Hi danilo, makes sense. So again a trade-off between speed and accuracy. If I would take the 5 mm pitch the whole machine would have to slow down to 5 meter speed for 3d work, while doing 2d it is not an issue....

BUT especially with 3d work resolution matters, so I wonder where the compromise lies, don't you sacrifice too much with a 10 mm pitch on your z ?

As with everything I am looking at industries examples ( not that that bif manufacturers are always right but still ) and I notice pitches around 4-5 mm are used on z drives most often !?

If you ever looked at some big iron machines, routers, lathes mills
you will find really large pitch ballscrews. like 20mm pitch

its because of high count encoders on the screw they get the precision not the pitch.
How do you think a router can achieve 80m / min with a 5mm pitch ballscrew? spinning it at 16.000 rpm ?

I always count my expected POSITIONAL ACCURACY by using a 400 (halfstep) resolution. A stepper motor will always tend to get close to a full or half step.
So with a 5mm pitch direct 1:1 belt you get 0.0125 mm accurate positioning , with a 10mm pitch its 0.025mm.
For me a 0.025 positional accuracy is fine even for metalwork. Most machines will flex more.
A backlash on chinese ballscrew is around 0.05 to 0.10mm for comparison on how precisely you can rotate a stepper motor.

Hi Danilo,

Thanks for your fast reply !

1)
I was talking about commercial machines comparable in size and function. Those machines you are talking which about I indeed know ( I work with companies that have 1 or more of those ) ... But they use servo's and ballscrews of 40 mm diameter with rotating ball nuts for X and Y ( you don not want to know the price for those ) and more of these exotics. They need reliable production speeds and accuracies well beyond what the average MM frame is capable off or intended for. So not comparable with the MM imo.

The lower to medium end commercial machines I was talking about, I noticed often using 10-15 mm pitch or higher for X and Y ( when ballscrew) and around 4 or 5 mm pitch for ballscrew Z slides. I think the shopbot for example uses a 5 mm pitch Z, (maybe not the best reference ).

2)
Your last paragraph; calculating with halfstep resolution is a helpful insight;

10 mm calculated at halfstep obviously is 5 mm reolution at fullstep ( which is what I was doing ).

But on the choice you made for 10 mm, are you mostly doing 3d work or 2d work - and did you apply this Z to an ( or your) MM ?

No ballscrew on my z , but I have some 5mm ballnut around which I might mount.

I used 10mm on a cnc drilling machine made recently. Mostly because of its 2500mm table which had to rewind back after drilling, 10m/min .... compared to 5min/min means time=money

They drill around 350 pairs of pipes a day so 350 x 15 sec = 1.5hr lost on rapid positioning more for a machine to get back

Thanks Danilo,

That situ and axis 10 or higher pitch makes sence.
I will give this some more thought, but probably stick with my original plan for 5 mm pitch for z.

Not dead yet - and instead of hijacking Tokamak's thread any longer :D - here is a sneak preview what I have been up to lately ...

The build had been delayed by paid jobs and life in general, and I still don't have enough time to keep the thread updated regularly, cause I am putting all my spare time in the machine again lately... So don't expect much more from me until it's actually running and sorted.

Here we are about 1 month (about 40 hours I think) away from the finish ( my best estimate).

My Z is almost finished ( completely custom design ) bolting together as we speak.
The table is unpainted but finished ( Rail have been cut, gantry has been rolling e chain mounted).
Controlboxes are wired and motors and spindle have been have been turning.

To do: all little things that eat up sooooo much time, the final electronics (proxies etc) and wiring up the entire machine (pull cables).



Ps.
Moved img to next post as forum was not cooperating ( with the 5 min edit limit)...

Grinding L profile to 28 mm +/- 0.1 mm, making good use of flat spoilboard and Geralds built in clamping space.

http://s30.postimg.org/fp5jf3hm9/grind_height.jpg

Grinding the V-angle on the L-profile to +/- 0,1 mm - first with 36 then 80 grit sandpaper stuck on 2,5 mm grinder disc with double sided adhesive tape.

http://s4.postimg.org/a5n9zxf19/grind_V.jpg

Random image before mounting ground rails to machine, (jacked on wooden blocks) with E-stop boxes in view.

http://s16.postimg.org/7l7yby2qd/machine.jpg

Using two control boxes ( power and control hardware divided ) this is PWR control box, using DIN rails to mount all goodies DIY 1000VA powersupply, got lucky on ebay with unused siemens VFD (60 USD !!!)

