CNC Router New Build

[PilotTom]

Hi all.

I'm really in need of some advise and reading through the threads here it appears I might have found the right place!

I previously had a useless MDF(!) CNC router that was a complete waste of money and I have regretted buying it ever since!

That was a few years ago and I am now after something new that actually works.

I already have a set of 4 Nema23 steppers (KL23H2100-30-4B @3.5N^.m. They don't seem too bad and drove a 4ft MDF gantry OK. I would like to reuse them to keep initial cost down and upgrade them if necessary later. Same goes for the 36v supply and driver (not sure of the drive make/model as I type).

As for the rest its a clean sheet design.

Requirements
Cutting area: 800x600x100mm minimum.
To cut: Mostly sheet plastics (5~8mm Acrylic) - This is the primary use.
Aluminium parts (hence the 100mm Z requirement)
PCB boards
Some engraving (but I know a guy with a laser engraver so hopefully not)

Budget
I am looking to spend between £800 - £1000.

Construction Ability
I only have a drill press, Mitre/Table saw and no access to a machine shop so anything I can construct needs to either be done by someone else or using these tools. I know a guy who makes gates and things professionally (but haven't approached him yet) so it might be possible to get things welded but I don't know.

Questions
So before I start planning I have a few questions.
1. I have seen routers on here that use aluminium extrusion and I think I can cut that accurately enough on the table saw but they use aluminium plate for the gantry sides and end plates which I can't construct. If I was to go down that path how much (as a ballpark) should I expect to pay to get them made for me? I need this to come in at least on budget.

2. I have also seen routers on here that are made from steel profile which (assuming I can get it welded) works out cheaper? Is there an advantage to using it over aluminium profile or is the profile better for my needs?

3. Screws. I was thinking of dual x-axis screws and singles on the rest. As for diameter and pitch I'm not sure what should be best over these distances. Some of you seem to favour 1610s, others 2005s. I don't mind using pulleys to drive them so I can adjust the ratio between stepper and screw as long as it doesn't add too much to the cost.

4. Rails. Profiled or supported? Cost is really the decider here I guess, and perhaps how I'm mounting the gantry. Perhaps when I have a design in mind I should ask this again! A bigger question is how do I mount either? I don't know how accurate either the profile or extrusion would be and have never used epoxy and don't have access to any milling or grinding machines.

I hope someone on here will be able to answer these for me or impart some advise on these issues. It will help me make some design decisions before I make a start.

Thanks all.
Tom.

[martin54]

Welcome to the forum Tom, my advice would be to have a read through some of the build logs as you will learn a lot just by doing that & probably answer some of your questions as well.
The nema 23 motors will be fine so will the power supply & drivers although you might want to think about upgrading the power supply & drivers at a latter date, better off running the motors at 70v rather than 36v.
Your budget should be fine as you already have the electronics sorted for now.
Can't answer your question on what you would pay for gantry side plates but there are guys on the forum that will machine parts for people so just ask for a price when you get to that stage.
Problem people have with steel is keeping it square & flat especially when welding which will distort it making mounting rails more difficult. Some people use an epoxy coat to achieve the flat surface they need. Some people will build the frame from steel but then use aluminium extrusion or square tube for the table & gantry.
Profile rails are much better than supported rails but it comes down to price, they are more expensive & supported rails will still do a good job. Some people will opt for supported rail for the x & y axis & profile rail on the z axis.
At the size your planning 1610's will be ok & will give you better speed & feed rates than 2005 ballscrews.

Once you have read a few build logs then you can start a new thread with a design for your machine, best to design it before you start buying parts, once you have posted a design or the start of a design then some of the more experienced members will help you make sure the design is suitable for your needs before you start manufacturing it.
Hope that helps a bit, good luck with it all.

[Ross77]

Martin has pretty much said it all.

Profile rails are much better but are are less tolerant to mounting errors so if you have limited access to tools then you will need to shim and grout to make them level. Otherwise you will lose the advantage of them.

Supported rails can absorb some mounting error but at the cost of rigidity as they have a larger radial clearance. TBR blocks have adjustable clearance so you can maximise their rigidity (data sheets show lower load capacity but I think that is because they are rated with max clearance, need to check that tho.)

For plastic and ali I would go for the 5mm pitch screw to keep the torque advantage. You can always gear up if using belts. Diameter is dependant on length/speed but 16mm should be ok.

There are so many options its probably best to Post some designs to help further. Good luck

[martin54]

For plastic and ali I would go for the 5mm pitch screw to keep the torque advantage. You can always gear up if using belts. Diameter is dependant on length/speed but 16mm should be ok.

Ross obviously I got this one wrong, still learning myself & haven't started machining yet other than a few test pieces. Reason I had said 10mm pitch screws was because I was under the impression that you had to use fast speed & feed rates for cutting plastics. Have I got that wrong or would you just gear up 2:1 for that.

[Ross77]

For plastic and ali I would go for the 5mm pitch screw to keep the torque advantage. You can always gear up if using belts. Diameter is dependant on length/speed but 16mm should be ok.

Ross obviously I got this one wrong, still learning myself & haven't started machining yet other than a few test pieces. Reason I had said 10mm pitch screws was because I was under the impression that you had to use fast speed & feed rates for cutting plastics. Have I got that wrong or would you just gear up 2:1 for that.

No not wrong at all. I just think that for Ali and plastic 5mm would be safer as the Cutting force is higher with Ali than plastic. If the speed is an issue then yes it is a simple job to gear up as plastic is lower cutting force and the steppers are 3.5N

You could take the other approach of gearing down a 10mm pitch which gives the same speed/force but the 10mm ballscrews are less rigid than the 5mm so you would lose out there.

Theres no real right or wrong way but I figure it is best to make it as mechanically as strong as poss and then pick/upgrade motors later.

[PilotTom]

Thanks for the advice Martin and Ross.

I have made a start on some designs after reading through a heap of build logs. Seems that for my size of machine I would be pushing the budget too far to get HIWIN 15mm rails on all the axis. Perhaps I will have to have HIWIN on the Z and build in some upgrade paths for HIWIN on X and Y in the future if I find the machine needs it.

Also thanks for the info on welding problems in regards of accuracy. I think I should be aiming for something similar to this one, in particular JAZZCNC's machines in the second post of this thread http://www.mycncuk.com/forums/diy-cn...ign-build.html

The info on the screws is useful too. I hadn't anticipated the torque required for aluminium, I was worried about whipping. Speed is of secondary concern after the accuracy. I would rather run for 10hrs and be accurate than 5hrs and be sloppy. I will design with pulleys so I can have a bit of choice over it.

I am having trouble finding Aluminium profile with prices listed to get a feel for what is affordable. Are there any preferred suppliers? I need to get a feel for how much I can expect to spend to help with design choices.

Thanks.
Tom.