When moving the z axis, it stops about an inch or so from the top and the motor starts binding up and making noise. This happens also while running a program on the machine. It is intermittent. It runs great for a while and then it binds up again. No visible problems when we looked inside the cover. Any ideas as to what is going wrong would be greatly appreciated. Thanks in advance...

What kind of axis drive motor is this? Servo?

Could it be a heat issue with the spindle? I've seen a hot spindle housing stick in the head until it cools down.

Does the Z axis motor fault out on overload?

How about parallelism of the ballscrew? Is this a professionally made quill box?

Odds are that you have a stepping motor BOSS machine. It is typical of these to stall and whine as if they are trying to move. You must understand what a stall is. The control accelerates the motor to a certain velocity. If the motor cannot keep up it will move bacward to the closest/strongest electromagnet (field). It then occilates between poles, hence the whine, and it does not move. The causes are insufficient voltage or current or drag on the motor or a weak motor. Some of these machines used screw in fuses which developed a resistance and would overheat. If you have screw in fuse holders (the original BPT were tan in color) replace them. The current at static (drives on and stationary) should be 8 to 8.2 amps DC adjusted at the ACC board. Always turn the drives off before pulling a fuse or hooking up a meter or removing a meter otherwise you mave blow one of the final drive transistors. At staic state from each of the DC drive fuses to ground, I would usually see about 8.5 to 9.5 volts. The most important reading is at the large transformer in the back. IE: wires 11 to 12 power the X axis. This should never exceed 64VAC or you will blow the final drive transistors like candy (2N6547). If other transistors are used I know immediately as the balance of voltage to current is off. Some times I have to clean the quill with kero to get rid of gumminess. Sometimes the graduated knob/dial at the end of the motor shaft rubs the cover and this can cause drag. When the motor turns at rapid the DC volts goes up to about 60VDC and the current drops to about 2.3 amps. As the magnets decay from heat and age, this current goes up which means that the same torque is not there and the axis can stall. This is also why when you turn the motor by hand you feel the poles as a growl. This is not a bad motor. But as the motor ages this growl diminishes. The RCK or ZCK board can be adjusted for a lower rapid rate and this can buy some time. I hope this helps.

George.

George,
Are you saying, in other words, stepper motors pretty much suck? ;) :D

When the old BOSS machines were designed (1970s), this was state of the art technology. It was aslo the most cost effective way to build a machine that a shop could afford. If you understand the machines, you will know their limitations but will also understand that you can have a cheap machine with a small footprint that will make you good parts. Also, there are spares out there to be found on the used market and a lot of parts are still available from Hardinge. The hardest part of this may be to find a Jurrasic service engineer like myself that knows these machines. I believe stepper motor technology is still used on Floppy drives, hard drives, etc. I never said it was trash.

George

I know George, I completely applaud your efforts to help out. Its me who has the bias against steppers :)

No problem. I find it interesting that most shops must move on to better and faster ergo more efficient equipment to stay competitive. The older stuff gets auctioned off to be used in garages or smaller shops that may have less overhead and pockets that are not that deep but can pay the bills and put food on the table with these machines. I believe that it is better to help and make life a bit easier. Life can be hard enough these days.

George

Thanks for all the great info. I really appreciate it.

One quick question....Inside the cover the oil is really gummy and sticky. What type of lube would you guys recommend for these BP's.

Thanks again

Matt

Mobil Vactra Number 2 is great and can be purchased at Grainger. But just about any 68 grade way oil will work.

George

Hello from Holland,

I bought a month ago a bridgeport serie 1 milling machine.
This week i will buy two ball spindels for the x / y axis, and an big table.

I want to make the machine CNC.
For this i want to use stepper motors.

The computer program i'm going to use workt parrallel.

Has somebody don this???

Wat is the diverence in price and prestage whith other motors?

Which program do you recomend?

And ferry important i want to put the z axis not on the head, but under the tabel, so i have more space to work.

Can sombody help me out with information, foto's, whatever???

Thanks and sorry for my grammar.

Latu
The Netherlands

Please take this how it is meant (as gentle and kind as possible). Unless you have a lot of free time, and this endeavor is for self fulfillment, then go ahead. You have a lot of data to acquire, and a lot of parts to machine or purchase. I suggest that it is more cost effective to find a used CNC factory made. Also look at the discussion at the link below.

http://cnczone.com/forums/showthread.php?t=5690

George W.

Hi Latu,

Yes it is tempting to put the z axis motor under the table, but remember table is very heavy. You will need a big stepper motor for that and problem will arise on how to make it backlash free.

Wow, somebody saw my "work" log. I'm not sure that the bp cnc's were as common in europe as they were here in the states. There are a ton of them here, and it's so much easier to fix them up as a good cnc than converting. I agree, in the States its a bad idea to convert a manual since it's so easy to buy a cnc that needs work.
Having said that, there was a recent discussion about converting a series 1 to cnc on cad/cam/dro yahoo group: http://groups.yahoo.com/group/CAD_CAM_EDM_DRO/ There's also a guy that is selling plans to cnc a series I for $35US, certainly worth it rather than trying to measure the bolt patterns and come up with a quill drive design. Sorry, no link for that.

Many of the bp cnc did use the knee as the z axis. I saw a knee ballscrew recently on ebay. Mine has a ballscrew built into the quill, so the knee is just an acme screw.
You must compensate for the weight of the knee which is generally done by supporting the knee with air springs. The mills like mine came with an air assist on the knee which I don't understand. Feeding air into mine just lets more air out into the atmosphere. Hate to have too much air in the atmosphere. Sure didn't make the knee any easier to push around, it's a monster, the knee, saddle and table weigh more than a series 1. I would like to motorize my knee, since it is a pain to move, but maybe I'll just counterbalance the thing.

All the BPTs that had series 2 iron had an air assist in the pedestal for the knee. The regulator was set at 50 PSI for an empty table. For each additional 100 pounds you put on the table, the regulator needs to be increased by 5 PSI. Too much air is not good either. The old NC2s had a stepping motor and ball screw on the knee. I was called in because the knee would not go down. Sure enough the air assist regualator was set at 90 PSI. There was an upward force of 800 pounds which the stepping motor could not overcome.
It is inportant to maintain oil in the air oiler because there is a leather cup in these. It is normal to see small bubbles of air leaking past the seal but no more than that.

George W.

All the BPTs that had series 2 iron had an air assist in the pedestal for the knee.
George W.

I guess my seal is leaking. Is the air assist a cylinder inside the screw? How did it work?

If you give me your email address, the next time I go to the office, I can scan an exploded/cross sectional view with BPT part numbers of the air assist built into a series 2 pedestal. I can email it to you as an attachment. It will be in PDF format.

George W.