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
That feed rate isn't a problem. What resolution do you need?
Irving's spreadsheet is worth a read for motors, but sounds like you want something special. Here's a link anyway . . .
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
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.
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).
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
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!
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...
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?
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