Thread: Accurate Strong Gantry
no tons here!! You have to read well the belt documentation! Find the belt tension formula on Gates web, calculate the tension for your exact setup and then using guitar tuner / or app on your phone/ tension the belt to the proper tension . This is a must to do it properly.
So the force you apply is not tons. Lets say its the force i can apply with one hand and using as a lever say 15mm screw driver against the motor and the frame. With say 20-25cm screw driver i exceed that force and over tighten the belt easily. Of course i have done it at the beginning with tuner, but now just know how a properly tensioned belt feels and sounds.
That means you have to design it so that you could lever somehow the motor with a wrench , screw driver or make some tightening mechanism. That does not mean introducing unnecessary idlers and tensioners.
So are you idlers bigger than 20 tooth pulley as per belts specification? Cause if they are smaller, misaligned or whatever not properly followed, may be thats the problem.
Yeah , i advised against long belts exactly cause people don't bother to read carefully 300 pages belts manual and maybe they miss something or do some basic mistake. Yeah, Deans machine works, but he has knowledge and experience so his machine is an example that there is no problem with the design, not that if say you, me or sb else could do it with the same success.
I will give you an example - Honestly how many people know point 6 below. About the idlers size and placement. Most people i have seen on the forums think that they could place idlers where they want and 99% of the idlers are made by 3x 608 bearings stuck together, which in diameter a much smaller than 20 tooth pulley/which is ok for 10mm wide belts but not 25mm as is this case/
Also look at number 4. The machine sides should be stiff enough.
What i mean is RTFM, do everything properly and all will be smiles and sunshine.
I just want to understand Sven's problem.
At the moment I am watching and listening to collect the proofed working solutions in order to make a good design.
It is useful information that you shared, I wish I were there in building
I read and will read any documentation what is necessary.
Thanks you more and more people knows about point 6.
The Following User Says Thank You to Clive S For This Useful Post:
I have finished watching it with sound off, complete it later.
As far as I know two standard steppers can simultaneously operate two ball screws
Hope listening to the narrator will make clear everything with easy servos
I was looking into the Hybrid servo from leadshine. There were some things that did not convince me:
-the price of drives and motors and all below combined cause at that price i jumped at top 400W second hand AC servos with drives.
-No AC, so still need a transformer, so rectifier circuit, ~45eur,transformer 80-90euro, time, shipping etc.
-basically the characteristics which are no better than normal stepper
-low encoder count
They could have gained me with absolute encoder for example.
I am not saying they are bad, just that according to me, and in my particular case, the servos seemed better option or stay with steppers. Still time will show, when the machine is ready.
Last edited by Boyan Silyavski; 01-12-2014 at 02:25 PM.
I would like to know where is limit in weight with the moving gantry that can be drive on reasonable way.
My redesigned one is still 100 kg made of steel with a 18 kg motor just for cheking.
I don't think I can go below 80-90 kg.
I don't care if it requires 20-50 W more just pls advice if this is over sized for a general strong gantry
The general opinion is that if >70kg you can not move it adequately with 2x3nm motors so you need bigger motors, which now puts you into position to find bigger but at the same time fast enough or go with servo, which to me seemed the better option.
Now i am looking back at your gantry design. What size are the profiles, why 4, why are not connected each other? Whats your idea there? At that size machine
2x 100x100x3 or 100x100x4 welded together with separation for ball screw or not /if back/ will be ideal. 100x100x3 weights ~9kg/m and the 4mm weights 12kg/m, So you co8uld still move that gantry by 2x3Nm nema 23
When I saw my friend machine with the moving bed I said I would not want to move to and fro 120-150kg mass with material so it would be moving gantry.
Entering to this 700x1000 mm machining zone with rigid steel design I have to revise myself.
I am seriously thinking of the moving bed option now it is just 5-700 mm longer space and can forget many trouble i.e the dual motor, heavier spindle
My goal is a bit better an more accurate machine than a router so called semi industrial so within a 4000 -4500 GBP budget I would like to reach the best performance.
Last edited by vargai; 03-12-2014 at 07:04 AM.
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