Build Your Own DIY CNC Machine : C-Beam Machine XL

Designed with precision and strength in mind, in a sexy double-wide format that is capable of milling Aluminium plate
with light cuts. Featuring easy to source off the shelf Openbuilds Parts in an adaptable design; dare I say, reduce its
width for a stronger machine. Just add your unique imagination by modifying the design, tossing in some more parts or
by making your own plates with this capable Hobby CNC Machine. Part of the fun is adding your individual touch to the
build for your own special requirements. Who knows where that might lead you and the brilliant ideas you will come up
• 750 mm x 330 mm X & Y axis cut area.
• Usable cut depth is dependent on how you mount your spindle/router, bit length used and spoil board height.
But as a ballpark measurement you are looking at 1 inch (25 mm) material. The Z working height is over 2
inches for deep carving.
• The physical footprint is 1000 mm x 500 mm (with the moving Y table protruding out about 170 mm at full travel,
front and back) with the High Torque Steppers sticking out about 140 mm from the frame at the back. Maximum
Height ( Z-axis fully up) is about 630 mm.
• All the precise Acme Lead Screws are faced away from flying chips to help keep them clean.
• Outside mounted Xtreme Solid V-Wheels™ used throughout for easy on machine adjustment, tuning and
• Doubled up and adjustable Acme Nut blocks on Y and X axes with an Anti-Backlash Nut Block on the Z axis to
reduce/remove backlash.
• Strong and accurate C-Beam™ and V-Slot™ Linear Rail with the new heavy duty C-Beam™ Gantry Plate
XLarge used for all Actuators.
• Openbuilds Router / Spindle Mount (71 mm inside diameter) designed for the Bosh Colt Router; but with some
additional shimming, it is also suitable for the Dewalt 611 Router and the 0.8 kw Chinese Spindles (65 mm

“Expectations and Limitations”

“It’s hard not to have high expectations, but it is wise to be realistic about the limitations of a hobby CNC”. It will never have the capabilities of an industrial CNC machine, but for the cost of an industrial machine, “Well mortgage the house!” that’s if your lucky enough to own your own or consider reducing your expectations and work within the evident limitations of something a small fraction of the cost, which will get you most of the way there and will teach you heaps in the process. The following is just to give you a basic understanding of some principles and should only be used as a rough guide.

So what are the expectations and limitations? The biggest and most common is the desire to go as big as possible, with every increase of size adding a non-linear increase in weakness to the machine, through increases in the flex of extrusions over longer spans compounded with inaccuracies from the whip from

longer drive screws with increased distances from stepper motors among many more things. So if the rigidity of your machine is your priority, the the simplest way to reach that goal is to reduce the C-Beam span of your machine.

We can’t just ignore the laws of physics, but we can work within them to get acceptable results, by reducing the loads on the machine by taking it easy, by firstly getting our feeds and speeds just right, starting off with a reduced depth of cut, reducing the material removed with each pass, thus reducing the load on the machine, then slowly increasing the depth of cut to find your machine’s acceptable limitations (sweet spots) with each milling bit size and type, and the the material you are using.

It might take longer to cut something out, but you will have better results by getting to know you machines limitations and strengths; just like a valued friend. Learn the basics, acquire more advanced skills from those that have been there before, practice and remember mistakes are just part of the learning curve. Then before you know it, you will be milling like a professional machinist, hopefully making others journeys a little smoother and giving you the knowledge needed to dream up your next improved build.

“Dream it - Build it - Share it”

C-Beam XL_1
C-Beam XL_2

“Putting It All Together”

Like most built things, there are a billion ways to put something together, this is just my take on it, with lots of pictures
and just enough words to give you an idea. Have a look and if you find a better way to do it and there will be, please
share in the build discussion to help the other builders out there.

To make it easy, I’ve broken it down into bite-sized bits, that make bigger bits..” from little things big things grow”. Just be thankful you’re not in some wacky parallel universe where you just have to blink your eyes and it puts it all together for you… “There definitely wouldn’t be any fun or sense of accomplishment in that, would there?”


“Stay Safe, use appropriate safety gear and follow safe work practices”

C-Beam XL_3


“The 7Ps” Prior Planning & Preparation Prevents Piss Poor Performance


The Cast Corner Brackets are designed for inline joints like in a picture frame, but can be used in crossing joints with just a little modification to make this kind of joints sit flush and strong like the buttress of a tree.

You will need a flat metal file and ideally a vice to make the job easier. A Benchtop Belt / Disc sander makes the job very easy; just don’t manicure your nails to the quick.

File off those annoying little nubs on one side (highlighted) flush with that side. Prepare eighteen (18) Cast
Corner Brackets like this and put aside for the moment. This needs to be done for the crossing joints in the build
so these sit nice and flush to make strong neat joins.

While you’re at it, practice keeping the file parallel to the face of the Cast Corner Brackets. 

The Trick is to keep your elbows and or wrists at the same level/plane of your workpiece like they’re sliding along imagery rails.

