4' x 4' x 8" Router Build

[JonnyFive]

Hi all, thought it was about time I broke my silence and made myself known on here. Building my own CNC router is something I've wanted to do for a long time. Over 10 years ago whilst pondering the best way to tackle a woodworking project I came up with the idea of a cross vise on a drill press using a router bit to create a low cost but reasonably accurate solution. It then occurred to me that I could put motors on each axis and voila my own CNC machine. A short amount of Googling later revealed I wasn't the first to have this idea and that using a drill press in this manor wasn't a good idea and that is when I stumbled across the buildyourcnc website. Over the years I have collected project ideas and developed my machine requirements to a point well beyond the limitations of an MDF machine which is when I settled on a design based on Joe's Evo machine.

A decade goes by and I'm now in a position where I have the space to build a machine, more importantly I have approval from the boss!! The only thing in short supply is time, a young family takes up the majority of time and energy that I would usually commit to hobbies but I've set myself goals to make this happen. I'm determined to start building this summer and have spent the last 6 months or so learning Fusion 360 and designing my machine. I'm a long term (18 years+) Pro/Engineer / Creo user and initially found Fusion really wasn't intuitive but I'm getting there slowly.

So on to my machine, as mentioned it started as Joe's Evo but I have made tweaks along the way and have ended up with something that doesn't have much in common with this starting point. I've settled on a cutting area of 4' x 4' x 8" with an increased travel (an extra 12") on the y-axis (still confused about which is x and y but it makes most sense to me for the long axis to be y not the gantry) to allow dovetailing or a 4th / 5th axis to be added at some point in the future. I'll be working mainly with wood, plastic and with the occasional bit of aluminium.

The base frame consists of 2 welded side frames (made from 50x50x3 box section with 100x50x4 for the top beams), a welded top frame acting as the machine bed, and lower cross beams. These are all bolted together and then the top beams levelled using epoxy.

The x & y axes uses 20mm Hiwin rails, the z uses 15mm. The x rails are mounted top and bottom of a length of 160 x 80mm aluminium extrusion. The z axis has the carriages fixed to the x axis and the rails on the moving spindle mount plate. I believe this will give me the stiffest setup.

Up until this point I am pretty happy with the design although there is a lot more detail to be added before I start building. I have a number of questions that I would really appreciate the benefit of everyone else's superior knowledge and experience:

1. How much over travel should each axis have, e.g. for the 4' x-axis how long should the travel really be? Is an extra 1" each side about right?
2. What should the clearance between the collet and the spoilboard be at maximum (lowest) travel of the z-axis?
3. What is the best transmission method for this size machine? A lot of people on here use ballscrews but there seems to be a move away from this within the Joe's CNC community for bigger machines (over 1000m). I'm currently using the CNC router parts rack and pinion unit but wondering if this is the best solution?
4. I'm a little stuck on how I maintain the parallel relationship between the y-axis rails and the racks. Once the frame has been levelled with epoxy it is straightforward to align the rails, but my assumption is that the epoxy is the only reliable datum and the side of the frame could be distorted / twisted due to the welding. The best I can come up with is to either mount the rack on a piece of angle fixed to the top of the epoxy or mount the rail and rack to a piece of aluminium extrusion to keep them both parallel?

I'm sure there will be hundreds of questions to come, thanks all for looking and any suggestions you have.

Cheers,

Jon

P.S. Ignore the left hand side in these pics, I have only concentrated on the right hand side for now.

[GrahamWhite]

Hi Jon,
I'm currently building a Joes Hybrid R&P 8ft x 4ft
my build is budget constrained so that's why I went with the cnc routerparts pinion drives but even for my machine at 8ft you can go ballscrews- they just need to be 25mm or bigger I was advised to stop the whipping.
If you are still thinking of the pinion drives then please be aware that the spur gear they use is a US imperial pitch size, so if you don't have any machining options they could be very expensive to change to metric- I was quoted £100 each spur! I found it difficult to obtain the Imperial Rack size here so had to sort it a different route.
Afraid that's my only input as I have followed most of the plans fairly closely.
Best of luck with the build :)
Regards
Graham

[routercnc]

Hi Jonnyfive

Overall design concept looks OK, but some comments.

1) An extra 1" travel will be fine to allow the machine to go slightly over the home switch/prox and reverse back to settle at the home position. Gives a small amount of room before any physical hard stop.

2) When the Z is at maximum travel the collet needs to be close enough so that the cutting bit can level the board. I notice on your design that there is still plenty of Z travel left when nearly fully down, which is a bit of a waste. It also means when the Z axis is fully up/home it is still fairly close to the board which will limit the maximum height of the part you can cut. If you want to do vice work this gap looks too small. Most people work to 150 mm from a typical tool tip to the spoil board when fully raised. Yours looks considerably closer. Just check this is what you want the machine to do. You will see other machines on here use vertical risers on the bed, or vertical extensions of the side members for the base frame to get the main beam high enough that the gantry then runs on.

3) Never used R&P so can't comment. Others may be able to chip in on whether you can go up from 16 mm ballscrew to 20 mm ballscrew as an alternative step before going to R&P for the long axis, potentially tensioned at both ends. Wait for advice on that one . . .

