New WM-DD center gear prototype is here (EDIT - final version is here)

I've very sorry to hear about your stroke, you have my sympathy, coincidentally my Aunty's husband also had a stroke, before that he used to repair electronics in his spare time, he's still up and able about though.
I'm trying to get a gear SLA printed because given that I'm on the other side of the world, my choices are attempt to make a gear or do nothing and wait for the gear to fall apart. I've read that SLA can produce some very high detail and durable prints. I plan on sending a 3D model to a 3D printing outfit. I'll be using Maya (3D program) to make the model, even though it's not CAD, I have a great deal of experience in Maya and hard surface modelling:
http://imgur.com/IYSvc00
http://imgur.com/3alTqNi

I'm planning on modelling it in 2 pieces and super gluing it together - I'm just hoping I get it right, if I do then I can share the STL file.

 

250 um is very thin, just twice the thickness of a beverage can; I think aluminium is definitely too soft at that thickness.
My question is : why screws ? screws need a thread in the hole and I do not think it is possible to create a thread in something thinner than 1 mm. Wouldn't it be possible to made the support ring of plastic too and glue everything with epoxy ? Moreover with a ring made of steel plus three screws to hold everything together, is the weight of the gear still manageable by the springs?
I think you already considered making everything with plastic (including the support ring) why did you discard the option ? 0.25 mm is very thin also for plastic, but once glued to the outer ring it should gain enough robustness.

I'm sorry if I have more questions than answers...

Enrico

 

If your going to model it in maya for SLA , may I suggest you bevel the peaks and troughs of the gear teeth a tad, otherwise at that resolution your SLA will be too sharp and brittle (I too have extensive knowledge of Maya ;-)
http://www.imdb.com/name/nm1117804/

Let me know how you get on. Formlabs tough resin seems the best option for durability, but that resin doesnt do fine detail that well... I still think Marians way will be the best way, and I think once he has a formula that works, we should all do what we can to help (£ & $). He doesnt need to do this all Han Solo

 

I wonder if Carbon Fibre may be an answer...

 

possibly a supplier on www.aliexpress.com may have suitable thin steel discs

 

I can donate to him if he has Paypal.

 

Thank you very much for positive replies.

While the gears are difficult to produce, the support rings can be made even at home using simple CNC router. The only problem is lack of time. Plus this research is not cheap.
I would like to avoid using glue, it does not bond to plastic material well. Plus I would like to make it more simple. Two rings connected with several screws. One of the rings is thicker (0.8 mm). This should be enough to hold thread strong enough. I will see when I get prototypes. May be titanium would be better. It's quite expensive but the amount of material needed to produce one is relatively small.
3D printer technology is still not good, I think. Here, details are important. May be laser cutter would be better.
Also, the tooth height is not standard. I had to tweak CAD software to modify it. Another thing that I have to solve is the screws. The countersunk head width must be reduced. I can order production of this custom shape but I do not need million pieces.
Let's wait until I receive ring prototypes. By the way, they're already produced but I wait until they finish pinch roller hubs, together with the rubber tires. This is what I'm also working on and I want to save shipping cost.

 

Thanks Marian, now I have a clearer picture of what you are trying to build, but I think a countersunk screw will always bend the lower and thinner ring. Did you design a countersink in the plastic gear ?
A flat screw (like the ones that hold the PCB) would be better but its head would then protrude below the gear. Not enough clearance ?

I have other questions/curiosities though:
1) how will the plastic external gear be attached to the inner metal core ? when in play mode, the motion of the external plastic gear must be transferred to the assembly pin so that it is then passed to the take-up reel clutch. While in FFW or REW it's the gear itself transferring torque to the reels, but during play the torque passes through the gear pin.
2) how do you plan to build the three notches that pull the head/pinch-roller assembly when play is engaged? In your early metal prototype there are three small metal pieces glued to the ring. will they also be used in the final version ?

thanks for your hard work !

