Browsing this months copy of ‘Model Engineering Workshop‘ I was taken by the idea published in the Readers’ Tips section by Bernard Towers for his ‘Bits and Bobs’ tray for his Myford lathe. A simple but obvious idea. Quite often I am machining small parts or need to make drill changes and the related items all get lost in the swarf, tools and detritus that has accumulated in the tool tray. Either that or I put them somewhere ‘safe’ on top slide and they get knocked off and lost …. we have all been there.
It was another grey and miserable lockdown day outside so the idea looked worthy of an hour or so of rewarding therapy. The nice part about Bernard’s design was the ability to slide the tray in and out on the top slide front edge with a spring loaded T slot retaining strip.
I had inherited a stock pile of surplus nickel silver flat pack RF screening cans with one or two pieces having pre-etched folding lines that would match the size and shape needed. Only a fourth side needing to be cut and hand folded. Conveniently these folding lines were just at the right height for the tray walls so they would not foul the cross slide rotation. Once all four sides were folded up a fillet of solder was run down each corner to seal it and any sharp edges removed. Nickel silver is one of my favourite fabrication materials being rust free, strong and easy to solder.
The tray is held in place with a length of T slot material and I created this as a 3D print in PLA. I included hex profile holes on the lower surface to take M4 Nyloc nuts. This meant I was inverting the retaining construction as shown by Bernard. I also used cap head screws to mount the pressure retaining springs.
A lovely and useful time filler project and I am indebted to Bernard for publishing his idea in MEW.
My TIG welding frustration suffered more than usual the other day .
I have an ESAB Warrior Tech helmet which works really well when welding but it would not stay flipped up when I wanted to see things in daylight. Every time I leaned forward the helmet would drop down over my eyes and thump me on the chest. Added to the fact I was trying to TIG some thin wall tubing I was no in no mood for distractions.
Before the helmet joined the happy hunting ground over the neighbours fence I took it apart to see why the latch up action was not working. Inspection revealed that the backing plate had cracked around the latching cam.
I could have bought a completely new head band assembly but the part in question might just be 3D printable. The Fusion 360 sketch ended up being very complicated based on eyeball guesses on curves and centres but on the second version I had a printed replacement which did the job …. for the time being anyway.
If anyone is suffering from a bruised chest let me know and I will forward the Fusion file.
You know how I keep on going on about how solutions to problems are often solved by coming at them from different and often unconventional directions, by utilising and marrying available resources ? It was a philosophy that I encouraged in my team while running my business and it has carried over into my way of working in retirement. A recent job brought his home to me.
A client had a very old clock that had had a new barrel wheel made and fitted but the clock would not run for more than a few minutes. There appeared to be an incompatibility either between the modulus of the new wheel and its mating pinion or the shape of the original pinion did not match the shape of the new wheel.
If you spun the barrel wheel you could feel the resistance build up as the synchronisation between the two profiles drifted out. Adding extra weight to the barrel helped but did not solve the problem.
So what to do ?
The barrel wheel was serious engineering and I did not fancy making a new one. The existing mating pinion was a seven leaf format and its leaves were what you might call pear drop shaped rather than the expected profile. The pinion arbor had a 72 tooth wheel driving the next part of the clock train but we did have a spare one of these to hand from the minute dial.
Calculations from the geometry of the barrel wheel resulted in a modulus figure of 1.86. A rather large value and not one that conventional cutters are readily available for. The pinion was perhaps something that could be drawn in Fusion 360 and then made on my Tormach CNC PCNC440 milling machine. The only snag was that the profile needed on the pinion would likely be weird and the world’s supply of brass could diminish rapidly while getting the profile correct.
Using Gearwheel Designer I created what would be the expected profile for a 7 leaf pinion with a modulus of 1.86. This was exported as a DXF line drawing into Fusion 360. This outline was extruded in Fusion into a 3D design and a boss was added to mount the 72 tooth wheel.
The design was 3D printed on my Sindoh 3DWOX printer and was mounted on a 6mm silver steel arbor. I added a driving disc that interlocked with the printed pinion and the crossings on the wheel to drive the assembly. Surprise surprise it didn’t run but it did mirror the regular pattern of stiffness of the original pinion.
I now had the test bed for quickly making and testing different pinion profiles. There followed a number of hours watching the engagement progression of the profile of the pinion into the barrel wheel and then trying to conceive a profile for the pinion that might run.
Fusion 360 made this process so easy and round 10 printed test profiles later I had success with a clock that now ran. The driving weight on the barrel was around 11kg and it looked to be worthwhile wasting some brass making a ‘proper’ one.
I took the 3D design and produced CAM code in Fusion. This would cut the profile ‘on end’ using an adaptive first cut with a 4mm end mill followed by rest machining the remaining material with a 2mm end mill.
The resulting brass pinion was mounted on the arbor and the clock ran with a strong beat. As expected the brass pinion gave less surface to surface resistance than the 3D printed part and the barrel driving weight was now able to be reduced down to 6.25kg.
I ran my Microset Timer on the clock overnight and had a first off timing error of 5 minutes per day which was fixable with a pendulum tweak. The movement had an instability of a few seconds per day which was quite astonishing.
The conclusion of the experience is that at first glance this seemed like a conventional pinion cutting exercise …. but M1.86 cutters are not readily available. If a cutter could have been found at less than a King’s Ransom it is likely that the resulting conventional profile would have been wrong to match the barrel wheel.
The alternative route that was taken of Gearwheel Designer to Fusion to 3D print to Fusion CAM to CNC machining solved the problem albeit with a final weird profile. The purists and traditionalists will groan. There will be a gnashing of teeth and a pulling out of hair.
Does it really matter if the result is new life for what could have become a heap of scrap metal ?
I had a need to run an armoured cable down a duct to an outbuilding. The duct had thoughtfully been installed a long time ago with the potential for use in the future.
The future arrived and it was a daunting cable run of over 25m. Armoured cable is pretty rigid which helps on the straight runs but when it comes to bends in the duct it had a mind of its own.
After struggling for some time I had the thought that some form of leader was needed to navigate the bends. After searching the workshop I decided a cable tie (zip tie) might be rigid enough but flexible enough. I snipped the fastener ratchet block from the tie and taped the residual length to the end of the cable as below.
A liberal coating of DC4 silicon grease and the cable shot down the duct and round the bends like a rat up a drainpipe.