Trying to finish a 15 year old project.

Hello. Sam here. I started a Hobby CNC router a long time ago, Around 15 years or so. I assembled the power supply and electronics, and fabricated the machine, then life got too busy and I never finished it.
Now that I am retired, I thought I would try to get it going. Attached are a few pictures of it as it sits now, I used salvaged ball screws on all three axis, so the pitch on all are different. I am hoping the software can compensate for this when I get it going.

I plan on using this to cut out balsa and ply parts for model aircraft. Travel is approximately 31" in X, 19" in Y and 5-1/2" in Z. Construction is MDF, When I stopped working on it, all that remained was connecting the home and limit switches, making the cables to connect to the electronics and computer, and installing some software.

So, looking at it, I now have a few questions.

First, the home location for X and Y are obvious, front left hand corner. But what about the home location for the Z axis? Two choices, where the bit touches the table, and with the bit fully raised. To me, it makes sense to be where the bit touches the table, so any movement would be positive Z up from there. But is this correct?

Next, software to drive this thing. What would be a good choice for the dxf to g code and the machine software? Free is good, but I have no problems buying some as long as it doesn't get too high (fixed income) My max would be around $200 for all software.

And finally for now, the plans show the limit switches as "per software" I'm assuming that some software is looking for normally open, and others look for normally closed? I need to know what style switches to mount. (unless I install a switch that has 3 contacts with both NO and NC)

Thanks for any help on this.

It doesn't look like this machine will work very well the way you've got it set up. It appears to rely entirely on gravity to keep the gantry from lifting up in reaction to cutting forces. You need to provide it with rollers underneath as well as above the table, so that won't happen. I also don't understand why you have two feet in back but only one in front. This won't be as stable as using 4 feet. There's no problem with using ball screws that don't match; you set up units per step on each axis separately, according to the pitch of each screw.

You can set the home switches at either end of the axis; it's your choice, but it's most usual to set Z at the top of its stroke. If you're only interested in 2D work, there are various programs you can download for free; just look for "free 2D CNC". LinuxCNC is a free CNC controller, but it only works in Linux.

The bearings on the gantry are an addition to help a bit, but underneath is a cast iron assembly with guides and the leadscrew. The whole assembly came out of a huge drafting printer lens assembly. All I had to do was add my stepper. It even has the homing and limit switches already there. It's hard to notice, but if you look at the first picture, you can just see the end of the cast iron frame bolted to the bottom of the torsion box.

The bed is an mdf torsion box. The three point stance is intentional so there can not be any twist imparted from an out of flat surface underneath. Believe me, as much as this thing weighs, it is plenty stable.

I've been looking at free software, but was hoping to get some recommendations from some current users.

Hi DM - Look at FreeCAD and fusion 360 is very popular. This will give you CAD and CAM (g code export capability) depending on your $$$ and sophistication level you can use ardinos to drive it or a break out board with drivers, or a all in one solution (look at Buildbotics which I'm using on my next machine) . I recommend UCCNC for your machine controller its low cost and works very well but an all on one like Buildbotics has many advantages and attractions. It's the fastest and least stressful path to making sawdust. Peter

Clearly the machine is in the workshop of a practical man.The OP doesn't mention any previous CNC experience and there are two ways of considering this; with some experience you have a head start on understanding the principles you need to apply or without experience you won't have to unlearn the ways of a particular piece of software in the event of choosing something different.

For my own home brew machine I chose to run LinuxCNC as a machine controller,partly because its free,partly because I have used Linux for several years and feel comfortable with it and partly because it makes fewer demands on older computer.Having said that, the very cheap Windows 7 box I found on ebay had enough hard drive capacity that I converted it to a dual boot machine in case I ever needed to run a Windows program that wouldn't work under Wine in Linux. I installed Freecad on both partitions for generating the Gcode and it does a good job once you learn it's quirks.

