[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.

[slkret]

BobF:
Thanks for the great link. I have seen high speed milling done with a hexapod robot but have not had a source for the necessary cutters and recommended chip load. I'll have to get a couple of cutters and try some aluminum. This is the true test of machine rigidity.

Karim:
check this out. It's a good starting point for your research.

Steve

[CNCMAN172]

Steve,

Very nice build in a very short time and you have great accuracy using the components you selected. Congrats. I have also cut many wood gears on my home grown cnc machine and it is great fun putting that stuff together. I still have on my shelf all the parts to make a complete wooden clock but need to fix my old lathe to get some of the remaining parts manufactured, hopefully I will get back to that project at some point in the future.


Karim,
You asked some questions concerning the spindle and what is required to cut aluminum. Well I have cut aluminum on my machine and a few keys elements that come into play are stiffness of the machine. Steve took steps in his machine design to keep the Z axis close to the table when required which was a good move. I have found that carbide endmill seem to work best and the spindle motor needs to be slowed down, so a variable speed spindle motor works best. I actually cut aluminum with the same spindle motor steve is using the Bosch Colt 1HP wood router and it seemed to work fine for about 4 hours. I then had the end bearing house begin to melt and the router died, so I took it back to the store and told them it was defective as it was only a month old, so they replaced it no questions.

Why did it die? Well aluminum puts a great deal more stress on the spindle than wood does as it is harder. Many factors play into the amount of stress such as feed rate, spindle speed, cutter, depth of cut, etc. There are many factors associated with just the endmill cutter than can also play a role. How many flutes, cutter material, coating, etc. I had to move up to a larger Bosch router (2-1/4 HP, with variable speed) as my next step in this learning process. The type of aluminum or other metal also plays a role as they typically come in various flavors, some are softer and others are much harder.

One of the important factors when looking at a spindle motor is the size and type of bears used in its construction. You will find that Dremel motors, and many other small router motors are built for home use on wood. Real CNC spindle motors have much stronger bearings and depending on the speed they sometimes even contain ceramic bearings, because they do not get hot like steel bearings.

Since your located in Egypt and probably have access to products in the EU more readily that many people across the pond, you might want to consider a die grinder or something design to work on metal. If you look under this forum you will find many people have selected grinder type routers from the EU and are very happy. I can not recall the name something like Kress or something. The reason they like them is they have heavy duty bearings and are about 900 watts.

I think you will enjoy your senior project.

CNCMAN

[shetos87x]

CNCMAN

thank you for ur informations

but what are the specifications of ur machine (motor torque, electronic drive and body materials ..etc..)

and in ur openion why did ur spindle failed (is it for cutting aluminum or because of the 4 working hours)

because in my senior project i wont need my machine to work in metals for 4 hours !!

but all i need is to build a cnc milling machine which has varios applications (only for showing and presentation of my work) like cutting woods, drilling, milling some soft metals)
but not for a "heavy duty" full time work in a work shop ..

so if ur machine could deal with metals for short time and low speeds and feeds thats will be ok with me and it will be suitable for my project

also Mr Steve had told me to use the (GEKO 540) as an electronic driver but i have found thats it is a bit expensive for me so do you recommend another electronic drive which can be more cheaper and still have those good qualities ??

and what about adding a 4th axis to my machine ?? would it be hard to design and construct ??

because i think it will increase my machine's applications (like plastic gear cutting as an example) ??

Note : i have a milling software "mach3" which is capable to run a 4th axis..

finally if you dont mind sending me some useful data and info about ur machine that can help me in my researches (photos, data sheets or plans, etc..)

and i will be greatful .....

thanks ,,

karim

[BobF]

BobF:
Thanks for the great link. I have seen high speed milling done with a hexapod robot but have not had a source for the necessary cutters and recommended chip load. I'll have to get a couple of cutters and try some aluminum. This is the true test of machine rigidity.

Karim:
check this out. It's a good starting point for your research.

Steve

Steve,
I saw that hexaod robot thing, but I can't remember now if it was a youtube video, or a show on discovery or science channel or something. It was pretty cool though.
Glad you liked the link.

Karim,
I think the keys to aluminum are machine stiffness as mentioned above, and feeds and speeds. You also need to realize we are talking about soft aluminum only. Slow down the cutter RPM, slow down the feeds and take small cuts. Look at the Onsrud chipload data to get an idea of how slow to feed. Get a variable speed router and know that the slower it is capable of the better.

4th axis
http://www.cnczone.com/forums/showthread.php?t=39588

[slkret]

Karim:
The Gecko 540 drive is what I chose for the reasons I mentioned in an earlier post. If I was a cash limited student as I was when I did my senior project 40+ years ago I'd be looking at the HobbyCNC drives. There are a lot of guys who have had great success with those drives.

As far as the 4th axis is concerned, the design is driven by what you expect to do with it. You mention cutting plastic gears. Doing that kind of work does not require a 4th axis. I cut gears using 2-1/2 axes. look at my pictures and you can see a gear that I cut. It is not a small gear but If I needed a small gear I could easily get down to 32 diametral pitch. The beauty of doing it the way I am doing it is that I use a simple end mill to do the cutting. If you want to mount the gear blank in a 4th axis I believe you will need to buy special involute gear tooth cutters. Way more expensive than a small end mill.

BobF:

The hexapod that I saw was being used with a high speed spindle cutting 6061 T6 aluminum without coolant. Alcoa was using it to machine suspension attachment points on the all aluminum chassis for the Plymouth Prowler. The machining cell was totally enclosed partly because the sound level was incredibly high. Alcoa chose to use the hexapod robot because the work envelope requirement was very large. The company that I work for made the aluminum space frame for the Ford GT. That spaceframe required extensive machining after it was welded together. We just happened to have a very large 5 axis CNC machining center from one of our tool rooms. Even so, it took multiple setups to get at all of the machined features. The hexapod probably could have done it in one setup.

Steve

[BobF]

Steve,
The one I saw was small and built by a small company for some other purpose. I did not realize that using one for machining was on a large scale was actually in use now.
I work for an aircraft company and we used to do a lot of machining in house. A lot of that is gone now, but the company still has a smaller machine shop and 2 of the larger machines were kept. One is a large 5 axis like the one you mention. The other is a multy spindle with 3 axis (I think). We used to have a larger multy spindle nearly identical to the one they kept except for having a bed nearly as long as the building that houses the shop. Don't know why they thought they needed a bed so long. It was nearly as long as the aircraft we build. We build great planes, but the auto execs shouldn't fly them to DC these days.

[ahren]

Steve,
Thanks for the feedback on the carriages. That's good to know about the set screws -- I have been considering replacing them with metal ones. The nylon is there to "give" a little to try and keep people from overloading the bearings, but I've also noticed some issues with them not being super robust. Additionally, if someone's determined to crank down hard, the plastic won't help their bearings. Anyway, glad the carriages are working out for you, and nice work on your machine!

Best regards,

Ahren
www.cncrouterparts.com

[BobF]

Ahren,
Seems like I remember seeing steel set screws with nylon buttons in the end. Might accomplish both at once.