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A design for a belt-driven Jacot Tool ...... ?


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In my previous question whether the direction of rotation mattered (https://www.watchrepairtalk.com/topic/26818-jacot-tool-does-direction-of-rotation-matter/#comment-223085) I bought into @HectorLooi idea that it could matter.

"If you subscribe to the idea that burnishing is able to move atoms by shearing of the metal lattice structure, then a bidirectional approach would be able to move atoms into a scratch from both sides of the scratch."

Since I'm in the design phase, I may just as well take heed from all members previous input and take all the rotational-direction doubts away by trying to design a pulsating Bi-directional motor/belt driven system, mimicking the original Jacot-tool Bow-drive.

The design criteria's I'm aiming for are:

1) In order to have both my hands free, to belt-drive the Jacot tool with a small 12Volt DC motor, fed from a 240 AC -> 12Volt DC adapter.

2) the driving system has to be pulsating bi-directional.

3) the RPM has to be adjustable.

There are already some idea's floating on the table:

a) For the adjustable PRM, using Pulse Width Modulation (PWM) with a 555-chip and a potmeter. (the beauty of a 555-chip is that its operating voltage lays between 4.5 and 16V, so no separate feed is needed when using a 12V DC system)

b) To change the polarity of the motor perhaps another 555-chip ( @HectorLooi ) in bistable mode controlling a relay to change polarity to the motor every 1 - 2 or more seconds. The operator of the burnisher determines the frequency of the burnisher-strokes and in my opinion they don't have to be fast. I guess it is more important to burnish in both rotational directions than the frequency therefor.

The relay can be a DPDT (double pole double throw). In the small schematic below the "Vmotor" can be a continues (adjustable) PWM signal from a 555 and the "Vcontrol" the switching of another 555 ?

DPDTrelay.png.923105d39b2df0dc07ec8bea127d0d33.png

I've to work these idea's out, but any help and / or other DIY idea's, fulfilling the design criteria's, are very welcome !

Looking very much forward to your input 😉

 

 

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@LittleWatchShop

Referring to your short video YouTube video (https://youtube.com/shorts/9TpAIyitI2Q?feature=share) gearing down is certainly an option!

However, I would like to have a bit more "flexibility" and the ability to have bi-directional rotation, as I believe that @HectorLooi has got a point.

I've been looking at 555 schematics and seen already some, when combined, whereby you can adjust, via a pot, the motor-RPM (PWM) and, via a 2nd pot, the duration of a certain directional rotation before it automatically switches over to the reverse direction for the same duration.

This addresses many valuable points members made in my other thread.

Just have to get the cobwebs out of my electronic-components cupboard, and far more importantly, out of my brains electronics-know how compartment 😂

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42 minutes ago, Endeavor said:

@LittleWatchShop

Referring to your short video YouTube video (https://youtube.com/shorts/9TpAIyitI2Q?feature=share) gearing down is certainly an option!

However, I would like to have a bit more "flexibility" and the ability to have bi-directional rotation, as I believe that @HectorLooi has got a point.

I've been looking at 555 schematics and seen already some, when combined, whereby you can adjust, via a pot, the motor-RPM (PWM) and, via a 2nd pot, the duration of a certain directional rotation before it automatically switches over to the reverse direction for the same duration.

This addresses many valuable points members made in my other thread.

Just have to get the cobwebs out of my electronic-components cupboard, and far more importantly, out of my brains electronics-know how compartment 😂

Using two 555s, one is configured as a pwm and the other with 50% duty cycle to control a driver. Maybe later today, I can draw up a schematic to do this. I think it needs some visual indicator to let you know when to reverse direction of the burnisher.

Edited by LittleWatchShop
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2 hours ago, LittleWatchShop said:

Using two 555s, one is configured as a pwm and the other with 50% duty cycle to control a driver. Maybe later today, I can draw up a schematic to do this. I think it needs some visual indicator to let you know when to reverse direction of the burnisher.

I have some rough idea's and schematics, but I need to fine-tune them. So far my rough thoughts are;

I don't have one single DPDT relay, but two 12V SPDT relays, each consuming about 30mA. To operate them simultaneously, the coils have to be parallel on the output pin3 of the 555. Depending on the current drawn (has to be less than max 200mA) and the rail-voltage left on pin 3 (whether it will still switch the two 12V relays), I may have to use a transistor or Mosfet, activated by the output of pin 3, to supply enough current and voltage to the relays

The schematic below has push-buttons to activate / de-activate the adjustable timer, but I can's see the need for them. Depending on the setting of the pot-meter, this timer can be set from 1sec to 100 seconds. Obviously 100 seconds is overdone, but adjustable between 1 and 10 seconds should be fine. As said before, to me it seems more important to burnish in both rotational directions than the frequency by which this happens. In, lets say 5 seconds, one can push the burnisher slowly against the pivot rotation, and pull the burnisher slowly backwards after the rotational direction has changed. If there is 1/2 second lost due to the "operator-out-of-sync", I don't think that will be the end of the world 🙂

Timer.png.ec512955702ed7747929fd5da1b564b9.png

 

This timer above will take care of the (adjustable) periodical switching of the relays (and therefor periodical switching of the DC motor polarity) at "VControl":

Polarityswitch.png.aad3c8dd96e309af9c5b9d98048d1cb0.png

 

The "Vmotor" is a constant PWM supplied by the schematic below;

555-Mosfet3copy.thumb.png.5cd50593bc88619feaed6bc6430e830d.png

These schematics combined should give me an adjustable duration bi-directional rotation combined with adjustable RPM.

