I found this on cnczone and reading his posts i think you are correct and it was used for cutting stone, he was in Indonesia. If i chose the earlier option of 2 box sections sandwiched between plate, would it be ok to use 10mm plate and use 20mm on the Z axis only. Just want to weight up all the options at the moment.
Just out of interest, i'm looking at using 1605 and 2005 ball screws, belts and pulleys if possible. I had a go at the weekend cutting the infamous Aztec/Mayan calendar, approx 12" size, after 3 hours i had cut less than a 1/5th. How much faster roughly would using ball screws make a difference.
Last edited by deannos; 26-01-2012 at 02:35 PM.
20mm is a good size plate for the Z-axis.
The efficiency of ballscrews is roughly twice that of ACME screws, so it will be significantly faster. For the Aztec calender acceleration is much more important as it's lots of tiny moves. The bearing nut thingy you're using will make the difference slightly less. The main advantage is 5mm pitch versus 2mm pitch - the kinetic energy in the screw is significantly less if it's rotating 2.5 times slower.
The most accurate comparison you're going to get is comparing with my machine, as I sold you the screw. I got 6m/min with the screw your using and 42:13 pulleys on Y. I ran it at less than that with smaller pulleys as that was too close to the critical speed of the screw (see my build log for actual values). With 42:14 (I think) and a 10mm pitch ballscrew I got 60m/min. That's much more than you'll ever need so I've left it on close to 1:1 to get better resolution and acceleration.
First I'm not knocking the Calculations or saying they are wrong but your both missing the POINT. . . .!! IT WILL DO THE JOB AND DO IT GOOD.!! . . . IT'S CHEAP AND EASY.!!
It's easy to build with absolutly minimal machining or drilling, far less Jonathan than my first design which yes is stronger but much more expensive.
Jonathan good design is about building the best machine to do the intended use accurately and effiecently. A good designer will always design a machine to do the required job with a certain safety percentage designed in and no more. Any more is just wasted expense and ineffiecent.
Working On your design criteria then you FAILED because you could have used far heaver gauge box section or steel plate rather than Aluminium or why not go the whole hog and Cast some Iron castings.!!. . You had the knowledge,equipment and abilty so why not.? . . . . . Because it didn't warrant the extra cost and effort to accumplish what you intended to do with the machine.
I've just checked price with my supplier and I can get 1x1800 & 2x1000mm 178x102 RSJ 8mm steel for £75 no vat cut to length delivered.
That will do both the gantry and the X axis. Or Just the gantry would be £37.!!
So Profile/plate way:
Ali plate 4mtr x 150 x 9.5mm = £86inc vat + £10 delivery = £96 (400mm left over)
Profile (as per my other design)1800 x 90x45H = £41.50 x 2= £83 + £10 delivery = £93 . . .or 1800x45x45 (As dean's design) =£43 +£10 del = £53 . . .OR. .
80x40x3 steel box section £39
Plus lots more Nuts and bolts so another £10
Total £199 OR 45x45 £159 OR Steelbox £145
RSJ 1800x178x102 £37
Nuts bolts £5 (far less required)
Also a lot less drilling work which will also add to the cost because of worn/snapped drills.!
Now taking the RHS route and regards the Calc's and price stand point theres also the issue that like for like dimensions where used. Now 180x100x6mm RHS is not a common size and the nearist would be 160x80x6mm Which is £160 so no saving there and it won't be as easy to work with as RSJ.
Also the calculated strength of the I beam is going to go up because of 8mm thickness not 6mm and the RSH will drop slightly due to lesser dimensions, it will still be stronger but the difference is less but more the point the Ibeam which is already more than suitable will increase.!
This is my POINT.!!
Last edited by JAZZCNC; 26-01-2012 at 03:26 PM.
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Dean yes 6" x 3/8" (150x9.5mm) plate would do fine and the Cad models I drew used them dimensions except for gantry sides and bearing plates which where 19mm plate and I'd recommend you use.
I totally agree with you that I beam would be sufficient for cutting wood. I just wanted to show Deanos the improved performance of RHS to explain Jonathan's point about how it could be better if you wanted to make it do more in the future.
I also can't fault your logic and argument on the cost side because that is very important for a home build.
Just for completeness, and not to start a war (!) I've done the calcs for the sizes you mention:
Flange/wall thickness ___8_______6
Mass (kg) ____________34______32
Tool deflection (mm)______0.009___0.00067
[all assuming 150mm between gantry centre and tool cutting tip - the moment arm trying to twist the gantry]
So the I beam still looks reasonable.
Last edited by routercnc; 26-01-2012 at 08:38 PM. Reason: format
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Looks like bloody good odds to me especially from such a simple and quick buildIf the nagging gets really bad......Get a bigger shed:naughty:
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