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  1. #1
    Im after some advice as I'm not sure where to start. Hope you guys don't mind me asking a whole swathe of questions.

    We had planned to purchase a Chinese CNC however this may no longer be an option so I'm thinking of building one instead. I've built a couple small machines but I seem to be hitting a block with a big unit. Extrusion and VWheels seem alot easier lol. The router will be 8 X 4, ideally 5 x 10 would be better as we work alot with 5 x 5 sheets of Birch Plywood but I'll go with what we can get. It's going to be used for MDF and Plywood production type shape cutting as well as 6mm 8 x 4 plywood sheets long sweeping cuts. HDPE, Plywood, MDF, Hardwood, soft wood and Ally machining for signage. The v carved or pocket cut type. I've also got an idea for machining 100mm thick laminated birch Plywood blocks into 3d (2.5d?) shapes.

    I've had a read through of the stickies and build logs but there are a couple of bits which are making it difficult for me to price up...

    Machine size

    What short of frame would I be looking at for the above sizes? 3 X 1.8m would be good enough for an 8 X 4?

    Bed/Stand

    Does this need to be made from steel? Could I get away with making it from 4x2 with a 40mm MDF top?

    Frame

    I've not welded since school but reckon I can weld together a frame if I have a bit of practice. Would 80 x 80 x 5mm steel box section work? I picked 5mm to allow for tapping. I'll get a design made up but currently I'm thinking of 3 long sections with 2 end pieces and 4 supports left to right, one every 600mm or so.

    Square rails

    Will 20mm rails work? I've only been able to find these at 2.7m so does that mean that 8 x 4 is the biggest I can go? I would be looking at Hiwin.

    Drive system

    25mm ballscrews, was my first thought but again, I'm still learning. Is there is a good quality supplier to get these from in the UK?

    Electronics

    I'm still learning about this. I've been reading stacks of posts from Jazz to try and get the right balance between cost and performance. Hoping someone could point me in the right direction in terms of specs or reading material. Fully understand I need to get the mechanical design sorted.

    Spindle

    I'm thinking 4.5kw with a 6kw inverter to run it. This is the sort of spec we were looking at in China. Is this overkill for what we need?

    Software

    I've seen alot of good to be said for UCCNC so I'm thinking this is where I will be edging towards unless I'm off the mark again.

    Budget would be up to 5k but ideally lower if at all possible. Does this sound doable or am I way off the mark here?

    Please feel free to correct me or ask any questions you need answering.

  2. #2
    AndyUK's Avatar
    Lives in Southampton, United Kingdom. Last Activity: 8 Hours Ago Has been a member for 2-3 years. Has a total post count of 232. Received thanks 53 times, giving thanks to others 22 times. Referred 1 members to the community.
    Quote Originally Posted by SweetAs View Post
    Square rails

    Will 20mm rails work? I've only been able to find these at 2.7m so does that mean that 8 x 4 is the biggest I can go? I would be looking at Hiwin.

    Drive system

    25mm ballscrews, was my first thought but again, I'm still learning. Is there is a good quality supplier to get these from in the UK?
    You can join rails - granted its a pain in the arse, but can be done.

    I think most machines of this size will use R&P; but theres been some interesting threads recently about rotating ball nut setups which might be worth looking into.

    As always with suppliers, Fred at BST Linear on Aliexpress. Email directly for a quote though.

  3. #3
    JAZZCNC's Avatar
    Lives in wakefield, United Kingdom. Last Activity: 10 Hours Ago Forum Superstar, has done so much to help others, they deserve a medal. Has been a member for 8-9 years. Has a total post count of 6,509. Received thanks 1,075 times, giving thanks to others 49 times.
    Ok straight of the bat drop any thoughts of building from wood as you will regret it and defeats the point in using components like linear rails and ball-screws. It will also cost nearly as much if not more in wood than it would steel and take longer to build.

    Next is the 5K. Yes it's just about do-able building your self but you'll need to be careful with what you buy and nearly all the major components will have to come from China.

    Regards how to drive it then this needs careful consideration, esp if you have little to no experience because when you get long things begin to get complicated fast.
    R&P is often used on large machines but it's the least efficient typicly around 50/60% with more backlash so it needs large motors/drives etc which cost more and needs the most maintenance.
    Gearing will be required so you need to factor which method to use and what ratio will be needed to give you the feeds you require and keep the motors in right RPM range to give torque while cutting. Get it wrong and you'll be chasing speed or constantly chasing issues with stalling motors and belts etc.
    The setup is simple but needs most maintenance adjusting the backlash to a minimum while at the same time not over tensioning the pinion causing excessive wear.

