Test Jig #2 - Clock Script
Derived from
Description
Current development version to be found on git hub here:
github.com/syvwlch/Printable-Clock-Project
It requires my clock builder script, which in turn requires the MCAD/involute_gear library and my clockwork library.
Particular improvements include:
1. herringbone gears, with suitable clearances.
2. no concentric shafts, no hands.
3. lowered pressure angle (14.5 degrees instead of 28).
4. minimum number of gears needed to test the escapement.
5. flanged drums on all wheels.
6. escapement/pendulum shares a shaft with the gear-train.
7. two-piece, connected frame to hold the shafts without applying pressure to the gear train.
8. thicker gears.
9. minimal sleeves to ensure clearance.
(UPDATE: if run using the latest clock-builder script, the escapement wheel will use club teeth, which should print better than the original ratchet wheel (thanks ssd, for the feedback on the original one).
I have uploaded the two modified parts, the escapement wheel and the escapement, as parts 02b and 03b respectively. The rest are unchanged and do not need to be reprinted.)
(UPDATE: the club-tooth version described above has been tested by TheRuttmeister and it passed all four tests! Major milestone. :-D We're going to work on mounting the string on the drum, rewinding it, and on a actual functional pendulum.)
(UPDATE: rustedrobot has also printed out the club-tooth version and with some post-print fine-tuning, got it to run for two minutes powered by a weight on a string! Video here: prototribe.net/vidplay/testjig2.html )
(UPDATE: improved back frame available, part 5b, which now includes countersunk hexagonal holes to hold the bolt heads and sit flush with the wall, as well as two wall mounting holes, same diameter as the bolts.)
(UPDATE: added a version of the drum with holes for attaching string, part 1b)
(UPDATE: part 03c is a variant of the escapement with increased drop, i.e. smaller impulse faces. The intent is to remove the need to shave the teeth before it works.)
Instructions
(UPDATE: Parts 02 and 03 have already been tested and the ratchet teeth print out too short. Please print out and test parts 02b and 03b instead!)
(UPDATE: with some manual post-processing, parts 02b and 03b do tick. There is also a part 05b available with improved frame features. Recommend you use all b variants available.)
(UPDATE: to avoid drilling a hole in the drum to attach the string, print part 01b instead!)
This test jig requires two shafts to slip the sleeved gears over, and another two to hold the frame together, outer diameter 3mm with a clearance of half a millimeter either side, so M3 will work... without drilling!
-----------------
Tests to perform:
-----------------
Test #1: with the escapement (03) in place, are there any escapement positions for which the escapement wheel (02) can rotate freely?
If yes, test failed.
Test #2: without the escapement in place, can the escapement wheel be made to turn by applying moderate torque to the drum (01)? How much flex is there in the frame during this test?
If no, test failed.
Test #3: with the escapement in place, and with moderate clockwise torque applied to the drum, does swinging the escapement slowly back and forth cause the escapement wheel to 'tick' forward by one tooth for every swing?
If no, test failed.
Test #4: repeat test #3, but instead of swinging the escapement back and forth, slowly push the escapement until the escapement wheel 'ticks'. When it does, does the escapement jump ahead a little, indicating that the wheel gave it an 'impulse'?
If no, test failed.
You must be logged in to post a comment.
Started working on making a snap-fit compound pendulum, since rustedrobot is doing such a great job on the winding drum :-)
Confirmed SSD's findings on the original escapement. If I had to guess, the last 1-2mm of the escapement wheel's teeth are missing (and the pallets are probably rounded off a little as well). I'm guessing skeinforge didn't even try to put plastic there because it fell under a minimum width threshold. People printing with narrower extruded diameters may have better luck, but overall it will be a hard thing to print.
Added a new version of the back frame, part 05b, as per suggestions from TheRuttmeister and rustedrobot:
1. includes mounting holes, and
2. includes countersunk hexagonal holes for the bolt heads.
Printed in PLA, picture to follow (and I need to find some m3 bolts!) Club tooth escapement.
Test 1. Passed.
Test 2. No flex in the frame (its PLA, its damn good stuff and I have the cuts to prove it!).
Test 3. Passed.
Test 4. Passed.
It Ticks.
IT TICKS!!!!
Just need a real pendulum now! :-D
Finally getting around to printing these (need to take a break from my current design, burning out
&
amp;gt;:o )
Not done printing yet but got some observations on design features to increase printability.
The spokes of the drum could be much thicker, they are currently thin enough to be harder to print. Same goes for the hub. And the spacer on top of the escapement could also be wider.
Its probably possib
le to change a value in openscad, but I lack the programming Fu to try.
And I don't know what you are planning on for the next escapement, but I did just peer into my watch and observe that its escapement wheel has a sharks fin tooth profile. No idea is thats any help at all, but I just found it in
teresting.
To answer your tests:
1) The (first) escapment doesn't engage the wheel when it is dead center.
2) The gears easily turn by finger, less easily by string. The string I have seems to slip on the ABS, but it can turn it if there is enough weight on it to develop friction. I've got some liquid electrical tape I might t
ry on the drum, but I have to be careful, as it melts the ABS.
I'd have to experiment more for the rest of the tests, and maybe secure my assembly a bit better. Will re-report after printing the new parts.
Thank you for taking the time to do this. :-)
Failure on test #1 is a big problem, because if the escapement disengages the wheel, particularly in the rest position, the weight on the string will just unwind clock at maximum speed. Not very useful!
Hopefully the club-tooth escapement won't have that problem... based on simulations in OpenSCA
D, it should at least pass test #1, even if it prints a little short.
I couldn't stand waiting any longer and went ahead and built this. (Am I the first?) Your gears are beautiful. I'm not sure if the tolerances of my machine are off, but the escapement doesn't quite bite deeply enough into the teeth. I'm out of long screws to hold it together, so its kind of jury rigged, so that doesn't help either. But it's a beautiful thing anyway. :) I almost wish I had printed the parts in different colors to make the gears stand out more. Let me know if you want more detailed feedback.
Thank you! Both for printing it out and for the feedback. :-)
I don't have my printer yet, and it will be a while before I have it and running even when I do, so I'm dependent on the kindness of Makers for real-world testing!
I would love detailed feedback. I take it from your description that the test jig, as printed, failed test #1? In other words, the es
capement does not quite engage the teeth on the escapement wheel, which spins freely?
I've just worked out an alternate escapement wheel design, which I will retrofit to the test jig. You should be able to print just a new escapement wheel, and new escapement, and slip them into place.
I'll post t
he retrofit here sometime today. :-)
License
More from syvwlch
Part 03c seems to work as-is with an unmodified escapement wheel. It will be useful to know if others have the same luck. One thing I noticed is I think the clock ticks faster with it, but i can't be positive.
That's interesting... Based on the video, I think it may be possible that the club-tooth escapement wheel is over-driven by the escapement, at least with 100g geared down by only 1:4. By that I mean that the impulse provided is too strong, and the pendulum is being shoved around, not gently nudged. It did seem a little slow for its length.
Perhaps the ratchet-tooth wheel is getting less of an impulse (I know the impulse face angle is less efficient, for example) and therefore more able to run at its natural period.
I'm just guessing, here. :-)