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wilfy
02-09-2012, 10:21 AM
hey guys, i'm starting to think about making a small cnc machine possibly around the 15" x 15" size, my original plans had me doing a 4ft x 4ft but i can justify the costs until i make and learn a smaller machine.


so my question is at what point should i steer away from a straightforward round rail and got to supported round rails. my hope is that with a machine as small as 15 x 15 i will get by with round rails and keep the cost down.

motoxy
02-09-2012, 11:11 AM
Hi Wilfy. I have learnt on this site that strength is very important. For accurate cutting you need to be able to control the cutter and that means that the frame must not flex. A weak point can be the rails. It all depends on what you intend to produce but the excepted wisdom is supported rails are always superior to unsupported as the deflection is greatly reduced.

Bruce

wilfy
02-09-2012, 11:15 AM
i'm thinking more about engraving and cutting small pieces of mdf and acrylic. i'd be happy to sacrifice speed, if it reduces the cost

JAZZCNC
02-09-2012, 04:30 PM
i'm thinking more about engraving and cutting small pieces of mdf and acrylic. i'd be happy to sacrifice speed, if it reduces the cost

Ok this is were people get it wrong regards speed and machine strength in relationship to materials, or more importantly what they think are soft materials.?

When cutting things like MDF and plastics like acrylic then you need certain amount of speed other wise the finish is rubbish and tool life is drasticly reduced. These speeds or feed rates are higher than most realise, so the small sacrifice in favor of costs becomes the Achilles heel of the machine.! . . . Normally not worth it. .. BUT.? . . . If decent sized rails are used with good end support then on a small machine like this then they can be ok.

Personally I wouldn't use them because the difference between supported and unsupported isn't great enough and the performance difference is substantial enough to warrant. Also if your thinking to keep short term then it makes the machine far more valuable and sell-able than one that doesn't.? Put it this way if someone says to me "what you think to this".? . . I'd say stay clear it uses unsupported rails.!!

Jonathan
02-09-2012, 08:09 PM
To save repeating myself, please refer to this thread:

http://www.mycncuk.com/forums/faqs-problems-solutions/4356-why-not-use-unsupported-rails.html

Bear in mind the rails I modelled there are substantially longer than what you will require, so as Jazz said so long as you stick to a large diameter (=>25mm) short rail you'll get away with it. However if you compare that to the price of say SBR16 supported rails from linearmotionbearings2008 on eBay the difference in price is not that great compared to the difference in performance.

wilfy
02-09-2012, 08:13 PM
To save repeating myself, please refer to this thread:

http://www.mycncuk.com/forums/faqs-problems-solutions/4356-why-not-use-unsupported-rails.html

Bear in mind the rails I modelled there are substantially longer than what you will require, so as Jazz said so long as you stick to a large diameter (=>25mm) short rail you'll get away with it. However if you compare that to the price of say SBR16 supported rails from linearmotionbearings2008 on eBay the difference in price is not that great compared to the difference in performance.


acctually looking at the prices of 25mm unsupported vs 16mm supported it works our cheaper using rough prices from zapp...

so my question then would using 16mm supported be better/as good as 25mm unsupported for a 15" x15" machine?

Jonathan
02-09-2012, 08:36 PM
acctually looking at the prices of 25mm unsupported vs 16mm supported it works our cheaper using rough prices from zapp...

Yes, which is why you don't use Zapp:

linearmotionbearings2008 | eBay (http://www.ebay.co.uk/sch/linearmotionbearings2008/m.html?_sacat=0&_nkw=sbr16&_sop=15)
4 SBR16-500mm rails+8 bearing blocks | eBay (http://www.ebay.co.uk/itm/4-SBR16-500mm-rails-8-bearing-blocks-/130712394633?pt=LH_DefaultDomain_0&hash=item1e6f10db89&_uhb=1)

etc... clearly buy as big rails as you can afford and also email linearmotionbearings2008 to get the best price for the exact sizes you need. For 15" travel a 500mm rail is about right. I wouldn't like to see much smaller as it's best to have a decent spacing to lower the bearing forces.


so my question then would using 16mm supported be better/as good as 25mm unsupported for a 15" x15" machine?

