Timescapes - Digital Timelapse Discussion

CNC Router Build
Page 8 of 12

Author:  edward [ Sat Nov 18, 2017 2:26 pm ]
Post subject:  Re: CNC Router Build

Looks pretty even until the end. It's worth investigating why. Maybe you can shim the rails somehow, or lap the epoxy surface very very gently. Have you tried rotating the glass to see what happens? No scuffs on the metal at all? Absolutely clean?


Author:  edward [ Thu Nov 23, 2017 2:11 pm ]
Post subject:  Re: CNC Router Build

Not as big as D1's, at only 700x900mm. This is what I am building now, in aluminium.




Author:  DISPLACEMENT 1 [ Fri Nov 24, 2017 2:01 pm ]
Post subject:  Re: CNC Router Build

Hi Edward looking good is that a Fusion model or Solidworks . My only word of advice as Kit as already mentioned make sure you have ways of adjusting everything . Now i am at the stage of get everything set up i wish a had built in more ways of gently tweaking things rather relying on banging things and re tightening or using shims and hoping it all works out .
On the driver front for the double ballscrews splitting power to the two motors didnt really work . I assumed their would be sufficient current from the driver i used but maybe not . So i split the step and direction signals to two drivers and that seems fine . All this may have been unnecessary as just one ballscrew just driving one side seemed to work fine bizarrely . Just looks like it wouldnt but the Hiwins are very good bearings and seem to prevent any jamming .

Author:  Kitwn [ Fri Nov 24, 2017 4:30 pm ]
Post subject:  Re: CNC Router Build

I'm surprised you couldn't get enough current for two motors from one drive, especially with the machine not loaded down by cutting anything. How does the rated current of the motors compare to that of the drive? You might need to look at the acceleration rates and speeds you have set in MACH 3 as motors can stall due to resonance effects and all sorts of wierd and wonderful reasons. Is the drive tunable?

On the adjustment front, One of those tramming videos includes using a temporary fitting for providing adjustments to the router alignment with a screw rather than tapping with a hammer. It doesn't all have to be built-in at the design stage.


Author:  edward [ Sat Nov 25, 2017 2:40 am ]
Post subject:  Re: CNC Router Build

D1, the important thing is that you got them going. However, you may have problems with interference once you have the VFD working as well, as some people have reported, but that's correctable.

My router has been designed using Fusion360, and these pics are from its built-in renderer. I haven't used Solidworks for a while now. I find Fusion360 quite annoying at times, for example it is a pain to find Joints and edit them after the event, but it is quite good in other respects.

Re the adjusting/tramming, well, with this kind of design it is not possible to tilt the gantry back and forth, so I am relying on getting it perpendicular through careful machining of the holding brackets. Afterwards I can shim it slightly if needed at the Z box assembly. Possibly with regulating bolts in the Z box, but I think a little shim is all I will need at most. For the left and right angles, that will easily be achieved with the little slack in the bolt holes and a few taps with a plastic mallet.

I am now reorganising the workshop to make room for the new baby:)


Author:  DISPLACEMENT 1 [ Sat Nov 25, 2017 12:30 pm ]
Post subject:  Re: CNC Router Build

Well i have had a frustrating day ! Both ballscrews are running and connected now with separate drivers for each . Maybe their wasn't enough current from a single driver but on paper their should have been . You may have to do some testing on that one Kit .
My big problem is feed rate its just crap ! Never a problem with my old mill as the Rpm of the spindle was so slow i never needed high feed rates .
With the Rpm of 22000 on the new spindle motor i will feed rates to match and i am no ware near . A big oversight on my part you might be right Edward and go for servos rather than steppers .
Best i can get on the bed axis 700 mm/m before it stalls out . I could get 1000mm/m with just one ballscrew but when two are connected up you have to be very careful aligning everything they can easily bined each other . And when they do its like a house of cards falling down one locks up the then other which will prob free the other but your gantry will be well out of line . A total nightmare as it would all have to be reset . A single ball screw is a lot easier optotion .
But as for feed rates i just dont know what i can do now prob need to be in the 2000 to 10000 range and that just isnt going to happen with current set up .
So may have to live with burning out cutters for fun ! :(


