Im new, am a 3D designer. Need a New cnc machine and need advice and guidance

[FlyHighRC]

I had planned on using one ballstrew for each axis... waht you see would have 100mm legs on each corner and would then have a piece connecting each side of the gantry that can be bolted onto the gantry sides to make assembly that bit easier

[JAZZCNC]

You are weakening the machine having that base like that and it's completely not needed. You need to keep the gantry sides height to a minimum and your creating 60mm more than needed and every bit helps if your wanting to cut aluminium.
If you want the best strength then having raised sides with rails on top with gantry sat directly on bearings is massively strong and much much more suited to an all round machine. If your wanting to cut aluminium then you WILL need 2 ballscrews on the axis moving gantry. This is not just an opinion it's hard learnt and tested thru building many differant machine designs trying to find the best design for an all round machine without being silly about design.

The machine your building with single screws will be fine for mostly wood use and occasional light duty Aluminium work but have no doubts it won't handle cutting aluminium correctly and give quality finish. At a minimum you'll need 2 ballscrews moving gantry to stand any chance and very beefy gantry.

Edit: Oh and the bed base needs far more supports than just one in middle.

[FlyHighRC]

So loose the second level of boxsection with the board ontop?

Keep gantry height to a minimum

Design in two ballscrews now rather than later

add more support for bed..

got it :) The general gantry design.. Is that ok? with a vertical piece and a 45 member to give some strength... How far should i keep the bearing carriages apart? from the faces that would touch..

[njhussey]

So loose the second level of boxsection with the board ontop?

Keep gantry height to a minimum

Design in two ballscrews now rather than later

add more support for bed..

got it :) The general gantry design.. Is that ok? with a vertical piece and a 45 member to give some strength... How far should i keep the bearing carriages apart? from the faces that would touch..

IF you've gone through the build logs then you'll see a pattern in the design of the routers built recently which are 90% (this one isn't...http://www.mycncuk.com/forums/gantry...ercnc_mk3.html) all raised rails above the bed like the pictures I posted previously. They'll also answer most of the questions you're asking about designing them. You don't have to go re-inventing the wheel! Most people on here want to cut the same things that you do (I do as I want to make parts for balsa and ply planes, carbon fibre heli frames and quad frames, ali parts for my helis and quad etc...) so their routers have been designed as a best compromise to achieve this. Re-read all the build threads to see how designs have changed along the build. Mine's a very good example of just this. I started with a similar design as the one you're doing and has evolved as I've read more build logs and asked questions...

[FlyHighRC]

IF you've gone through the build logs then you'll see a pattern in the design of the routers built recently which are 90% (this one isn't...http://www.mycncuk.com/forums/gantry...ercnc_mk3.html) all raised rails above the bed like the pictures I posted previously. They'll also answer most of the questions you're asking about designing them. You don't have to go re-inventing the wheel! Most people on here want to cut the same things that you do (I do as I want to make parts for balsa and ply planes, carbon fibre heli frames and quad frames, ali parts for my helis and quad etc...) so their routers have been designed as a best compromise to achieve this. Re-read all the build threads to see how designs have changed along the build. Mine's a very good example of just this. I started with a similar design as the one you're doing and has evolved as I've read more build logs and asked questions...

Not trying to reinvent any wheel, I have lowered the bed...I am still going to keep the sides now as they are good for more strength and will also save me using 3mm poly as a way to stop rubbish going onto the rails...Im quite happy with this though it may need more support on the underneath... I need to make bracket on either end and either side of the machine to hold the motors and ballscrews...

My one concern is the accuracy in welding...if i take the parts to a welding shop will they know how precise this had to be? Dont want them to weld it up and realise its off by a few mm

[routercnc]

.. How far should i keep the bearing carriages apart? ..

With a single ballscrew in the centre then racking becomes a problem whereby the gantry can rotate or twist if you are cutting anything towards the edge of the gantry. To minimise this you can space out the bearings further, but there is a compromise on travel.

With twin ballscrews all these problems go away, which is why it is highly recommended. The gantry cannot rack as a ballscrew holds it at each end. Your considerations then come down to placing the bearings so that the centre of gravity of the gantry (which will be somewhere behind the spindle centre line) and the cutting tool centre line both lie within the region between each bearing, as viewed from the side. If you need to deviate from these positions then don't worry as the profile linear bearings will take quite a load.

As I guide I would say between 100-200mm is about right, probably going closer the 200mm end of the range, giving you maximum travel.

[Jonathan]

Also bear in mind that the deflection of the axis, due to the linear bearings, for a given cutting force is inversely proportional to the square of the bearing spacing. A relatively small increase in the spacing you choose can therefore make a big difference, assuming the stiffness of the system isn't dominated by another weaker part. The reason for this is that the force on each bearing decreases with their spacing and the deflection of the tool also decreases for a given bearing deflection if their spacing is increased, so overall you get a quadratic relationship.

for a good machine what is recommended, A router or spindle? cant see any bvious advantage or disadvantages to either... Yet to see anyone give a preference on any of the build logs

Simple answer is get a proper spindle. But please read the build logs more - people have already linked to some good ones in this thread, yet all the questions you've asked so far are already answered in the logs.

[routercnc]

The 'routercnc_MK3' is my machine and I'll explain why it looks like that.

It was much easier to build it like that based on a simple evolution of the previous version. It is only intended to cut balsa wood, liteply, and plywood and it works very well. I've been using it recently for cutting some 20mm thick aluminium upgrade parts, but that is not the main use.

If I do cut aluminium on my machine (6mm carbide 2 flute cutter) I can run at 1.0mm depth of cut and about 800mm/min feed. Any deeper and I get chatter.

If you want to cut a fair amount of aluminium the raised X axis designs are far superior and probably the best DIY CNC arrangement without simply converting a bridgeport mill to CNC. If you are starting from scratch there is no reason not to really.

[njhussey]

The flat bar was as well as epoxy...best sort of taps are spiral flute taps...buy a load on ebay from China they're cheap as chips. Most taps are made for steel, even the cheap black spur ones they sell in pound shops. If you've a good printer, a decent centre punch and a hand drill you can make a decent gantry. Sure a mill helps but ultimately care and attention to details and hand tools are enough if that's all you've got and you want to make a CNC router ;)

Sent from my Galaxy S5

[FlyHighRC]

Its not that milling would be a problem, My taid (Wlesh for grandfather) has a workshop for model engineering...he builds those little steam engine that pull 20 people... Also I dont mind getting a few parts done on a laser either... my budget can go up a couple hundred which i can use some for parts to be made...allot of company quotes to come haha. If they all turb out to be stupid in price then ill do it myself.