Joe's 1000x600x200 steel and aluminium router started

I just looked up the hiwin specs, they say 130um over 500mm max allowable surface height error between two rails in the same plane, so I think this equates to an angle of 0.015 degrees or 53 arcseconds, I would be around 4x that with the rails mounted directly to the first slot. It would probably be absolutely fine but anyway.

I've made up some feet from spare plate. These are bolted into the bottom of the extrusion and will then be clamped to my milling table.

Attachment 26920 Attachment 26921

I've just trammed the head to the table, and checked the table over the entire X travel. The table is within 0.01mm, i.e. I can't measure any error with a 0.01mm resolution DTI. Think i'm just going to flycut the top and bottom of the entire extrusion, then I'll have the option of mounting to a slot or tapping into the centre. No time to do it today taking the kids to see the new star wars film this afternoon.

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Originally Posted by devmonkey

another option is just to mill a few mm each side of the slot so the rail can sit flat, this would also preserve the 3 planar points (both corners and centre) in case I mess up.

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That's likely not such a bad idea as it could give some lateral stabilit - Hiwin suggest sitting the rails in such a groove in the manual. However you'll need to do it accurately as it removes the option for tweaking alignment to some extent.

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.Then again the centre of this extrusion will be stiffer than either slot as it i supported equally whereas the slots are supported on one side by the unsupported corner. No idea really.

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Routercnc's point about using a tapped strip rather than individual floating nuts might help this.

Well I've milled 4mm either side of the slot flat on each side of the extrusion. Setup took a long time making sure everything was flat with the dial indicator, nipping up the gibs to try and counter the sag from the long overhang. I pretty pleased with the result, seems at least as flat as the extrusion. I need to get some rails mounted to it and make the Y bearing plates so I can see if it is sufficiently parallel to be usable. DOC was about 0.25mm with a carbide endmill, could feel it was cutting deeper on the outside due to the increased slope as discussed in the previous posts.

I had to make the cut in two steps, moving the beam and refixing between cuts since the mill table wasn't long enough. I can see the transition but cannot feel it. Nice hatch marks show the head was in tram.

Attachment 26926 Attachment 26927 Attachment 26928 Attachment 26929 Attachment 26930

Nice work, hope it sorts it.

I agree with voicecoil. My only suggestion when you cut the other one would be to support that overhang with an elastic luggage strap from the roof of your shed.

Kit

Hi Kit, I cut them both in one sitting yesterday, i measured the effect of the sag over the saddle with a DTI 4mm offset from the spindle (I used an 8mm endmill for the facing operation) whilst lifting the weight of the overhanging part, didn't really have any effect with the gibs tight as you would expect given the table pivots on the saddle. Probably not an acceptable way to fly cut but with a small endmill it works. I thought about slinging the overhang to my engine hoist but the problem with that would have been as the table is moved to the other end you would need to reverse the force since it becomes overbalanced the other side.

I think the best possible way to balance a job like this is to put a sliding counter weight inside the extrusion and move it through as the work moves (in the opposite direction), but I couldn't be bothered in this instance, if I was using the large fly cutter I would have had to bother else it would have cut a tapered scallop in the top surface.

Interesting :)

Milled the Y bearing plates, just need to counter bore them. Lower plate wraps around the rails on the Z front plate to reduce coolant splash up inside the Z assembly, it is also recessed to accept the rear Z plate press fit so that it is easy to line it up with the upper Y plate. The row of 4 holes that will be used to bolt the lower Y to the rear Z plate are undersized as I want to use them as a drill guide for the tapped holes in the rear Z. The Z is too tall to stand on my mill so these will have to be drilled on the pillar drill or with the cordless.

Also the spindle mount arrived from Canada, very nice bit of kit.
Attachment 26935 Attachment 26937 Attachment 26938 Attachment 26936

Got the rails mounted on the milled gantry, worked really well. I've tightened them down but not yet aligned straight, for that I will mill up a couple of precision setting tools.