Author:  edward [ Sat Nov 25, 2017 1:54 pm ]
Post subject:  Re: CNC Router Build

There is some possible route to take before you despair:)

Build yourself a toroidal power supply outputting 68V. Use drivers that can take up to 80V, such as the AM882 which are dead cheap from China. This will give you a massive increase in revs and torque too.

The AM882 drivers have stall detection that works a treat. You can drive your axis all the way to the end of the line and it will just stall without causing any damage, although limits are still recommended. They are also smooth as hell. You will never look back, I promise.

Building the PSU will cost you around 100 quid. I have one I bought ready-made from Zapp for my mill, but I am going to build one very soon, as Leadshine are not bothering to re-stock it, it's dead easy to build and hardly any soldering.

Also, I don't know why you want to run your spindle at 22000, if you are cutting ali, 8 to 12K is the optimum, and the spindle can handle this lower revs. However, wood is different, with 5mm pitch screws, you need all the stepper speed you can get.

I must say, I am not totally convinced about the two motors myself, particularly on a small router as mine. But I want to try it. Then if it's too much hassle, I will just change the design to a single central servo on one single ballscrew. Your machine is larger though, and it may experience racking when you cut at the ends of the gantry width, though there are cheap ways to minimise and even eliminate racking using some clever tensioned steel rope.

Have you measured the maximum revs you are getting with the current steppers? You are not using crazy amounts microstepping, are you? With the AM882 you can use minimal microstepping and still get beautiful smoothness and of course, more torque.


Author:  DISPLACEMENT 1 [ Sat Nov 25, 2017 2:35 pm ]
Post subject:  Re: CNC Router Build

Hi Edward had my tea and a break which is always good :D .
On return to shed things have improved slightly the long axis i shall call it X as settled down not sure why which is worrying but can get to 3000mm/m . As you say power supply my not be the perfect solution . The other axis are still at 3250 mm/m which may suffice .
Had a look at specs on other stepper based systems and 3000 to 5000 seems to be the range i imagine the higher value is possible using ballscews of a higher pitch then 5 .
This seems quite a nice machine http://stoneycnc.co.uk/axiom-ar-sf-specifications/ might have been easier to buy one of these as they do a 4ft by 2ft one .To late now for that though .
Even at 12k rpm the feed rate as to be quite high especially for timber . Some do quote over 10000 mm/m but it does seem rather speedy !
As for double ballscrews on the X axis if ya can get away with one substantial one i would go that route on a smaller bed and maybe increase the pitch . On mine its not really possible to mount one in the middle of the bed because of the rotary axis . I have built a lot of adjustment into the X axis ballnut mount but even with this amount its still difficult to get everything running free . If you trim the gantry square to the rials this might make the mounting point of the ballnut out of whack and vice versa
[flickr]Image2017-11-25 18.19.03 by D 1, on Flickr[/flickr]
All very annoying
Their may be another issue with two ballscrews on the X axis . If the pitch is 5 and you know the number of steps for a revolution then you should be able to calculate the distance traveled per number of steps . I did and over 100mm it was 3mm out is this down to slight manufacturing difference so the pitch isn't quite 5 and if ya have two ballscrews with slight differences this may cause problems to ?

Author:  edward [ Sat Nov 25, 2017 2:47 pm ]
Post subject:  Re: CNC Router Build

3mm out on a length of 100mm means something is wrong with the stepper/ driver, it's missing steps like mad!

Even using C7 ball screws the difference in pitch errors between screws is infinitesimal, so I think it's either the driver, or maybe the stepper encountering some resistance that makes it lose steps.

