Suggestions needed from cnczone

[Jii Dee]

I'm wanting to build a machine that has a milling area of A4 size for the purpose
of cutting plastic card for models and the occasional pcb board.
I'm having a hard time deciding on a number of things. My instincts say that
a moving table design would be best as i won't be milling any heavy materials like wood.
I'm wanting to keep the size of the machine to a minimum, which sounds silly considering i'm prone to a moving table design, but i feel this would be the best approach. Having a relatively heavy gantry moving vs a light table isn't likely to be good for accuracy in my mind.
So the question becomes which design to use. Most of the diy router designs
are moving gantrys...though i do remember seeing one that had a moving table
along one axis with a stationary gantry that provided y/z movement...though
i can no longer find it. The machine one can find on intructables.com looks
appealing in terms of simplicity, but i fear it won't give me the accuracy i want.

The final question then becomes what kind/size of leadscrew to use. Having never done cnc before i don't have an instinctual feel for what would be suitable. I had a gander on the Mcmaster site and the precision/miniature
stuff i saw looked ridiculously small to me..mind you it was in inches and i'm a metric man but a dia of 0.14" sounds to me to be too small to be of use for anything(looking at my ruler). So does anyone have any suggetions? It seems the more i read, the more complex and uncertain the whole thing becomes.
Any reccomendations for sources of leadscrews would be welcome. I've looked at marchantdice on ebay but i have no idea if they're considered a decent supplier for what i'm looking for. thanks.

** Edit** Forgot to mention i'm in the UK so uk suppliers of leadscrews etc would be preferable due to shipping. chao

[epineh]

For a machine you describe I would just use threaded rod, get some 8mm or 10mm stainless steel threaded rod and tap some blocks of HDPE or Delrin with a normal tap for the anti-backlash nuts. This will give you very good accuracy for PCB's and small parts.

What you don't get is good rapid speeds, but for the size you are talking even one metre/minute is generally acceptable. Another advantage is that you won't need huge steppers to push it along, something around the 200oz/in mark will be fine, this makes your driver selection a little easier.

As for the gantry, that is a whole discussion in itself with many opinions, but mine is that it is easier to get a rigid machine using a fixed gantry/moving bed setup with the kind of tools the "average" person has lying around the house. Moving gantry is certainly better as the machine size increases, and if designed properly will be just as accurate as a moving table machine, there are so many variables that can affect a machine it is impossible to say that one design is better than the other, it depends more on the workmanship of the builder.

Having said all of that, I built a moving table machine with threaded rod for the leadscrew, I was happy with the result, but looking back I should have made it smaller, something like you intend to make. Here is the link if you want to have a look :

http://www.cnczone.com/forums/showthread.php?t=22101

I am currently retrofitting it with servo's so it is out of action for a while but intend to get it going again soon.

Good luck !

Russell.

[gandalf1]

My table top machine is the size you have mentioned,
I have just changed from M10 and M12 threaded rod to 12 mm x 3mm trapezoidal threads from Huco (min card order £10) but made my own tap from a short length of thread for the trial plastic nuts. I will when the pension permits buy bronze nut from Marchantdice as they charge the same for bronze as Huco do for plastic and not much more than 1/3rd the price quoted by Kingston Egineering who actually make them on site (£20 each).
I ended up with two metre lengths of thread £7 and a bit each) to be able to keep my costs down and now have plans for the thread left over.
Where in UK are you? I'm just South of Peterborough myself so maybe not far away.
My little machine uses 60 oz steppers geared down with toothed belts to give 0.01 mm per step, control using bipolar boards from Qasar and use MasterCNC from the Colin Usher website. I feel this software would be fine for you as it will work straight from a DFX drawing and ideal for panels such as you describe and it is free.
For more info PM me at home for photos etc.
John.

