1220 × 2440 build

[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.!

What dimensions are those gantrys Dean?

Sent from my SM-G935F using Tapatalk

[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?

Sent from my SM-G935F using Tapatalk

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.

[HullMark]

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.

Thanks for that, this is exactly the route I'm looking at now. Makes sense to use the profile for exactly those reasons.

Sent from my SM-G935F using Tapatalk

[routercnc]

Nice machine Dean - have you made one before ? :)

Out of interest do the profile rails down the side also bolt horizontally into the steel sections or just on the support brackets?
Would the ballscrew be drilled and tapped in the ends to bolt through the supports ears? Or the supplier may prefer to machine external threads and use a nut to tension.

Mark, as you are starting out then study this machine as it contains lots of nice features that would be missed be the casual observer. At all the critical interfaces there is scope for alignment and adjustment so you can dial it in.

[JAZZCNC]

Nice machine Dean - have you made one before ? :)

No not made one using this technique because I've got large Granite surface table so use different methods to get surfaces on the same plane. Mainly to save costs because the profile is expensive compared to steel.
However, I know from experience using lots of profile this technique will work great and would certainly use it my self if needed.

The Model shown is just basic layout to give some idea of the concept and that all fit together without any hidden surprises. (Which if got keen eye will see this model does have one in gantry area which would be pain unless corrected.?)
The original design was actually setup to be R&P but also did Configuration for ballscrews which shown.

When I actually build then I model to the last detail and actually use dimensions for cutting list etc.
This way I know 100% there will be no hidden surprises or costly cock up's. Only need to be off few mm's in some key areas and can cause your whole world of pain or worse still compromise the machine.

Out of interest do the profile rails down the side also bolt horizontally into the steel sections or just on the support brackets?
Would the ball screw be drilled and tapped in the ends to bolt through the supports ears? Or the supplier may prefer to machine external threads and use a nut to tension.

The plan was they would bolt in both directions. This would allow more setup adjustment.
The ball screw would be threaded on the ends so can put tension on them. The brackets allow adjustment for alignment.

Mark, as you are starting out than study this machine as it contains lots of nice features that would be missed by the casual observer. At all the critical interfaces there is scope for alignment and adjustment so you can dial it in.

Adjustment is Key at the DIY level and the more you build in the easier and quicker you'll dial in the machine. Unless you have large Gantry Mill to machine surfaces flat, parallel etc then the only way to achieve accuracy is with adjustment and lots of patience tweaking as you go.

[JAZZCNC]

Here's another simpler to make design. Warn thou it's heavy. Those lower beams are 300x200x6.

[HullMark]

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.

I guys hope all is well. So much to do with so little time! When I've been looking at doing something like this, I've been concerned about how to attach the profile to the steel so it's strong and minimises lateral forces. Are you really sure just bolting it on the bottom via those brackets is strong enough?

I don't know how clear it is in the pictures I've sent, but I've used 90mm box section with 160 x 40 profile sat on the top. This gives 35mm overhang either side and would allow me to bolt the profile from the top down on the inside and outside edges of the outer steel lengths. Also does the gantry look strong enough now? Cheers.

Sent from my SM-G935F using Tapatalk

[JAZZCNC]

I guys hope all is well. So much to do with so little time! When I've been looking at doing something like this, I've been concerned about how to attach the profile to the steel so it's strong and minimises lateral forces. Are you really sure just bolting it on the bottom via those brackets is strong enough?

Never said was just bolted to brackets. In fact, it's not that simple.!
There would be adjustment bolts between profile and steel to get the two rails parallel because couldn't rely on the frame being perfectly square.

These are the hidden things which cannot be seen but make a huge difference to how well the machine performs. Again can't stress enough always think adjustability when designing.