starting from scratch- router 1st project

[idefix]

Hello, Jazz
Thank you for these valuable comments and suggestions. I have rebuilt the gantry with Hiwin style rails and blocs. size 15 for the Z axis and 20 for the Y axis and future X axis.
You are definitely right, the size 20 is almost same cost than size 15 for a much better strength...
I have tried my best to keep the Z moving plate as close as possible to the gantry beam (not so easy). Z axis travel is 170mm
Following your advice I have plugged the beams with covers (but do not decide yet where to place the plugs to fill/remove the dry sand)
To achieve correct geometry of the sitting planes for the rails, I can have access to a large milling machine at the company workshop (this will minimize the efforts of the alignment step)
The ballscrew type has been changed to 1610 for Y and Z axis and will be driven by timing belt ratio 1:1 (with space left to replace for 2:1 ratio whenever necessary)

Some pictures of the changes:




Again a few more questions :

Do you think it would be better to design a cover on the Z sides (to limit dust and debris penetration) ?
For lubrication, should I use grease (with the nipple) or should I already design oil pipes from now ?
For the Z axis stepper motor; should it be facing downward or facing upward ? (would depend mainly on the position of the ballscrew...)
Regarding the long X axis driven by two separate ballscrews and separate timing belts + motors, I plan to link the steppers on 2 different axis via mach3 sofware. Does its sound ok ?
Last question related to ballscrews: does the chinese ones so called "antibacklash" realy fit the requirements ? or should I go for the coupling of 2 separate nuts as exposed in Jonathan thread (a sufficiently strong machine) ?

Again thank you for your very valuable support.

[JAZZCNC]

Hi

Ok first my mistake and should have made clear, Only use 1610 on X & Y axis use 1605 on Z axis.

Yes I would have cover over Z axis has it protects everything.
I would only go to the trouble of oil system if access is difficult and really wouldn't go to all the trouble of Oil pipes when access is easy like yours would be.

Motor position doesn't matter really other than ease of fitting and working on pulleys etc, I tend to always position them with motor down and thread the motor holes has it makes for easy adjustment and fitting. Either works fine thou and I've done both ways.

Single or double Nut will depend on your requirements but for most router type work then single is plenty good enough and even for moderate accuracy milling work they are ok. If your wanting very fine tolerences, say for PCB or Engraving work then yes 2 nuts are best but then I'd say you've built the wrong machine anyway.!!

Regarding the long X axis driven by two separate ballscrews and separate timing belts + motors, I plan to link the steppers on 2 different axis via mach3 sofware. Does its sound ok ?

This I'm not 100% sure what your meaning.? . . . . If your asking is it ok to use 2 motors for one axis and slave in Mach3 then yes that's fine and is done all the time. You just have to be aware of it's limitations and tune the motors correctly other wise you can stall one motor while the other keeps going which can be very messy and destructive.!!

[idefix]

Ok fine and clear ! Thank you so much Jazz for these directions.
Will stay with the grease nipples and will correct the Z screwball type for 1605
For the X axis with 2 motors yes I plan to slave them in Mach3.
Let's finish the design work and will come back in a few days.

[Boyan Silyavski]

Hi

. . . . If your asking is it ok to use 2 motors for one axis and slave in Mach3 then yes that's fine and is done all the time. You just have to be aware of it's limitations and tune the motors correctly other wise you can stall one motor while the other keeps going which can be very messy and destructive.!!

Dean,
i have always wanted to ask that question, hope you know the answer- if the motors that drive the gantry don't drive it directly but with pulleys 1:1 ,if the gantry is racked by chance, wouldn't the belt give away and just start skipping instead of destructing something?

[JAZZCNC]

Dean,
i have always wanted to ask that question, hope you know the answer- if the motors that drive the gantry don't drive it directly but with pulleys 1:1 ,if the gantry is racked by chance, wouldn't the belt give away and just start skipping instead of destructing something?

