View Full Version : BUILD LOG: New Build Log ... 2440 X 1220 X 300

15-10-2014, 03:36 PM
Well I posted in General as an introduction but didn't even get a 'Forget It' comment. So I will try again.

I have need of a machine to cut Ply and MDF from 8X4 Sheets. I am thinking an Extrusion based build using a Kress spindle. 20mm Aluminium Plate for Gantry Sides, Rack and Pinion for the long (X?) axis and Lead Screws for the Y(?) and Z. Or possibly one Lead screw positioned centrally under the bed (prefered option)

One end open to facilitate loading would be necessary. Here comes the Interesting (but not original idea) I would like to build in a 4th Axis across the machine for spindle work. If it's not feasible then I will find a Lathe instead.

Suggestions for Min/Max Extrusion sizes and appropriate linear bearings eg Hewin or supported Rail (I am concerned there may be too much dust/debris for Hewin type Bearings) would be much appreciated.

Questions about motors etc can wait but I will again be looking for any help I can get.

A Workshop (read Shed) is being built to house the beast as we speak and will be ready by the time I have collected all the bits and pieces needed (I hope).

15-10-2014, 04:02 PM
'Forget it' is not a bad start but I'll stick my neck out and give it a go. :cower:

First it's a big machine for a first build, not impossible but just saying.
For spindles most use the 2.2kW or 3kW water cooled ones, make 2.2kW your minimum size.
20mm plate sounds good for a lot of the parts.
Not sure about using extrusion as I've no experience with it but a lot of people use it. Steel would be cheaper, for the frame at least, but you'd need to weld it.
Rack and Pinion is not the first choice but it might be okay for your size machine and application.
Ball screws are what you need for Y and Z. If you use these for X also, then one centrally mounted is a definite NO NO, you need two, one each side.
4th axis integration is fine, it just means the machine will be longer to accommodate it.
Hiwin or similar rails are much preferred over round supported rails but are more expensive.

Wait for more people to chip in then using that information knock up a drawing. Unless you already have some CAD software, 'Sketchup' is commonly used because it's free and easy to use
Look through the build logs and get ideas there. http://www.mycncuk.com/forums/253-DIY-CNC-Router-Build-Logs

15-10-2014, 04:19 PM
Okay thanks for that ... I'll look into spindles. I can weld (in a fashion) so I'll look at steel pricing. I've just had a lightbulb moment (don't laugh) If the bed was correctly stressed I could mount the ways for the 4 th axis into the bed. Just remove a section of bed to reveal the space. The centreline of the 4th axis does not need to be higher than the bed. I have an unused Wood lathe I can use for the ways and tailstock, a Stepper/belt to drive the Headstock assembly.

15-10-2014, 04:29 PM
The links I posted here might be of interest ?


15-10-2014, 07:32 PM
Is Mild Steel box 100 X 50 X 3mm okay for frames or would I be better using 5mm

15-10-2014, 08:28 PM
Well I used 50x50x3 and 100x50x3 albeit on a smaller machine. These sizes were ideal and provided the design is right there should be no flexing of the structure. You do though have to consider that the 3mm thickness is not much if you intend making threaded holes in it, and you will for the X rails at least. In my case I glued a piece of 30x6 flat strap inside to beef the threaded thickness to 9mm.
I think you should go with the 5mm thickness

15-10-2014, 10:57 PM
First let me say for a first machine this will be challenge so don't go rushing into it without carefully researching and drawing up a detailed design.

Forget driving gantry from centre and really forget using ballscrews for the long axis unless your prepared to get into rotating ballnuts etc. Rack & pinion is the way to go for the long axis. Using R&P brings it's own challenges but they are much easier and cheaper to solve than ballscrews and mostly just means choosing the correct motors and ratio's.

Profile is fine and easy to work with but it's very expensive compared to steel. For a machine this size then you'll want minimum 80x80x5 steel.
Build it in such a manner that you don't really have gantry sides, make the sides of the machine high and sit the gantry directly on the bearings. There are several builds here that use this setup so just look around the build threads.
Hi-win style profiled linear rails are what you need so forget round rails and they easily handle the debris, infact much better than round rail does.

