looking for some help with an engineering project.

[yadnom1973]

I’m struggling with attaching a nylon gear to the end of a steel shaft. It’s part of the drive for a small rail based dolly that is hand pushed with a 5.5kg flywheel inside geared up to x9 or x2 by the time it hits this nylon gear so I want it to be a solid connection. It’s a 65mm diameter by 15mm wide helical gear with no boss, the shaft is 12mm diameter but could be increased to 15mm if that was needed. So far I’ve these three ideas:

A. Drill and tap a M4 or M5 hole through the shaft then drill right through the gear one side to the other and have a threaded bar the width of the gear run through it.

B. The same but instead of drilling through the gear and damaging the teeth I could cut a slot into the face of the gear and slide it into place.

C. I could machine a 3mm counter bore on the side of the gear. Weld a little metal disk to the end of the shaft then sink bolts through the disk into the gear. This is by far the most solid option but I'm worried that it would result in the gear no longer being true.

I’m new to all this kind of stuff and really struggles to find any sensible advice so I thought I’d come here and ask you guys. Dose anyone know of any better ways to go about this?

 

[Blogwitch]

It would be good to know what part of the world you come from so that someone close to you may be able to help do the conversion for you.

Here is a rough sketch that should overcome your problems, the gear should sit perfectly upright and it will be able to be placed anywhere along the shaft to line things up.

John

 

[Whitney]

Along the lines of your number 3 option take a look at this site. http://www.metallmodellbau.de/Sleeve_Valve_Engine.php
It is in German but the pictures are worth a thousand words, scroll mostly to the bottom of the page and observe how the propeller is attached.

This is what I recognize as a dutch key and is easily created with a bit of patience and cautious setup.

I am interested to see your final solution.

~Whitney

 

[yadnom1973]

Thanks for both taking the time to reply. The gear is sandwiched between a panel and a large flywheel at the end of its shaft with about 3 or 4mm clearance on either side. I should have made this clear first; this is the course of all its problems. I’ll have another look at the design today but if I have to give it clearance for the boss in this design, it’ll lose a lot. I’d have to run the gap from one end to the other of the whole dolly just for this gear and shift the balance of centre of the camera above, not nice so I’d really like to find a way to fix it to the end of its shaft.

https://postimg.org/image/ko78ivdkz/

I even was wondering if the folks who make the gears can machine a bore that’s the shape of a smaller metal gear, then attach that and slide the nylon over the top. They do make internal gears so they must be set up for it bit it’ll push the cost up and with the helical producing axial force as well I’s still have to fix the nylon in place.

 

[Blogwitch]

Y,

Now we know the whole story, maybe this age old solution might come to your rescue, but it would need a rather rigid setup to stop the drill deflecting into the softer nylon gear. If I was doing it, I would in fact use a milling cutter to make the hole as they don't deflect very easily.

John

 

[yadnom1973]

I did consider a keyed shaft but was concerned about the nylon wearing and the gear becoming loose on the shaft. This solution looks a lot better than the 4mm key that’d be on this 12mm shaft. The problem I foresee is that I’m presuming once you drill these three holes you tap them and this thread, once the grub screws are in holds the gear in place stopping it from moving laterally but I’m not sure if you can tap nylon or more importantly if it’ll hold the thread. The helical gears produce an axial force when in motion I’m told.
I do like this way of fitting a gear though and will remember it.