[mmech]

i am planning on building a three axis router using an sp-3/ht stepper system from stepperworld.com, 5/16-24 ready rod as lead screws, and linear ball bearings that ride on 1/2 colled rolled round steel. i was planning on working dimensions of 2' x 2' x 1'. i have not figured out what to do for antibacklash nuts. i am wondering if anybody could predict the accuracy of this machine.

[ViperTX]

Let's see the horizontal accuracy will be determined by the backlash from your "nuts" plus or minus the accuracy of your leadscrew over 12 inches.The vertical accuracy will be determined by the accuracy of the z-axis leadscrew...backlash should not be a problem as gravity will help unless you make some fast z-axis movements in both directions. Also affecting the z-axis accuracy is the straightness of the CRS and the weight of the z-axis causing the CRS to sag.

[jeffs555]

I don't know what you plan to cut and what kind of accuracy you are after, but unless it is continuously supported, 1/2" crs sounds kind of small for those dimensions. A 2.5 ft piece of 1/2" round steel, with supports only at the ends, will deflect over 0.06 inches with just a 10 lb load.

[mmech]

thanks for the replies. i am waiting on the arrival of the stepper system from stepperworld.com. i will look into ways to support or upgrade the crs.

[solarchimesam]

1/2 rod for X rails..I would go with gas pipe maybe?
Best of luck to you no matter what.

JEFF

[pminmo]

jeffs555,
Maybe you can shed some light on your deflection calculation, and ponder on this though. Assuming your 2.5' piece of 1/2" steel, two of them supporting the axis with 4 linear bearings supporting the 10 lb weight. Each pair of bearings would be seperated by 8" on the same rail with the rails 2' apart. Would the deflection be the same or less? I don't have a clue how to calculate. I've seen the single load deflection calculators, but wonder if it truely fits.

Phil

Phil

[jeffs555]

For quickly checking deflections, I use "beamboy". http://www.geocities.com/richgetze/

For one 2.5 ft rail, spreading a 10lb load between 2 bearings spaced 8" changes the deflection from a little over 0.06 inches to about 0.055 inches, not much of a change.
As for spreading the load between two rails spaced 2ft apart, if the load is directly in the center, the deflection will be about half that of one rail, however, when cutting near the edges, the total cutting force will be carried by only one rail.

Increasing the diameter of the rails from 1/2" to 1" would drop the deflection from 0.055 to 0.0035 inches which is a major difference. Also, there is very little difference in deflection between using solid rod or using hollow pipe, so the suggestion about using gas pipe is right on, and a lot cheaper.