Woody – Page 4 – Woody's Workshop

January 18, 2025January 18, 2025

3D Printed Jigs to the rescue

How did we survive before 3D printing ?

I have been struggling with seeing where I am going on my Polly V live steam locomotive on the Club raised level track. It is the time of year where the cold weather quickly condenses the exhaust stream and you end up heading into a ‘white out’. This is not too bad if you trust the track but if there are ‘hokey cokey’ sections where your weight distribution is critical to remaining on the track it can be a bit unnerving and not good for your underwear.

I resolved to solve this before the New Year’s Day running session by making an exhaust diverter. I sketched this up in Fusion to use 32mm (1.25″) brass pipe forming a simple 120 degree Y shape. (The chimney bore down to the petticoat is 32mm).

The design was easy to model in Fusion but did require me to revisit the ‘plane on a path’ function. I first printed a 3D model of the diverter and this fitted nicely down the funnel. The next problem was going to be cutting the 30 degree angles on the end of the brass tubes. What was needed was some means of holding the tubes in the bandsaw so they could be flipped 180 degrees while making the 30 degree cuts and while also maintaining the protruding length. It struck me that I just needed a 32mm bore Stephenson Collet block with a reference edge – something not currently to hand nor in regular demand in my workshop. Then galloping over the horizon came my Qidi X Smart 3 demanding to provide one.

Back to Fusion and a few quick sketches gave me a model to hold the tube with a grub screw grip and with a reference placement lip on the front edge of the block. This worked a treat and I quickly had the three pieces of brass tube cut to length and mitred ready for assembly.

The preparation ended up being the easy part as I now had to hold all three pieces carefully in position while I braized them together. I reverted to three pieces of wooden rod gripped in each tube and the rod in turn fastened down onto my brazing hearth bricks. Crude but effective albeit potentially a fire risk.

The moral to the story is that in the past I would never have considered machining up a relatively large block of metal just to cut six mitres on some brass tubing. 3D printing has completely changed my approach to model engineering and the PLA recycle bin is now busier than the metal recycle bin (that used to contain not just swarf but also those ‘didn’t quite get it right’ rejected parts). It is not only this change but also the ability to get on with something else while the 3D printer creates your solution or path to a solution or just your ‘I wonder if that would work’ dreaming.

Result – I can now see where I am going as I chug round the raised level track and my laundry bill is much reduced. Here are some final images.

Just a closing thought while in Fusion mode – how about a more flexible version ?

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January 7, 2025January 8, 2025

Drawing a parabola in Fusion

Using the sketch conic curve function

This is an interesting one and I admit to not fully understanding the result.

The conic curve function in Fusion allows you to set the two end points of a conic curve and then ‘pull back’ the curve to its apex and enter the rho value. When the rho value is entered as 0.5 this will create a parabola. (If you enter rho as >0.5 it will create a hyperbola and if <0.5 it will be an elipse).

With a rho value of 0.5 the focus point is the same distance from the curve vertex as the curve vertex point is to the directrix. The directrix is a mirror line behind the curve that at the parabola vertex is the same distance from the back of the curve as the focus is to the front, hence the 0.5 rho factor. (Best to see the sketches below …..).

If you draw a perpendicular line from the directrix to the curve and then from the curve to the focus, then in a true parabola the length of these two lines should be equal. (This is why parabolic shaped dishes are used for radio communication links. In simple terms, any parallel radio waves incident on the dish will have the same reflected propagation distance to travel to arrive at the focus point where the detector device will be located. There is a cumulative addition of the incident waves at the focus. This is the power gain factor achieved by the dish in amplifing the signal.

All good so far ?

The problem I encountered was I could create a random conic parabolic curve using the Fusion function (two end points and vertex using a rho of 0.5) but the paths from the directrix to the curve and the curve to the focus did not match.

Until quite by chance … I had drawn a parabola conic (0.5 rho) where the diameter of the curve (curve peak to curve peak) was twice the vertex peak to the directrix line. Using this ratio always gave me equal path lengths between focus and curve and the curve to directrix.

Conclusion – the conic curve function in Fusion is not necessarily producing the result you might expect of a true parabola shape. I think it is almost certainly to do with the equation of a parabolic curve which the Fusion function is maybe not fully addressing.

