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

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

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

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/50002297/50024017/Milling_Machines/Turret_Milling_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

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

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.dll?ViewItem&rd=1&item=3836946559&ssPageName=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

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

I need a supplier but the UK sucks for this stuff :boxing:

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

Cheers,
Tom

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.

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

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 :)!

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

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
Look at the specs for the ones you found at eBay .
"Back EMF Constant, ke = 65 V/kRPM" That means to drive them to 1750RPM in no-load condition, you will need 114V DC. And if you need torque at that speed, add more volts. I guess you would be looking for around 150V DC.
The Gecko's will be fried long before you get there.

That doesn't mean you can't use them, just that you will not get full speed and power from them. If you got motors better suited to the voltage usually found in hobby grade drivers and with the same power you get from these, they will be smaller and lighter.

Ok Im with you on the servo and drives, perhaps I would be better off getting some fanuc servos and drives to handle the load this is obviously going to need.

My problem here is that while I find lots of info regarding model numbers on the fanuc stuff I cant really find any specs so some advice on brands, servos and drives would be good here.

Thanks for the help here guys you are being very helpful :)

Cheers,
Tom

I would stay away from Fanuc unless you intend going with a whole package, you may have a problem integrating separate Fanuc motors amps, unless they are used older style DC/analogue type And were talking big bucks. There are deals to be had on ebay and you have to decide which Servo's you want to use DC or AC, DC are a bit easier to match to other DC amplifiers, if you go with AC, I would suggest getting the matched amlifiers.
Motors to look for are Reliance, S.E.M., Electro-Craft, Kollmorgen, Aerotech, CMC, Gettys.
Amplifiers are also the same make as well as A-M-C. and Copley Controls. The current method is to use the amps in the current mode and this way you do not need a motor with a tach.
Al

Ok Ive decided to get real. I need to use a tried and tested method and IJ.'s example of how it should be done is my inspiration.

IJ. If you could supply the exact model number for the servos you are using in your X, Y and Quill Z drives I will find a supplier for them and spend the money to make sure its all going to work. Im also going to use the world servo drives you used. I know its plain old copying but as the saying goes dont throw good money after bad and if it costs a few hundred more to get what works then thats what Ill do.

Cheers,
Tom

Tom: The Servos are Kollmorgon Silverline 700w but are discontinued, I think any of the larger Servo's from 700w up will do the job fine if geared 2:1!(My motors will spin to 3000+ Rpm so even gearing it down the rapids are acceptable, any faster and the mass of the table will cause problems with braking)

The Drives I'm using are World Servo SST1500's this combination while not being cutting edge has proven smooth easy to set up and reliable so far!

I'm using DeskCNC's Controller to run it all as I can use my old Laptop (P3/500) and this doesn't become a bottleneck as when using a Printer port driven solution.

I think I'll try to replicate it when I do my Lathe retro!

ToMMy2000,

let me see if I can help, since you have a full sized BP clone.

take a look at some pics of my mill conversion here
http://www.motovidia.com/stuff/MILL%20pics

I also have new servo motors (if youre interested) , they are an OEM version of Baldor MT-4090-BLYCE, dc brush, torque is 40 in/lb. I use these with US Digital 1000 line differential encoders.

Femi

Femi: that sounds interesting, the spec seems good.

Im not after mega supersonic speeds, although it would be nice so looking at the performance graph:

http://www.baldor.com/products/servomotors/dc_servomotor/perf_graph.asp?catalognumber=MT-4090-BLYCE

It looks like the RPM tops out at 2500rpm with a supply of 100vdc. So on a 2:1 drive thats 1250 at the screw, 5mm screw = 625cm/pm = 246IPM.

That looks like more than enough speed for me so as for the torque I dunno what exactly I will require. If you could give me a price for 3 of these drives I would appreciate it, Ill also need encoders as well so if you have some of those handy or could supply the drives with ones fitted that would be really helpful.

If I am wrong about the IPM or any crazy ideas I have please correct me as Im still on the steep bit of the old learning curve.

Cheers,
Tom

ToMMy2000,

you calc. sounds right.
I run these motors at 170Vdc, with 2:1 reduction, 5mm pitch ballscrews, that gives me about 325 IPM max.
Most of the commercially available knee mill cnc systems use 23-30 in/lb motors. Is the 40 in/lb overkill? some might say yes, but one good thing is that, even after running my machine all day, the motors are only warm (if you touch them), lots of "headroom".

I have 3 US digital encoders, you can read the part # and check the us dig. site for more details
http://www.motovidia.com/stuff/MILL%20pics/us_digital.JPG

The backplate needs to be removed (2 screws) & machined for the encoders to fit.
http://www.motovidia.com/stuff/MILL%20pics/1k_enc.jpg

the motors are new & unused
I'll email you pricing for motors & encoders

I plan to use this machine in manual mode to get used to machining and make the materials for the CNC, I have the option of a powerfeed, but how usefull that will be once I move to CNC I cant say...any suggestions?

Cheers,
Tom

Tom,

If you plan on doing the cnc conversion "soon", save your money don't buy the powerfeed

Femi

Ive gotten confused about what Ill need to drive these motors...with the geckos it was simple.....


PC
|
+-- Servo Drive -- Servo Motor
|
+-- Servo Drive -- Servo Motor
|
+-- Servo Drive -- Servo Motor


So to drive these motors from femi what am I going to need excluding PC?

Servo Drives, Servo Amp, Servo controllers?!?!

Cheers,
Tom

Tom,

You'll need your pc + cnc controller (eg, Mach 2, DeskCNC etc)
+
amplifiers aka drives (eg, Gecko, Rutex, AMC)
+
servo motors

Femi

ok so my shopping list is nearly complete...I need to ring the bank :)

Femi: about those drives, I definately want them but I am short on capital at the minute. Could I send you a deposit and in 2 months send you the remaining payment?

