hey guys
im weighing up building a pretty large format but basic 3 axis table, im in central brisbane. (probably curring area of 2450 x 1250 x 300) rationale is that at some stage i will want to make a kit for something out of a sheet of marine ply, is there any strange reason why i should start with a smaller machine and do stuf in bits? (apart from space, of which i dont have much!)

now im sure im not the first one to be asking these questions, if there are other threads on here that cover this stuf please let me know.

The frame i can construct from aluminium channel, i was planning on using a system of aluminium angle and roller bearings [as used on that MDF machine mach 3 or whatever] above and below the channel sections for my bearings, but what are the benefits of those track-type linear bearings? they seem easier, but i am trying to be cheap!

anyway is there a local (or at least australian) place to get bearings like that?

also i need the usual; motors, screws, nuts and bushes, controller, power supply and router/trimmer. where from? ebay seems to have a bit of stuf, but not everything.

my Z travel will be around 300mm for doing 3d stuf, how do people go about extending the router collet so that it can reach into a 250-300mm 'pit?' (and not touch the sides) And if you want to do a 300mm vertical cut for instance, how do you without a 5-axis machine?

also for a machine this size, what should my decisions be on motors/screws, id rather go fast and innacurate, but it has to be cheap.

so anyway im a uni student, study architecture, but i build boats in my spare time with any spare cash. having one of these machines will expand my horizons. moral is, must be cheap, i have about 2 grand set aside bit if i can get change on from that itd be good.

am i dreaming?

cheers
nick

Hi nflutter

a mate of mine just finnished building a large router 5ft x15ft here (http://www.mechmate.com/forums/showthread.php?t=1218) is the link

cost him about $3500 plus motors and controllers and the design is free helpfull forums aswell and the machine seems to work really well we are using it to cut out plane parts
and he is about to cut out canoe for another mate

cheers
Harty

hey Harty
thanks mate great thread, pretty impressive build! and the result is immaculate, right down to the stickers! yeh mine wont look that good.
It would be nice to have a donor machine for the electronics, sounds like it worked out pretty well really. all that info like where to buy parts etc is really useful i think ill be using that thread as a reference
nick

Linear Bearings in Brisbane can help. I got a 3m screw and all my bearings from them.

Regards

Noel

an update:

construction has started, most of my aluminium is cut out and ready for a weekend of drilling holes. The design has evolved quite a bit, and im sure its not perfect but im quite satisfied with it at a starting point. im sure ill be changing it and adding bits and pieces as i go. like all designs it is a compromise between a few main needs - weight, accuracy, cost etc.

its all cut from extruded aluminium planks, like for builders/painters/tressels. these were the cheapest and biggest strong looking bits of extrusion i could get. i think theyll work well. a main design criteria was for it to be easily movable, light, so weight was traded off for extra stiffness

on some good advice ive decided to use timing belts as racks, or proper steel racks and pinions, for the x axis. Possibly will use the same for the Y axis as well. i prefer timing belts (glued to 10 x 25 alum. extrusion) because there is potentially less backlash. is this a good assumption? there is a problem gluing it down, but ive seen it done so ill have a crack. contact adhesive. good stuf. not really..

also unless i gear it down, the gantry will move 42mm per revolution of the motor instead of 10mm with the screw. is that a bad idea? it means i get 0.3mm resolution on that axis. i think i can live with that.

are there any drawbacks to having a screw on the Y and a rack on the X?

for the Y and Z ill use whatever lead screw i can get cheap, and make a nut out of solid teflon. ill look into that linear bearings place, cheers for that noel.

motors will be the 430oz-in ones (pack) from ocean controls or similar. they should be enough i reckon.

attached is an image, (ignore the crappy galv. texture) i couldnt upload the rhino file (.zip) for some reason, so pm me if you want me to email it to you.

cheers
nick

You better bief up those legs a bit or she'll be a shakin

Noel

Hi nick

running direct drive you will see the steps in you curves aspecially the tighter ones unless you get good microstepping drives 450oz-in should be heaps
if you spring load you pinon for the steel rack you will have trouble seeing any backlash and it certainly wont be enough to cause you any trouble for your machine
I would expect the same could be said for the belt but i have no practical experience using belts in this way i have looked at it but had trouble finding a cheap source in long lengths

as for the screw i just purchased 2 c7 grade 25mmx5mmpitch ball screws and nuts with the ends machined size was 25inches long and 58inches long from this guy (http://stores.ebay.com.au/linearmotionbearings)
delivered from china including freight $504au very good to deal with also
the closest price i got in oz was $1900au for a lower grade
they are for a beaver mill (bit bigger than a bridgeport) conversion that i have just finished and they seem to work really well