I then finished the Y bearing plates and bolted everything together. Everything slides very smoothly with bolts tight, very exciting! The Y bearings have the same smooth action across the entire length with no hint of any variation so I presume the gantry milling was sufficiently parallel.

Attachment 26939 Attachment 26940 Attachment 26941

One thing I need to do before too long is hit the corners of these plates with a sander, they are razor sharp and I keep bleeding all over the lovely shiny parts.

Happy new year everyone!

Small progress update, I have finished the gantry end plates and X bearing plates.

Attachment 26970 Attachment 26971 Attachment 26972 Attachment 26973 Attachment 26974

I have about 6 small plates to make for stepper and bk mounts then finished with the manual milling.

Nice work Joe!
I see you are milling small slots to locate perpendicular sections to each other...... I enquired about doing just that in another forum with almost no reaction.
It seems to make sense to me ( no expert) What better way to ensure components are aligned correctly?

How have you found the process? A good idea or problematic?

I'm considering doing the same thing...when I eventually start my own build.

I see you have maximised the distance between your x rails, by placing them top and bottom of the Gantry.
Did that make things excessively more difficult?

Steve

Hi Steve,
Joe won't be out of bed yet:sleeping:

There's a fair amount of stuff on gantry design on the forum. Putting rails top and bottom has the advantage of pulling the Z axis closer to the gantry and reducing the overhang. It also gets the rails as far apart as possible for the chosen height of the gantry but makes the construction of the Z back-plate more complex. Alignment of the rails is not 'automatic' in any way and must be done with care.

The option of mounting rails directly on the front of the gantry pushes the Z axis out but can be easier to align, especially if you're using epoxy leveling or a machine-ground plate to ensure a perfectly plane surface. It also makes the Z axis back-pale into a single flat piece. It all comes down to what tools and measuring instruments you have access to.

As long as the first machine you build is adequate to cut out the pieces for a second, better version then you will be on an upward evolutionary slope.

Kit

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Originally Posted by Sterob

Nice work Joe!
I see you are milling small slots to locate perpendicular sections to each other...... I enquired about doing just that in another forum with almost no reaction.
It seems to make sense to me ( no expert) What better way to ensure components are aligned correctly?

How have you found the process? A good idea or problematic?

I'm considering doing the same thing...when I eventually start my own build.

I see you have maximised the distance between your x rails, by placing them top and bottom of the Gantry.
Did that make things excessively more difficult?

Steve

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Hi Steve,

I also thought twice before milling the locating slots on the different plates. On some joints it is not so critical, such as attaching a stepper mounting plate but when you are joining two plates that locate the axis at exactly 90 degrees such as where my gantry end plates join the X bearing plates it is super critical. In this example it was also critical the slots in the top of the X bearing plates were not only planar with the plate surface but also identical depth on both X bearing plates.

When I mill out shapes from plate I clamp the plate to MDF so the cutter clears the mill table. MDF (particularly when it has sat in the garage for a year) is not sufficiently uniform for accurate Z milling. Therefore I mill these slots after the outside profile has been finished. I set the Z height on the mill and lock the axis then I clamp each X bearing plate to the mill table directly and mill the slot. I do both plates without unlocking the Z axis so they should be identical.

Before doing any of this critical stuff (particularly milling the gantry extrusion flat where the Y rails are mounted) I checked the mill table was flat within 0.01mm over the entire travel with a DTI in the spindle. You don't want to do this if your saddle is sloppy or any long work really.

I'm an amateur machinist at best, only been playing around with the manual machine for a few months really so take this advice with a pinch of salt. The slots are within 0.01mm in depth over their length which is good enough and no worse than the milled plate itself. It is quite satisfying when you get a friction fit on the joint between two plates.

Also bear in mind that the milled plate isn't exactly whatever nominal dimension you purchase, mine in nominally 16mm but is infact 16.055mm thick, also your cutters are not exactly whatever dimension they are supposed to be. This means if you just mill the slot to the DRO readout it wont be the correct width.

