#31 Assembling Aluminium CNC Machine #31 / MGN12 Linear Rails / XYZ Axis / Spindle Mount

#31 Assembling Aluminium CNC Machine #31 / MGN12 Linear Rails / XYZ Axis / Spindle Mount


In the last video I prepared some water jet
cut aluminium plates by drilling, countersinking, reaming and tapping out their holes to the
correct sizes. In this video I receive long MGN12 linear
rails and continue with the assembly of my CNC machine. So my longer rails have arrived today as well. I’ve got the 100, 65. This rail is the only unusual ones. Everything else is pretty consistent. What I’m going to do now is leave the blocks
in some alcohol. All of these have the letter B engraved on
them and this one has a W. Don’t know what that means. This is what the methylated spirit looks like
after the rail blocks have been in the solution for about three days. I painstakingly check each rail block, replace
any lost bearings and placing the block on a rail. If I don’t think it sounds or feels smooth
I carefully move the block to another rail – picking the best combination. Eventually I got everything working smoothly
bar one length. To just illustrate the problem I’m having. These are really good. Good. Good. Good. Good. This one, everything is difficult. I bought these from a seller on AliExpress
and asked them what they suggested I do and they suggested trying to seat the blocks by
hammering them. So this rail is not ground properly. It’s a bit too thick so I need a replacement. Instead, I actually used a thin piece of diamond
abrasive which I drew along the length of the channels the bearings would ran along,
and this actually improved things. This might be bowed as well. Once it’s pressed flat against the aluminium
extrusion it should be a lot better. It’s not as good as the other rail. I did try hammering some as well, but that
didn’t seem to make much of a difference. It is clear some run better than other but
they range seem passable. I’m going to put the best moving rail on
the fixed section of each plate and the slightly coarser sounding rail on the section with
the slotted holes. I’m now making the spindle mounts. To save time and material I’m going to do
this by cutting the outer shape first – this is a 117mm square on the table saw. I then making a cradle to hold them on the
CNC machine while I mill the clamping hole. I made the cradle slightly undersized and
re-sized the hole till I got a tight fit. I’m using 16mm acetal which is an engineering
plastic, and a really nice material to work with on the CNC machine. I then cut the hole out using tabs or bridges
to hold the off-cut in place. After which I take that way and make a second
pass while the piece is still in the cradle to mill the bridge away. I check the first piece on the 3d printed
mock up, and happy with it I cut the second one out as well. I then mark, drill and tap all the holes on
the spindle plates. The ones at the rear will be for fixing the
plates to the z axis pate, and there is also a clamping mechanism at the front. I use a bed vice to hold the material in the
right position and also use a bit of 6mm ply to stop the material squashing and changing
shape while drilling. I drill the holes out with a 4.2mm stub drill
bit and thread the opening with an M5 tap. I assemble and check things as I go along. For the clamping thread I first had to drill
an openings a little wider than the shaft of the tapping bit through the clamping section. I spot marked the material with the larger
drill bit. You can see I used a bit of 6mm sheet material
to top the material flexing while drilling, and then swapped over to a 4.2mm bit to make
the hole before tapping. What I’m going to do now is just cut the ends
of the rails. I’ve got a piece of C-beam that’s just shy
of 30cm. I don’t want to have to buy another rail
or cut a larger spare piece down so this’ll have to do. If I’m careful I shouldn’t weekend the
rail too much. I then began setting the first rail the correct
distance from the edge of the c-beam – and used my dial gauge jig to line up the second
rail. I explain how this works in a previous video
so I’ll brush over this. So it’s about 0.03 – 0.02 between the rails. I’m using stainless steel machine screws
here but later I swap over to high tensile ones. I then fixed one side of the rail blocks to
the plate using 8mm machine screws, followed by 10mm machine screws with a washer on the
opposite side. One side fixed securely while the other, the
longer machine screws, bottoms out in the threaded holes and allows for a little flexibility
in the movement. I’m now cutting the standoffs for the nut-blocks. I had to surface the acetal down to 10mm and
then cut the shapes out. I’m cutting a few more than I would need
in case I build other machines in the future. I measure from the top of the material each
time but I could in theory measure from the waste board upwards. But what I’ve noticed with the bCNC – just
went to make a cup of tea and the thing just kicked itself off. I should have really put more tabs there. I got another two and then I had to just stop. It started to sound a bit funny – I could
hear a crunching sound as it was going down and I can’t tell if that something else breaking. That was the last job I was planning to do
with this CNC machine as it is. The clamping plates are starting to crack,
and I’ve got all the parts ready for the new version of the machine and these pieces here
that I just cut are the stand offs for the nut blocks. Time to die. The last thing I need to do, is drill a hole
through this nut block. I’ve actually fitted some on already. I just simply held it in place and put the
machine screws through and all I need to do now is tap the nut block so I make the centre
of the hole and where that lines up with the plate. I use a parallel punch held in the bearings
at 90 degrees to the plate, knocking it with a hammer to make a mark on the blank nut block. I then drill a 7mm opening and use a TR8 tap
that I made some time ago to make the thread. I decided to make my own tap because I’ve
noticed there are slight variations depending where you buy the leadscrew and blocks from. Some just don’t fit at all despite being
listed as compatible. This is because some threads are square and
rounded. Even some sets even from more reputable places
can be quite difficult to thread – so for best results I found making my own was the
solution. I also drill a smaller opening for an M5 threaded
which accepts a grub screw to tension the nutblock. When it is in position, I will also add a
