Steel frame cnc router design/build

[JAZZCNC]

Thanks kingcreaky - i've spotted a Ferm 100A unit on ebay that comes with basic accessories that looks like it should be enough to get me started.

No Don't buy 100A welder you need more Amp's spare for duty cycle. Biggest problem with cheap Arc welders is low Duty cycle or better put the time you can weld before the it trips out from over heating is short.!!
Now your not going to be running long welds or in a rush so it wouldn't probably be a major problem but for £10-20 more you could get 140-160A and have decent duty cycle with less stress on welder.

Like Matt says 6013 rods but more important is ONLY buy decent quality IE: branded name BOC, MUREX etc none of this rubbish you see at Aldi or car boot sale etc and keep very dry.

Regards 6013 it's the AWS standard (American Welding society). Rods usually have prefix like E-6013 and it breaks down like this.!!
E= Suitable for MMA welding and flux coated
60= Minimum tensile strength in KSI(Kilo-pounds(force) square inch) IE 60Ksi = 60,000psi pounds(force) per square inch.
1= Suitability for welding positions . . . IE: 1= All positions 2= flat & horizontal positions
3= Flux coating type and suitable Current types IE: 3= High titania potassium (Rutile) AC or DC+ current.

See here for a good Arc tutorial and loads of info.
Arc Welding Tutorial

I'll look at frame and come back to ya.!!. . . . Get ya hard hat on ready. . .Lol

[JAZZCNC]

Ok I'm back with my wrecking ball . . Get ready.!!. .

So I see you've been paying attention with using the high sides and gantry sat on rails design which is great for twin screw machines but in this case it's actually hurting your design badly.?

Because your wanting to use single screw (with option to upgrade) this means having gantry cross brace but with those high sides it means having long gantry sides which are acting has levers. They will flex, twist and stress the bearings, they will also resonate like crazy, this all transfers back to the work or like Matt hinted at make the bloody thing dance around the room if bad.!!. . . Not good design for this way of doing it.!

Really because of your budget restrictions then your going to have accept a bit of compromise on design.? In this case it's flexibility regards cutting height and materials you'll be able to cut. The high sides with gantry on rail design works very well if you want strong rigidity and flexibility of lifting the bed but it just don't work for use with single screw.

So your going to need a way to keep Gantry sides short has possible but yet high enough to give clearance you'll need for cutting what you want to cut.? . . . . It's simple enough you can't have high clearance and high strength,it's always a compromise with this way of doing it.
So best thing is first decide the lowest clearance you can work with a build frame that allows gantry to be kept short and strong.!

There's several ways to build frame to allow this and I'm not going to try telling them all I'm just going to show the sort of thing I'd build for this Budget and upgrade has you can afford way of doing things. (It's just something I knocked up to show principle not finished design)

This gantry/frame design will be very strong and use's roughly 2.5 x 7.5mtr lengths of 80x40x3. It can easily be converted to twin ballscrews.
It's shown has desktop machine to keep cost's down but making it free standing would be simple enough just cost more.

Hope this helps and carry on it's perfectly do-able to build strong machine even on budget.

Oh one more thing or Tip with modelling.? . . Get accurate dimensions or better still Cad models for the things you plan to use, like ballscrews, motors etc has it's easy to think I'll use this or that like this and then it doesn't fit or interferers with something else.

[CraftyGeek]

Thanks Jazz.
I have made a few changes since I posted that last image...the main one being the removal of the single leadscrew option. I've decided that I want to do a decent job of this, which means it'll take me longer to get it running - but the end result will be worth it...so dual leadscrews from the start - hopefully driven from a single motor.

I'm still very much tinkering with the overall dimensions - I have shrunk the z depth & reduced the overall height a bit as well.
I hope to have a bit more time to spend on it tomorrow to make some more changes, then i'll come back for another slap on the back of the head :-)

On the gantry you posted above - I assume that the spindle mounts between the *ahem* open legs?
Question...does the distance fore/aft that the spindle is mounted (relating to the x rail bearings) have any effect other than allowing the cutter to reach different areas of the table?