Regards a 4th Axis then if your wanting to use like a Lathe then forget using a stepper motor.! They just don't spin fast enough or have enough torque.
Even if you want just a rotary axis for 3D work then I'd look at using a Rotary Axis converted with a Stepper motor.? Reason being is the Resolution. Steppers connected to pulleys don't give enough ratio so the resolution is low and for better or more detailed work then much higher ratios are preffered.

Make the Axis rails longer than the bed and put the 4th axis on the end has messing around with removing portions of the bed will soon become a pain. Also if the 4th axis is below the bed this means the Z axis is over extended giving much greater chance of flex and poor finish. Having the 4th axis on the end higher up makes much stronger giving better finish quality.
Another reason for the top rails extending past the end other than 4th axis is that you can machine the edges or ends of panels or cut dovetails etc this is very useful in many ways.

Like I say this will be a very big challenge for a first machine but it is do-able but not if you rush into it so go carefull, be patient and ask questions.

Oh and forget Kress spindles they are toys. Like eddy recommends 2.2Kw or larger is the way to go.

16-10-2014, 12:45 AM
Thanks for the pointers.

Okay, let me get this right. Minimum 80X80X5 steel box ... Build frame with bed set to give max Z needed directly off the top of the frame (I haven't worded it very well but I know what you mean).

R & P for X and Y with Lead/Ballscrew for Z. Hewin rails on all Axis. 15 or 20mm or what?

Rails mounted on face of Gantry or top and bottom, which would keep Z close to Gantry?

I thought thick Ply for the bed with replaceable MDF as a spoil board.

The machine will only be used to cut Ply, MDF(Ugh!!!) and natural Timber.

Good thinking re running the gantry past cutting area for edging etc.

I already know the maximum dimensions/diameter that the 4th axis work requires so maybe I can build it into the walls of the frame parallel with the Gantry(the work is not complex or detailed, imagine an egg timer but with a spheroid shape of smaller diameter instead of a narrow neck with a tenon and slot at each end They are the upright supports of the Rocking Horse frame).

Is there a way to work out what size motors/ gearing I will need to get good accuracy/repeatability/resolution?


16-10-2014, 08:28 AM
20 mm rails minimum, forget 15 they are a pain to grease for one thing, I would never use that size again.
Gentry Y rails top and bottom keeps Z close to gantry
I use ply for the bed 2 x 18mm birch glued together and bolted down, plus spoil boards. It's strong but will flex under load if not well supported by frame cross members underneath.
The 4th axis is great but you could machine the supports in 2.5D as two halves you glue together lengthways.
I think Jonathan posted something about motor sizing, use the forum search box.

Clive S
16-10-2014, 08:35 AM
I think Dean was suggesting R & P for the long axis only with ball screws for the other two. ..Clive

16-10-2014, 08:58 AM
Thanks guys ...

16-10-2014, 04:32 PM
I think Dean was suggesting R & P for the long axis only with ball screws for the other two. ..Clive

Yes I was but R&P on both isn't a problem it's just easier and better to use a Ballscrew and you can easily getaway with one at this width so best to do so.

Regards Motor sizing then this is where it's easy to go wrong for first time builders building this size machine. You will need Nema 34 motors for the X axis with R&P, roughly around 6Nm depending on Gantry weight etc. But these need the correct drives to get the performance you'll require and it's here most new builders often get it wrong. You will need AC drives to give the best performance not the usual DC drives you'll see around. These are more expensive or seem it until you factor in that they don't need a DC power supply and run direct from the mains. This offsets the cost makes them not so expensive but still more than DC drives but worth every penny and a must for good machine running Larger Nema34 motors with higher inductance.