Better so long as you mount them to something substantial - i.e. not MDF. Once you use supported rail the force is transferred to the material it is mounted on, so if you mount them to a piece of cardboard you don't gain much! Use steel box section (cheap) or aluminium extrusion (expensive) and the stiffness will be significantly greater. Another advantage with the rail being supported is the resonant frequency is much greater. Think of the unsupported rail like a string on a musical instrument - you apply a force to it and it will vibrate. This motion is transferred to the cut resulting in a poorer surface finish. Of course this is a very general statement, with the right diameter rails, bearing spacing and mount you can make it work with either type of rail. It's just a lot easier with supported rails.

wilfy
02-09-2012, 08:48 PM
brilliant info as always guys thank you very much, and yes i had planned steel box section, it isn't that expensive and i've bought myself a mig welder so although a small machine it will be well built and now on 16mm supported rails.

i have a question about the spindle but that can wait for a while, i want to get some of the frame built first and see how money works out.

thanks again

TrickyCNC
14-09-2012, 09:10 AM
Whilst I agree steel is stronger than card board , and supported rails are stronger than unsupported, there are plenty of wooden/MDF machines out there working very well. Also there are ways to support 'unsupported' rails.

JAZZCNC
14-09-2012, 09:27 AM
there are plenty of wooden/MDF machines out there working very well.

Yes they do work very well.???. . . . . Has Spoil boards and Fire wood. . .:joker:

TrickyCNC
14-09-2012, 10:25 AM
I just wouldn't like someone to be put off, because all of a sudden it got too expensive !.MDF is 'almost' free LOL and a great way to learn. Major components can be re-used later if neccesary

JAZZCNC
14-09-2012, 04:13 PM
I just wouldn't like someone to be put off, because all of a sudden it got too expensive !.MDF is 'almost' free LOL and a great way to learn. Major components can be re-used later if neccesary

Yep I get your point.! . . . Respectfully thou I don't agree.!!. . . And here's why.?

Steel box section is relatively cheap and 50mmx3mmx7.5mtr lengths compares roughly around the same price has 25mm 8x4 Mdf sheet, I pay 26 per length of steel.
For a small machine then it would probably take a full sheet MDF. One 7.5mtr length steel will build the same small machine.

The sundries involved IE Screws, nut's & bolts etc both need. Steel doesn't have to welded and can be bolted thou for sake of 50 a welder makes slight work of it.
Just because something looks expensive or hard to do doesn't mean it is.?
The difference in performance and longevity are night and day and it's a one time affair still with lots of learning and enjoyment.!! . . . The fun just last's longer.!

Well that's my take on it anyway.!!

TrickyCNC
14-09-2012, 06:50 PM
I found steel to be more than that in 1 off's, it came down a bit if you bought 2 or 3 lengths.Maybe I'll shop around a bit, as I have nothing against steel except it's price for a 1st timer. I was pricing up for an 8x4 machine though, so was looking at a lot more steel and larger sections. Even then, I've heard of 2x3" steel box gantry's need beefing up because they were flexing when cutting wood.

Most people that build a machine, use it for a while and want to change it or make it bigger. So it doesn't necessarily need to last

Oh, and I built mine out of 12mm MDF :hopelessness: LOL, it gets 3 or 4 hours use most days for the last 6 months ... the parts come out the correct size and everything !

Tenson
15-09-2012, 03:45 AM
I got my steel from 'The Metal Store' who do some smaller lengths like 1.5M and 3m and also offer a free cutting service at the checkout stage (cutting not 100% accurate but that doesn't stop you putting your screw holes in the right place).

martin54
15-09-2012, 02:06 PM
Sorry hope I'm not hijacking this thread but I was looking for some info on rails & wasn't sure where to look being new to all this. Is there some sort of guide as to what diameter rail should be used when looking to build a machine. Realise there are probably a lot of factors to take in to account but just a very general guide that maybe gives some sort of idea what size rail to use for different length or width tables.

JAZZCNC
15-09-2012, 04:06 PM
Sorry hope I'm not hijacking this thread but I was looking for some info on rails & wasn't sure where to look being new to all this. Is there some sort of guide as to what diameter rail should be used when looking to build a machine. Realise there are probably a lot of factors to take in to account but just a very general guide that maybe gives some sort of idea what size rail to use for different length or width tables.

