Add-on CNC build log

Though I'd start a log to have somewhere handy to put random notes etc...

Copying from [ame="http://www.mycncuk.com/forums/showthread.php?t=1030"]my intro posting[/ame] with a few updates:

Plan is to add a removable CNC sub-table (X-Y) to my existing milling machine, a Deckel FP1. The CNC table would simply be clamped to the existing worktable. As the vertical head is easily removable on this machine I plan to make a new head which will incorporate the Z axis slide.

Beauty of this plan is that there is no need to create floor or bench space for a new machine and in a few minutes of heavy lifting (ideally crane assisted) the mill can be back to its normal manual use, and the CNC bits tucked under a bench. Or for simple profiling I could just use the X-Y CNC subtable with manual Z and existing machine spindle if I can't be bothered changing over the vertical head.

As the mill also has a DRO, this can effectively be used to add travel i.e. if I have a Y axis travel of 150mm on my CNC subtable then that can be effectively doubled (at least some of the time depending on the part) by CNCing the frist half, then using the milling machine's original Y slide to move exactly 150.000mm via the DRO and then do the rest on CNC, no reclamping required. Assuming that it's all aligned perfectly... which may not be entirely trivial.

If it doesn't work out as an add-on (I suspect it may just be too much hassle changing it over and aligning it each time) all I have to do is clear some space (ha!), make up a beefy frame, and bolt on all the bits to make a stand-alone CNC mill.

Will be machining mainly lumps of alloy I think, plus doing random bits of engraving.

Anyway what started me actually getting on with it was more or less impulse-buying this on ebay:

Slide/ballscrew assembly on Ebay

Got it a few days ago and looks pretty good, slides are in great shape. Ballscrew (16 x 5) is rolled and has a few tiny bits of pitting but it'll serve for now.

Current plan is to use that as an X axis. It will sit on 400 mm slides (just bought from Ebay USA - he's got some more BTW:

Slides on US Ebay

(Cheaper than any UK ones I could find, and even 15mm Hiwin stuff new is almost twice the price. Incidentally German Ebay also has loads of slides which seem often cheaper than UK - search for "Linearführung". Also some cheap alu profile e.g. this seller)

Anyway those NB slides will sit under the X axis Airy points on a 20mm+ thick alu plate which will be the machine baseplate (approx 350 x 450). Will be trying to find an affordable bit of flat tooling plate type alloy for this as my milling machine only has 250mm or so of travel so I can't easily accurately machine flat the 400 mm Y slide bases.

Ballscrews for Y and Z are yet to acquire. Z slide blocks (or may use 25 mm rails) also still to acquire. Not sure either yet what sort of spindle to use - will probably build one around a straight shank ER32 collet chuck. Not sure re spindle motor either - will see what comes along.

As for the electronics I'm planning on getting the 3Nm/5A system from www.diycnc.co.uk as everything I've read has been super positive about his stuff and I'd rather spend a few quid extra and get the UK support than buy drivers etc from China.

Power supply will be three 350W computer power supplies (free from a mate) in series for 36V, 20ish A :-). More than required most likely... but price is right. Will build in some nice analogue panel meters to show output.

All of the electrical connections (steppers, limits, e-stop, spindle) will be plug-in via XLR or similar plugs so once unplugged, the control box and computer can just sit under the bench too. Have yet to decide on controller software and CAD/CAM options.

Will use belts to gear down the motors by 2:1 or so (assuming other ballscrews also end up 5 mm pitch). Looking like 220 mm X travel and 200mm or so Y travel currently.

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My general way of working is to get all the various bits and pieces required in my hands and only then do a detailed design in CAD. This lets me scrounge around for the cheapest bits and bobs then adapt the design to suit.

This log will be a bit random note form... will do some pics later too.

Latest additions - got 4 x 15mm Hiwin carriages cheap off Ebay USA and a 500 mm C7 ballscrew from Marchant Dice via Ebay auction - £43 + post ...

Also got the steel enclosure as per here to house the electronics.

And BTW you can download all of the Hiwin rail, carriage etc CAD files in 2D and 3D for free here.

80servo? Yup he's got loadsa nice kit and pretty good prices IMHO. And he's one of those sellers who never sleeps and answers emails ridiculously fast...

Just had the DIYCNC kit delivered and also the MD ballscrew - looking forward to playing with it all after work!

Just got four Hiwin 15mm blocks from 80servo (for Z axis) - took just a week to get here, and no customs hit. Brand new for about £15 each all in. :yahoo: Will order some rail from MD at some point...

Still waiting for the Y axis slides also from him...

Also, anyone needing XLR connectors should check out this UK ebay seller. Just got a load off him - really nice quality and he does deals and combines shipping :beer:

Picking up computer PSUs from my mate tonight - turns out 200W not 350W each but should still be more than ample with three in series.

