Rookie 1st build with pictures

[slkret]

I have been a lurker on this forum for a long time. I'm a wood gear clock builder who is tired of hand cutting the gears. I've been thinking about building a CNC router for that purpose but I wasn't sure I really wanted to do it. Around Christmas time 2008 I scored a good supply of 8020 extrusions, fasteners and misc other parts for free. That pushed me over the edge in favor of building a machine. After all of the reading, I made a few basic component selections for the design. I decided to use the axis bearings from CNC router parts, the anti-backlash nuts from Dumpster CNC, Gecko 540 drives, Kelling 425 oz-in steppers, a Kelling 48 volt power supply and a Bosch Colt router for the spindle. The majority of the remaining components I got from McMaster Carr including the 1/2"-8 two start acme lead screw stock. They are a little pricy but they ship very fast and I have never had a problem with them. I decided to plan for the future a little bit. I don't really need a huge machine to cut wood gears but I figured that I might as well make it a bit bigger just because you never know what you might want to do in the future. I decided I wanted an honest 24" X 36" X 12" work envelope. No science in that, it was a completely arbitrary decision.

I spent about 2 weekends sketching out the basic construction (on paper) and an additional 4 or 5 weekends building the machine. It really went together easy. I used my table saw and a carbide tipped blade to cut the extrusions. I planned the cuts so that I cut all of the parts that needed to be exactly the same in one setup. That helped control the stack up of tolerences. Still, tolerances do stack up so in some instances I just measured and cut to fit. That worked out pretty well as there are no shims anywhere in the machine. One thing that I did that I have not seen on this forum was to create an auxilliary "Z" axis. Let me explain. Since I wanted to have a 12" work envelope in the Z direction, I was concerned about the large cutter to Z axis bearing offset that I would get. So, what I did was to create a frame that carries the Y and Z axes and mounted that frame to the gantry frame using the 8020 plastic bearing system. this allows me to move the Y and Z axis assembly up and down on the gantry frame and thus minimize the Z axis travel. if you look closely at the pictures you can see how it works. I'm really happy with this feature and as it turned out I can easily clear a 17" high object on the machine bed. The actual Z axis travel is about 5" with an additional 12" available by moving the Y-Z frame up and locking it in position. You can also see in the pictures that I made my stepper motor mounts and bearing supports out of white delrin plastic. I support both ends of each lead screw in radial ball bearings with a pair of needle thrust bearings on the end opposite from the steppers. I made adjustable threaded collars out of delrin rod to apply preload to the thrust bearings. I made an acme tap (for making the collars) from a piece of left over lead screw. I used a small grinder to form the flutes just like a commercial tap and saved a pile of money. Getting the bearings, anti-backlash nut and steppers aligned took a little patience but I got it all done in an afternoon.

If you look at the pictures, you can see that each axis is set up with 2 limit switches. I got them from McMaster Carr as I wanted better quality than the switches you see at Radio Shack. I gave a lot of thought to the problem of wire management. I looked into buying cable chain but that got to be a bit expensive. I looked at making my own cable chain but decided that it was going to take more time than it was worth to me. If you look at the pictures you can see my solution. I took 2 old dull 1/2" bandsaw blades that I was saving for no particular reason and mounted them in the bandsaw. With the blade running I ground the teeth off of the blade with a die grinder. I then used plastic spiral wrap material and secured the stepper and limit switch wires to the blade material. This works really well and was really cheap. The power cord to the Bosch router is attached to the vacuum hose and seems to be ok that way. I wanted to keep it as far away from the other wiring as is practical. The vacuum system uses some plastic electrical conduit elbows and while it works, it is not 100% effective. I do get some dust on the X axis guides that I need to clean off from time to time. I thought that this might be a problem with the CNC Router Parts bearing blocks. I may attach some small air jets to the bearing blocks to blow the dust away ahead of the bearings or maybe I'll make some rubber scrapers to try to keep the guides clean.

In the pictures, you can also see the stand that I made for the computer and electronics. This was also made with 8020 material. The computer and the Gecko drives are on the lower platform. There are 2 upright members that support the platform with the LCD display, keyboard and mouse. The upper platform is adjustable up and down using the same 8020 plastic bearing material that I used on the auxiliary Z axis described above. when the platform is all of the way up, it is at a comfortable height to use while standing. there is a mid level position that I use in a sitting position and then there is a low level position for stowage. if you look closely at the picture you can see that in the stowage configuration the computer and drives fit under the bottom shelf supports (I didn't have the shelf in place when I took the pictures) and the display and keyboard platform fits between the shelf and the machine table. I did this to save space in the shop when I'm not using the router. The stand has casters so it can be moved around. You can also see that I'm running Mach 3 to control everything. I'm currently using the freeware version and living with the 500 line G-code limit and the 25 kHz step frequency. When I did the motor tuning, I found that the machine could easiy stand up to the maximum velocity and acceleration available through Mach 3. I have left the velocity maxed out at 187 in/min but I cut back on the acceleration to 6 in/sec/sec. I may increase that acceleration sometime in the future, but i don't see a need to do that at the moment. In a couple of the pictures you can see a gear that I made. I run the cutting speed at 25 in/min. I accidently did some cuts once at 100 in/min and all that happened was a little degradation in surface quality. Those speeds are with a depth of cut of .25" with a .125" spiral upcut router bit in Baltic birch.

