Beating a dead horse.....

[jjacstcy]

I know this has been brought up a gazillion times, but I have been sitting here for 4 hours reading all the threads on acme lead screws and end support till I have absolutely confused myself. I have figured out how I am going to support the ends of the screws if I can't find anyone to turn them down for me. What I need to know is about the lead screws themselves. General purpose 2 start, or precision 5 start screws? Would the cheaper general purpose be okay if a good backlash nut was used? What suck is we threw away a 25 year old Linde torch table 3 years ago that I could have got all the parts off of but didn't think about it. I need a machine at home now as I am to busy at work on my multicam to even think about cutting anything for myself anymore. Sorry for beating the dead horse about the rod, just trying to get a plan together so I can get something going.
Thanks
Jimmy

[microcarve]

Hi Jimmy,

It depends, is the answer.

Depends on how big your machine will be. You may want
thicker faster traveling screws. If it's less than about 30"
or so, 2 start will give the quick-enough speeds as well
as the mechanical advantage that lets you use less expensive
Nema 23 motors in the 250-380 oz range.

If you have more than 30", then you may want to take a look
at the faster 5 start, or maybe rack & pinion.

How precise do you actually need your cutting to be done.
What materials will you use.
Access to tools and machinery will decide how accurately built
your machine will be. No need putting the best screws on a machine that
can't use them. What router.

Lot's of people don't know exactly what they want to make, but that's
the thing that decides all else when making a machine. For wood
projects, you won't need super precision....meaning a machine
can be cheaper to make. If you want to make PCB's then a small machine
is the better choice with better fitted and finer parts.

Without a idea of what it is someone expects from their machine, many
answers may cause more confusion than provide any useful help.

Number one question is...what do you want to make?


John

[crane550]

This may help. Enjoy!

Alex

[crane550]

Sorry, here it is

Leadscrew Pitch Tutorial

[jjacstcy]

Hi John and Alex,
Thanks for replying to my questions. I plan on using the machine to cut wood, acrylic, and some aluminum. If I can get my parts to be within .005-.010 I could live with that. I was also going to use the 3 axis kit from cncrouterparts.com with the nema 23 motors. The machine will have a cutting area of 24" x 48". Most all of the machine parts will be made out of 1/2" aluminum cut on my router at work so the machine its self will be pretty accurate. Going to use the linear carriages from cncrouterparts also. Just so many decisions...
Thanks
Jimmy

[ger21]

There are no general purpose 2 start screws that I'm aware of. All multi start screws are considered "precision" screws. And carry a price tag to let you know.

I use 1/2-8 2 start with a 30x45 cutting area. My 30" axis has a 40" screw, and is good for 190ipm.
The longer axis, though, suffers from whip, which limits speeds to 155ipm, and causes some rippled edges in certain positions due to the whip.

[jjacstcy]

Thanks for a reply Gerry. I have decided to go with the 1/2-10 5 start screws after I read a few more threads. Also decided to go with the 34's and not the 23's after all. I jockeyed a few things around to get the price back to where I want it without sacrificing any precision. Gonna try to get my gantry uprights cut this week. I will start a build thread in a few weeks.
Thanks guys for your help!
Jimmy