I assume you are using 3.1 Nm steppers for your heavy router. I also assume that you are calibrating each stepper separately so that you set the initial settings for the movement by mathematical calculation, but then you actually measure the physical distance and adjust the number of steps accordingly, which may differ slightly from your calculations. Each motor has to be done separately.

So basically if you write g-code to move 100mm, it should move exactly 100mm. If it doesn't, you just adjust the steps in the program so that you end up with a movement of exactly 100mm. I am sure you know that anyway, just checking:)

Author:  edward [ Sat Nov 25, 2017 3:05 pm ]
Post subject:  Re: CNC Router Build

Also, when doing all these checks, make sure that the balnuts are pre-loaded in the right direction of travel, because cheap ballscrews and supports have some backlash. I think you need to drink another cuppa and start afresh, by the sounds of it.

Author:  DISPLACEMENT 1 [ Sat Nov 25, 2017 3:12 pm ]
Post subject:  Re: CNC Router Build

Hi Edward just calculation method amused this would give the correct distance per steps obviously not. So toms job is to set up each ballscrew individually not a prob Mach 3 as a wizardy thing for that . You should give Mach a go it as some very handy functions .
The motor is a 4n dont think we missing steps runs fine within its limitations . I can check this tom with dial gauge to make sure it goes back to right place Wish i had got slightly higher pitch ballscrews though you may want to consider that before you order yours .

Author:  edward [ Sat Nov 25, 2017 3:29 pm ]
Post subject:  Re: CNC Router Build

I have Mach3, but I prefer KMotionCNC.

I deliberately ordered my ballscrews with 5mm pitch as I can get the speeds necessary, particularly if I use servos.

I ordered branded TBI ballscrews made in Taiwan, grade C5, with double ballnuts. And C5 BK supports too. Not taking any chances!

Let us know once you sort it.

Author:  DISPLACEMENT 1 [ Sat Nov 25, 2017 3:42 pm ]
Post subject:  Re: CNC Router Build

Think you going to end up with a very accurate router. I will do battle with my lump tom i was hoping to be cutting out some storage boxes this weekend . Dont think that will be happening :(

Author:  Kitwn [ Sat Nov 25, 2017 6:06 pm ]
Post subject:  Re: CNC Router Build

Don't dispair just yet! Edward is right about an improved power supply. All your current (no pun intended) problems could come down to an inadequate power supply. I don't recall you showing us that side of the build, but many problems in electronic systems come back to the power supply.

If no steps are getting missed then the two motor setup should work fine, plenty of people use it sucessfully.

Do you have a good design for a linear PSU? I'm never sure how much capacitance I really need for a CNC machine supply and it's caps that are the most expensive from the usual suppliers.


Author:  DISPLACEMENT 1 [ Sun Nov 26, 2017 2:47 am ]
Post subject:  Re: CNC Router Build

Good question Kit never built a power supply before so any clues would be helpful.
Just about to enter shed for a day of fiddling joy :(
By way Kit what sort of feed rates are you getting and what sort are you finally aiming for . You see your way of evolving a design rather than jumping in at the deep end may be the better approach .

Author:  edward [ Sun Nov 26, 2017 4:42 am ]
Post subject:  Re: CNC Router Build

Kit and D1,

This is the power supply I am going to build. I will take some photos as I make it and post them, as well as links to the suppliers. This will give 68V ideal for 80V drivers. 68V gives you the leeway for the voltage spikes. I will add a fuse to it.


Toroidal transformer 24V, 24V wired in series, or a 48V, 48V wired in parallel, 625VA:


3x of these capacitors or similar, I've chosen a temperature rating of 105deg, but I think 85deg is fine too, and cheaper:


The rectifier:


Author:  Kitwn [ Sun Nov 26, 2017 5:27 am ]
Post subject:  Re: CNC Router Build

I'm assuming you're current power supply is the standard Chinese switch-mode variety, of which most of us have collected several in our years of constructing camera sliders and other assorted machines. Check what the max voltage rating of your stepper drivers is and use the highest voltage allowed, less a margin for safety. 36 - 48v is very common. Alternatively use the calculation based on the motor inductance given in the Gekodrive guide linked below.
It's the current that does the work, but the higher voltage gives you more torque at higher speeds because the current rises to it's set limit faster during the very short pulse for each step of the motor.

