First time build - Steel Frame CNC Router

[examorph]

Thanks for explaining this to me Clive. Reason for LinuxCNC was really just because it was free, but after looking at the boards it may end up being cheaper and easier just buying a Mach 3 License and one of these boards.

I updated the design slightly to raise the Y Axis ball screw by sitting it on some box section, similar to the X Axis (not sure if it would be stiffer buying wider box section and turning it 90 degrees or maybe also taller and having it sit at the base of the 'L' ?). Another reason for doing this was that I found on kincreaky's build log that Chai could supply these so I added them to all 3 axis and will get them with the rails/screws as it will save shipping.

Attachment 17152Attachment 17153Attachment 17154

This also gives me enough space to go with a belt to drive the gantry screw which might be better?
I remember reading somewhere that 25mm end machining is recommended when using pulleys, will this be enough in my case or do I need more?

[routercnc]

The X axis bearing connection looks better now. For info you can buy ballnut mounts off e-bay which are longer than the one you have drawn so give a bigger footprint and are stiffer. They are connected by 4 bolts, not 2 which is better.
http://www.ebay.co.uk/itm/Ball-Nut-M...QAAOSwHnFVjdoi


On the Y axis the 2 ways of mounting the ballscrews you have drawn are probably similar in stiffness so go for what seems most practical to make - but how will you mount that box section end-on? You mention turning it around which would be better.

[examorph]

but how will you mount that box section end-on?

I was planning on welding it direct to the gantry box section as its all going to be out of steel, would this be ok?

You mention turning it around which would be better.

Ok thanks, will turn the ball screw supports on the Y Axis around and use 70 x 50 box section to leave some clearance on each side.

[routercnc]

[QUOTE=examorph;75595]I was planning on welding it direct to the gantry box section as its all going to be out of steel, would this be ok?

Sorry, missed that it was a steel gantry. Then end-on as originally drawn in post#7 would be slightly stiffer. Go easy on the welding to minimise the gantry warping.

[examorph]

CannonGuy - Thanks for spotting the upside down rails on the one side, it was me being lazy and mirroring everything along the mid plane!! Will probably leave it as a mirror as the feature tree on the SW assembly is already starting to get crowded.

routercnc - Thanks for confirming. I read on a few build logs that people have been keeping the temp below 60C to reduce warping, so will probably stick to this. I have a stick welder but can get a mig arranged if you guys recommend it?

Speaking of welding, do you guys recommend the epoxy leveling route on the x axis for a build this size? With the Y and Z axis do you normally not do this?

[routercnc]

In principle epoxy levelling is worth-while on both the X (longest) and Y (across gantry) axes otherwise you are only getting some of the advantages.

In your case the Y axis will be difficult unless perhaps you epoxy the top rail, then when dry and the rail is fixed turn it upside down and use a DTI to dial in the other rail whilst it has a fast setting compound under it? I've not used them myself but I think Dean has talked about some kind of putty instead of shimming?

For the Z axis epoxy is not required as you would ideally use Aluminium EcoCast plate which should be pretty flat to start with. Alternatively you can use standard aluminium plate and skim it flat on a milling machine as the part is quite small.

With the welding MIG is nicer to use, but should be OK with stick/ARC for what you are doing.

[JAZZCNC]

I see a few things I'd look at. (I realise now why it looks strange.? You have drawn box section with square edges and normally they are radiused which makes the tubes look larger.1)

Gantry mounting is weak point. No end support will let it resonate with only lower bolts supporting the upper rectangle. You are using only fraction of the plate to sit it on and with only 4 bolts inline. You would be better extending gantry width to cover the whole bearing plate width and have square 4 bolt pattern.

Has I mentioned in reply to your PM I'd look at ways to protect the ballscrews from debris. The screws are a little high and funerable. I'd be looking to add gantry sides which drop down the sides to allow screws to be lower and drop on the inside of the screw so covers can be added without interference from bearing plates. The gantry side also strengthens the gantry.

Regards welding then you have a lot of tubes all intersecting at the same points which means a lot of heat will be generated there. Idealy you should try to offset any tubes so the don't all meet at the same points. This will reduce warping and stress.
You also have tubes you don't need the Centre vertical ones for instance. The diagonal ones are enough and it's less welding, less heat and distortion. (see pic)

Mig welder is far better than Arc when comes to heat so if you have access to one I'd use it.

I'd also extend the Top rail 100mm past the end this will allow spindle to pass end giving more flexabilty to machine.

Regards PMDX then you want 126 BOB not 122 it's far better. If you go with Belts then buy Cslabs IP-M.

[Clive S]

Examorth The board that you linked is the pmdx Is an excellent BOB but for the best results it will need a motion controller like say the Ethernet smooth stepper as the PP on pc's these day are flaky to say the least. There will be more support on this forum with Mach3. Good luck with the build.

[DigiSoft]

You can check out my thread I am almost finished with my machine.
It is 90% steel

http://www.mycncuk.com/threads/5237-...LD-please-help

[examorph]

Dean - Thanks for clearing things up for me, I will be doing some aluminium work on it but was going to go down the route of using a mist rather than flood cooling, will this still be OK with the ply wood sealed base and spoil board setup? Also, probably a silly question but what are the typical depths for the ply wood base and spoil board? Just checking as I want to make sure I leave enough space bellow the spindle.

DigiSoft - Thanks for the link, I remember seeing it previously. Really nice buildd!