Vertical CNC Mill: X-axis work table

[mm_cristi]

This is my first post on CNCZone, alltough I am a member since I don't even know when. I was just reading and watching with interest what others have built until now. I started aquiring parts for a vertical CNC mill, and hopefully my dream of building my very own performance CNC mill will become true. But I need help for this. I am planning to build something simmilar to what this guy built:
http://www.5bears.com/cnc.htm
But sure, if I manage to make something at the fraction of the quality of that machine I would be very happy. And I will use steppers instead of servos, my budget like maybe yours is very limmited.

I want the machine to be able to cut aluminum with ease, and possible other metals as well, nothing fancy tough, no steel and stuff like that. I want to be able to use the machine to also build parts of other machines, like a future CNC router. When I start putting parts together I want to post pictures as well.

Today I was thinking of what I will use for the table. So first question:
Is it ok to make the table out of a piece of aluminum profile?
I have seen that usually a cast iron T-sloted table is used, but I currently have no idea where I could easily acquire one.

The profile I am talking about is an 160x16 extrusion like the one found here:

http://catalog.item.info/Onlinekatal...00021847/26590



Any help would be greatly appreciated.

[mm_cristi]

I've started building my second CNC machine about a year ago. Here are the pictures with the first parts i've got:



Used linear guides from ebay for the Z axis:



My silly atempts at squaring the ends of the big Z axis Al profile:


I think I've learned a lot since then from my mistakes, anyway here's a picture of a temporary assembly to get a feeling of how rigid and square I can get it to be:


The biggest problem is that I don't have the proper tools for the job. And since there aren't many machining enthusiasts where I live that I could ask for help from, I try to improvise as much as I can, my little toy milling machine isn't up for this job unfortunately:


Another shot from the back:


I haven't worked on this project much in the last half a year or so, since I was busy with a software project. I am a programmer, machining is just something I like to do and learn in my spare time. But since I don't have the proper tools I realised that maybe it is better to start with something else. So crazy as it may sound I started building a very simple CNC Lathe. Currently I just have a used mini mill X2 xy table with some missing parts. So I am trying to build the missing parts and attach two stepper motors to it and use it as a tool holder/changer. I might be going in the wrong direction, but I don't have to many options currently. I hope to be able to post some pictures with what I'm trying to do next, I've got into some trouble and ruined one of my leadscrews. That's how you learn that hammering a leadscrew is bad.

I mentioned at the beggining of the post that this is my second CNC machine because the first attempt was part of my college diploma thesis. Back then I had even less tools at my disposal, and sure less money to waste on such ambitios projects. Here are a few pictures with that improvisation:















I've also written a dedicated control/simulation path editing software for it, this was actually more rewarding then building the machine:


I know it doesn't look like much, didn't have experience, didn't have knowledge, the right materieals nor the proper tools, I know it is a piece of junk, but I learned a lot doing it.

Hope to read some comments from you more experienced people out there since as you can see I am nothing more then an amateur, but everyone's got to start from somewhere.

[mm_cristi]

You know that when you build a machine the feeling of enjoyment is something that is very hard to explain, but for sure you felt it when you built something interesting that actually works. This is the feeling I've got in the last couple of days since I managed to build my first CNC and actually create some small parts out of steel, which for me is totally amasing. You can watch some short youtube videos about it here: http://www.youtube.com/watch?v=7BpFNcWLOxE]Homemade CNC first cuts - YouTube
http://www.youtube.com/watch?v=Pst_Rhc1J1I]First CNC part - YouTube

You can find some technical details about this build in the description of the video. I think I learned a lot from this and the cool thing is I can make parts. At the moment only the X-Y axis are motor driven. Plan is to build with this machine the parts for the third axis.

Hope you like it.

[mm_cristi]

I've started working on a simple vise for my CNC. You can see some of the progress in this video:
http://www.youtube.com/watch?v=caB9PJJGmFc&feature=plcp]Homemade milling machine vise - YouTube

[TechGuy5002]

Today I was thinking of what I will use for the table. So first question:
Is it ok to make the table out of a piece of aluminum profile?
I have seen that usually a cast iron T-sloted table is used, but I currently have no idea where I could easily acquire one.

Yes you can build a table out of aluminum, but you can also build it out of steel. Instead of milling out T-slots its possible to use a couple pieces of flat bar stacked to form the T-slot. The flat bar pieces will have diffrent widths so that the top piece is wider than the bottom peice. You can bolt the two pieces together and either bolt them to a plate or to a frame. This might be more practical than cutting a t-slot if you don't have access to a milling machine to cut out the t-slot with a t-slot cutter. I suppose you could get a solid piece of alum. and use the machine your building itself to cut out the t-slots. But that might be a bit tricky since it will be the first piece you will need to machine, and its likely that you might have a technical issue (perhaps with the CAM software, g-code of your program, etc). I would recommend cutting the table out of wood first to make sure your setup works correctly before cutting out of alum. You probably would need to use laminated peices of wood (ie 2x4's) since I expect plywood will not machine well for a t-slot profile.

