Build Log: 3-4 Axis Mill/Router

Fairly new here but I've finally got started on my design. The machine will be used for cutting ally, tool steels and other metals, it may do the odd bit of timber/MDF/plastics.

I'm hoping to get a working area of around X1200 - Y700 - Z250 so obviously it'll need to be strong.

The frame is 80 x 40 x 4 steel box section, I've not drawn the stand yet but it will be constructed of the same.

The gantry sides are 800 x 300 x 25mm Ecocast. They will be better supported than currently drawn, some good old viagra bits to be added . The crossbars are currently drawn 100 x 50mm. I'm hoping I might get away with some ally extrusion to try and keep the weight down but not if it's going to compromise the strength too much.

I'm hoping I can afford HIWIN RG Series linear guides @ 25mm for the Y and possibily 20mm for the XZ.

I've thought about having 2 linear guides per side of the Y axis, top and bottom. Overkill do you think?


Any thoughts on the design so far? I'm not the sensitive type so fire away.

Cheers
Ian

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Originally Posted by IanS1

Fairly new here but I've finally got started on my design. The machine will be used for cutting ally, tool steels and other metals, it may do the odd bit of timber/MDF/plastics.

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This design won't cut Tool Steel or Mild Steel it's absolutely no where near strong enough. It will only just about handle Aluminium.

If you want to cut Tool steel or any Steel then I'd suggest converting a Milling machine or at the very least build a Moving table machine and massively beef up the frame.
A moving gantry machine is not the right choice and the Gantry and frame would need to be 5X stronger than what you have designed and then require the correct spindle.

The twin rails while adding some extra support in one area actually weaken the machine in another has the rails they sit on can no longer be supported and thr frame work between them would need to be made very strong with lots of triangulation braces. You could gain just has much support and save money while increasing machine strength with just one set of rails/bearings by making the bearing spacing much wider. Obviously this would require the machine to slightly longer to achieve the same cutting area but would be far better.

Honestly scrap this design or heavily redesign and beef up if you want to cut any Steels other than Alu.!!

Perhaps I'd better kurb my enthusiasm for cutting tool steel then Jazz, to be honest I'd be happy cutting ally.

Right, so the 2 linear guides either side wouldn't be of any real benefit. That's good, that'll save me a few quid and hopefully make the overall design easier.

What about the linear guide width, 25mm OK? Bearing distance, there's about 105mm between the ends at the moment. Would you recommend at least doubling that?

Thanks for your input.

Would skinning the frame around the table with some 5mm thick sheet steel beef it up enough or would I need some angular trusses in between the uprights and base cross bars too? I was going to skin the inside around the table with some sheet steel anyway to help contain the chips.

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Originally Posted by IanS1

What about the linear guide width, 25mm OK? Bearing distance, there's about 105mm between the ends at the moment. Would you recommend at least doubling that?

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when you say 25mm I suppose you mean Rail not carriage width.? If so then yes that will be fine if your using supported round rail but massive overkill if using profiled rails like Hi-wins. 20mm will be fine for profiled, even 15mm will handle far more load than you'll throw at them but 20mm carriages workout easier to use has they larger and suit better.

To be honest the Min/MAX distance for separation on Y axis( Which I call Z axis) will depend on several factors like number and location of ball-screws and rail used. 300mm total bearing plate width will be fine in most cases and less if using profiled rail and twin screws close to the bearings. 200mm will even work if the gantrys strong.

Regards the gantry then you need to seriously beef up this area with bracing. I'd also use wider stronger Cross beams between gantry sides.

Skinning is ok for containing chips and looks etc but wouldn't rely on it for strength and the down side being it's very resonant and you want to avoid resonance if possible.
Stronger base frame work is the best way then skin for cosmetic reason if you feel the need.!

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Originally Posted by IanS1

The gantry sides are 800 x 300 x 25mm Ecocast. I'm hoping I might get away with some ally extrusion to try and keep the weight down but not if it's going to compromise the strength too much.

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Can I ask why you went with ecocast?

