Acme thread for cnc router

[level head]

i am going to be purchasing 12 feet of acme threaded rod for my 4*4 router i am building i will get the rod in half inch size ,but what pinch of thread should i use .i will be cutting plastic ,aluminum ,steel.

[level head]

does anyone know

[lugnut]

I just bought 3 ft of Enco's Acme 1/2 inch threaded rod and it's 10 pitch. I don't know others are differant or not. I do know that they sell it in 3 or 6 foot lengths. See page 621 of thier catalog.

Mel

[Mcgyver]

I don't know how much pitch selection there is in standard sizes, so you take what there is and control your feed rates by gearing. you could go two start - it prevents whip on your most rapid feeds, ie traversing. Do your research on feed rates etc and design from there - it will determine the ideal pitch, gearing etc. feed rate combined with depth of cut and what material you are cutting determines the required horse power and cutting forces involved, which determines the rigidity and mass you'll need. apologies if you know exactly what you are doing, but when i read you want to machine steel with a 4x4 envelope, I'm thinking you are either in for a big surprise, or you're building the mother of all homebuilt cnc's! it you need to cut steel, you'd be a lot better off looking at converting and manual mill or redoing the contols on an older burned out cnc.

[level head]

i willl get a photo bucket account and show some pictures of what it looks like so far..
why do you say mother of all machines

[Mcgyver]

because steel takes a lot of cutting force, so machines that can cut steel are necessarily massive, big heavy beasts. one that can cut steel with decent removal rate, and have a work envelope that big would be a very large diy machine! then again we've got people here that make their own tractors so i'm not ruling it out.

usually when you hear of someone wanting to cutting steel with a diy cnc router, you are dealing with some with unrealistic expectations regarding cutting steel (like i said, apologies if you're the exception) I don't mean to discourage, it may still be a great machine for those other materials, but handling the forces of cutting steel takes more rigidity than than most diy router machines and spindles can handle....small micro mill yes, 4'x4' router, no. Like i said, if cutting steel is important to you, you'd have more luck converting an old Bridgeport to cnc. post some pics when you get a chance.

[level head]

so aluminum would be fine and easy to cut

[Mcgyver]

to definitely answer that you'd need three things. 1) you need an engineer or at least someone able to calculate all the loads, vibration and deflections, 2) the removal rate, and type of cutter, 3) detailed machine design info.

To me engineered or engineering means figuring out all this stuff so that whether it works or not is predetermined, not be accident - your question can't be answered without a detailed knowledge of the machine and a lot of work.

What can tell you is 1) it will have a much better chance of cutting AL than steel and 2) lots of diy routers cut AL.

Post the design & pics at you'll get better answers, but still its unlikely someone is going to have the time to calculate loads and deflection - that's the designers job! :D

[CCWKen]

...then again we've got people here that make their own tractors so i'm not ruling it out.

Who Dat? :D ;)

Besides what was already said, I think you'll be unhappy with the "slop" you're going to see in standard acme rod. Especially with a CNC setup. The nuts and/or rod will wear so fast, you'll loose your index or crash a bit. If you're building a router that large and for steel, you might consider ball-screws. They're not cheap but neither is certified acme rod when it's replaced all the time.

[sch]

For some idea of the simple type of variety available a search on www.mcmaster.com for acme thread (rod) and ball screws will give you a primer of the more common varieties of both. Rolled thread ball screws are not horrendously expensive in the smaller sizes, they make up for it in the nuts. Friction is much lower with ballscrews and backlash is much reduced. The lower friction can mean items float around more so the motor control is relied on to maintain position under cutting forces. From the size it sounds like you will be cutting a lot of sheet?
Steve