Thread: Leadscrew
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26-02-2011 #1
Hi all i'm new here, i want to build a lathe for a special purpose, and i'm currently trying to find out if i could use an off the shelf lead screw for my purpose.
I want a minimum feed rate of 2 or 3mm per minute. Can anyone point me in the direction of any reading material or threads / info that may help me. Also advice on motors to drive the leadscrew. Although i do have machining experience it is limited so any pointers would be great. Thanks
Great forum
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26-02-2011 #2
That feed rate isn't a problem. What resolution do you need?
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26-02-2011 #3
Hi Fusionkid,
Irving's spreadsheet is worth a read for motors, but sounds like you want something special. Here's a link anyway . . .
http://www.mycncuk.com/forums/showth...tor-do-I-need.
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27-02-2011 #4
Thanks guys, by resolution you mean what measurement divisions "on the dial" so to speak?
Well because of the purpose i don't think measurement is critical, i'm building a recording lathe (that records are made on). The cutter carriage has fixed start and end points for the cutting range other than that the actual measurement i don't think is critical. So the answer is i don't know!! But the feed rate must be down to about 2mm/min. Are there methods for working out what i need?
I posted a pic of a commercial recording lathe in another post here:http://www.mycncuk.com/forums/showth...siastic-Newbie
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27-02-2011 #5
Yes.
With the low feedrate you're after clearly the problem is getting it to run 'smoothly', i.e there needs to still be a highish step rate. I think you could achieve this in two ways. Either gear the stepper motor down with a timing belt and pulleys, or use a high microstepping division. The latter wont help with resolution but it can get the motor running very smoothly.
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27-02-2011 #6
Ah, that changes things. Normally a stepper motor would be used as it's easy to set the feed on but you need a continuous feed not a stepped one (otherwise you will hear each step). How many revolutions do you get on a record? Is it the same spacing all over? Do you need to vary the spacing (IIRC there is a trade off on the groove width between quality and run time).
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27-02-2011 #7
That's right about stepper motors, for this application they're not good you risk modulating a pattern on the groove spiral. What i will use is a servo motor with analogue feedback. The motor geared a high ratio to the leadscrew.
In this application the feedrate is continuously variable, louder music has wider grooves on the disc you need to compensate for this. It's a balancing act between loudness, time, and quality
So i need to read up on how to work out leadscrews and their gearing, if anyone got any links etc
Thanks
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01-03-2011 #8
So i've been looking at commercially available leadscrews online, ball, acme, trapezoid etc. I am unsure as to what i need, is there any good info online that can help me? Or any reading material that can be reccommended?
I'm keen to progress my lathe project but i need more knowledge!
Thanks
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01-03-2011 #9
You're not looking at high forces and backlash shouldn't be a problem as you're cutting in one direction so no need for a ballscrew. I think you're looking at a plain acme / trapezoid leadscrew with maybe a delrin nut. You'll want the leadscrew to be good quality so it moves smoothly and the guides for the cutting head should be quite heavy duty - maybe think about further damping the movement by using dovetail slides covered with a thick oil (I believe there are oils that are particularly sticky for that kind of application).
Good picture of a lathe on Wikipedia...
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05-03-2011 #10
Becuase my application needs a feedrate of approx 2mm/min i ideally need a feedscrew with a very low lead. I have seen one feedscrew off the shelf that has a lead of 0.050"/rev but it seems low lead screws aren't that common off the shelf. So have i got this right?
Can anyone suggest a supplier of a feedscrew of this type?
Thanks
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