1250 x 1250 cnc router (from scratch)

[JAZZCNC]

Does the length of the gantry pose a problem for general machining and would it be able to handle cutting aluminium? As long as the strength is there will it be ok and will the precision still be to a fairly high standard.

Yes Gantry length will greatly affect the machine but not so much for precision but more the quality of finish from machine. Precison or accurecy is down to combination of components and quality of build.
That doesn't mean you can't have long gantry but it does mean it will have to be very strong and substantial to resist resonance and flex which are the enemy of finish quality.
Take this strength to another level if you want to cut Aluminium and achieve good Finish quality. Really unless your only cutting Thin Alu sheet or Profiles etc that don't need good finish then forget cutting Aluminium on such a wide or long moving gantry machine. Yes it will do it but not very well.!!

The support in the Y direction behind the gantry was to mount the motor in the centre with pulleys to the X ballscrews, so didnt really want to add a support the other end as this was to allow material to be fed in / out but if i can position it in a way that the material can be slid under the support i may add this in.

No need One end support will be fine so long the frame is braced well, my machine has this one end setup and it works fine.

If your into wood can I suggest you have the rails slightly overhang the end of bed. Doing this simple thing will give you some nice options easily achieved.
Namely will allow end machining of boards etc for hinges, locks, Dovetails and oversize or oversize awkward parts by clamping to end of machine.
Also if you want a 4th axis makes it very easy to add one see pics for some idea of what I mean.
It's only a cad mock up so pay no attention to details like gantry has thats actually a design I use the other way round it just saved me some drawing time for showing the person it was intended for. It could be used that way round thou.!!

[D.C.]

Jazz on those piccys you posted doesn't it make more sense to put the 4th axis level slightly lower than the table instead of several inches above the table?

That way you can fit the same diameter stock in there without needing several more inches of z-axis travel.

PS this design looks like it is meant to do almost exactly what I'm designing my machine for (the 4th axis and the ability to fix pieces vertically for doing dovetails etc) Have you actually built one like this and does it work ok?

[JAZZCNC]

Jazz on those piccys you posted doesn't it make more sense to put the 4th axis level slightly lower than the table instead of several inches above the table?

That way you can fit the same diameter stock in there without needing several more inches of z-axis travel.

Not sure how you work that out because putting it lower will mean more Z axis extension required so longer Z travel required.? Also the longer Z extension will increase chance of chatter so keeping it to shortest requirement would be preferable.

But in any case like I said this was just a rough knock up model to give the person some visual idea of what I meant and in reality then it could go any height you like.

Regards actually building the machine then Yes and NO.?? . . . Yes I've built a few where they extend for end clamping option but not built 4th axis option on any yet.
My machine extends like this and have cut many tall or awkward parts using the end for clamping but I don't have the 4th axis bit but it wouldn't be very difficult to throw something together.
To be honest I'd probably use a converted rotary table to give higher resolution or high reduction gearbox.?

[D.C.]

Assuming your z-axis can reach just below the top of the bed for surfacing it for doing flatsheets then that will be the lower limit of your z-axis travel. But for doing fourth axis work the lowest limit you need is the centre of the spindle, any material lower than that gets rotated upwards towards the cutting head.

So if you have the 4th-axis centred on the the z-axis limit of travel, you can cut 6 inch radius stock with 6 inches of z-axis travel. If you move the centre of the 4th axis up 2 inches this means you can only cut 4 inch radius stock with 6 inches of z-axis travel because the 2 inches you have below the centre will never be used for doing 4th axis work but your z-axis still needs to be travel that far to reach the bed when doing flat sheet work on the rest of the table.

Putting the centre at the same height as the bed results in the shortest required z-axis.

In reality you can position the 4th axis centre slightly lower than the top of the bed because your z axis will reach down that low for surfacing the bed and you never ever want to cut all the way through a piece of spinning wood that requires the support of two centres because it will fly off the machine at great speed doing a great deal of damage to any fleshy human type objects in it's path.

[JAZZCNC]

Putting the centre at the same height as the bed results in the shortest required z-axis.

No it doesn't it puts it at the longest Z extension. It will only be shortest when cutting at the outer radius and ever millimetre towards the centre the extension gets longer weaker and therefore the chatter will get worse.
I know what your saying but really it's down to the size of radius you want to cut or the size your most likely to do often. Why would you want the centre 7" away when your mostly turning 2" stock.? You wouldn't set your rest 7" away from centre on a Manual lathe if you where turning 2" stock so why would you in this case.? . . .That would just be creating a weaker machine for the Odd occasion when you want to turn larger diameter.!

The ideal would be an adjustable position and that's what I'd probably do in reality.! . . BUT.!!. . . . Like I said it's only a mock up and if you wanted 6" from the floor then go for it. But this was drawn just to show the principle with simple Leg or spindle turning in mind so that's why it landed there. . . Oh and it's 4.5" away there so thats 9" Diameter which is more than enough for most 4th axis work.!!

[D.C.]

I suppose it depends on exactly what you want out of the machine. If you do more work on sheetstock using the bed than you do turning it would mean having an extra long z-axis for whenever you are doing all your sheetwork.

Unless you need far more clearance on the bed to insert really thick material than you do on the lathe which makes it a moot point.

[JAZZCNC]

I suppose it depends on exactly what you want out of the machine. If you do more work on sheetstock using the bed than you do turning it would mean having an extra long z-axis for whenever you are doing all your sheetwork.

Unless you need far more clearance on the bed to insert really thick material than you do on the lathe which makes it a moot point.

Like I did say several times these drawings where just for showing the principle and general layout. Alex has specific needs, which I knew ence how it's roughly drawn and he will design the specific heights etc around his needs.
Obviously if he or anyone else was just cutting 1" panels then the Gantry and so therefore the Z axis and it's overall extension would be less so yes in this case you would want the 4th axis lower but it's horse for course's and really that's a different machine a "Panel router".

To be honest if I wanted to turn legs etc then I'd use a lathe because building a 4th Axis that can spin fast enough for turning and still give high resolution for good 4th axis detail is very expensive, not hard just expensive. 4th Axis come into there own when you want to engrave or decorate, flute or barly twist etc and it's for this I'd use one and not for the actual turning.!!

[alex wight]

These were the photo's Dean sent to myself, which will serve me very well. I,m looking at doing spindles, table legs ect with the odd 3d items thrown in at some point. I,m keeping it as high as possible, as opposed to as low as possible. The higher you go the less z travel there is which will keep it stronger. What the photo's dont show is that Dean has an adjustable table, which i will have as well. When i,m doing 200mm deep material (engraving fire mantles), the z is going to travel 30-40mm, and the table will be removed. When i come to do thinner materials, i,ll fix the removable table, which will allow the z to travel, again, 30-40mm, which will keep the machine as strong as possible. Once i get a start made to it, i,ll be running things by Dean just to make sure that i,m heading down the correct road, as i only want to build one machine once. I look forward to seeing your progress D.C.

[alex wight]

When I say spindles, it will be wrap around detailing I'd be doing, as opposed to just making normal spindles I knew what I meant lol

[JAZZCNC]

When I say spindles, it will be wrap around detailing I'd be doing, as opposed to just making normal spindles I knew what I meant lol

Ah ah yes I knew what you meant or wanted has well Alex that comment was just for the benefit of others.!