http://s28.postimg.org/i4laz1ril/control_power.jpg

This is the DRIVE controlbox, using Eding CNC (former USBCNC) CPU 5B ethernet.

http://s30.postimg.org/4x7z0025t/control_drive.jpg

This is the CAd of My 100% custom Z-slide with 55 cm of stroke. 35 kg of pure steel and aluminium (!) All parts have been made, bolting together but no picture at hand.

http://s30.postimg.org/9apckrldd/z_slide.jpg

I look forward to your comments on my page each morning. Good to see that you have posted some updates. You are way ahead of me on the electronics. I wish I had my motors turning. Nice compact box layout.

I read somewhere about VFD electrical noise causing issues in the control box. Not sure if there is any proof of that. But after reading it I decided to mount my VFD away from the controls. Still need to find a box for that.

That is why I mounted all power (noisy) away from all control electronics. Each have their own metal cabinet on the machine. My Eding CPU5B with ethernet is also much less prone then mach3's parallel port to this noise.

The Eding CNC company advertises in their manual with machines with vfd in the same box without problems so it might be overkill, but better safe then sorry imo.

I have two boxes which are each 60x40x25 and my setup is now way fuller then I anticipated when I started... bigger controlboxes are always better :D But this is all I could fit under my table ( they will be on the far end of the X under the spoilbaord mounted in rubber )

Fox,
Nice to see your progress. nice controlbox. some remarks for your z axis.
Is the green slide including your spindll going up and down, or is the purple plate fixed to the y car. In that case the motor has to pull 33 kg up and down. there will be a chance that if you don´t power the motor controller your z axis will sink down by its weight. can be avoided by choosing an other gear ratio between stepper motor and spindle, or mounting the gas spring
I builded almost the same concept, but when I start running the machine the z axis started vibrating when running curves. it was to heavy in the top. finaly I made a new, shorter one, and this one has no vibrations.
think allready where you want to place your limit switches and home switch, and drill the holes in advanced. save you some time in assembling and disassembling the z axis

Nice to see another ball screw + linear guide Z-axis.
If I were to do mine again, I would couple my motor to the screw with timing belt like yours.
BUT I would have the motor mount at the back to gain 80~90mm of Z-travel.
Mine is direct coupled, the alignment took a bit to time to get right & I feel the motors is to high in the air.

FYI, In a control penal 6" or 150mm is consider "Far Away from". 2"/50mm is marginal.

If I get a few minutes this weekend I might even post a picture IF I finish assembly of my Z.

@ Rik,

I have an electromachanical brake on my ballscrew (blue cirkel topleft).
It is enabled when there's not power to my drives, and when there runs power to my drive, there runs power to my brake, which is then released.

The mass is a worry I had, but I have a backup plan for that already that will eliminate it for such a problem for sure... so we'll see..

The entire Z was drilles and tapped 100% by CNC taken into account all mountings like proxies etc in advance. It was made accurate to 0,01 mm... I was lucky to have some friends in the right places. (the entire assembly still costs me a lot of money though).

It's really lego. But the stupid thing is i have all parts but I am now waiting for all the right bolts to arrive.

@ Ken
the rails on my Z are on the moving part (stiffens) so you can't move the motor to the back and gain travel... you would actually loose travel ( when the motor hits the fixed plate). I had thought about a rotating ballnut, but thought it was too complex for now.

All my alignments of rails and wagons are taken care of according per Hiwin manual, so just bolt it down and lock it against the shoulders should take care of that.

Last note about teh control panel I don't understand

Here's some bigger pics of my Z.

I have even built in the possibility to tilt my Spindle a true indexed 45 and 90 degrees. Not that I need that straight away, but can be helpful to do some crazy stuff in the future ( as I do a lot of crazy stuff :D )
Also I built ins some basic dust protection for ballscrews and wagons. I have the option to go fully enclosed in the future with bellows.

Spindle is my big friend (380 Volt 3,2KW)

http://s15.postimg.org/4q3tt7ow7/Z_big_1.jpg

http://s15.postimg.org/rp0jc4kw7/Z_big_2.jpg

http://s15.postimg.org/5455st8zr/Z_big_3.jpg

http://s15.postimg.org/hg826awuf/Z_big_4.jpg

I was referring to the spacing of components inside the control penal.
BTW, I don't have any breaks on the screw, it won't go anywhere.... Mine didn't move a bit... and even if it moves, it would be the ball park of 0.1mm when power down. Nothing I can't live with. There will be a handsome saving on whatever breaks you can come up with.