I don't think ecocast is structurally any stronger than 6082, (Jazz can probably confirmor refute this) it is just precision ground which is useful for mounting rails on but not required for the gantry sides. With the dimensions you provided, 6082 from aluminium warehouse would cost £90 +vat each as opposed to £125 +vat each for ecocast.

Edit to add, don't worry too much about the weight of the gantry, there is a really good spreadsheet here that allows you to play with figures and a few extra kgs has very little effect.

http://www.mycncuk.com/forums/faqs-p...do-i-need.html

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Originally Posted by D.C.

I don't think ecocast is structurally any stronger than 6082, (Jazz can probably confirmor refute this) it is just precision ground which is useful for mounting rails on but not required for the gantry sides.

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Yes and no really it's not structurally stronger but it is more stable has it's cast not rolled, and yes it's precision ground. That said your still correct it's a waste for things like gantry sides etc where ground plate isn't required.!!. . . . Use it for bearing plates and Z axis mostly the rest will be fine with normal plate.

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Originally Posted by JAZZCNC

when you say 25mm I suppose you mean Rail not carriage width.? If so then yes that will be fine if your using supported round rail but massive overkill if using profiled rails like Hi-wins. 20mm will be fine for profiled, even 15mm will handle far more load than you'll throw at them but 20mm carriages workout easier to use has they larger and suit better.

To be honest the Min/MAX distance for separation on Y axis( Which I call Z axis) will depend on several factors like number and location of ball-screws and rail used. 300mm total bearing plate width will be fine in most cases and less if using profiled rail and twin screws close to the bearings. 200mm will even work if the gantrys strong.

Regards the gantry then you need to seriously beef up this area with bracing. I'd also use wider stronger Cross beams between gantry sides.

Skinning is ok for containing chips and looks etc but wouldn't rely on it for strength and the down side being it's very resonant and you want to avoid resonance if possible.
Stronger base frame work is the best way then skin for cosmetic reason if you feel the need.!

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Yes, 25mm profiled rail. I'll look at 20mm instead. When you say twin screws, do you mean one either side? If yes, that is my intention, driven by a single motor using pulleys and belts.

Yes, the gantry need some serious beefing up and is in no way finished in the drawing. I'll do some more work on it and post again.

With regards to the resonance, I know some folks have used kiln dried sand to fill the box section but has anyone used sound deading materials stuck to the back of the skinning to help with resonance control? I have some sheets of a bitumen based damping mats which work very well for killing resonance. More info here: Bitumen Based Damping Mats [01] - £0.00 : SoundProofing Services, Sound Insulation, Acoustic Insulation, Acoustic Foam, Acoustic Panels

No particular reason for the Ecocast, 6082 it is. Thanks for the motor sizing link D.C., be useful that.

Being fairly new myself I tend not to be to much help when it comes to machine design but why don't you look at buying a proper mill & possibly converting it to cnc if you want to cut mainly aluminium & other metals. Would seem like a far better investment for what you want a machine to do.

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Originally Posted by martin54

Being fairly new myself I tend not to be to much help when it comes to machine design but why don't you look at buying a proper mill & possibly converting it to cnc if you want to cut mainly aluminium & other metals. Would seem like a far better investment for what you want a machine to do.

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Good point but I feel table travel size could be an issue. Most of the ally I want to cut will be 500 x 500mm plus. Correct me if I'm wrong but I think most mills are quite narrow on table depth/travel. Being able to cut tool steel really isn't an issue, it was really just a nice to have feature. Thanks for your input though.

There are guys on here that run machine shops so probably better placed to answer this but at a guess I would think it would depend on intended use, budget & space. OK so I'm old school having done all my machining on manual machines & I have to admit to being a bit spoiled being in the RN because the workshops had just about everything.
Small mills seem to attract a lot of attention & sell well probably because a lot of people have a limited amount of space & are looking for a small hobby type machine, add to that the fact that they are normally single phase so plug straight in to most peoples domestic set up & can be shipped with relative ease & I suppose it's no wonder they sell.
Take a bigger industrial type machine that's going to cause more problems & expense to move, plus needs more space & either a 3 phase supply or someone who knows enough to run it off a single phase supply & the interest drops & you can pick up bargain machines if you look about.
If looking at a serious business machine then that's what I would be looking to do, not sure how easy conversion would be but would certainly investigate. If your looking at a hobby type machine that's more for your own use then a router might be a better choice. Speak to some of the guys on the forum who know what their talking about & they will tell you that routers aren't really suitable for machining any metals although you can use them for that sort of work.