“Be one with the tool and become the machine, Grasshopper”


To make the squaring up of your build easy and ultimately the performance of your machine accurate as possible, you will need to make sure all your extrusions ends are square. 

Likewise, the 250 mm, 500 mm and 1000 mm lengths of C-Beam and V-Slot need to be the same length. It doesn’t matter if they are slightly longer or shorter, just exactly the same length with square

The squarer the ends, the easier it will all go together and the better your machine, so spend a little
time on this part, it will be worth it in the long run.

Well, I lie a little, the one 1000 mm 20×40 V-Slot will need to be cut down to 960 mm or just a tad less to make fitting easy. 

Note that this measure is dependent on the length that the 1000 mm C-Beam ends up; – 40 mm.

In reality, you will only need to make two of the 250 mm C-Beams exactly the same length (Frame uprights) the odd one out will end up being used for the Z axis actuator. 

So make you job easier and use the closest pair and just make the other one nice and square.


When filing the ends of the extrusions to same length and square, try to vary your angles of approach and check often with a square. Its a slow process but you will get there. 

Marking the end of the shortest extrusion or low points with a marker pen will give you a strong visual indication when you’re gone too far with the filing. 

Test your work by laying a piece of extrusion on a flat surface and bringing the piece you’re working on in at right angles and butting it against the side; there
shouldn’t be any gaps.

If you have a Mill, trued up Drop Saw, or Disc Sander, you should know what to do, to get it close, but finish with a
file and square for the best result.


Measure what you ended up with after squaring the 1000 mm lengths of C-Beam and 20×60 V-Slot.  

Use that measurement and subtract 40 mm if you like sailing close to the wind and having an extremely tight joint or 41mm if you just want things to go together easily. 

If you make it even just a fraction too long, it’s not going to go together.

“Measure twice cut once”

Using a square mark this measurement on the 20×40 V-Slots top and side faces. 

Marking the V-Slot with a dark thick marker then scribing through that mark with a pointy sharp thing will give you a clear line to follow.

A couple of blocks clamped along the sidelines can help guide your cut. Take it slowly and let the hacksaw
teeth do the cutting. 

File the cut end flat and square and you’re done.


Tap the untapped holes in the ends of two non-Z axis 250mm C-Beams and the four lengths of 20×60 V-Slot. Use
Aluminum tapping fluid if you’ve got it, though WD 40 or Kero will do just fine, just use something. 

Aluminum is sticky stuff, so try to keep your Tap clean between taps to make the job easier with better results. This is where a shot glass filled with WD 40 comes in handy to dip your tap and a short sharp blow between taps should be enough to clean the Aluminium chips off. 

What works for me is to go in as straight as possible, pushing two to three full clockwise turns in then backing it out a turn anti-clockwise to break the chips and repeat until you are at the required depth (~15mm) then go a bit deeper to be safe. 

The hardest part is getting it started straight, so bevelling the entrance hole a little with a countersink bit or an oversized drill bit helps. Starting it off is kind of like how you start a wood screw… Push and turn a quarter turn at the same time, then repeat until it bites. Sight straight down your tap and extrusion to see if you’re going in straight, then adjust if needed. 

Note: little taps will break in a heartbeat and with little force, so if you’re forcing it, you’re going in crooked, so back it out and start again and take your time. If you haven’t done it before, I suggest practicing on the bit of 40×20 V-Slot that you cut off, first. 

Once you get the hang of it, it is easy. Another easy option is to use an M5 Drill Tap (available in the Open Builds Part Store) and a cordless drill at low speed, but always lube it up well.

“Little bits for the Frame”

Frame Assemblies

90 Degree Joining Plate Assembly (A1)


MINI BOM (BOM= Bill of materials)
• (4) 90 Degree Joining Plates
• (8) 10 mm Low Profile Screws M5
• (12) 15 mm Low Profile Screws M5
• (8) Tee Nuts

Makeup two mirrored pairs like in the picture, with the 15 mm screws down one edge, the last two holes get 10
mm screws with Tee Nuts. 

A trick is to put a bit of tape on the 15 mm screw heads to keep them together or just put them aside till needed. Just get the tee nuts threads started so they are easy to slide into the V-Slot later.

90 Degree Joining Plate Assembly (A2)

• (6) 90 Degree Joining Plates
• (18) 10 mm Low Profile Screws M5
• (12) 15 mm Low Profile Screws M5
• (18) M5 Tee Nuts

Makeup three mirrored pairs, with the 10 mm screws with Tee Nuts down one edge, the last two holes get 15
mm screws.

A bit of masking tape over the 15 mm screw heads will keep them in place for the moment or just put them aside.

Cast Corner Bracket Assembly (B1)

• (18) Cast Corner Brackets (with nubs filed off on one side)
• (36) 8 mm Low Profile Screws M5
• (36) M5 Tee Nuts

File the two nubs off if you haven’t. Makeup eighteen (18) B2 assemblies to put aside. 