What I do is designate one side of the slot as the reference since my cad drawing assumes 16mm plate, then mill that. Then open up the slot and use a piece of clean spare plate to test the slot until you get a nice fit, this is much more accurate than trying to measure with a vernier or micrometer as the slot is too shallow.

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Originally Posted by Sterob

I see you have maximised the distance between your x rails, by placing them top and bottom of the Gantry.
Did that make things excessively more difficult?

Steve

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Not really no. If you want the rails to sit flat then you have to mill the extrusion anyway particularly with 15mm rail on 8mm slot.

When you set the rail you will need a setting tool to offset the reference edge of the rail from the edge of the profile, I am making the assumption that the extrusion itself is straight. The setting tool with be a pair of L shapes milled together so they are identical with a hole so they can be bolted to the T slot. The short part of the L will then form a reference surface to locate the rail.

Note I'm referring to the rails on the gantry as the Y rails.

To get the separation of the Y bearing plates perfect is a little more involved since it is very hard to accurately measure the extrusion depth, again this is a nominal dimension when you purchase the profile, mine is nominally 160mm but is infact around 159.8mm, and now a bit less after I milled the flat for the rail.

So I slot joined the lower Y bearing plate to the rear Z plate but I didn't slot joint the upper Y bearing plate, I think this would have been impossible. Rather, with the Y bearings on the rails and bolted to their plates, I assembled the lower plate onto the Z axis and tightened. I then clamped the upper plate with a long clamp across the back of the gantry tensioning it against the lower plate and slightly pre-loading the bearings, then spot drilled through the holes in the Z plate into the upper Y bearing plate.

This means you only have to locate the holes in the rear Z plate to around 0.5mm accuracy...also should note that I'm using M6 bolts for these joints and I drilled 6mm holes, the 0.2 or so play of an M6 bolt in a 6mm hole is generally sufficient to align things if you are milling accurately, you don't need 6.5mm holes for M6 as is usual, although I could only do this as I counterbored with a 12mm endmill in the milling machine rather than an M6 counterbore which would have required 6.5mm holes.

I think it is much better with the rails top and bottom not just because of the increased distance between them but because of the reduced spindle overhang. My last machine which was much larger than this had the rails on the gantry face and although it was very simple to mount them it was less stiff due to the overhang.

Quote:

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Originally Posted by Sterob

Nice work Joe!
I see you are milling small slots to locate perpendicular sections to each other...... I enquired about doing just that in another forum with almost no reaction.
It seems to make sense to me ( no expert) What better way to ensure components are aligned correctly?

How have you found the process? A good idea or problematic?

I'm considering doing the same thing...when I eventually start my own build.

I see you have maximised the distance between your x rails, by placing them top and bottom of the Gantry.
Did that make things excessively more difficult?

Steve

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Got to be careful here because it can and often does actually does make things harder for your self and not always more accurate by milling slots etc.? Reason is unless you can accurately machine all the major areas of the machine accurately then you will need some room for adjustment.

If you have read the forum you'll see I've said it many times that at DIY level the key to a great machine is to build in as much adjustment as possible. Nothing as changed in this statement.
Groves etc that are fixed will limit your ability to adjust out any errors coming from other areas that haven't been done to the same level. This is when you regret doing it.
The larger the machine the more this adjustability comes into play.

A better way I find at DIY level is not to limit adjustment with slots etc but use dowel pins that can be drilled and reamed after the machine adjustments have been made. This locks the machine in place but doesn't limit adjustment.

I would only consider milling slots etc if you can build the whole machine to the same level.! . . . . If not you will regret limiting the adjustments.

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Originally Posted by JAZZCNC

Got to be careful here because it can and often does actually does make things harder for your self and not always more accurate by milling slots etc.? Reason is unless you can accurately machine all the major areas of the machine accurately then you will need some room for adjustment.

