Advice on Bridgeport BPJ to CNC

[ToMMY2ooo]

Ok where to start…this may be long but please bear with me.

Ive been lurking here and other places for the past 6 months, learning and doing as much research on the web as possible while trying to decide what to buy.

I have a budget of about £5k and want a ultimately a CNC milling machine, but I don’t mind getting a manual one learning how to use it, making the parts for the CNC conversion and then doing the retro fit.

Im the sort of person that doesn’t want to buy a kit, I would like to get each part based on its own merits and then assemble them altogether. In the past I have found this principle to have worked for me so I don’t want to risk going about it in another way (plus I like to make things and mess with (ie break) stuff 

I want to mill steel, alu, copper to make various parts with a view to some light production work when I move to CNC. Im not sure exactly what size requirements I am going to need just yet but I know that a Taig/Sherline/Grizzly wont do what I want simply due to their small size.

I’m in no rush, and want to do this properly and in return payment of all the help that I have seen given and resources that are available I will document the CNC conversion of my mill to a stupidly detailed level. Perhaps even offer the retrofit parts to other users for a small cost to cover the materials as I know I have had a really hard time getting my head round it all.

I have been looking at a BRIDGEPORT BRJ VARI SPEED. This one (see attached piccy) is selling for £2.5k, I have seen others for less but the rule you get what you pay would surely apply here?

The next step would be to convert this over to CNC and so Geckodrives 320’s have caught my eye here, what do you think? Do I need the step pulse multiplier versions? Perhaps I should have asked that in a second or two…

I want to gear my mill using 2:1 ratio belt driven servo system, so perhaps the PLL pulse multiplier bit comes in now? So what servos do I get…Im more interested in brands and model numbers than the spec of them although I would need both to accurately compare them for price/performance etc. Im in the UK and stuff is harder to come by CNC wise so if someone could give a good listing of several brands/specs that would be really helpful.

As for the power to the beast Im aware that it is likely to be 3 phase, and so some conversions need to be done in order to keep the table drive, Im an electronics person mainly so I expect I can come up with a homebrew phase converter without the need for an additional motor and Ill post that with PC board and kits if there is a demand.

Ive got lots more questions, some basic and some perhaps advanced electronics stuff but no doubt Ill get there in the end.

Any help is appreciated so thanks for your time reading and Ill keep you all updated with how I go on.

Cheers,
Tom

[Al_The_Man]

If you are thinking of converting a BP, Nook industries sell a rolled ball screw conversion for these mills. I have a couple of Excello's (same size as BP) and they use S.E.M. Motors (UK). 26inch/lb 2 to 1 belt reduction. Then you will want to also put a ball screw on the Z. (see the conversion done by IJ Australia) in this forum. Personally I would not convert the knee to CNC other than maybe motorize it for manually moving. You should not need three phase if you put a VFD on the spindle, you get Sph in 3ph out for the spindle motor, I converted mine from the vari-speed pulley to fixed ratio with VFD. and control the spindle from the CNC controller. I used Acroloop Acromill 4 axis card which gives 3 axis and Handwheel. The other way is to look for a small CNC mill that need a retrofit.
Al

[ToMMY2ooo]

Ok well in the UK here we seem to work in newtons and from what I can see from this link:

http://www.techno-isel.com/Tic/H860/HTML/H860P006.html

1 lb/in = 0.1129848 newton/metres

So a 26lb/in motor would be a 3n/m motor.

This gives me something to work with. I have seen the prices of some of these motors and its amazing how much they cost, £600-700 for something of this type!

Now I have been looking at some specs and if I were to choose a motor of this type what sort of rpm would I be looking at...I have a choice of:

2400, 3000, 3700, 4000.

Im going to get some prices from this manufacturer.

Cheers,
Tom

[ToMMY2ooo]

Ok let the spending vast amounts of money begin...