For small machines, you might be able to order replacement (cast iron) tables from grizzly or little machine shop that sell replacement parts for the small milling machines they sell. Although you have to design your x-y movement for the table since the table mounts may differ than your design. The cast iron table will have pre-existing mounting points.

[mm_cristi]

Thank you for the tips and for posting on my thread, I've been waiting a long time for someone to notice it

Anyway, I have to appologise, because as you can see this thread has become a little of a mess, since I posted info from different projects from different time frames.

I should explain maybe a little. The current thing I'm working on is a CNC conversion/build using some parts of the chinese mini mill, with some other scrap parts I found. The initial post was a while ago, when I didn't have the mini mill parts yet, but badly wanted to build a CNC machine and ordered some structural aluminum parts and linear ways and ballscrews from ebay. I wouldn't go that way if I were to start again. It was a bad decision to start with, because I didn't have enough knowledge. More importantly I didn't have the proper tools to make my parts. It is obvios that one needs a good milling machine to make a CNC machine. If I were to invest again I would directly buy something like the mini mill that you can find on littlemachineshop or other places and convert it to CNC. So it makes not much sense to talk about the T-slot table too much, because I already have one now, but it's just mounted on this mini mill monster. I want to use it to make the parts to improve itself and to make the parts for another machine that will use ballscrews and linear ball bearings for motion and aluminum for structure.

Meanwhile I'm working on building up tools and knowledge using this intermediary project. At the moment I am trying to make a vise as you can see in the previous post. And actually I am not sure if I went the right way here either. Not sure if the friction force between the jaws and the table will be enough to keep the jaws from pushing eacheother away from the piece. We'll see... I'm just happy for the moment that this improvised machine can cut steel well enough to make my vise and t-nuts.

[aarggh]

Thank you for the tips and for posting on my thread, I've been waiting a long time for someone to notice it

Don't worry, usually many, many people watch the thread, but not always will you get a comment.
Good luck with this build! Looking forward to seeing your progress.

cheers,
Ian

[mm_cristi]

Hi guys,
just a short update, I made another youtube video with the progress on my homemade CNC and the vise I've been working on, and the 3D printer project I'm trying to make parts for, check it out if you have time:

http://www.youtube.com/watch?v=uPQZNsSnp_I]Finished homemade vise and first parts - YouTube

I had some problems with the speed controller of the spindle motor. Maybe someone can give me some hints what is going on. I tried to find the cause of the electric shocks I happened to get sometimes. I tought it's becuase I don't have proper grounding. I have the machine on a flat balcony. When I touched the machine and the window frame I got a pritty bad shock. I was ok, but I decided I have to do something about that, it happened a few times before but much gentler. So while trying to figure out why I have about 100 volts between the machine and the window frame, I managed to shortcircuit my homemade controller. I am not an expert in electronics and electrical stuff, but I have basic knowledge, I studyied computer science, so we had a lot of courses on electricity and electronics. But this is beyond me. I could even light up a bulb by touching the machine and the window frame. That was scarry. Anyway, I couldn't measure any direct short circuit between the power lines and the grounding wire. The grounding wire from the motor was connected to the body of the machine and to the metal controller box. I have a rectified 220V~ from the mains with diodes, and controlled with two POWER MOSFETS trough PWM, the signal to the MOSFETS is controlled by a microcontroller separated with optocouplers, so the logical circuit has always been safe and protected, and I didn't have any trouble with that even when the main power line were shorted by accident and the rectifier didodes were busted. The PWM signal is about 20KHz, and this is where my knowledge somehow is at a dead end. Do you think that it's possible I have inductance in the grounding wire which runs along the pulsed power signals to the motor I am just thinking, 300 Volts (220 rectified) pulsed at 20KHz, I don't know I don't have yet another explanation. What do you guys think ?

Strangely enough the voltage appeared only when I connected the ground of the motor to the ground of the incoming 220V~ mains line. I also had some other stuff connected to that line like two computers. I know it was bad , I am changing all that. Meanwhile I prepared by drilling some holes trough walls to have a grounded power line to the balcony. That is almost complete. But even that is not perfect yet, I did a small mistake and connected directly the copper wires to the aluminum wires in the wall socket I modified, and I have to change that someday soon I guess because of oxidation problems, atm it's fine to at least start fixing my controller box, this time I'll try to isolate better the circuit from the box.

