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

[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

[JAZZCNC]

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

Don't waste your money because they won't be able to stop distortion only lessen it and in any case you will still need to either use shims or Epoxy method.
Only thing you want to pay special attention to is Twist. If the base frame is twisted then the rails are not on the same plane, Epoxy method is good for sorting this but if you pay carefull attention when welding up then it's possible to get away with just light shimming of the rails. . . BUT with your design the Epoxy method will be much easier and more accurate than your capabiltys to measure rails are on same plane.!

Squareness of base frame isn't critical either square to 1 or 2mm is fine, obviously less is preferable. The important area is the gantry is square to the rails.
The base the cutting bed sits on needs to be resonably flat but again it's not critical as you'll surface the bed before using and this will bring it flat parallel plane.

Like Neil says you really need to go reading some of the build threads more closely and pick up the tips and you'll see whats needed and where your design Lacks or CAN be improved.

[FlyHighRC]

I have spent allot of time on the build logs so far. Im seeing allot of parts that require a mill and to me that dsrives up cost and complexity. Im sure it increases strength but above my computer I have K.I.S.S which is proving handy :D

A couple questions where I cant seem to find the answer..

When the epoxy is applied to the steel and sets, to bolt on the rail im assuming you just drill and tap? otherwise that must be a very fiddly job getting all them nuts down there haha

carriage space seperation, Is there an optimum distance between the bearings? im assuming the further apart the better but that obviously reduces work area so i guess there is a happy medium somewhere, right?

[njhussey]

I have spent allot of time on the build logs so far. Im seeing allot of parts that require a mill and to me that dsrives up cost and complexity. Im sure it increases strength but above my computer I have K.I.S.S which is proving handy :D

If you made the gantry out of steel or Ali extrusion you wouldn't need a mill.

A couple questions where I cant seem to find the answer..

When the epoxy is applied to the steel and sets, to bolt on the rail im assuming you just drill and tap? otherwise that must be a very fiddly job getting all them nuts down there haha

Depends on the thickness of the steel. If you've read Eddys build log you'll see he glued in 6mm flat and drilled and tapped into that...

carriage space seperation, Is there an optimum distance between the bearings? im assuming the further apart the better but that obviously reduces work area so i guess there is a happy medium somewhere, right?

Pass...i settled on 200mm as a good compromise between losing cutting area and strength...



Sent from my Galaxy S5

[FlyHighRC]

Thanks, I prefer the epoxy method thatn gluing some flat bar onto the frame... Purely because it sounds simpler :) Thanks on that! I was thinking nuts inside the box section would be very tedious...any special taps Id need for steel? I have a set of taps but arent made for steel...

In terms of what i said about a Mill, I was talking more along the lines of motor mounts, Even saw one guy with a very nice machine who had his whole gantry cut by laser...

[Clive S]

When the epoxy is applied to the steel and sets, to bolt on the rail im assuming you just drill and tap? otherwise that must be a very fiddly job getting all them nuts down there haha

I used 5mm box section and drilled and tapped through the epoxy post 6 here:- http://www.mycncuk.com/forums/gantry...st-router.html is the epoxy being poured. Eddycurrent has used a similar system but he glued a flat plate with gorilla glue inside the box section to give more of a bite for the threads. ..Clive

[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.