BTW, my ball screw Z-axis. here

Hi ken,

brake is for peace of mind, when I hit E-stop I am sure my brake keeps the Z where I want it, for example it won't drop on anyone else his fingers while the spindle slows down.

I still don't understand the control box comment, you mean my spacing is too small ?

2 reasons I went for the ball screw Z were
1) more rigid (& it actually is)
2) no need for gas spring or what ever for holding... (3 years & nothing drop except for loose spindle clamp because I forgot to tighten the screws...)

Think about it, stepper motor is named such because it move a step at a time. & we "perceive" it is moving continuously when actually it is a strings of steps at different intervals. If and when motor power is cut, unlike other motors, stepper motors makes no more steps & stops abruptly...

No, didn't even wipe it clean after use....

I just enjoy simplicity. too lazy to work on extra precautions which won't happen, most importantly, I don't have the budget to over do. :p

As with "bigger is not always better", "more is not better". Its just me, anyone may do whatever they like.

As for the control penal, I'm trying to say politely your spacing distance is enough. Any more and you will be way over the top.

Now I understand, and I totally agree my z is way-over-the-top-future- proof, but I have my reasons :D. As with my control boxes.

Ps1.
Of course your linear z is also already "overdoing it" compared to Gerald's plans... I just took it to the next level. I am happy with it, but its by no means meant as an advice to follow for aspirant builders. Stick to the plans will be good enough for most.

Ps2. when there's no power to your stepper it won't hold, it will have some magnetic resistance in a rotation, but that's it. You rely on the friction in your rails/wagons, ballscrew/ballnut, and drive ratio to hold your z up, which in most cases i agree is indeed enough. I have also never used the airbags in my car, I had to pay extra for them when I bought it:rolleyes:.

More space in the penal is actually a good thing :D
Honestly, My Z-axis is considered minimalist in comparison :D could had go for smaller rails & thinner aluminum base plate. BUT I don't consider it over-doing, it is a rational improvement.
Why external break is not required.
1)The stepper motor do have detention torque & it is fairly significant just have a look at your stepper motor specs., which is another unique stepper motor feature.
2) the ball screw has higher mechanical ratio in-comparison to the original MM rack & pinion setup minus the weight of belt reduction.
3) My slide assembly (alone) has a static friction which require 16kg pull force to overcome. (I'm sure you will measure yours after you assemble yours).

Conclusion
I have one working hassle free for years :D
I'm saying all this in good intention to tame your worries & avoid unnecessary expenditure.... electro-break is additional cost, the aux equipment to make it work are also additional cost. Maybe all this saving will pay for your A axis or a second gantry.
I rest my case.

Appreciated as always, ken.
'Problem' is I already have my brake, and the aux controlling it...as well as an a-axis :D

V Rail Bevel Variations
 

Fox,

Revisiting our conversation about smoothing the V Rail to remove variations I mad a measurement.
Installing a dial indicator to measure the variation of one when I measured + and - .010" (.25mm).

Seems to be worth checking. Easier to check after the Gantry is rolling.

John

Are you referencing to my other topic about preloading the y rails, to compensate for the bending of the tubes due to the weight of the y car ? Or what did you actually measure ?

Fox,
Sorry for the confusion. This was referenced to post #159 of my build.

http://www.mechmate.com/forums/showt...?t=2526&page=6

We were discussing the need to sand the X V-Rails with a longer V-Block to reduce variations from the grinding. The dial indicator in the picture is measuring the variation in the rolling height of one V roller as it moves in X. The change in height is due to the inconsistency in the cut of the bevel on the top of the rail.

John

Ah, yes, I see now. I did use the v block !

Hi guys,

I am very close to firing up the beast to make a first cut, but have a quick question:

I have powered up my steppers and jogged the machine for the first time. Already felt great to see it move under own power !

But amongst some other things i need to sort, I noticed that with the motors enabled, but not moving (sitting idle) they make a hissing/stuttering sound, not really loud, but enough to be heard when standing next to the table. Is this normal ? It seems not ok to me, but it's my first CNC so I can't judge. When jogging/moving it seems to diminish/be overhelmed by the other sounds.

I use 86HS9801 motors and leadshine AM882 drives.
I feed them with 71 volt.