keep up the good work its worth every cut and bashed finger the first time you machine moves on its own

and what noel said

cheers
Harty

yeh point taken, ill just make the legs short. like 100mm. or maybe some diagonal braces, have some leftover steel so no worries. have been thinking about that but i decided to wait and see.
cheers for the link harty, that guy is cool. ill have a sift through, everyone says "dont bother with acme threads, get ball screws. you wont regret it."
so i might go that way.
nick

nick

ballscrews are brilliant had a small mill drill i cnc'd 6 years ago after about 2years i converted to ballscrews and it gave me a new machine better cuts faster speeds could climb mill no backlash very sweet would not use anything else on a mill
acme is good at raising the table on your drill press not cnc

cheers
harty

Hi nflutter

Dreamer, yes you are, but dreaming is the best thing in the world.
I spend 20.000 dollars, on a machine you dream about. 4' x 8' cutting area.
See you @ the BBQ in July.

Cheers

Jorgen

Hi Jorgen
its nearly done actually. cost about $3000 so far including electronics, ive pretty much bought everything. Machine is rolling, electronics are together, computer (free) is sorted, just gotta install the mechanical components and motors and im off. hopefully. some design issues with that which im sorting out, and dont really have time at the moment with uni.
went for rack and pinion drive on the x axis and y axis, ball screw on the z. got steel racks for $25/m and ball screw for $40 (400mm). chassis cost about $700 in materials. the machine is stiff and im happy from an amateurs perspective with the design, will see how it goes. only concern is that the motors might be undersized, but i can sort that out if they are. i just went with 'a bit bigger than was recommended', but they still look small.

heres are some kinda old photos from my phone,
nick

Hey, just an update
machine goes, im fairly pleased with it. tolerances are within what i wanted, motors seem fine. doesnt shake, twist or bend any more than i allowed for. the problem i get with racks is that the x axis is a bit bumpy, or jolty, because the pinions are too light against the teeth. my axle may be a bit bent too, because i used stainless rod and it wasnt perfectly straight. i might get a better one now i know what i need. something to play around with.

heres a video
YouTube - MOV06722

some pics too. the first one is prior to final assmebly, the other one is of the first real cut. material is compressed bamboo, its probably about the same as hardwood. the bit is just a standard 1/4" router bit, single flute.

just getting the G-code side of things up to scratch, using mastercam to create the toolpath. seems pretty simple, though ive had to delete the first few lines of code to get rid of this annoying blip where the the zero value for the z axis resets to +20, and then it goes to the new zero without the spindle on. which is potentially not good because it just jams the bit into the material. so i was using foam, but i have to sort that out at some point.

also on the go is a cable management thing, a vacuum and probably a dust-proof booth for it, like a big clear curtain. but i have a couple of jobs that cant wait so ill have to make do for a little while

at the moment i get rapids of 3000mm/min and cuts timber with no real problem at between 500 - 1000. the cut in the video was a bit slow, im trying to work out how to ramp it up in mastercam so that i can see where the limits are

speaking of limits i have one annoying limit switch that trips occasionally, mot sure whether its because the wire isnt shielded or because the switch is faulty somehow. or because the connection is bad. might sort the last one out better and then see.

cheers
nick

cutting like mad, doing architectural models, mostly terrains out of particleboards, softwoods and hardwoods. even machining 100x100 hardwood posts with good accuracy and speed. cutting up to 4000mm/min and have had it up to 9000 without missing steps in lighter materials.

heres an example - its approx 1200 x 1200 x 60 terrain model of north bank, brisbane. 1:1000. its a bit rough, i think i put it back on and re-surfaced it at a finer spacing

anyway thanks to everyone on here who helped me out to get this thing together and going. these forums have been a great resource.
cheers
nick

Wow, congratulations, it looks to be going really well! :)

it looks good.

Hi Nick,

Congratulations on your machine – it seems to have fulfilled your design objectives and only exceeded your original buget by 50% - that's pretty good.

I am attempting a somehwat smaller machine (1420 x 940 x 140) and I considering using aluminium planks for the frame – but I couldn't think of a good way to join them to each other and to other components. Seeing your machine has encouraged me to revisit the idea.

:confused:

How did you join/fix your plank sections? I have looked at all of your photos and the video – but I can't see how you did it. Did you use self-tappers – or drill access holes to allow for nuts and bolts?

Hopefully you still check back here occasionally and can enlighten me.


Regards
Wanna