Shaft Diameters

Currently scratching my head about gauging shaft diameters. I highly doubt I'll be going for something exotic like titanium - probably more likely to stick with a tool steel or other similar engineering grade.

Naturally the larger the diameter the better but I'm struggling to figure out where it just becomes excessive. I was looking at 25mm (1") for drive elements and 50mm for the lifter shaft I'm working on.

How do you all gauge it?

Gut feeling, mostly. I'd say, depending on the design, those numbers sound heavier duty than you could get away with but are otherwise right. Spinning weapon shafts are typically in the 40-60mm region (so for a lifter this would be nice, but perhaps overkill) and 25mm is a heavy duty drive shaft. If the latter is somewhat exposed, I'd say stick to that sort of size. I know that many machines use as small as 3/4" without issues but that feels a bit borderline to me!

For reference, Pulsar's weapon shaft is 45mm EN8 solid steel rod (cheap), and the wheel shafts are 30mm steel too. I know I just said 25mm is big - Pulsar's wheels are relatively exposed and I didn't want any issues stemming from the downwards shocks of a vertical spinner.

Pulsar's wheel shafts are live and supported by dual bearings:
http://i.imgur.com/ZSyBzRl.jpg

I would do this again, but perhaps go with tube rather than solid to save weight and I'm sure 25mm would have worked fine.

Attachment 6189

The award for the most overspec'd shaft goes to us :)

90mm diameter titanium supported at either end by 80mm bore bearings. The titanium was actually really quite cheap off ebay

I'd go for EN19 alloy steel tube of the largest diameter you can fit. Solid shafts take up a lot of weight and are only slightly stronger than a tube of the same diameter, so I'd rather increase the diameter and use a hollow shaft.
EN19 is a high tensile steel and is perfectly suited for shafts, it's more expensive than EN8 but nowhere near titanium

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Originally Posted by Ellis

Gut feeling, mostly. I'd say, depending on the design, those numbers sound heavier duty than you could get away with but are otherwise right. Spinning weapon shafts are typically in the 40-60mm region (so for a lifter this would be nice, but perhaps overkill) and 25mm is a heavy duty drive shaft. If the latter is somewhat exposed, I'd say stick to that sort of size. I know that many machines use as small as 3/4" without issues but that feels a bit borderline to me!

For reference, Pulsar's weapon shaft is 45mm EN8 solid steel rod (cheap), and the wheel shafts are 30mm steel too. I know I just said 25mm is big - Pulsar's wheels are relatively exposed and I didn't want any issues stemming from the downwards shocks of a vertical spinner.

Pulsar's wheel shafts are live and supported by dual bearings:


I would do this again, but perhaps go with tube rather than solid to save weight and I'm sure 25mm would have worked fine.

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Some good considerations there - cheers! I'll do some weight estimations and see what could be saved be reducing the lifter shaft (just in case) but it's good to know that I could possibly drop it down a little if needed or even consider tube.

Quote:

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Originally Posted by typhoon_driver

The award for the most overspec'd shaft goes to us :)

90mm diameter titanium supported at either end by 80mm bore bearings. The titanium was actually really quite cheap off ebay

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Better to be safe than sorry! Actually just checked on eBay too and there's some surprisingly cheap round bars. What grade would you recommend if going for it?

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Originally Posted by Liftoff

I'd go for EN19 alloy steel tube of the largest diameter you can fit. Solid shafts take up a lot of weight and are only slightly stronger than a tube of the same diameter, so I'd rather increase the diameter and use a hollow shaft.
EN19 is a high tensile steel and is perfectly suited for shafts, it's more expensive than EN8 but nowhere near titanium

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Tube is something I never considered until Ellis mentioned - it would actually make it easier to get the whole assembly together, cheers for the input!

The majority of the titanium you find on ebay in larger form will be grade 5 or Ti6Al4V or Ti6-4 (all the same).

It's the same material we got a hold of. Nice and strong but a bitch to machine.