    Rotating ball-screws are far better-regarded efficiency typically around 90-95% and require slightly less power but they come with there own issues, namely screw whip at higher feeds. So again a careful selection of right screw diameter and pitch is required along with motors. Thicker screws whip less but the inertia is a lot more so more powerful motors are required, again more costly. Alignment also requires careful set up so there's more to setting up the machine. The upside is that when it's done it's done unless you have a major incident and skew the gantry up badly, in which case you usually knacker the screws anyway so it's all fubar.!

    Rotating ball-nut setup works the best in my experience but these are not something you can easily buy of the shelf and very expensive. So the only option is to build your own which isn't something most people can do unless they have access to a lathe and mill and know how to operate them to hold high tolerances.

    Next option and one I'd suggest you consider is using a belt drive.? It gives a combination of Screws and Rack. It's very efficient at around 80% with low backlash and if done correctly can give very close to the ball-screw performance. It still requires gearing to give you the correct feeds etc but with much less hassle than R&P gives regards setup and adjustment.

    Regards the rails then 20mm will easily handle the loads etc but 25mm works better on a machine this size and to be honest, the difference in price isn't massive so not worth not using. Highwin Linear rails can be joined easily enough but you can buy them up to 6mtr in length in the UK. From China, 2,9Mtr is about the longest you'll get if using air freight. If you ship them by sea you can get longer lengths but is a pain in the arse and takes longer.

    The goal when building a machine this size or any machine, to be honest, but esp at this size is lowering vibrations because they affect the performance and finish also increasing tool wear. So with such a wide machine, the gantry becomes a tuning fork. So a substantial gantry and rail system pays off big time.
    Don't let the fact your cutting MDF and Ply fool you, to cut correctly and make machine this size worthy you'll need a strong gantry with a spindle that can handle a good depth of cut at correct feeds. You'll also need a good dust extraction system so factor this into your Budget.!

    Regards the spindle then you'll need a Z-axis Motor with a brake otherwise it will fall under its own weight when powered down or strain the motor when at standstill for long periods. These things are all adding to the costs and highlight just how quickly costs can rise.

    My Strong advise is to buy NOTHING until you have finalized design to a relatively high level with a full understanding of what building and why you are using those components. If not then you'll just blow money, waste time and frustrate your self daft when things don't work as expected.

  4. #4
    Machining 100mm blanks might be an interesting challenge.First you need to find long cutters and then you need to be sure of getting them to and from the workpiece without digging a trench.

  5. #5
    JAZZCNC's Avatar
    Lives in wakefield, United Kingdom. Last Activity: 10 Hours Ago Forum Superstar, has done so much to help others, they deserve a medal. Has been a member for 8-9 years. Has a total post count of 6,509. Received thanks 1,075 times, giving thanks to others 49 times.
    Quote Originally Posted by routerdriver View Post
    Machining 100mm blanks might be an interesting challenge.First you need to find long cutters and then you need to be sure of getting them to and from the workpiece without digging a trench.
    Not with the right spindle and design of the gantry / Z-axis. All the machines I build at this size will cut 100mm depth and retract the tool above the workpiece. However, The cutters are expensive and not easy to find. Work holding also becomes a fun challenge.!

  6. #6
    Kitwn's Avatar
    Lives in Exmouth, Australia. Last Activity: 2 Hours Ago Has been a member for 2-3 years. Has a total post count of 241. Received thanks 30 times, giving thanks to others 4 times.
    Quote Originally Posted by JAZZCNC View Post
    Next option and one I'd suggest you consider is using a belt drive.? It gives a combination of Screws and Rack. It's very efficient at around 80% with low backlash and if done correctly can give very close to the ball-screw performance. It still requires gearing to give you the correct feeds etc but with much less hassle than R&P gives regards setup and adjustment.
    This is the first comment I remember seeing about the potential relative performance of belt drives, they don't seem very popular but have a lot going for them. Have you seen the Everman variation aimed at reducing belt stretch? This link is to the US patent for the design.
    https://patents.google.com/patent/US20090301237
    Last edited by Kitwn; 1 Week Ago at 03:32 AM.
    Engineering is the art of doing for ten shillings what any fool can do for a pound.
    Wellington.

  7. #7
    JAZZCNC's Avatar
    Lives in wakefield, United Kingdom. Last Activity: 10 Hours Ago Forum Superstar, has done so much to help others, they deserve a medal. Has been a member for 8-9 years. Has a total post count of 6,509. Received thanks 1,075 times, giving thanks to others 49 times.
    Quote Originally Posted by Kitwn View Post
    This is the first comment I remember seeing about the potential relative performance of belt drives, they don't seem very popular but have a lot going for them. Have you seen the Everman variation aimed at reducing belt stretch? This link is to the US patent for the design.
    https://patents.google.com/patent/US20090301237
    I was involved in the thread on CNCZone with Mike Everman who designed this system long before the patent went in and I've built 2 machines using this setup, and 6 machines in total using a belt drive. However, I moved away from it because ball-screws came down so much in price it wasn't worth the trouble for small to medium machines I mostly build. While belts are a good choice for larger machines they do put restraints on the machine regards the best place to locate them to avoid debris, then you have wear and maintenance to consider. Ball-screws are much simpler and far less maintenance.