I've finally managed to get some time to make progress on my mill design so your thoughts/critique would be much appreciated please folks.

As I want to machine Ally and other sheet steels I've taken JAZZ' advice onboard and decided on a fixed gantry / moving table design. The overall length is 1500mm ish, overall width is 1200mm ish and the Z axis has 220mm movement. This should give me approx 750 x 750mm cutting area.

The 220mm Z axis movement is required for machining/drilling 200mm wide Ally plates stood on end. Most of the time I will be cutting Ally plates which will be no thicker than 10mm which gives me the dilemna of a huge Z axis movement or some sort of adjustable bed/table.

I have thought about having a fixed bed with some sort of stackable table which will allow for less Z Axis travel but this obviously opens up potential problems with stability of table because of the distance from the rails/bearings to the cutting surface.

How difficult would it be to implement an adjustable bed/table? Any thoughts on the stackable table?

The gantry ends are currently drawn with the intention of looking into getting them cast, could be way to expensive though. They're approx 450mm width x 400mm height and 80mm thick. If the cast turns out to be to expensive they'll be machined out of 40mm thick Ally and sandwiched together.

The gantry ends can also have some triangular supports added to the outsides for even more stability if needed. I also have a 20mm thick plate across the back joining both gantry ends and hopefully adding even more strength/stability if needed. Would bolting the gantry ends all the way through the 80 x 40 x 5 frame with QTY 8 x 16mm bolts per side be sufficient?

The gantry crossbars are drawn at 80 x 80 x 1100mm and braced from the back with a 25mm thick plate.I'm still not sure if this will be strong enough, any thoughts?

The Z Axis/Spindle support plate is drawn at 600 x 240 x 30mm thick. Will this be thick enough? Any thoughts about the actual spindle? Is the 2.2kw chinese spindle any good for cutting Ally or will I need something better?

The plate thickness around the gantry carriage is 30mm front, 20mm rear and 40mm top and bottom for the bearing plates. The motor mount/support plates at the top of the carriage are 25mm thick.

The frame is made up mostly of 80 x 40 x 5 box section accept for the four corner posts which are drawn at 80 x 80 x 5mm with 10mm thick base plates which will have an adjustable foot attached to each corner. I want to try and keep the front of the frame open to allow for easier loading of Ally plates.

The table still needs some work doing, perhaps a 40 x 40 box section frame underneath to give it some support. The table plate is 900 wide x 750 length x 30mm thick. Would that need extra support underneath?

Still loads to do but I'm hoping the basics for a strong machine are there.


Attachment 8863Attachment 8864Attachment 8866Attachment 8869Attachment 8870

Hi Ian,

Ok I can give you a solution that is perfect answer to all your issues but it's a bit off the Norm and cost's a bit more, will also mean a redesign. . . BUT. . . The plus,s are many and well worth the trouble if your cutting Ali and Odd sized material.?

Make it so the gantry lifts up and down not the Z axis.? Infact you don't have a Z axis the Gantry becomes it. The spindle is fixed on a plate that just moves across the Gantry.
There are only a couple of advantages to this design but they are BIG ones.?

Finish is improved massively because you only have the tool extension from spindle extending down from Gantry so stiffness and resonance is improved massively so tool chatter is far less, it's about good as it gets in tool rigidity and therefore finish.

There's virtually no restriction in material size that can be machined and still have Ultimate Tool strength has the tool Extension doesn't change only height of gantry. The Only limiting factor is how high you build the Columns that the gantry run up & down on. The flex and rigidity of tool will never change whether you machining 2mm Ali or Top of an Engine block has the distance form gantry to spindle never changes because spindle is fixed to plate running across it. Only gantry goes up an down doing the job of a normal Z axis giving the absolute minimum amount of flex, which can only come from the tool it's self.