I have more questions now than ever which Im sure for those time served machinists may seem obvious.

DeskCNC looks like a good package but for now I need to buy the mill, servos, controllers and get it all fabricated and wired up. Then Ill worry about the controller, software and GCode.

Cheers,
Tom

Tom,

Ring the bank? I'm sure Prince Charles would be glad to loan you a pound or 2 (or should that be a Euro or 2)?

In your last post you said "drives", do you mean motors?
email me at femi@motovidia.com, let me know what you're thinking & we'll try to work something out

haha, its still pounds over here :)

IJ. Couple of questions...

Ballscrews:when you say blank, you mean the thread goes right to the ends?

In your thread (where I should have really posted this I suppose) you mention the hardening being close to where you had to machine.

If this is so, how did you clamp the ballscrews in the lathe?

Also how did you remove the thread on the Quill Z Axis? Grind it first then machine to perfection or...?

I guess what Im asking for is a explanation on each ball screw of what you did and how you did it.

Cheers,
Tom

Hello There
I live in the UK and have a bridgeport series 1 CNC Machine with a boss 5 control the control went on the blink some time ago and I was not getting anywhere with the repair, so in the end I decided to shop around and in the end bought a Ajax CNC control. At the moment with the exchange rate as it is they work out quite reasonable, and the conversion dose'nt take long, and the result is it works straight away with very little messing about. although I have three phase power I now run it all on single phase, this is done by using a single to three phase inverter the rest of the system runs on single phase with a computer running the software provided. hope this might give you some encouragement. Cheers for now Colin

Well Im a little stuck here....

I want a bridgeport, but I know of two clones I can buy new...the Eagle:
http://eagle.en.alibaba.com/product/50002297/50024017/Milling_Machines/Turret_Milling_Machine.html

or the SEMCO:
http://www.semcouk.com/

Now do I buy a used Bridgeport or a new SEMCO or Eagle?

I know that I could buy a new machine but the build quality might not be as good as the used Bridgeport which could alyways be re sprayed if I really wanted it all shiny.

I have a 5k budget for the machine so which way do I go...??

Advice would be appreciated.

Cheers,
Tom

PS

I have decided to get SAMSUNG CSM servos and the amps that go with them.

800w motors, 3000rpm @ 2.5n/m rated values, 7.0n/m peak torque....plenty of power :)

They take step and direction so I can easily hook my PC computer port up with the kit.

I am looking at getting OncCNC XR Advantage to take my Rhino models :)

Finally I know what I need :)

Cheers,
Tom

Well Im a little stuck here....

I want a bridgeport, but I know of two clones I can buy new...the Eagle:
http://eagle.en.alibaba.com/product/50002297/50024017/Milling_Machines/Turret_Milling_Machine.html


Would you buy directly from China?
When he has some resellers around that told him that if he send them junk, they will stop buying from him, or that even may have their own people on site to do some quality control before shipping. What do you think he will do with those that did not come out very good?

Also AliBaba.com is not a good omen. Maybe you'll have to deal with one of his 40 ..... "merchants".

If you buy the same brand from a British company you pay a bit more, but you stand much stronger if what you get is not what you paid for. Of course German, French and so on is also close enough for you to have the same benefits.

PS

I have decided to get SAMSUNG CSM servos and the amps that go with them.

800w motors, 3000rpm @ 2.5n/m rated values, 7.0n/m peak torque....plenty of power :)

They take step and direction so I can easily hook my PC computer port up with the kit.

I am looking at getting OncCNC XR Advantage to take my Rhino models :)

Finally I know what I need :)

Cheers,
Tom

Tom,

I'm contemplating a CNC conversion of my Bridgeport clone (actually, a Unimac), so I'm following what you are doing with interest. If you could tell us the costs of the parts you are selecting, it would help me a lot. After all, if price were no object, this would be pretty easy.

I'm waiting to get some price info, but I'm looking at (the specs of) a Glentek, Inc GM4020-60 servo. It's 23 lb-in (2.6 Nm) cont. stall torque -- 5 times that peak -- .80 HP at max speed. The fact that it's max speed is 2200 rpm seems like an advantage in this application. A 5 pitch leadscrew would give 440 IPM. For my use, it would seem that 4:1 gearing would let it top out a 110 IPM (it seems faster when you say almost two inches per second). And the effective torque would be quadrupled. That brings it to about 8 pound feet. Or consider turning that six inch diameter wheel at the end of the axis. That's a 1/4 foot radius. So to equal the motor, you would have to apply 32 pounds of force to it. Oh yeah, and you would have to do it at many revolutions per second. That's the continuous spec for the motor. You would have to be able to apply a peak force of 160 pounds.

I guess I'm saying that there is such a thing as overkill. I suspect if you anchored a heavy vise to the table and accidently hit it with the quill, you might knock the ballscrews right out of the machine.

Good luck and, please, keep us informed.

Ken

Hi
For ball screws you should try Hiwin they have kits for most manual mills
I use NSK myself as for motors AC servos are alot better than DC motors
They cost a little more but will run your machine a lot better I use Yaskawa
and I can give you all the spec if you want You can Email me at
fernmac49@att.net I have done 8 Bridgeport Boss 5 now and 28 other machines
some 3 4 and 5 axes I will post some photos of one that I have almost completed which is a Boss5

Regarding ballscrews, take a look at the ones from http://www.rockfordballscrew.com/

Some ballscrews have nuts that cannot have backlash adjusted out as they wear, while some have "double" nuts with adjustable backlash. I believe the Rockford kits are adjustable while the Hiwin ones are not.

Good luck-

Paul T.

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


Do you have a price on these items?