So, how does it work? Excellent! I have checked everything with dial indicators and have the axes square to each other within a few thousandths. The 8020 construction is quite rigid. I have not measured the actual stiffness but you have to push pretty hard to wiggle the dial indicators. the only issue that I have not worked out yet is that I've got about +/- .005" of backlash in my X axis. I have about +/- .002" on the Y and Z axes. I think that the issue is in the thrust bearings and shaft collars but I haven't got a good way to measure that yet.

I hope that what I've done here will act as inspiration to others and in some small way repay all of those that that I learned from.

Steve

[shetos87x]

thats wonduful
but can this machine cut aluminum too
by changing tool or something ???

because i want to build one but i need to select a motor which is capable to deel with soft metals

and all i have now is a 280 oz in bipolar stepper

and i want to know if its enough

and what do u recommend if not

[slkret]

I have not tried any metals with it yet. I have a mid level of confidence that I can cut aluminum or brass. It alway comes down to feeds, speeds and depth of cut. Since cutting forces will be higher, the rigidity of the machine is important. While this is pretty rigid, it is not like my regular milling machine.

[Grunblau]

Looks great! Enjoy your machine! I wish I had your shop...

[shetos87x]

thank you 4 your reply

but i have another question

what about the type of stepper motor u r using ??

and am curious to know how much time does it take to built hardwares of a machine like this ?? (by using plug and play electronic drivers and softwares)

and if am starting from zero how much could it costs ????

Note:
i am a student in
Alexandria University (Egypt)
Faculty of Engineering
"Production Engineering Departement"

and i want to build a cnc milling machine for my graduation project next year

[slkret]

shetos87x:
Sorry I didn't answer your questions properly.

First, in my opinion, 280 in-oz could be adequate for most small machines. It comes down to basic engineering. With 280 in-oz of torque and a fine pitch lead screw you can develop very high forces. Enough to cut metal which seems to be your aim. However, there is a tradeoff. The fine pitch screw generally leads to slower speeds. This may or may not be ok for you. Your drive electronics and stepping strategy may be able to help with the speed issue. If your computer can issue pulses fast enough and you do not use a fractional stepping strategy, you can recover the speed but you will do so at the expense of precision. Lots of tradeoffs to consider. I am using 425 in-oz steppers with a lead screw that results in .25" of travel per revolution. My Gecko drives use a 10 micro step strategy which means that I need 2000 pulses to produce 1 revolution of the lead screw. This means I need 8000steps to go 1 inch. After doing all of the calculations I believed that I had a good overall compromise between power, speed and precision based on what I intend to use the machine for. As an engineering student you have all of the necessary math skills to do the calculations. The problem engineers usually face is that you always seem to have more unknowns than equations so you can't arrive at a closed solution. Experience and judgement make up the difference. This forum can really help there.

How long does it take and what does it cost? Well, it took me 6 or 7 weekends from the start of the design to cutting the first gear. That does not count my considerable time reading and learning from this and other DIY CNC sources. In addition I've got a well equipped shop for making stuff and I've been building things for 50+ years. If you have access to a good shop at the university that is a huge help. if not, spend some time reading what some of the guys on this forum are able to do with limited shop equipment....it is inspirational. The relatively short build time for my machine was also helped by the fact that I used the 8020 extrusion system. The whole point of 8020 materials is to speed up the fabrication of specialized equipment. Most of the guys on this forum seem to focus on using wood for the structure. It is readily available, inexpensive, easy to work using simpler tools. This obviously works well and is probably way cheaper than the all metal machines. If you elect to do a wood machine, there are several very successful designs available on this forum. If you elect to design your own in wood, just remember that stiffness is a key design factor and that mathmatically it is E*I. wood has a low elastic modulus compared to metals and so you must compensate by having larger cross sections in your structural members. I just lucked out getting all of the 8020 materials for free. If that didn't happen I would have built a wood machine.

Cost? I didn't keep track of cost. I'm not rich but cost wasn't the driving factor in my design. I only wanted to build the machine once so I opted for buying ready made components where it made sense for me and I chose highly respected electronics. All of my software is freeware and I live with the limitations. If I had to guess, I'd say I've got maybe $800 in the machine. I already had the computer, I got the metal for free and I bought mid priced ready made mechanical components and higher grade electronics. Your cost will be highly influenced by your creativity, yoour ability to make quality parts yourself and how good you are at scrounging materials. Remember that in general, time and money are interchangable quantities. If you don't have much money to work with then you'll need a lot more time. If I were you and needed to have this done next year, I'd start working the design right now.