nut to lock it off once in the correct position. So if you going in from the bottom, make sure
you put the washer then the locking collar. I’m just loosening the tension-ing grub screw. It’s a bit hard to see but make sure your
tensioning grub screw is extended out a fair bit because you may need to push the tab in
while you’re putting the leadscrew through the threaded hole. If it’s not in the right position it can actually
pull the smaller section that has a thread on it away from the main body and tension
it before you have a change to actually use the grub-screw and locking nut. So you should be able to twist it in by hand. Locking collar, washer. Ok that feel really solid. So I’ve just placed the hard stops in position,
somehow I’ve over looked it but this is really close to that. The distance between the back of the plate
and the face of the aluminium extrusion that faces the plate is 30mm and that’s correct
so the error is in the acetal plates I cut… Nooo, the error is in me having reduced the
thickness of the plates but not doing so in the model 3D model, and compensating with
the positioning of the spindle opening. As we get closer to the end I’ll share more
of my cock-ups. So that’s even more reason to be pleased I
didn’t cut these in aluminium. In future what I could do is just add a curvature
along face of this curve here and at the rear, because they’re both identical and that would
create enough room for the spindle to pass. So the rails are a couple mill longer and
I’m not going to by another length of aluminium extrusion, so I’m just going to cut these
down with an angle grinder. I’ve just put all the t-nuts on. So I’ve just put the t-nuts and the M3 machine
screws in, so this is in position. What I do now use the same jig on the opposite
side to set the first three machine screws at the correct distance… I’s almost like a hole in the centre would
be really useful for setting these. So one problem I think I can foresee, is how
to attach these limit switches underneath the plate. I don’t particularly want to do them now because
I haven’t really through about that stage. I then tried to rehearse the assembly imagining
this had been screwed down. I think it’s going to be really tricky. I think what I’m going to do need is some
kind of 1/4 inch ratchet that can get in there and tighten these up when I need to. I don’t think it’s worth putting these on
and wiring them now, because I just don’t know how I’m going to do these. Whether they’re going to be normally open
or closed. The other thing I’ve just realised as well,
if I grab a straight edge from one of the squares. If I push that down on one side, you can see
that these are not lining up properly. Carpenters use winding sticks to do a similar
thing on boards, and I should have used this method earlier to identify any major twists
before assembling a good deal of the machine. What occurred to me, unfortunately after fixing
at least three of the plate using the slotted holes, was that I could have used a different
method – shims. The plates can pinch and restrict movement
when tightened to twisted rail blocks. While I can still move my plates when everything
is fully tightened, it’s preferable to get things running as optimally as possible so
there’s less strain on the motor and parts. What I should have done was to check the distance
at each threaded hole on the rail blocks, with a feeler gauge and a straight edge – pushing
the edge down against the un-slotted rail bocks as my reference – and after identifying
the gap with the feeler gauge used some thin 0.2mm shim washers to pack out the gap between
the plate and the block. Now the twists could be the rails or rail
blocks themselves, but I also have had the experience of receiving aluminium profile
that’s not been square. There’s not much you can do with the latter
but the shims would help with the former. So these sliding nuts will be for the angle
bracket that adds a little more support to the y plates when they’re screwed down. I’m going to jump ahead a little – as
I’ve essentially installed all the rails using the same method as I showed on the z
axis. In addition to this, I changed the 3d printed
90 degree brackets under the waste board with aluminium ones. Ok I’ve just
noticed something that I need to change in the design and it’s these plates here. The bottom section here which screws into
this 20x40mm piece of ali-extrusion is a little bit shifted to one side and if this end is
in line with that face of the plate the rail block actually hits into that and can’t move
the full extent. So I’mg going to have to change the design
for the plate but to get around it, I can just use it lined up with this side of the
c-beam. I’ve just fixed everything together, apart
from this section here. The two support pieces at the front and back
are a bit too wide, so I’m going to measure it, dismantle it and cut it down. I also had to make a simple tap to further
adapt the y plates nut blocks to run more smoothly along their threaded rods, but in
the end I had this for my efforts. I’ve plugged it in, the limit switches are
not connected so i can’t home the machine but I can move it around, and it does seem
to be working. I can’t home the machine yet as I still
haven’t installed the limit switches but it’s moving, and it’s a little quieter
than the previous version. Again I overlooked some additional things
including not lining up the motor plates properly to the aluminium profile, and there not being
enough space for the drag chain to fit along one of the y axis c-beams where I intended
it to go, and that the x axis leadscrew is so long if I move to one end, it flexes on
the other side. I didn’t notice this before in the previous
machine because the leadscrew was facing away from me and this will be a problem if I hit
the hard stops, or work on harder material or cut too quickly. One way I get around this is to put a locking
collar on the outside of the plate – fixing the leadscrew on both ends. I could still install a drag chain where I
had intended, but that would reduce the width of the cutting capacity. So every time I get a step closer to finishing,
I realise there’s a ton more things I overlooked or new ideas I’d rather follow despite being
half way through realising the previous ones. But hopefully in the next video, which should
be the final one, I’ll just need to install the drag chains, fit the new limit switches,
and remove the old wiring for the proximity sensors – and then I can actually make something. Fancy that.