As said, this is a roughly how I have the setup (currently) in my mind.

What do you say ?

 

Edited by Endeavor
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Problem is that these days getting electronic parts, which I used to get cheaply out of China, is not an option anymore. The "wonderful" EU closed that door with horrendous import taxes and "handling-fees".

Luckily I bought in the years before the "outside-the-EU-prohibition" lots of parts and have a reasonable stash. Everything in the schematics above I have and I'm afraid that's were I have to work with.

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I don't think that reversing the voltage instantly while the motor is running in one direction, is a good idea. 
You will get very high currents, overvoltage and mechanical stress to the motor during reversing.

Frank

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1 hour ago, praezis said:

I don't think that reversing the voltage instantly while the motor is running in one direction, is a good idea. 

Last night I've been thinking the same. I'm not too worried about the high currents and mechanical stress on the little 12V motor, but more about the sudden change in direction, and perhaps the forces involved to the watch-wheel being burnished.

As @nickelsilver mentioned yesterday, one has to start with a slow RPM to avoid that the wheel jumps out of the runners bed, but I realized that when you suddenly change the rotational direction, in the middle of the process, that may bring risk if the burnisher is not (correctly) placed on the pivot 🙄

Also @JohnR725 was so kind to send me a quote out of George Daniels book, in which George recommends about 15mm light strokes with the burnisher per 50mm strokes of the bow, with a stroke rate for both of about 1x per second.

There was another thing Nickelsilver said I've been pondering about;

"I know everyone is terrified of the Jacot tool".

This includes me, but now having some George Daniels guidance in how to operate the bow & burnisher, by how much and the frequency thereof, AND just tested it, it seems much more controllable than I thought. I feared that my body movement, due to operating the bow, would be greater and therefor jeopardizing the steadiness of my "burnisher"-hand. During my small test, this doesn't seem to be the case and the 50mm bow-stroke is more like just a wrist movement.

Perhaps I'll try to master the "bow-skill" and if that doesn't work, come up with a motorized idea, perhaps more controllable via an Arduino chip.

 

 

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I agree with Daniels' "throws" for the bow and burnisher, not less, possibly more. For me personally and those I know who are proficient in Jacot use, I would say the cadence is faster, like 2 back-and-forths per second. But that's not really important.

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I would like to know your answer when you  burnishing pivots in a lathe because as you know it operates one way when you are undertaking the task. If your answer is it is the right way of working then it makes no difference what other tool you use. 

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9 minutes ago, nickelsilver said:

For me personally and those I know who are proficient in Jacot use, I would say the cadence is faster, like 2 back-and-forths per second.

For now, as a started, I'm very happy with George Daniels recommendations. For sure, I'm not going to argue against his tremendous wisdom 🙂

I would assume that, after a while, one finds your own comfortable rhythm.

 

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2 hours ago, Endeavor said:

Lasr night I've been thinking the same. I'm not too worried about the high currents and mechanical stress on the little 12V motor, but more about the sudden change in direction, and perhaps the forces involved to the watch-wheel being burnished.

I agree. Motor reversing is not an electrical problem. Perhaps a mechanical problem as you suggest...I don't know. I am content with a unidirectional drive. Worst case, it takes twice as long to burnish.

 

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6 hours ago, oldhippy said:

burnishing pivots in a lathe because as you know it operates one way

Yes this is a question I'm curious about. I know a lot a clock people that will use a lathe to spin whatever their burnishing and yes it only typically goes in one direction. Plus polishing in a balloon Chuck in a lathe is only spinning in one direction. Then conceivably if you're doing it in a lathe you going to be spinning faster than with the bow will it have any effect?

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7 minutes ago, JohnR725 said:

Yes this is a question I'm curious about. I know a lot a clock people that will use a lathe to spin whatever their burnishing and yes it only typically goes in one direction. Plus polishing in a balloon Chuck in a lathe is only spinning in one direction. Then conceivably if you're doing it in a lathe you going to be spinning faster than with the bow will it have any effect?

Great points

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7 hours ago, praezis said:

I don't think that reversing the voltage instantly while the motor is running in one direction, is a good idea. 
You will get very high currents, overvoltage and mechanical stress to the motor during reversing.

Thinking about this I realize I've seen these concerns before in the firmware of 3-D printers. It's probably in all the firmware but I'm way more experience with tweaking Marlin. Where you find a whole section of sometimes mysterious because people don't actually know what they're supposed to be acceleration numbers for both starting and stopping. Yes if you have a 3-D printers you should always tweak your firmware.