This design will need ballscrew down each side to lift gantry up and down but could be driven with single motor connecting screws with belts across top. The Columns can be braced across the top so still very strong and rigid and provide perfect mounting for motor/belts etc. If heavy gantry then counter balance down side each column will neutralise the weight so won't need massive motors.

In your position with your needs then this would be my route without shadow of a doubt.!!

Hope this helps.

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Originally Posted by JAZZCNC

The flex and rigidity of tool will never change whether you machining 2mm Ali or Top of an Engine block has the distance form gantry to spindle never changes because spindle is fixed to plate running across it. Only gantry goes up an down doing the job of a normal Z axis giving the absolute minimum amount of flex, which can only come from the tool it's self.

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So if the gantry is mounted on spindly rails both sides this will not be transmitted to the tool. ?

A Z axis usually has twin rails close together on one plate.
You are proposing two Z axis so 4 rails well spaced apart ?

If you were making a fixed bed (moving gantry) machine, then I would suggest the following:

Since you only need the Z-travel to machine plates 'stood on end', you can leave the bed at the best position for cutting what you will cut most often and just clamp the plates on the end of the bed to machine them. If the bed ends just inside the X-axis travel, then you can move the gantry (just) off the end of the bed for machining the plates.

Here's an example in case that's not clear:
Attachment 8871

If you put a vice of some sort on the end of the bed then it would be quite efficient.

However, since the bed is moving you wont gain so much from doing this, maybe 100mm less Z-travel required. That's still a big gain for virtually no change in the design. You might even be able to get the full 220mm length to fit by allowing the plate to pass between the bed supports. Clearly that severely limits the X travel in that configuration, but you don't need much.

You really need some diagonals on the back of the frame. Don't leave it open like that as it will make the stiffness parallel to Y quite poor. Getting the gantry sides cast would be nice, for the right price, however if this option is unrealistic there's no need to use 40mm thick plate. A solid cross section is a waste of material when subjected to bending forces, so in this case a box section would be better. For example you could use four 20mm plates to create box-shaped gantry sides and the difference in strength between that and solid material would be small. If you can give the dimensions of the gantry sides then I can say roughly how big the difference would be. The reason for this effect is the material towards the center in a solid cross section is subjected to very little stress, so contributes very little to the overall stiffness.

Thanks for your input folks.

JAZZ: I think there's a video somewhere on here showing a much smaller machine with a similar design. Can't remember who posted it now though. I had considered it but thought it would be way to difficult/costly to scale up to the size I'd need. Will have another think about it.

JONATHAN: A moving gantry design would be my preference as I originally wanted to build the extra axis for turning at the end of the bed, not a huge problem with a fixed gantry as I could mount the turning axis on to the table as and when needed. Baring in mind this machine will only be used to cut ally and sheet steels would a moving gantry design work as well as a fixed gantry? I was under the impression a fixed gantry would be generally better.

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Originally Posted by IanS1

Bearing in mind this machine will only be used to cut ally and sheet steels would a moving gantry design work as well as a fixed gantry? I was under the impression a fixed gantry would be generally better.

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You could design a moving gantry machine as strong as the current design without too much difficulty.

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Since you only need the Z-travel to machine plates 'stood on end', you can leave the bed at the best position for cutting what you will cut most often and just clamp the plates on the end of the bed to machine them. If the bed ends just inside the X-axis travel, then you can move the gantry (just) off the end of the bed for machining the plates.

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If you are doing a lot of repetitive work of the same size then you could also make a slot in the table and clamp it down low.

I have seen vertical moving gantry's on routers before, in fact I mentioned it when I first started and got talked out of it. As John said it is just transferring a massive load to the gantry sides and the distance vs bearing spacing would be huge. Not impossible just difficult and defiantly not a cheap or quick fix.