Think Jonathan posted a long head aching thread some where on round rails.? Do a search if you want your brain numbing.!!

Really thou it's not rocket science and it will ultimately boil down to a few factors like Budget and machine size/use. Here's a quick run down for typical DIY use.
Stay away from unsupported round rails unless short lengths =<400mm and even then 20mm or more.

My rule of thumb with Supported round rail is 16mm for small light duty machines =< 600mm. 20mm =< 1500mm 25mm => 1500mm
If Profiled linear rail then it's a completely different and 15mm will be more than most DIY users need in terms of load capacity's but maybe not physical size so 20mm tends to get used often has the bearings sizes etc suit better. It also tends to be more common second hand has it's common size in industry.

hope this helps.

TrickyCNC
15-09-2012, 04:39 PM
Also, depending on budget, and how much "DIY" you want to do, there are lots of other home made options, like angle and skate bearings, or steel tube, or steel plate and bearing tucks etc. etc.

JAZZCNC
16-09-2012, 01:16 AM
Also, depending on budget, and how much "DIY" you want to do, there are lots of other home made options, like angle and skate bearings, or steel tube, or steel plate and bearing tucks etc. etc.

With all due respect but in my experience thru helping others it 90% of the time leads back to the same thing.? Wasted time and money.!!
If they do get them working they are high maintenance and usually lacking in precision. I think I have helped folks who have used just about all the available options and all of them regretted it.
I know what your probably going to say " It's a cheap entry to CNC" BUT IMO it's also a good way to drive newcomers away has well when they try fail and give it up has a bad job.!! . . If they only knew before hand that for not lots of money and far less time they could have real rails and bearings that are far more accurate and reliable I know for sure they surely would have taken that route on hind sight.

Yes I know there are some very capable machines running DIY setups and someone you've mentioned earlier Gerry(Ger21) who I know quite well runs a very nice machine but think even he'll tell you it's not a simple affair and takes very good design, patience and care to get it right. . . . Do-able Yes, easily No, success rate Low, frustration levels high.!!

My advice save up and save the stress.!!

martin54
16-09-2012, 02:08 AM
Jazz I understand what you are saying but from the little I have seen during researching building a machine Profile rails are very expensive & this would be more likely to put me off trying to be honest. If you are lucky enough to have money then I suppose you may not think of them as being expensive but on the limited amount of money I have available it's just not really possible & at my age I would probably be dead before I could save up enough lol.
If I do manage to build a machine I'm not actually sure just how much use it would get or what sort of accuracy I would require. Yes I can think of one or two things I would like to do with it & I realise that once it is done I might be able to come up with other ways to use it but I still can't see it ever getting more than a few hours a month run time.

wilfy
16-09-2012, 02:17 AM
Jazz I understand what you are saying but from the little I have seen during researching building a machine Profile rails are very expensive & this would be more likely to put me off trying to be honest. If you are lucky enough to have money then I suppose you may not think of them as being expensive but on the limited amount of money I have available it's just not really possible & at my age I would probably be dead before I could save up enough lol.
If I do manage to build a machine I'm not actually sure just how much use it would get or what sort of accuracy I would require. Yes I can think of one or two things I would like to do with it & I realise that once it is done I might be able to come up with other ways to use it but I still can't see it ever getting more than a few hours a month run time.

he's not saying to use profile rails or else.. but there is an inbetween which are known as supported rails... now they are still quite a big cost of the total machine, but through doing my own research i personally have decided not to scrimp on rails or screws..

having said that if you check out trickyCNC's thread you can see what can be achieved by not using supported rails and by using mdf to build the frame, i feel this may suit you somewhat better.

the reason i asked this question about the round rails was to clear some things up... the outcome is that my planned 20mm round rails wold be better replaced by 16mm supported rails and have less room for error at roughly the same cost

Ger21
16-09-2012, 03:05 AM
Yes I know there are some very capable machines running DIY setups and someone you've mentioned earlier Gerry(Ger21) who I know quite well runs a very nice machine but think even he'll tell you it's not a simple affair and takes very good design, patience and care to get it right. . . . Do-able Yes, easily No, success rate Low, frustration levels high.!!

