Worm Gear

[colin hamiltonParticipant @colinhamilton16803]

<p style=”text-align: center;”>I would really like to make a rotisserie grill something like this</p>

But I have no idea if its possible to make a worm gear

I was thinking of buying a lathe leadscrew and cutting the gears that would mesh with it.

Thoughts??

Thanks

Colin

[BazyleParticipant @bazyle]

There are better ways of achieving the end result – eg chain drive.

[FulmenParticipant @fulmen]

You can use a tap to free hob a worm gear that will mate with a threaded rod.

[duncan webster 1Participant @duncanwebster1]

The advantage of the proposed design is that the individual skewers can be picked off without affecting the others. However the photo shows a very quick pitch ‘worm’. I’d more likely call it a skew gear. It would probably work with a leadscrew and worm wheels, but the leadscrew would have to rotate more quickly (in reality still quite slow I suspect)

As you don’t need continuous rotation you could achieve the same result by having a rack and pinion set up withe the rack oscillating to and fro. Advantage straight cut teeth.

[colin hamiltonParticipant @colinhamilton16803]

The speed thing is very interesting and good news. I’ve made a couple of spits in the past and getting the speed down [to less than 5 rpm] is always a pain.

Rack and pinion is also interesting but I’m not sure about the rack sticking out past the grill!!
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[duncan webster 1Participant @duncanwebster1]

Use a stepper motor

[Anonymous]

As shown the gears are not really a worm and worm wheels, more crossed helical gears.

If using a leadscrew as the driver then mating worm wheels are not necessary. Helical gears, with a helix angle equal to the angle of the thread, will be fine and are pretty simple to make. The only hiccup is that if the TPI/pitch of the leadscrew is rational then the DP/module of the mating gear will be irrational. So custom tooling will need to be made, but again pretty simple once the calculations are done.

Andrew

[FulmenParticipant @fulmen]

The equipment in the video is very well made. It looks like all shafts go at the same low speed, which would simplify both design and logistics. The low speed is not a problem for a commercial design, geared motors are cheap and readily available.

For a diy build a worm gear makes more sense since it can provide significant gearing. Wear will probably be worse, but it’s probably not going to run 8hrs per day, right?

[HopperParticipant @hopper]

Interesting contraption. One thing you might have to watch out for if using a conventional lathe leadscrew and worm gears is that the gear teeth might tend to ride up over the thread on the leadscrew as the skewers are only sat in slots, not retained in bearings. The pictured right-angle skew gearing puts force on the skewers largely axially, not radially like a worm and wheel arrangement would. But enough weight in the skewer handle might do the job.

There are a lot of gears and worms and wheels etc for sale cheap on Aliexpress. You might find something like that arrangement if you search around enough. They are very hit and miss with terminology so its a bit of a treasure hunt though. But to buy that many individual gears will add up.

To machine that long helical skew gear in the video would be quite an undertaking. Looks like it is 6 or 8 teeth or so. Would need to be done in a milling machine,

 

[FulmenParticipant @fulmen]

Here’s a video showing free hobbing with a tap:

[JuddyParticipant @juddy]

Use a chain drive, the skewer with the sprocket on one end can just be placed onto the rotating chain from above, no gear needed

[colin hamiltonParticipant @colinhamilton16803]

Thanks for the feed back everyone. I’ve ordered a couple of bits from Alex press but I really want to have a go at making something. So it’s free hobbing with a tap for me to start with (thanks for the video link!)

Cheers Colin

[FulmenParticipant @fulmen]

Yeah, it’s a fun little trick that should work well for low loads. Tail stock support is probably sensible if you have the clearance for it though.

[Howard LewisParticipant @howardlewis46836]

A chain, along the bottopm would substitute for a rack, with a sprocket on each skewer.

Sources?

Bicycle chain and the smallest sprocket obtainable, (probably 12 or 13T)

And unlike helical gears / worms, no end thrust.

Howard

[colin hamiltonParticipant @colinhamilton16803]

<p style=”text-align: center;”>I was going to use a chain but then I bought the lathe and mill so was to use gears!</p>

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