Help a new guy:)

[h3ndrix]

Hey ppl,

First of all, Hi to all CNC'ers out there. Im kinda new to the CNC scene and trying to learn some stuff. If you guyz can help me out and kinda guide me, I'll be really grateful.

I got this small bridgeport in my hand, It is an old machine and mostly disassembled. Its not a full-size bridgeport and its not a tabletop, its the one in-between. Its got its own cast base, but has a 18 by 6 table, not bad really. So, I want to convert this machine into a 3 axis CNC, with possible auto-tool changing ability and a 4th axis rotary table later on.

Allright, so this is what I want to do so far;

- I want to use servo motors instead of steppers, they seem to be prefered more so than steppers in terms of efficiency and quality.

- I want to use this program called OneCNC XP. I have been looking into programs for a while and it seems that this program is user-friendly and has similarities to Soldiworks (which I am pretty good with). If any one has experience with other programs of the kind, please let me know.

- I want to be able to machine cold-rolled steel with this CNC, not only soft metals like aluminum etc.

Here is where I need help ATM;

- I got no idea on what type of servo I should be looking for; DC, AC, PLL...what kinda amps, rpms (I know I will need slower speeds maybe for steel), torque and such.

- I have very little understanding of drivers, signal amplifiers and controllers and which type and what I should be looking for.

- I have very little understanding of G code. For example, would I need another software that converts what oneCNC XP gives me into G Code or how would this work?

- I have some idea on how to convert the ACME screws on the mill to ballscrew but I would be glad for further advice.

- I got no idea on how to hook-up the mill so I can adjust rpm automatically instead of manually.

this is what I can think of right now, If you guyz can suggest ideas or directions, ill be really happy.

Thx,

Baris

[HuFlungDung]

Hi Baris,

You've got quite a shopping list there

Of course, maybe the first thing to ask about is your budget. I am not familiar with such a small machine table. Are those the travels or the actual table size? What is the range of spindle extension?

Tell you what I'm driving at: you are going to spend some coin, but a machine that is so small is not very versatile. I have to be careful with the tool selection on my small mill which has a 5" Z (spindle travel), but the table motion is 28" x 14", table size is 10 x 49, with about 8 inches on the knee travel.

Typically, I don't want to be cranking the knee up and down in mid program. However, on a small machine like this, you might actually want to run a servo on the knee, just so you can get a decent range of working depths.

Check out the maximum Z height you will have too, with a vise mounted on the table, and a 1/2" drill in the spindle. Is there any room left to work?

I'm just pointing out what you should consider before you begin. For very little more money, you could retrofit quite a bit larger machine, but be 100 times as versatile.

RE: what type of servo? I would suggest DC brush type servo. These are the least expensive, and give good service. They only require "one axis" each, of a motion control system, too. The fancier AC servos require 2 axis per motor ( But, I could be mistaken about this, please someone correct me if I am wrong )

Then, buy PWM servo amplifiers to run the servos. I've used AMC (Advanced Motion Control) brand with no problems, and think the prices are typical.

Re: spindle rpm: use a variable frequency AC drive.

Re: OneCNC: this program makes the gcode for you. It does indeed go hand in hand with Solidworks. If you are comfortable with Solidworks, you can import your models into OneCNC and machine them. Or, you can design them completely in OneCNC, since it does have solid modelling capability. However, you need to get Mill Professional XP (not Mill Production XP) for creating solid and surface models.

Note: all the stuff I have recommended is just typical machine shop quality stuff, not cheap as in "hobbiest budget", so you can take that into account when you reveal your budget.

[BIG AL]

Welcome Baris! You have come to the right place for help, there a number of ways to get to where you want to go with your project, any number of kits out that are on the web for the bridgeport and it's clones. It really comes down to that old question from my racing days of " how fast do you want to go = how much do you have to spend? and part of all of that is how much you can do on your own to get to where you want to go. I know this will seem kind of terrible to you but sometimes it cheaper to find a different ride to get to where you want to go. I mean by that your old Bridgy has value as a manual machine and has a wider appeal to the home machinest than a cnc mill. Cnc Bridgeports can be had cheap and that right machine is out their waiting for you, kinda like a race car that a guy you used to know had and it just wasn't fast enough for him anymore or it's broke and cost to much for him to get it back on the street again. That might be where you want to go. A restro project on that old mill and (cherry it out) you might get to where you want to go a little faster. just a few of my thoughts. And your sure to get alot more advise than just my ramblings here.

[Bloy2004]

Hello Baris,
Based on the return questions from HuFlungDung, I would suggest as a basic step for help here at this site is to get different angled pictures of your machine and post them here so everyone that can assist has a good visual. I think this would also generate more interest and possibly feed a broad range of ideas for your situation.
John

[h3ndrix]

Thanks for the quick replies guyz, appreciated

First thing I should mention is that my machine is in pieces right now, but I know that the metal shop in my school has the identical machine (with some taiwanese parts instead of original bridgeport stuff) up and running. I should be able to get a picture here tomorrow or the next day. This way it will be much more easier like Bloy2004 pointed out.

HuFlungDung: Thanks for the welcome
Im not totally ready to dash out the cash in one straight motion and buy everything at once, but I believe I can do it in parts and put it together in couple of months rather than weeks. So, that won't be too much of a problem. That said, I still would like to be conservative and buy equipment that is more of a "bang-for-the-buck" type deal.

The size I gave 18x6 is the table size (which is cast iron, nice fine grey iron) not the travel size. The machine is about 6 feet high, its not a tiny thing, That will become more clear with the images that I will post I guess.