Ive decided to get a new mill...is this a good idea? Anyways for £3.5k I can get a BP copy - see this link:

http://eagle.en.alibaba.com/product/...g_Machine.html

Ive ordered 4x Reliance Electric DC Servo motors (3 for the machine, one for the rotary table when I decide to spend more money) from a guy in the states who will ship them over to me - $509 They have 500line quad encoders. Does that mean 500 pulses per rev? They spin at "Nominal Speed Rating: 1750 RPM" so geared 2:1 that make 875rpm at the leadscrew. What would that mean in terms of IPM?

OT: Whats a VFD?

They have a torque Constant, kt = 5.5 lb/in/Amp so Im looking at Geckodrives to power them at 7A max, 38.5lb/in (616oz/in) if all is good.

Im on the Nook Industries website...what specific ballscrew am I looking for?

I have also found a supplier of aluminimum stock near to me so when I get the machine I can cut parts for the conversion Im feeling more confident now about what I need and how to get it.

Cheer,s
Tom

[Al_The_Man]

Tom, The IPM will depend on the lead of the ball screw, typically 4 to 5 turns/rev i.e. 1 revolution will move you .25" for 4 lead screw. you just do the math.
VFD= Variable Frequency Drive, it takes the 50/60 cycles power optional single phase-3ph in and converts it to variable frequency 3 phase out up to 100/120 hz for operation on a standard induction motor.
effectively doubling the rpm of a standard 4 pole motor.
I will try and dig up the info on the Nook, BTW it includes the dogbone you need for the crossing of the ball screws. (they are made for BP but you may be able to adapt.)
Al

[ToMMY2ooo]

ahh you just answered a question for me about IJ. retrofit, I wanted to know what the dogbone was for.....and now I know

As for the IPM thats no problem..all I need is the ballscrew specs, much appreciated all this BTW

Ok so Im pretty much set, does $609 sound a lot for these motors Im getting?

http://cgi.ebay.co.uk/ws/eBayISAPI.d...e=STRK:MEWA:IT

Im not getting them off ebay as the guy has a stock but Im not really aware of prices for second hand gear like this so advice would be appreciated.

Cheers,
Tom

[Al_The_Man]

For Ebay thats big coin, I picked up the same size aerotech for $35.00 ea. BTW I meant to include that the 500 line encoders will give you 4x500 = 2000 pulse resolution when used 4xp mode, this reads the rising and trailing edge of two squarewaves which essentially gives you 2000 p/encoder.rev.
Cheers
Al

[ToMMY2ooo]

I need a supplier but the UK sucks for this stuff

hmmm any other suggestions for getting some decent sized servos at decent prices..based in the USA or otherwise?

Cheers,
Tom

[IJ.]

Just had a thought if you use the HiWin kit the ballscrews are 5 mm pitch so you'll need at least 3000+ Rpm Servo's if you gear it 2:1.

[ToMMY2ooo]

I need another 0 adding to the end of the cost of all this. The ones from ebay are rated at 1750rpm

So if I drive it 2:1.5 (a little odd perhaps) that may well work.

Comments?

Cheers,
Tom

[IJ.]

You're gearing Down for torque and to keep the motors in the meaty part of the power range!

If you get slow motors and gear up they may not have enough torque/power to move the HUGE weight of the table around!

I think "budget" isn't applicable to a BP retrofit as it's a very different beast to building a Router.....

Think of a price then triple it and add 20% and you might be close !

[Al_The_Man]

The Nook preloaded ball screw part Nos are X axis table 36" 4976-36-01 ~ 42" 4976-42-01 ~ 48" 4976-48-01.
Y axis 9" table 4976-09-02 ~ 12" 4976-12-02.
Bracket (dogbone) 1541-00-01. .. 0.2"/rev precision rolled leadscrews.
I am waiting for a new scanner or I would have scanned the page in.
Most software packages allow you to calibrate the revs/unit of movement to what ever your system requires.
Al