As far as configuring the machine is concerned you can find a lot of knowledge for any course of action you decide to take.I looked at Arduinos and found I didn't really understand the language they apply to the operations.They do a good job and seem to be utterly reliable once you understand them.I found it a little easier to use the breakout board that came with a Longs motor 3 axis stepper kit although specific advice was scarce at the time.Setting up LinuxCNC wasn't too hard but I was puzzled by the process of testing the motion by moving plus and minus 30mm until I understood the movement that was described didn't mean exactly what I thought it would mean. I still need to set up home and limit switches,but since I found that the location of the home position persists even after you switch the computer off,it hasn't been too pressing and I'm having more fun making stuff than I would tinkering with switches.It is on the "to do" list.The good thing is that you can download LinuxCNC and transfer it to a DVD or a memory stick and run it as a live installation without changing anything on your computer.You can do this as often as you like and if or when you decide to install it isn't hard to do.You can also download the Arduino GRBL or Universal Gcode Sender (and others) to try out.If you don't like any of them the option of buying one of the systems that operates on Windows will still be there and you can take it up.

I recommend LinuxCNC. Free. Powerful. Stable.

Software can deal with different screw pitches on different axes.

Limit and home switches: normally closed is preferred as a break in the wire will cause an error. All software should be able to deal with NC or NO.

Z should have home switch at the top. The travel is defined in software as negative 5.5 inches to zero. So up is still a positive move.
(Because the bit length varies you can't have the home switch at the bottom of Z travel.

For a simple and inexpensive 2.5D drawing package, have a look at SimplyCam from MR-Soft Nc Software Tools

This can be used for drawing as well as to generate the G-Code to drive the machine. Depending on the controls you have it also has an inbuilt GRBL interface.

You can download and try a fully functional copy to see what you think of it as well as run the inbuilt simulator. Unlicensed it will only generate 100 lines of code and won't allow you to save your drawings. For about $50 it's very good value for money.

Pippin88

Thanks for the reply. Concise and helpful with the reasons for doing it that way.

OK, I bit the bullet and now have Linux loaded on the computer for my machine. Now to download linuxCnNC.

Started rounding up NC switches for the home and limit. Next thing is to get them mounted and wired in.

Sam

You may have to backtrack a little,the LinuxCNC download includes the Linux operating system.If you have already downloaded and installed another operating system it won't be a particularly big deal to do it again.

Yes, the easiest way is to install LinuxCNC as a full operating system install. That way it comes with all the necessary packages.

Downloads

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Originally Posted by routalot

You may have to backtrack a little,the LinuxCNC download includes the Linux operating system.If you have already downloaded and installed another operating system it won't be a particularly big deal to do it again.

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OK, I didn't see this in time. I have installed two different linux iso packages, lxle and iunbuntu on my old Win XP computer. When the LXLE failed to load, I tried the Lunbuntu. Neither one went in clean, and trying to run the linuxCNC on the current Lunbuntu crashes... So, I need to remove the existing Lunbuntu from my old win xp machine. How do I completely clear the partition so I can load the LinuxCNC iso cleanly?

It shouldn't take too much to sort out the situation.Once you have the LinuxCNC downloaded to your computer you can either burn it to a DVD or make a bootable memory stick.The idea is to create a medium that will allow you to boot your computer from it and you may have to tweak the computer settings to change the order of drives it scans and the order of priority they should have when booting-you may have to press F2 or F12 as the computer boots to edit this setting.

Once you have the preferred drive as the primary boot device you can load the LinuxCNC operating system as a live install.This means it will run from the boot medium and use the memory of the computer quite extensively,so it won't be as fast as a full install at this stage.If it appears to be running correctly you can check out the bundled applications.If it doesn't run correctly you need to determine whether the downloaded file is corrupt or has other faults and maybe a checksum routine will be called for if you haven't already.Assuming a clean live install,you may find a utility called Gparted is available for use-if so start it.If it isn't there click on software sources and see if it shows up there and then download it.With Gparted you can format the partitions on which you have the Linux installations you don't need and probably merge the free space created to give a bit more capacity for the new installation.