My advice save up and save the stress.!!

Did I miss something here? :concern:

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. :topsy_turvy:

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 (http://bell-everman.com/products/linear-positioning/servobelt-linear-sbl)

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. :playful:

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! (http://www.cnczone.com/forums/diy-cnc_router_table_machines/45844-start_new_design.html)


New Machine Build Z - CNCzone.com-The Largest Machinist Community on the net! (http://www.cnczone.com/forums/cnc_wood_router_project_log/138890-z%B2.html)

TrickyCNC
16-09-2012, 08:19 AM
Did I miss something here? :concern:


Hi Gerry

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 .

wilfy
16-09-2012, 09:01 AM
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

TrickyCNC
16-09-2012, 09:23 AM
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

TrickyCNC
16-09-2012, 09:47 AM
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 !

Ger21
16-09-2012, 12:41 PM
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.

JAZZCNC
16-09-2012, 12:42 PM
Jazz I understand what you are saying but from the little I have seen during researching building a machine Profile rails are very expensive & this would be more likely to put me off trying to be honest.

Yep quite agree but I never said profiled rails I said supported rails. Your new so probably didn't know that supported round rail is quite cheap when bought from china.

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.


Hi Gerry

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.

The MDF vs Steel and accuracy wasn't the whole debate it was has much the cost and effort.

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.?



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..

CNCRP type trucks cost more to build than buying supported round rail. The plate has to be good stuff can't be rubbish or it wears quickly and needs to be uniform in thickness else they bind. They are high maintenance regards keeping the plate free from chips,resin etc so need a wiper system in some cases.
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.!!

TrickyCNC
16-09-2012, 12:49 PM
So, to sum it up ...


....................................
So all I'm saying is YES wood can work very well but it ain't easy and it isn't always cheaper.!!

:adoration:

JAZZCNC
16-09-2012, 12:53 PM
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 !

Come on.!! . . . Do the same with an 8x4 sheet.!! Give it to Rolf Harris and he'll play you a tune.!!!

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.!!

TrickyCNC
16-09-2012, 12:56 PM
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 :) )
http://i121.photobucket.com/albums/o238/RichAAC-UK/IMG00082.jpg

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.

Ger21
16-09-2012, 01:39 PM
Gerry in all honesty now.!! If you had both options available IE full Access to machinery and resources would you build from Wood.?


It would probably depend on the actual machine. If I needed a 4x8 (or larger) production router, then it would really need to be steel. For anything say 4x4 or smaller, I'd still go with wood. Mainly because I like working with wood, steel not so much. And I know how to use wood and make it work well.
As you alluded to, wood is much cheaper for me than aluminum.

The gantry beam in the pics has $30 in MDF, and $35 in phenolic, and about $15 in glue. Say $100 complete for a 68" (1700mm) long beam. I couldn't get an aluminum structure that would be as strong for anywhere near that cost. The Hiwins that mount to it were $350 (20mmx1700)

Calculations are showing a deflection of about .02mm with a 200lb load. I actually believe it will be stiffer due to may laminate construction, which appears to be about 2-3x stiffer than regular MDF.



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'd definitely recommend the aluminum extrusion. Or is it aluminium for you guys? It costs more, but is by far the easiest for a novice imo.

I'm with you on the CNCRP carriages, btw. Don't care for them at all.

TrickyCNC
16-09-2012, 01:42 PM
remember Gerry is building a massive 8' x 4' machine , and he likes 'designing' (really likes designing! ), and he is getting the thin MDF for free, so laminating it.

Wilfy is building a 15" x 15" machine. Smaller than mine at 24 x 24 + which I built using very easy methods - no cnc or vacuum press etc.

Wilfy ... Have a read of this, if you have a few hours ! LOL!
You will learn more than you have learned already !

My Newest Desktop machine - CNCzone.com-The Largest Machinist Community on the net! (http://www.cnczone.com/forums/diy-cnc_router_table_machines/109390-my_newest_desktop_machine.html)

TrickyCNC
16-09-2012, 01:51 PM
ooh crossed posts....

