Tower clock with epoxy composite timing gears.

[Ian PParticipant @ianp]

John

I love your clock, but have a few more questions.

Presumably there are flanges on the timing belt pinions as they don't show well on the picture. Are the belt tensioner rollers the full width of the back of the belt? In my experience once tensioned the belts do not slacken off, so were you concerned about the composite pulleys wearing?

I have not used the grooved ballraces before but I have used flanged races to do the same job as the ones in your clock.

0.01mm accuracy is probably far higher precision than you need for a belt driven clock but it come free with laser cutting, the best thing is that the accuracy is maintained over large distances so errors are not usually cumulative.

Ian P

[Sub MandrelParticipant @submandrel]

I'd better acknowledge that this is a truly fascinating bit of work, especially the detail that is coming out!

Now to veer back off-topic:

Les,

The clock is clearly marked for the German time signal, not the MSF ex-'Rugby' signla.

You were wrong about dismantling – I was carefully looking for a clue when it slipped from my grasp and hurtled to the floor – it's a self-disassembling mechanism. After some deep consideration, I moved the hour hand back by about the right amount, clipped teh slightly cracked front back on, crawled around to find the battery and put it in. Admin took it out and put it back in the right way. Ten minutes later it's showing the right time.

The only problem will be if the Central Euriopaen clocks ever on different dates to ours!

Neil

[Sub MandrelParticipant @submandrel]

I'd better acknowledge that this is a truly fascinating bit of work, especially the detail that is coming out!

Now to veer back off-topic:

Les,

The clock is clearly marked for the German time signal, not the MSF ex-'Rugby' signla.

You were wrong about dismantling – I was carefully looking for a clue when it slipped from my grasp and hurtled to the floor – it's a self-disassembling mechanism. After some deep consideration, I moved the hour hand back by about the right amount, clipped teh slightly cracked front back on, crawled around to find the battery and put it in. Admin took it out and put it back in the right way. Ten minutes later it's showing the right time.

The only problem will be if the Central Euriopaen clocks ever on different dates to ours!

Neil

[Sub MandrelParticipant @submandrel]

I'd better acknowledge that this is a truly fascinating bit of work, especially the detail that is coming out!

Now to veer back off-topic:

Les,

The clock is clearly marked for the German time signal, not the MSF ex-'Rugby' signla.

You were wrong about dismantling – I was carefully looking for a clue when it slipped from my grasp and hurtled to the floor – it's a self-disassembling mechanism. After some deep consideration, I moved the hour hand back by about the right amount, clipped teh slightly cracked front back on, crawled around to find the battery and put it in. Admin took it out and put it back in the right way. Ten minutes later it's showing the right time.

The only problem will be if the Central Euriopaen clocks ever on different dates to ours!

Neil

[John McNamaraParticipant @johnmcnamara74883]

Hi Ian

For the small driving pinions commercially made aluminium timing gears with steel flanges were used. In small sizes not very expensive.

The composite pulleys are a different matter they were not available from stock and had to be made as specials, quite expensive for four.

Anyway making your own is always better!

As long as you have a lathe to turn the chipboard or other material mould outer ring and the steel centre boss in position for concentricity, the only limitation for this method is that a belt with the right number of teeth is available.

I don't believe wear will be a problem: The saddle of the lathe that was used to make the clock parts has been running on an epoxy based bearing material, sliding against the V ways for the last 4 years without a problem. it is a full size toolmakers lathe and the saddle weighs a couple of hundred kg, a link follows.  

http://www.model-engineer.co.uk/forums/postings.asp?th=50671

For a high speed drive I would use steel or aluminium pulleys, I am not sure how you would dynamically balance composite material, and I would need to do safety testing, maybe the material would need to be reinforced if running at thousands of rpm. However for slower speed applications for example: positioning in CNC, telescopes, clocks etc, I think the method definitely has application. Most designs requiring high ratios are slow speed anyway.

Re Bearings:

Grooved ball races are available in a much larger range of sizes (Up to huge) and size for size are less expensive than the flanged type. I used both types using the same method in the CNC router I posted on this forum a while back.

The ball bearing tensioners were overhung by the belt by a couple of mm each side. Not ideal but I as this drive is extremely slow and lightly stressed I did not worry. I did make the diameter large to avoid stressing the back of the belt, well in excess of the belt manufacturers specification sheet. Something you should always check.

There are 4 idler shafts in this clock all at fixed centres. two stages each for the hours and minutes. The step motors are adjustable via small slots so really a tensioner for the first stage was not needed there. The second stage driving the hands is not adjustable, It could have been made so by slotting the bearing mount, this was not needed because the tensioner adjusted out any slackness in the belt. Due to the clock running continuously I think the tensioners are worth the effort, Just in case the unforeseen happens.

