I scored several 20mm diameter 20mm lead NSK ballscrews from a parts queen we are removing from work. Is this too aggressive a lead or pitch for a router? The ballscrews already have bearings and timing pullies on the ends, but I'm not sure what the pitch is on the gears. It measures 5mm from tooth to tooth, but checking on the net it would seem there are several different 5mm sizes out there. The robots I pulled the ballscrews off of were running on NSK linear bearings model number LGY25. Would these work with a router. The track seems like it would be susceptable to contamination, but they are very heavy. NSK products work great in the semiconductor industry, but I'm worried about using them in "dirty" environment, but what the heck they were free :).
https://home.comcast.net/~jkerbo/bsc1.jpg
https://home.comcast.net/~jkerbo/bsc3.jpg
https://home.comcast.net/~jkerbo/bsc2.jpg

The top Pic is going to be the Z-axis, the assembly in the middle is mounted on a nice cast iron plate, so I thought it would work for the gantry. I must weigh 20 lbs though :(. I scrounged three Vexta pk268-01A motors with mounts that with give me 187oz in unipolar mode or 240oz in bipolar. Is that enough for a router? I'm hoping to get a 34" x 36" work area. Any advice would be appreciated. I'm an Equipment maintenance tech at a semiconductor fab in Hillsboro, Oregon with a lot of experience with precision robots and stepper motors, but none on a cnc router.


Thanks,
James

Um, SCORE!
You have the basis for a very nice router there my friend. NSK slides and ground ballscrews!
5mm between threads equates to about 5 TPI. If you go with Gecko drives and high voltage power supply (60V or so) on your 240 oz. in steppers you should have reasonable amount of power. That gantry with Z axis and spindle will be heavy to move and stop though, you will likely have to ramp your acceleration down a bit or use a heavier stepper on that axis. Servo's would be nice on such a machine too.
Those slides should have dust covers to keep the gack out, and regular maintenance will keep them going strong for a long time. Make a point of designing your router to keep the slides under the table and that will help a bunch too.
You really do have top quality components there, you will be able to make a vary accurate industrial quality machine.
Colin

Thanks Colin,

oops........I meant the spacing on the timing gear teeth is 5mm, trying to figure out if the timing pulleys are 5mm HTD or 5mm GT2. So if I was going to overvoltage the motor, should I go with a chopper style driver or just install some power resistors? The ballscrews have a lead of 20mm (one rev of the shaft equals 20mm linear movement) which works out to about 1.25 TPI. Is this to aggressive of a pitch?

Thanks,
James

Definately go with a chopper type driver, and at least 10x the motors rated voltage if possible.

20mm is actually just a little more than 3/4". You may want to gear the motors 2:1 or 3:1. THey may not have enough power to direct drive that screw, but with gearing they should be OK.

Oops. I misread 1.25 as 1.25 inches per turn, so you were right. :)

James,
Do your stepper motors have 6 wires, or do they have 8 wires? This page shows the torque curve for those motors. http://www.orientalmotor.co.jp/cgi-bin/WebObjects/UPOMStep.woa/wa/F3?typeNameId=1&modelName=PK268-01A&seriesId=2PK&frameSize=56.4 It only shows the curve for unipolar mode which made me think they might be 6 wire motors. The unipolar curve at 24 volts is good for less than 200 rpm, so you will want to go with a much higher voltage, and won't want to gear them too high.

Jeff

Jeff,
They have six wires. If I could run at 100 RPM I would be happy. That would give me 78 inches per minute.

James

Yes, but 78ipm at 100rpm is only if it is direct drive. At 1.25 tpi, your screw will generate about 1/2 lb of force for each in-oz of stepper torque, or only 75lbs of force from 150oz-in. Might be a little weak without gearing it down. If you really want to find the performance you will get, you can download the calculator described in this thread. http://www.cnczone.com/forums/showthread.php?t=17236

Thanks Jeff :)

Sure have learned a lot the last several days :) THANKS!!!!!

I was allowed to take a 72 inch NSK ballscrew (25mm diameter, 50mm lead) yesterday off the parts queen. So I've changed my plans to a 32in by 60in work area router :). To build up some experience, my 12yr old daughter and I have started a smaller desktop router. Constuction will be out of MDF and utilize the stepper motors I scrounged at work along with a bunch of smaller ballscrews and linear rails. I ordered a Xylotex 4-axis board and 24v power supply yesterday and started to resurface the top on the old radial arm saw to true it up some. I figure with the over head routing attachment, the RAS will be awsome for machining MDF.

Does anyone have any suggestions for what to drive the the full size router with when we start it? I've looked at the Geckos, but would like some alternative choices. I figure I'm going to need at least 1200oz motors at 6 amps, what should I drive them with?

James

Geckos will work fine with 1200 oz motors, and there aren't really any affordable alternatives. For a 32 x 60 router, 1200 is probably overkill. 600 would probably be more than enough. You'll want to gear down that screw with 50mm lead, as it's 2 inches per turn.

Gerry,
What type of resolution should I be looking for with a router? The higher the step count per revolution the smoother the cut right? But I have to worry about going to slow and burning wood too :(.

Thanks,
James

The cuts not any smoother, unless you get to a full step size that you can actually see or feel. I'd try to have a full step max size of no more than .001 to .005. What kind of speeds are you looking for?

I'm not really sure what kind of speed I need. I know the tool the ballscrews came out of throw a 45kilo robot around with amazing precision and fast!!!! The bot moves 65 inches in less than 5 seconds. Of course the robot isn't cutting anything, its just moving a wafer around. I intend to build my big router out of welded 2.5inch square tube mild steel. The Y-axis gantry will combine the 20-25lb cast iron plate in the pictures above with arms made of square tube, so the gantry should weight around 70-85lbs with the Z installed. How fast is reasonable in a production machine?

James

My gantry (40" wide) is made of Baltic birch plywood, and probably weighs close to 75lbs with the Z-axis. You'rs will probably weigh a bit more. :)

How fast is a production machine? Depends. In the cabinet industry, state of the art routers can cut over 2000 inches/min. Our 8 year old machine can only cut at 400. Depending on what you're cutting, what tooling you're using, and depth of cut, you'll reach a point where the spindle is the limiting factor. Just a guess, but the max speed you can get from a 3HP router (PC7518 for example) is probably in the 200-300ipm range. Taking multiple lighter cuts will let you go faster. But again, material and tooling plays a big part in this. Keep in mind that with a lot of the homebuilt machines you see here, 100ipm is considered fast. :) It's all relative.

What kinds of materials do you plan on cutting?

I was hoping to cut ply and some hardwood for new kitchen cabinets. This is a new hobby for me though, so anything is possible.