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Thank you!
Bruce, I printed your toothed pulley of 15.9 Diameter... And in the two cases (it's the same with mine)
have the film that a very little hangs !
I compared the 2 STL files... By superimposing one, we see that the spacing is the same just a smallest Diameter.
In both cases it does not change anything, it’s pretty good !... Not much missing !
... The teeth fall well into the holes but if we turn, after a while it is slightly offset with the 2 STL models!
If we decrease or enlarge the diameter of the pulley maybe we need to change the number of teeth?! ...
Otherwise the spacing of the teeth remains the same.
I admit my brain is starting to burn out... I continue the tests, it's really a crazy story.
Thanks Stan for your Hot off the press manual !
Attached Files
Last edited by Kamel Ikhlef; February 20, 2020, 10:44 AM.
Stan, thanks very much for the updated v5 manual, will study it later this evening.
Kamel, the tooth positioning is the same, 12 teeth in 360 degrees = 30 degrees separation per tooth.
The problem is that at 30 degrees, the more the diameter is increased the further apart are the tooth tip spacings.
The higher the teeth are from the root diameter of the toothed pulley (sprocket) the greater the mesh problem becomes.
My 3D printed sprocket has an overall tooth tip to tooth tip diameter of 17.6mm and its working with my S8 film (actual STL file overall tooth dimension is 8.058mm).
It would be possible to increase the diameter of the toothed pulley but only by 1 tooth, 13 teeth instead of 12, not sure if this would make much difference. It would increase the diameter by approximately 4.2mm.
I will make a 13 toothed pulley, it may take a few days before I have time.
The green coloured circle represents a film strip wrapped around the capstan toothed pulley.
Regards - Bruce
Sorry this - (actual STL file overall tooth dimension is 8.058mm)
Should have been - (actual STL file overall tooth dimension is 18.058mm)
Just realised my mistake and am not able edit anymore, must be a time limit on editing.
No problem Bruce. You show graphically how the film fits nicely with the smaller diameter. The larger diameter causes issue. I studied this a bit today to root cause the issue and this is what I came up with.
When you have a semi rigid strip of some thickness and you try to bend it, there will be stress forces on the inside and outside of the strip. The forces on the inside try ti squeeze the strip and the forces outside stretch it. At some point in between the inside and outside there is an equilibrium and no stress forces. Where exactly that point is we do not know but as a result of these forces the film strip becomes shorter on the inside and longer on the outside. So going back to Kamel's calculations:
Kamel used the value of pi=3.14 which is not enough precision.
Using pi=3.14158 I get
Dia = 50.76/3.14158 = 16.1575 mm
This is the diameter without stretching or shrinking and is somewhere say mid point of the film.
So, in order to get the inner diameter where the film meets the pulley, we have to subtract 1/2 the film width.
New dia = 16.1575 - 0.1397/2 = 16.088mm
This is pretty close to Bruce's dimensions. Obviously the neutral line may not be in the center line of the film and some experimenting is needed.
I would start with Bruce's dims and then go from there.
And another constraint is that the teeth height is not too high to make sure that meshing is still ok which Bruce presented above.
Thank you everyone for your suggestions and advice. I redid the design of the toothed pulley. Withe your advice, I selected a 16mm Diameter pulley with 12 teeth.
I slightly reduced the size of the teeth (width 0.7mm instead of 0.8mm, depth 0.65mm instead of 0.75mm). I also centered better with respect to the perforations by slightly changing the "Back" STL file. It seems to work better.
That is good news Kamel. I contacted https://www.treatstock.com/c/3d-rapi...tateId=1362372 and the owner (Sam) responded saying that the parts were printed with 250 micron and that he is willing to reprint it in 100 micron. I also suggested to go with PETG. When you enter Treatstock order page you can only specify the material, supplier and infill and that is it. Sam told me that they pointed this out to Treatstock but no action from them.
Treatstock is just a middle man. But one ice thing is that on their web site you can instantly compare the prices from different suppliers.
One thing I haven't tried yet is metal-based filaments (bronze, brass, etc.).
In the absence of resin!...
I will be ordering some samples for testing on my printer the next week.
Hi Stan, Hi Kamel, thanks for the new 16D STL's, with metal based filament you may need hardened steel (or equivalent) nozzle as brass will wear over time.
Stan please be aware that if you print at 0.1mm layer height (depending on slicer of course e.g. Kisslicer can adjust each individual layer Ht to get exactly the right Ht) the tooth height from the bed will be slightly reduced from 0.75mm to 0.7mm. To maintain the same, one needs 0.15 or 0.075 layer Ht. I know this is insignificant but just wanted to point this out.
Stan have been thinking about your comments above, the S8 film rolls on and off the teeth much like gears in mesh (only different process of course) this makes me think that the tooth sides should have a curve equivalent to the pitch between each tooth. The down side is it makes the tooth smaller, and would it make any difference in reality, there is so little reproducible detail with such a small tooth print anyway.
Very good comments Bruce. The curved tooth surface makes sense but may easier slip off when capstan has to pull the film through. With your latest capstan I think there is enough slack between the perforations and the tooth that the curved surface is not required. But it is a good thought if the clearance becomes critical.
I think I will go with the 0.1 layer height as a next step and see what I get. PETG is more expensive. Almost double with this particular supplier but I will try it. There are several other suppliers that are lower cost (around $17 for the whole batch in PETG).
Stan, I do not think it is worth paying double just for PETG, ABS would be ok or even PLA (although it has a low melting point, as long as the motor shaft does not exceed say 50 deg. C PLA would be ok).
Just printing at the moment with a layer Ht of 0.075mm, see how it turns out.
EDIT:- At this 0.075 layer Ht its very fine, I prefer 0.15 or even 0.1 would be ok.
Printed a sprocket with the new curved tooth profile, not really good, the teeth are too small and short, better to stick with Kamel's tooth profile.
Last edited by Bruce Davis; February 22, 2020, 11:18 PM.
Yes Bruce. I have a full metal hot end. no problem.
But I have to change my bl-touch and I have a heating problem on the bed, so a little delay.
I have not tried below 0.1mm because it takes a long time to print, but my printer can go as far as 0.02.
I don't know if this will improve. Your calculations help a lot, thanks for that.
We will end up getting an excellent result. Your last idea is very good,
but, I don't know if the teeth will slide on the film...To test...
Last edited by Kamel Ikhlef; February 23, 2020, 07:10 AM.
Thanks Bruce. Are your STP files that you send previously up to date? Also which back-pulley would you recommend, taper or no taper?
One more thing, when you get a chance, if you could post the R8 pulley STP file. I am getting an old R8 film and can test it.
I will try to get your design printed as a starting point but might have to tweak the dims after I get the parts. Also would like to see how the design with no inserts works.
Will try to work with the supplier. Possible send them film clips so they can try it right there at the source.
I purchased my camera and just opened it for inspection and testing. Unfortunately it appears to be damaged. I've requested assistance through the Imagesource web site but thought I'd ask a "stupid" question here. Is there Kaptan tape over the image sensor? I see faint scratches on the surface as well as the artifact but don't see any obvious parting line around the perimeter.
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