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got 4 x 15mm Hiwin carriages cheap off Ebay USA

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Are they the MGWs ? I was after them myself for my bed-top cnc lathe conversion. ;)

Mmm, must be different ones, mine are just HGH15C carriages: linky.

In that case, I'll off the fatwa ;)

Minor progress last night - opened up one of my donated Dell ATX PSUs and armed with a multimeter started looking around for the ground-to-case connection as per the various instructions around e.g. here. Aiming to link three PSUs to give a 36V 10A supply.

Turned out to take about ten seconds - just follow the black wires back down to the PCB and there was an obvious jumper (J23) over to the case via a screw. Bit awkward getting in to cut it so ended up desoldering and pulling it out with needle nose pliers. Checking after with meter revealed it did the trick, so I did the second one as well.

Still a bit of wiring to sort and need to get some power resistors to provide a bit of load for them to go at but that's the main hurdle over I think as far as the PSU goes.

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Originally Posted by bikepete

Minor progress last night - opened up one of my donated Dell ATX PSUs and armed with a multimeter started looking around for the ground-to-case connection as per the various instructions around e.g. here. Aiming to link three PSUs to give a 36V 10A supply.

Turned out to take about ten seconds - just follow the black wires back down to the PCB and there was an obvious jumper (J23) over to the case via a screw. Bit awkward getting in to cut it so ended up desoldering and pulling it out with needle nose pliers. Checking after with meter revealed it did the trick, so I did the second one as well.

Still a bit of wiring to sort and need to get some power resistors to provide a bit of load for them to go at but that's the main hurdle over I think as far as the PSU goes.

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Doesn't need much of a load. 100mA on each +5V rail is usually sufficient (50 ohm, 2W).

Thanks.

Can't wait until the new Maplin store opens up in September here in York - would be dead handy for this sort of thing, especially as it happens to be on my way home from work :-)

Register with Farnell... cheaper than maplin, postage free, no minimum order

Here you go 10 for a £1

Also check Rapid Electronics
http://www.rapidonline.com/

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Originally Posted by bikepete

Minor progress last night - opened up one of my donated Dell ATX PSUs and armed with a multimeter started looking around for the ground-to-case connection as per the various instructions around e.g. here. Aiming to link three PSUs to give a 36V 10A supply.

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Just a note for anyone else planning to do this... a safety point that is not stated in the article referenced:

When connecting two or more supplies in series to give 24, 36, etc volts - the one that isn't modified (i.e. still has the case connected to the negative output) MUST be the bottom one in the stack. I know its probably obvious but its not explicitly stated and is a big omission IMHO..

Thanks both - had ordered from Rapid before but had forgotten Farnell - do remember their paper catalogue from years ago!

Good point Irving.

Another point is that once you stack three of them up it gets pretty bulky. I'll also need to make quite a large cutout or series of cutouts in the back of my enclosure for all the fans to exhaust through.

Thanks for editing that Irving :)
(It's a real pain to edit with Opera on an PDA )

For some reason

http://cpc.farnell.com/

seems even cheaper than normal Farnell - and free shipping if over £10 today at least...

Quote:

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Originally Posted by BillTodd

Also check Rapid Electronics
http://www.rapidonline.com/

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Their prices are good, (50p for 100 CR25 resistors, single value) but postage @ £4.95+VAT

Just compared costs for my BOB & 3 axis driver - Farnell £32.21, Rapid £33.18 both inc VAT. Rapid don't have the range Farnell have.

Quote:

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Originally Posted by bikepete

For some reason

http://cpc.farnell.com/

seems even cheaper than normal Farnell - and free shipping if over £10 today at least...

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Cheaper on some items, strangely much more expensive on others and a much smaller range than the base Farnell service.

My test list: Farnell £32.21, CPC £40 (inc £4.25 delivery charge), both inc VAT.

Good price here on Ebay for e-stops. Ordered two. Already got one e-stop in with the DIYCNC bundle but want one on the driver box, one on the machine (X-Y section) and another on the Z-axis assembly.

Quote:

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but postage @ £4.95+VAT

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No postage for me, they're just down the road ;)

Just a note that this build log isn't dead - work and life intervened! Loads of parts still in a pile waiting to be worked on. Hope to get back to it in next few weeks and cut some metal...

I hereby nominate this as the 'longest-ever-dead build log finally revived'... evening all!

Life intervened in a big way along with pretty much zero spare cash or time available for CNC. Now getting together a little of both I hope! Have been looking in occasionally and lurking but not letting myself get really back into it until other things were a bit more sorted...

Did manage to get the control box finished and tested - see attachment - went a bit OTT with blinkenlights and meters but I like it :-). Don't like sticking out cables so put on the alu channel for the XLR sockets. The other bit of channel on the right hand side is where the mains comes in from the back (and there are also two mains outlets for spindle power etc which are also controlled by the main isolator switch). Did an OTT e-stop scheme with time delay relays, links out to e-stop a future spindle VFD, etc etc. Will do a proper write up at some point...

