Need some advice

[Kiwi 007]

Well I've lurked here for quite a while and when I bought my Mill Drill I had the intention of converting it to CNC at some point.
The Mill Drill I got is a Optimum BF46 with 40 taper spindle and has proven to be pretty ridgid. This machine also has a CNC kit available for it which uses 17 NM stepper motors.......I would rather use servos instead of stepper motors.
Since I bought this machine the cnc version of it is almost available, I thought of trading mine and buying the cnc version........until I found out the price, over 5 times what I paid for mine. The cnc version uses Siemens 802 control and isn't 4th axis capable......add about anther 200% onto the price to be 4th axis capable.

Most of the aftermarket kits I see use 850in oz steppers and I have found an 1125 in oz stepper setup........The Optimum kit uses 17NM steppers which converts to approx 1800in oz steppers.......am I reading something wrong?
Does anyone make a servo kit that has the equivilant torque of the Optimum kit?

This is a link to the Optimum site with specs on the Mill Drill and the CNC kit.
Optimum Machines: Complete and add-on BF 46

[The Blight]

Man you are lucky! Thats the same machine I have been looking at for some time now (I have around 40-50 tool holders that fit this machine).

I will be following this topic with great interest to see how you solve the CNC problem.

[cyclestart]

.The Optimum kit uses 17NM steppers which converts to approx 1800in oz steppers.......am I reading something wrong?

Between the German text and the tiny print it's hard to tell exactly what those numbers represent. The screws appear to be belt driven so the torque applied to the screw depends on the ratio of the 2 pulleys. This link may be of some interest:
IH CNC vs. Other Mills

The BF46 is similar to an Industrial Hobbies in size and weight ? There are many examples of cnc IH and IH clones on this site, look at what motors are used and ask questions. Owners love to talk about their machines.

EDIT/ There's more info in that link than I noticed originally. The steppers are listed as 12 n-m. Seems like a lot of money for a stepper system but who knows, Siemens is a big name as you're aware.

btw: what's in the photo background ? You're holding out on us Kiwi

[Kiwi 007]

Between the German text and the tiny print it's hard to tell exactly what those numbers represent. The screws appear to be belt driven so the torque applied to the screw depends on the ratio of the 2 pulleys. This link may be of some interest:
IH CNC vs. Other Mills

The BF46 is similar to an Industrial Hobbies in size and weight ? There are many examples of cnc IH and IH clones on this site, look at what motors are used and ask questions. Owners love to talk about their machines.

EDIT/ There's more info in that link than I noticed originally. The steppers are listed as 12 n-m. Seems like a lot of money for a stepper system but who knows, Siemens is a big name as you're aware.

btw: what's in the photo background ? You're holding out on us Kiwi

Thanks, yes the stepper motors are 12 n-m which equels 1700 in-oz. I would like to setup a closed loop servo control with similar torque.......does anyone know a servo kit of this size that is available?

As for the background, its the same as the optimum but sold as a Luxcut where I got it........the photo shows the lathe when I bought it. Now it's equiped with Newal C80 CSS 3 axis DRO and the constant surface speed feature is fantastic.


This will be joined by this when I finally get it all together.


and this after I complete a rebuild on it

Kiwi

[cyclestart]

Thanks for the photos, you have some seriously nice machines.

I've only begun exploring servos myself so probably should have stayed out of this conversation. I'll offer some thoughts anyway. Power characteristics of steppers and servos are apples and oranges, think in terms of machining force. Servos are not typically run 1:1 and they don't need to be as their power doesn't fall off with speed as seen with steppers. 850 oz-in servos 3:1 would probably be gobs of power but a supplier could give some real world numbers. The bf46 comes cnc prepared with drop-in ball screws available if you choose to go that route. Most of us should be so lucky.

Wish I could be more help

[wildwestpat]

Hi Kiwi 007

Nice machine to convert to CNC.

There are three main factors that decide the choice between servo or stepper apart from price that is!

1. Work out the torque needed from the motor. Here is a link to a very good on line calculator:-
http://www.kollmorgen.com/en-us/supp.../motioneering/
It is vital that a stepper system which is effectively open loop (i.e. has no positional feed back) does not loose steps under all conditions of load / inertia acceleration/ tool reaction etc.

2. Positional accuracy required. A stepper system has minor variations in the steps making up one complete revolution. Some motors are better than others this limits the step accuracy. Also the effect of backlash of screw, coupling and mounting bearings are not compensated for.

3. Stepper output torque falls rapidly once 1000 rpm is exceeded with parallel operation of the coils. For series operation above 300 rpm sees the available torque start to fall.

Feed back servos reduce these problems and with suitable glass scales or laser devices the positional error can be all but eliminated BUT at a cost.

To use that calculator you will have to guess weights of table head etc. It appears that most people copy what others have found to work rather than calculate motor sizes. There is nothing wrong with that it means you have to weigh or guess the weight of the parts so that the torque needed to counter inertia can be calculated. That said a few guestimated runs will soon give you a feel for the size sensitivity of the servo drive torque.

Hope this helps - Regards - Pat

Hope this helps

3

[Kiwi 007]

Thanks Pat very helpful information.

Does anyone know of a servo kit that is available, and will Mach3 run servos?......Kiwi

[Kiwi 007]

I ordered the ball screws today, Chinese precision ground ball screws with an accuracy guarantee of 0.005mm. These will bolt straight in.......now all I have to do is locate a servo kit to fit to it.

Which servos are recommended for a closed loop setup?.....Kiwi

[Kiwi 007]

Well nothing much has happened since my last post apart from a well deserved holiday..........anyway I got home from holiday and my ball screws have arrived for the BF46.

Also while I was away the CNC version of the mill arrived, I still want to see it in person but the photos look good



And for more info about it have a look on this website.......you will also find smaller units........Kiwi

Optimum Machines: M4 CNC /M4HS CNC