[Bob La Londe]

I've done serious mods to my Taig, MaxNC, and Chinese noname router. I retrofit an early 1980s Hurco KMB1 to Mch 3 control. Now I am starting my first frame up build. This is a "test" build so I'll be skimping on a few the things, but if it works out well I'll build some more with more care.

Its a simple concept. Table moves in Y, Spindle moves in X & Z. I am considering a horizontal table design for the future to help with chip clearing when pocketing, but this first one will probably be a nice boring regular flat table setup.

Say hello to Metal Nibbler 5.

[ger21]

Personally, I'd ditch the round rails and try to find some used THK's on Ebay.

[Bob La Londe]

Personally, I'd ditch the round rails and try to find some used THK's on Ebay.

Why?!? I asked in several places about rail choices, and got really no response until after I made the purchase for this build. I asked if there was some inherent benefit to flat rails over round rails what would be the best compromises on a first experimental build for price and functionality. I listened to the crickets chirp for a couple weeks.

I did not find any posts or comments that said, "Round rails are inherently bad!" either.

~~~ Now that I have some on hand (besides those that were already on my Chinese router) I have found one or two things that make me go, "Hmmmm...." I'll have to mount up something that keeps them rigid and see. I can't feel any straight side play in the bearings but I seem to a feel a little end to end wobble. Almost like maybe they are good in the middle and a tiny bit loose towards the ends. I can see them maybe being designed that way on purpose so they are easier to start onto a rail.

[ger21]

I don't have any personal experience with them, but I've read the occasional thread where users point out that they are not as rigid as they'd have liked. If you read the Big Bamboo thread, I believe he points out that the round rails cause the most flex in his machine.

The specific type of mounting blocks may have something to do with the rigidity.

You may find that they perform perfectly fine. But I have seen several users that have had issues.

[Bob La Londe]

Have you got a link to the Bamboo Build handy? Did he use supported or unsupported rails? I have read a few articles mentioning unsatisfactory amounts of flex in unsupported rails. All materials have some flex. Mass can help over come flex to some degree. Most materials except granite and other hard stone have measureable flex in the distances we work with. Even titanium and tungsten carbide.

Well, this build will progress with what I have and I'll go from there.

Frame: $348 including freight. (Have since found source for $300)
1" Aluminum bar stock for the frame. 1 would prefer cast iron but the cost is prohibitive.

Table: $150 + Freight (Have since found source for $105apx + Freight)
Cast Iron Table - from cheap import XY table. Minimal machining on my big mill should get it within .001 of square. Amazingly its within a couple thousandths already. Better than I expected. (I am already considering a version for the future with two tables joined together for a larger fully supported work piece.)

Ways: $350 including freight.
20mm supported round rails and circulating ball bearing blocks.

Screws: $?.?? (300-500 maybe)
I have not decided exactly what screws I am going to use, but probably single nut ballscrews in 1605 for now. I can make dumpster style antibacklash nuts for acme screws, but I don't want to have to replace them very often. The nut part wears ok, but the mounting ears tend to flex, compress, and wear requiring tightening or replacing periodically. I have a set on the MaxNC from when I upgraded the screws and added fixed bearing screw supports. I also want high speed for rapids to reduce production time on detailed 3D work. Ball screws will be faster. Double nut ballscrews are available, but I the ones see for sale preconfigured appear to just be two nuts locked together. Not spring loaded as is required for true anti backlash. I'll probably make my own double nut setup if I build a second version of this same machine, but for now it will probbly get cheap single nut ballscrews. I have several of them in 12mm and 16mm (both new and used) laying around that I have acquired as the opportunity arose and the price was right.

Electronics: $1000 (computer and software not included) - More if I use a Mesa card.
I have built up or upgraded 3 stepper machines, and one servo machine. I really like the servo machine. Even when it faults because I did something stupid I don't lose position. I'll be running a servo based system on this machine and any future ones I build. I think 350oz nema 23 servos will make machine like this scream.

Spindle: ???
I am not totally decided on the spindle for this machine. More horsepower is nice, but I am torn between making it a 120V only machine or a 230V. I only have three 230V outlets wired in my shop and they are purposed already. One goes to my big welder. One goes to the aircompressor that will sit in the corner someday in place of my roll around, and one goes to the Hurco mill. Also, the sub panel that feeds the shop only has room for a couple more 120V breakers. No room for another 230V breaker.

[ger21]

http://www.cnczone.com/forums/cnc_wo...t_started.html

[louieatienza]

I'd have to agree that for a machine as you intend, you may be better off with 4-way profile rail instead of round rail. The supported round rail has varying load rating depending on direction, while the 4-way profile rail has equal load rating in all directions.

[Bob La Londe]

Well, now I am working my way through axis drive decisions. From practical experience having both servo and stepper systems I am really leaning towards building this with servos. Super high rapids is not going to make a big difference in production rates, but feed and acceleration will. I'ld like to have decent acceleration and torque in the 5-100IPM range. With a typical 4700 RPM servo a direct drive gives a theoretical limit of a little over 900IPM with 5mm pitch ball screws. (Reality with drag, friction, harmonics, whip, etc is probably closer to 600) Initially I was going to look at going direct drive, but I really need to be able to CUT at 5-100 IPM, not rapid at nearly 1000. This has me looking at adjustable tension timing pulleys instead. A 3:1 gives me all the torque in the world I could need with a modestly small motor. Cutting speed from 5-100 would certainly be doable with that, and rapids of 150-200 would probably still be possible, but that gets me worrying about acceleration. Motor size is not a huge issue with only a couple hundred dollars difference between complete controls and motors from 350oz/in to 1100oz/in. My big concern with the bigger motors is still acceleration (and deceleration). They have more power, but they also have a lot more moving mass. HELP! LOL.


P.S. Another builder who used the same round rails to build a machine said, "MAKE SURE THE RAILS ARE TIGHTLY FASTENED TO THE SUPPORTS."

P.P.S. I have accumulated a few THK box rails and am considering building two machines side by side. One with round rails and one with box rails.