It writes!! - Amsterdam, NL

[rischoof]

fox,
I had the same with my energy chain, it was not straight.
I didn't like it, so I made them straigt.
get out the yellow buttons en disassemble the chain.
I removed a little material with my table saw from the black part
it's small ammount I removed and after a copple of parts I re-assembled and looked if it was flat. I had to re-adjust the table saw a little and then the ammount of material I removed was OK to make the chain flat.
finally I didn't install the yellow bottons back

[Fox]

@Danilo, @Ken, @Ross, @ Rik:

THNX guys, much appreciated, between the 4 of you, you have answered all my current doubts/questions enough I think to be moving on to the next steps !

Ordering rack and pinions tomorrow.

Gantry I hope to finish begin of next week.

I try to order my cables and some connectors this weekend ( have to do some research ).

Kitchen table project starts this weekend. I will see if I can fit in the rail grinding first week of July, and have the kitchen table project finished by then. That would mean a final push in the second week of July to get it all assembled and aligned and making the first cut, and then well-deserved holidays with the family ( they are lucky we go abroad so I can't play with the MM - and maybe it's better for me as well )...

Upon my return play with it for a week or 3, and then disassemble for paint ( so I can still do that outside ).

Wel... that's the plan, let's see if life/work does not get in the way...

[Fox]

Started on my modified-Z 3d drawings today to work out a teahnical drawing and order sheet:

1)2 ground slabs of alu, indexed& milled for parallel linears with tapped holes - check -
2)2 bought 20 or 25 mm linears guides + 4 carriages - check -
3)Ball screw - question below-

1) What have those of you who are using a ballscrew for your Z used ? - Does a 25 mm ISEL with 5mm Pitch sounds like a good plan for a 700 mm extended Z ?

[rischoof]

fox,
25 mm is big, use smaller diameter. the weight of spindle has te be accelerated and slow down, thinner is lighter. will be easyer to turn from left to right for you stepper motor

700 mm? I don't know why you need that length. I had a spindle 50 cm stroke, total 700 mm length, motor on top. the point of gravity is to height. when mounted on the Y car. I can see that it is shaking. i don't see it in my cut quality, but i can see and feel that it is shaking. that's the reason I built a shorter spindle, and keep my point of gravity low

[Fox]

Hi Rik,

I have a Nema 34 ( same like X and Y planned ) for the Z ( a bit overkill, but already got it ) so I think it will work with the 25 mass ? I mean ... I was chosing 25 over 16 because it would be stiffer introducing less whip on the 700 mm Z. Still think I should go smaller ? What are you using for the pitch ? 5 mm or smaller... I was in doubt on that pitch for increasing the resolution on the Z.

I want/would like the 500-700 mm for future projects ( like foam cutting under the current level of the spoil board ). In normal position it behaves the same like a standard length Z, it would just point up in the air. But it's interesting to learn from you that the Y-car is not up to the job of holding it up steady and straight. I would think that it would, when you tighten make the Z slide of massive alu fit exactly in between the mounting points. Are you sure the shaking is not from the Z itself, but the Y car flexing ? That would change my game plan considerably. I thought the only 'weaker' point in the MM Y&Z was the Z slide with the bent spider, whcih can be improved upon with a custom Z.

Was your 700 mm Z an modified Z with linear guides and screwballs ...between two massive 15-20 mm aluminum plates ?

[rischoof]

http://www.mechmate.com/forums/attac...1&d=1327290909
this is my first Z as the slide is fixed to the y cart. and the unit is moving up and down. the motor is mounted on top an massive aluminum mounting block. this makes my spindle top heavy. this is an aluminium frame with single row bearing on each side. the weight the motor has to move up and down is 18 kg and when the motor is powered off, it just will stay in position

with my new spindle I am trying to improve. so the axis is shorter, stroke is still 30 cm, my ball screw spindle was not shorter.
This time the spindle is mount on the slide, so the unit is mounted on the y cart instead of the slide. motor is mounted lower than in my previous one.
the weight the motor has to move up and down should be lower, I expect Half.
I will upload some pictures on my building log from my new spindle

[Pajka]

you don't want to go lower than 5mm pitch as you will loose a lot of speed.

///Danilo

[Fox]

@ rik, interesting to say the least.. i'll email you for some more pics and details. My plans where pretty much in that direction dimension wise and layout wise, as the linear rails will be pointing away from dust, and they stiffen the longer slide...., Although my calc did not accumulate to 18 kg, it still is much higher then moving it the other way round. The nema 34 weighing in at around 4 kg does not help when mounting it on the moving part of the z.

@ danilo with the standard mm layout the z has the same speed as x and y, but with a 5 mm pitch ball screw ( taking into account stepper maxing out around 1000 rpm ) it means a max z speed of around 5000 mm per minute, so what would one actually need as a minimum z speed to be not limited in functionality !?

[rischoof]

fox, in my building log you can see more pictures from my spindle.
for 3 d, you z has to move quickly. but I don't have experience with that. I can play with my speed just changing the ratio from the belt drive between stepper and ball screw spindle. I didn't mount the stepper directly on the ball screw spindle but with belt drive, I used for my previous one 1:3 (motor small, ball screw large) this because I need some torque to hold my 18 kg in position. I have a gas spring laying around but didn't install it.

[danilom]

If you plan to do 3D work then all 3 axis should move in similar speed or you will lose performance because other 2 axis will slowdown for Z. In 2D cutting there is no such problem and 5m/min Z should be ok.

I used 20mm dia, 10mm pitch ballscrew recently... from Hiwin .. must say its fantastic but the ballnut alone was around 180 eur

[Fox]

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 !?

[danilom]

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.

[Fox]

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 ?

[danilom]

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

[Fox]

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.

[Fox]

Not dead yet - and instead of hijacking Tokamak's thread any longer - 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)...

[Fox]

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



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.



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



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 !!!)



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



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.

[Tokamak]

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.

[Fox]

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 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 )

[rischoof]

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

[KenC]

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.

[Fox]

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

[Fox]

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 )
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)

[KenC]

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.

[KenC]

BTW, my ball screw Z-axis. here

[Fox]

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 ?

[KenC]

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.

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

[KenC]

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.

[Fox]

Now I understand, and I totally agree my z is way-over-the-top-future- proof, but I have my reasons . 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.

[KenC]

More space in the penal is actually a good thing
Honestly, My Z-axis is considered minimalist in comparison 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
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.