[aarggh]

Strangely enough the voltage appeared only when I connected the ground of the motor to the ground of the incoming 220V~ mains line. I also had some other stuff connected to that line like two computers. I know it was bad , I am changing all that. Meanwhile I prepared by drilling some holes trough walls to have a grounded power line to the balcony. That is almost complete. But even that is not perfect yet, I did a small mistake and connected directly the copper wires to the aluminum wires in the wall socket I modified, and I have to change that someday soon I guess because of oxidation problems, atm it's fine to at least start fixing my controller box, this time I'll try to isolate better the circuit from the box.

This is extremely dangerous and could kill!! I can't stress that enough.

It sounds to me as though you have a crossed Active/Neutral. Normally in most countries one of the lines is tied to earth, in OZ it's the Neutral, and the Live is switched, so that if there was a short it goes to ground to minimise risk of electrocution.

If Neutral is tied to earth, but you have a socket on equipment that has the active/Neutral wires crossed, at one end you are tying Active to ground, and at the other end you are tying Nuetral, so if you touch the machine, you are touching Live tied to earth.

The other possibility, is you have a broken, faulty, or dry earth connection at the end of the electrical circuit your plugging the machine into, and the earth is "floating" more or less. Electricity will take the path of least resistance, your machines frame being one. Check your wiring and sockets, and even your mains outlets to ensure the colours match up.

cheers,
Ian

[erikjgreen]

It also sounds like you're rectifying mains AC to DC for power and not using an isolation transformer. Are you using a transformer to isolate from the mains?

I wouldn't try to do anything with the machine but work on this problem until it's fixed. It could kill you.

Erik

[mm_cristi]

Hi guys,
I understand the seriousness of the problem and will not use it again until I make sure it's safe. I somehow took this lightly and risked too much. I'm happy to be alive.

Anyway, the circuit is now partially busted, and I need to fix it. I started working on reconfiguring but won't be a quick fix as I wanna make it right this time.

Yes, I am rectifying directly from the mains without an isolation transformer. I remember reading about such a separator transformer some time ago but didn't understand completely the reason behind it. I have to find that thread again. Anyway, I inspired from the schematic of the original chinese spindle motor controller for the chinese X2 mini mills. Check out this link: Motor Controller Repair
There are parts of that schematic which I didn't understand so I just took the principle and made a much simpler board.

I just read some things about isolation transformers a few minutes ago

Benefits
Equipment connected to an isolation transformer is protected from electrical noise in the power lines. Also, noise produced by motors, switches, and other industrial equipment is prevented from propagating back into the power system. Technicians repairing electronic equipment first connect it to an isolation transformer to prevent shocks caused by faulty grounding. Audio isolation transformers prevent hum from sneaking into sound mixes, and protect people using microphones against shock hazards.

from

What is an Isolation Transformer? | eHow.com

And yes, I also had an ungrounded mains connection. I already took care of that after the incident and now I have a grounded socket in my "lab". But as far as I understood from my brother, there is actually not much difference between the neutral and the grounding except that you know exactly which one is the neutral (ground) since it's a separate connection, and that it normally never interrupts (it doesn't have a safety fuse). So this also raises the question, was it really the missing
grounding ? If I assume I had grounding, most likely the fuse would have blown off, since when I made a connection between the window frame in question to the drive box, there was a big spark, and a part of the drive was busted.

So I still am not sure where the problem was, probably some questionable isolation. I have to put it back together to start testing again. I'll try not to kill myself !

[erikjgreen]

You use an isolation transformer for the reasons you mention, but the number one most important reason is to keep any part of your equipment from being tied to the mains voltage potential with reference to any metal object near it, like a window frame, or the rest of the world. With the transformer, your circuit can be at 220v potential but only with reference to the other transformer lead.

Remember that your house electrical system is probably grounded to water pipes, a stake in the ground, etc. Without isolation, that means if you touch the AC mains hot wire then another part of you touches anything else conductive with a path to that ground, a circuit is formed that can carry full mains voltage and amperage.

This isn't as big a problem if you have the wires in the plug correctly connected to your circuit, but if you have the wires switched...

If you took electronics courses but don't understand the need for an isolation transformer when using mains power and also the difference between the wires in the mains plug (hot/neutral/ground), I suggest you get your books back out and do some research before you proceed with your project. Really, it's not a trivial or esoteric thing to know, it's basic to working safely, and not knowing that is a dead giveaway that you don't know enough to safely do what you're working on.

All things considered, blowing up part of your power supply is the best thing that could have happened to you... the worst would probably be accidentally killing a family member with electricity.

Good luck,
Erik