If you have read the forum you'll see I've said it many times that at DIY level the key to a great machine is to build in as much adjustment as possible. Nothing as changed in this statement.
Groves etc that are fixed will limit your ability to adjust out any errors coming from other areas that haven't been done to the same level. This is when you regret doing it.
The larger the machine the more this adjustability comes into play.

A better way I find at DIY level is not to limit adjustment with slots etc but use dowel pins that can be drilled and reamed after the machine adjustments have been made. This locks the machine in place but doesn't limit adjustment.

I would only consider milling slots etc if you can build the whole machine to the same level.! . . . . If not you will regret limiting the adjustments.

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Wise words about infinite adjustment.

I've built 4 machines in the last 20 years and milled slots in all of them for plate-plate, albeit these were all done on CNC not a manual mill. My approach has always been to make each sub-assembly locally square/aligned and only adjust between sub-assemblies (usuallly by shimming bearings). For example my gantry end plates are squared to the gantry and X bearing plates in 3 dimensions helped by milling the slots, this complete gantry/Y assembly will always be locally square assuming I can setup a milling machine properly to take a straight cut which I can. However the gantry itself could be twisted, unlikely but wont be known until final assembly, in which case X bearing interface with X plate will need shimming.

Sometimes you can't accurately determine a location for a joint until assembly in which case I estimate it and drill the pilot holes for the bolts then spot through to the joining plate with a centre drill once assembled, this was the case with the upper Y bearing plate on this machine. I don't use slots for this type of joint. However the slot in the bottom Y bearing plate guarantees that the two Y bearing plates (and therefore the Y bearings) are exactly the same distance behind the Z axis.

If I was using a hand router to cut aluminium as some brave chaps on here do then I definitely wouldn't be milling slots.

Once I fit the gantry end plate assemblies to the gantry I wont be able to mount the Z assembly without removing one of them, therefore I think this it is time to align and tighten the Y rails to the gantry in their final location.

For this I have just machined some precise setting tools, they were machined as a pair to ensure they are identical.

Attachment 26988

Here they are attached to the gantry, they bolt into the T-slot. Plan is to snug them up, the milled faces should then act as a reference surface to match up the reference edge on the hiwin rail, they will be moved along for each rail bolt. Note that I made them long enough so they extend across two of the high points that are on the reference plane on the face of the gantry extrusion.

Attachment 26989 Attachment 26990

First gantry end assembly bolted in place, I used countersunk M8 bolts rather than cap head to reduce the amount of material removal for the counterbore, meant the countersinks had to be done on the mill as there is very little adjustment vs a cap head. As well as the 8 M8 bolts into the end of the extrusion there are also two M6 bolts bolting up through the X bearing plate into the two T-slots on the bottom of the gantry.

Attachment 26983 Attachment 26984

Bottom view showing bolts fixing up into extrusion:
Attachment 26985

Plate-plate joint using the alignment slot:
Attachment 26986

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Originally Posted by devmonkey

I've built 4 machines in the last 20 years and milled slots in all of them for plate-plate, albeit these were all done on CNC not a manual mill.

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This is my point unless you have the tools and knowledge to use them then it's better that you don't limit adjustment and instead lock it down when setup.

As you probably know Mr. Enstein comes into play when setting up a CNC machine.? Any adjustment usually an equal and opposite reaction somewhere else and you soon end up chasing errors around the machine. This is when you appreciate the adjustment you built into the machine, esp on large machines because small errors get big very quickly as it gets wider and longer.!

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Originally Posted by JAZZCNC

As you probably know Mr. Enstein comes into play when setting up a CNC machine.? Any adjustment usually an equal and opposite reaction

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Mr Newton I believe.

Yeh don't mill slots unless you have a mill.

Y rails are now fixed in their final position using the setting tools described above, worked very well and was super quick to do. Both gantry end assemblies are aligned and bolted to check final fit, everything looks good. Note rubber mallet, this is a precision build honest ;-)

Attachment 26987

Other than ballscrews everything from the X plates upwards is now complete, will move back to the steel frame next, need to decide whether to pour epoxy or attempt to rig up a mobile surface grinding contraption to bring the frame into plane.

