2nd Generation CNC Mill

NexMill 15 -Part 5

Z-Framing & Controller

This is the sub-table screwed down with heavy end-cap screws...

It's 1/8" Aluminum plate and offers an additional element of rigidity.

It took the better part of a morning to align and measure the tapped holes in the linear bearings and the driving nut. (They are all free-floating in a sense and the metal plate ties them together.)

I pumped the co-ordinates into Corel Draw, printed out a template, punched and drilled off it without incident.

The mill has sat like this for a few weeks...

I'd look at the mill and try to visualize the gantry support framing... But what I saw in my head just didn't appeal to me.

There were 2 (two) recurring themes, one was a box like framing support off of one side with braces to the corners, and the other required the removal of the monitor/keyboard shelf (where the hell are they going to go? - that was a step backward...)

My wife knows that I'm too fucking tight to buy myself tools, even when I really need them, so under the guise of a Valentines present I found myself the proud owner of a miter/chop saw.

It's actually very well constructed, minimal plastic, very nice castings, and a great big angle guide with stops at common angles and a sturdy clamping fixture... I waited a week before procuring a 10 Abrasive disc for metal cutting, well it's broken in now... As I'm babying it on the metal I hope it's not totally whacked for trim work and it's intended purpose (wood work)...

I opted for a slightly less Right Angle structure, but was able to retain the shelf for the monitor & keybrd.

This arm will be bolted to the 1/2" rod support plate, and have a shorter version offset with cross members welded between them,

The square tubing 1/8" walled seems heavy enough with the longest pieces measuring a 17" span.

The parts are held by magnets recovered from defective hard disks.

The magnets have to removed as well as any screws and circuit boards before the Alum framing is melted down.

A completely un-related project required clearing some UV-Proms, after a week under a generic black-light, they weren't cleared...

And after 15 minutes exposure to the flash from an arc welder, they still weren't cleared... I think the only thing that will clear these is a real UV light...

Now you can say with some authority, there is insufficient UV off a welder to clear a UVProm.

The magnets are holding up well and make positioning pieces a lot easier...

But I did notice that they were less than half as strong once I was done welding...

My guess is the heat kills them easily, though they were part of the path for the arc to the steel base I was welding on...

It's not as if there will never be another defective hard disk in the world...

After a bit of grinding they look not bad...

The welds are not pretty, nor do I ever expect that they will be, but the edges of all mating pieces were beveled and every joint has lots of material holding it together.

I did manage to blow a few holes through at spots I dwelled on too long, but nothing that will have any mechanical issues.

The main beam has a slight drop downward, as it's slightly out of true, but I'll use a hydraulic jack to nudge it up a degree or two...

The bracing bracket won't stay at the back, but will be front mounted...

Once it's final position is set, I'll make another template, drill and tap the framing... a last test fit, adjust as required, and use the same template to drill and tap a fixture for welding the 2 pieces in the exact same positioning and orientation, but without hauling the mill out to the welder.

After the final welding is done, more grinding, drill the Z-axis mounting holes, and then paint.

Notice that the actual table is in place over the Sub-table.

This machine has been an exercise in frustration, largely due to how the table movement ended-up.

But the one plus in this orientation is that there are no moving cable harness to wear out, except the AC line to the mill-head.

Another stumbling block that I've finally over-come is the controller that will drive the steppers.

Originally I was going to run heavy Bi-Polar steppers, but the drivers I have would require more time and effort than I have available. The second idea was to switch to a more progressive controller design... There are some fantastic designs available via the Open Source forum at www.cnczone.com and posted at www.pminmo.com ...

I actually spent a couple of weeks comparing designs, parts, benefits etc... The controllers featured above are better, and if your a DIY builder, than they have a solution for you. What I kept coming back to was that I'd never missed a step with the design I used on the first mill, and of all the issues I've had with that mill not one has been related to the controller or it's function.

I cleaned up the PCB layout, fattening runs and removing features I didn't use on the original, like home and limit sensors...

I found a great use for high end glossy magazines... This is a good page as it has no pictures or screened ads just small type text.

The toner is set to dark on the laser and it's just caked on the paper.

It almost looks suspended above the page.

The actual transfer to the blank PCB is even better.

This is miles ahead of the photo-paper that I was actually paying for in the past.

It took 3 tries to get it right, but I anticipated that and printed 4 sets of prints, so one wasn't even used.

All things considered this has to be one of he best boards I've ever etched...

There were a couple of runs that were etched through, but that's my fault as I knew they were there, but forgot to touch them up before the acid bath...

Of all things that I engage in my soldering is one of the few areas where you'd know that this guy really can't see what he's doing...

Though by comparison the ability of welding by feel is working out better than I'd ever imagined, as I could never weld properly when I had full use of my sight.

These blobs will fall under the scrutiny of the Macro Cam before power is applied...

The reason I even considered changing from this design was the availability of the Allegro 5804B IC's... These units are out of production and quickly becoming scarce...

I have to thank Jeff T. in North Dakota, and Dave M. in Alberta for sending me spare chips that they had...

Also I had a pang of anxiety that I'd need spares and will be building another mill after this one is done... So I posted a general inquiry looking to buy allegro's...

I eventually made contact with Dave Rigotti from www.hobbycnc.com. Dave set me up with 10 chips at a very fair price... Sure I paid for them, but this is a guy that makes his living designing, building and selling controllers... So if I was looking for an assembled controller or steppers hobbycnc.com is where I'd stop first...

As this installment draws to a close, I'm still optimistic that this mill will run by March, but definitely toward the end of the month. I'm finding the demands of the Foundry course I'm in are more than I'd anticipated... not unrealistic, but I have to be careful to not drop behind...

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