Bridgeport Manual to CNC conversion...

[Davek0974]

I'm going to have a go at dismantling i think, try that first.

A 2.0kw AC servo would be best but a toss-up between money and easy-fit;)

[Davek0974]

Well, I spent a good few hours trying to dismantle this motor while being very careful not to risk damage, I could not even get the drive disc off the long shaft, seized well on. There is also a pressed-on fan at the top to shift which would likely bend/break so i carefully replaced what i had done and left it.

So my choice is now to build the cabinet and wire for the VFD / motor OR throw one of these in...

http://www.aliexpress.com/store/prod...037588952.html

I have asked the guy for a 2kw or 2.2kw 3000rpm unit but not had a reply yet, seems the bigger servos don't have the speed needed.

Fitting would be easy, but the only benefit i would really see is the easy and accurate speed control - I don't need/want rigid tapping although i think it would be useful for smaller taps maybe - what is needed to gain rigid tapping?? Is it just a setup option or do i need more CSMIO modules??

[Davek0974]

Pulleys/belt - 44t HTD8 x 30mm should handle it ok.

[m_c]

You'd need an ENC module if you wanted to do rigid tapping.

The motor will most likely run for a long time before the bearings get bad enough to cause issues. If you could get some fresh grease into them, it would most likely make them last even longer and quieten them down.

[Davek0974]

I guess if i do fit the servo, adding the enc module is a no-brainer really, daft not to fit it.

The bearings are sealed and hidden completely in this motor, i could likely get some WD40 in there but no grease. My main issues with fitting it are that it will fail some time, probably when i need it, and will then need my cabinet pulled apart to change from VFD to serve drive etc.

It sort of becomes a "might as well fix it now" option i think, then i can benefit immediately from the improved speed control etc. If i sell my tapping heads they would likely fetch enough to pay for the servo drive anyway :)

[Davek0974]

Decided to exercise my minimal CAD/CAM knowledge and plunge into a slab of 15mm ally for the Y axis motor plate.



Took 44 minutes on the mini-mill, used a single 5mm tool for the whole job and pocketed all the waste out ;)

Fitted perfectly...



Seemed a better place than hanging down below I think.

[Davek0974]

Decision is now leaning towards throwing the old motor back on!
Why?
One reason was that i don't have any idea if a 1.8kw servo will be a good replacement and 1.8kw seems to be the only (affordable) size that runs to 3000rpm, also, fitting an encoder for the rigid tapping module would be a total ball-ache on a Bridgeport - there is no clear access to the spindle shaft and I wrongly thought it would use the motor encoder signals which it does not.

So, back to plan 1 until the bearings fail 100% is to use the standard motor with my VFD and use the variable mechanical speed to give me two electrically variable speed ranges that overlap.

[Davek0974]

Hi all,

been a while since this thread

For those who don't know, my Bridgeport was rebuilt with servos and larger motor, plus i added an auxiliary high speed spindle for aluminium work. The job in hand is shown in the pictures below, 5mm Aluminium, lots of holes and intricate features. I use 2mm single-flute and 5mm single-flute carbide tools for these.

Previously, I had already built a custom mini-mill to make these (and learn CNC) and still have this (its currently up for sale but no takers yet).

My reason for adding the aux spindle to the Bridgeport was two-fold - one, to save space and two, to make more use of the very expensive Bridgeport conversion which would otherwise only see intermittent use.

Now, when doing these on the Bridgeport, I am seeing bad vibration or chatter on the tool, it appears to be vertical oscillation but tonight also suffered bad enough radial oscillation to break a 5mm tool ! When it goes into oscillation it makes you jump as its very noisy and you instantly know it will end badly either in poor finish or broken tooling. Tonight I was testing tool sent from my supplier as a "Better" option this was a two-flute carbide, probably the reason for the breakage as two-flute tools need a more rigid setup.

So, something is not happy - my reservation is the spindle mount (shown below) - its canted out over to one side and although it's clamped to the quill and into an R8 collet in the main spindle, it must be allowing deflection from the cutting forces.

Ok, so I have a bad situation, is there a way forward here?

Obviously I can take the dust-sheets off the mini-mill and carry on but I just don't have the space long-term and wanted to make more use of the Bridgeport as mentioned. I really want a one-size fits all solution here.

If I run the small tooling on the BP main spindle at 3000rpm (top whack) the run time per part-set will go from about 30minutes to several hours probably - feed rates go from 900mm/min to 25mm/min so i don't think thats an option - it needs more RPM's.

What can be done here guys???

Spindle-speeders?? I have seen these but they have mixed reviews and i doubt they would like a 5mm tool much as mostly used for engraving etc.

One idea I quite like is to spin the ram on the BP around and build a custom Z-axis completely, and mount it where the BP slotting head normally sits. This could be built as heavily as desired with linear guides and a servo or stepper etc.

[m_c]

The first thing that springs to mind, is how much play is in the quill?

By bolting onto the quill the way you have, any play in the quill will be greatly magnified at the second spindle, so it's probably not taken much extra wear to go from tolerable to a problem.

Creating a new Z-axis assembly sounds like the best long term solution.

[Davek0974]

Yes, I was working through this on the drive to work this morning ;)

There will be play, must be or it would seize, plus being umpty years old i guess there will be a measurable amount.

The setup is perfect on the 2mm tools or engraving etc so it seems somewhere between 2mm and 5mm tooling is a point where cutter force and reaction come into play and bite me in the arse.

I am leaning towards a fully custom Z axis now, this brings about its own set of issues of course -

Will have to move machine away from rear wall,
..Can't move machine away from rear wall as the head hits the roof truss,
....Will have to radically modify roof truss to make clearance,
The list goes on - sometimes i hate my garage shop.

Next is - steel or aluminium build??

I am visioning it as being just a larger version of the Z axis on my mini-mill so two flat plates with rails and a screw sandwiched between, servo motor to drive and a toothed belt?

It does not need massive rails as the biggest tool is likely to be 5-6mm max so probably the same 20mm HiWin and a 1605 screw, maybe use stuff with a pre-load this time??

The hard part is working out the connection to the rear of the ram and where to put strengthening trusses/plates etc - the rear of a BP ram is a spigot maybe 50mm tall, 110mm wide and 100mm deep with a 20mm hole central - that is all i have to mount off of.

So, something like 25mm tooling plate all round or go steel and weld etc where possible.??