Planning and build of my "8020" aluminium CNC Router

[monza]

Hi guys,

Well been making a nuisance of myself on here for a week or so and I think it's time to make a thread 1 to get some ideas from you lot and 2 so I can put all my ideas in one place for my own reference :)

The plan is a 2' x 4' fixed bed made from aluminium extrusion and then a moving gantry style for the movement. I have sourced a trim router from an old router table and am looking at using the skate bearing style linear movement. This will run on a sheet of cold rolled steel bolted onto the outside of the ali extrusion. This should give me smooth rolling and a nice straight edge to run along. It will also allow me to get the gantry rock solid by tensioning the top and bottom runners.

I am still undecided on my drives at the moment might go with timing belt anchored at each end of the bed and then the stepper mounted on the gantry with a pulley and idler roller. I will be driving both sides of the gantry to avoid racking and hopefully give me enough rigidity to allow me to cut lightweight metals. I have looked into leadscrews and ballscrews and allsorts but I think the cost is prohibitive for a hobby machine.

Primarily I will be using it to cut Balsa and other sandwich materials as a core for my carbon stuff which will then be vac bagged with epoxy. The length will hopefully allow me to make rc planes and eventually a new kiteboard. I would like to be able to machine aluminium blocks but I doubt I will get it anything like for doing that.

So that's the overview. I will bulk the thread up with many ideas and pictures. Also need to get cracking in Sketchup and make a plan :)

[ptjw7uk]

I'm thinking of going the 2x4 route as my micro mill is just not big enough.
I favour the timing belt route over screws but so far not found a source of long lengths.
I am also being a little constrained as I have run out of workshop space and am also persueing a vertical bed design but not sure what the forces would be?
So I have plenty of ideas but I'm afraid not much advice to give you.

Peter

[monza]

This will probably be a useful thread then for both of us ptjw as I am now looking at a fair few different ways of driving it I want to stay away from leadscrews really have been looking at rack and pinion but that seems even more expensive than leadscrews. I have a theory of using a timing belt that self meshes and running it through a couple of pulleys and over a stepper. This should then mesh against the fixed side which is attached to the ali so instead of 4' of timing belt to sag and keep tight it is running against itself which in my head means it will be a 3" part of the belt that is free the rest is self supported. I have sketchup and illustrator open so let me draw it then it will make more sense :)

[ptjw7uk]

Hi Monza
Have a look at this http://www.youtube.com/watch?v=OdJoVh6DRPA
Does what I had in mind to do.

peter

[monza]

That's scary I just drew up my idea in illustrator.

http://img.photobucket.com/albums/v495/sharemaster/beltdriveroughsketch.jpg

My theory is that the meshing of the belts will minimise backlash and should hopefully give a nice fast accurate and stable movement :)

[irving2008]

have you considered chain drive rather than timing belts? buildyourcnc (http://buildyourcnc.com/blacktoe.aspx) has an example for a 4x2 and 8x4 blacktoe design

[monza]

The one with the roller chain drive? I saw that he was doing that. I think that might be a bit heavy duty for me also I can see the foam and acrylic dust sticking to it and it becoming a real mess as it has to be lubricated. Also my cellar is not the most stable with regards humidity so rust might be an issue. There are many ways of skinning this cat I just need to decide on one so I can crack on with the build.

[Tom]

.... looking at using the skate bearing style linear movement. This will run on a sheet of cold rolled steel bolted onto the outside of the ali extrusion. This should give me smooth rolling and a nice straight edge to run along. It will also allow me to get the gantry rock solid by tensioning the top and bottom runners.


Hi Monza,

You won't regret using skates and CRS rails. That element of my router is absolutely rock solid - it feels very robust indeed. More assembly and tweaking time to get it running right than, say, ball bearing carriages, but also MUCH cheaper.

The machine you're building sounds alot like my next one!:whistling::naughty:
Alu section is the way forward....! :smile:

All the best,
Tom

[monza]

I think the cold drawn steel will help a lot with stiffening up the bed as well if it is well thought out. I am hoping to build it once and use it lots so I think over engineering now rather than a catch up job later will serve me well. are you using the 6 runners on a block style or a different version Tom? Have you used them on all of the axis as well?

[monza]

If a few people are building the same machine then maybe we should all get our heads together and come up with a good scaleable design which will let us get discount on some things and get other bits imported etc in the same box?

[Tom]

I think the cold drawn steel will help a lot with stiffening up the bed as well if it is well thought out. I am hoping to build it once and use it lots so I think over engineering now rather than a catch up job later will serve me well. are you using the 6 runners on a block style or a different version Tom? Have you used them on all of the axis as well?

The rails were actually surprisingly floppy. The X are 50x6mm section. Y are ~30x6. The Z plate is 210 x 125 x 6. I think I've got Y and Z steel left over if you're interetsted - you're welcome to some / all of it for cost + postage (minus a bit because it's going no-where at the moment!).

There are some pics attached to give you more of a flavour of what I did...

[monza]

Ah good stuff Tom I need to go visit my local steelholder they are a good set of guys so hopefully they will be able to source me some. If not though I shall take that spare stuff you have and add it to the parts collection :)

These are the linear carriages I am looking at, they are finelineautomation ones and are a nice compact simple unit. I need to change the hole arrangement around to get them to bolt up to my aluminium extrusion for the gantry mount I am thinking of one rolling on the top and another rolling on the bottom of a sheet of CDS or possibly along a sheet of oilon plastic I need to check the rigidity of it but it is a self lubricating HDPE plastic. that should give me a rock solid gantry and hoefully belt driven should be able to shift it's weight around quite rapidly.

http://img.photobucket.com/albums/v495/sharemaster/LinearCarriage.jpg

http://img.photobucket.com/albums/v495/sharemaster/LinearCarriagetop.jpg

[Frank Sanfey]

Don't know if you already contacted us and this is not really advertising but 80-20 is a US designed aluminium profile system. You would be better off with a UK system such as ours www.valuframe.co.uk (http://www.valuframe.co.uk) which will be "properly" metric.

[monza]

Hi Frank,

I did, I called the other day not sure if it was yourself I spoke to. I will be pricing it all up to see if I make the minimum order value and then getting some bits ordered up :) is there a metric profile that matches the 8020 spacing wise so I can use some of the stuff the American guys are making?

[compfranon]

I plan on using the fineline carriages too, just waiting on mate machining the blanks for me. In general i'm planning a similar build using belt drive and 8020 or similar, so will be interested in following your progress.