size of 4th axis drive

[converterk]

I am in the process of retrofitting a 1999 Birmingham bed mill with 41x20x23 travel. It has a 12x60 table. What size servo motors would you recomend? I may add a 4th axis later on, what is the size of the 4th axis drive so I can leave room in the cabinet for it. thanks, Terry

[Al_The_Man]

Where there not motor on the original set up that you can go by? What is the pitch of the Ballscrew? what reduction is there, if any?
Al

[converterk]

I should have mentioned that the original motors were 29in-lb, the ballscrew is 5 tpi and it has a 2:1 reduction. The shaft size is 5/8. What is the shaft size of your 29 and 40in-lb motors? Terry

[Al_The_Man]

I do not have that same machine, but is there a reason you are not using the same motors or have they been removed? What control do you intend to use, and what make was the original control?
Are you replacing the Motor drive's?
All these questions help in assessing what you need, 29"/lb motors with that reduction I would say are ample. Although it depends on the weight of the table, and how much the max load carrying capacity of the table. And what max. feed rate.
Al

[converterk]

It had a Direct Motion control, I want to use the Ajax control so it is the same as my other machines. It comes with a digital drive and i/o combo board as part of the package. I will use this for prototyping and short runs so I would think rapids of 150 would be ok. Terry

[Al_The_Man]

The old motors were fairly beefy but if they were DC, the modern AC motors are physically smaller for the same torque size and have lower inertia, so you could go with larger torque for the same physical size if you so wish. 150" min in rapid is not that high.
Al

[Al_The_Man]

A thought just occurred to me, what I do if I am buying the whole system from a supplier is send him the details of the machine and get him to spec. in his motors and drives etc. If they are supplying the whole package then there is a certain amount of input they should be supplying if they want my business.
Al

[converterk]

Al a question, I found that I have 9 good used Contraves dc servo motors that the Bridgeport Boss 7 & 8 used. They are rated at 1.68 in-lb per amp. Amp cont is 6.3 , amp peak is 58. They have a 5/8 in shaft which is what I need. Would these be powerful enough? How do they normally rate the in-lb's of servo motors?,cont or peak or do they use something in between? I am selling the original servo motors with the control, they have a website at www.directmotion.com they want $12,500 for it. Probably good for someone that dont know g code. thanks, Terry

[Al_The_Man]

Terry, If your going with the Ajax control, I understand you have to use their motors and drives?
If not I believe the Contraves are a tad small for your application.
Al

[converterk]

You dont have to use their motors. On the last retro I did I used CMC motors with their $125 2000 line encoders. The servo amps are included in their retrofit package. I believe they sell SEM motors on their site. Terry

[AjaxCNC]

Terry,

Hello. The 4th axis drive measures 6.75" x 9" x 2". We usually install it on top of the servo3IO if there is enough depth to the cabinet.

As for the motors, both our 29in-lb and 40in-lb have 5/8" shafts. They are a NEMA 42 frame. These ratings are continuous torque.

Concerning the motors you have, I believe them to be too small. They are only about 11in-lbs cont.

On a typical 12 x 60 table, we would use the 40in-lb motors, belted 2:1.