Design Help Pt2 Required for CNC design/Build

[MikeyC38]

Mike I agree with the others completely that 2 ballscrews is much much better and prefered. . .BUT . . . I do know from experience with pritty much the same size machine it will handle wood, even hard woods no problem. Yes you won't be able to be has aggressive as if you had twin screws regards DOC etc but it will do the job ok. It will cut Ali but very light duty with shallow cuts.
You will need to widen the distance between bearings, more the better, and make the gantry as stiff as possible. The gantry width on the pics I've shown is 220mm with 240mm of actual bearing spread because it use's profiled rails not round and the bearings are slightly longer than the mounting pads so effectively 240mm wide gantry.

If you can stretch to twin screws then it's a no brainer just do it.!. . . but if not then I recommend you design the end plates for twin screw upgrade in future. The machine I showed in the pics is done this way. . . .Simplizzzzz.

JazzCNC - this is a brillant suggestion :tup: !!! Improve what I have but design in an upgrade path so that the existing investment is not totally lost!!!. A question springs to mind for everyone - in a twin ballscrew setup with 2 motors on the X-Axis (and I presume 2 stepper drivers) how do you ensure equal power output and speed to avoid crabbing the gantry? The Solsylva solution uses a single motor and belts so you don't get the problem.

Now that you guys have planted the seed of doubt in my mind :confused:, I will work up a twin screw solution as you've all suggested and do the numbers to see if my budget and timelines can take it !!!

Thanks All for your patience and interest

Mike

[JAZZCNC]

A question springs to mind for everyone - in a twin ballscrew setup with 2 motors on the X-Axis (and I presume 2 stepper drivers) how do you ensure equal power output and speed to avoid crabbing the gantry? The Solsylva solution uses a single motor and belts so you don't get the problem.

The control software IE: Mach3 handles this side and so long as you don't over tune the motors then it's not usually a problem.

That said PERSONALY I don't like slaving motors for several reasons.!! . . . Main one being that when it does go wrong, which more often than not is at high feeds, the damage thats done can be massive. Imagine the one of the motors stalling coming to a dead stop while the other keeps on going.!! . . .It's like a train wreck and scarey shit, esp on larger machines.!!
To be sure to avoid this you have to effectively de-tune and run slightly lower acceleration/velocity than you can using belts.

There are other reasons like keeping the gantry absolutely square is fiddly to setup and requires good quality accurate home switch's to be absolutely sure it's square every time you home.
Basicly What your doing with the switchs is setting the start point or zero position for each screw and by positioning the switchs you set the gantry square. . . .This is less than ideal to me.!! . . . Mainly because every time you home the machine the gantry gets twisted and co-jolled into square by touching one switch then the other potentially putting strain on the machine.
If you don't use home switch's to square then you can't be absolutly sure the gantry is square and if the motors start dropping the odd step here and there, which can and does happen if you push the machine too hard or over tune motors or it's not perfectly aliagned or setup causing binding.
Basicly it slowly loses position putting the screws out of sync and the gantry out of square.! . . . or if you stop the machine abruptly from high feed one of the motors can slightly run on more than the other due to inertia and position is instantly lost with no easy way to get back in position. . . . With belts this never happens.

Like I say it's a PERSONAL thing and there are lots that use slaved motors and are very happy with them. I've built machines that use slaved motors without any problems.!
It's just MY PERSONAL PREFERENCE to use belts on my own machine because I feel it's safer and more accurate and ounce setup it's pritty much done forgot and never changes.
Yes belts can snap but I've only snapped 1 in 4yrs and that was my fault not belt failure.!

(I'LL SAY IT AGAIN TO STOP ALL YOU SLAVED MOTOR USERS JUMPING ON ME.. . . . . IT'S MY PERSONAL PREFERENCE )