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1671

General Mach Discussion / Re: Bridgeport Knee Mill Conversion?

« on: May 23, 2016, 04:09:45 PM »

Ok, I'm holding the alterations to the spindle drive for the moment, will keep the vari-speed and modify later - better things to focus the cash on.

Drives and motors...

These are the drives... http://www.aliexpress.com/store/product/New-Servo-motor-and-driver-set-2-4N-M-0-75KW-3000RPM-90ST-AC-Servo-Motor/314742_760999511.html

I have one on the bench for testing with the CSMIO and an old Mach3 setup.

Do servo drives need any setting up ? I have set the motor model in the drive but the rest of the million settings? Never used a servo before

Anyone know these specific drives?

1672

General Mach Discussion / Re: Bridgeport Knee Mill Conversion?

« on: May 22, 2016, 10:17:25 AM »

Thanks for the parts offer Hood, appreciated, they do look like the right bits.

I will price it up correctly tomorrow with timing pulleys, what size belt - 25mm x 5 or 8 pitch?

1673

General Mach Discussion / Re: Bridgeport Knee Mill Conversion?

« on: May 22, 2016, 08:08:35 AM »

Thanks, that helped a lot

Had another play before I started tearing her down for a full strip/repaint/rebuild

If I kept the existing power setup, there is a possible working option where I can set the head at two positions - 700 and 1500 and then using the existing VFD I at a reasonable 25Hz to 75Hz range I can get full speed variation from 40rpm in back-gear to 3000rpm in high - having the vari-speed in there to multiply the torque where needed allows for power lost in running at lower Hz it seems it would all work.

HOWEVER, it's not as much fun as having just one high range and one low range with the luxury of full G-Code control - the main question is - is it worth the £400 approx. that it will cost to do the conversion???

The input shaft on the head is a nice 1.375" so no issue getting a taper-lock pulley on there, the motors seem to be 19mm so again no issue, 1:1 poly-v pulleys and belt would do it along with a new motor mount plate.

As it is it's going to need new bushes for the sheaves and a new main belt at least, not finished stripping yet.

SO, what would you guys do - rip it out and splash the cash on luxury OR repair and refit??

1674

General Mach Discussion / Re: Bridgeport Knee Mill Conversion?

« on: May 22, 2016, 06:01:59 AM »

Thanks Hood, the analogies do actually help

One thing I had omitted in my last post was that I still have the back-gear for low-speed high-torque as before so maybe I really don't need such a large servo, just one that will cover down to say 500rpm and then drop into back-gear for the heavy stuff.

Or is it better to just stop polishing the turd and use the vari-speed head as a step-pulley with the additional range variation by VFD??

This is a tougher decision than fitting the damn ball-screws!

I guess the servo spindle is always a future-fit option if i leave room in the cabinet etc.

Or i could fit a roof extension to the shop and get a proper machine which probably would cost less

1675

General Mach Discussion / Re: Bridgeport Knee Mill Conversion?

« on: May 22, 2016, 03:37:24 AM »

Thanks Hood, that calculator rammed it home, seems with a 5Nm motor it would only be able to power-tap to M8 in steel, in reality thats not too bad as I probably would not expect it to do anymore than that on the original head, I always hand-tapped the big stuff.

Now if you go direct drive, you only ever have 5Nm available at the spindle.

Got it.

You will only get full power at full rated speed. Half the speed, you only get half the power, but still 5Nm. Quarter the rated speed, quarter the power but still 5Nm.

This is where my brain fogs-over again - does the lower power matter when cutting or does it just mean less electricity is used to do the work?

If my calculator says i need 4Nm to do a task at 100rpm and the motor is rated 6Nm at 3000rpm - it will do the task easily yes?

This is why most VMCs have such high power spindles. If they didn't, they simply wouldn't have enough torque for tapping, or large cutters/drills

That bit makes sense now, thanks.

Moving on, it would seem if i want to keep all my (theoretical) power, I would need a 3.8kw / 15Nm servo - this is possible BUT I would not have the power to reliably run it along with the table servos etc at full whack the spindle would need 14A alone - back to square one but lessons learnt and no money spent, thanks guys.

So it seems my choices are to use the original vari-speed head and fix the worn out bushes, or try and find a step pulley head which so far has been unsuccessful.

With a step pulley, Mach would know what pulley it was in from the last run and the VFD could give a useable speed range from G-code, my little macro tweak from earlier would tell me what pulley to switch to depending on code.

OR

Use the (repaired) vari-speed head as a step pulley - mark the speed dial 1 - 2 - 3 and instead of changing pulleys, just twiddle the knob to that setting and again use the VFD - this sounds like a reasonable idea to me??

What you reckon....

1676

General Mach Discussion / Re: Bridgeport Knee Mill Conversion?

« on: May 21, 2016, 05:24:40 PM »

Will check spreadsheet tomorrow, thanks

But isn't torque what i need here?

Surely it does not matter if it takes 1kw to create 5Nm or 3kw - the torque is what does the cutting and kw are what is required to create that torque???

1677

General Mach Discussion / Re: Bridgeport Knee Mill Conversion?

« on: May 21, 2016, 02:02:59 PM »

I was comparing kW and Nm from AC servo to AC motor.

I thought 6Nm was 6Nm regardless but the servo would do 6Nm at 100rpm and the same at 3000rpm whereas the AC motor would ONLY be 6Nm at 1450 or whatever it was rated at - am i wrong? Obviously not grasped the whole power - torque thingy yet;)

Most of my stuff is done without back gear, only really used it when running the big fly-cutter but don't use it now as not building steam engines anymore.

I tried one of my normal jobs with the mechanical control up high and the motor down low - pretty much the worst case scenario and it worked fine so I should guess that a 1.8kw servo would be better as no de-rating and less transmission losses.

1678

General Mach Discussion / Re: Bridgeport Knee Mill Conversion?

« on: May 21, 2016, 12:19:42 PM »

Something like this...

http://www.aliexpress.com/store/product/New-5N-M-1-5KW-3000RPM-110ST-AC-Servo-Motor-110ST-M05030-Matched-Servo-Driver/314742_760988112.html

1679

General Mach Discussion / Re: Bridgeport Knee Mill Conversion?

« on: May 21, 2016, 12:11:13 PM »

It shows about 6Nm from the servo and listings show about 5.5Nm from a standard AC motor on a VFD of similar power so I am guessing a 1.8kw AC servo will be a decent replacement and also mean NO back-gear etc - full power across the board

1680

General Mach Discussion / Re: Bridgeport Knee Mill Conversion?

« on: May 21, 2016, 11:06:42 AM »

After messing with the speed control and vfd settings today , I have a sort-of workable solution but there are drawbacks - the head has some issues with worn bushes, the speed range is a bit limited, power will be affected. I also only have the smaller 1.5Hp 1440rpm motor which is odd as I thought I had the 2Hp model, oh well.

So, improvements... Is a servo motor torque really linear from zero to rated speed?? I.e. will a 1.5kw AC servo really give me 1.5kw or 2Hp at 100rpm AND at 3000rpm or have i read it wrong??

Would I be better off just fitting a 1.8kw AC servo motor for the drive and connecting at 1:1 ratio??

If it was correct then I would have full power from 1 to 3000rpm at the spindle - sounds ideal.

Would this play well with my upcoming CSMIO/A conversion - would Mach give speed control and correct rpm readout??