Help Me Again to create a Band around two Cogs

[ianhughes7UFVF]

Hi

So I got help with creating a Track around cogs, which turned out to be making the tracks first and then the cogs which was great.

But this time I have two cogs that are set in place that need to be as they are and I need to make a band around them with inner teeth on it that can be 3d printed in flexible filament:

I carnt work out how to do this as this seems to be an internal design rather than what I was doing before. The first piece of work was making a track. This is a band with internal pieces to slot into the cogs as it turns by a motor.

Could anyone advise me on how to create this this time.

I have added the two cogs in their relative positions.

Regards

Ian

[davebYYPCU]

Exactly the same, pattern the teeth,

Extrude join the banding as separate step.

Might help….

[ianhughes7UFVF]

Hi

I am not sure its working.

Because this is smaller the blocks that sit in the gaps would be about 5mm, I am confused on making the polygon.

I had to make a 20 sided polygon to fit the size I need, but I appreciate adding the band on after, but carnt seem to get further than this, I make a block but I will need a block and then gap and then block and gap to allow for fitting on the cog.

Could you help with a sample drawing for me.

Regards

Ian

[ianhughes7UFVF]

Hi

What I am trying to achieve is this:

Done properly with the inner ridges all the way along.

I just did a sketch on the cog for this but wouldnt know how to get it equally spaced so it works.

Regards

Ian

[laughingcreek]

I would not print (or model) this in it's oval shape.  either create a straight flat section and splice it together to make a loop like it's done commercially, or model and print it as a circle.

(edit: unless you just need it for a visual representation in the model)

[HughesTooling · Accepted solution]

EDIT updated file saved as an f3d.

One problem you might run into is you can't just pick the centre distance and have it just fit with the number of teeth and a set pitch. For XL pulleys for example you pick the number of teeth on the pulleys then the number of teeth on the belt and that gives you the centres between the pulleys. I guess you could go from the centres and teeth on the pulleys but then you'd need to calculate the pitch of the belt and pulleys (not how you'd normally work with chains and pulleys).

I've attached a file I made a long time ago for calculating XL pulley centres given the number of teeth on the belt and pulleys. The pitch is fixed at 5.08mm (0.2in) by the XL standard. You might be able to modify the design to create something that works for you.

[HughesTooling · Accepted solution]

Here's another file where I changed the teeth on the pulleys to 8 and 20 on the belt.

[davebYYPCU · Accepted solution]

I am sorry,

8 teeth and valleys on the cog are 16 sided polygon.  How 20 would work is above my paygrade.

Just as the bolt holes were the datum factor for the tracks, half height of the teeth depth is the path position for the tooth pattern.

Again you say the wheel base is determined before knowing the length of belt, in real life the belt has an inbuilt tensioner in the system somewhere.  (Spring loaded idler?)

Not sure if Marks 8/20 system matches to your wheelbase. 

My second track set with the droop, needed a shorter wheelbase to make it work.

Might help....