I use wood too, and am very happy to make it not bend.

Others work with wood.

I was just trying to put forward the view, that steel isn't for everyone, and wood can do a very good job, after wood was being bashed as "no good"

different options for bearings too. Never tried CNCRP trucks, so can only go by C1's use of them. again , just saying there are alternatives, as John (Microcarve) will testify to with unsupported round rails and oilite bearings !

Even building a big machine in steel, isn't easy . the design needs to be right, or it will flex badly.

I guess I'm playing devils advocate for wood, and budget builds :)

TrickyCNC
16-09-2012, 01:55 PM
I'd definitely recommend the aluminum extrusion. Or is it aluminium for you guys? It costs more, but is by far the easiest for a novice imo.



for ease yes, but remember it's not even just a case of buying an 80x20 extrusion 1700mm long ! a BIG chunk of ally is needed to be rigid at this length

Jonathan
16-09-2012, 02:35 PM
for ease yes, but remember it's not even just a case of buying an 80x20 extrusion 1700mm long ! a BIG chunk of ally is needed to be rigid at this length

If you made a torsion box type construction out of aluminium or steel sheet that can be very strong compared to the volume of material it uses.
It's interesting to compare the young's modulus of aluminium and MDF:



We can loosely say aluminium is 14 to 28 (hard to find accurate figures for MDF) times stronger than aluminium based on the ratio of their young's moduli and similarly steel is 40.6 to 81 times 'stronger'. That implies that you can use 14 to 28 times less volume in aluminium than MDF for an optimally designed structure with each material.
Aluminium is currently roughly 5.50 per kg which equates to 14850 per cubic meter.
MDF, based on buying 18mm 8x4' sheets is 320 per cubic meter.
Jazz says 26 for a 7.5m length of steel, which is 4.4kg/m making steel 6627 per kg.


Therefore aluminium is 46.4 times more expensive than MDF per unit volume and steel is 20.7 times more expensive.

Taking into account the 14-28 ratio for the strength, we can conclude that the same strength structure should cost 1.7 to 3.3 times as much in aluminium (much more if you price up aluminium extrusion per kg), or 0.24 to 0.5 times the cost of MDF if you use steel.
So in conclusion... if just purely go by comparing the, for want of a better word, strength of the materials then steel costs less than MDF(!) and unsurprisingly aluminium is expensive. Clearly there's more to it than this simple analysis - as has already been alluded to there are many other factors in using each material that can override differences in cost.

martin54
16-09-2012, 02:52 PM
Jazz, my apologies. having read a few different posts on the subject I obviously picked up what you were saying incorrectly, easily done on the internet I think. As for supported round rail well I had looked at that but it seemed to be a bit expensive as well, never considered buying in from China as I know people who have had their fingers burned doing just that. Problem with buying in from China (well how I see it anyway) is that for every good supplier there are two or three that you don't want to go anywhere near & unless you know exactly what you are doing or have recommendations from people who have actually dealt with a company over there then there is a good chance you will get it wrong. Can be a very expensive learning curve & one that I would rather not take.
That's one of the reasons for me joining the forum in the first place, knowing next to nothing about a lot of the components used & where to source them the best place to go is to those people who have already done it.

TrickyCNC
16-09-2012, 03:25 PM
Jonathon ... keep it REAL - not theory !

JAZZCNC
16-09-2012, 03:27 PM
Jazz, my apologies. having read a few different posts on the subject I obviously picked up what you were saying incorrectly, easily done on the internet

Yep agreed and I wasn't in the least offend or upset just wanted to clarify what I said.

Regards buying from china then yes there's good and bad, but that holds true for lots of country's this one included.!
If you want a recommended supplier one that I've dealt with for years and bought 1000's worth and sent literally hundreds of people to then Chai @ linearmotionbearings is your man.

Regards the MDF vs Steel then each to there own but just don't dismiss it on cost is my advice, it's not, if at all, that much more expensive and It's a lot more work to get the same strength built in MDF.
Accuracy becomes mostly a factor of effort, skills and patience and again it takes less effort in steel.

