BuildingAfloat

[Robin Hewitt]

Jazz is the man, you won't go far wrong if you have faith and simply do everything he says.

Incidentally, putting 2 steppers on one axis usually ends in all sorts of problems.

[BikerAfloat]

Jazz is the man, you won't go far wrong if you have faith and simply do everything he says.

I have followed Jazz's inputs on varied posts and have to say from what I have read I do have faith in his advice, however I was brought up to question everything where you have doubts, so I wont follow anyone blindly :-)

Incidentally, putting 2 steppers on one axis usually ends in all sorts of problems.

I have read that this idea can cause problems, yet one of my favourite machines out there is the Heiz from CNC-step, This was the inspiration for this feature being included in my build. They can't be that bad (well at least I hope they aren't) as their sales are in the 1000's now!

Advantages I see are:

1) Open bed design, this is important for me as I will want to get awkward shaped engine components in the machine for engraving.
2) More grunt for moving the heavy gantry.
3) Even loading of gantry to prevent, or at minimum reduce, racking.
4) Reduced component count
and 5) Possibly better accuracy when compared to a single central motor & belt system?

Disadvantages I see are:

1) Increased cost, but this should be a one-off.
2) Synchronisation/Alignment of the screws at the assembly stage, again this should be a one-off.
3) Machine ties itself in knots if one motor looses steps
or 3.5/4) Worst case scenario machine goes completely to peices should one motor stall or stop all together.

Prepared to accept any more Pro's and Con's before I freeze the design.

1 & 2 aren't my biggest worries, as a) this is an expensive tool anyway and I think (hope?) the advantages are worth it & b) this b@rst@rd is going to have so many adjustments required to get it straight and true, one more won't really matter :-)

3, 3.5 & 4) Scare the living daylights out of me!

Any advice to how best to go about reducing the risks and or providing the single motor & belt drive within my construction requirements would be gratefully received.

Cheers,

Geoff.

[Jonathan]

however I was brought up to question everything where you have doubts, so I wont follow anyone blindly :-)

Excellent

I have read that this idea can cause problems, yet one of my favourite machines out there is the Heiz

Your options are limited to having two leadscrews on the X-axis - there is no way you'll get away without two when cutting metals unless the gantry is exceptionally strong which is almost never the case.

I use two motors on my X-axis and have not had any problems due to using two motors. When testing I have had one motor stall, but the gantry is sufficiently strong for this not to cause noticeable damage, especially since once one motor has stalled the other will invariably stall a fraction of a second later.
You can save a little money by only having one motor and using pulleys, but since you want the motor and driver later for a 4th axis you could always start with two motors and if you're not happy with it link the screws with a timing belt and use the now spare motor and driver on the 4th axis.

I urge you to reconsider not using ballscrews. I would add up the cost of the 4 leadscrews you are intending to get along with all the parts they require, then send Chai on eBay a request for the price to get the 4 ballscrews (and rails) you would need with the standard end machining and bearing blocks. I'm sure you will be pleasantly surprised.

You mentioned using the 3Nm motors from CNC4You. These are a good choice since they will be more than adequate for this machine and offer the best price per Nm in Nema23/24 frame size. Currently you've got all the leadscrews direct drive which gains simplicity, however using timing belts gains a lot more than that. You can change the drive ratio (important to get a good feedrate if the leadscrew is quite a low pitch), motor alignment is no longer so critical, plenty of people seem to have problems with couplings breaking and belt drive provides damping which helps reduce resonance issues to name but a few...This is a good place to get the timing belts and pulleys.

Putting a sheet of aluminium on the back of the gantry will greatly increase it's stiffness since it will essentially eliminate bending of the gantry sides parallel to the Y-axis, thus reducing the tool deflection in the same axis.

[JAZZCNC]

I have followed Jazz's inputs on varied posts and have to say from what I have read I do have faith in his advice, however I was brought up to question everything where you have doubts, so I wont follow anyone blindly :-)

Good upbringing because I wouldn't want anyone blindly following my advice and I only offer it to help the person come to the best design for there needs and hopefully steer them clear of any issues I know thru experience will come from what I see or comment on.!

I have read that this idea can cause problems, yet one of my favourite machines out there is the Heiz from CNC-step, This was the inspiration for this feature being included in my build. They can't be that bad (well at least I hope they aren't) as their sales are in the 1000's now!

Ermm I wouldn't be so sure and they are certainly massively over priced IMO.!

Advantages I see are:

1) Open bed design, this is important for me as I will want to get awkward shaped engine components in the machine for engraving.
2) More grunt for moving the heavy gantry.
3) Even loading of gantry to prevent, or at minimum reduce, racking.
4) Reduced component count
and 5) Possibly better accuracy when compared to a single central motor & belt system?

1) preference really but open bed is generally less accurate and more time consuming to set-up accurately.
2) Yes
3) yes
4) Erm not really when you take account of electrical side, wiring etc.
5) Absolutely NOT and the reality in use is that they can possibly be less accurate due to any missed steps in one or both motors slipping by un-noticed until the error shows it's self in the work, which is far too late for me.!!

Disadvantages I see are:

1) Increased cost, but this should be a one-off.
2) Synchronisation/Alignment of the screws at the assembly stage, again this should be a one-off.
3) Machine ties itself in knots if one motor looses steps
or 3.5/4) Worst case scenario machine goes completely to peices should one motor stall or stop all together.

1) The cost difference isn't so much after buying belts and pulleys.
2) Big disadvantage and you'll be doing it all the time (every time you use the machine if you want to be sure of accuracy) either by butting up to adjusted hard stops or using home switch's to sync.
3,3.5/4) Massive potential for serious damage when it happens and unless the slaved motors are run well within there limits then it will happen for sure and it will scare the living day lights out of you at best.!! . . . Best case it will tie it''s self in knots wasting a few hours setting and adjusting backup.!!. . . . Worst case with high probability if it happens at high feed rates damage will occur leaving you crying and shacking in the corner. .

Slaved motors work fine if run within very safe tolerances regards tuning. They are very very intolerant of poor design causing any binding or miss alignment and will cause problems with stalling one of the motors while other continues on it's merry way causing chaos.!!

Belts completely remove this problem with very very good accuracy and are basicly fit and forget.!
In over 3yrs hard use my machine hasn't lost position regards screw sync more than few 10th mill and that was just in first few weeks due to pulley slippage and settling down.
In normal cutting use it has never missed a single step or lost positional accuracy. Again unless I cock up with programming and embed the cutter in something hard or try to run the gantry of the end it never stalls motor.!!. . . and if It does then no big deal just re-home the machine and I'm back on track with no damage to machine or hours straightening the machine out.!

The only down side to belts IMO is the look and the extra work designing into machine.? both more than worth the sacrifice or effort IME.