This is nothing magic but worth a mention. Being fundamentally lazy I don’t like to assemble and solder electronic multi-way connectors. There is never enough room to work on the contacts and the cables never lay up how you would like them to. This could have course be a function of my eyesight ..
I am currently working on boxing and installing the Tormach USB Expansion Board which has a USB connector interface. I wanted the cable to pass through some form of gland into the box but didn’t want to cut a standard USB cable and remake the connector at one end of the other.
After some head scratching I came up with the following simple cable gland/cable grip. It is nothing revolutionary but made life easy and the parts only took 20 minutes to design in Fusion 360 and then 3D print on the Sindoh 3DWOX.
It has two identical semicircular halves that hold the cable and there is a ring that pushes over these on the outside of the box. A small flange holds these in place on the inside of the box. The hole in the box and the ring inside diameter are both 16mm to allow the USB connector largest dimension to pass through. This is also one of the standard cut rings on a cone cut hole drill which makes cutting the hole in the box very straightforward.
Not rocket science but you never know it might come in useful and the dimensions can be tweaked to suit other cables and connectors. Similar or related subjects : –
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.
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.
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.
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.
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.
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.
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.
When plugged into the Microset all seemed to work well. Here is a typical PC display of the Microset data.
I now need to get it installed in the church tower.
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.
It has been a quiet period leading up to Christmas and it has lead to some low level activity catching up on items on the ‘Things to Do’ list.
One of these was to make a graphical representation of what the Fusion 360 Feeds and Speeds dialogue box means and the calculations behind it. To be honest this tab in the Fusion CAM section used to frighten me but I have become more confident with it. The problem is I can’t remember what each box affects so here is a visual representation which might help others. Note that the dialogue changes between a ramp into the stock (such as when cutting a pocket) and a plunge into the stock (such as when drilling).
I hope that makes sense and I have got it right. It certainly helps me to understand what is going on and the calculations going on in the background.