When you say variable frequency AC drive, I kinda get dazzled because although I know what that stands for, I need more specific recommendations from guyz like you. For example, tell me something like "go look at the bosch blah blah AC drive and check out the yaskawa blah blah drive"...cause I really don't know what I should be shopping for, thx

BIG AL: Thank you for the warm welcome I understand where you are coming from with that example, but here is the situation: I can't really sell this machine, I was given this machine to work on by my school and to make it functional. So, basically they dumped it on me to fix it up and do whatever I want with it as long as it stays in the school. The school already has 4 full-size bridgeports that are functional and they seldom get used, but I do not really want to touch them because of in-school department politics. This machine has never been used, it is in parts because it was never put together when it was donated to the school from god knows who. So, my idea is to retro it into a CNC and use it to make stuff and teach ppl how to make stuff with it, maybe even teach a class on it That's where I am coming from.

Thx to all and I will be coming back with the pictures real soon

Baris

[HuFlungDung]

Baris,

Well, we've done our duty and at least warned you of the limitations.

Re: AC Var frequency drives: Baldor would be one choice. Note: if you will be running this machine from a single phase power source, you can pick an oversize drive (by hp rating), and get three phase out of it. I am assuming the machine would be equipped with 3 phase electrics. At any rate, you must use a 3 phase motor with a variable frequency drive.

Baldor makes both Vector and Vectorless drives. What this amounts to is the method of providing motor feedback: Vector is likely out of your budget, because it requires a spindle encoder for feedback. This style of drive gives much better torque and accurate, consistent speed.

The other type, the Vectorless drive, uses some kind of internal logic to estimate the speed and load, and tries to maintain it. Low speed torque is not good on these drives. Likely they are intended for applications like HVAC where the maximum range of motor speed would be within 50% of rated motor rpm. I've used both types on mills, and the only place where I've had trouble is tapping with a Vectorless drive. The results of the spindle speed command is a crude guess at best, and this makes it difficult to guess the feedrate for threading. Plus, the torque is simply missing for low rpms.

You simply need to make the choice about which type of drive you intend to use, and tell the salesman about your motor hp and description of your input power source (single or 3 phase).

[Al_The_Man]

Baris & Hu, The other point to make on the subject of VFD is that if you have a 4 pole ac motor (1740 rpm) you can usually run it up to the speed or a little higher of a 2 pole motor i.e. 3420 rpm.
A lot of VFD salesmen will tell you you should buy a VFD rated motor due to the higher winding insulation etc. But I have not experienced a problem using regular motors, as far as top speed is concerned, the test to do is to set the VFD to 120hz max and with the motor disconnected to whatever you are driving, gradually increase the speed above its rated speed and check for high vibration which indicates an out of balance condition. If everything is smooth you should be OK. I would not suggest going much higher than the rated rpm with a 2 pole motor as you may get the armature fly apart on 120 Hz.
Hu, I believe you are referring to sinusoidal commutated AC servo's driven by motion cards such as Galil, which require to two axis assigned to one motor/drive. But there is an alternative which is to use DC brushless which has a couple of up sides and that is that there are no brushes and the top motor rpm is usually around double the DC brush type. Practically all DC brushless motors have a built in encoder alongside the commutation tracks. So with things like planetary gearboxes (cheap on ebay), a high reduction can be used resulting much smaller motors and good motor-to-load inertia which is normally kept to less than 10:1.
The down side is with very low reduction ratio's they are not that smooth at low rpm.
Al

[balsaman]

Many times the special motors will also let you run very slowly without blowing up. IME this is a bigger issue than overspeeding. I would go with a regular motor and monitor it. Usually it's fine.

Eric

[h3ndrix]

Hey guyz, here are the pics, the machine in these pics is real similar to what I will be working on real soon, but my machine has quil feed and slightly bigger statue.





I am also confused about the automatic tool changing and what kind of collet system I should be using, anyone have info on this that can help me, thx

[BIG AL]

Qute, is this one from the 1930's? I would love to own a mill like that, just like it sits. the table is in really nice shape for a machine that old.

[HuFlungDung]

What size and type of taper does that spindle have? Can you remove the chuck and post a picture of it?

I would really have to say that equipping that machine with an automatic tool changer could be bass ackwards. This would cause the entire machine to become an accessory for the tool changer , the proverbial fifty dollar saddle on a dead horse!

Seriously, tool changers take up valuable working space, no matter what size machine they are on. For that one, maybe you could rig up a rotary axis under the turret ram to swivel the whole head around to a tool carousel on the side or the back. Turn it into a robot!

[h3ndrix]

BIG AL, I do not know the exact date of manufacturing, but I think I can check that.

HuFlungDung: I agree completely, thats why my priority is to hook up the 3 axis drive first and then add components like auto tool changing and automatic tool height sensor later, but I still ask for guidance so I can plan ahead and modify the machine accordingly.

Because my machine has quil feed unlike this machine, I am kinda confused as to where the Z axis motor should be mounted: on the quil or the table bed. I would like some advice on that.

I forgot to check the collet type, but I am not sure if my machine and this one use the same collet, it looks like it, but not sure. This particular machine is missing all of the collets that belong to it, except one. The machine I have has some of the collets but I would have to check what they are.

BTW, I have been looking at these;

http://cgi.ebay.com/ws/eBayISAPI.dll...category=11806

is this the right item to control the spindle motor, or am I way off?

thx guyz