Rails and Angle - Going out of my mind

Hi All,
This is driving me crazy now. I have 5m of 3/4" aluminum angle already but I keep swaying towards using pipes as rails. I have all the bearings too.

My ideas are below. Do I mount the angle on the side of the torsion box as indicated or use pipe? Do I mount the pipe on the top use angle?

This machine will have a total size of 27" x 20" (700mm x 500mm) and is made from 3/4" MDF. Height of the torsion box (including top and bottom skins) is about 5 1/2" (136mm)

It will be used for engraving and cutting acrylic and mdf up to a maximum depth of 10mm.

P.s. I can't afford proper rails or 8020 at the moment. My budget is really small so I can't be throwing money around.

Please somebody save me from insanity.

Neal

http://i.imgur.com/0cuwK.png
Also posted on CNCzone.com

Think i'd go with the design on the left, but using the angle rather then the pipe.

If the design on the left is to scale then there dosnt look to be much mdf left after sinking the pipe.

.Me

Neal, I would seriously think about putting up a design for the machine you are building or starting a build log, you could save yourself wasting money, time & effort which if you are on a tight budget is going to be of real value.

I already have a couple of reservations from what you have said, not sure that 3/4 ally angle is wide enough for use with skate bearings ( I assume that's what your using) secondly what gauge is it as 1/16 won't be suitable.

What sort of router do you intend using & how are you going to control the spindle speed which you will need to do for cutting acrylic.

Quote:

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Originally Posted by martin54

Neal, I would seriously think about putting up a design for the machine you are building or starting a build log, you could save yourself wasting money, time & effort which if you are on a tight budget is going to be of real value.

I already have a couple of reservations from what you have said, not sure that 3/4 ally angle is wide enough for use with skate bearings ( I assume that's what your using) secondly what gauge is it as 1/16 won't be suitable.

What sort of router do you intend using & how are you going to control the spindle speed which you will need to do for cutting acrylic.

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Hi martin,
I think you're right. Better to give you guys the whole scope of the build instead of little bits and pieces. I had a fixed plan in my head, but everytime I look at somebody's build log, I change little things here and there.

I have 1/8" thickness aluminium angle mate. I bought a router recently for trimming parts to size and making grooves, but I didn't think It would be good for a cnc router. Its a bosch POF 1200AE as in the pic below. I'll probably be going for a dewalt palm router and build a motor control circuit to vary the speed.
http://i.imgur.com/1lHRc.jpg


Is the angle still going to be too thin at 1/8", because if it is then I'm definitely going for 1" steel pipe instead.

Neal, in the Build your own CNC book they use 1/8" all angle so thickness is OK but I am not sure 3/4" is wide enough to mount the bearings on. The book uses 1" or 1 !/4" ally.
As for router they say you can use any DIY type router but the problem with them is speed control. Even variable speed on it's slowest is to much for acrylic & melts it rather than cuts it. The guy I know who has already built one of the book machines tried everything & eventually had to buy a super pid to control the speed.

Quote:

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Originally Posted by martin54

Neal, in the Build your own CNC book they use 1/8" all angle so thickness is OK but I am not sure 3/4" is wide enough to mount the bearings on. The book uses 1" or 1 !/4" ally.
As for router they say you can use any DIY type router but the problem with them is speed control. Even variable speed on it's slowest is to much for acrylic & melts it rather than cuts it. The guy I know who has already built one of the book machines tried everything & eventually had to buy a super pid to control the speed.

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I cut a lot of acrylic with a router and the trick is to get the cast stuff and possibly even use a coolant. If its not cast acrylic, it will melt no matter what.

Neal, I'm also going down the cheap route. In fact I've got most of the bits already (bought before sense was knocked into me by members on here!) and as they will noo be up to cutting everything I want to I'm going to make 2 routers. The main purpose of my router was going to be for cutting out balsa and ply bits for my RC models but as I've thought about it more and got into RC helicopters I want a machine that can cut CF and also Aluminium.

My cheap router will be used soley to cut 1000mm x 100mm strips of balsa (and the odd bit of 3mm lite ply) and therefore has been designed accordingly. I've got the cheap and nasty TB6560 3 axis driver (24V absolute MAX) and some cheap Nema 23 steppers from old printers and 12mm Trapezoidal rod for the leadscrews. All the other bits I'm getting out of the scrap bin at work or buying through work (to get their discounts!)
Attachment 7375


My other design will be along these lines (changes are afoot....for the 1,000,001st time!!) but using fully suported 20mm rail, 3Nm steppers, propper drivers (50V at least) etc. etc.....

Attachment 7374

The best advice (as given by Jonathan, Jazz et all etc.etc.) will be to use supported rail and all the good things that you can't afford as you'll only be dissapointed by the machine's performance and will end up spending the money anyway on a second build....but.....if you've got a design in mind then I'd say stick to it as long as you're happy with the fact that there will be limitations to the machines abilities. There are 1000's of people out there with MDF machines who are very happy with their machine.

I've gone for 3/4" NB red band pipe which will be drilled and tapped and bolted to the MDF sides (sort of supported rails :) ), there are cross braces under the 18mm skins of the base (torsion box) to further strengthen it. The Z axis will sit on the same pipe (377mm wide) which will again be bolted to some 1" 10 gauge Ali box etc. etc....you get the point, see below.

Attachment 7376