The current rating of the supply must be up to the job and this is where the switch-mode supplies are weakest in that they will not tolerate an overload even for short periods whereas a 'linear' supply of the type Edward is suggesting will tolerate short-lived overloads without a problem. Many are rated by power (watts) rather than max current (amps) but you can get the current by dividing the watts by the volts. There is no problem using a separate supply for each motor driver but don't parallel up the supplies themselves to get more current. Good grounding is essential, read the Geko notes.

For testing purposes, 3 car batteries in series will give you about 40v with effectively unlimited current.
Linear supplies tend to be more expensive, physically larger and less efficient than switch-mode so you takes your choice...

Gekodrive has a page on choosing and using power supplies at http://www.geckodrive.com/support/step- ... asics.html

Re the feeds and speeds:
My speeds are limited by the lack of mechanical rigidity in the structure of the machine. To keep it happy I've been cutting plywood with a 3mm tool at 3mm depth increments using a speed of 500mm/min with the spindle speed higher than it should be, but have used up to 1200mm/min with 2mm cuts. There's a real burning risk at the lower rates but I get too much flexing otherwise.
I don't do proper feeds and speeds calculations at present but should upgrade my methods when I finish upgrading the machine. I think the spindle motor controller has a frequency output so I should be able to make a tachometer for it. Yet another Arduino project!!

Fingers crossed your present problems are mere teething trouble.

Your post popped up while I was typing. That's less painful on capacitance than I was expecting. I must have another look at designing a supply for my upgrade rather than buying yet another Chinese SM unit. I've browsed the site linked below for design parameters but not put pencil to paper as yet. As a young recruit at the BBC Engineering Training Dept I was taught all about choke-input linear supplies which have less ripple and are kinder on the rectifiers, but that was for a lot more power and 35 years ago!


Author:  DISPLACEMENT 1 [ Sun Nov 26, 2017 6:28 am ]
Post subject:  Re: CNC Router Build

Firstly thanks for all the help everybody thats why i like this little forum theirs not a lot of us but the information is always very useful .
I seem to be getting their and its prob a basic mistake i have been making for years now .Will have to go back and re wire things me thinks . The steppers i use are eight wire ones http://cnc4you.co.uk/resources/Stepper% ... %204Nm.pdf
Which give you three wiring options i have always prob mistakenly wired the in series . I assumed you got same torqe for less current according to the specs . I am coming to the conclusion this is not quite as simple as that .
I have now wired the motors up in parallel which use twice as much current for same torque . The result is the motors are a lot stronger much to my relief. I am now getting a max feed of 9378 and this is limited by the max kernel speed of 25khz of my old putter . I could drop the microstepping to maybe push it further but i am already down to 4 times .
[flickr]Image2017-11-26 13.07.43 by D 1, on Flickr[/flickr]
This is what i am up to at mo

Yet again just one ballscrew at mo and you cant stop the gantry by hand . The sudden stop by way is the estop been pulled out . So i will connect the other ballscrew and start re wiring all the motors in parallel prob run out out current then so yes a linear transformer will be next project . So any pics lists etc Edward would be great .
But first i really want to cut out my storage boxes :D

Author:  DISPLACEMENT 1 [ Sun Nov 26, 2017 7:35 am ]
Post subject:  Re: CNC Router Build

My bad forgot to alter steps per unit after altering micro stepping so getting max speed now of 3500mm/m thats with second ballscrew connected and it def takes about 1000m/mm of top speed . You would think it would increase it but not in my world .