Update : Looking back to my amateur radio microwave activity I remember the true focus of a dish was derived from the formula f=D²/16d where D is the dish diameter and d is the depth of the dish. From this you can calculate the focal ratio f/D. For efficient illumination of a centre fed dish the f/D ratio had to lie between 0.3 and 0.45.

By chance my choice of 120mm diameter and 30mm dish depth provides a 30mm focal length and the Fusion conic curve graphing is correct and gives an f/D 0.25. I think for any other f/D ratio the Fusion conic curve will not be an exact match to a true parabola curve (that is the focus to curve and curve to directrix path lengths will not be equal). I think this is because Fusion assumes the focus point is on the same axis as the end points of the conic curve. On this basis any conic curve created in Fusion with an expected rho value of 0.5 (a parabola) must have the directrix positioned at a distance equal to half the distance between the two end points. The conic curve is then ‘pulled back’ to the directrix line and the rho value of 0.5 entered. This could be automated using parametric functions. If the focus is not on the same axis as the curve end points some head scratching will be necessary and any resulting conic curve will not be a true parabola.

A construction related comment.

Never trust the accuracy of a floating Point placed based on just a selected grid position in Fusion. You must dimension lock the Point back to the sketch reference otherwise any resulting sketch using the Point will not be constrained. The parabola sketch is an example. I placed the two end Points for the curve, the curve centre and the directrix centre as my initial sketch postions. Then using the conic curve function clicked on the two curve ends and pulled the vertex back to the directrix point and entered the rho value of 0.5. The curve line immediately came up in black to indicate it was fully constrained. If any of the Points had not been dimension locked, the curve will appear blue – unconstrained.

To conclude this waffle and complete a solid version of the parabola, use the offset command to draw a parallel line behind the parabola curve and then ‘seal’ the end of the two curves with a short line and also add a short centre dividing line. You can now select half of the solid in extrude mode and rotate around the centre line axis to give a complete solid parabola. Here is a step by step process.

Here is the resulting solid parabola. This might be an interesting 3D print …..

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December 14, 2024December 14, 2024

GyroCut versatile scalpel replacement

One of those tools you wonder how you managed without it

While attending a model engineering show here in the UK I happened upon a stand (booth) demonstrating the GyroCut cutting tool. Their strap line is ‘works like a pen …. cuts like a knife’.

After standing watching the demo for more than a few minutes I came away with two of their cutters, one for me and a child friendly version for my granddaughter.

The GyroCut does what it says on the tin. You use the tool like a pen to trace the outline of the object you want to cut. It is available with different blades depending on the medium you are working with. It is now in regular use in my workshop. I would put it almost on a par with my 3DConnexion SpaceMouse for its impact on my way of working. (It has the added benefit that I am not needing so many sticking plasters to staunch my scalpel induced blood letting).

I have no affiliation with GyroCut, just very pleased to have discovered this useful tool. Have a look at their website to see it in action.

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November 29, 2024

A useful Amazon sourced small item storage system

An attractive way to store small items

My capacitor storage system was a mess and the arrival of some new stock kicked me into investigating a different approach to storage.

My initial thoughts were along the lines of buying one of the many pill storage systems offered online but they all seemed to be in garish colours and overprinted with days of the week etc.

In the course of further searching I came across this enclosed set on Amazon

https://www.amazon.co.uk/dp/B0839J2TV1?

For the price being charged (~GBP10) I was dubious about what the quality would be but on delivery I was pleasently surprised. The individual cases have a good action snap shut clasp on the lid and the outer container also closes and latches well.

I labelled up the individual cases using 6mm black on white tape using a Brother P Touch Cube printer (a lovely little machine).

While my initial need was for capacitor storage, I can see one or two more of these collections appearing in my workshop.

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November 25, 2024November 25, 2024

Further experiments milling PCBs

Implications of milling tools and FlatCAM settings

I have spent many hours CNC milling circuit boards and I have documented my process elsewhere on this blog. The workflow is to first design the board in Fusion Electrical (or any similar CAD package) and export the manufacturing package as Gerber files for the copper artwork and an Excellon file for the drilling information. The manufacturing files can be imported into FlatCAM to convert them to CNC files for milling operations. This is all documented in my various ramblings. Double and single sided board are both accomodated by the FlatCAM software (you just need to get your head around manipulating the artworks).