Jazz when you fettle beams holding the X rails into plane do you just scrape by hand checking with a precision level and blueing off a surface plate large enough to span the two X beams? Or do you just level each beam locally then shim one side to bring into plane? My last larger machine had X beams that could be adjusted independently up and down with the rail attached, this one has beams welded to the frame.

Cheers, Joe

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Originally Posted by devmonkey

Mr Newton I believe.

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That's the bloke, another clever sod. Lol

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Originally Posted by devmonkey

Attachment 26987

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Is there any pros/cons to mounting the x-axis linear rails on top and bottom, compared to mounting both on the front side? One thing that I can think of is:

- Mounted on front side is easier to get aligned but will not use table area as efficiently as top/bottom mounted rails. Any difference in stability?

Both on the front tends to reduce spacing between them, hence more leverage for a given cutting force - but this leverage is in the plane of the screw fixing. It also pushes the spindle out from the gantry which could increase the twisting moment on the gantry. However it does increase clearance under the gantry and can allow a greater range of movement in Z. Top and bottom has greater spacing and hence less leverage on the rails, but it's then sideways which might not be so good unless you've milled slots as Joe has in this build. And you'll lose something like 30-45mm clearance under the gantry depending on the size of rails & thickness of mounting plate you're using. So there's pros and cons both ways, in the end it will all depend on your design as a whole.

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Originally Posted by NordicCnc

Is there any pros/cons to mounting the x-axis linear rails on top and bottom, compared to mounting both on the front side? One thing that I can think of is:

- Mounted on front side is easier to get aligned but will not use table area as efficiently as top/bottom mounted rails. Any difference in stability?

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Don't lose any sleep over either choice, choose whichever suits your requirements best because the difference is minimal and both will work fine provided you got a good strong gantry foundation.
I've built several machines using both methods and there is no obvious difference in cut quality or performance so build to suit your needs.

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Originally Posted by JAZZCNC

Don't lose any sleep over either choice, choose whichever suits your requirements best because the difference is minimal and both will work fine provided you got a good strong gantry foundation.
I've built several machines using both methods and there is no obvious difference in cut quality or performance so build to suit your needs.

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The gantry foundation will be a 160x80 aluminium extrusion and the sides will be raised so that the x-axis is as close to the y-axis as possible. Right now my design ia with front mounted rails but I figured I am loosing quite a bit of work area because of it. Do you think it would be sufficient to change it to top and bottom mounted?

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Originally Posted by Voicecoil

Both on the front tends to reduce spacing between them, hence more leverage for a given cutting force - but this leverage is in the plane of the screw fixing. It also pushes the spindle out from the gantry which could increase the twisting moment on the gantry. However it does increase clearance under the gantry and can allow a greater range of movement in Z. Top and bottom has greater spacing and hence less leverage on the rails, but it's then sideways which might not be so good unless you've milled slots as Joe has in this build. And you'll lose something like 30-45mm clearance under the gantry depending on the size of rails & thickness of mounting plate you're using. So there's pros and cons both ways, in the end it will all depend on your design as a whole.

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Thanks for this very detailed answer. So to draw a conclusion for this is that if you are more concerned about work are that Z-axis clearance/travel, one should go for the top/bottom mounted rails, since it will most likely result in a little bit stiffer construction?

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Originally Posted by NordicCnc

Do you think it would be sufficient to change it to top and bottom mounted?

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My last post said it all really. Do which suits your needs best.

You needn't lose too much work area, but there will always be a certain zone where the cutter cannot reach (unless you make your Y axis rails longer than the bed). This is because you want to have a decent distance between the carriages on your Y axis for stability (I went for 200mm IIRC), hence the machine will be at least this much longer than your cutting area.I arranged things on mine so the cutter reaches to within 30mm of the front of the bed, with the "dead space" behind.Decide on what X, Y and Z capability you want then as Jazz said choose whichever layout fits it most convieniently.