4) I've seen racks shimmed in using a DTI mounted to the carriage of the rail, ensuring it runs parallel. Either use proper shim stock or aluminium foil if the gaps are not that big. One thing to consider is that the stiffness of that axis depends on the stiffness of the rack mounting so I wouldn't favour angle brackets and the like, rather a very solid shimmed mount back to the main gantry.

Best bit is when it is all built and moving you will be able to say JonnyFive is alive

[JonnyFive]

Thanks for the replies.

Graham:

If you are still thinking of the pinion drives then please be aware that the spur gear they use is a US imperial pitch size

I knew it was an imperial rack but had assumed it was of the standard DP type that isn't too hard to find? Do you know what pitch it is? What is the solution you have come up with?

routercnc:

1) An extra 1" travel will be fine to allow the machine to go slightly over the home switch/prox and reverse back to settle at the home position. Gives a small amount of room before any physical hard stop.

OK, I'll go with 50" travel, I'll round up to 1300mm as I'm a metric kind of guy.

2) When the Z is at maximum travel the collet needs to be close enough so that the cutting bit can level the board. I notice on your design that there is still plenty of Z travel left when nearly fully down, which is a bit of a waste. It also means when the Z axis is fully up/home it is still fairly close to the board which will limit the maximum height of the part you can cut. If you want to do vice work this gap looks too small. Most people work to 150 mm from a typical tool tip to the spoil board when fully raised. Yours looks considerably closer.

This is why I was asking so that I can adjust the offset between the spoilboard and the gantry, it's at a random arbitrary dimension at the moment which I agree looks too small. I guess my question should have been how much does the shortest cutter stick out from the spindle, so long as that just touches the spoilboard then I can adjust my gantry height from that point.

Just check this is what you want the machine to do. You will see other machines on here use vertical risers on the bed, or vertical extensions of the side members for the base frame to get the main beam high enough that the gantry then runs on.

Not entirely sure waht you mean by this, can you explain please?

4) I've seen racks shimmed in using a DTI mounted to the carriage of the rail, ensuring it runs parallel. Either use proper shim stock or aluminium foil if the gaps are not that big.

I can see the advantage of a ballscrew as there are only two points that need shimming.

One thing to consider is that the stiffness of that axis depends on the stiffness of the rack mounting so I wouldn't favour angle brackets and the like, rather a very solid shimmed mount back to the main gantry.

I hadn't considered this, it's a really good point thanks!

Best bit is when it is all built and moving you will be able to say JonnyFive is alive

This day is a long way off but I can't wait!

Cheers!

[routercnc]

Ok the vertical risers comment- I meant at the moment the side members that the long axis rails sit on would need to move up to push the gantry up and that it would be stiffer if the vertical parts of the lower frame were longer rather than finding a rectangular section which was very tall and slim. In fact I would probably not go with side members quite as rectangular as you have drawn them but make them a bit more squarish. Then get the height you need by making the base frame vertical parts longer. Very tall large open rectangular sections will start to lozenge when they get pushed sideways by the cutting forces. Away from pc so I can’t sketch something.

[JonnyFive]

Understood. They were originally 50x50x3 like the rest of the frame but I changed them to increase the second moment of area. I can change them back easy enough.

[GrahamWhite]

I bought my rack while the parts where on their way from USA, noobie error on my part! lol
I only matched up the 20 degree angle not the DP
End up buying new 60tooth gears with a hub on and new spur gears for mod 1.0 rack and drilled out and reassembled the drives, at least now if I ever need to replace the spur gear they're only £5 :)

[Neale]

Good luck - it's a fun process!

I built something roughly similar a year or two back - here. Probably more useful if you look at the "what I would do different next time" comments!

Joe's CNC guys go rack and pinion because it is a heavily US-based community. R&P can be bought from US manufacturers who don't seem to make ballscrews which generally come from China. Not a popular choice for US builders, unlike UK/Europe. Seems to be almost a fashion thing rather than technical choice. Both can work but unless you really need R&P, ballscrews are much easier.

[JonnyFive]

Thanks for your input Neale, just read your thread - great work on documenting everything so thoroughly!! It'd be nice to see some photos of the entire machine, looks like I'm heading along a similar path to you.

Interesting what you say about the R&P. My understanding of the ballscrew / R&P decision was that although ballscrews are more accurate & efficient anything over 1m should use R&P because the ballscrew whipping limits performance - is that correct? There doesn't seem to be much of a cost difference between the two?

[JonnyFive]

I bought my rack while the parts where on their way from USA, noobie error on my part! lol
I only matched up the 20 degree angle not the DP
End up buying new 60tooth gears with a hub on and new spur gears for mod 1.0 rack and drilled out and reassembled the drives, at least now if I ever need to replace the spur gear they're only £5 :)

Sounds like it might have been a costly way of doing things? I had considered designing my own version as there's nothing clever about it really but thought the costs would be more than buying from CNCRP.

Out of interest where did you get your aluminium extrusion from please?