[Trucks]

Ok guys, been surfing and searching the forum for the past 2 days now and I am still not exactly clear on what to do. So far i have the table of my machine built, its 3'x5' and i have my x-axis rails welded together i went with some mild steel tubing and angle iron, and i am making the skate bearing rails. The gantry will be made out of MDF and a piece of steel or two and the router i plan on running for now is a small trim router, but eventually would like to run a high hp router or a 1.5 or 2kw spindle.

After reading through many posts and seeing many different ways of making the gantry move there are several options. Such as the following:

Belt Drive, Chain Drive, ACME Screw, Ball Screw, ect.

My first question is this: Can i get away with a single screw in the center of my gantry underneath or is it better to try and put a screw on each side of the gantry?

Secondly: I am really leaning towards the ACME screws since they are wallet friendly for my recently graduated engineering unemployed self. They are under $7 per foot at Rotron, and i am looking at say a 1:1 speed ratio, but what about starts and TPI? Any recommendations? Also i have been reading about the "backlash" i plan on getting Anti Backlash nuts from dumpsterCNC.com.

Third: After looking at speed ratio's if i go with a 1:1, mcmaster says it would move approximately 1/10th of an inch per revolution, would i gain more precision and accuracy out of the table if i did a gear reduction from a stepper motor to the screw? or would direct drive provide me with more than enough? I plan to cut mostly wood, do some carving, and cut aluminum.


I appreciate any help i can get, I am new to the construction aspect of a CNC, but i have used many including some large HAAS mills in an internship and at college during an automation course. I will be using MACH 3 for my controlling software and purchasing steppers from wherever, looking in the 300 oz/inch + range when i get that far.

Thanks, Andy

[ger21]

If you go with acme from Roton, these will give you much more speed, with the correct motors and drives.
http://www.roton.com/Mating_Componen...family=7060986

With direct drive, 1 revolution will move 1/2".


Keep in mind that the motors, drives and screws need to work together as a complete system. So you'll need to choose motors and drives that will work with those screws, and your machine.

[Trucks]

Thanks Gerry,

After looking around the forums all day, i see what you are saying about using a "slow" or low travel per revolution on a screw, the machine would be sooo slow.

I think i am going to go with what you have posted above, and along with their anti-backlash flange nut as well. Question is will that rod come with machined ends for bearings? or will i have to outsource that?

Thanks for the help.

Its greatly appreciated!

[Trucks]

Another silly question.

Does anyone else sell anti-backlash nuts for that type of rod?

I was looking at the one for that rod that rotron sells, and it says its good for 25lbs?? I think my gantry is going to be more than that. Should i upgrade to a larger diameter rod?

Thanks.

[finishlinewrx]

Here are the ones i run
http://www.finelineautomation.com/st...g?tag=LeadNuts

And here are another type
http://www.dumpstercnc.com/

Not sure about the 25lbs rating. I havnt broke one yet and im pulling a 100lbs gantry.

[Trucks]

Thanks Nick,

Well if you are pulling that around, then i think i will not have any problems.


Andy

[finishlinewrx]

I do have two drives on X.

And remember that it is a rolling load. My gantry weighs close to 100lbs but might only take a few pound to move it.