[JAZZCNC]

On the gantry you posted above - I assume that the spindle mounts between the *ahem* open legs?

Yes just slapped some bearing and front Z plate on to show see pic.

Question...does the distance fore/aft that the spindle is mounted (relating to the x rail bearings) have any effect other than allowing the cutter to reach different areas of the table?

Some would throw math's and moments of inertia etc shit like that at ya but in reality it's nothing to worry about really, so long has your not daft about it.
I just try to keep the overall weight balanced on the X bearings. Mostly It's just balancing act between losing or gaining cutting area.

[CraftyGeek]

Chaps - i'm dithering about with the gantry quite a bit...can't come up with an approach that i'm happy with yet.

I've been looking around at a lot of build threads on here & cnczone...I haven't seen a gantry design that seems to suit what i'm doing.

Firstly - do I need to be concerned about weight. ie, am I ok using steel box or is this something that I may regret later?

Secondly - Jazz, the mock up design that you posted earlier in this thread - the gantry on that has 2 lengths of steel box attaching to vertical end pieces. I assume this would have to be a weld - my concern here is alignment & the lack of adjustment. Is there another way of going about it?

I'm trying to keep the range of materials that need to be purchased down...i've been looking at using aluminium box with a vertical plate - but it starts upping the budget quite quickly.

I'll also drop in a note here that I also really like the simplicity of KingCreaky's gantry...cheaper than some options, but the ally rect box & front plate add up quite quickly.

Any thoughts?

[kingcreaky]

Chaps - i'm dithering about with the gantry quite a bit...can't come up with an approach that i'm happy with yet.

chaps, im going to stick my neck out here, and before I even say anything Ive only made one machine... but what I do have in common with CraftyGeek is I am also DIY, so this was my gantry approach, slate it if you will, its not perfect but it was all done by hand with pillar drill hand punch and ruler.

[JAZZCNC]

Firstly - do I need to be concerned about weight. ie, am I ok using steel box or is this something that I may regret later?

No but within reason, weight is your friend when cutting has it allows deeper depths of cut, obviously there's a limit and it affects other areas of machine like motors, drives, screws etc if you go too heavy. Stay within 80Kg and you'll be ok with steppers.!!. . . Heavier than this and you'll be into servo territory.

Secondly - Jazz, the mock up design that you posted earlier in this thread - the gantry on that has 2 lengths of steel box attaching to vertical end pieces. I assume this would have to be a weld - my concern here is alignment & the lack of adjustment. Is there another way of going about it?

Doesn't really matter because all the adjustment is taken care of thru the rail mounting and were gantry sits on X axis bearings. . . The only requirement is that it's not twisted.

There are several ways to do different and I just drew this quickly to give an idea of easy and strong which go with single screw.
Really how you go about it depends on the job in hand, like in creakys case it was simple but would only really be suitable or woodwork type cutting any harder material like aluminium or if higher accuracy say for fine engraving, by that I mean in brass or Aluminium, PCB's etc where required then this is when weaknesses show thru quickly. . . . Resonance and vibration being the enemy has hollow aluminium box isn't stiff enough.! . . . It's also only works with twin screws and with single screw wouldn't be very good at all.!!

Your problem or complexity/weakness comes from using single screw.!!

[JoeHarris]

Your problem or complexity/weakness comes from using single screw.!!

Get onto old Chai he'll sort you out with an extra screw for a bargain price and you won't look back!

[CraftyGeek]

See here for a good Arc tutorial and loads of info.
Arc Welding Tutoriall

Had time to have a quick look at that page this morning - that's a fantastic resource, Thanks!

[CraftyGeek]

I'm looking for more local sources for materials. I have a good local steel yard 5 miles up the road that i've used several times before - so am happy to use them for the framework, but their aluminium stock is low, a bit battered & unreliable.

I've found that there's a branch of Blackburns Metals not too far from where I work - does anyone have any experience with them as a supplier for aluminium?...quality & prices ok?