Workshop resources all coming together like clockwork

Another JSN Job ?

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. 

Original arbor , pinion and wheel with the driving disc and a test profile
The original arbor, pinion and wheel together with the driving disc and a 3D printed pinion test profile. The driving disc has screws to lock it to the wheel and two protruding pins to lock into the 3D printed pinion profile under test. The 3D printed profile was a tight pressure fit onto the new 6mm arbor.

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. 

3D printed test profiles
Various trial profiles and the temporary driving disc to engage with the 72 tooth wheel

 

Test pinion in place on the new arbor
A test pinion in place showing the 72 tooth wheel and the driving disc

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. 

Images of the Fusion 360 process of creating the new 7 leaf pinion
The Fusion 3D model of the pinion, the CAM simulation of the leaf cutting, first adaptive cut of the leaves and rest machining final pinion

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.

new pinion mounted in the clock
The finished pinion mounted in the clock on the new arbor

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 ?

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Replacing the Sindoh 3D Printer Bed Lamination Sheet

I have had my Sindoh 3D printer for quite a while and it is a lovely machine to use in conjunction with Fusion 360.   I have printed all manner of items for the workshop, for projects and for friends and family.

For some time it has been a problem to print objects central on the bed.   While they would print OK, they are reluctant to come away from the bed surface and then having removed them from the bed, the raft would be very reluctant to leave the printed object.   I have got round this by offsetting the print position in X and Y on the table.   If I have a large object to print that overlaps the problem area I sprinkle talcum powder on the bed surface to ease freeing the object from the bed but this does not help the raft removal.

The print bed is an aluminium sheet that slides in and out of the machine.  This has a PTFE style laminated coating sheet held in place by adhesive. If I inspect the centre of the plate I can see the clear outline of bubbles under the lamination sheet.   These have got worse as time has gone by.  I imagine the bubbles create a finite air gap that upsets the temperature stability of the plate in the damaged area.

The situation had reached a frustrating peak today and lead to me totally removed the laminating sheet to leave bare aluminium.   The printer could not cope with bare ally and the PLA would not stick.  Some other laminating medium was going to be needed.

I had seen discussion regarding the use of what we in the UK call Masking Tape as a laminating medium.   I use 3M Blue Multipurpose Builders Masking Tape for Super Glue mounting of stock on the milling machine.   Having this to hand, I thought it worth a try. The tape is 48mm wide so I had to fix a number of strips across the plate to cover it completely and then trim the edges.  As you can see below, I didn’t quite get them parallel and butted to each other I was keen to run a test print.

Maybe I was lucky but the job came off the tape easily and the raft pulled off straightaway with no damage to the print.   The tape hasn’t bubbled or coming  off in any way so it looks good.

builders tape on Sindoh 3D printer bedplate
3M Blue Builders Tape on my Sindoh print bed

I am not sure how long the tape is going to last but I have got a full reel to keep swapping it out.

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Sindoh 3DWOX DP200 Raft Printing Problem

My close friend in France also has a Sindoh 3DWOX DP200 3D printer.  We bought them at a similar time.  He has probably been a busier user of the machine.   He has designed and making a very complex camera mount for tracking celestial objects.  He is using an Arduino as the controller and has never written code before.  He is having fun and keeping his brain stimulated.

A few weeks ago he reported that the raft that the machine was laying down before printing objects was not uniform and had ‘holes’ in it.   The result was that the PLA being extruded for the object being printed, would droop down into the void in the raft and spoil the finish of the object while also making it hard to separate from the raft afterwards.

We swapped ideas remotely about what might be the cause and tried various tests and experiments but to no avail.

As it happened a few days ago we were travelling down into France and calling in to see him for lunch so I had a chance to see the problem first hand.   More head scratching until …. I had the printer bed in my hand near the window and the sunlight caught the surface of the plastic laminated to the metal bed.   My eye caught a slight bubble in the plastic surface where the adhesive bonding the plastic to the metal had presumably parted company.   This was the problem !   The air bubble, small though it was, was causing a discontinuity in the bed temperature profile leading to the PLA not flowing from the nozzle correctly.

We ran a print and put the object on a different area of the bed where there was no bubbling or scratches and the raft and the print were good.

New bed plate ordered ….

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Black Saturday and a Napkin Ring

Had a bad day on Saturday.   I was milling a small tooling plate on the PCNC440 and got distracted.  Result was a coolant puddle migrating into the bottom of the Tormach keyboard followed by a broken Haimer tip.  Doom and and major gloom.  The keyboard was a write off as the fluid had got into the capacitive keyboard laminated sheets.

As it turned out a new keyboard was much cheaper to buy from Amazon than import another one from Tormach being only GBP6 and the Haimer tip while a bit more expensive was imported from Germany via Amazon.

I was in the process of trying to work out why the Z settings appeared to be changing while drilling the matrix of holes on the tooling plate.   The drill bit length was still the same figure as entered in the offset tooling table but the hole depth had reduced.   I think it might be the Tormach Tooling Collet not being fully seated into the spindle and it had jumped home.   Having just installed a new air compressor for the Fog Buster and the tool changer, it could be the air pressure was a bit low and not fully opening the R8 collet. As soon as the new Haimer tip arrives I will get back to it.

While ‘off-air’ so to speak I have been doing some 3D modelling on Fusion 360 to create some home grown Christmas gifts for the kids.   First one off is a customised napkin ring with a brass ring at each end.   The exercise  taught me how to form text around a circular body (thanks to John at NYC CNC for the demo video).  Not very sexy but functional.

sindoh, Fusion 360, kennedy power hacksaw
3D created napkin ring designed in Fusion 360 and printed using Sindoh 3DWOX and embellished with two brass rings

I struggled with cutting the brass rings and was about to design them out and go to all PLA when I had the idea to use the Kennedy Power Hacksaw like a bacon slicer to cut off thin circular shims of brass from a 2″ tube.   It worked well, was more efficient on waste than parting off in the lathe and gave a consistently wide slice.

Next request is for customised wine bottle stoppers.  Not sure wine bottles stay unfinished long enough in our house to justify this but let’s see what Fusion can deliver for the kids.

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