BF-20 CNC Conversion

[JBV]

Hello!

I recently bought a Optimum BF-20 Vario mill and intend to convert it to CNC!

So far i have only made the mounting plates for the x-axis and will start making the y-axis tomorrow... I'm going to use the standard leadscrews to begin with so i'll make my own custom Oldham type couplers as you can see in the pictures.

When i get the mill running under CNC control i will make better stepper mounts and replace the bearings with angular contact ball bearings. And later i'll buy ballscrews. I don't want to start with that because i have to modify the base and the y axis carriage to fit the nuts.

I'll take some photos when i have made the couplers!

/Jay

[KPDamen]

Hi,
I am making a set for converting the BF20 to CNC as well. I have finished my initial designs, have included some pictures of it. The kit will become available at www.damencnc.nl after testing is finished. The parts will be made from laser cut stainless steel plates. Covers are in the making so work can be done with coolant.
I had some question about your design, which is interesting:
Are you using the motors coupled directly to the axis? Don't you have problems with resolution? Even with microstepping, a direct connection often causes problems unless huge steppermotors are used.
I am using belts so that smaller motors can be used... Have runs mills like these with 1.5 to 2nm motors and they work great..

Greetings, Kevin

[JBV]

Yes i'm doing a direct coupling... Its just a temporary setup that i can make all parts on the manual mill I have read that steppers is best with direct coupling because of the torque curve.. You don't gain so much (if nothing) with gearing because the stepper have to run faster and the torque of it goes down.

I have 2,2Nm steppers and plan to counterbalance the head to be able to use them for Z too! (not the fine feed)

/Jay

[JBV]

Here is some pictures of the mounting plates (The front Y plate is not shown)! This is the first parts i have ever made on a mill so they are not pretty But then again... Its only temporary parts until i get the mill converted. Can't wait! Hate to turn those hand wheels

/Jay

[JBV]

By the way... I really need to build a bench for the mill... The table that i use now is very unstable, and i didn't want to drill bolt holes in it so i just clamped the mill to it with MDF boards

[andy55]

been using a stepper converted opti BF20 for about 2 years now:
http://www.anderswallin.net/2004/11/...g-of-mdf-plug/

note stack of counterweights we use behind the machine as we have coupled the Z-motor to drive up/down the whole spindle box.

the DC motor burned out during a longer run so had to replace it
http://www.anderswallin.net/2005/11/...ew-opti-motor/

I find the stock leadscrews and the dovetail guides are really limiting the precision that can be achieved. With backlash compensation it now runs accurate to about +/- 0.05mm in the Z axis and probably a little better for X and Y.

another problem is the center accuracy of the spindle. we now have something like 0,05mm of eccentricity which is no good for vibration/surface finish.
this might be way better on a new machine as we have done maybe 10-15 long (4-5h)runs in steel/alu which might have damaged the spindle or the bearings a little...

If I remember correctly the steppers are 280 Ncm torque and they are driven by geckodrives running off a 70 V powersupply.
max feed when cutting wood is about 1000mm/min, for aluminium 300-600mm/min with very light cuts.

well, I guess you get what you pay for. I think we paid 1300eur or something for the mill, MK2 collets, some endmill, fixture kit etc...

I'm now planning a new bigger machine with linear guides+ballscrews...

[JBV]

I have seen your page before! I'm not planning on using this machine for very long... One of the major reasons i bought is was to be able to design and build linear actuators and structual parts for a hexapod... Perhaps i sell this when i'm done

/Jay

[JBV]

I made the torque disc and one part of the coupler today, nice fit to the leadscrew/key and the disc... Should be no backlash in the coupler when i'm done!

[ejkoeze]

Hey, this is nice.

I'm also working on a BF-20 CNC conversion. I'm going the Servo way using homebrew servo controllers (DIY Servo controller)

I may be using 1:3 reduced Dunkermotor 63x55 on the X and Y axis and a 1:3 reduced Dunkermotor 80x80 on the Z axis. Another option is to leave the planetary gearboxes (1:7) on and use them that way.
Dunkermotor 63x55 is 100W 3500RPM 0,27Nm continuous
http://www.dunkermotoren.de/data/tec...x55.pdf#page=1
Dunkermotor 80x80 is 240W 3500RPM 0,62Nm continuous
http://www.dunkermotoren.de/data/tec...x80.pdf#page=1
They run @ 40V and have 500CPR encoders which gives me a theoretical resolution of 6000 pulses per main spindle revolution. When the conversion is complete I'll have built in 16x5 Ballscrews in X and Y and 25x5 ballscrew in Z giving me a resolution of 0,001mm. Which is way more than the accuracy of the machine.

Conversion will first use the standard spindles and when all is working the way I want I'll get me those $$$$ ballscrews.

When completely done I'll be able to get rapids up to 6m/min (100mm/s). With the planetary gearboxes this should still be 42mm/s which is also more than adequate.

I'm still deciding which way to go. The gearboxes are quite heavy. To hang those from the table is not very desirable since it may start to hang causing extra wear. Motor with gearbox is 3,4kg!

Decisions, decisions, decisions....

I'll see how this thread goes.

Erik Jan

[JBV]

What ballscrews/nuts will you use? I made a solid model of the mill to try out the possibilities of ballscrew conversion and there is not a lot of space! :P Will you modify the Y "carriage"? and/or the base? I have been thinking of trying to build DIY rollerscrews that would fit the current space!

Interesting about the controller! To bad i already have the steppers hehe

[ejkoeze]

I'll use Isel ball screws.
If you can read German I suggest you read the thread
"Optimum BF20 Vario gesucht, gefunden!" in Hobby Machinen on www.cncecke.de registration required.
You'll find a wealth of information regarding the machine including mainetance, bearing replacement, ballscrew conversion, cnc conversion both with steppers and with servo's.
Their is a complete documentation of a ball screw conversion including photo's by Thomas74 that I recommend you read.

Erik Jan

[phil burman]

Hi Erik Jan,

Dunkermotor 63x55 is 100W 3500RPM 0,27Nm continuous doesn't sound like a lot for 240 inches/min on a BF20. Also what about backlash in the gear reduction system.

Or do I misundestand something.

Phil