I'm looking to build/rebuild my 8x4 CNC. I currently use one of the SheetCNC routers, it's a 25mm MDF frame which is chain-driven and runs on steel wheels on angle iron. It has worked well for the last 4 years doing what we need it to do, cutting 6mm Marine Ply, but work is changing so we need to move ahead. I'm currently going through the process of figuring out a new machine which will take its place.

The new machine is going to be run on a production basis, machining 18 and 25mm Ply/MDF. This last two weeks for example I've machined 24 sheets of 18mm Ply and last week I did 32 sheets of 25mm Ply...all at 2000mm/s and 4mm DOC. It took forever lol, hence the reason to push and get this done. I don't have tons of money to throw at it, but I do need it to run as quickly and efficiently as possible, so the biggest bang for buck on each component is what I'm looking at.

Originally I had planned to upgrade this piecemeal and on the cheap, but I've taken a step back, decided to stop my penny pinching and am looking to invest some (not all) money into creating a machine I can use for work. I've got shorter arms and longer pockets than a Yorkshireman....

I planned to make a steel/birch ply composite 1.5mm Steel plate/36mm Birch Ply/4mm Steel Plate for the gantry, and run it on SBR20s or 25s, belt driven and then use the 3 x 3Nm open loop steppers I currently have...this is what I'm thinking of now...

What I need it to cut -

Occasionally I may cut the occasional bit of Diabond (plastic/ally or plastic/0.3mm steel)

Frame Base - The machine I currently have uses a 25mm MDF and 25mm ply frame. Im planning on still using that as the base (think bench top machine) and then the rails will be mounted on 100 x 50 x 3mm steel box section. The 100x50mm will also be fixed to the MDF/Ply base every 450mm or so and I can always put a brace between the steel for additional rigidity.

Frame Gantry Uprights - Looking to use 30mm box section which has been laser cut and folded. The plan would be to get the laser cutter to cut holes where I want to run bolts, I will then add a 4 or 6mm steel plate to each side and bolt through. Effectively making a wide, strong steel upright. My welding skills are not great at the moment, hence the plate and bolt construction. I've given some ideas below on shapes etc, by all means, let me know if I should look at some other designs. Getting the supplier to do the majority of the work saves my time so it just becomes a buy and bolt together, a big kit.

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Gantry - The plan was to create a 200mm, square torsion box from Birch ply and then line the outside of it with 1.5mm steel plate. Now Im thinking of going with a box section frame and bolting/screwing steel plate to that, bascially making a big box section. This will be 200mm square. We can go bigger, ideally, I would like to have 200mm under the gantry just in case we get asked to machine any oak beams etc.

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Motor/Drive - I have 4 Open loop 3Nm steppers currently on my CNC, I originally thought about using those but if I'm going to upgrade I'm upgrading. What do you guys think to these Nema 34s, they are 4Nm, and they also do a 4.8Nm version. If we think that a set of closed-loop 23s is enough, then I'm happy to save the money on them.

Drive - Looking at using MOD 1 Rack with the below gearbox, can I direct drive from the steppers, through the gearbox into the gear onto the rack? Recommendations for MOD1 rack suppliers in the UK?

Rails - Man, these things are expensive lol. I had looked at the SBR20 or 25s as they are cheap enough for the length that I need but again, if it's an upgrade, then do it properly. The weight wont be ridiculous so can I get away with HGR15 or do I need to look at 20, at least for the long axis? Any recommendations for linear rail suppliers in the UK?

Spindle - I've got a 2.2 or 3kw spindle on the machine at the moment, think its the 3kw one. Im going to keep this for the time being but can upgrade once the machine is done.

Software - Im planning on keeping Mach 3, I don't need anything super special, just something that works when I need it to and I can show someone how to use. If you have a better recommendation, let me know!

Here are a few ideas on mounting options for the rails/rack

Gan 1 - The Gantry sits on a 100x100 steel angle iron, the cars are offset slight to allow access. The angle iron is cut in line with the composite.
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Gan 2 - The gantry sits on a 100x50mm angle iron, this then extends out of the side of the composite and the cars are bolted to it. This gives the advantage that the gantry forces go straight down.
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Gan 3 - The Gantry sits on sections of C Channel and then everything is through bolted on either side. These then extend out of the sides like Gan2, allowing the forces to go directly down.
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Would love to hear any recommendations, information or feedback!