But 3-D printers are big and heavy and how much force can you really put or should you put on whatever your spinning with the bow? Maybe one of the ways to prevent bad things from occurring is to shrink your motor size down something much smaller so you're dealing with less force .

 

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16 minutes ago, tomh207 said:

As @LittleWatchShop will testify, 3d printers run on stepper motors, whole different ball game than standard DC motors.

I’m sure you do know that John.

Oh really those are stepping motors how odd? Did you notice my reference was to tweaking the firmware and reference I made was to this quote

11 hours ago, praezis said:

I don't think that reversing the voltage instantly while the motor is running in one direction, is a good idea. 
You will get very high currents, overvoltage and mechanical stress to the motor during reversing.

So 3-D printer or this application have a similar problem of acceleration and deceleration of an item. I was just pointing out on 3-D printers is handled in the firmware.  Which then brings up the problem of the concern of what I quoted here of is it going to be a problem of starting and stopping and the motor rapidly?

Then somewhere in all of this @Endeavor I think was thinking of using a Arduino to make a speed control In which case you could program all of the stuff in or?

Or is it really necessary at all? Were Spinning a really tiny mass so do we really need a big motor. A much smaller motor perhaps even a lighter weight belt and then how fast you really want to go etc. or the novel idea of clock people do you really have to stop at all could you just go in one direction because that's typically what clock people do with the polishing pivots in a lathe. That is not just clock people there are attachments for watchmakers leads to polish pivots and typically they would be spinning under the power of the lathe in one direction.

29 minutes ago, tomh207 said:

I’m sure you do know that John.

Then yes I do know that there's a difference between a stepping motor and a DC motor. But occasionally the worlds overlap for a variety of reasons. Including this discussion of rapid starting and stopping is that going to be an issue? Or perhaps there's a simple way of working around the problem.

 

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Maybe the whole idea of simulating the bow action is a dead-end street?

There are experts who say that a Jacot tool cannot produce a really round pivot, you will always get an egg-shaped cross section - different from machines that turn in one direction only, like industrial ones do.

If the file is still moving while the pivot rests or reverses, you get a flat on the pivot. With continued action this flat will not disappear but get more distinct!

Frank

 

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2 hours ago, praezis said:

Maybe the whole idea of simulating the bow action is a dead-end street?

I'm still trying to figure out whether bi-directional does make a difference; perhaps it does or it does not. But I start to wonder whether those differences are "measurable" in real life?

Am I making it myself difficult for something that possibly is of very negligible influence? After all, I like to be able to burnish pivots of 19th / 20th century pocket-watches, which aren't exactly chronometer-grade to start with. Neither are the bulk of the watches I'm working on.

The author of an article I read didn't mention specifically whether the pivots were burnished in either direction (I did get the impression that they were not), but the burnished pivots shown under a 1000x magnification looked better than in my wildest dreams, certainly way over the standard I would like to achieve.

So, perhaps my idea of mimicking the bow action is out, not for the possible reason you mention, but for practicality and my doubts over the difference in the end result.

For me there is also a "rule of thumb"; 80% is achieved by 20% effort, the remaining 20% is going to cost me 80% effort more.

Worth it ? 🤔

 

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I'm thinking that it would be safer not to use a motor at all.

What would happen if the pivot jumps out of the pivot bed on the runner or the burnisher slips up on the arbor while the motor keeps spinning? In the latter case one would quickly have to remove the burnisher from the pivot bed on the runner - which would make the pivot jump out of the pivot bed  - or quickly try to get the burnisher back into position - which could take long enough to damage the arbor. I could be wrong, but I wonder if the drawbacks outweigh the benefits 🤔

I would think that for a majority of people, it would only take a few hours to (worst case scenario) a day or two to really get the hang of using a bow or a yoyo keyring to spin the pulley back and forth in a controlled manner.

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On 6/27/2023 at 2:17 PM, Endeavor said:

For me there is also a "rule of thumb"; 80% is achieved by 20% effort, the remaining 20% is going to cost me 80% effort more.

Worth it ? 🤔

This is very true for most things. I was thinking about the very logical thought that Frank put forward, that if for any reason the motion of the pivot stops but the motion of the burnisher does not. Resulting in a flat being made on the pivot that then has to be removed. Maybe only a micro flat but happening over a few times in the process of burnishing could add up to a non cyndrical shape. I think this would be more liable to happen with a motor driver jacot that is disconnected from us. This is probably where the great skill of keeping perfect rhythm between both hands makes a master at the tool. Do we know yet if there is any difference between a one way rotation and a two way rotation.

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2 hours ago, VWatchie said:

What would happen if

Anything could happen, I suppose. But, on my setup, the spindle turns at about the speed a bow would turn it. And the motor runs only as the button switch is pushed. If something goes off track, just release the button. Reaction time would be similar to a bow...I am guessing.

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