Time for mk2 upgrade!

[routercnc]

Hi all,

The time has come to retire mk1 cnc router and build a better one! Mk1 used mainly wood for the frame and gantry, and had too much flex. Photo of mk1 attached, which is now dismantled.

Attached is a render of the mk2 machine. Spec is as follows:
system3 all in one board
33v power supply
3Nm steppers on X and Y
1.8Nm stepper on Z
ball screws all axes, dia 16mm with 5mm pitch
X axis ball bearings running on base frame, with adjustable side preload
Y axis rail and carraige (20mm)
Z axis rail and carraige (15mm)
1.5Kw water cooled spindle motor (Chinese)
1.5Kw VFD from Moeller

Photos show the mk2 progress on the base frame, gantry, and Z axis. Tomorrow the ball screws are being machined to fit into angular contact bearings
The aluminium side pieces need to be replaced with longer ones because during the build I decided to move the side rails out to make the gantry bearing system work better. Another job to do !

Photo of my spindle and VFD unit, to replace noisy router, including mains filter and 200W braking resistor. I intend to use a ThermalTake 850i water cooling unit (for PC CPUs), as I've seen this used elsewhere for this application.

[routercnc]

Bit more progress. The render, which I forgot to attach last time(!), shows the design I've settled on for mk2. I've decided to completely seperate the power signals from the data signals, using seperate energy chains running under the bedplate. Power will go up one side of the gantry, and signals up the other.

The render shows large energy chain, but I've actually source a much smaller version to allow me to add support under the cutting bed (which is a bit open at the moment).

The ballscrew ends have all been machined (Arc Euro website has a link to this machinist based in Long Eaton, just outside Derby). They fit into the angular contact bearing blocks perfectly, however, one of the 12x1mm nuts (which I bought off ebay from China) was not tapped straight and binds. Anyone know where I can buy quality nuts in the UK? They are square with chamfer edges containing grub screws.

I changed direction on the way the gantry mounts to the baseframe, and am running bearings on the top and underside, with bearings on preloading plates in the lateral direction to hug the baseframe. Glides well when pushed by hand, and now that the ballscrew is attached I can feel that it is unlikely to rack when cutting thin play, liteply, and balsa.

Mounting bracket for the spindle is complete and looks like it will work well (not shown).

Still lots of small jobs to do like the stepper mounts, the Z axis ballscrew lower bearing plate etc. Plus, as mentioned elsewhere on the forum, new bathroom fever has struck this house too! More when I have it . . .

[routercnc]

Brief update on progress, with more photos ....

Ballscrews machined and fitted. Spindle bracket complete and fitted. Stepper mounts complete and fitted. Energy chain support rails still to do, plus end pieces of baseframe, limit switches, and base plate to fit. Also water cooling system to buy and install.

Jogged the axes around yesterday and all move well

May upgrade gantry sides to aluminium, but I'm mainly cutting balsa and lightply so we'll see how it goes.

Already thinking about version3 :exclaim:

[GeorgeD]

Do you get any gantry side shake with using a roller bearing slide like that?

I was told that the lower the gantry the less side movement and a more precise cut using the linear rail system.

[routercnc]

Hi George,

I've not finished it yet so not cut anything, but . . .

If you mean translating sideways, then none at all. What I've tried to photograph (but it's not eay to see) if that there are a pair of roller balls in plates on the side of the gantry legs, which run against the side wall of the aluminium extrusion. These are the types used to support big sheets of wood or steel and provide a friction free rolling surface, or they are used to push cargo boxes onto planes. On one side they are fixed rigidly to the leg, and one the other side they are pre-loaded by means of two bolts so that the base frame is hugged by the legs. Does this make sense?

If you mean flexing, then even though the sides are 2 x 18mm ply, I can flex them by pushing quite hard. But given that I'm cutting liteply and balsa, I think this will be OK. I've done some calculations to show that if you want to reduce the sideways flexing (due to gantry legs bending), without upgrading or changing anything else, you can significantly reduce it by simply lowering the ballscrew in Z. If you put it down at the same level as the cutting tool, there is no bending load on the gantry sides at all, only translation loads which are reacted by the side bearings. I've got it all on a spreadsheet which I may post when I'm happy with it.

As you can see on my current design, with the ballscrew right at the top, I worked this out after much of the construction was done! Next time though . . .

Lowering the gantry height would help, but I want the clearance to the workpiece if I want to do other jobs.

If you can afford it profile linear rail is about the best there is I believe. Next best is probably supported rail, and way down is running bearings onto the ali section. But it is a big step up from the unsupported 1200mm rail that I had before, so making progress.

[GeorgeD]

How much did you pay for the Ally extrusions supporting the Y axis,if you don't mind me asking and where?

I'm making my own foundry to melt and cast ally parts for the CNC build.

Cheers.

[irving2008]

George,

You need to start a build log of your own... two actually - one on the CNC machine and one on the foundry (also on my list of things to try out when I get the time)

[GeorgeD]

Irving,been watching youtube vids on melting and casting Ally,very instuctional.

The best homemade foundry or melting pot is the Propane bottles,take the tap off and cut the lid off,line it with fire cement,dig a hole in the side for an air to propane torch and the melting is in no time..

Gotta find a round steel or cast iron tube for the crucible though.

Put "casting aluminium in sand" without the quotes in google and the youtube will come up.

[AdCNC]

Speaking of foundry.. heres a link you might find usefull http://metalcast.boorman.us/index.html

[GeorgeD]

Nice one AdCNC. :clap: got about 5 kilo's upto now.

I'm told the best ally to melt and cast is the type thats already been casted before.

Cheers