  8. #8
    Ok so first off, thank you for the replies.

    Looks like I've got a huge amount to figure out and get planned in. Im more of a figure it out on the fly than a planner kind of guy but I understand the need for it in this situation so I'll get my head down.

    In terms of size, what sort of frame footprint should I be looking at to begin with and will I be ok with the 80 x 80 x 5mm steel box section, can I go smaller or do I need to go bigger?

    In terms of creating more mass to remove or dampen vibrations, is this why some machines will have additional weight added to the machine?

    I don't have an issue with sourcing from China. The previous small builds I have done have all been China sourced and we have imported machinery before so we understand the process.

    Forgive the confusion with the 100mm blanks, imagine doing a 2.5D carving or a mountain. That's close to what I'm thinking of, apologies I can't give out more of an idea. Sort of like a thick relief carving.

    You right in the sense that I have little experience of big machines like this. My engineering side is fairly on point for what I understand but more than happy to take on board the comments 're the belt drive. What sort of size belt would I be looking at, they must be wide! Are you thinking of the usual single belt or would it be doubled up, is that even worth it? Do the issues with belt stretch still apply? Would it be better to look at an ally extrusion gantry to keep weight down if I'm looking at belt drive? Will belts not chase additional issues in terms of machine rigidity or am I over thinking it with the applications that I'm looking at?

    Thanks again for taking the time to reply, I'm super excited about giving it ago but at the same time trying to keep the focused at what appears a mountain to climb lol.

    Apologies for any spelling mistakes, I'm writing this out on my phone so autocorrect loves to kick in.

  9. #9
    JAZZCNC's Avatar
    Lives in wakefield, United Kingdom. Last Activity: 10 Hours Ago Forum Superstar, has done so much to help others, they deserve a medal. Has been a member for 8-9 years. Has a total post count of 6,509. Received thanks 1,075 times, giving thanks to others 49 times.
    Quote Originally Posted by SweetAs View Post
    Im more of a figure it out on the fly than a planner kind of guy but I understand the need for it in this situation so I'll get my head down.
    Resist the temptation because it will cost you money and frustrate. Key to a good machine built within budget is planning along with careful research and asking lots of questions.

    Quote Originally Posted by SweetAs View Post
    In terms of size, what sort of frame footprint should I be looking at to begin with and will I be ok with the 80 x 80 x 5mm steel box section, can I go smaller or do I need to go bigger? .
    I cannot answer to what size machine you need only you can know that.! What I can offer is that if your chasing space then consider looking at a vertical machine. it offers a big space saving along with other advantages. See video

    80x80x5 will work but wouldn't go less for 8x4 or 10x5. I use 100x100x6.

    Quote Originally Posted by SweetAs View Post
    In terms of creating more mass to remove or dampen vibrations, is this why some machines will have additional weight added to the machine?
    It's not so much weight more density that's required. Adding extra weight just costs money because takes more power to move it around. The goal is to reduce vibrations but doing that by making things stiffer and adding weight can actually introduce vibrations because becomes more resonant. Materials that absorb vibrations are more beneficial which is why cast iron is often used in machines.


    Quote Originally Posted by SweetAs View Post
    What sort of size belt would I be looking at, they must be wide! Are you thinking of the usual single belt or would it be doubled up, is that even worth it? Do the issues with belt stretch still apply?
    25-30mm will work. If you want the best system then follow the Everman type setup as it keeps belt stretch to a minimum. That said if you use the correct belts then it's not an issue.


    Quote Originally Posted by SweetAs View Post
    Would it be better to look at an ally extrusion gantry to keep weight down if I'm looking at belt drive? Will belts not chase additional issues in terms of machine rigidity or am I overthinking it with the applications that I'm looking at?
    Better than what.? Regards ally extrusion then that's what I mostly use on all my router machines for the gantry. It offers several advantages over steel when comes to fastening rails etc and is very good at reducing vibrations. It's also much easier to work with if you haven't got a mill or machines to help.


  10. #10
    Quote Originally Posted by JAZZCNC View Post
    Not with the right spindle and design of the gantry / Z-axis. All the machines I build at this size will cut 100mm depth and retract the tool above the workpiece. However, The cutters are expensive and not easy to find. Work holding also becomes a fun challenge.!
    That is an unusual amount of Z axis travel and really useful when you find a taller job that needs doing.I have had to work on 70mm thick jobs on a machine with 85mm of Z travel and it was quite,er absorbing.The comment about work holding is actually something that needs to be brought into this discussion; T slots in the table,threaded inserts or a vacuum system could all come into play.

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