Steve

[shetos87x]

Dear Mr. Steve:

First of all, I want to thank you very much for your attention and cooperation and thank you for providing me with this precious information

You have really helped me,

I want to know if you have any extra information about:

These power calculations for choosing the materials to deal with (no hard materials only soft copper and aluminum with small depth of cut and feeds)
Specially the torque of motor and the pitch of screw in the (x,y axis) and (z axis)
But also keep my speed and precision for wooden work pieces.

And do you recommend any special company to buy motors and electronic driver from?? Because you have mention that u have used a good type of electronic systems, so how can I know good stuff from bad stuff ..


Finally, I really appreciate your effort and help

Thank you Mr. Steve

karim

[slkret]

Karim:
The machining questions that you ask do not have short or easy answers. First, I am not a machinist, I am an engineer who does this stuff as a hobby. I have a small lathe and a small milling machine in my shop. From manufacturing classes I took in college I know the basic principles and can tell you that you can probably find reference materials in your university library and on the internet. When I want to machine a metal thing on my lathe or mill, I generally dont care about how efficient I am with the metal removal. I just take shallow cuts, slow feeds and it takes as long as it takes. So, I can't be of much help here. here is another thing to think about. There is a very large difference in spindle speeds used for woodworking compared to metal working. Generally, wood routers run at 20,000 to 25,000 rpm while small milling machines run at speeds well below 5,000 rpm. There are exceptions to this in certain cases but those speeds are common. I dont know of a simple "hobby spindle" that has that kind of a speed range.

As far as the electronics are concerned, my only personal experience is with the Gecko 540 4-axis driver. It has worked flawlessly. Gecko drives enjoy a very good reputation from what I read on this forum. There are others that are also highly regarded. Do some searching on this site and read what others have to say about the various drivers. If I was severly budget constrained, I would be looking at the HobbyCNC drives. A lot of people use them with good success. My overall advice in all of this is to read, read, read.

Good luck

Steve

[shetos87x]

Thank you Mr. Steve

and am gonna start reading and searching ....

thanks for help.

[lovebugjunkie]

Nice build.

Looks like you are running the carriages from CNCRouterParts. How do you like them?

Nice seeing a machine up and running that is using them.

[BobF]

Steve,
Very nice machine you built. Looks like it should give you years of service.
Here is a good resource for feeds and speeds in all kinds of material. Also, they make great cutters.
https://www.onsrud.com/xdoc/FeedSpeeds

[slkret]

lovebugjunkie:
Thanks..
Yes, those are the CNCRouterParts bearings. Yes, I like them. they are well made and pretty darn solid when installed. One small issue for me though. On each end of the block there is one bearing that is adjustable to allow you to exactly match the bearing spacing to the thickness of the steel guide rail material. This allows you to deal with material thickness tolerances. The adjustable bearing is mounted in a slotted hole. There is a 1/4-20 plastic set scew that you use to move the bearing mounting bolt in the slotted hole and thus take out the clearance. I personally found the plastic set screw to be inadequate for the task. It took very little torque on the hex wrench to strip out the hex hole. I suspect that they use the plastic set screw to prevent damage to the bearing mounting bolt...not sure about that though. What I did was to buy a regular steel set screw of the same size to replace the plastic ones. The set screws that I bought have a cup point that I thought might interfere with the proper adjustment and tightening of the bearing mounting bolt. To deal with that potential, I ground the end of the set screw flat. With that modification everything worked fine for me. I have not read of anyone else taking issue with the plastic set screws. At the end of the day, no big deal. I'm sure that they looked at the idea of using an eccentric for adjusting the bearing and rejected it as too costly especially considering that you will probably make the adjustment only once. The only other issue that I have is the problem of keeping the cutting debris off of the X axis guide rails. What happens is that cutting debris gets on the rail and when the bearing rollers run over it, it can kind of build up on the bearing and the guide rails and cause a bit of binding at some point. I saw that as a possible issue before I bought the bearings and figured that I would be able to keep everything clean with a vacuum system. Well...almost. My vacuum system is not 100% effective so some dust still gets on the rails. I installed a shield just above the rails and that helps quite a bit but still not perfect. Right now I am simply cleaning the rails after every part I cut. I will see if I can make a guide scraper that will keep things clean. I'm also thinking about mounting some air jets on each bearing block to blow the dust off of the rails and bearings.

Overall, these bearings work very well and are reasonably priced and I like them. If you place any value at all on your time you can't beat the cost/performance of these. The other thing about them is that they integrate nicely with the 8020 extrusions that I used in my build.