Leadscrew sizing

[snooper]

Can anyone please help: I've got a motor with shaft dia. 12.7mm and need to know what dia. threaded rod to use. Will 8mm be too thin?

[jp49]

It depends on how long and rpm the screw is going to turn.
so it will not flex.

[snooper]

Yes, I forgot to add that; length will be 700mm. I'm aiming for about 10 000 - 20 000 rpm.

[Guldberg]

What kind of motor is that? Even at 700mm, my guess is that the rod will flex at above maybe 2000rpm

[snooper]

This is the motor I'm planning on using...

http://www.kelinginc.net/KL34H280-45-8A.pdf

Suggestions?

[project5k]

i dont think that your going to get that kind of rpm out of that motor, infact i would bet that you wont.. i dont know that even if you geared the motor to turn 1 and the shaft to turn 10 times you'll even get half of that...

May i ask what it is that your trying to do that you need to turn a threaded rod that fast??

at 10krpm, even with a 10tpi screw it will travel 16.666 inches per second, that means it would travel the full length in under 2 seconds, not allowing for ramp up and down...

[snooper]

Ah, my inexperience shows...

10k rpm was a SWAG... I'm just looking to get a decent speed without corkscrewing the leadscrews... What would be realistic, and should I consider "upgrading" to something thicker? (For the screws, I think my skull's thick enough as it is... )

[project5k]

here is a little chart that i keep looking at.....

i would suggest figuring out what you really want/need your rapid speed to be and then figure it from there..
if you need 100IPM, then a 10tpi screw may not be for you...(it would have to spin at 1000 rpm) now if you wanted something like 50ipm, then you might get a 10tpi screw to work at 500prm, given that its the right thickness.. the general rule is the longer it is the thicker it needs to be, and the faster you wanna spin it the thicker it needs to be....

for my rig, im gonna use 1/2inch screws, 10tpi, and at 72 inches long i cant really spin them any faster than 400 rpm, so thats 40 IPM travel... if i spin the screw that is... if i spin the nut, then i can spin it much faster and not have shaft whip...

the other thing to consider is the amount of thrust you will be applying to the screw.. if you have a big heavy gantry, then that will apply more force to the screw than a smaller lighter one, and so the thickness of the screw will play into how fast and hard you can shove the axis around...what im finding out is that this is just like that like from Mad Max.. speed is just a question of money, how fast do you want to go???

[snooper]

Thanks project5k!

According to the chart, an 8mm screw will just fall short (I need about 2032 rpm to attain 100 ipm), and with an estimated gantry weight of 12kg (26.46lbs), I'd rather settle with a 10mm or 12mm screw...

I noticed that the heading on the chart is "Unsupported Screw Length," but I guess supporting the end wouldn't make much difference, would it?

[project5k]

well, yes it will make some difference, a single bearing on each end shouldnt be turned as fast as double bearings on each end... take a look at this....

http://www.nookindustries.com/Acme/AcmeGlossary.cfm

if you read that page and then go on to the next page, there is tons of information on mounting, sizing load limits, speed limits and so on.. if you read these 2 or 3 pages and understand it all, or at least most of it, then your way ahead, this should help you figure your length, speed, size, and supporting methods...

[ger21]

Depending on how it's supported, it can make a large diference. Check out the info at www.nookind.com They list critical speeds for 4 different types of supports.

[project5k]

ger you and i were headed in the same direction at the same time hehehe