Having made space for a new installation you will find an option for installing LinuxCNC from the running live version and it is just a matter of an occasional click to confirm things like time zone and language.You may first want to check out the CNC section of the menu and run the test for latency as it will never be a worse figure.Once installed to the hard drive there will be an improvement.Good luck.

OK, I have LinuxCNC on the hard drive and working. Took a bit to recover my Windows XP after deleting the partition since I didn't have the original disks anymore, but was able to download one. After that, the LinuxCNC installation went ok.

Have been trying the examples and a few run OK, but most stop with the error "linear move on line XX would exceed joint 2's positive limit". When I loaded LinuxCNC, it asked if I wanted to copy the machine setup and put an icon on the desktop. I did, but I have not configured it yet since I am still tracking down the stepper and leadscrew info. I am assuming that the copied setup has too small travel in one of the axis and that's where the error comes from?

Getting the limit switches installed. Should I leave a little "overrun" distance past the switch point or set it right when it runs out of travel? Also, when I put the home switches in, how much before the limit switch should I allow?

Thanks for all the help. I did find an original picture... I dropped this project in 2001... so it has been closer to 18 or 19 years in limbo....

Sam

You can use a single switch as both home and limit. In almost all cases this is easier and does not have a downside.

The move would exceed error can mean two things.
1. The move is bigger than the machine travels (or what is defined in the config). For example the GCode is trying to move 1200mm and the axis travel is only 1000mm.
2. You are trying to run the program in the wrong part of the machine travel. Either not homed correctly, or touched off incorrectly.
E.g. an axis has 100mm of travel. The line wants to move 60mm. That will be fine if you are starting from 0 to 39mm along the axis, but if the axis is already at 50mm, then there is only 50mm of travel available and the move will error.
In CNC there are multiple co-ordinate systems. LinuxCNC has documentation about these on the website.

Travels are set in the .ini file in the config directory.

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Originally Posted by desertmoose

Should I leave a little "overrun" distance past the switch point or set it right when it runs out of travel?

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..this would depend on the machine/axis if, ....a Runaway at full speed would to occur in the + or - direction.

my two cents,
DJ

OK, I installed the home and limit switches and ran the wiring. Also, the computer now has Linux CNC up and running fine,

Then I have spent several; weeks fighting the connection of the wiring to the DIN connectors that came in the Hobby Cnc kit. I just don't see well enough anymore to do the fine soldering. It has gotten so frustrating that I am about to give up on the whole thing.

So, before I do, what would it take to buy the electronics and connect to the machine I have built? The steppers are NEMA 23, 6 wire bipolar, and all the switches are installed.

Looking on the net, it appears that I would need three driver boards, a breakout board, and a power supply. Is this correct? Can anyone recommend a proven setup I can buy and get this thing working? Something that does not involve close up soldering?

Thanks, Sam

Quote:

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Originally Posted by desertmoose

Then I have spent several; weeks fighting the connection of the wiring to the DIN connectors that came in the Hobby Cnc kit. I just don't see well enough anymore to do the fine soldering. It has gotten so frustrating that I am about to give up on the whole thing.

Something that does not involve close up soldering?

Thanks, Sam

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Sam,

Is there a local Men's Shed, Electronics or Amateur Radio Club in your area? Perhaps you could reach out to them and one of the Members could help with the wiring and fine soldering.

Just a thought.

Quote:

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Originally Posted by desertmoose

... what would it take to buy the electronics and connect to the machine I have built? The steppers are NEMA 23, 6 wire bipolar, and all the switches are installed.

Looking on the net, it appears that I would need three driver boards, a breakout board, and a power supply. Is this correct? Can anyone recommend a proven setup I can buy and get this thing working? Something that does not involve close up soldering?

Thanks, Sam

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I'd recommend a Gecko G-540. It combines a breakout board with 4 pre-installed drivers, and while it did require some crimping of pins onto wires, I don't recall any fine soldering being required. Pair it with a 50vdc 10a power supply, and you're off to the races.