Ball/Leadscrew questions:

[Dave's_Not_Here]

I am new to the CNC world but am committed to building my own Router Table.

I have read how a lot of you have scored some good deals on Ebay and have been researching for the past month or so. I have also received countless catalogs and visited mfg's. websites. Bottom line: I cannot afford full blown retail, so Ebay is my choice at the moment.

That said, I am faced with collecting compatible components. I am going with Servos from Jeff Davis of HomeCNC, eventually, and 80/20 extrusions from their Ebay Garage Sale. So now I am faced with trying to purchase the Screws form Ebay.

Question:

Does they X,Y and Z axis have to have the same screw spec's, ie. TPI, Lead, Diameter, Pitch etc. How much mix-n-match can you do if any?

Can you mix Lead and Ballscrews?

If I drive the X axis with two screws, can they be easily synchronized or am I borrowing trouble…

Thanks for any assistance you can lend. I hate to bid on any Screws unless I know if I can mix-n-match or have to remain consistent throughout…

Dave's Not Here…Man

[CerveloRod]

I'll throw out some things here;

I think it depends on your cnc software about mixing and matching. I use MACH2 and have mixed different pitch leadscrews, and now ballscrews on X and Y, stock rack and pinion on Z. Today my task is to put the ballscrew on Z. In MACH2 it's all about how many steps to go one inch. Was pretty simple for me.

If I had to do it all over again, I would have ripped my mini-mill apart as soon as I decided to CNC it, and put in ballscrews. Then again all the wasted parts when a leadscrew missed a step, got some money at the recycler. Once you hold a ballscrew in your hand, you will never want to use a leadscrew. Now you don't say what kind of machine your are looking at, and my friends Bridgeport clone has very nice leadscrews, but it's still a lot of turns per inch. I gained TONS of torque with ballscrews by being able to turn my steppers slower to go the same distance, ie 20 tpi leadscrews and 5 tpi ballscrews.

If your not a machinist, which I am definetly not, I would have someone turn the ends of the ballscrews for you if possible. I got my X and Y from homeshopcnc.com and he delivered them with the ends turned very nicely. I bought my Z without machining, and I know now why it costs so my to turn them. I had to made a collar to get it centered in a 4 jaw axis, then take small cuts to get throught the hardened threads. It was a learning experience, ya that's what is was....

One the 2 screws per axis, I have never done that, but MACH2 supports slaving steppers together for exactly that design. You must be building a gantry router to want that.

BTW you've found the best place to ask questions, and you probably can get more pointed answers in specific forums, i.e mini-mill, router, etc. There are some very knowledgable people here.

Good Luck!

Rod

[Dave's_Not_Here]

.... that I could at the very least, mix the Z axis but was not sure on the X and Y. My assumption was that the X and Y could be different configurations and that it would just mean that one would travel faster than the other, all things being equal with the servos, etc.

If I had to wait for exact matches on Ebay, the mill would never get built...

Yes, it is a Gantry design... wanted the slides on top of the X rails and possibly drive each slide with a seperate screw to keep the table area cleared underneath and minimize the material use needed to drive a single screw from the bottom, as well as eliminate the skewing of the Gantry using the single screw on one side of the Gantry.

Don't want the cantilevered radial pressure on the slides that some of the Gantry's have by dropping the Gantry sides next to the X rail sides.

Thanks, Rod... enjoying the forum

[Bloy2004]

The three main axes (x,Y,and Z) and any for that matter, can all be different. their setup is handled by the software. If you are using two screws for one axis (probably the X), you should have a matched set.
Depending on the size of your machine, for instance, your Z axis screw could be a lot smaller than your X axis. Size IS relative to length of travel, mass, forces applied, and a lot more considerations.
Much more could be said, but this is pretty much the very basics.

[Dave's_Not_Here]

Bloy...

Thanks for the info. Pretty much confirms my suspicions. I have some good 20mm items as well as some 3/4" items. As long as I keep any dual screw axis applications identical, I think I should be okay. I don't see any issue with mixing metric Y axis with Imperial X axis... 20MM and 3/4" should handle a 50" Router Table....