Hi from Glasgow

[bartdietrich]

Hi all,

I'm a hobbyist based in Glasgow. I know my way around electronics, 3D printers and programming but am new to machining. A couple of years ago I bought a cheap used desktop CNC mill from eBay intending to use it to route/drill printed circuit boards. This seemed like a good idea especially for double-sided boards where layer alignment can be an issue. For two years I haven't done anything with it, usually blaming lack of time and the fact that I'm quite good at aligning layers on double-sided boards for the usual etching techniques. What with the virus going around and me being stuck at home, I don't really have the lack of time excuse anymore so I dug up the mill and decided to give it a go.

It's a cheap Chinese job I think (see photo, I bought it second-hand from someone in the UK so can't be certain but it looks like some I've seen online). I extended the x and y axes by 10 cm so as to be able to do the largest PCBs I would ever normally do. The mill basically works. I'm getting usable results (ok but not amazing): I realise I can't expect too much for £120. It's got a few issues which I'm trying to iron out one at a time as I'm familiarising myself with it. The latest is that the z-axis rods have a bit of play inside their bushings so that as the tool touches the PCB surface and begins pressing down, it slides forward on the copper surface by a tiny distance before penetrating it while the motor carriage repositions itself as much as the play between the z-rods and bushings will allow. I've ordered some Igus bushings: hopefully they'll be a tighter fit and sort that particular problem.

The most annoying issue however is the centring of the tool with the spindle axis. Whenever I change tools I have to fiddle with the two grub screws that attach the chuck to the motor shaft to get the tool aligned with the motor axis again. I have, to some extent, figured out a system to it, but it still involves a lot of loosening one grub screw, moving the tool/chuck a bit, tightening the grub screw, and spinning the chuck by hand to see if the tool is centred. Given enough time, I can get it centred pretty well but it's extremely annoying and time-consuming. Something tells me it shouldn't be like that.

Is there a repeatable and sure-fire way of centring the tool with the motor axis? I think the motor shaft itself is ok: there doesn't seem to be any wobble when I spin it and it doesn't have any sideways play. Have I managed to deform the chuck itself (I did crash the machine a few times)? Or can someone point me to where I can buy a replacement chuck of better quality? I've read about ER11 collets, would this be the way forward here? My mill is quite small (and so is the motor) so any replacement chuck would have to be fairly small as well. The current chuck is about 3 cm long, fits on a 3 mm diameter motor shaft (measured as 2.91 mm) and takes collets for 3.175 mm tools.

Apologies if this is something really obvious or stupid, but it's doing my head in! Any suggestions or pointers would be very welcome!

Thanks,
Bart

[Boyan Silyavski]

You need a spindle ER11 collets as you say.


The play in the Z is either from the ballscrew nut, ends or from the rails and carriages. If the play is in the ball screw nut , you need a new one 0 clearance., pour graphite epoxy in the ball nut or print a 3d ballnut with a tight fit. If its from the ends its the bearings, change the bearings. Check that connection from ball screw to motor.

Machine like that is full of problems and the more you think the more you will want to smash it. But if you analyze the problems you can find the solution easy and dyi the solution from things laying around in garage. It does not have to be pretty

[bartdietrich]

Hi Boyan,

Machine like that is full of problems and the more you think the more you will want to smash it.

Oh YES! You have no idea how much sometimes...

I've replaced the brass bushing on the Z axis with bushings from Igus (igus.co.uk): they seem to be a tighter fit than the ones that came with the mill. This should improve some things.

Off on eBay/Amazon now to find fitting ER11 chucks...

Bart

[Doddy]

Agreed with the ER11 chuck. If you struggle to find a UK supplier then I could throw one in in the post....



...though I had one bad experience of boring one of these for a mate with a similar designed PCB router (the shaft is hardened - I tried heat treating it but with little success) - I'd see this as letting someone else experiment with a solution.

You may find that you have run-out on the spindle motor as well - the biggest problem you're going to face is all the float in the system - from bushes through to the spindle to get the resolution that you need for PCB without smashing end-mills (I prefer the 0.3mm end mills to the v-cutters, but if you look at one of those endmills wrong you'll snap it).

Having wasted the weekend investigating toolchains I'd be interested in hearing what software you're using for this.

EDIT: Having just been over to eBay - plenty in the UK. I'd seriously recommend getting a couple of pillow block bearings and creating your own spindle, driven by belt from the existing spindle motor - then you can manage the runout and end-float easier than inheriting from the motor.

[bartdietrich]

Agreed with the ER11 chuck. If you struggle to find a UK supplier then I could throw one in in the post....

Hi Doddy,

Sorry for the delay, got caught up in the 3D-printing-face-shield-frames-for-health-workers thing and then completely forgot about this forum!

Thanks for the offer but I'm not even sure what that picture is of or how I would go about attaching this bit to my setup. It looks quite long anyway, it might not fit between my spindle and the bed. Here's a picture of the business end of my machine with a ruler for scale. It's quite small:

You may find that you have run-out on the spindle motor as well - the biggest problem you're going to face is all the float in the system - from bushes through to the spindle to get the resolution that you need for PCB without smashing end-mills (I prefer the 0.3mm end mills to the v-cutters, but if you look at one of those endmills wrong you'll snap it).

Run-out on the motor is possible although that is about the only thing on the mill that looks and feels like it might be ok. The motor shaft doesn't feel like it has any play and it looks like it's spinning cleanly. Or at least cleanly enough for what I want to use it for. Although obviously that's very difficult to judge by eye. The problem is that there is no way to attach the chuck to the motor shaft in a repeatable centred way: the two grub screws allow all sorts of tilted orientations because the motor shaft is thinner than the inside of the chuck. Do you know of any chucks with some kind of reliable attachment systems?

