Router/Plasma CNC Build From Down Under

[Boyan Silyavski]

Hi,

IMO you should reconsider some main points:

1. Z axis travel, bed depth ,4rth axis, gantry

-Z 200mm is ok and going more will lead to another problems, which would need reinforcement, that would l lead to more weight and that to servo motors.
I am doing a similar build so 200mm is ok for all, even for plasma, as i intend to do also.

-that singular gantry beam contradicts with the 200mm Z travel. 2 beams, say 100x100x4mm welded together will be better. Vibration wise.

-that removable bed you have drawn is mistake. Either make it proper removable bed like some designs here make it, not with angles but bolted directly side of the beams, or calculate the correct bed depth for 200mm axis and make it fixed. For a fixed bed, depending on design you need more or less 300mm from gantry beam when all mounted.

-4rth axis is no problem with say 300mm deep bed/from gantry beam/. The most ridgid 4rth axis worth for that type of machine, could be made from mini lathe, as i intend to, and it enters in 300mm bed from gantry, or you could make the axis inside the bed if you intend to spin things bigger than 300mm OD


2. Z
you should concentrate on the Z, draw it strong in all directions and all will start from there. Rails on the moving plate, and so on. Then the gantry, then the gantry sides...

3. Now that you have all this clear, you should decide how to move it. If you decide on servos, go back and make it as much strong as its reasonable.

4. Check if in real life the ball screw on the long axis will allow to be mounted like this. Will it pass once all welded.

5. As far as i read 4 inch deep plasma water bed is ok, so that will be removable, no need to be bolted onto anything.


Once you have it clear which way you would go, especially the motors, everything will speed up.

[TonyD]

One consideration I fell fowl of was that I was also constrained on space, so as I order plywood for a project now I need it cut at supply. If I were doing it again and could have made the space I'd have gone for a design that could take a standard 8x4 sheet of wood straight from supply.

[Tinkerer]

Hi Tony, thanks for the feedback. I have grappled with the same issue, but I believe I can source plywood at the smaller lengths here (or get the saw out!). Even if this were not possible, the space availability is an issue, so I will err on the small side for now...perhaps for the next build!

[Tinkerer]

Silyavsksi,

Thanks for your feedback. I've learnt much from your posts (don't know how you keep up with them!). I'll attempt to address each of your points in the order you have raised them.

1. Z axis travel, bed depth ,4th axis, gantry

-Z 200mm is ok and going more will lead to another problems, which would need reinforcement, that would l lead to more weight and that to servo motors.
I am doing a similar build so 200mm is ok for all, even for plasma, as i intend to do also.

The Z travel I have is 220mm, which is a standard length by THK Actuators, so presume you are saying this okay. The THK actuators at this length are very accurate, so I need to concentrate on the gantry to ensure it is robust enough/will not flex. I'm not sure what it will cost me, but I still feel it will be more accurate than what I will construct, with less effort!

-that singular gantry beam contradicts with the 200mm Z travel. 2 beams, say 100x100x4mm welded together will be better. Vibration wise.

I wander if this is over engineering it? My gantry (pictured above) is RHS 250 (height) x 150mm (wide) x 5mm (thick), reinforced partially by two welded 10mm steel plates over carriages for X axis. I have utilised RouterCNC's extremely useful stiffness calculator posted, and using my dimensions and cutting aluminum, came up with deflection of Z = 6.3um and Z - 1.6um, which I find more than acceptable. Using the new Stand-alone Z axis calculator, at the extreme Z Axis extension of 220mm (which I would only use for wood turns), I get a deflection of 4.185um. Unless I am using this tool incorrectly, I would think this accuracy is more than enough for most builds?

Perhaps there is good reason to make it more robust. You mention vibration. Is this a similar consideration to deflection, or something else that needs to be factored?

I've attached the spreadsheet below.

-that removable bed you have drawn is mistake. Either make it proper removable bed like some designs here make it, not with angles but bolted directly side of the beams, or calculate the correct bed depth for 200mm axis and make it fixed. For a fixed bed, depending on design you need more or less 300mm from gantry beam when all mounted.

Thanks. I inserted brackets for greater accuracy so that the removable bed could physically sit on something solid (I am concerned that side bolts will have play and the removable bed would shift considerably when removed and then re-attached (without resting on something solid (i.e. bracket) - bolts move)). I could also bolt the removable shelf to the main frame for greater sturdiness. If there are sturdier and easier designs can you point me in the right direction?

The fixed bed is already there for the maximum Z axis / 4th axis (approx 373mm distance from tool).

-4rth axis is no problem with say 300mm deep bed/from gantry beam/. The most rigid 4rth axis worth for that type of machine, could be made from mini lathe, as i intend to, and it enters in 300mm bed from gantry, or you could make the axis inside the bed if you intend to spin things bigger than 300mm OD

Thanks. I think we have similar designs in mind, but I do need to give more thought on what the 4th axis will be (phase 2 of the build which needs more thought now!). I've discovered your dialogue on your most recent build which I'm absorbing!

Again, many thanks for your interest and input!

[EddyCurrent]

Nice drawings.
I can't compete with silyavski on the frame design but I did notice the spindle is cantilevered well out, have a look at this diagram where it shows the spindle should ideally be inside the footprint of the bearings at each end of the gantry. http://www.cncroutersource.com/do-it...NC-router.html