Evening all, I've had an avid interest in CNC for about 3 or 4 years, bought a CNC machine off a chap that never arrived and got my fingers burnt. Hey ho... I've got the itch to build myself one now and would like to make it out of Aluminium Extrusion rather than mdf.
It would have to be a work in progress machine as I can't really afford to go out and buy everything at once and then sit piecing it together. Do you think it would be better as my first build to follow some plans, or adapt some plans? (assuming I can find some suitable to adapt). I'm quite practically minded and not too daft when it comes to tools. I've only found one (well one free) set of plans that use extrusion and thats all in imperial, which is a bit difficult to get here The only thing I'm really unsure of is the mechanics and making sure I get it right. I don't have the ability to make nice diagrams to show you my ideas, i'm old school with a pencil, ruler and a piece of paper :heehee: I can alter them quickly then too!
I'm after a cutting area of around 1000x800mm and 3-axis. If I designed my own I'd probably start on the X and Z axis. I get the feeling I should start from the ground up and build the base first then up and up, but I'd like to tackle the hard parts first.
So anyone reckon they could guide a newbie with some extremely daft questions? :heehee:
So far I would opt for Hiwen Rail and Bearing blocks on an aluminium extrusion frame... opinions?
Many, many thanks!
Can't help with the mechanics of the build,Monk as I'm in the same boat as you at the moment,but here's a site for all and every piece of extrusion you might want for the build.
You have to completethe formto download two seperate PDF's one for Pricing and tother for profilesof what extrusion they do.
The drawback is...Minimium order is £100
I'll help if I can.
Can you scan and post your scribblings to give us a rough idea of where you are at?
Sounds like your on the right track with ali extrusion and linear rails tho,
We find ourselves in much the same boat: similar position, similar design goals and similar decisions- as far as they go :) I can offer little in the way of construction help as I've never done this before, but I wish you luck.
I'm still at the point of deciding if the end justifies the cost (1), to that end I need both a cost and an understanding of design limitations and to that end I need a design based on my budget. All a bit chicken and egg (2), lol.
To get the ball rolling I've downloaded a couple of CAM packages to look at and a trial copy of Alibre Design, collecting models of various parts that may make it into the final design (3) - testing parts is cheaper this way ;-). I hope this will get my head into an engineering mind-set and playing with some design software feels to be the right place to start, after all there is little point building a computer controlled machine if you have zero understanding of the software required to make it all work :)
(1) Cost... Ouch. The old mantra, buy cheap buy twice, haunts me every time I look at ball-screws. Hiwin rail and blocks just make me cry and I know a lower speed spindle will be a must and.... I'm probably preaching to the converted here.
(2) Silly phrase, evolution of course dictates the egg must have come first.
(3) What the ....? Register, register, register, everywhere I go it appears the same. I'm trying to give you guys some money, why do you make me go through loops and hoops to get a model of some profile or even just a price list? Grr. "We want to track all our prospective customers". Fine, do that, but isn't email address enough? Name, address, telephone number, colour of socks, so old fashioned, so last decade </rant>
Last edited by ecat; 11-08-2010 at 12:08 AM.
You might find the following post useful. I listed some terms which might help, plus others have added helpful comments:
Maybe we need a glossary of terms section in this forum which anyone can add to...?
Anyway, you can always go to the local library and get a sketch scanned in and email it to yourself, to then post here. Picture paints a thousand words as they say. By the way, if you need to cut aluminium profile, several of us have found out you can use a chop saw with metal cutting blade. Do some trial cuts on wood to get the blade as square as possible.
Hiwin profile rail and ali profile make a great combination. Almost as good, but cheaper, is the supported rail and open bearing. 16mm is popular, as sold by Zapp and others.
Post away . . .
Thanks for the advice guys. I have a scanner at home so I scan my sketches/drawings/doodles in and post them up. Seemed everyone was doing stuff in CAD and making it look really smart and professional, then you'd look at mine and go erm... :heehee:
I will try and get a drawing up of my proposed Z and part X axis up in the next few days, I'm away for the weekend and got loads to do before hand so time is a bit tight.
For the extrusion I have found a place KJN Ltd off a search on here that does good prices, also Marchant Dice does extrusion but is pricey. However for small bits it may be cost effective and they cut to requirements! I've looked at Zapp as well for rails and bearing blocks. I kind of know where to get parts, its making them a) fit together and b) work
KJN sell their own extrusion and also Bosh Rexroth stuff as well, if you look closely each item will show which is which. I have found that for some of the Bosch stuff can be got cheaper from Hepco ( http://www.hepcomotion.com/en/mcs-ma...m-pg-14-get-31 ) You have to juggle between the two sites doing a bit of maths. KJN also do a whole lot more sizes than you can see on the site ... just email and ask.Tim G-C
“I disapprove of what you say, but I will defend to the death your right to say it.”
(attrib. Voltaire but written by Evelyn Beatrice Hall "The Friends of Voltaire" 1906)
Ok no sniggering at the back! :heehee:
I had some time at work to mess around. Ok it only shows three components but its a start! This is the x-axis I was going to make out of 4080 extrusion. Fixed together in a L shape with the rails on the top and bottom. Will this be strong enough over approx 1200mm or should the extrusion be bigger. Also when the bearing blocks are fitted, do I build off the blocks to account for the ballscrew between the rails, or should I mount it behind and build the z-axis to sit acutally over?
If I fixed the aluminium plate or extrusion for the z-axis to the bearing blocks it would sit quite close to the x-axis.
Its not a question of strength... that'll hold quite a weight... its a question of rigidity... how much will it deflect, vertically and horizontally, in the middle under load?
In the catalogues you will find design tables which shows how a particular type of extrusion will deflect and that will give you a clue. If you look at page 49 of the Hepco catalog they give the formulae (use the simply supported arrangement as a worst case) and page 50 the parameters for their 80x40. If you work the math it suggests a deflection of 0.00084mm in the 80mm direction (vertically) and .003mm in the 40mm direction (horizontally) for each Newton of load for a 1200mm length. (someone check these, they seem a tad low)
Your 'L' structure is slightly more complex. The vertical deflection is inversely proportional to 0.5 * w * h^3, where h is 120 and w = somewhere between 40 and 80 (I'll hazard a guess the effective value is around 55). So if a simple 40w 80h deflects X vertically, your complex beam will deflect less, roughly 25% of that. Similarly in the horizontal the ratio is roughly 30%... these are very much rough and ready, others (Ross, routercnc, et al) can do the more detailed analysis... and tell me I am wrong!
Typically the horizontal load for a wood router is due to cutting forces and 5 - 10N would be a good allowance, giving a deflection of roughly 0.003 * 30% * 10 or 0.01mm horizontally. Vertically you have the weight of the z-axis and the router/spindle - that could easily weigh 5 - 6kg or 50 - 60N, so a deflection of .0008mm * 25% * 60 or 0.012mm in the centre of a 1200mm run.
Incidentally the deflections for a piece of 80w x 120h would be .003mm horizontally and .008mm vertically, better but at the expense of added weight.
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