Just bolting a fixed gantry to a moving gantry design is also not the most effecient way to do things. I would redesign as new and if you went for the fixed gantry then you can get rid of the high sides at each end as they are not doing anything. It would be stronger if you went for an 'A' frame arrangement (two a frames opposite each other. Main gantry at the top and transmitting load to the ground through the legs, the bed can sit at the horizontal section of the 'A' and extend as far as required to support the table. As the gantry is fixed the cutting load is only directly below the cutting head therefore all the force is contained and distributed within the A frame. table only needs to support its own weight


The moving table also needs beefing up, as it is there will probably be deflection in the middle. Most designs I have seen have the rails at third points. The table itself will then need strengthening to overcome deflection in the middle and the cantilevered edges. To some degree having a fixed gantry just inverts the flexing problems associated with the z axis and to the table as this is now compromised.

A fixed gantry will get you closer to cutting steel as you can really beef up the design, the same weight and strength on a moving gantry has to be accelerated and decelerated which means big motors and drives.


Edit
The moving table is all wrong. It should be the other way up. bearings fixed to the frame and rails mounted on the table. that way the work is always fully supported under the cutting tool and the bed support can be drastically reduced. And will fit within the 'A' frame I mentioned, look a VMC designs. You basically looking at a 2 sided mill arrangement. Fixed gantry machines are a completely different design to moving.

Ok a bit more thought and I think your answer is little bit of everyone's idea.

That is a fixed gantry design that a has a short Z axis mounted on on it say 50 70mm for machining operations but then use Jazz's suggestion of adjusting the height of the whole beam using a clamp/unclamping system to change to height depending on the work piece. The A frame idea could easily have this added as long as there is still a brace bar at the top.

This is not exactly revolutionary as this is the same principle that mills have been using for years!

Thanks for your input Ross.

The A frame type design is interesting I'll look into it. The mechanically adjustable height on the gantry is worth some thought too but immediate concerns are, being a pain to set the gantry parallel to the bed every time.

The table definitely needs more work with regards to support/beefing up. I am very intrigued though about the idea of fixing the bearings to the bed and the rails to the table, I will look into it.

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Originally Posted by IanS1

Thanks for your input Ross.

The A frame type design is interesting I'll look into it. The mechanically adjustable height on the gantry is worth some thought too but immediate concerns are, being a pain to set the gantry parallel to the bed every time.

The table definitely needs more work with regards to support/beefing up. I am very intrigued though about the idea of fixing the bearings to the bed and the rails to the table, I will look into it.

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Yeah adjustment would be the tricky bit. You can either predrill holes at say 50mm ccs and its just a case of un bolt, move, rebolt (could still give alignment issues) or go for linear rails and lead screw to guide and adjust, then reclamp to to make it solid.

This is the way I was going to do it on mine if went down that route, except id add encoders to the lead screws and a dual display to show the position, i figure ballscrews are ott as the weight of the gantry will keep the load on the leading edge of the screw so no backlash will be present. Add hydraulic clamps job done.

After loads of thought I've decided to stick with a more traditional router design for my first machine. The frame work is almost built so now my attention is more focused on the gantry design. To start with, this machine will be used for cutting aluminium, plastics, acrylics, MDF and plywood. If the machine is successful I will eventually build a dedicated machine for cutting the acrylics, MDF, plywood etc and keep this one for aluminium cutting only, hence the strong heavy frame. Overall the cutting area will be approx 700 x 1400mm and I'm hoping to get around 100mm for the Z axis travel. The bed will probably be a 30mm thick aluminium plate.

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The frame work is built mostly from 80x80x5mm, the overall size of the frame is approx 1160mm wide, 2000mm long and 650mm to the bed height. All of the diagonal bracing is 40x40x3mm.

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The Y axis section is 100 x 50 x 8mm, I still have to add the bracing for either end of the Y axis. The extended Y axis is for future plans of a possible ATC at the rear, a rotary axis and a clamping system for machining the ends of ali plates at the front.