Author:  edward [ Sun Nov 26, 2017 8:14 am ]
Post subject:  Re: CNC Router Build

Yes, I connect my steppers in parallel too. I use the 3.1Nm from the same source.

However, looking and listening to the video above, these steppers don't sound too good to me, to be honest. It also sounds like there is resonance. I may be wrong...

Author:  DISPLACEMENT 1 [ Sun Nov 26, 2017 8:47 am ]
Post subject:  Re: CNC Router Build

Think it sounds worse than it is lots of lose things rattling about .
But the big issues is the ballscrew when just using one everything is fine . So i separated the connector from the gantry to ball nut left the bolt in but left a 6mm ish gap on one ball screw .
This is it at right extreme of travel
[flickr] Image2017-11-26 15.43.16 by D 1, on Flickr[/flickr]
notice the gap

this is in the center of travel
[flickr]Image2017-11-26 15.42.43 by D 1, on Flickr[/flickr]
gap closed

and this is the left extreme of travel
[flickr]Image2017-11-26 15.42.14 by D 1, on Flickr[/flickr]
gap opened up again

This is constant to it repeats every time and the ballscrew still driving the gantry is spot on back to zero every time on a dial gauge so no missed steps their .
When both ballscrew are connected to gantry it was the center of travel ware it was likely to lock up .
All very puzzling i think a call to CNC4YOU tom is in order

Author:  edward [ Sun Nov 26, 2017 9:19 am ]
Post subject:  Re: CNC Router Build

If I understand it rightly, the gap should be equal in the mid distance too, i.e. same gap as shown in the extremes. Have you tried this test but this time with the other ballscrew on the opposite side and see if the gap is the same, i.e same gap at both extremes, but closed gap in the mid distance. If it's not the same, that explains why it's jamming a bit around the mid distance.

You could also physically swap ballscrews and try this test with the other ballscrew in place, see what happens re the gaps. C7 grade has some tolerance, but you are showing around 3mm, that's just too much.

Author:  DISPLACEMENT 1 [ Sun Nov 26, 2017 10:59 am ]
Post subject:  Re: CNC Router Build

Hi Edward yes the gap should be constant more or less i know they are only C7 but the tolerance should be i believe +/- .05mm over 300mm.
Dont think swapping over will make any difference basically they are both been turned by the same steps. One could be faulty both could be faulty hard to tell . If both were faulty in the same place then the gap in photo would be constant . But machined pieces dimensions would vary depending ware on the bed they were machined.
Cant think what else is causing the gap to open up .

Author:  edward [ Sun Nov 26, 2017 11:29 am ]
Post subject:  Re: CNC Router Build

Well, I like to eliminate all possibilities and it looks like you haven't tried the other ballscrew.

However, I very much doubt that the screw is faulty, and I think it is more likely that the stepper is missing steps somewhere in the middle. Have you tried a G command to take the gantry just to the mid travel, and is the a gap then? Equally, zeroing in the middle and then sending a G command to take it to the end. Is it possible that the controller takes you from A to B correctly but the average calculation for the middle distance is a little off?

Author:  DISPLACEMENT 1 [ Sun Nov 26, 2017 12:00 pm ]
Post subject:  Re: CNC Router Build

Me Again if it was a missed step issue the gap would not be able to open up and close again in fact as you traveled from left to right it would just get bigger do to missed steps .Dont think theirs a way you can get more steps by missing steps and as i say the ballscrew driving the gantry is spot on no dropped steps after travelling almost full length of bed and back .
I will swap over sides tom and i assume the result will be the same . After looking round interweb daul ballscrews can be a nightmare when they go wrong i means the gantry as to be re squared every time . Some say single motor with belts to both ballscrew or just go for single ballsrew down center of bed which i cant do .
Best test would be place ballscrew side by side and drive them from single motor with no load and see how ball nuts relate to each other as the travel from one end to the other . This would take ages to set up may just go with one ballscrew on one side at this rate .
Ps 4000mm/m seems the safe speed not great but will do
Double ps the controller is controlling both steppers with split step direction signals so even it it was doing odd things this behavior would be shared by both motors