Tune the drives to motors by Leadshine software and the RS232 cable provided with drives.

Hissing to some extent is ok. it should not be loud just audible when you get very near the motors.

Ok, I will see into this, I autotuned them by flipping the dipswitch (4 I believe) and thought that might do until now, cause I don't know what I need to do to tune them.... but will look into this.

It is audible, but no loud, but also not only when I put my ear near them. I think from about 2 meters away when there's no sound in the room. In this room I can also hear the relais click in my controlbox, when there's no other sound. (it's empty besides the MM with stone walls)

Hey Guys,

another issue:

My Sicce Nova impeller pump, benchtested perfect, but now struggles to pump the coolant round. It barely makes it, and there's not enough flow left at the end of the lines to keep my spindle happy I am sure. I am using 8mm od (6mm id) Pu tubes. Table is 2x3 meter Z = 80 cm.

So what do you use/should I use ? I would like to try and keep the hose size relatively small ( 20 mm hose would fix the problem maybe, but won't fit in my energy chains i think, and there's the restraint at the spindle anyway with those tiny inlet en outlet of 4 mm. Basically I think I need a higher pressure pump to pump coolant trough the system ?

I'd prefer a submersible pump.

This is overhead chart, your pump is declared at maximum 1.5m where it will pump about 50L an hour "maybe" . Comparing it to my atman 104, 38W pump you need at least the "Extrema" model since its 32W pump. and has a maximum overhead at 2.5m

http://www.sicce.com/backend/prodott...nova_curve.jpg

thanks for your quick help, I think I will even go to their syncra line then, because my line restriction will make the flow considerable less I imagine, I see on alibaba a lot of 75 watt pumps are used at 3000 l/m for the spindles, where they screw a copper inlet restircion of 6 mm on:

http://img.alibaba.com/img/pb/125/00...000125_751.jpg

So maybe their syncra 3.0 ?

http://www.sicce.com/backend/prodott...s_20-25-30.jpg

Fox, I mounted my small cheapy pump right on the y car to avoid running into all of the problems you have stated, I really didn't have space on the energy chain to run a line, it hardly weighs anything, I ran 12v to it so far it works great. I don't know if others have done anything similar or if it will last long but it keeps the spindle very cool.

I contemplated that solution ( still am as a makeshift solution - I am sur ethat woudk work, as I beanctested it with 10 meters line or so )

But in then end I would like to get it off the gantry. Reasons are it's already very heavy in my machine, and cluttered, the slushing etc. Plus I already have everything in place. Just need a different pump now :-(.

What kind of reservoir, spindle, and pump are you running on there, and do you use a radiator ( I try to avoid that, os I do not have it laying around here now; another expense ) ?

I have a 3,2 KW 380 volt spindle btw. So above MM average.

Hey Fox, Stick your pump in a bucket of water and hang it from the ceiling already and make that YouTube video ;)

I promise the video and pics will follow soon :D but this is not the only thing I need to check before firing the beast up.

But I am less then a week away for sure. EXCITING

I do have a fan and a radiator also on the gantry. The pump has a reservoir built-in, not very big something like 150 mL or 250 mL

No radiator, just a industrial coolant pump & reservoir as per any lathe & milling colant set up.
I reckon even with its good heat insulation property the long PU tube (8~9m to-and-fro )already dissipated enough heat from the water even without the heat mass of the reservoir.

Hi Tom, yeah I though so, so the in between is ,without extra expense a no go.
@ Ken, good to know, that's what I was aiming for as well with my intended trough e chain setup.

On the hunt for a pump that can be delivered tomorrow or at least before the weekend as we speak.

Fox,

Put the pump and reservoir on a table next to the machine at the same height as the spindle. The pump won't waste pressure lifting the water.
Put a thermocouple in the outlet hose of the spindle. A lower flow will allow the water to heat more on the way through the spindle. A higher flow will not heat the water as much on the way through. In either case the water is cooling the spindle.

More flow decreases the outlet water temperature but doesn't necessarily cool any better.

Heat loss (watts * .239) = cal/sec
Flow (GPM * 3784/60) = grams/sec
Water temperature rise= (cal/sec)/(grams/sec)

I play an engineer on TV.

John

That was when it barely made it ;-) when I put it in position it did not make it go round. New pump already ordered !

that makes sense, but it was really not flowing enough to cool.

Thanks for the formula's I will run them.