Thread: round rails
Gerry in all honesty now.!! If you had both options available IE full Access to machinery and resources would you build from Wood.?
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'm with you on the CNCRP carriages, btw. Don't care for them at all.
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!
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 :)
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.
Last edited by Jonathan; 16-09-2012 at 12:42 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.
Jonathon ... keep it REAL - not theory !
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.
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'
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.
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