To save some time, leave the Tee Nuts and Screws off the nub side of eight (8) They will be used for the Y-Actuators.

Cast Corner Bracket Assembly (B2)

• (18) Cast Corner Brackets (with nubs filed off on one side)
• (36) 8 mm Low Profile Screws M5
• (36) M5 Tee Nuts

File the two nubs off if you haven’t. Makeup eighteen (18) B2 assemblies to put aside. 

To save some time, leave the Tee Nuts and Screws off the nub side of eight (8) They will be used for the Y-Actuators.

Double L Bracket Assembly (C1)

• (2) Double L Brackets
• (8) 8 mm Low profile Screws
• (8) M5 Tee Nuts

Makeup two C1 assemblies and put aside.

Black Angle Corner Assembly (D1)

• (4) Black Angle Corner Connectors
• (4) 10 mm Low Profile Screws M5
• (4) 8 mm Low Profile Screws M5
• (4) M5 Tee Nuts

Make up four D1 assemblies. The 8 mm Screws get the Tee Nuts.

Spindle/Router Mount Assembly

• (1) Spindle/Router Mount
• (4) D1 assemblies
• 3 mm Allen Wench

Use the 10 mm screws to attach the D1 assemblies to the threaded mount holes on the outside like in the picture.

“Building the Frame”

Frame Side Assemblies

• (2) 500 mm 20×60 V-Slot
• (2) 250 mm C-Beam
• (4) A2 assemblies
• (8) B1 assemblies
• (4) B2 assemblies

• 3 mm Allen Wench
• Square

Slide in two B1 assemblies into the two upper slots in the 500 mm 20×60 V-Slot like in the picture, 100 mm back
from the end and snug them up but don’t tighten the tee nuts in the slot, you just need to stop them from
slopping about. Square them up and locate them centrally in the slot.

Slide-in two B2 assemblies with the filed side down in the middle slot and loosely snug them down and locate them as
in the picture with their centers:

* being at 30 mm and 50 mm.

Add two more B1 assemblies, centring them in the slots with their back edge flush and square with the end of the V-Slot.

Tighten these two as they will be what the others are referenced from in the join.

Lay it on its side on a flat surface and slide a 250 mm length of C-Beam into the joint, like in the picture. 

Some wiggling and loosening of Tee-nuts might be needed. Getting all the Tee-nuts pointing in the same direction is the hardest part.

Push down on a flat surface the loosely joined 60×20 V-Slot and C-Beam, then tighten the connectors, checking that the joint is nice and square with connectors centered in their slots. 

If you did a good job squaring up the
C-Beam there will be no gaps where it buts up tightly with the 60×20 V-Slot.

Slide a plate into the side slots, front
and back and snug up the Tee-nuts
level and square to the ends and top
of 60×20 V-Slot

Make up a mirrored copy and your done making the Side Frames.

Front & Back Frame Assemblies

• (2) 1000 mm 20×60 V-Sot
• (4) A1 assemblies
• (12) B2 assemblies

Makeup pair of Front/Back Frame Assemblies.
Remove the screws and tee nuts from nub side of four B2s and slide them into the top slot, followed by one intact
B2 (nub side down) and another at the other end. Then slide in A2 plates.

Makeup a mirrored pair and put the cast corners aside for attaching to the Y-Actuators later.

Joining the Frame Base

Remove the tape holding the 15 mm screws in place on the plates. Then introduce the corner joint together like
in the picture. 

Now join the four corners of the base
frame using the 15 mm screws through the corner plates into the tapped holes you spent all that time getting right.

For a tight joint, tighten the 15 mm screws into the tapped holes first, followed by the tee nuts on the plate finishing with Cast Corner Bracket Tee-nuts. Check for squareness as
you go. 

You will end up with something looking like this.

X-Axis Frame Brace

• (1) ~960 mm 20×40 V-Slot
• (2) C1 Assemblies
Introduce the C1 Double L Bracket Assemblies into the V-Slot like in the picture and tighten them flush, square
and centered to the outside ends of the V-Slot

Introduce the X-Axis Frame Brace into the inside slots of the Side Frame Uprights and slide down till flush.

Snug up the Tee-nuts with the brace flush with the top of C-Beam.

If the 20×40 is a bit tight going into the mouth of the C-Beam, either lubricate the joint a little or sneak the 20×40
down to the freezer for a bit of a snooze and grab an icy pole “frozen ice on a stick” while you’re there. 

While waiting for the 20×40 to reduce in size in the chill, smooth off the sharp edges of the C-Beam mouth with some sandpaper and a little flat stick.

If the 20×40 is a bit tight going into the mouth of the C-Beam, either lubricate the joint a little or sneak the 20×40
down to the freezer for a bit of a snooze and grab an icy pole “frozen ice on a stick” while you’re there. 

While waiting for the 20×40 to reduce in size in the chill, smooth off the sharp edges of the C-Beam mouth with some sandpaper and a little flat stick.

“Basic Structure Complete”


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