1220 × 2440 build

[HullMark]

If you was building a plasma machine I'd say that's perfect. But if you want a serious router then it needs lot more work.

The Bottom Pic looks very much like Merchant Dice machine and just ask anyone about how well MD machine performs..

Your gantry design is week and far too weedy for decent router this size.

What would you recommend instead Dean? I keep thinking about the logistics of it, I don't have a forklift at home haha

http://www.ukcnc.info/forums/showthr...-November-2014

I was impressed by this one but haven't (can't) work out how much it'd cost.

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[Clive S]

The Bottom Pic looks very much like Merchant Dice machine and just ask anyone about how well MD machine performs..

Funny that I have to go and sort a MD machine on Monday. I actually think the MD machine is better

[JAZZCNC]

the guy jazzcnc sent a link to an American site that looked good, they have a preassembled part that I really like the look of

https://www.aliexpress.com/item/CNC-...6ab831b0ZkP59s

Wouldn't buy that either.? Those ball screw bearing blocks are not designed for this purpose and will almost certainly have some end float.
Also the price is ridiculous. You can buy all the bits and build your own better for lot less.

[JAZZCNC]

What would you recommend instead Dean? I keep thinking about the logistics of it, I don't have a forklift at home haha

Well all can say is build it stronger or should say Stiffer. If your limited with logistics then build it sections so can be easily moved. It will add another level of complexity because still need to maintain accuracy which is harder to do with more pieces.
Going to say this again because cannot stress enough. Your Gantry design is WEAK and if you build this it will show in the quality of finish.

The Gantry and Z axis are key areas. Malcolm as already mentioned to his pain that Z axis is key area and soon shows any weakness in the cut.
I don't agree that is Gantry is over built and changing to lighter Section profile wouldn't give any better performance really and could potentially cause other issues with resonance when cutting deep or hard materials.
Better having strong gantry that is little heavier than light gantry that will flex when cutting hard. If higher feeds are required then better to size the screws or motors to suit rather than under build.

Under building because of Logistics or weight is just going to compromise the machine performance. Better to think smarter and design around any restrictions.

[malcolm01]

I recon my gantry weighs at least 100kg, surely reducing that alittle with a lighter profile aluminium wouldn't hurt??

[JAZZCNC]

I recon my gantry weighs at least 100kg, surely reducing that alittle with a lighter profile aluminium wouldn't hurt??

Ok I guess your main profile is 160x40 and top/bottom profile 80x40.? The weight difference between HD and light for 160x40 is 3Kg per meter and 2.5kg perM on 80x40.
So lets say gantry is 1500mm wide so in total your only saving approx 12kg and this won't make a huge difference in performance. The extra strength it provides will be more beneficial when cuttng hard than the any slight speed it may gain.

[HullMark]

Hi Mark,

Ok first off let me say straight away that Clive is correct with 3K you cannot build the machine you describe or one that is any good.

When you get into 8x4 or above the game changes in lots of respects and cost is one of them.

Now regards your idea of farming out the welding to engineering firm then be careful because I've seen this done many times and fail.?
The problem comes from the fact most welding firms will weld the frame up as thou it's just workbench and CNC frame requires more careful approach.
They won't take the time or care to spread the welding so as to keep distortion to minimum. They also won't constantly monitor any twisting that might occur from the heat. And most certainly won't take the time to make sure the Rails surfaces are on the same plane.
Any distortion or twist will have to be dealt with later otherwise it will affect how the machine performs. So anything that can be done to lower this the better and this takes time and most welders haven't got the time to wait for welds cooling etc so will just weld it up in one go which will cause you issues down the line.

The rail surfaces must be on the same plane and will need careful attention when welding or they will cause you lot more work. Even then if carefully done your still going to have either Epoxy level or have the surfaces machined flat.
Don't be fooled into thinking Box section is flat because I've yet to see one that is and certainly not one nearly 3mtr long.!

Now regards Gantry and 10mm plate in L shape layout then forget it.! That's just not going to be strong enough for gantry that will be 1600mm wide.
To give some idea the last 8x4 I built which you'll see in pics uses 120x80 HD Aluminium Profile arranged in L shape and I consider that a Minimum for a machine this size.
It's not just the weight it's carrying but got to also think about resonance/vibrations that will occur from the cutting. Resonance will give poor finish, cause excess tool wear and shorten component life.

Next comes linear motion. If your wanting Ballscrews then you really need to know what you're doing and what to buy because when you get past 1500mm things get wobbly real quick.
First, you have the obvious thing to deal with which is screw Whip from the long length. But you also have to think about alignment because long screws are merciless when comes to alignment. The slightest misalignment and they'll turn into gyrating skipping rope which will cripple the machine performance.
Getting this right is a careful balance of selecting the correct ballscrew with regards pitch and diameter along with correct tensioning and alignment. Get anyone one wrong and your in for world of pain.

This why Rotating ballnuts are often used for long lengths but this gets expensive and complicated unless you can make them your self.
Rack & pinion is the common solution for machine this length but again this brings with it's own challenges and problems/costs.

Coupled with all these solutions comes correct selection Motors/drives etc and is one of the reasons why you cannot build a machine this size for £3k.
Long, large diameter screws require bigger motors which along with high power drives get expensive quickly.
Ballscrew or R&P there is no difference really here because R&P is less efficient so still requires large motors to compensate. You also then have more backlash to deal with from R&P. Also R&P will require gearing to give you the Torque and resolution required which adds another layer of costs/complexitys.

I Strongly advise you to think long and hard before you take this project one with No experience because it's very very easy to get it wrong and all the research in the world won't prepare you for just how much more of challenge it is building an 8x4 than say 4x4.
The extra length really does change things that much and the slightest errors get magnified.

But one thing I can 200% tell you is that cannot be done properly or legally for £3k.!!

Here's two for you one with R&P and other with Ballscrews and mounted vertical.!

Attachment 23837Attachment 23838Attachment 23839

What dimensions are those gantrys Dean?

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[Boyan Silyavski]

When all is short , it looks very sturdy. In 3m length even the 100x100 box section feels like makaroni. If steel, i would say gantry will have to be minimum 100x200x3 beam at the very least. So for aluminum i dont know what Dean uses, but i think 2x 90x180 in L configuration will do the job.

If you want as cheap as possible you have to do all from steel. There is no escaping that. The bigger the steel you use, the simpler the structure will be. 100x100 will need no diagonal bracing, if done right. If you get your hands to 100x200x4 or thicker, that will simplify greatly the whole build. 100x100 is the maximum a Rage saw can cut, hence the maximum you could cut at home.

[JAZZCNC]

What dimensions are those gantrys Dean?

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Gantry is HD Item section 120 x 80.
Frame is 100x100x6

[JAZZCNC]

Here's design that will allow you to be more flexible with the frame. Although the base here is in one piece it could easily be made in 2 or 3 pieces and bolted together.
The important part is the full-length profile section running full length down each side. This will allow you some flexibility in adjustment so can get both rails on same plane without messing around epoxy resin etc. Must stress thou the accuracy will only really be good enough for cutting woods and softer materials. It will also take lot of setting up and tweaking until spot on.
In my experience profile is relatively flat and straight enough for wood router and does make fitting rails, ball screws etc much easier. The downside is cost so mixing steel and profile gives good balance of strength, costs and accuracy with ease of building which doesn't require too much machineing or timely and costly techniques for leveling etc.