Regards R&P you'll want Mod 1.5 and with a ratio between 3:1 & 5:1 depending on resolution and speed your aiming for and motors used etc. Resolution required for wood is not massive so not a big issue but speed can be more important so you'll go with ratio and pinion size that gives the best balance of both.
The pinion size used along with ratio will determine the pitch and resolution. The usable Motor RPM will have to be factored into the equation to determine the best balance of speed, resolution and torque.
For instance a Mod 1.5 pinion size of 20 teeth will give a pitch of (20x1.5)xPi= 30xPi= 94.25mm pitch which is massive but then we apply 3:1 ratio so this becomes 94.25/3=31.42mm pitch which is still quite large but better. Now factor in that typical Nema34 motor gives aprox 900Rpm of usable speed before torque drops away then you have Rapid speed of aprox 28,300mm/min with a resolution of aprox 0.2mm based on a micro stepping of 1600.!!
Now great Rapids but lowish resolution which will be higher than the calcs suggest as micro stepping isn't or shouldn't be relied upon for resolution.
So lets do the same for 5:1 ratio. So 94.25/5=18.85mm pitch 18.85 x 900 = 16965mm/min with resoultion closer to 0.01mm better and about right.

Hopefully this will give you an idea of how to determine the ratio and pully sizes etc to get the speed and resolution required.
The pinion size is important for both pitch and tooth engagement, too small and not enough teeth engaged in rack so can slip or shear teeth etc. Too large means larger pitch and more ratio.
More ratio means larger Pulleys on the driven side which makes building harder. Ie 20T @ 5:1 ratio means 100T on the driven pulley which is a large pulley.
Often when the ratio gets large then your better with a gearbox but comes with factors that need to be looked at, backlash being one and expense along with extra motor power for the extra friction compared to timing belts which are very efficient compared to gears in gearboxs.!

So again as you can see it's a little more complex than just saying I'll use R&P and if you don't size and factor these things like motors, drives and ratios etc then you'll 99% get it wrong and be disappointed.

With ballscrews it's easier in some ways except when it gets long like the X axis due to whip and interia etc. Even on the Y axis you will again still need to size the ballscrew size/pitch, motor, drive relationship correctly. Here it will go something like 20mm Dia 10mm pitch with nema34 6Nm motor on AC drive.
Wouldn't use 16mm dia as it's just a little on the long side and 20mm dia is a little large at this length for nema23 motors. Staying with 34 motors and AC drives for X & Y will give a better balanced machine electricly.
Use 16mm dia 5mm pitch for the Z axis with 3 or 4Nm nema 23 motor running 80Vdc drive with 68Vdc PSU. This will give you best performance with a heavy spindle setup and some overhead on the drive and power.

Hope this helps and shows why you need to go slow and design correctly.!!

16-10-2014, 06:56 PM
Thanks everyone. BUT all change!! (for the better I think, read cheaper and Easier!!) I have spent the day on the floor with paper templates that I will be using. I have discovered that I can fit the the templates onto 2 half sheets IE 1220 X 1220 with very little waste.
So Ball screws all round and Hiwin 20mm blocks and rails.
I have sketched a frame for your perusal and comments that I will post shortly (when the kids have finished homework). Is there a preferred format?

16-10-2014, 07:17 PM
Just upload jpeg snapshots of the drawings from whatever software you use.

16-10-2014, 08:05 PM
First Draft.


Gantry to fit on 20mm rails atop the frame. Z travel needed 350mm

16-10-2014, 08:50 PM
I think you would be better with something on these lines.

You don't need a back in it and your top beams are not suitable for carrying the X rails due to the legs coming up through.
If you notice, my top beams are bolted to the frame, this allows for shimming to get it within a gnats knacks, ready for the epoxy.

16-10-2014, 09:00 PM
No very difficult to build that way and too weak in key areas. Not enough bracing at bottom and the top rails will be very hard to get on same plane.
Look at this and Work along the same lines as this with regards bracing etc but without the adjustable bed if not required with slightly lower sides and you won't go far wrong.
This machine is in progress and will have 4th axis on the end when it's finished.

Also Why 350mm Z axis travel.? That is quite a lot and if your planning on cutting anything hard you'll get lots of flex and resonance giving a poor finish.

Edit: Opp's Eddy beat me too it.!!. . . or like Eddy's done. . Lol

16-10-2014, 09:37 PM
Why 350mm? Because the whole idea of building the machine is it to perform two tasks, firstly to cut forms from 18mm Birch Ply and then when the forms are assembled by stacking one on top of the other to mill to the final shape. If I cannot have 350 mm of cutting depth I am throwing money away.