TrickyCNC
16-09-2012, 03:43 PM
Regards the MDF vs Steel then each to there own but just don't dismiss it on cost is my advice, it's not, if at all, that much more expensive and It's a lot more work to get the same strength built in MDF.
Accuracy becomes mostly a factor of effort, skills and patience and again it takes less effort in steel.

unless like me (and Gerry) you have a table saw, and nail gun, as opposed to a Jr hack saw and hand drill ! LOL!

I can knock up a torsion box/beam gantry in under half an hour from MDF. I just don't even have the tools to cut or drill steel easily !
Like you say - EACH TO THEIR OWN is what it come down to. one is NOT better than the other. :)

I can work with metal, as my dad had his own metal fabrication company. Yes, if you have the tools, metal is very easy to work with. But not everyone has metal working tools. Lot's like me, have sawdust between their ears :) and prefer working with wood.

All I wanted to get across in my posts over the last few days, is that it can be done cheaply and very easily in wood/MDF. Which it 'seemed' wasn't accepted on this forum.

I built one ... it WAS EASY, and I know it works !

tell me I was wrong when I said , if you pick up that 7m length of steel, it will flop about like a floppy thing ! as will most steel 'off the rack'

martin54
16-09-2012, 04:06 PM
Being completely new to this I have no opinion on what is the best material to use to construct a machine as I simply haven't done enough research to be able to form a reasonable opinion yet but if you were to ask me which of the 3 main materials I would prefer to use then I guess the answer would have to be wood followed by aluminium & steel would come last.
This is based purely on the equipment I have personally & my own experience working with each of them. Sure everyone is different but personally I have the most experience working with steel but have next to no equipment I would be happy using to construct a machine from steel. When it comes to using wood I have the equipment I need & am confident using plus enough knowledge to be able to go ahead with a build. Aluminium falls somewhere in the middle as far as knowledge goes but not 100% sure about equipment & the price is high compared with the other 2 but I still feel I could do a better job with aluminium that steel.

Ger21
16-09-2012, 04:35 PM
Like you say - EACH TO THEIR OWN is what it come down to. one is NOT better than the other. :)

Let me jump on the other side of the fence for a moment and agree with Jazz, that yes, steel is better. But it is possible to build a quality machine from any materials, if the builder has the skills and knowledge to do so.

8 years ago, most people were building MDF machines, because there weren't many other options available. Most of these people ended up building better machines, usually from aluminum, as they realized the limitations of the MDF, and as more quality components became available.

Also consider that people have vastly different expectations, and vastly different budgets. I consider my standards and expectations are far higher than most. I don't think any other wood machines out there would come close to meeting my expectations, but I know that I can build one.

You can easily build an average machine from wood, with very few tools needed. If you know how to use them, you can do amazing things with a handheld router and straightedge. If you want a pretty good machine capable of making deep, fast, high quality cuts, then wood is not going to be your best choice, unless you want to spend considerable time designing and engineering, as I do.

I think if your budget is under $1500-2000 US, then wood will get you a decent machine. If you're budget is $2500 US and up, go steel or aluminum. The extra money spent won't be that much overall and you'll be better off for it.

TrickyCNC
16-09-2012, 04:48 PM
I mostly agree, except on the definition of 'better'. If you just don't have the budget **, then the 'better' (more expensive) material, just wont do :)
I just felt wood was getting a bashing on this forum - without any real reason , and wanted to make the case for it. it seems to have worked a little bit, so I am happy to have done that .


EDIT> ** or means to work with it

TrickyCNC
16-09-2012, 06:19 PM
Come on.!! . . . Do the same with an 8x4 sheet.!! Give it to Rolf Harris and he'll play you a tune.!!!

Get a grip man it's all about design and bracing.! With MDF/WOOD it means more bracing, much more to get near steel.



Sorry, I missed this one.

I completely agree :)

I know ... and you know ... , but some people might be inclined to think steel is just rigid.

JAZZCNC
16-09-2012, 06:21 PM
I just felt wood was getting a bashing on this forum - without any real reason , and wanted to make the case for it. it seems to have worked a little bit, so I am happy to have done that .

AH AH . . .Lets see if they still think the same after they have taken your advice.?????

