BP conversion

[brian257]

Just ordered the Rockford ball screws from Microkinetics for my Bridgeport conversion. I also have one KL34-180-90 1125 in oz servo motor, Gecko driver, encoder, and power supply on the way from Automation Technologies. I ordered just one motor now so I can experiment with it and make sure that it is what I want before I get the other two. I will do a temporary hook up to the Z axis to make sure it is enough torque and see what ratio pulleys I need. From there I will make all the motor mounts, etc. before I take the machine apart and put in the ball screws.

My plan at the moment is to leave the acme screw for the knee, but I will see if I need to change my mind after the motor experiments. I will probably add a few hundred pounds of gas springs also.

I have a project for this machine to make a bunch of parts that I need in June so this will hopefully be a fast and no frills build.

I will most likely be adding some type of disconnect for the pulleys and servo so I can still use the machine manually. Maybe a locking pin to lock the pulley to a hub that is mounted on the shaft or maybe a belt tensioner type of arrangement. I am assuming at this point that the servo will not back drive easily. I will get that figured out once I get the servo here.

I have a K-2 CNC router and a Sherline CNC conversion already, but neither has the rigidity for the parts I need to do now.

I will add pictures and details as things progress. Let the chips fly!

[brian257]

Got the first servo motor today and since it is not a geared motor it is very easy to turn by hand. Looks like my possible plan of having to put in some type of clutch mechanism to disengage the motor when operating the machine manually won't be needed. I will see once the motor is driving through a reducing pulley if that is still the case.

Should have the power supply tomorrow. Might be a few days before I have time to hook it up and run through Mach since I have a bunch of work projects to finish.

[brian257]

Finally got around to testing the servo a few days ago. Seems that it does lock up pretty solid when not moving. Makes a growling noise when it is stopped. Guess that is the motor just going back and forth. Tried playing with the PID pots a little and that quiets it up some. Not ready to tune them yet. from what I can tell it takes a good bit of torque to move the motors by hand when they are holding position.

Got some pulleys and belts ordered yesterday from Stock Drive Products. They should be here tomorrow. I ordered an 18 and 20 tooth pulley for the motor and 36, 40, 60, and 70 tooth pulleys for the ball screw end. That will give me ratios of 2:1, 3:1, and 3.5:1 to try. I spoke to someone at Automation Technologies and he recommended 5:1, but I don't think I need that much reduction and they don't make pulleys that big in GT2 form. I also wanted to keep the pulley on the lead screw a reasonable size. I have seen others with servos using 2:1 and 3:1. I will do some testing and see what works good.

Got a call from Microkinetics that the ball screws were going to take 3 weeks, then got an email that the price went up to $1,255, but they can get them in a week. I ordered from MK because they were less than the price of buying direct from Rockford. (Not a big fan of Microkinetics since a system I bought from them years ago never worked correctly) Canceled the order and tried ordering direct from Rockford, first call and message never got a return, called the next day and was told that I needed to order from a distributer, distributer still has not called back with pricing. Been working on trying to get this ordered since Monday. Called MK this morning and told them that if they can confirm that the screws they are selling are Rockford and see if they can get a lead chart for the screws that I would reorder from them. No answer as of yet.

I did manage to get a very nice Rital 15" X 24" X 8" steel enclosure yesterday that my work was throwing out. That will save me a few hundred bucks. Just got a free aluminum backplane for the box today also and starting to lay out the inside of the box now. I am going to leave space to have drivers for five axis in the box. Might also do some switching so that I can use the same box and computer for the eventual CNC upgrade for my lathe. Not sure yet if I will try to put connectors for the motors and encoders on the box or just run the wires in through glands and connect to terminal blocks.

I am also thinking of putting a small form computer directly in the control box. Have not decided on that yet.

[rjmorel]

Brian, I for one would like to see pics of your build. I converted my Taiwan BP mill to Mach3 PC 3 axis. Used Hi-win ball screws that cost around $1200 15 years ago. Still trying to learn all that mach3 can do. Mainly job shop and build plastic injection molds with it. rj

[metal mite]

I went threw the ballscrew findings and went with hi- win too. They have kits there for the different size lengths and also give you the yoke . Here is a place to get the z screw.

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[brian257]

I will put up pictures soon.

I thought hard and seriously considered the Hiwin ball screws. My final decision for the Rockford was due to the adjustable preload and no backlash. Kind of curious what backlash you are seeing on the Hiwin. I figure with the max of .003 per foot inaccuracy on the Rockford and others with DROs reporting that they get much better than that I can live with it. Add the fact that I am getting a lead chart to program out the inaccuracy I think I will be able to make more accurate parts than if I got the ground screws with backlash. I will also do a good bit of manual machining and Rockford claims you can climb mill without backfeeding. We will see.