Well yes and no dependant on motor type used.?
With steppers In reality what happens if one motor stalls is the other keeps going until the other motor stalls, by which time a number of things can happen depending on speed it was travelling at time. Often motors usually stall at higher feeds has that's where torque is lowest and machine incorrectly tuned for high velocity and high Acceleration just to compound the matter.!

Now often when first motor stalls due to low torque the other motor isn't far behind on available torque so it doesn't take much to bring both to a halt but that's not what causes the damage.? . . . . It's the 50-60Kg gantry travelling at 150mm/sec (9mtr/min Av rapid speed) just at one side which does the damage.!! . . . Doesn't matter how fast you are at reacting to seeing the motor stall you can't stop the machine fast enough and in the few seconds it takes to hit the "Oh shite" button before one side has travelled 300+mm further than the other side.!! . . . I'll leave the rest to your imagination has to what can be damaged or screwed up.

Now if you were using Servo motors then yes possibility it would strip the belt teeth but chances are it wouldn't stall either and the drive would detect any following error and E-stop anyway.

So the moral of the story is when slaving either be conservative on the tuning, use drives that detect stalling or use a different approach.?
I've done all 3 and my preference is single motor with belts connecting screws but I'm also ok with slaving you just have to be aware of the limits and this is why I like drives that help and take some of the risk away.!

[idefix]

Hi everyone,
I'm back after some time...
First of all let me wish you and you beloved relatives all the best possible for this new starting year. May 2014 be placed under new creative spirit, and wonderfull designs (as usual !).

I have taken some time to digest all the valuable informations posted on this thread and finally started the construction after some revisions on my design.
The parts of the main gantry beam (supporting Y and Z axis) have been welded together and the tube sections filled with vibration damping material. It has been coated with epoxy paint for durability and ease of cleaning and it is now ready for machining to generate the reference planes and associated straight edges. The overal weight is now 17Kg.
Some pictures:




As you can see, I've finally chosen to drive the X axis with its 2 ballscrew sets with one single stepper plus HTD 5M-25mm timing belt and 24 tooth pulleys. The belt tension device is not yet defined.
The beams will also be filled with antivibration material compound.
The rails supporting X axis will be leveled using epoxy technique.

There will be a cover for the whole Z axis assembly and an other one for the front belt drive system.

Need your advice for the axis end sensors: Do I need 2 sensors for each axis or only one sensor activated by 2 separate fingers (one at each end) ? What are you using on your own machines ?

Looking for your comments.

Philippe

[Boyan Silyavski]

Nice development.

To be honest i have similar size machine and though i have bought the sensors/the smallest mechanical ones, that people around forums say work fine/, i have never mounted them. May be others will disagree but for this size machine, driven by steppers i don't see a reason to put sensors at all. I use the soft limits and with some care am ok. The worst that could happen is for the motor to stall at one end of the axis. Yeah, it happens some times and nothing breaks.

[JAZZCNC]

Need your advice for the axis end sensors: Do I need 2 sensors for each axis or only one sensor activated by 2 separate fingers (one at each end) ? What are you using on your own machines ?

Looking for your comments.

Philippe

For the limit switches I use 1 x Proximity switch per axis that travels with the axis and is triggered at each end with adustable target. The switches are PNP NO(normally open) and wired in parallel sharing just one input.

Home switches are Fixed and Use proximity.

[EddyCurrent]

Regarding the long X axis driven by two separate ballscrews and separate timing belts + motors, I plan to link the steppers on 2 different axis via mach3 sofware. Does its sound ok ?

Philippe, It may not be obvious but if you use two motors you will need 2 drivers, a slightly bigger power supply, more wiring. In my case it added about 100 GBP to the cost. I'm not complaining it's just that I did not fully think about it at first but I still like the 2 motor idea best. The alternative of course would be to use one motor and longer drive belts to each ball screw.

I see you have been following the frame construction threads closely