Author:  edward [ Sun Nov 26, 2017 12:13 pm ]
Post subject:  Re: CNC Router Build

Well, by your reasoning, if the ballscrew was off in the middle, then it would carry that error to the end too. If you are absolute sure that the end distance is bang on, then it has to be something with the computation between A and B. If you calibrated your steps per unit using a distance of 100mm, then a G command to the middle of the long axis, say G0X500, should measure exactly 500mm from start.

I would also try the same but moving slowly, using a G1 F xxx command maybe?

It's quite a challenge, but fun at the same time, particularly when you crack it:)

Author:  DISPLACEMENT 1 [ Sun Nov 26, 2017 12:47 pm ]
Post subject:  Re: CNC Router Build

May be fun for you but its giving me headache :( .
If ballscew off in middle it doesn't necessarily have to carry it to the end . Its like winding string round a broom handle you can have the same length of string but ya can wind close or wide apart in different areas and still cover same amount of broom . I think! dont have a broom to hand at mo .
On a totally different subject as my head is spinning. I intend to do a lot of figure work on the rotary axis so have been looking for something nice to machine quickly for tests .
You can buy machining wax but even better you can make your own https://leedshackspace.org.uk/2016/05/0 ... nable-wax/ I have used commercial stuff in the past its usually blue and it does machine very nicely .

Author:  edward [ Sun Nov 26, 2017 2:42 pm ]
Post subject:  Re: CNC Router Build

Interesting, these wax pellets, I'll be trying some 3D milling too, so we will exchange notes no doubt.

I will eat my hat if the ballscrews are off by 3mm. due to a defect in the rolling. Well, I hope it's not the ballscrews. I am sure it's something else, as no doubt you will discover in due course. Good luck with it anyway.

Author:  DISPLACEMENT 1 [ Mon Nov 27, 2017 4:15 am ]
Post subject:  Re: CNC Router Build

Well more measuring. Just doing one ball screw at a time measuring over 140 mm their seems to be a .2mm difference between the two . So if if ya divide the full length of ballscrew 1400 mm by the 140 test length that could lead to a potential 2mm drift .No lost steps running slow and had a dial gauge on both and measurements consistent
Will test another part of ballscrew i think some areas are worse than others or is .2mm acceptable ?

Author:  edward [ Mon Nov 27, 2017 9:20 am ]
Post subject:  Re: CNC Router Build

Hi, that means that you have an error of just over 0.4 on a 300mm length, far too much.

Could you do a video of your measuring procedure, or is it a pain?

Are you definitely preloading the ballnuts and BK holder, i.e, doing all the measures whilst only jogging in one direction of travel ?

BTW, on my milling machine my backlash is between 0.045mm and 0.054mm for each axis, i.e. including the BK bearings, etc. Apparently that's quite reasonable for Chinese screws.

Author:  DISPLACEMENT 1 [ Mon Nov 27, 2017 10:22 am ]
Post subject:  Re: CNC Router Build

Hi Edward think going to have a bit of a break from this as its really working my head . Spoke to people at CNC4YOU today helpful as always, They have never had any probs with the ballscrews and as they are C7 the the +/- 0.05 over 300mm is what they ship at . My over 2mm drift is just not possible at that amount the ballnut would just lock up . I think you suspected this too and i tend to agree . If the issue was less then i think we could blame some manufacturing fault .
So the next cause is the drivers i would be happy with this if everything didn't go back to zero on a dial gauge but it does . So i cant be something as simple as skipped steps .So next time ( when my head as chamed down ) I am going to swap the drivers out for two fresh drivers disconnect all other axis and check the wiring .
Interestingly they did say running at 10 microsteps and 400 steps should be better than calibrating with gauges etc . Just go by the maths route which i suppose make sense .
Any ways going to have a whisky and chill for a bit :D .
Ps if i get tolerances to two decimal places rather than three i will be more than happy

Author:  edward [ Mon Nov 27, 2017 12:25 pm ]
Post subject:  Re: CNC Router Build

Yes, good idea to take a break!

