BF30 CNC retrofit ...

[katran]

This week , my new BF30 Vario will be here ... I want to retrofit the
damn thing... ballscrews , steppers and **** ... Is not a really big thing but...

i am not sure what kind of ballscrews to use ( as in how big / diameter
and pitch ) ... I have a couple of NSK's , but they look somewhat small
for that beast ( 1605 , ground ) ...
I already ordered 3 steppers from keling ( 1200 oz/in , 34 frame ) ...

So , any input will be great ... thanks.

[grf]

the factory cnc kit comes with 20mm for the x and y axis and 25mm for the z. apart from that the use steppers with reduction drive. i have a bf-30 but no money at the moment to convert it. it would be nice if you document your project.

[katran]

you are right about the factory kit ... but the damn thing is so expensive... I made some
research and this is what I did : I ordered a set of ballscrews from ebay with the exact
specs as original screws ( diameter , lenght , endmachining ) , from a chinese seller
( linearmotionbearings ). Made the project for conversion acordingly ( I will keep the
hand wheel for X and Y axis ) The 1200 oz/in steppers will move the X and Y axis
without any problems but for Z axis I will use a set of 2 pneumatic lifts ( cilinders )
to compensate for the weight of the milling head .Theese cilindres will push the head
up with a force equal to the preload value ( 60 lbs ) , so , there is no need for a
more powerful motor .

I will post some pics with the project ( made in Rhino 3D ) and others reprezenting
the actual process of conversion .

Speaking of money ... of course is cheaper to D.I.Y ...the ballscrews were about 300
the motors another 400 ... some aluminum plates came at 200 ... the control box
will cost about 350-400... Let's say 1500USD overall ... I can live with that ...

Gabriel .

[grf]

what are you going o use for electronics at that price?

someone wrote this to my the thread i have for my bf-30

check longrats conversion. its not so simple installing ball screws, but its not hard either. it depends what size you want. the ball nut on most good precision screws is large and some modification is usually needed.

as for the motors. yes, they are much overkill. theres a few things to take into account when picking a motor.

- cutting loads.
- way friction.
- mass for acceleration.
- top speed.

cutting loads are pretty basic. take the torque of the spindle in in-lbs multiply by 4, and thats the most load youll ever see. so you have 2.2hp at 3000rpm (im ignoring the low gears here). thats 46 inlb - or 46lbs on a 2" cutter and shy of 200lbs on a 1/2". smaller cutters will snap with that kind of torque, and your low gears will be used most for bigger cutters. for reference, a 1/2" cutter 3/8" width and 1" depth at 3000rpm in hrc35 4340 steel at .003 feed per tooth on a 4 flute tialn cutter is a mere 83lbs.

sooo. 200lbs of force is aboot 800 newtons.

friction to overcome on a 150kg load (table and work for example) is between 700 and 1000N depending on how tight you make the gibs.

acceleration at a rate of .1G (not a bad clip) requires another 150N.

accounting for ball screw drag and some safety we divide by .8 and get 2400N on the high side. a more reasonable number is around 2000. but may as well have a good safety margin.


sooo, how much torque does it take to push all that? on a 5mm screw thats about 0.7NM of torque, or 100oz-in.

yup, you read that right. and thats an unrealisticly heavy cut WHILE accelerating full tilt. so why do people spec crazy motor sizes? i dont really know. even marris at gecko is on record saying smaller motors often yeild better performance. the smaller motors usually have more decent torque at speed as well.

they key here is, you want that 100oz-in of torque at a useful rpm. for our example, 1200rpm (20rps) gives you 236ipm, which is probably a good start. so simply find any motor with a graph that covers you with some saftey and make sure the psu and drives are well matched. i think youll be surprised that alot of the motors that meet the requirement ar higher voltage nema 23's.


and, for some proof of my maths:

YouTube- ZAY MIll converstion with NEMA23 and G250

YouTube- ZAY MIll converstion with NEMA23 and G250

[katran]

Electronics will be from Keling ... 6,5Amp drivers , 700Watts power supply ,
a break out board ... plus shipping .
Ballscrews RM 2005 ( for X and Y ) and RM 2505 ( for Z ) .

The ballnut block on Z axis will be modified ( the hole will be machined to
acomodate the ballnut of 2505 screw / 42mm ) . The ballnut blocks for
X and Y axis will be remachined from scratch .

The BF30 Vario is heavy ... around 280 Kg ...I am not sure that a nema 23
motor will move that monster ...even with a reduction kit ... so I am
overbuilding ... just to be sure .

Thanks for reply ,

Gabriel.

[abfa9358]

check longrats conversion. its not so simple installing ball screws, but its not hard either. it depends what size you want. the ball nut on most good precision screws is large and some modification is usually needed.

The difference is with the Optimum BF30, it is designed from scratch to take ball screws unlike the Weiss or Warco machines. Theres loads of room for the X screw under the table. All axes have bearings at either end and looking through the CNC conversion manual theres no more that a days work to retro fit ball screws. Worst part of it appears to be taking the head off its carrier.

[katran]

Some pics with the 3D drawings ...in Rhino . Is not complete , and I am not
sure that the dimensions are acurate . It is just a preliminary drawing , so
I can make an idea what will look like . The milling head is not represented
because is not necesary in this project .

[ihavenofish]

if im not mistaken, the bf30 already has a z axis counter balance strut inside the column. i know the weiss version does. so your external ones may not be needed.

[katran]

No , it doesn't ... the mill is in pieces now , and I would have seen it ...
There is only the screw and the gear mechanism ...

I will make a 3D drawing of the mechanism inside the column as it is
now , then with the ballscrew / stepper retrofit .

[ihavenofish]

Originally Posted by katran No , it doesn't ... the mill is in pieces now , and I would have seen it ... There is only the screw and the gear mechanism ... I will make a 3D drawing of the mechanism inside the column as it is now , then with the ballscrew / stepper retrofit .

huh. good to know.

[abfa9358]

I will make a 3D drawing of the mechanism inside the column as it is now , then with the ballscrew / stepper retrofit .

check out the link kindly posted by ricardas
http://media.mruni.lt/ricardo/
on this thread
http://www.cnczone.com/forums/showth...ht=BF30&page=5
It is a really useful link to the user manual and the CNC conversion manual for the BF30. The user manual has exploded diagrams of the machine.
You can make a good start for 3D CAD from there. I'm using the machine drawings and TurboCAD to space plan my shed for the arrival of a BF30. If you have a detailed look through the various drawings you can see that the BF30 Vario is a quite a different beast compared to the Weiss / Warco offerings BUT there is a price penalty ~£2090+VAT.
For what its worth I'm planning to do the same as katran - purchase the machine and then add my own ballscrews.

[katran]

Links are O.K ... BUT ... the real problems are :

1 . what are the exact specs of the ballscrews ( lenght , diameter ,
endmachining / dimensions )

2 . shape of the ballnut blocks / dimensions / holes . ( for X and Y )

3 . what kind of machining is necesary for the ballnut block of Z axis
( is better to modify the original one , it's made of steel and is
very strong )

When I bought the mill , it came with all the manuals ... diagrams
and all . You can take SOME dimensions from there , but not the critical
ones. For example : distance from the surface of the working table to
the screw axis ( my caliper show 60mm but I am not quite sure )

Mounting the motors is not such a big deal , there are a lot of ways to do it.
I intend to mount my motors direct drive ...

The link with the CNC conversion is actualy pretty good ...some good
pointers there , thanks !!!

Anyway , my ballscrews will arive in a week or two , so expect lots
of pictures ...