DIY CNC Router Build (large Format 5x10ft, Rack and Pinion)

This is a not so little summary of the build of my homemade CNC router, aka The Overpass. This instructable is more of a documentation of how I built my CNC and is not to be mistaken as a tutorial for buidling a CNC.

The initial target of my build was to make a large format CNC router which does not compromise on the quality and functionality. This was a little hard to achieve on a tight budget but I managed it nonetheless.

As for the inspiration and info for my build, I had a lot of help from the Joe’s CNC forum. Also I was much inspired from the CNCrouterparts machines and learned whatever I could from their website. I highly recommend to check them both out. I also watched a ton of youtube vid for an unaccounted number of hours (or days maybe lol).

Step 1: But How Much Did It Cost?

This is one of the most asked questions that I get when people see my machine. How much did it all cost?

The answer is 3500$ approx including the parts, services and the shipping/travelling costs. The cost of the laptop and software license is excluded though. From the commencement of the build to the end it took me around 4 months to complete. Cosidering the price and the hardware used and the fact that I was able to build it all by myself I'd say this was worth it. Plus nothing can beat the experience that I gained from this build. Even if I were to do a build again now, I could do it for even lesser and in much less time.

Step 2: Designing the Machine

Being a student of design I had only a faint idea of the engineering and mechanics of a CNC, so the first natural thing was to study the various nick nacks of a CNC. As stated Joe’s forum was a great source for this and also CNCzone were quite helpful.

So I started the design on sketchup and roughly sketched out the frame and gantry sizes I was intending for my build. I later detailed the model a bit by adding the gantry plates, extrusion profiles, linear bearings and the rack and pinion assembly. Later on I moved to fusion360 and modelled an accurate design that I could refer to build my final machine.

The machine is designed and constructed in such a way that there is no need for welding. All the parts are bolted together in place. This gave me the advantage to make the machine in a somewhat modular fashion i.e. one can easily scale up or scale down the build without having to buy a completely new machine (much like CNCRP builds). The gantry height is adjustable and can be raised or lowered if the situation arises. Although if I had a welder and some welding experience I would have tried to build a welded frame as it could have been a little cheaper yet more durable.

It’s a rack and pinion build and is capable of going upto 20000mm/min or faster. I generally keep the rapids under 15000 for safety reasons. The machine starts shaking noticeably if I try to go any faster. The effective cutting area is 58”x 108”. I have used a somewhat experimental way to engage the rack and pinions which works quite well for me and has saved me some money than if I had used other rack and pinion drives.

ps:
my final design is somewhat different from what I designed originally in Sketchup and/or fusion.

Step 3: List of Materials and Hardware

This is just a quick list and description of the parts I used and not the complete BOM. I apologise if I have missed any.

1- 40x80mm aluminium extrusions + t slot nuts :–

All the extrusions used in this build are 40x80mm modular profiles (except for the leg bracing which are 40x40). I used these since these were the largest profiles I could easily source for my build plus it makes it easy to work with one type of profile. Also since the whole assemble is bolted we need a lot of T-slot nuts, like a LOT. I used around 700-800 nuts in the build. I was able able to source these nuts at less than 20$ for a set of 100 (1 T-nut+1 bolt+1 washer x 100).

2- Various angle irons –

I self-fabricated all the brackets used to join the profiles together by cutting down pieces of angle irons and drilling holes in them. This was one of the most tiresome and time consuming jobs of this build but at the end I saved around a couple of 100 bucks than if I had bought them prefab. Angles have also been used to reinforce the gantry and as a support for the gear racks.

3- Mdf sheets –

Apart from the spoilboard I used MDF as a backer plate for my gantry and also to cross brace my table legs to the top frame. I would advise to use aluminium for this purpose but this is what I had lying around at the time and it worked out well.

4- Nuts and bolts –

Needles to say, one is gonna need a few assortment of nuts and bolts for this

5- 10mm steel plate for the gantry –

I was not able to source aluminium plates for my build (at least not a decent price for DIY purpose), so I bought some rectangular steel plates cut to size.

6- 20mm Acrylic plates for z axis carriages and ballscrew assembly (description covered in the article below)

7- Linear bearing and bearing blocks –

I used THK linear bearings for this build. I could have saved some money by buying Hiwins but its already done now. I used 25mm ones on the sides and 20mm on the gantry with 4 bearing blocks for each type of rails.