Attachment 8105

Anyway, the plan now is for a self-contained milling machine not an add-on as originally planned. I seem to have gone a bit more OTT with the frame than I'd anticipated too - managed to get a massive 180x180x12.5 steel beam off ebay from a friendly farmer for £50, and he torch cut it into bits for me. It weighs approx 64 kg per metre so handling it is an issue. The short bits at 750ish long are not too bad but the 1150mm column is tricky. Cleaning up the ends of the short bits is about at the limit of my milling machine... not yet sure how to handle the long bit. Will find a way...

Attachment 8106

Main reason for this posting is to help me decide between two frame designs. Ruled out welding as with such heavy section would have to farm it out and also don't want to deal with the distortion/creep issues.

Attachment 8104Attachment 8102

Quick and dirty mock-ups in Alibre. The PDFs attached should let you rotate/zoom etc.

The first is my original plan: two lengths support the X-Y table base, with the column passing down through both, braced with 75x50x8 unequal steel angle top and bottom, all bolted together with masses of M12 bolts (super cheap at Screwfix). Lots of holes to drill (may get a mag drill for this) but should be seriously rigid. Don't need to accurately machine any faces particularly (a potential problem as I have short travels on the milling machine, plus the difficulty of mounting the heavy column). Offers good support for the X-Y table base.

The second design I recently thought of and am rather tempted by. Column butts onto a single horizontal beam and would be bolted to it into tapped holes from underneath - then the side pieces are bolted on too with many bolts. I like the simplicity of this and it saves buying the angle steel. Not as many holes to drill. Easier to mount onto a bench or stand. Machining the (shorter for this design) column end and its seat flat should be just about do-able I think. Not sure it's as rigid though, especially for front-to-back loads on the column, and the X-Y base overhangs rather. The long diagonal cuts for the side pieces should be do-able with some repositioning, with the mill in horizontal mode.

On both the X-Y base plate is actually made up of three thicknesses of tooling plate which I bought cheap from the chap who recently advertised on here (Sutton Coldfield) after seeing them on Ebay. Can't really afford the equivalent thickness in new Ecocast at the mo (ground flat steel would be even better!). Wanted to use tooling plate to give an accurate base for the rails - max travel on my mill is 250mm so would need to reposition for 400mm rails. Plan is to 'laminate' the three thicknesses with epoxy, then also have this sit on a bed of epoxy to provide a level surface on the tops of the steel beams. Might be good for damping as well as avoiding the need to buy new materials :-)

Talking of damping, plan is to fill (partly if not fully) the main beams with sand to damp vibrations. May use plastic guttering down the middle of the beams to reduce the volume required. Will also have to make a very solid stand (weight could be approaching half a ton eventually!), but waiting to find some cheap steel for this.

Alignment (tram, nod) will all be taken care of in the Z axis, details to follow. Spindle also still to be decided - will likely make it interchangeable between three different ones (stepper driven for tapping, plus brushless DC type for engraving, plus VFD/three phase motor for general purpose). Keen to avoid the weight of a big motor being driven up and down with the Z, have some ideas for that...

So - anyone got any thoughts on the two frame designs? Main objective is to maximise rigidity - may as well make the most rigid machine possible with the materials I have. One issue is that the surfaces of the steel beams aren't terribly accurate or clean - the beam has been bashed around a bit in its previous life - so bolting sections together will not necessarily result in very even contact, though I'm pretty sure it'll be sufficient with multiple M12 bolts torqued up tight. Epoxy between the surfaces might be an idea if necessary, though I'd rather try without it first simply to avoid the mess involved...

On reflection I'm going with the original design (double beams at the bottom) but I'd better do it properly with epoxy between the main joints. I'll see if I can machine the surfaces where the column intersects the base beams to a tight sliding fit, too - when clamped this should lock up solid.

Not much else new, still cleaning up the ends of the beams, takes a while for each cut:
Attachment 8161

And sorted out cable entry to the Z stepper: small diecast box off ebay with a rather crude cable clamp bolted on and a hole drilled in its bottom face for the motor cables, then epoxied onto the stepper:
Attachment 8162

I used 0.75mm^2, four core SY cable for this - motor is stationary on this axis so won't be flexing repetitively (CY cable usually preferred for that). I know 1.5 mm^2 is usually recommended for stepper wiring but that's getting a bit fat to go into the XLR plugs neatly. Using this calculator: ePanorama.net | Audio | Video | Circuits | Electronics Design and assuming 5A current max and 2m length max (will be shorter) gives under half a volt dropped due to cable resistance... acceptable I think, and they also say 0.75 is good for 6A in instrument cables.

Pleased with the cable labelling at the plug end - printed text onto self-adhesive mailing labels on the laser printer, cut to size and wrapped round the cable. Then protect with 1/2" heat-shrink tubing. Works a treat:

Attachment 8160