 

looks like its time for a lot of DDs to come back to life

 

If Marian is successful, it could increase the price of DD Walkmans.

 

Hi all.

I received gears and new support rings prototypes. It is much better, now. There are still few things to solve but it's on good way.
@Enrico - thank you for support. I think you will find answers on the next images.

Here you can see two support rings. The upper one (left) contains three notches. Three holes contain threads, thanks to them, it will be possible to join two support rings and gear together.


Countersunk screw was selected, as you said, to minimize clearance. But later I decided to use flat screw and omit the bottom ring. The reason is that it is too thin and deforms easily.

Here is view from the upper side:



And here from the bottom side:



I decided to omit bottom ring and attach it using three screws with flat head. Now I need to find special screws with wider head. Probably they will be custom-produced.



Now I just need to test, how it will work.

Marian

 

Thanks Marian for the update and the hard work.

I think that with the new configuration, a bit of adhesive between the upper ring and the metal core of the gear would help as it would distribute more evenly the torque from the teethed outer gear to the metal core. Otherwise the three screws (or better the section of the heads touching the metal core) would have to provide all the strength to keep the outer gear and the metal core together. That would require to tighten the screws more firmly thus increasing the risk of cracks in the plastic due to compression.

It is a good idea to have the three screws also acting as the notches that pull the head/pinch-roller assembly into play position. The lever that gets pulled by the notches is made of metal and in the current plastic gear all plastic notches shows signs of wears due to friction with metal.

keep-up the good work !

 

Excellent work Marian.

 

POC (proof of concept) is successful. Now I have fully working gear with modified and simplified design.

What modification I did?

1.
use 6 screws, instead of 3. The reason for this change is that plastic gear has to be perfectly pushed to the support ring on whole length - when only three screws are used, there can be gap between gear and ring on some places

2.
Reduce gear thickness on the place where holes are located
It's because original metal wheel thickness is 0.5 mm, while gear thickness is 0.8 mm. I need to reduce the thickness of gear to 0.5 mm, right below the screws. This will enable to precisely join gear, metal wheel and support ring, using few screws only. Also, I will be able to use screws with flat head of 0.5 mm height, which is quite standard. Also, it will ensure that no glue needs to be used and screws will not be pushed to plastic gear.

I used standard M1.4 screws that I bought from seller on eBay (1.3 mm height). They fit but it would be better to use screws with wider head. I will search, if they can be custom made.

Now I have to solve the last problem, which is financing this project. As I mentioned here, I already have confirmed final design. But these modification will require production of new plastic gears. I prepared technical drawing and I'm waiting for quotation from my producer. Today I bought final production of support rings (with 6 threads). Now I have to wait until I earn more money to order new gears

I can also use the gears that I currently have. It is not big problem to drill 3 additional holes and reduce gear width around them. But I'm limited on time. I will not be able to sell them because I will not have time to modify them.

Marian

 

I can help and i am sure other members can contribute as well

 

I am happy to help, too.

 

Me as well.

 

Thank you, I'm glad that so fantastic members are here

Today I got quotation for new gears production. I succeeded to convince them that it should be less than before. By the way, it's USD 693. Cost of model for injection molding is the most expensive part. First, it is not easy to cut teeth with such precision, second, it is very difficult to estimate mold dimensions. It must be about 10% higher than final product - as plastic material shrinks when cooling down.
Today I will send them sample of original gear so that they could compare tooth shape and size. The result is always little different than the drawing that I send them.

Marian

 

I will definitely make a contribution to this too Marian. I have another DC2 that would love to have one of your new centre gears fitted!

 

Well noted Thank you so much. Those who will contribute will get gears for personal use for free. Or I can help and fix your walkmans.
The new and final version of support rings (with 6 threads) will be produced in 10 days. Then I will order version two of the gears. I also started negotiations with screws producer. I hope they will accept smaller orders. I do not need million pieces. I'll keep you informed.