8- SBR16 rails and linear bearings for z axis

9- 16mm 10 pitch Ball screw and nut for z axis

10- Rack and pinion gear drive (description covered in the article below)

11- 3 nema 34s for X and Y

12- 1 nema 23 for Z

13- 4 stepper drivers

14- A parallel port Breakout board

15- Shielded wires

16- Spindle or router –

I used a 2.2 kw Chinese water cooled spindle with a HY variable frequency drive.

Step 4: ​ Tools Used

Apart from the few necessary tools, the only power tools I used for this build are as follows :-

Drill press – I have a heavy duty drill press in my workshop. As monotonous it might have been using this machine, I could not have imagined to build a the CNC without this. If you are thinking a hand drill will work well enough please reconsider.

Angle grinder – Well it goes without saying that when working with metals an angle grinder is a must. I think I used up around 10 discs in this build. Majority were depleted in cutting the 10mm steel plate.

Chop saw – This made the job much faster and easier to cut down lengths of extrusions and angle irons.

Step 5: Its All About That Base!

The base started as two symmetric side profiles with three legs each joined by brackets and cross braced using MDF for stability. Now the extrusions that I used were somewhat light duty as compared to the 80-20 range which many people use around the world. So I came up with a way of attaching the MDF to the side profile such that it provides some additional support to the profiles while bracing them to the legs. The pictures might be able to explain this a little better.

Now once these were complete I started to join the leg profiles with each other using equally cut lengths of aluminium extrusions. For better understanding visit CNCrouterparts website. I made my base assembly in a similar fashion to theirs.

Once the base was up and standing it was time to slide in the linear bearings on the sides and slide the bearing blocks over them.

Step 6: ​ Gantry Beam Design and Supports

As you have might seen in the above pics my gantry design is more like a torsion beam. This is so because I had to use the 4080 extrusions to make a very solid gantry which won’t flex and this was the only plausible solution I could come up with and it turned out good. The beam is really solid and does not flex at all. I even sat on it while it was supported on two edges.

Coming down to the supports I decided to keep it as simple as possible. Rather than making a large support plate I took a rectangular plate of 10mm steel, printed a 1:1 scaled template that I had pre designed on CAD and stuck that template over the steel. Later I just drilled and tapped the desired holes. Once all the holes were done I mounted the plates on the bearing blocks.

Now I took two small lengths of the 4080 extrusion and just vertically bolted it on the gantry plates. I checked if both the sides were at the same height with respect to the linear bearing on the sides. Then all I needed to do was to take the gantry beam and put it over the extrusions and fix them in place using the brackets. I reinforced these with some pieces of angle irons at the back of the gantry to prevent any forward/backward movement. This sort of setup gives me the flexibility to raise or lower the gantry in the future as desired although it is understood that the higher you take your gantry from the base the less stable the machine would be.

Once the gantry is mounted I slipped on the linear bearing and the bearing blocks.

Step 7: The Rack and Pinion Setup-

There was no doubt that for the scale of the machine that I was building, I would be needing a rack and pinion setup, so I started looking all over the internet for rack and pinion drives. It seemed like almost everyone was using the drive from CNCrouterparts for their DIY setup but that was not an option for me. I calculated that it would cost me upward of 200$ after shipping and import taxes for each drive and I needed 3 of it! So like every other millennial I turned to aliexpress for a cheaper option. I was able to find a 5:1 gearbox for nema34 specially intended for CNC routers. I was able to buy 3 these for 250$ in total after import duties and taxes. Score!! The gear racks were ordered to make locally.

Now after buying the gearboxes there was a challenge on how I would be able to keep the rack and pinion under tension. This would not have been a problem with the CNCRP drive as there is a spring loaded tensioner on their drive. After a few days and nights of thinking and browsing internet I was able to find a solution. If people are interested I will make a separate instructable of how I did this and link it here. This description will get somewhat lengthy otherwise. Until then try and figure it out from the pics that I have put up.

After this I just fixed up the gear racks in place and calibrated them equidistantly with the linear bearings. Now I fixed the gear box on the gantry plates making sure the pinion was engaged tightly with the gear rack.

Step 8: ​ Z Axis Carriage –

Z axis is one of the most crucial parts of your CNC. As it works in a sort of a cantilever fashion it is very important that it does not give away in any form else the cuts won’t be clean.

Before I proceed I want to justify my choice of material I used for the plates on here.

I know acrylic is comparatively weak and very brittle as compared to aluminium but as stated above I wasn’t able to source any aluminium plates so I needed an alternative. The only materials in sheet form I could find locally were acrylic, plywood, pvc, MDF & steel.

PVC sheets weren’t any thicker than 10mm so that was a no go.