Cheers
John

Edited By John McNamara on 10/05/2013 00:50:02

Edited By John McNamara on 10/05/2013 00:54:07

[John McNamaraParticipant @johnmcnamara74883]

Hi Ian

For the small driving pinions commercially made aluminium timing gears with steel flanges were used. In small sizes not very expensive.

The composite pulleys are a different matter they were not available from stock and had to be made as specials, quite expensive for four.

Anyway making your own is always better!

As long as you have a lathe to turn the chipboard or other material mould outer ring and the steel centre boss in position for concentricity, the only limitation for this method is that a belt with the right number of teeth is available.

I don't believe wear will be a problem: The saddle of the lathe that was used to make the clock parts has been running on an epoxy based bearing material, sliding against the V ways for the last 4 years without a problem. it is a full size toolmakers lathe and the saddle weighs a couple of hundred kg, a link follows.  

http://www.model-engineer.co.uk/forums/postings.asp?th=50671

For a high speed drive I would use steel or aluminium pulleys, I am not sure how you would dynamically balance composite material, and I would need to do safety testing, maybe the material would need to be reinforced if running at thousands of rpm. However for slower speed applications for example: positioning in CNC, telescopes, clocks etc, I think the method definitely has application. Most designs requiring high ratios are slow speed anyway.

Re Bearings:

Grooved ball races are available in a much larger range of sizes (Up to huge) and size for size are less expensive than the flanged type. I used both types using the same method in the CNC router I posted on this forum a while back.

The ball bearing tensioners were overhung by the belt by a couple of mm each side. Not ideal but I as this drive is extremely slow and lightly stressed I did not worry. I did make the diameter large to avoid stressing the back of the belt, well in excess of the belt manufacturers specification sheet. Something you should always check.

There are 4 idler shafts in this clock all at fixed centres. two stages each for the hours and minutes. The step motors are adjustable via small slots so really a tensioner for the first stage was not needed there. The second stage driving the hands is not adjustable, It could have been made so by slotting the bearing mount, this was not needed because the tensioner adjusted out any slackness in the belt. Due to the clock running continuously I think the tensioners are worth the effort, Just in case the unforeseen happens.

Cheers
John

Edited By John McNamara on 10/05/2013 00:50:02

Edited By John McNamara on 10/05/2013 00:54:07

[John McNamaraParticipant @johnmcnamara74883]

Hi Ian

For the small driving pinions commercially made aluminium timing gears with steel flanges were used. In small sizes not very expensive.

The composite pulleys are a different matter they were not available from stock and had to be made as specials, quite expensive for four.

Anyway making your own is always better!

As long as you have a lathe to turn the chipboard or other material mould outer ring and the steel centre boss in position for concentricity, the only limitation for this method is that a belt with the right number of teeth is available.

I don't believe wear will be a problem: The saddle of the lathe that was used to make the clock parts has been running on an epoxy based bearing material, sliding against the V ways for the last 4 years without a problem. it is a full size toolmakers lathe and the saddle weighs a couple of hundred kg, a link follows.  

http://www.model-engineer.co.uk/forums/postings.asp?th=50671

For a high speed drive I would use steel or aluminium pulleys, I am not sure how you would dynamically balance composite material, and I would need to do safety testing, maybe the material would need to be reinforced if running at thousands of rpm. However for slower speed applications for example: positioning in CNC, telescopes, clocks etc, I think the method definitely has application. Most designs requiring high ratios are slow speed anyway.

Re Bearings:

Grooved ball races are available in a much larger range of sizes (Up to huge) and size for size are less expensive than the flanged type. I used both types using the same method in the CNC router I posted on this forum a while back.

The ball bearing tensioners were overhung by the belt by a couple of mm each side. Not ideal but I as this drive is extremely slow and lightly stressed I did not worry. I did make the diameter large to avoid stressing the back of the belt, well in excess of the belt manufacturers specification sheet. Something you should always check.

There are 4 idler shafts in this clock all at fixed centres. two stages each for the hours and minutes. The step motors are adjustable via small slots so really a tensioner for the first stage was not needed there. The second stage driving the hands is not adjustable, It could have been made so by slotting the bearing mount, this was not needed because the tensioner adjusted out any slackness in the belt. Due to the clock running continuously I think the tensioners are worth the effort, Just in case the unforeseen happens.

Cheers
John

Edited By John McNamara on 10/05/2013 00:50:02

Edited By John McNamara on 10/05/2013 00:54:07

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