Are you guys sure that gantry weight is not a problem? I was thinking I could use extruded aluminium profile, but it needs to be quite thick to be stiff, so I'd prefer to go with solid 20mm aluminium. Alternatively I could go with thin sheet and re-enforce it with carbon fibre struts.
Extrusion is good for the gantry, but quite expensive. Consider steel box section or a combination of aluminium flat bar, extrusion or steel. You'll find plenty of examples of ways to do it with these if you search in the build log section.
Thanks Jonathan. I saw you used steel box section for the frame of your machine. Trouble is I can't weld! I only have a gas bottle torch for doing a bit of plumbing, and I have little experience with it.
My plan at the moment is to use aluminium profile for the frame and 20mm plate for the gantry. Given the cost of aluminium profile I don't want to use it for the machine bed, although it seems ideal for easy clamping, it would come to about £300! I have some 13.7mm aluminium honeycomb panel for another project so I thought I'd use that as the bed, and then fix some MDF on top as a sacrificial layer I can screw the cutting material on to.
That honeycomb stuff looks interesting, ty for the link.
With regards using plate for the bed, is there any advantage in bolting say 20x80 or 40x120 profile to either the top or bottom of the plate? Full cover or just certain strategic locations?
Also this stuff as a bed plate surface? http://stores.ebay.co.uk/Vakuumtisch...=p4634.c0.m322 , certainly not cheap but very convenient.
The basic question is, just how much benefit does one gain when increasing thickness by bolting two plates etc together?
DONT buy a cheap Mig thou they are NO GOOD for boxsection, you need good quality high power for material over 3mm. . . . Stick is cheap, relatively easy and eats 3mm boxsection for breakfast. With a few hours practice on some scrap you'll be surprised what you can do and how much you improve.
That said you don't need to weld!!. A steel framed machine can be easily bolted together using plates. You will need an half decent drill press which you'll need regardless whether you use profile, steel or what ever and it's a must have tool for building a CNC machine, and a good grinder with a selection of grinding and cutting disc's.
When you buy the steel buy a strip of 80 x 6mm flat bar and chop it up for the required plates with grinder.
Doing it with plates means you have loads of adjustabilty which you need in a DIY machine to account for the lack of precision grinding and equipment you don't have.!!
It will also save you a shit load of money compared to profile and be stronger.
There are a couple of things with profile just about every body who hasn't used it before doesn't realise.
1: It's even more expensive than they thought because the extra's like T-nuts and brackets etc which you need to keep it easy simple bolt together cost nearly as much as the profile it's self and if you try to skip them to save Wonga your into a world of pain and akwardness that's just not worth the cost.
2: Often it's not just simply bolt together and often needs counter bores drilling so bolt heads fit between slots etc so again requires a good drill press and little jigs so every thing aligns together.
Personnaly I find it far simpler and quicker using steel and the slight plus profile as in that it makes mounting things like switch etc easier is far too costly IMO and with good design every thing can be done with steel and Alu plate for less than half the price and really not that much longer to build.
I would have thought the honeycomb over time would eventually crush under plunging forces which can be very high. With a bit of experience you learn to avoid plunge machining and try to avoid it as much as possible because it knocks the shit out the machine.
Personally I don't like 1 piece beds like the German stuff because one cock up and the whole thing is knackerd. Far better to use individual pieces which can then be replaced relatively cheap if you Foo bar. On my steel framed bed I used 16mm x 38mm strips of Ali to create a T-slot bed and it works very good and is about the cheapist way (at the time) get a good bed.
The other route I'd consider is to use profile side by side with the bennifit being you have 2 shot's at killing it.!!! So if you damage a piece you can turn it over and use the other side before it's knackerd. These guys also sell single sided 80x16 at £14mtr which aint bad. http://www.metallin.co.uk/shop/index...ory&path=3_125
Last edited by JAZZCNC; 27-03-2012 at 06:40 PM.
I have a drill press and also a Makita table-saw with a steel cutting blade. So I could drill and cut box steel.
How accurate is water-cutting? There is is place near my Mum's home that does it, would it be precise enough to do the end plates and bits for the gantry? If it cut the outside dimensions and made a few marks where I need to drill for the mounting of rails etc.. then that could work well for me.
Water cutting can be very accurate. With 60,000psi and a garnet additive you can accurately cut 2" steel.The more I know, I know, I know the less. (John Owen)
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