I was hoping to be able to store ply sheets ( I buy 10 at a time) under the bed. However with all the triangular bracing everywhere that also appears to be a No No ... Oh well back to the drawing board.

16-10-2014, 09:46 PM
For some reason, after reading you're other thread, I had it in my mind you were laminating at 90 deg. to that shown in the photo.
It's okay milling to 350mm depth but what length cutting tool do you envisage using ? you don't want the spindle crashing into the job.

16-10-2014, 09:47 PM
I'm sure I said fore and aft ... nose to tail anyway now you see the size of the profiles that are cut.

Typical Forums ... lol ... Half say no need for Epoxy on a machine cutting wood ... the other half say it's absolutely necessary.

The Legs didn't come through the tops!! 'capped' they would have been flush ... I hadn't planned running the rails across them anyway. Thinking about it they could have been raised at the back to provide hard stops and mounting limit switches.

16-10-2014, 09:52 PM
Typical Forums ... lol ... Half say no need for Epoxy on a machine cutting wood ... the other half say it's absolutely necessary.

This is for you to decide.

16-10-2014, 10:00 PM
you poured your epoxy in small sections ... how did you get them any more level than the posts they were poured on already were?

16-10-2014, 10:00 PM
Ok well in this case then you'll be ok to some degree because the roughing of the forms doesn't require any decent finish and the 3D tool paths will be small step overs so very little tool pressure. Just build the Z axis strong with a good design and you'll be ok.

Regards the Bracing then it will still be possible to store sheets under with a few tweaks here and there so not a big deal.

16-10-2014, 10:06 PM
you poured your epoxy in small sections ... how did you get them any more level than the posts they were poured on already were?

Sorry I don't understand this, I poured all at the same time in one big section i.e. two rail beams and two bridges.

16-10-2014, 10:11 PM
Typical Forums ... lol ... Half say no need for Epoxy on a machine cutting wood ... the other half say it's absolutely necessary.

Ye because the half that say you do haven't built one before. . .Lol

No doubt you'll read in various threads that I say build in has much adjustabilty as possible. There's a reason for this and I'm sure eddy and those that have built larger machines will agree being able to tweak any error out is a big help when setting up.
Your design with top rail having no adjustabilty is restrictive and rely's completlely on you making sure both rails are on the same plane when welding up or using the Epoxy method and completly relying on it working. This is fine for someone like me with plenty of experience and some nice long accurate straight edges etc but if your tool limited with little experience then believe me you'll be grateful for that adjustabilty.!

16-10-2014, 10:31 PM
Eddy, I saw the little square pours and the 'joints' between the uprights and the rail beams and thought that was where you had laid the epoxy, then I read backwards ...

Okay so epoxy will correct minor differences in the rails and the beams, where else can I build in adjustability I don't include basic adjustment in the feet (they were there to take up floor unevenness)

I can get the rail carrying beams milled top and bottom to give me a sporting chance and have a the lip milled in for the datum edge of the rails.

16-10-2014, 11:26 PM
As Jazz said, try to design your top rails with adjustability built in instead of relying on epoxy to save the day. If you look at my frame design you will see 10mm plates at the top of each upright on the frame. These have 10mm bolts going through them to fix the top rail in place. If I need to adjust the levels of the top rails, with this design I can use shims under each plate to tweak the levels. I may still need to use epoxy but the chances of getting away with it are better with this design.


17-10-2014, 12:25 AM
I assume you have fitted a plug into the uprights with a tapped hole then drill a hole in the top of your beam large enough to get a socket through followed by a smaller one through the lower part for the bolt. Close the holes when shimmed and pour epoxy onto the upper surface of the beam ...

17-10-2014, 09:50 AM
No, I bolt upwards through the plates into the bottom of threaded holes on the top rail.

17-10-2014, 09:57 AM
No, I bolt upwards through the plates into the bottom of threaded holes on the top rail.

Like he said, and with your 5mm section it might be okay but if not, as in my case, I glued in a piece of 30x6 flat strap using Gorilla Glue to increase the wall thickness.

17-10-2014, 11:20 AM
Okay thanks, yet another use for the dreaded Gorilla!! So the plates overhang the uprights enough to fit bolts through ... I get it now.