I have been reasonably happy with the results that I achieve but as ever I tend not to rest with a process which has some niggles. As a result I keep searching for a breakthrough lightbulb moment or at least an interative advancement to make the results more repeatable/easier etc.

The first irritation was the cost of the milling tools I was using. I bought these in from Think and Tinker in the US and they cost around USD20 each for a 5 thou end mill. One careless twitch and your bank account takes a hit.

Let’s take a step back and refresh. The FlatCAM process produces a file that moves the cutter around a copper clad board to leave isolated representations of the copper trackwork. The gap between the wanted trackwork and the rest of the unwanted copper is defined by the width of the milling cutter. FlatCAM allows you to widen the isolating gap by taking additional milling paths side by side to each other with a defined overlap. With a 5 thou cutter I used to take two parallel cuts with a 10% overlap so the resulting gap was 9.5thou. This is a pretty narrow gap. The second time round cut does tend to raise burrs/slivers of copper and these can easily cause a bridge between the wanted and unwanted trackwork.

I make this more difficult for myself as I prefer to tin the copper after milling. (Scrub the copper clean, daub with flux and then deftly swish a soldering iron across the copper). The end result is good but the road to it is fraught. Before tinning, the board needs to be checked for milling shorts and all milling debris removed and scrubbed clean. After the tinning process there will be a number of self induced solder bridging shorts which also have to be cleared. A quick post tinning run round the board with SolderWick is a fast track route to remove these. The process works and the tinned end result looks much better than bare copper.

The first area of my current investigation was the milling tools. Could a larger diameter milling tool be sourced at a price advantage to the US parts and how much larger diameter would be practical to give acceptable artworks. The solution came from APT Tooling who are one of my regular suppliers of tooling. They provide a range of micro milling tools starting from 0.3mm (11.8 thou) and upwards. A single pass at this size would achieve the same isolating gap as the two passes with overlap with the 5 thou parts. Potentially a single path would reduce the swarf debris. APT offer two versions of the micromills with different hardnesses.

My PCB artworks are not high density and with my eyesight constraints I tend to stick with through hole components whenever possible and 40thou trackwork. I ordered in 0.3mm and 0.4mm milling bits (55 HRC versions) and ran the FlatCAM simulations of the 0.4mm isolation routing. The 0.4mm (15.7 thou) had the distinct advantage of creating a wider isolation gap while still allowing inter pin gaps to be cut. Adding a second cut with the same 10% overlap created a very acceptable artwork with a generous isolation gap. FlatCAM is nice in that providing the first pass can cut 100% of the isolation artwork, the second cut automatically truncates cutting gaps that would not be compatible with the artwork and damage the geometry. Here are some FlatCAM simulations

Here are the actual results of an artwork cut as a single 0.4mm cut and as a double cut with 10% overlap. (I terminated the single cut as the resulting partial artwork was enough to make a decision on). Notice that the double cut does leave mini floating islands between wanted trackwork as shown in the simulations. These can be easily removed with a hot soldering iron.

Whenever I get a new supply of PCB material I strip peel a small section and measure the thickness of the copper and the overall thickness of the board. Currently I am using RS single sided board (RS#219-2123) and this measures 2 thou copper and 60 thou overall. With this material I am running a 4 thou depth with a feed rate of 10″ per minute. I run all PCB operations on my Tormach PCNC440 with my home made vacuum plate.

Conclusion – for my level of artwork density I now believe I can get acceptable results using a 0.4mm cutter in either a single cut or overlapping double cut process. The APT 0.4mm tools are much lower cost than the US sourced parts and being larger diameter will hopefully be more robust. To date I have only tried their 55RHC versions. Note I always run both the milling cuts and drilling routines with spray coolant from a Fogbuster with my normal spray coolant (QualiChem Xtreme Cut 250C) . This has the advantage that the fluid enters the cuts and shows as a clear black line when the cut depth is correct or at least deep enough to go through the copper.

If anyone wants more information about my process, please get in touch.

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