Something else to consider is the complexity of the Z-axis back plate. Rails on the face can allow this to be a simple flat plate whereas rails on top and bottom will require two accurate and rigid square joints.

Good point..... 'Complexity and Less Overhang' verses 'Simplicity and more Overhang'...

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Originally Posted by Sterob

Good point..... 'Complexity and Less Overhang' verses 'Simplicity and more Overhang'...

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If you have access to a milling machine I would definitely put them top and bottom. If you want to mount them on the face and keep the same rail separation then you need a deeper gantry, if you use 160x80 profile for the gantry then the Y rail centres will *only* be 120mm apart (distance between outermost slots), the same profile with top-bottom mounts gets you ~180mm centres. On my last machine I used 160mm ali box section for the gantry and with face mounting close to the edges got around 140mm centres.

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Originally Posted by devmonkey

If you have access to a milling machine I would definitely put them top and bottom. If you want to mount them on the face and keep the same rail separation then you need a deeper gantry, if you use 160x80 profile for the gantry then the Y rail centres will *only* be 120mm apart (distance between outermost slots), the same profile with top-bottom mounts gets you ~180mm centres. On my last machine I used 160mm ali box section for the gantry and with face mounting close to the edges got around 140mm centres.

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So do you think the difference with 40-50mm extra offset will make any notable difference to stiffness?

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Quote:

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Originally Posted by NordicCnc

So do you think the difference with 40-50mm extra offset will make any notable difference to stiffness?

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Say your overhang to spindle centre from gantry centre (assuming a rectangular gantry profile) reduces from 150mm to 100mm as a result of mounting rails top/bottom then you have decreased the torque applied to twist the gantry to 2/3rds for a given force applied to the spindle, so it really depends on the torsional stiffness of your gantry and the spacing of X bearings. Ideally the front X bearing wants to be at or forwards of the spindle so usually face mounting the Y rails increases the X bearing spacing, this is no bad thing but it does mean the machine needs to be longer to accommodate the same X travel.

For reference the difference in gantry twist for a given spindle force between when the Z is fully up and fully down will be greater than the difference in twist saved by shifting the spindle 50mm backwards.

As everyone says on this forum it depends on what you want to do with the machine as to how stiff it needs to be, having built previous machines that weren't stiff enough I now make every design choice around increasing stiffness. My choice to top/bottom mount the rails was both to increase stiffness and produce as compact a machine as possible as it is going into my garage so I don't have to traipse down to the large workshop in the woods in mid winter.

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Originally Posted by devmonkey

Say your overhang to spindle centre from gantry centre (assuming a rectangular gantry profile) reduces from 150mm to 100mm as a result of mounting rails top/bottom then you have decreased the torque applied to twist the gantry to 2/3rds for a given force applied to the spindle, so it really depends on the torsional stiffness of your gantry and the spacing of X bearings. Ideally the front X bearing wants to be at or forwards of the spindle so usually face mounting the Y rails increases the X bearing spacing, this is no bad thing but it does mean the machine needs to be longer to accommodate the same X travel.

For reference the difference in gantry twist for a given spindle force between when the Z is fully up and fully down will be greater than the difference in twist saved by shifting the spindle 50mm backwards.

As everyone says on this forum it depends on what you want to do with the machine as to how stiff it needs to be, having built previous machines that weren't stiff enough I now make every design choice around increasing stiffness. My choice to top/bottom mount the rails was both to increase stiffness and produce as compact a machine as possible as it is going into my garage so I don't have to traipse down to the large workshop in the woods in mid winter.

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So what I plan to use the machine for is mostly wood and aluminium milling and occasionally very very light stel milling. Based on what you and everyone are saying I am leaning towards top/bottom mounted rails since stiffness is critical.

Have you built any machines with face mounted rails and 160x80 extrusion gantry that was not stiff enough to mill aluminium efficiently?

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Quote:

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Originally Posted by NordicCnc

So what I plan to use the machine for is mostly wood and aluminium milling and occasionally very very light stel milling. Based on what you and everyone are saying I am leaning towards top/bottom mounted rails since stiffness is critical.

