Thread: round rails
My current machine is wood with skate bearings. I designed it 9 years ago, when DIY CNC was in it's infancy, and the only linear rails available were used from Ebay. While it's probably quite a bit better than most similar machines, the bearings are the main limitation.
Today, I strongly encourage anyone to use supported round rails at a minimum. With the inexpensive rails from China, it really doesn't make sense to go with anything less. If you're on a really tight budget, sure, you can use cheaper methods, but don't expect great performance, or quality cuts. If you have the skill to make the cheapest method work well, you probably wouldn't be using them in the first place.
As far as wood goes, I'm a big proponent of wood construction. But, as Jazzy eluded to, not your basic MDF design.
I'm currently building a (mostly) wood machine, with the goal of outperforming most of the extrusion machines I see. Both in speed, and strength and rigidity. It'll have HiWin linear bearings on all axis, and belt drive X and Y. Not your typical belt drive, though. I've designed a stepper version of the Servobelt
Building a high quality wood machine requires some high tech construction techniques (IMO). Anywhere that metal parts are fastened to wood, I have aluminum or phenolic "mounting pads". This keeps the wood from being crushed and maintains precision.
Most of the wood parts I use are made up of laminations to increase rigidity and stability. In addition, everything is sealed in epoxy to minimize moisture absorption, and subsequent movement. Whenever possible, torsion box construction is employed to again maximize strength and stability.
I am using some aluminum for mounting the linear bearing blocks, but in some cases it's bonded to baltic birch plywood, which let's me use thinner panels.
Oh. It's going to have two spindles.
Today I cut the parts for my gantry beam. It's about 1700mm long, made of MDF. Front and back of the beam are 1" thick, made up of a lamination of 4 layers of 1/4", glued with plastic resin glue in a vacuum press. Phenolic mounting pads for the linear rails were epoxied on.
My day job is in a cabinet shop, so I have access to a 5x12 Morbidelli router. This is what I ended up with. Sorry if this is off topic. If anyone's interested, I've been documenting the evolving design at CNC Zone for the last 5 years.
Start of a New Design - CNCzone.com-The Largest Machinist Community on the net!
New Machine Build Z² - CNCzone.com-The Largest Machinist Community on the net!
I mentioned you on another thread, where a member here was convinced MDF was too bendy and metal is the ONLY way to get accuracy . I made mine
from MDF torsion box/beam sections and was trying to explain that MDF can be made to not bend, and that you , - definately not a newbie - choose MDF to build your new machine.
As for rails ...
I agree that supported precision rails are the best, but a lot of people would be perfectly happy with the results from DIY supported pipe and skate bearing trucks, for example. or for a bit more, steel plate and CNCRP type trucks like CarveOne uses.
There are even people out there very happily using drawer runners and allthread screws, and it does everything they ever wanted ! or, they use it to make parts for a second machine , etc.
On the other hand, Microcarve has extremely accurate machines with unsupported round rails - used to their limits - and made from MDF and plastic pipe ! LOL .
ok i'm going to re-phrase a little of what i said... yes MDF can be made strong.. but when the cost is not to far away from each other then imo using steel box section looks far easier than that setup that gerry above is going for.. and for what it's worth a simple DIY guy is not going to have access to the tools that gerry does.. you can see from his second and last drawing that there is a hell of alot of work for him to create just his gantry beam and that he by the looks of it is using another CNC machine to make the cuts for his new machine
i am making my machine on a budget and had originally thought about using mdf but i honestly believe that using steel box section is not much difference in price and looks a hell of alot easier to get strong
I got no problem with steel at all Wilfy, I was just a bit frustrated that you thought my machine could only be bendy because it's made from MDF ! lol
Also, dont under estimate the 'bendyness' of steel
Just think about the title of this thread. What the round rails are made of, and what you need to do to stop them bending.