One of the things I mentioned as a possibility is that the A to B computation is correct, and therefore it takes the move accurately to the B point. But I suspect that the average positioning in between could be wrong because you have acceleration and deceleration to bring in the equation. I am not sure how you deal with that with your controller, but with mine, I go for the maximum acceleration possible before stalling.

In reality, you are unlikely to need precision cuts separated by one metre! You cuts are likely to be made in one area at a time, so this is the important bit you need to measure and get as accurate as possible. With higher voltages you can also have higher acceleration so maybe look into building your own PSU. Your router is heavy, so you need the meat to move it. Also, without a linear transformer the back electromotive forces (EMF) when going back on fast deceleration could ruin you PSU/drivers.

Today I ordered all the bits to start making my PSU and I will do it as soon as possible. It cost me a little bit more than I thought because I decided to go for good quality capacitors rated for 105deg and 5000 hours. I think they cost 11 quid each, and you need three.The Toroidal transformer cost £69.90 including VAT and courier, so altogether it's going to cost a good £120, but I think it's worth it.
Good luck anyway.


Author:  DISPLACEMENT 1 [ Tue Nov 28, 2017 12:52 pm ]
Post subject:  Re: CNC Router Build

Well seem to have removed the extreme drift between the two ballscrews on the X axis. Yeah i think !
Changed the drivers out completly CNC4YOU seemed to suggest this was the problem . Their are 16 micro-stepping options a dry joint on the dip switches could possibly select 5 instead of 4 . That seems a good solution but it doesnt really explain why my gap closed up in the middle of the rail then opened up again . Surly if their was a subtle difference in step rate the gap would either open up or close up over the length of the ballscrew . So i dont know i only know its not doing it now .
Theirs still a slight issue with the ballscrews they are 1400mm long .If ya tell Mach to move 140 mm in three different places on the ballscrew (left right middle ) Ya get three differnet readings and i must have done this about 50 times over the last 3 days so results are consistent .
These are the results

Left 139.93mm
Middle 139.81
right 139.64

This is the set up
[flickr]Image2017-11-28 14.40.51 by D 1, on Flickr[/flickr]

I know not the most scientific method and the veriers might not be spot on but all the measurements will be consitently out . Its the difference between the different measurements thats important . So you may get zero backlash and a spot on return to zero but 100mm might be differ in different locations on the ball screw so if ya after precision it might be wise to do test along the length of the ballscrew . I know my ball screws are extremely long and this prob emphasise the issue but if ya have two working together and the discrepancies are at either end then this multiplys the problem on the gantry .
Next problem i have come across because i have had gauges on just about everything the brackets between the gantry and ball nuts is just not up to the job . Gantry is so incredibly rigid but that is all wasted on the connection between it and the ballnut .
[flickr]Image2017-11-25 18.19.03 by D 1, on Flickr[/flickr]
So that up for a re design when i ever get round to ali casting.
Note on feed rates max is know 3750 but when those two steppers fail on your X their goes your gantry alignment . One big nema 34 and steel banded timing belt next time .

Author:  edward [ Tue Nov 28, 2017 1:44 pm ]
Post subject:  Re: CNC Router Build

Well, at least you are getting to understand your machine. Making new sturdy brackets shouldn't be too much work.

In a way, after hearing you woes, I am glad I ordered branded C5 screws. Mind you, my router is much shorter, so maybe even using C7 I would be fine, only time will tell. Still waiting for parts to arrive.

Once you start cutting something maybe these discrepancies won't matter much?

Even if you had used belt and pulleys, you still would've had the problem with two ballscrews not synching. Shame you can't adapt your router to using a single screw in the middle.

