12-27-2008, 04:01 PM
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| | | Join Date: May 2008 Location: Malaysia
Posts: 10
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8020 & Belt driven. Need input :D | |
I'd been collecting stuffs for a JGRO build for quite some time, the only thing i haven't got yet was the electronics (BoB, PSU, Driver and Stepper).
One day a kind elderly man who've had a near death experience and got insurance money from it decided to donate some money for me to finish the project, he was fascinated about the idea that a layman could build such a precise machine. The fund is more than enough for me to finish my JGRO, so i made decision to make a bigger machine that would stand a commercial usage so that if it happens to be so i could then repay him. I don't feel good about receiving such sum from someone i've just got to know. After all, he has also bought a nice semi-pro SLR (with 3 flashgun) and sticker plotter machine for a friend to kickstart this friend's business. So it seems like a good idea to add a mid/full size CNC router. Budget :US$1450 - US$1700. Let's just assume $1450 is all i have and spare the balance for contigency (custom tax etc.)
I live in Malaysia. Raw materials are quite cheap here. Anything produced locally is cheap compared to prices i see on the internet of stuffs in the US or Europe. Steel and aluminum is also considerably cheap, which is why you might see my thread in the Mechmate forum, steel is now US$130 per tonne here. Linear motion (Hiwin type), stepper motors, drivers, ballscrews however is rather expensive. I've seen cheaper price on US and UK sites, like MotionControlProducts.co.uk or automation4less.com for example. MCP ballscrew for example i find is impressively affordable, even though the screw isn't ground, but it's sufficient for a DIY budget build.
Table Size & Design :Most boards (MDF, Plywood, PE, PC, Acrylic etc) comes in size of 8x4 in my country. The ability to provide space for a fullsize board onto the table is convenient. Howevery i need to also consider the fact that i might get a job someplace 3 hours away, sometime early 2009. So i need a design that if dismantled, no parts would be longer than 6 feet so it could fit into my car.
After playing around with sketchup, i think it would be wise to design a "nearly square" 8020 build where the Y (table length) extrusion could be used as the X support shall i find it's time to make the 'final' full size version. This way there would be no waste.
For 8020 i'll be using it's China clone.
40x40 mm costs US$52 per 6.0m
80x40 mm costs US$95 per 6.0m
40x40 & 80x80 angle bracket cost $0.85
It's a pity that they dont have the linear motion accessories.
Linear Motion :I'm not sure yet on what system of linear motion to use.
The cost of Hiwin type of linear motion is prohibitive. I've found a local company selling one of those type of rail system, the brand is CPC (taiwan), but still too expensive for my budget. A short block costs $28 each and 1500mm 13mm rail costs $371 per piece.
a viable option is rod shaft. But i couldn't find a local supplier that sell open type block, i'm afraid using end supported shaft might cause deflection.
Kawada 20mm chrome plated hardened shaft costs $37 for 1500mm (they have up to 3000mm).
Kawada 20mm linear bearing with pillow block costs $10.
I will search further for open type block.
i appreciate if anyone could explain if end supported 20mm rod is good enough for an 8020 gantry? kawada spec sheet is here
if all else fail, i will look into building one like this.
Linear DriveBelt Drive, of the type which the motor will be at one end of axis. I like the motor on the moving part type especially after watching Bell-Everman's ServoBelt, but this is my first build so i try avoid anything needs to be machined. I try to design while keeping in mind to make it adaptable for such technology later on.
This prospect of a possible conversion from 4x4 to 8x4 also means that leadscrews/ballscrew is not suitable. Y leadscrew will no longer be reusable.
Some cnczone members already achieved 1000 ipm using belt and report no problem with his setup. Chain is cheaper, but i think it will be sloppy with the grease and all. The only thing need to be replaced is the belt. I don't know much about belting and it's cost, so advice needed on the right type of belt and some estimate of it's cost. I read somewhere that T5 type belt is the most suitable for linear motion drive, but i try not to buy stuffs from US. There's an automation supplier nearby that sells Mitsuboshi belt system. They also sell KHK gears shall you guys think it's better for me to go the rack & pinion route.
Any input on costs estimation is very much welcomed.
Electronics :
Motor : 4 x MotionKing 34HS9801 (4.9Nm/694OzIn in Unipolar). Net cost US$354.00 (inclusive of shipping).
Driver : 1 x GeckoDrive G540. Net cost US$330
BoB : Not required.
PSU : 50V 12-14A. Will source one locally. Shouldn't be more than US$100.
About my choice to pair G540 with 34HS9801, it's all about budget. 34HS9801 produce quite a torque. It's enough to run a Mechmate if geared (it has to be geared to increase precision anyway). Now that i don't think Mechmate is suitable for me (yet), it's more than enough to run any other machines especially if made of aluminum or MDF. Even if it means i lose 40% of torque it still means i still get a good 400OzIn. I've seen people using 200-300 OzIn motor on a 4x4 yet still perform well. Marcus from Gecko have said the 34HS9801 paper specs may work nicely with G540, it's inductance is well within the range of G540. If it's too strong then i guess i'll just reduce the power supply voltage/current a bit. Please advise if it's not okay to do so.
limit switch and cables will be financed by my own money, it shouldn't cost much. As a rule of thumb, whatever it costs in the States, divide by 3, provided it can be manufactured and available locally.
Spindle :Emmm... I have a Dremel. Hehe... I'll spare some money for a router. If later a full size router costs too much (shouldn't be) a palm router or trimmer router would do. Found one for $70. A friend, professional woodworker and owner of furniture workshop told me he bought one for $130. I should be able to buy one, but i leave this to be last item in my shopping list because upgrading is a simple matter of changing attachment plate to the z axis. Stuff paid :
Stepper Motor : $354
Driver : $330
balance : $766
now, how to get the most out of that....  |
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