TrickyCNC
16-09-2012, 06:43 PM
AH AH . . .Lets see if they still think the same after they have taken your advice.?????

if they build it properly, it will work :)

martin54
16-09-2012, 07:10 PM
Regards buying from china then yes there's good and bad, but that holds true for lots of country's this one included.!
If you want a recommended supplier one that I've dealt with for years and bought 1000's worth and sent literally hundreds of people to then Chai @ linearmotionbearings is your man

Can't argue with that Jazz but at least if you have problems with a UK supplier then it's easier to try & get hold of them plus it is generally easier to get after sales support from a uk supplier. Before I spend a lot of money with any supplier I generally look around & speak to other people who have dealt with them if I can plus it's easy enough for me to give them a ring myself & ask any questions I may have. Will have a look at the supplier you mentioned thanks, having looked at the prices from a couple of Chinese sellers I can see what you mean by the difference in price not being huge. Couldn't find anything close to those sort of prices from suppliers in the UK.

TrickyCNC
16-09-2012, 07:16 PM
Anyone getting stung with import duties and the like, from these chinese sellers ?

JAZZCNC
16-09-2012, 09:37 PM
Anyone getting stung with import duties and the like, from these chinese sellers ?

No Only extra is VAT which is based off the price put on the paper work and often they fill it out low so low Vat charge and a rip-off Admin fee by UK courier usually around 10.

JoeHarris
31-10-2012, 11:29 PM
I know I'm a bit late to add my 2p worth but I started out and more or less completely drew up an mdf machine before I started reading threads on this site and I think the wood bashing is very justified! Even on a tight budget steel Ali and 'proper' bearings make sense. I got change from &#163;30 for 1500mm sbr20 rails from china - by the time you have bought Ali angles and skate bearings you have spent that... For a comparably rubbish set up. To me it's a no brainer!

martin54
01-11-2012, 12:56 AM
I know I'm a bit late to add my 2p worth but I started out and more or less completely drew up an mdf machine before I started reading threads on this site and I think the wood bashing is very justified! Even on a tight budget steel Ali and 'proper' bearings make sense. I got change from 30 for 1500mm sbr20 rails from china - by the time you have bought Ali angles and skate bearings you have spent that... For a comparably rubbish set up. To me it's a no brainer!

Not quite sure where you shop Joe but it cost me about 30 squid for the ally & bearings for all 3 axis on a 4' x 2' MDF machine. For what you spent on your rails I bought everything needed to build the machine & had enough change for a fish supper or two. Excluding the electronics of course which pushed the cost of the machine through the roof by comparison.

Depends what you want to do with it really but the total cost of the machine worked out to about 600. I know a guy that has been using one for about 9 months now & thinks it's great, does everything he needs it to without problems. OK it's not used on a regular basis & it's not used for any heavy cutting which would be beyond it's capabilities but it's OK for what he needs.

Only reason I changed my mind was because I wanted to be able to cut materials that the MDF machine wouldn't be able to cope with.

JoeHarris
01-11-2012, 01:01 AM
Not quite sure where you shop Joe but it cost me about 30 squid for the ally &amp; bearings for all 3 axis on a 4' x 2' MDF machine. For what you spent on your rails I bought everything needed to build the machine &amp; had enough change for a fish supper or two. Excluding the electronics of course which pushed the cost of the machine through the roof by comparison.

Depends what you want to do with it really but the total cost of the machine worked out to about &#163;600. I know a guy that has been using one for about 9 months now &amp; thinks it's great, does everything he needs it to without problems. OK it's not used on a regular basis &amp; it's not used for any heavy cutting which would be beyond it's capabilities but it's OK for what he needs.

Only reason I changed my mind was because I wanted to be able to cut materials that the MDF machine wouldn't be able to cope with.

Fair played and he has a machine which is more than I can say for now. Just glad I looked on here before I started building in mdf...

martin54
01-11-2012, 01:10 AM
Yer I'm not saying your wrong, in fact I did the same as you only got a lot further before I found the forum. I am finishing the machine off now as I have been told by people on here that it would be best to do that now, just had to make sure the electronics I bought could be migrated to another build when I found out the MDF machine couldn't do half the things I want it to. lol