Plywood and MDF had some room for flex and didn’t seem like a good choice to put them over a machine made of metal.

Steel could have been a choice of material here but I wanted the keep the load on the gantry at a minimal and adding steel seemed like a lot of unnecessary load.

Acrylic like other materials can be very weak when thinner sheets are used. I used 15mm acrylic although I recommend 20mm and would probably replace the 15mm with the latter in the future. Such thick sheets can be quite tough. I tried my best to bend it or break it manually but failed. It is mostly the impact force that could crack an acrylic which I won’t think would be a problem on a CNC machine. As far as bending is concerned the amount of force required to bend and break this thick acrylic sheet is way more than what a DIY CNC machine is capable of putting. There are other things that will probably fail before this happens (eg. Bits breaking or spindle stalling etc.).

Also there are a few advantages of using acrylic. It could be easily and accurately laser cut. I got mine laser cut. Also its very easy to make threads in acrylic with a regular tap. I have used no nuts on the z axis. All the bolts are held by threads tapped in the acrylic plates. These threads hold the bolts very tightly and securely and not one has come loose since my few months of using this machine. Apart from everything else it looks super cool.

Now that all the plates were cut and tapped it was just a matter of time to screw all the parts for the z axis together. I used a small piece of steel C channel to join the top bearing blocks to the z axis plates which in turn were directly screwed on to the lower bearing blocks. Then I was able to mount the final gearbox on these plates which would drive the Z carriage.

Step 9: ​ Electronics

Now since I am an electronics noob I would prefer not get into the depth of this topic as there are much better sources to learn from. All I can say is it is not as hard as it seems. If I can do it I am sure pretty much any one can. I will put up an internet image of a simple wiring diagram that goes into building a CNC.

A word of advice here is that before you order any electronics remember to study them online. Know what size of a machine you are building and how much power you will need. This will directly impact as to what size motors, drivers or power supply you are buying. Just remember to read the datasheets of your components carefully and follow them accordingly.

As a small generalization the electronics needed are:-

Stepper motors

Motor drivers

Power supplies for drivers

A breakout board

Power supply for breakout board

A router or spindle (also a VFD if a spindle is used)

Not necessary but try to order the electronics in the respective order as above if you are planning to build yourself a CNC.

You will of course need some electronics accessories along with the main electronics like an E stop button, Proximity switch (not necessary), Connectors, a computer etc.

Although still unfinished I stacked up and connected everything inside of a laser cut box. Everything seemed to be working well so the laziness got the better of me and I never completed the enclosure lol.

When making all the connections I recommend getting shielded wires for connections as it could make a world of difference as to how well your machine functions.

Step 10: ​ Wire Management –

Initially I just fixed a small arm like temporary fixture on the machine which carried the wires over it. Its better represented in the pics. But that used to vibrate as machine went back and forth.

So I designed and made a drag chain on my own which seemed to work really well. This way I saved quite a few bucks than I would have if I had bought an off shelf drag chain. This is one of the things I was really proud of making for this machine.

The details of this will be covered in a separate instructable. The files will be made available too. Stay tuned.

Step 11: Connections-

One of the few questions people asked me was how did I manage to get my CNC working with a parallel port using a laptop. Here I got a little bit lucky. I had this ten year old laptop lying around. Although it good for nothing today but it just had sufficient specs to run a CNC program. This laptop had a PCMCIA slot which is nothing but a fancy name for a laptop parallel port. All I needed to do was to have some sort of a PCMCIA to DB25 converter. Again aliexpress to the rescue and I found just the thing I was looking for. I did need to intall a fresh copy of xp on the laptop. Keep in mind to disable the ACPI setting before doing a fresh OS install. Google on how you can do this. Once everything was ready and drivers were installed it couldn’t have run any better than it would have on a PC.

Step 12: Concluding

The machine was up and running and all I needed to do was to lay down the Mdf spoilcaord which I fixed onto the table with t nuts and bolts.

If you are wondering on well does it cut, I am able to cut 10mm MDF in one pass at quite good feeds. I could cut thicker sheets in one pass but don't have the proper endmills for the same as of now. Above are some first cut examples of furnitures that I did on 18mm MDF using the machine. I'd say they came out fairly well and it took me less than 10 minutes to cut them out each.

I know there are still a lot of topics to cover like the software, endmills, dust collection etc. but these might really vary from people to people and their respective machine. Further this machine will always be a work in progress for me and I will keep building on it and perfecting it somewhat.

So I'l end the instructable here and hope that this might prove useful to some people who are buidling their own machine or are planning to build one.

Cheers.