Also, you say you prefer 0.3mm end mills to v-cutters. I have what was described on eBay as 30 degree 0.3mm end-mills. Because their tip is a V-shape I thought these were V-cutters?

Having wasted the weekend investigating toolchains I'd be interested in hearing what software you're using for this.

Well, I still use what probably most people who have just got into this use: FlatCAM for creating the G-code from Gerbers or drill files and then Universal G-Code Sender to send it to the mill. They're both free software. Can't tell you whether they're any good or how they compare to other software packages. These are the only ones I've ever used! They seem to work well enough although I'm finding the most recent version of FlatCAM to be quite buggy.

EDIT: Having just been over to eBay - plenty in the UK. I'd seriously recommend getting a couple of pillow block bearings and creating your own spindle, driven by belt from the existing spindle motor - then you can manage the runout and end-float easier than inheriting from the motor.

Do you mean plenty of ER11 chuck/collets on eBay? I'll have a look but the ones I've seen so far are all for bigger machines. As for the building my own belt-driven spindle, I'm not sure that can be done while keeping the whole thing to a reasonable size that will fit on my mini-mill!

Bart

[Voicecoil]

The problem is that there is no way to attach the chuck to the motor shaft in a repeatable centred way: the two grub screws allow all sorts of tilted orientations because the motor shaft is thinner than the inside of the chuck. Do you know of any chucks with some kind of reliable attachment systems?

Bart

From this statement it sounds like the problem is the attachment bit of your chuck - to have any chance of good centering the hole that the motor shaft goes into is going to need to be an extremely snug fit. I've had a wee search and like you not had much success with finding an ER11 chuck with a 3mm shaft entry. I did however come across one or two motors with ER11 chuck fitted that look like they might fit your machine on the Bay of fleas for quite reasonable money (£18....25) - might that be a way to go?

[bartdietrich]

From this statement it sounds like the problem is the attachment bit of your chuck - to have any chance of good centering the hole that the motor shaft goes into is going to need to be an extremely snug fit. I've had a wee search and like you not had much success with finding an ER11 chuck with a 3mm shaft entry. I did however come across one or two motors with ER11 chuck fitted that look like they might fit your machine on the Bay of fleas for quite reasonable money (£18....25) - might that be a way to go?

Indeed, I don't think my current chuck is worth me spending any more time on trying to fix it. What keywords did you use for the eBay search? Can you post a link to one of the results you found? The ones I've seen all seem too big. I need a motor of 29 mm diameter and the mounting holes need to be 22 mm apart. Since I don't have the capability to machine my own motor holder I am pretty much stuck with the hardware that came with the mill. I'm toying with the idea of getting a Ooznest WorkBee milling machine. I could use that to make a motor holder for a different size motor for the PCB mill (not just for that, it would complement what I can do with the 3D printer and would come in handy for work too), but that's just a vague plan for sometime in the future. So for the moment I'm stuck with that size of motor for the PCB mill. Speaking of which, any opinions on the WorkBee?

Bart

[Doddy]

Indeed, I don't think my current chuck is worth me spending any more time on trying to fix it. What keywords did you use for the eBay search? Can you post a link to one of the results you found? The ones I've seen all seem too big. I need a motor of 29 mm diameter and the mounting holes need to be 22 mm apart. Since I don't have the capability to machine my own motor holder I am pretty much stuck with the hardware that came with the mill. I'm toying with the idea of getting a Ooznest WorkBee milling machine. I could use that to make a motor holder for a different size motor for the PCB mill (not just for that, it would complement what I can do with the 3D printer and would come in handy for work too), but that's just a vague plan for sometime in the future. So for the moment I'm stuck with that size of motor for the PCB mill. Speaking of which, any opinions on the WorkBee?

Bart

If only you could find a forum where people had such machines that could cut something for a different sized motors :(

Don't let the diameter unnecessarily constrain you. I would offer some assistance but I've... erm... had a bit of an accident with my mill and am waiting a delivery from China. Just don't throw a lot of money at that machine.

[Doddy]

Understood - that image was of a ER11 collet on a 150mm spindle - useful for home-builds but I've since realised that you can easily buy similar with a much more usable clamp onto the spindle motor that you have. Pretend I didn't say anything on that side.

You're right about the V-Cutters, but the one I prefer is a 0.3mm diameter straight mill - so the cutter is about 2mm long before that bells out into a more conventional 1/8" shank - if you tried one of these with any runout the cutter would snap pretty quickly. V-Cutters are okay but they suffer if you have a warped PCB substrate. Isolation routing is not the easiest thing to get right, particularly if on a weak machine. You've got some fun ahead :)

[bartdietrich]

You're right about the V-Cutters, but the one I prefer is a 0.3mm diameter straight mill - so the cutter is about 2mm long before that bells out into a more conventional 1/8" shank - if you tried one of these with any runout the cutter would snap pretty quickly. V-Cutters are okay but they suffer if you have a warped PCB substrate. Isolation routing is not the easiest thing to get right, particularly if on a weak machine. You've got some fun ahead :)

If by straight mill you mean what I know as end mill then 0.3 mm is crazy thin! How does that stay in one piece for any time at all!

I've actually made a simple one-sided PCB the other day. Actually over a week ago, before I even started this thread. Incidentally, it was for a optocoupler interface for the axis limit switches for the mill. The PCB came out ok (but not great) but after soldering I found that the solder would bridge neighbouring pads extremely easily. And it did it in such a subtle way that the bridges were very hard to find even under a microscope. In the end I binned the PCB and am thinking of just etching it instead. I'm not exactly new to soldering so my soldering technique is not the issue. Is this a common property of routed PCBs? In retrospect, maybe I should have deburred it before soldering...

Bart