New Build - For Your Amusement - MK-2 build

[Karl]

For members amusement some details and images of my newly (today) commissioned MK-2 CNC machine.


Details:

• Primary use: hardwood v-carving and associated 2D cutting.
• Effective working area: 800 x 500mm
• Designed max velocity: 1,800mm/min (typical v-carving 600-800mm/min)
• Removable raised MDF base to accommodate deeper work objects.

Main components:

• 80mm aluminium extrusion gantry (KJN) on 40mm steel frame (local stockist)
• Electrics: 4 Nema 23 motors (X-axis x 2) with 542 drivers and two 42v PSU (Zapp)
• Rail: X- & Y-axis 20mm supported (Zapp); Z-axis 20mm unsupported
• Ballscrew and bearings: 1605 (ebay Linearmotionbearing and smpart)
• MACH3
• {Very large floor mounted E-stop switch (a 'piece of cake' to install)}

To do:

• Fit limit switches
• Install dust extraction - dust shoe design.
• Select and fit water-cooled spindle.
• Modify to MK-2.1 - create larger working area - transfer X-axis components to Y-axis and puchase additional extrusion, supported rail and ballscrew for X-axis. Hopefully a quick win.

*** A gold star awarded for identifying which forum member's design this machine was based on.


And next - steel frame already constructed for MK-3 machine - sized for working 8' x 4' board.

Don't be too harsh - it's a hobby.

Karl

[Jonathan]

Having bought 80mm extrusion, combined with not having a tall gantry you have the potential for a very strong machine.
I notice you have chosen TBR rails over SBR, which is good since they are stronger yet significantly more expensive as you can't get them from China (eBay seller linearmotionbearings2008). Using supported rails on the Z-axis and swapping the rails round such that the rails are mounted to the Z-axis would make the Z-axis significantly stronger since the overhang is reduced.

Minor point as it's probably only temporary anyway - I'd solder the motor wires since if one pulls out of the terminal blocks whilst powered there's a good chance the stepper driver will be broken.

Still, for V-carving you'll be fine.

[Karl]

I notice you have chosen TBR rails over SBR, which is good since they are stronger yet significantly more expensive as you can't get them from China.

Still, for V-carving you'll be fine.

Many thanks. This is where I admit to not knowing the difference between TBR and SBR rail: I just bought some rail. What's the difference?

Karl

[Jonathan]

Many thanks. This is where I admit to not knowing the difference between TBR and SBR rail: I just bought some rail. What's the difference?

The aluminium support for the TBR rails is stronger than on the SBR rail, and the bearing blocks for TBR are bigger and flanged, which spreads the load again making them stronger.

Compare the pictures here:

http://www.zappautomation.co.uk/line...g-c-24_93.html

I would still but the SBR rails from linearmotionbearings2008 on eBay because the price difference means you can afford a much bigger rail which is clearly stronger:

http://www.ebay.co.uk/itm/2-linear-b...#ht_729wt_1087

[JoeHarris]

Looks great, is there any issue with using sbr / tbr rails on their side - particularly on X and Y axis - cantilevering off them rather than bearing straight down?

[Jonathan]

Looks great, is there any issue with using sbr / tbr rails on their side - particularly on X and Y axis - cantilevering off them rather than bearing straight down?

Yes - the load rating of the bearing blocks varies depending on the direction of the applied force. In other words if the force is in the direction attempting to pull the bearing off the rail clearly the deflection will be greater. For that reason it's best to mount them so the rail supports are facing each other. This evens out the deflection, so you effectively have medium deflection all round instead of large deflection when cutting one way and small deflection the other way.