21 thoughts on “#31 Assembling Aluminium CNC Machine #31 / MGN12 Linear Rails / XYZ Axis / Spindle Mount

  1. Hey, at min 16:00… Why you put the washer in between screw head and plate? This is supposed to be in between plate and bearings! Hahaha! Nice design BTW 🙂

  2. One thing that can help with the X axis lead screw is using a KFL08 bearing (find it in Amazon). This is a face mounted bearing. You can use oversized screw holes to compense any misalignment between the lead screw nut hole and the bearing holes. Maybe that is causing the bending issue.

  3. if you buy the expensive name brand rails and blocks they are fitted with different size balls to get the right preload. You should fill the bearing blocks with grease. If those C-beams are the V-groove type I find that the grove is so wide that it is marginal that there is enough for a 12mm rail to seat against

  4. So it was 7mm you drilled out your holes to for the trapezoidal lead screw tap. Probably 2 years too late for the guy that asked on the video where you initially made the tap. Lucky for me though, I just made a tap today to make a replacement nut for the x axis of a mini-lathe I'm converting to cnc. Strictly speaking though, a hole for a tap should be the nominal diameter minus the pitch of the screw. So if the pitch of your leadscrew is 2 you should drill it out to 6mm before tapping.

    Feeling you on the getting to actually make something thing. This lathe project has been going on 2 months and There's no doubt a million and one snags I've still yet to his before i complete it. In the meantime, Ideas for other Smaller projects keep coming but I know i need to focus on the lathe or I won't finish it!

    Loving your poor man's rail alignment stop idea for the mgn12 rails btw.

    Wishing you the best of luck in getting your machine finished. You'll get all the kinks out eventually I'm sure. Looking forward to seeing the finished machine doing it's thing.

  5. ohh, 1 more video — really? I DO NOT believe you. I know it from experience, you'll always find something to improve/tweak 🙂 — love this series

  6. These MGN12 rails and blocks are really like playing a lottery…. preferably buy everything you need in one batch because every batch they make there in China seems to be different…. Also a lot of sellers don't ship it in strong cardboard tubes but just in a plastic bag. I've received some bent items….

    They won't care for negative review if they just made 100+ euro's from you….

  7. You should use ballscrew for your x axis.leadscrew that long will wobble. I have same experience with you

  8. This looks good in YouTube videos but if real they are so bad. It will be an head ache purchasing such low quality products. It needs replacements and spare parts tooooo often. The after sales service is too bad. Sorry guys you will get better Korean products in the market just for few hundreds more. My advice through experience. Please don't buy.

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