[Kipper]

Here's my thoughts.....Do a search on evilbay/fleabay for a guy by the name of widgitmaster...he posts to the UK for less than the UK suppliers will...Confirm with him first though!. You could always buy The Midi Router And then post back for deciding which stepper motors etc to buy....If it wasn't for the fact of the specs needed being posted in the advertisement...I believe the settings for Mach are all sorted too! I'd send him my money if I only needed/wanted an A4 work envelope. And be aware he machines semi naked

[martinw]

Dear Jii Dee,

Kipper posted this...

http://www.slidesandballscrews.com

Prices look good, but maybe the one he mentioned above beats them on overall cost.

IMVVVVVVHO, a moving table will always be a better bet than a moving gantry. The problem just boils down to the question of space. Either you have it, or you don't. Alas most people do not. And no, I have neither the space, nor either type.

Best wishes,

Martin

[Kipper]

Cheap start Almost enough to make me want to quit the home-made linear slide idea....Limited stock though!

[Jii Dee]

I think i'll adopt the time honored tradition of using what i can afford at the present time, then once i have some experience of just what the thing can do, then...perhaps...budget permitting upgrading bits and pieces like the leadscrews
or bushings etc. I've been toying with some rough ideas in sketchup, when i have time i'll put 'em on my webspace if anyone is interested. Don't be expecting anything super slick though.
Thanks for all the suggestions so far. I may be that i just haven't seen the thing
but i would imagine a sticky purely for the purpose of linking popular/reliable sites/suppliers etc of parts might be an idea.
Watch this..someone is going to come back and give me the link to just such a thread and include a "learn how to use search" for good measure

I have seen wigitmasters fantastic alu routers. I'm sure one of them would be just the ticket, however then i loose out on the experience of making one myself.
Plus those rigs are pretty expensive(from my point of view, yes i know they're cheap by comparison). Of course i'm sure that i'll probably end up spending more than that on my own but if i tease it out over a period of time i can fool my brain and my wallet into thinking that i've saved money.

[epineh]

I forgot to mention to have a look at the JGRO machine and the Joe2006 machine, both free downloads from this site and very good machines, the JGRO is a little smaller and may be suitable for you.

Russell.

[Jii Dee]

I've have seen the Jgro and Joe machines. Mighty fine looking. At one point i
considered simply down scaling the jgro design, but i still think a moving table
is what my needs require.
Heres some mock ups i did in sketchup of a few ideas. I'm sure idea 1 and 2 would work, its simply a matter of which one i did, but i'm wondering what people think of the 3rd one. I can see that when milling on the very extremes of the board i might have an issue with deflection...but to be honest i'm not planning on milling anything heavy like metal or wood, plus i added in a bracing peice of wood underneath. If people think this could work i might go with that as space is at a premium, but needs must.
Idea 1 and 2 Idea 3

The metal looking square blocks underneth the table are bushing blocks from merchanddice. the one in the 2nd pick is a SC20WUU, 10cm long

[Jii Dee]

Seeing as i didn't get a response to the 3 previous pics i plowed ahead at the weekend and started dooling based on the 3rd, shorter table idea.
It is far from complete in my opinion. For a start i think the z axis is going to be too heavy so i recon i need to either lighten it up or reinforce the X axis rails.

shot1 shot2 shot3 shot4

In case you're wondering, the Y stage in this travels on 2 of these but i'm beginning to have doubts as to whether this is the best way to go, or just stick with trusty skate-o-rails. I also think my X axis is actually sitting a bit far back, but i guess i won't know for certain until i make up my mind as to what kind of tool is going to be use and what method of collet/attachment device.
If anyone has any better ideas as to how to go about doing the Z carriage then i'm all ears. At the moment its kinda based off of Joe's 2k6 Z stage, but looking at this design i can't for the life of me se how he secures those Z rails without the use of blocks, unless he simply designed everything so tight that they literally just push snugly in, which isn't on the cards for me.

[Oldmanandhistoy]

Hi Jii Dee,

You may find this thread an interesting read http://www.cnczone.com/forums/showthread.php?t=15835 nice machine imo.

John

[Gir]

Of course i'm sure that i'll probably end up spending more than that on my own but if i tease it out over a period of time i can fool my brain and my wallet into thinking that i've saved money.

I like the way you think... Good luck on your endeavor!