The picture to the right is of the power supply, drivers and the breakout board from Probotix. I had originally used a different breakout board but had problems. The opto isolated board from Probotix saved the day when it came to this build. Lets just say I am no electrician by any stretch of the imagination. Word of advice check your ground on the AC side of things prior to building anything. If your transformer isn't grounded then beware of the pop and smoke that follows. Speaking from experience. Learned the hard way and about two computers latter discovered this problem thanks in part to help I received from the Mach Support forum. Great guys and very knowledgeable in this area. I also want to add I'm running Mach 3 the best CNC control software for the hobbyist or professional.
The Y axis gantry. I decided to use MDF board because of the uniform density through out the material. Unlike conventional wood MDF is free of voids that natural or plywood have by default. It is a little heavier than I expected but decided to go with it anyway. It's super cheap also and can be purchased at your local hardware store. Extremely rigid for what it is. The linear bearings came from VXB.com I went with 20 mm case hardened chrome plated shafts with a Rockwell hardness on the c scale of 62 for all three axis. The bearing trucks have two bearing inserts per block. They are of the recirculating ball type in each. The mounting holes are 6mm . The lead screws came from Roton I am using 5/8 - 5 TPI 2 start lead screws with bronze nuts. I used the 7" X 10" mini lathe to machine the ends of each lead screw to accept the angular contact bearings and latter the spider couplers. I broke down and purchased a 15/16-16 tap from MSC . I made my own mounting flanges this way. Almost forgot to mention the business end of the Y axis has 1" thick lead screw support block with two matched pair of angular contact bearings and nema 23 motor mounts.
The Z axis is constructed of 3/8" and 1/2" thick T6-6061 aluminum bar stock as are all the parts that are aluminum are of T6-6061. Holes are drilled and counter bored for 1/4-20 SHCS. The router itself is a Porter Cable model 892. I decided to only use one clamp and have noticed others using two. I think one 1/2" thick clamp should suffice for now. If not then I will build a second of course.
The X axis was cut with my table saw and I made a few patterns on the mini mill then transferred them to the MDF. I have some alignment issues to sort out with the X axis. Where the Y axis gantry and the X axis meet is all aluminum. I used 1" angle aluminum and 3/8" bar stock to make the mounting of the X axis. Again 5/8-5 lead screws 44" long. The foot print of this machine is 48" X 32". Something I haven't mentioned is the shaft support brackets are 3/8 thick aluminum bored holes to .7878 for the 20 mm shafts. I used a 1/4-20 set screw and ground a small flat that can't be seen on the shaft to secure the shafts on all three axis. Not going anywhere. On the Y axis I have a piece of 1/2" thick aluminum which I bored out to accept a radial bearing to support the end of the lead screw from radial movement only. I have voided my warranty on my motors and don't suggest you try this. I drilled out my holes on my stepper motors from 5 mm to 7mm to accept 1/4-20 SHCS. I put my cordless drill on the X axis lead screw and gave it a go. Nice and smooth after I cut another piece of MDF for the lead screw support block and re drilled my pattern I made this time all lined up nicely. Angular misalignment fixed. As you can clearly see I haven't made a end support for the X axis yet. I am going to basically box that area in with MDF and use another 1/2" piece of aluminum 2" square with a radial bearing as I did the Y axis. I think if I where going to do this project again I would order enough lead screw to accommodate the 48" frame. Trying to go cheap and didn't really save anything as the 48" was the same price as 44" . :O)
Here is a close up of the lead screw support blocks and nema 23 mounts. I used 3/8" thick aluminum for the mounts and stand offs. There are four 1/4-20 SHCS holding the two angular contact bearings down. I bored the holes .0005 over size for the angular contact bearings giving them a light tap with my dead blow hammer and block of wood for a nice press fit. I left .003 to sit above surface of the pocket to allow the cap screws something to hold down. Not going anywhere. Oh the dimensions of the support blocks are 1" X 2" X 3" .
Big excitement today my spider couplers arrived.
Don't have much to say accept glad they made the journey alright. I didn't
have any 1/4-20 SHCS long enough for the X axis motor mounts that
connect to the MDF board. So I went to the hardware store and
bought a hand full of 2.5" long 1/4-20 hex head screws and hand full
of 1/4-20 lock nuts. The kind that have the nylon retainer built into
them. That is also what I used on the lead screw ends is a 3/8-16 lock
nut with nylon insert.
I'm powering the CNC hobby router with the
24 volt Ac transformer 10 amps which when rectified produces actually
35 to 36 volts DC 10 amps. The motors are 425 oz inch bi-polar rating
or 3 N-m . If we wire unipolar drives the N-m is 2.15 or 305 oz inch
unipolar rating. Same motor different drives make this so. I decided
to go unipolar with the router first to see how it performs. Will try
make a video soon with results.
Update 07-20-08. Today I discovered I have major sag in the X axis due to the heavy weight of the Y and Z axis. 20 mm shafts are not going work for the X axis. I have a disappointing sag of almost .063 from either end to the center. About the only thing to do is redesign the X axis and definitely use different linear bearing style. Will post updates on the new design of the X axis when complete.
Another update 07-22-08. I'm going to have to wait on the redesign of the X axis. It is a matter of funds. To get by until then I have shimmed my work piece from one end about .063 and that seems to be working. So the shim actually believe it or not corrects my run out problem and allows for correct Z accuracies. I should mention my over all table length is 54" X 24" wide. I have about 3 inches hang over on either end to have something to clamp to.
07-27-08. I have posted a picture of my first parts made at the bottom of this page. A couple of table legs for a funky table my sister designed, thought I would share this. And to the right is the table top complete. Saving up to redesign the X axis. Will try to keep you updated on this. I used Vectric V Carve to engrave the table top. My first project using my new CNC hobby router. The table diameter is 18" X 27" tall. The wood I might add is clear poplar .750 thick. I am very impressed with the efficient tool paths of the new software and its capabilities.
11-01-08 . Update I have been asked what purpose do the angular contact bearings serve. I will try to answer this without adding confusion to confusion. I have added a drawing of two angular contact bearings to the right . Ok the angular contact bearings job is to take up the load of the radial movement as well as the lateral thrust loads. I have noticed a lot of DIY CNC kits using direct drive from the stepper motor to the lead screw. This will probably be ok for the short term but in the long term when the bearings in your stepper motor wear out because they where not meant to serve as lead screw support blocks you are going to have to replace your stepper motors. If you have ever done a repack of the wheel bearings on your car you may be familiar with tapered roller bearings. Angular contact bearings are very similar. All your commercial CNC machining centers use angular contact bearings if this gives you any indication as to the importance of these jewels. Hope this makes sense and I hope the drawing does also.
One thing I haven't mentioned is the travel of this cnc hobby router. The Z axis travel is about 3" inches and Y axis travel is 20" inches and the X axis has about 36" inches of travel.
09-01-2011. Update. CNC Router Plans are available for download.