Router related questions.

[martyscncgarage]

I want to build a 4x4 router. But I am going to likely go with one screw right up the middle for the Y axis in order to avoid the issues you have. Heavy linear guides and trucks on the sides.

Don't do it, Marty, it's not worth it. Twin screws are much better on a wide gantry and provided you use Stepper drives which have Stall detect feature then there is nothing to worry about. Anyway, correctly set up and tuned stepper based machine should rarely losses steps so not an issue.

Marty...
I agree wholeheartedly. Single drive = 2' wide max

Why?
I would imagine it depends on the rigidity of the machine?

[jazzcnc]

Why?
I would imagine it depends on the rigidity of the machine?

Easy to see just lock one side and turn the screw and measure how much other side deflects. Obviously will depend on what and how your cutting to how much forces are involved but some deflection will occur. The question is how much you are prepared to accept.

Twin screws take this away.

Also you don't need 32mm Profiled linear Rails for that machine 25mm and even 20mm will be more than handle that gantry with plenty to spare.

[Gary Campbell]

Marty...
Did you post that picture as one that was rigid enough to need require a dual drive? If so, I would suggest that it is one that would need it for sure. Machines like that can skew a tenth of an inch in a heartbeat, just from cutting force on one side of the table to the other.

I even spec dual drive on my small 24 by 36 ATC product because of the toolholder accuracy requirement and the inability of most machines to retain square.

[martyscncgarage]

Then why was it designed with one screen up the middle with DC brush servos?

[Gary Campbell]

To save money over what a dual screw setup would cost and make it more saleable? Once running, and since there is little chance that you will dislodge the servo position, apply 20, 30, 40, 50# of force front to back on one side of the gantry while watching a dial indicator on the other. Then you will believe what we are saying.

[martyscncgarage]

I dunno. If you have a rigid gantry, with outriggers for the linear trucks to meet the linear rail, it would seem to me it works with one screw and motor.

Take a look at Patrio's machine. While I can't see under the table, I guess I would have to test it to see if it did as you guys suggest. I find it hard to believe it would deflect that much given the cutting forces. Now if the frame/gantry were of less rigid design/material, I could see that being a factor.

http://freedomcnc.com/machine/patriot-4x4/

[Gary Campbell]

Marty...
Not saying that isn't a well built machine. But on the other hand, there has to be some reason that virtually all US mfgrs have eliminated single drive gantry machines.

[mael]

Dont do it marty...hekhek
I build mine with only a 2 foot workable bed and it still has a little play,
But then again i didnt use those heavy duty rails (i wish i had though when i was buying my stuff for it).

I am planing on adding another simple rail using bearings on the bottom to make it more rigid.

This is my new build in the works (still using the same type of rails coz i bought them together with the other one).
go easy on me guys.

[martyscncgarage]

Dont do it marty...hekhek
I build mine with only a 2 foot workable bed and it still has a little play,
But then again i didnt use those heavy duty rails (i wish i had though when i was buying my stuff for it).

I am planing on adding another simple rail using bearings on the bottom to make it more rigid.
image1.jpeg
This is my new build in the works (still using the same type of rails coz i bought them together with the other one).
go easy on me guys.

image3.jpeg

Ok, Ok, I get it.
Thing is I would like a 4th axis, and using slaved motors takes that away. Acorn only has 4 axis.
I am also reconsidering the 4x4 size. Shop space and need for that size router.
I have plenty of time before I build it. Actually hoping I find a 4x4 or smaller commercial CNC router with a dead control.


Why are you going with a larger table? Just curious.

Thanks for the input.

[mael]

Dont do it marty...hekhek
I build mine with only a 2 foot workable bed and it still has a little play,
But then again i didnt use those heavy duty rails (i wish i had though when i was buying my stuff for it).

I am planing on adding another simple rail using bearings on the bottom to make it more rigid.
image1.jpeg
This is my new build in the works (still using the same type of rails coz i bought them together with the other one).
go easy on me guys.

image3.jpeg

Ok, Ok, I get it.
Thing is I would like a 4th axis, and using slaved motors takes that away. Acorn only has 4 axis.
I am also reconsidering the 4x4 size. Shop space and need for that size router.
I have plenty of time before I build it. Actually hoping I find a 4x4 or smaller commercial CNC router with a dead control.


Why are you going with a larger table? Just curious.

Thanks for the input.

You can connect two motor drives in 1 axis. The big table of mine will still have a 4th rotary axis. The trick is on the home switches of the dual motor axis which jazzcnc talked about in earlier posts.

Im building the larger table as an investment for future jobs. Cant seem to find good work for my small CNC.