As far as updates, I did finally get the ball screws ordered Friday. I found that I can buy them from H&W machine repair. I can highly recommend them. Spoke to Debra there and she seems to know the Bridgeports very well. There were other parts I wanted pricing on and she knew exactly what I was talking about. They stock the Hiwin screws and can order the Rockford. She had the price right away and called back 20 minutes later for the price on the lead chart ($60). They also had the precision bearings in stock. It has been over a week now and I still don't have the price back from Motion Industries even after three calls to them and tried another company Thursday that also has not called my back. Guess that is the difference between ordering from an industrial bearing company with a sales person that does not even know what a Bridgeport is and a Bridgeport rebuild and parts company that understands customer service. I am betting that if I ever do get a price from the other companies they will be more than I paid from H&W.

I did get my pulleys and belts from SDP Friday. I bored out the 18 and 20 tooth pulleys 1/2" to fit on the motors. I ordered a set of broaches from Enco and expect them today or tomorrow. I will bore out the bigger pulleys to fit on the Z shaft sometime today and start a temporary motor bracket so I can do some testing and see what ratio to use and if a gas spring is necessary.

I did notice backlash in the bevel gear on the Z axis. Have not look at it closely yet since I have the table on and can not see the gears. Is that adjustable somehow?

[rjmorel]

My hi-Win BScrews have .001 in X and .002 in Y roughly. But I think the yoke is flexing not so much backlash between screw and nut. Duane at Elrod explained this to me and it makes sense. Put an indicater up in the knee cavity on the yoke and you can see it flex. Thats why he makes his own heavy duty yokes. rj

[metal mite]

Same with mine .0012 in X .002 in y I think it was a .0005 per foot tolerance on the ground ball screws I bought from them .I did check out Elrod but the diamater of their Ballscrew was smaller then Hi win.Good luck Brian it sounds good .

[brian257]

Just got a new keyway broach set today (not really sure how I managed to have a home machine shop for 25 years and never had any broaches before) and found out that for some unknown bizarre reason the Keling servos have a 1/2" shaft, but a 4mm keyway. I tried to find a new 4mm broach and found that the broaches in that size are style B1, but the 1/2" bushings are style B. Called Dumont and was told that they do have special bushings for about $50, but my best bet is to get another 1/2" B style bushing and machine the slot for the larger B1 size broach. Thought about making the keyway on the motor 3/16" instead, but decided against that when looking at the shaft and motor. It would be a real pain to try to clamp that short protruding shaft in the vice and accurately cut a new keyway on three motors.

Ugggh, this is why a simple conversion can take forever!

I did get the connectors I am going to use for the motors so now I can start the connector plate that will be on the side of the electronics enclosure. They are a D sub type of connector with three big high amperage pins. This was much less expensive than any of the high amperage circular connectors I could find. Here is the type of connector I am using. http://dkc3.digikey.com/PDF/US2011/P0307.pdf The big 10-12 AWG pins are good for 30A and they have some that are for 8 AWG wire good up to 40A. I thought about using the combo type connectors they have with a few big power connectors and the smaller connectors for the encoder, but decided against having the encoder signal that close to the power connections in the same shielded backshell. I will use standard DB-9 connectors for the encoders.

[rjmorel]

"Ugggh, this is why a simple conversion can take forever!"

I've been working on mine for 20+ years. Started with AH-HA pc control, then added ballscrews, then when AH-HA went out of biz , I switched to Mach2, then Mach3, then added BobCad , then added/upgraded z drive several times as well as x,y drive motors
But thru it all I have to say none of them ever scraped out a part on me and always came thru when I most needed them to.
I'm at a point where the conversion far outways my ability to know how to use it all.
Just saying, rj

[brian257]

Been slacking on updates lately with a bunch of other things taking my time.

Got the Rockford ball screws about a week and a half ago. They look great and I was happy to see that they were well packed in a box with wood block ends so they came without damage. The lead chart I got with them shows from .0025 to .003" per foot error on the X axis and .0015 to .002" on the Y axis. I am happy that I spent the extra $40 for the lead chart so I can program that out with Mach 3 even though the error will be pretty much negligable for what I will make on the machine.

I made a temporary motor mount for the Z axis and tried running it with the motor a few days ago. With a 2:1 pulley ratio the table moves noticeably slower going up than down, but still moves it pretty fast. I bored and broached the pulley I have for 3:1 ratio, but have not tried it yet. My tests were just hooking the motor direct to the power supply so I still need to bring the computer and Gecko drive out and do some real testing to see what speed I can move the table safely and accurately. I am confident from my preliminary test that I can get good results without adding gas springs, but might add them anyway.

Been doing a good bit of work on the drive box also. Should have time next week to put up some pictures.

[brian257]

Still slacking on the updates. Been slacking on the conversion also with a bunch of other stuff to do.

I bought a hydraulic lifting table from Harbor freight to help with getting the table off the machine when it is time to put in the ball screws. have not tried putting them in yet though.

I did try to run the Z axis off of Mach III and found that the table would go down fine, but had problems going up. Seems the motor has enough torque when driven directly off the power supply, but not when driven from the Gecko drive with their 20A current limit. I bought two 2" bore pneumatic cylinders from Automation direct and an air tank to help lift the table. That will give me about 640 pound of lift at 100 PSI in the tank. That ought to do it. I made mounts and might have time to mount the cylinders in the next few days.