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I'm really pleased with the way it has turned out so far. Using a spirit level across the bed and across the X/Y axis indicates it's pretty flat but with the adjustment I've built in and if needed the use of epoxy I should be able to get it clocked in quite nicely I would think.
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Anyway, on to the gantry. The design I've gone for is fairly straight forward and hopefully strong enough. The gantry is mostly drawn in 25mm plate with the Z axis plates done in the 30mm. All plates attatching to the bearing blocks are drawn in 30mm. The overall gantry width is 1250mm and height is 270mm.
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The bearing blocks on the Y axis are spaced at 370mm end to end and the X axis are spaced at 230mm end to end. The linear rails on the Z are spaced at 150mm and the bearing blocks have a vertical spacing of 310mm.
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Would really appreciate some input on whether this gantry design will be up to the job.

Any thoughts on the gantry would be very much appreciated.

Ball screws: Would a 16 be OK to use on the Y axis or would I be better off using a 20? It's going to be about 2000mm long.

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Originally Posted by IanS1

Any thoughts on the gantry would be very much appreciated.

Ball screws: Would a 16 be OK to use on the Y axis or would I be better off using a 20? It's going to be about 2000mm long.

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Gantry will be fine Ian it's tried and tested. 2000mm is just too long for 16mm so definately go with 20mm. To be honest at this length it's worth using 20mm pitch not 10mm and using a 2:1 ratio so you get the same speed as 10mm pitch but half the screw speed. This reduce chances of Whip.
The ratio increases torque as well so your in front here as well thou the higher pitch looses some mechanical advantage but still your in front and the slower screw speed is more beneficial as the inertia is lower than 20mm 10mm pitch screw.

Thanks Jazz. How you fixed for machine time? Fancy building me a gantry? :thumsup:

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Originally Posted by IanS1

Thanks Jazz. How you fixed for machine time? Fancy building me a gantry? :thumsup:

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Sorry mate I'm massively behind already due to family issues so couldn't even think about taking on any more work on.

Hey no problem and no apologies needed. Thanks for your input though. I'll put a post up in the RFQ section.

I'm now starting to look into control/motors etc. Anyone using a CS Labs + Leadshine combo?

http://www.cs-lab.eu/en/produkt-2,-C...onnectors.html

http://www.leadshine.com/producttype...y-servo-drives

Could I get away with 25mm thick 6082 plate for the machine bed, size approx. 1400 x 800mm. I'm assuming the frame shown in post 23 will be plenty strong enough to use 25mm 6082 instead of 30mm Ecocast.

I'm considering re-designing my gantry to something more suited to self build. The hassle and cost of machining it all from ali plate is putting me off the current design. My only worry is the hassle I had with the out of square/bowed/twisted 80 x 80 I used for the frame, would make building a gantry nice and square very difficult indeed.

Any thoughts on using a heavy duty ali extrusion, say 160 x 80, instead of RHS/SHS? Would it be possible to build a gantry from extrusion strong enough for machining mostly aluminium?

Any thoughts on the Ali extrusion please folks? I'm still thinking of using the same gantry ends but with 2 extrusions top and bottom with a 10mm plate across the front for extra support. Workable in the short term?

Hi Ian, if you look at Kingcreaky's build and EddyCurrent's builds you'll see that they went with the Ali extrusion and plate on the front route for the gantry so it's a perfectly viable solution.

The gantry was easy to build using 100x50x6 aluminium box section with a front mounted 6mm plate.
http://www.mycncuk.com/threads/6565-...5076#post55076
Aluminium angle is much better than steel for being straight but you have to make sure it's all on a very flat surface before gluing and screwing, I used a cast iron machine bed for that purpose.
Also on the front plate, countersunk screws would have looked better, but because the holes were marked out and drilled by hand I didn't want any screws pulling the plate in a wrong direction as they settled into a slightly off centre countersink.

After completion I did some stiffness tests here.
http://www.mycncuk.com/threads/7155-...6572#post56572

Thanks Neil, Eddy,

I have had looked at both builds before. Just wasn't sure how well they would perform on a machine mostly cutting aluminium. Eddy, are you using your machine for cutting aluminium? The stiffness figures you've quoted seem pretty good.

No, just wood but I've no doubt it could cut aluminium easily it's just I don't have it geared up for coolant sloshing about.
It's a pity that stiffness thread wasn't refined with a process and added to by others