Second attempt at new design

[CtrlZ]

This is my second attempt at this design per everyone's advice. Thanks to everyone who helped and I appreciate any further comments.

I pretty much started over and tried to make this design more substantial. The table is 56" X 96" made from 4" square tube stock. The gantry clearance is about 13 1/8" so I can mill a 12" part easily. I intended to make a removable bed for milling thinner parts but now I don't think it's necessary. (I could be wrong) The Z travel is a little over 13".

I'm not showing the drive components, but intend to use AC servos and ball screws with direct drive couplings. Probably 1 1/2" drive for the X axis, 1" for the Y axis and 5/8" for the z axis.I may add a fourth axis later.

Thanks for your thought, don't hold back.

[eloid]

Looks abit like the Arty
http://www.legacycncwoodworking.com/arty-cnc/

If i was design a steel fram cnc I would not use ball screw for your y axis
use rack and pinion and save your self a future upgrade also you dont need
the bottom ballscrew brace on your gantry making it lighter if you go R/P

look good so far

[CtrlZ]

Eloid, thanks for the comments!

If I use rack and pinion for the X axis, does it have to be driven from both sides, or can I get away with just one side? One of our copy lathes has R/P for the X and is only driven from one side but the rails are only about 8" apart. It seems the wider span would require driving from both sides to prevent chatter, and every R/P table I've seen are driven from both sides.

I like the idea of using R/P for the X, but if it will require two drives, I'm a little intimidated by the prospect since I don't have any experience or knowledge of doing anything like that. I will be using AC servos we already have, and I have enough matching servos to do the job, but I don't have a clue how to sync them together. Does it require special wiring, hardware, software, etc?

[Phife]

Looks good!, my only concerns would be where the Y/Z gantry meets the X rails, it looks like that big heavy gantry is supported by those thin plates that the bearings get attached to, I think some sort of beefing up there would help. Also that gantry is heavy, your going to have alot of mass to accelerate and decelerate, perhaps you could make that out of 2.5" - 3" square tube? try to save weight on the moving parts, having a heavy gantry will only slow you down.

Also, I would try to get my Z axis thinner, it looks like it hangs out quite far, any chance you could move the Y rails to the back so your router is closer to the Y beam?

As for adding a second motor to the X, its really not hard to do, Mach3 does all the work (slaving the second X motor), all you need to do is have an additional servo driver and wiring. And 2 limit switches on the X helps keep everything lined up and square.

Those are my suggestions, Good job so far!

[CtrlZ]

Thanks for the comments Phife! I feel like I'm getting close to a final design.

I made the gantry heavy to accomadate the extra Z travel, but maybe I could lighten it up a bit and still be ok. I was planning on using Mach3 so I think I'm going to go ahead and plan on R/P for the X axis since you told me I can easily set up the second servo as a slave. That will also eliminate a lot of weight. When I redo the gantry, I'll also see what I can do about the Z axis hanging out so far.

I'm off to make some modifications, will update.

[eloid]

[QUOTE=CtrlZ;803370]Eloid, thanks for the comments!

If I use rack and pinion for the X axis, does it have to be driven from both sides, ( yes I recommend)

or can I get away with just one side? One of our copy lathes has R/P for the X and is only driven from one side but the rails are only about 8" apart. It seems the wider span would require driving from both sides to prevent chatter, and every R/P table I've seen are driven from both sides.

I like the idea of using R/P for the X, but if it will require two drives, I'm a little intimidated by the prospect since I don't have any experience or knowledge of doing anything like that. all done in mach just requires some
configure mach to see other motor as a slave.

I will be using AC servos we already have, and I have enough matching servos to do the job, but I don't have a clue how to sync them together. Does it require special wiring, hardware, software, etc?

nothing special software just mach...

Looking at your design i would may add a addtional support like you have in the mid spam of your y axis having 2 mid span support per y axis would be ideal..

[HereinCS]

Originally Posted by eloid Looks abit like the Arty http://www.legacycncwoodworking.com/arty-cnc/

That's an interesting looking machine. Is the rotary axis a direct mount servo motor?

[eloid]

Originally Posted by CtrlZ Thanks for the comments Phife! I feel like I'm getting close to a final design. I made the gantry heavy to accomadate the extra Z travel, but maybe I could lighten it up a bit and still be ok. I was planning on using Mach3 so I think I'm going to go ahead and plan on R/P for the X axis since you told me I can easily set up the second servo as a slave. That will also eliminate a lot of weight. When I redo the gantry, I'll also see what I can do about the Z axis hanging out so far. I'm off to make some modifications, will update.

why not do x and y r/p? and z axis ballscrew

[Phife]

Originally Posted by eloid Looking at your design i would may add a addtional support like you have in the mid spam of your y axis having 2 mid span support per y axis would be ideal..

I dont agree here, He already has a aluminum plate running the entire Y axis, surely that is enough support between the 2 Y beams.

Adding a midspan support just adds more weight to the moving gantry.

[eloid]

Originally Posted by Phife I dont agree here, He already has a aluminum plate running the entire Y axis, surely that is enough support between the 2 Y beams. Adding a midspan support just adds more weight to the moving gantry.

Not to the "gantry ( gantry is fine )" but the long axis Y it only 6" worth of tubing
it does weigh much.... when you start welding , you find you tubing is not
the same any more... this 6 tall tubing will help with high freq....resonance vib in this rail


If you do any cabinet work or drawers... etc you may want to make a cantilevered front so you can dovetail / dowel pin work..
see attached picture.. and videos

YouTube- ShopBot Cutting Dovetails YouTube- Dowel and Assembly Test

[CtrlZ]

Eloid, I think the extra support is a great idea. I also like the R/P idea for the Y axis.

For milling the edge of parts, couldn't I just clamp the work piece in the center of the table and cantilever it over one of the middle supports? I may also use a sacrificial piece of plywood for some work.

[Phife]

Ahh, I see where the problem is Eloid, what you call the Y, I call the X.. sorry for the mis understanding, I agree with you.


CtrlZ,

You will want to have a permanent table on your machine, you will have to machine it flat with your spindle, and it will probably be a pain to remove. So if you plan on doing any panel edge work like the videos eloid posted, you will want to have an overhang off the end, or a table designed with this in mind.

I have used various beds on my machine, and I have settled on 2" MDF with a 1" HDPE Vacuum table top, 1/4"-20 holes spaced 2" apart on the "islands" of the vacuum grid. I find this works best for me as I do alot of carvings, signs and panel work.