Have you built any machines with face mounted rails and 160x80 extrusion gantry that was not stiff enough to mill aluminium efficiently?

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No every machine i've built, including one that was substantially made of MDF with an underslung gantry rail with only a single igus carriage on each X rail on which you could rock the gantry visibly by leaning on the spindle, were capable of machining aluminium. You just need to back off the speed and depth of cut if you lack stiffness, all the accuracy is delivered on the finishing cuts anyway, just as with a normal mill, tool deflection particularly with the thin tools we use in routers is usually as much or more of a problem. That said it is easier to produce accurate work on a stiffer machine, so depends what you are making. If it is machining a few plates out with accurate vertical edges and holes that is one thing, if you are running 3D paths to build molds etc then you need a stiffer machine, and a machine that is significantly stiff over the Z travel you need.

Note though that if you want the rails to sit flat on extrusion it does have to be milled irrespective of which face you bolt them to. I don't think many people do this on this forum but most still get completely acceptable results.

Quote:

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Originally Posted by NordicCnc

Have you built any machines with face-mounted rails and 160x80 extrusion gantry that was not stiff enough to mill aluminum efficiently?

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Very few on this Forum can answer that question regards 160x80 profile because they won't have needed to change if done one before the other.!

I've built 5 machines that use face mounted and 14+ machines that use top/bot and all cut aluminum perfectly fine. These machine sizes range from 4 x 2 to 10 x 5 and the 6 machines with face-mounted are all 8 x 4 or 10 x 5 machines because saving space wasn't an issue. So in this case, I went for the easiest method of fixing and setup, also fewer parts to machine.

Honestly, it's not something you need to worry about on router that's mostly going to cut wood with occasional aluminum work.

One other method I use often, esp when needing to keep gantry low but with the highest clearance is to mix n match bottom rail on the front, top rail on the top. This gives the most clearance under the gantry and keeps gantry height low.

So like I say use the method that suits your needs because no one is better or worse than the other. You won't see any difference when using the machine.

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Originally Posted by JAZZCNC

Very few on this Forum can answer that question regards 160x80 profile because they won't have needed to change if done one before the other.!

I've built 5 machines that use face mounted and 14+ machines that use top/bot and all cut aluminum perfectly fine. These machine sizes range from 4 x 2 to 10 x 5 and the 6 machines with face-mounted are all 8 x 4 or 10 x 5 machines because saving space wasn't an issue. So in this case, I went for the easiest method of fixing and setup, also fewer parts to machine.

Honestly, it's not something you need to worry about on router that's mostly going to cut wood with occasional aluminum work.

One other method I use often, esp when needing to keep gantry low but with the highest clearance is to mix n match bottom rail on the front, top rail on the top. This gives the most clearance under the gantry and keeps gantry height low.

So like I say use the method that suits your needs because no one is better or worse than the other. You won't see any difference when using the machine.

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Okay thanks for the information. I might just go with the top/bottom because to me it seems more rigid that way with larger spacing between the linear rails. I think I will be cutting mostly aluminium, some wood and occasionally steel with very light cuts.

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As Joe said "if you have a milling machine...".

Perhaps the really clever trick is to design your gantry to take both front and top/bottom mounted rails. Front mounting the rails with a simple Z axis plate would then give you a machine which may be good enough to machine the parts needed to then convert it. Let the machine pull itself up by it's own boot laces.

Kit

I have been thinking about this. I like the idea of placing the rails on the side of the extrusion( for simplicity), but I would like the wider spacing top and bottom mounting gives.( for ridgidity )

How about using 2 smaller extrusions, spaced apart so the ball screw will fit in between them, and use a say a 10mm Ali backing plate to stiffen the extrusions?
That could bolt to the Gantry arms as well?

I guess aligning 2 extrusions may be a bit of work?

Been thought of already?...lol

Attachment 27039

It's been done plenty of times. It's weaker than a large section.