Mega V Bed Leveling

[beatle567]

How can I go about levelling the bed on the aluminum mega V XL? There's about a 1mm difference between the front and back.  I've tried placing shims under the corners but that isn't working.  It is the aluminum bed so using a surfacing bit is out of the question.  Has anyone had success with a z-probe to do auto leveling?

[oldtech]

The usual solution is to put a spoil board on top of the bed and then use a surfacing bit on it.

[beatle567]

Wouldn't that defeat the purpose of having the aluminum bed? The purpose being to have the tracks to easily clamp things down?

[oldtech]

Not necessarily. There are two options. One is to make the spoil board a sequence of narrow slats that fit between the aluminum bed slots so that you can use every other t-slot.

The other is to make the spoil board a fixture board. The one I am currently using has m5 threaded inserts arranged in a grid.

[beatle567]

I like that idea. What kind of clamps do you use, and what do you use to fix the spoil board to the t track?

[oldtech]

The spoil board is attached to the t track using counter sunk holes so that the surfacing bit will not hit them. I'm using M5 bolts, but M6 could also work.

To secure work pieces, I'm also using M5 bolts with clamps made from 1/4" 1" aluminum bar with a slot down the middle. I've looked for other options, but the simple clamps are among the lowest profile. I've invested M5 bolts of varying lengths including M5 threaded rods. You can also use double sided tape, or glued single sided tape. If using adhesion, and MDF for the spoil board, it is better to paint the spoil board. That's also the case if you are using cutting fluids so that the MDF will not be as absorbent. And, of course, you could also use other materials for the spoil board.

I've also found that the head of 1/4 carriage bolts will fit into the slots so you could use those as well for a cheaper solution. Carriage bolts have a square shank just under the head that fit in the track slot so that they will lock. And 1/4 carriage bolts are available at you local big box store. Just check your track to make sure they will fit. For the carriage bolts, I have even ground off the sides so that they can be inserted into the track at any location.

I've also found pins useful for aligning work pieces and I made a few MDF pressure clamps for securing work pieces against the pins.

[oldtech]

FYI: Auto levelers are simple in theory but some what complicated to implement. There is a software program called "AutoLeveller that takes a g-code file and adds a probing section to the beginning before the milling operation. When the modified g-code file is run on the CNC Machine, it first probes the surface of ... in a grid pattern and maps the flatness variation ... Then, when running the program, it adjusts the height of the tool bit on the fly so that the actual depth of cut is consistent, regardless of how flat or not it is."

So to be practicable you would need a tool changer with a probe and the ability to integrate with your g code sender.

[beatle567]

I think I'm going to go with your idea of doing the spaced MDF sections (so I can still use the mega v rails) fixed to the plate with generously counter sunk holes and surface it with a 1" bit. I thought the auto levelling function was a "do it once and save the settings" kind of deal. I see why they reserve it for PCB milling.

[maikeru]

Feb 5, 2021 14:22:41 GMT oldtech said:

Not necessarily. There are two options. One is to make the spoil board a sequence of narrow slats that fit between the aluminum bed slots so that you can use every other t-slot.

The other is to make the spoil board a fixture board. The one I am currently using has m5 threaded inserts arranged in a grid.

Hi Oldtech,

I don't suppose you'd be keen to sharing the spoilboard file to the folks here?

[oldtech]

The fixture board is a square of MDF with 5.5 mm loose fit holes for m5 bolts on a 50mm grid. To provide the thread on the back I use a threaded wood inserts for M5 thread. You will also need some counter sunk holes for attaching it to the t-slots.

The size is up to you as well as the grid spacing and the size of the bolts. You do not have to size it to your machine. You could make a small one to see how you like it.

If you are going to being using coolant or mist then I'd recommend using a plastic board or at least painting MDF with a water resistant finish.

If you want to use slots then just size them to fit over one t-slot leaving every other t-slot open.

Note: You may not need a spoil board depending on what you are doing. For example, if you are just cutting out flat material with through cuts then you could just use some scraps for the spoil board and adjust your stock to insure complete cuts.