinder lubricator which had been a bit too liberal with its feed delivering a snotty chimney edge and a fine mist of oil to my face while driving. The adjustment screw was unlocked and moved back a small amount.

All back together and a good days work. A lot learned which is always a bonus and less fear of the black art of steam engines.

The next day I took the engine down to the club track and made quite a few circuits on the raised level track. The engine sounded and ran quite differently. It ran much better on lower levels of steam pressure. I also did not get a bath of lubricating oil but judging by the edge of the chimney there was still sufficient being passed into the cylinders.

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February 5, 2019February 5, 2020

Stretching FlatCam and PCB milling on Tormach PCNC440

Tormach M Code Expansion Card

I have got a project underway to use the Tormach USB M Code expansion board in association with an A axis rotary table. Details of this will follow in due course. The expansion card when added to a Tormach mill allows the operator to embed M Codes in their CNC program which will operate up to 4 dry contact SPCO relays or accept 4 inputs as handshaking acks.

My Cabling Masterplan

As part of this project I need to have cables from the USB expansion board to various devices and in a rush of blood to the head decided to use standard readily available Micro USB cables for this. Now the cable connectors are pretty small and the PCB mating socket is even smaller with its 5 connections. Glibly overlooking this I asked a colleague to produce a PCB layout for the connector to a breakout connector strip. Dave duly produced a layout and a scratching of head resulted. How was I going to produce the PCB and how was I going to solder to the connections assuming I could see them ….

FlatCam to the Rescue

Elsewhere in my blog there is mention of the use of FlatCam to create a CNC GCode listing from PCB Gerber and Excellon files. This program works really well and many successful PCBs have been produced but I have never attempted to mill such fine PCB tracks. A number of problems needed to be addressed to make this successful. The PCB sheet needed to be held very flat on the PCNC440 tooling table and the correct milling tool with its associated feeds and speeds needed to be chosen. In the past I have used strips of aluminium to fasten the PCB blank down on the tooling table. This is never perfect and leads to variations in the pressure around the edges of the board. With single sided PCB there is a natural curvature of the board material as a result of the surface tension of the laminating process. A single sided blank has a concave surface on the copper side. I needed to create something more repeatable.

Milling Window Restrictions

Before I bought the Tormach PCNC440 I had a discussion with John Saunders at NYC CNC and he recommended going for the biggest machine I could fit in my workshop. I could have squeezed the 770 in at a push but I would have had to sell off my Myford VMB which I was reluctant to do. My order therefore went through as a 440. With hindsight this decision has been justified on two counts. I rarely need a larger working area than the 440 offers and the VMB gets used very regularly for quick jobs that don’t justify CNC. This project was an exception. I wanted to make a frame that would clamp the PCB blank down onto the tooling table. In order to get the maximum working area for the PCB blank the clamping frame would have to sit outside the machining area. How was I going to manufacture it ? Fortunately my tooling plate was designed to have a mix of M8 clamping holes and 3.7mm tooling holes and I was going to use this to advantage. The clamping frame would be symmetrical. By adding some matching tooling holes in the frame I could cut just over half of the frame and then flip it round 180 degrees and cut the second half. Here is a picture of the CAD showing half of the machining on what will be the underside of the plate when in use. The outer holes are for the M8 clamping to the table and the four smaller holes are the tooling holes. Being tight with my materials I did not want to just mill out the centre of the plate and have a mountain of swarf (chips). Instead I designed it with two slots as shown, one for the clamping surface and one that almost cut through the stock. The partial cut was to ensure the central piece did not flip out once cut free and damage my cutter. First one half was drilled and cut and then the plate was rotated 180 degrees and the second half cut. This left the central island just held in place by less than 0.5mm of material. This was easy to hand cut through to liberate the central area. The plate was then turned over and the cut edge cleaned using the same tooling position and doing the same 180 degree rotation. To my surprise the rotation process on the tooling pins worked very well with only a minor step transition at the overlap point on all cuts. This was probably more down to my 3.7mm tooling pins being not quite concentrically turned from 4mm silver steel. With this finished I now had a much more robust clamp for the PCB material. I had made the clamping step 4mm deep so I could put sacrificial backing boards behind the PCB being run. This would allow drilling through as needed. Checking the flatness of a clamped PCB blank with my Haimer showed variation of a few thou in the top surface of the PCB Z position. The worst case variation in Z was at dead centre where the PCB’s natural bow was most dominant.

Tooling and Feeds and Speeds

The next problem was the milling tool and feeds and speeds. I experimented with various V shaped routers but was not happy with the results. The 5 thou tip on a 10 degree V tool was incredibly fragile. Also because the tool was V shaped, any residual bow on the PCB surface lead to a variable width cut. In the end I opted for Think & Tinkers 15 degree, 2 flute tapered stub (P/N EM2E8-0051-15VC). This has a 5.1 thou cutting tip which is parallel for the first section so depth variations have no impact on the width of cut. I ran the program at 10,000 RPM (PCNC 440 maximum) and at 150mm per minute feed rate. The PCB does not look particularly beautiful after milling as there are burrs and shavings present but a gentle rub over with a fine wet and dry removes this and leaves a remarkably clean cut tracking. The images below show some of the results. The fine tracking for the USB connector connections is shown on the microscope with a scale for reference. This shows the five fingers occupying 120 thou with fairly similar track to gap widths of around 15 thou. So now I just have to solder the connectors in place …. I will let you know how it goes.

Overview shot of the clamping plate in position on the my tooling plate on the PCNC440

Finished clamping plate in position on the Tormach PCNC440 holding down a 6″ square piece of single sided PCB.

Tracking on the USB micro connector mounting

Zoom shot on the USB connector tracks with the graticule giving an idea of scale (small divisions are 0.5mm)

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