It's exactly the same for steel box section. It will need supporting and bracing too.
not knocking it, just reminding you and anyone else reading this, to think about the design, as much as your chosen material.
As a very extreme example, pick up that piece of 50 x 50 x 7m long box section Jazz mentioned, in the middle, and it will bend and wobble like a bendy wobbly thing !
At the end of the day, it's not so much the material you use, it's how you use it. Everything bends and flexes. For a machine of any construction to work well, it has to be designed to resist bending and flexing. I hate working with steel. If you don't mind it, it's definitely cheaper to weld up a massively strong and solid frame. But it's no free lunch, as most likely your bearing surfaces won't be flat, which brings about a lot of other issues. I have equipment at my disposal which allows me to easily get perfectly flat surfaces from wood, so that's the route I take. Aluminum extrusions are expensive, but easiest to work with for most people. But I'm not sure if there as rigid as some people would lead you to believe. Or rather a lot of people use smaller sizes than they should, in the interest of cost savings.
I say build with whatever material you like, but you need to know how to use each material properly, and to it's strengths.
Also, with regards to linear bearings. Take a good hard look at what the total machine cost will end up being, and in a lot of cases you'll find that upgrading the linear bearings may only end up being not more than £500 more, which is well worth it in the long run.
I've just been given prices for full set(3axis) of rails & bearings for a friend to build 700x700 cutting area machine and they cost $79 usd thats £49 plus shipping. Can't tell you accurately the shipping price because there were lots of other stuff on the quote but I reckon the shipping will be about the same has rails so for less than £100 you have accurate and relatively reliable hassle free rails.
By the time you have bought bearings,bolts,pipes,angle etc for what ever method you choose it will cost almost that much and I pretty much guarantee you won't be happy with the results and like I say high chance of still ending up buying the supported rails.
Gerry highlighted perfectly well just how much work needs to go into a wooden machine, Vacuum Laminating, epoxy resin, phenolic pads, etc non of it easy or cheap.! Then look at all the Work that goes into forming torsion box's. For Ger it's relatively easy has he has access to some very nice machinery and facility's along with probably very cheap source of wood compared to UK.!!. . . Most blokes in a shed don't and therefore the quality of build drops drasticly which it can't afford to with wooden skate board construction. This leads to a high failure rate and lost money most of which can't be recouped or reused on the next machine.
Gerry in all honesty now.!! If you had both options available IE full Access to machinery and resources would you build from Wood.?
Equally if you didn't have access to either equipment and had little to no experience using either wood or metal/Alu profile.! . . Say an office worker just looking for a DIY hobby in the back shed which of the two options would you say gave the best chance of success FIRST TIME of an accurate, reliable machine.?
I helped someone who started a build using this system with actual CNCRP (CNC router parts) components and it was nothing but hassle and high maintenance, constantly cleaning and chasing it with adjustments.
Swapped it out for Chinese round rail and hasn't touched it since and never give a days trouble and it cuts ply wood van linings all day long 6 days a week.
So all I'm saying is YES wood can work very well but it ain't easy and it isn't always cheaper.!!
Get a grip man it's all about design and bracing.! With MDF/WOOD it means more bracing, much more to get near steel.
I have worked both materials for years and have equipment to use both and if I could build just has strong, accurate, reliable and cheaper machine from wood then I would. I can't simple has that.!!
Something that you miss completely Jazz, is that for some people, the idea of building a CNC from scratch, and from bits and pieces lying around, and testing different methods etc. is just as much (sometimes more) enjoyable, than using the thing afterwards.
When it came to my Z , for instance, I had an old bed side that I had kept (would come in handy one day :) )
My Z works perfectly (cutting wood) , and is driven by allthread and a couple of standard nuts, with rails made from that bit of bed, and some skate bearings.
Also, some people want to cut steel, others are happy cutting foam - completely different design philosophy for both !
That's why I called my build "Scrap heap challenge" it's fun - and can be very accurate.
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