View Full Version : NEW MEMBER: Hi
02-11-2008, 10:06 AM
Just joined. I've just ordered the parts for two projects, my first foray into CNC.
The first project is to build a PCB machining unit, essentially a small vertical milling machine with limited Z axis travel. I managed to scrounge two Velmex A4000 Unislides (see here: http://www.velmex.com/manual_cross_sections.asp?series=4000) for just £30 the pair, already configured as an X-Y table. What's really handy is that the screws already have 1/4" ends on them where the knobs fit, so they will be easy to hook up to steppers. These only have 100mm of movement, but they should be OK for my hobby purposes. The Z axis will most probably be my existing PCB bench drill, modified with a stepper driven quill.
The other project is a medium sized router table, primarily for composite mould making. The plan is to get to grips with CNC on the small machine, before starting the big one.
Hardware ordered so far includes 6 off NEMA 23 180N-cm steppers from Arc Euro (just £18.50 each, on special offer), a Smoothstepper USB drive board, a 3.5A triple stepper drive board and a 24V, 14.5 amp power supply. I plan to use the same electronic box for both machines.
I'm still pondering about which rails, screws etc to get. There are some relatively cheap suppliers on eBay, but I've no idea of the quality. The only UK supplier I've found looks to be pretty expensive, which is a shame. Ideally I'd like someone who has stuff in stock that I could go and look at, or at least get a recommendation from someone here in the UK who has bought from them.
Software will most probably be Mach 3, plus the Warp9 software to drive the Smoothstepper. My existing CAD software (AutoCAD and Rhino) should be able to export files in the right format, from what I've read.
02-11-2008, 10:33 AM
Welcome to the forum.
That initial 100mm x 100mm project sounds fairly straightforward, should get you running in no time :D That work area is fine for many PCBs and if you want to go larger you'll just have to be creative about registration methods/jigs.
Screws and rails on Ebay - you're probably refering to MD (we've all bought from there with varying experiences) - but have a look at Gary's site http://www.slidesandballscrews.com/ also Lee, the site owner, may be able to help.
Don't forget to post your build log!
02-11-2008, 10:48 AM
Thanks for the welcome, Irving, and many thanks for the web site link - it looks to be pretty good from what I've seen so far.
You're right, the other site in the UK I'd found was MD. The puzzle with them is that their eBay prices don't seem to tally with their direct web site pricing, with the eBay packages being a fair bit cheaper. Unfortunately, none of their eBay package deals is really the right sort of size for what I have in mind - maybe that's why they're a bit cheaper.
I'd better get back to looking at the "slides and ballscrews" site!
02-11-2008, 03:29 PM
I hope it works out to be interesting!
I've recently converted a small motorcycle to electric power and would like to have a go at making a streamlined electric trike next year. One way to make the body would be to machine slices of thick extruded polystyrene into rings, then glue the rings together to make the body. The foam can then be covered in epoxy/glass (or maybe kevlar) composite, to produce a complex 3D foam sandwich monocoque. The idea is to use the body shell as the chassis, with bonded in hardpoints for suspension mounts etc.
A CNC router would be an ideal way to accurately make these mould slices, as (with luck) I should be able to just take the slice layouts from Rhino and pass them to Mach 3 to drive the machine. My plan is to build something with a working volume of around 750mm x 600mm x 300mm, with a fair degree of accuracy but without any need to be able to cut heavy materials.
I've already tried hand-held hot wire cutting foam, but it's challenging to get a fair enough shape; the hand-held hot wire leaves a lot of small ripples that need to be sanded out, even when used with guide templates.
Having made a few foam composite parts now (by hand) I'm impressed with the technique. I can see why Burt Rutan (of Scaled Composites fame) developed this technique for his home-built aircraft projects, as it's well within the bounds of a normal DIY skills, yet produces light, stiff and remarkably strong structures.
02-11-2008, 05:33 PM
Hi welcome to the forums, anything you see on slidesandballscrews.com i will price match thats not a problem.
02-11-2008, 08:58 PM
Rhino was pretty alien to me for a long time, as I've been using AutoCad for years. I forced myself to get to grips with it a couple of years ago, when we went on a quiet holiday (no TV, phone, internet etc). I took a laptop, loaded with Rhino, plus a printout of the manual, and spent a week un-learning AutoCad and translating things to Rhino.
I think the problem, at least for me, is that Rhino is quite intuitive, provided that you've not got 20+ years of AutoCad experience. I'm pretty sure that it's the Autocad interface that's really the problem, as intuitive it isn't.
Rhino is worth persevering with though, especially if you want to produce nice 3D surfaces. Like all 3D CAD packages it's approach seems a bit odd for those of us with years of working on paper, then CAD systems that emulate paper.
05-11-2008, 06:24 PM
Hi Jeremy and welcome to the forum.
If you are looking for a reliable supplier of kit then you will not go far wrong with Zapp (Slides and Ballscrews). I'm sure Lee will also be able to help out in that regard equally.
I'm intruiged to see some sort of design for the router project to see how you plan to acomplish a 300mm Z. Really looking forward to tracking this build :D.
05-11-2008, 07:47 PM
Thanks for the welcome.
I'm not underestimating the challenges of getting enough rigidity to allow 300mm of usable Z travel, I hope!
What will probably help is that I don't need heavy-duty cutting capability for making tall foam parts, which should ease the problem a bit. I think that one way to make the gantry stiffer is to opt for moving the table in the Y direction, rather than the gantry.
I may opt to make a lower level, removable, stiffening brace to allow heavier work that needs less Z clearance, to be done, as I might like to do some cabinet work with it at a later date.
I'm in a bit of a quandary about the small machine at the moment, as, although I have acquired a pair of very nice Velmex Unislides, I am getting increasingly tempted by the Sable machine advertised on eBay. See here (for those that have not spotted it yet): http://tinyurl.com/5ad6du.
I have a small benchtop milling machine already (a kit-built Dore Westbury) but this isn't really suitable (IMHO) for a CNC conversion, as the only way to provide Z travel is to drive the quill. Apart from only having limited travel, the quill drive has a fairly high degree of inherent backlash, as it's rather similar to the rack and pinion drive on a pillar drill. I have toyed with the idea of getting a small Sieg and then fitting a CNC conversion to it, but the slow spindle speed would be a problem for milling and drilling PCBs.
If the small eBay machine turns out to be as stiff as it seems, then it may well be up to doing light alloy machining (with small cuts). If this turns out to be the case (I'm awaiting a further report from a CNCZone member who has just purchased one) then my best compromise might be to keep the Dore Westbury as a manual machine for heavy work, get the Sable for light work and PCBs and use a combination of both to make the large machine for making big mould formers.
I've already purchased all the electrical bits, so I can crack on with building a multi purpose driver/interface box. Hopefully this will work with whatever machine(s) I finally end up with!
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