Author:  DISPLACEMENT 1 [ Tue Nov 28, 2017 2:49 pm ]
Post subject:  Re: CNC Router Build

Understanding is a understatement and you do get obsessive about measuring things!. For making furniture, boxes etc think the tolerance will be fine perhaps Iam asking to much from a large ish machine to do tolerance stuff to .
A single motor and steel banned belt and pulleys on the end of the ballscrew is the way to go i think . Two steppers just to sensitive accidents happen theirs always a chance of running the tool into the work piece and stalling out the steppers . Then their goes your gantry alignment theirs no chance the steppers will stall exactly in sync with each other . At least with a single motor and belt the motor just stalls and a 25mm wide A5 steel banded synchroflex wont skip a tooth .Only prob i have on that one is the max length steel banned belt i can get is 2000mm not long enough . But this is a future thing i think just want to make my storage boxes at mo . They will be the most expensive storage boxes ever :( .
Going off central ballscrew now with my issue with the brackets that connect ball nuts to the gantry . With the center ballscrew the thing that connects to the two ball nuts would have to be extremely rigid and a lot i have seen dont seem that robust .
Hey Oh

Author:  Kitwn [ Tue Nov 28, 2017 6:53 pm ]
Post subject:  Re: CNC Router Build

I'm beginning to wonder if I should go rack and pinion next time :D


Author:  DISPLACEMENT 1 [ Wed Nov 29, 2017 12:50 am ]
Post subject:  Re: CNC Router Build

I am beggining to wish i had never started .
But i def dont like two steppers I think getting the gantry square is prob the most important calibration and prob the hardest to get spot on . Now i might end up re calibrate every time i have a bump . Not good :(

Author:  Kitwn [ Wed Nov 29, 2017 5:02 am ]
Post subject:  Re: CNC Router Build

I know they concentrate on machines for cutting wood, but the CNC section of www.routerforums.com often mentions commercial manufacturers of machines who almost universally use the two motor approach. Don't forget that if your ballscrews really do have a significantly different pitch along the length, that will mess up the accuracy of any cuts you make regardless of whether you use one or two of these screws for the axis. Such screws are useless in any configuration.

Sorry to sound so negative, but you have to separate problems related to the basic two-motor design and those related to possible errors in the specific ballscrews you have bought.

Fingers crossed it all works out soon.


Author:  edward [ Wed Nov 29, 2017 5:25 am ]
Post subject:  Re: CNC Router Build

Well my TBI ballscrews have been dispatched today, so I will get them soon and we will be able to see if there is a difference, although to be fair we are not comparing apples with apples. Yet, a lot of guys in the CNC forums use twin motors with cheap ballscrews without any problems (that we know of). Maybe they are not so demanding. And you are right, Kit, a lot of the big machines use twin screws. The best machines are rack and pinion with geared motors, I think.

Luckily I will be able to adapt mine to single motor/screw if I need to. I hope not.

Author:  DISPLACEMENT 1 [ Wed Nov 29, 2017 5:54 am ]
Post subject:  Re: CNC Router Build

Slowly getting their i cut a circle today yeah ! only taken me a year something i could do on a bandsaw in a couple of mins.
[flickr] Image2017-11-29 12.58.33 by D 1, on Flickr[/flickr]
Yes a lot of commercial routers have twin motors all i am saying if ya building one and can avoid i would .
On the ballscrew front CNC4 YOU do assure me normal drift on a ballscrew that length should be around 0.07mm which sounds about right . They did point out the quality of ballscrew mounts can be critical and mine arnt great. Another factor is the spring type of flexible coupler iam using they recommend XD couplings which i tend to agree with mine do have a lot of give .
May just neaten everything up now calibrate it and use it till the inevitable crash on the x happens. Also got to sort axis orientation all running opposite to what i am used to.
Might be able to cut my boxes out though :D

My phone does seem to emphasies the noise not that bad in real life

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