[smithwick]

Being new I hope I am in the right forum section, if not "sorry" please direct.
I've been researching info for months now, and of course have many questions, but will only ask one at a time as I have filling other ones will get answered with each one I ask.

My question is: Can I use a [SINGLE] ball screw on my Y axis 9' I plan on using a rotating ball nut ($$$ ouch) and fixed screw.
going to use steel for the frame 2x6 .25 box for rail support found a place to have them milled flat $200
4x4 .25 for legs and 2x2 .125 for table and any bracing needed.
my gantry I want to use aluminum, I do have someone that can weld aluminum. I want it to cantilever over one side for my rotary axis like a (Camaster)

No drawings yet as this is going to greatly affect my design. as the bottom of gantry needs to be attached under table [which should make it more stable] if I can use one screw.
yes I do have concerns (why I'm asking) and i hope there wrong as I would like to be able to do this.

[Jim Dawson]

Why not make a moving table machine? That way you have a fixed gantry and can make it as strong as you like, no weight restrictions. A single lead screw works fine with a moving table design, and you can turn the lead screw rather than the nut. Makes a much stiffer machine, but the downside is that it requires a larger footprint than a moving gantry machine.

[pippin88]

Strongly recommend using two screws for your long axis. This means you can support the table from below. With a single screw you can only support the ends of the table, and you will run into racking problems.

[ger21]

Yes, IF you make the gantry, and frame that connects the two sides under the table rigid enough so that it can't rack. This requires a welded steel frame under the table, at least 12" wide. See this thread:

http://www.cnczone.com/forums/cnc-wo...ing-posts.html


Another downside is your table is suspended at the ends, which can lead to vibration, and flexing.

[NIC 77]

I don't really understand this design.

I had a look at the camaster 4th axis system so I think I get that part. What I don't get is the 4' x 8', so does this dimension include the 4th axis part?

Smithwick, it sounds to me like the 9' you are talking about is your gantry, and the 4' x 8' is the cutting area for the table that doesn't include the 4th axis portion?

Not really sure what you're saying to be honest.

My preference would be to use two ballscrews to drive the gantry back and forth on such a large machine, with rotating nuts, however you could also use rack and pinion. Yes, a single ballscrew is possible, but may present it's own challenges.

This gentleman upgraded to rotating nuts:

http://www.cnczone.com/forums/cnc-wo...gineering.html

That's about all the help I can be I'm afraid.

[smithwick]

Yes, IF you make the gantry, and frame that connects the two sides under the table rigid enough so that it can't rack. This requires a welded steel frame under the table, at least 12" wide. See this thread:

http://www.cnczone.com/forums/cnc-wo...ing-posts.html


Another downside is your table is suspended at the ends, which can lead to vibration, and flexing.

This was what I was thinking. Table and rails separate gantry will run on the 2x6 box and table on it's own 2x2 box frame. I would or will make the drive screw under the table up as close to the cutting area as possible. The racking I had a concern but more so from the torque of the spindle.

[smithwick]

I don't really understand this design.

I had a look at the camaster 4th axis system so I think I get that part. What I don't get is the 4' x 8', so does this dimension include the 4th axis part?

Smithwick, it sounds to me like the 9' you are talking about is your gantry, and the 4' x 8' is the cutting area for the table that doesn't include the 4th axis portion?

Not really sure what you're saying to be honest.

My preference would be to use two ballscrews to drive the gantry back and forth on such a large machine, with rotating nuts, however you could also use rack and pinion. Yes, a single ballscrew is possible, but may present it's own challenges.

This gentleman upgraded to rotating nuts:

http://www.cnczone.com/forums/cnc-wo...gineering.html

That's about all the help I can be I'm afraid.

Yes the main cutting area is 4x8 with the rotary being off the side thus my gantry being cantilevered on one side over the rotary, will make it 5' wide. Sorry for any confusion getting from my head to words lol.

[ger21]

It probably need to be a bit bigger than 5ft.

[smithwick]

ok I went to the thread "project over kill" that is one unbelievable machine. if this is what it takes to build a cnc I'm in way over my head.
the whole camaster machine I'm looking at does not weigh as much as the gantry he built.

[NIC 77]

It probably need to be a bit bigger than 5ft.

Yes, I agree. I would think just for a 4 x 8 table the gantry tube would be near 6ft. So 7ft or so?

ok I went to the thread "project over kill" that is one unbelievable machine. if this is what it takes to build a cnc I'm in way over my head.
the whole camaster machine I'm looking at does not weigh as much as the gantry he built.

It's called project over kill for a reason.

I've browsed through that thread a few times, some seriously nice metal working! I have wondered how it turned out in the end and if they were happy with the finished result.

I have been thinking about this a bit more. I think the under the table drive could just cause more work for a machine so big. In your shoes I would do dual drives mounted on the sides, and either put the rotary inside the main frame, perhaps with some removable table sections OR come up with a chip deflector to keep from getting debris directly into the ballscrew next to the rotary if you do it like the camaster.

If you use rack and pinion then you don't have to worry so much about debris from the rotary gumming things up IMO.

Servo drives for this?

Also I'd personally use really big tubes to keep the frame design as simple as possible. Do you have an overhead hoist or crane?

That's all I really have to say, unless you make some drawings, then I may say more.

Good luck .

[smithwick]

Yes, I agree. I would think just for a 4 x 8 table the gantry tube would be near 6ft. So 7ft or so?



It's called project over kill for a reason.

I've browsed through that thread a few times, some seriously nice metal working! I have wondered how it turned out in the end and if they were happy with the finished result.

I have been thinking about this a bit more. I think the under the table drive could just cause more work for a machine so big. In your shoes I would do dual drives mounted on the sides, and either put the rotary inside the main frame, perhaps with some removable table sections OR come up with a chip deflector to keep from getting debris directly into the ballscrew next to the rotary if you do it like the camaster.

If you use rack and pinion then you don't have to worry so much about debris from the rotary gumming things up IMO.

Servo drives for this?

Also I'd personally use really big tubes to keep the frame design as simple as possible. Do you have an overhead hoist or crane?

That's all I really have to say, unless you make some drawings, then I may say more.

Good luck .

Thanks for your information.
Here is a link to a machine I was basing my thoughts on but only with one rotating ball nut 1.5" dia. In middle. If I can't get one screw to work I think this will be the way I go.
https://youtu.be/1XlA7qdp63w

[ger21]

I pointed you to the project overkill, specifically for the framing under the table that the ballscrew is connected to, that ties the gantry sides together. This entire assembly, with the gantry, needs to be so rigid that if you were to clamp one side in place, the other side shouldn't move at all, with about 200lbs of force on it,

Imo, there's very little benefit to using a single screw, other than cost.