Thanks, so there is no difference in current draw if a 3ph motor is running on 3ph or on converted single to 3ph via a vfd (apart from the internal vfd usage) ??
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Thanks, so there is no difference in current draw if a 3ph motor is running on 3ph or on converted single to 3ph via a vfd (apart from the internal vfd usage) ??
Just got a reply from my supplier, in a flat-out full-load situation, the draw on the supply will be 22.5A, above that then the inverter will start reducing speed, prolonged load will trigger a shutdown.
Question is - can a small Bridgeport actually USE 3Hp/15Nm at the spindle :)
That depends on where you're measuring the current, which is why you use the KW rating to work it out.Quote:
Originally Posted by Davek0974
I was going to mention just how much the VFD will allow the motor to run above it's rated power, but I see the supplier has answered that.
Although the motor is rated at 3HP/2.2Kw, that'll be at 50Hz speed rating. When you increase speed, you can think of AC induction motors just like a steppers, in that the key factor is how much current you're putting through the windings.
So double the speed, and you can double the power, which means your 2.2kw motor running at double the 50Hz speed could produce well over 4kw.
Off course as with steppers, you need to monitor temperature, and if running at low speed a lot, you may want to consider getting a forced induction kit for the motor (aka a cooling fan that bolts onto the motor) to avoid overheating the motor.
Thanks, i had it running tonight and it draws about 3A idling.
It has a PTC built in for the temperature and that will be wired in to the VFD in due course.
Looks like i have exactly 10:1 speed ratio from 10 to 100Hz which figures, works out nicely at 300 to 3000rpm.
Stopping in 1s is pretty impressive :)
Now to configure it for cnc control...
Will the momentum of the spindle and cutting tool not damage the belt if you continually stop quickly?Quote:
Originally Posted by Davek0974
Probably not the belt but it will shag the keys and keyways up in the back gear unit.
That and the varispeed sheaves which Dave has got rid of are the weak points in these heads.
No idea why anyone wants to stop that quickly anyway, it's not like a Bridgy is a production machine and saving 1 second on 15 auto toolchangers is a game changer
Yes, its hard on the head and it sounds hard on the head, thats my reason to slow it down a bit, there really is no point in sudden stop on a machine with splined quill and all that other crap up top ;)
The chances are that most of the dog-clutch wear was caused by my using it for running a 12-1/2" dia fly-cutter when cutting the saddles on the traction engine cylinder block and chimney base and perch-bracket - these would take many hours of running in back-gear and really worked the old girl. It was a job for a HBM really but when you have a Bridgeport you can do pretty much anything;)
The tiny splines and those dodgy dogs are certainly a weak spot, rarely fail but wear a lot and get very vocal, you can wreck the dogs by being a jack-the-lad and changing gear while the spindle is running, would never do this but have seen the carnage caused.
The belt i have fitted is good for something like 60-70hp so i doubt that will be bothered ;)
Been messing with rigid tapping - looks like it will be good:)
Also have live spindle speed on screen by changing the DRO from 202 to 39
Have set the vfd display to show load in kW - i could mount the display remotely or fit an analogue 0-10v meter which would show 0-150% of motor power. So far i have not made it go over 600W :)
Getting there.
Fun little Sunday morning project to aid my education in Fusion, CAM etc...
Support bracket for the high speed spindle when not in use :)
Junk bits of 15mm ally plate, rigid tapping, chamfers the works ;)
Attachment 19463
Attachment 19462
Future thoughts...
Machine is working very nicely so far. However I still have big doubts about the weakest link in the system - the Z-axis drive, its a pretty tortured setup, the connection to the quill is poor being just one bolt, the block face is only around 15-20mm square where it bolts on, there is around 75mm from the quill to the ball-screw so there is a massive twisting moment acting on the joint and the ball-nut.
There is already movement visible between the nut and the quill - you can see the connecting arm twisting when nudging the ball-screw pulley by hand so it would be pretty rough under drilling or plunge-milling forces. I can see a very short life for the ball-nut as they don't like twisting moments, axial or radial but not twisting.
It was assembled with loctite but with only the one bolt I doubt that would do much.
I have a feeling it would have been better to go with the drive idea in the pictures below, the quill rack is designed to take all the Bridgeport can do, there is not much backlash and what there is could be helped with a gas-spring maybe to keep it under positive pressure.
No idea what the pinion gearing ratio is but likely something like 3" per turn so would use a bigger reduction from motor.
Just looking ahead, but as i said, I can see issues here already and thats only after a few jobs....
Attachment 19486
Attachment 19487
Dave, look for the head off a BOSS 1 to 5 but you will need the ram as well as that head is a really solid fixed head that doesn't suffer from the nodding and endless tramming that the rubber Bridgeports suffer from.
Best thing with the BOSS head is the quill is the ball screw. The balls run round the outside of the massive quill so no bolts and no trying to tip to one side.
This is one reason I posted in post #3 to look for one and not do the conversion. Don't know what the conversion has cost but got to be loads more than upgrading an existing CNC.
Hell for a grand you could have had my 10 x 54 CNC Beaver in fully working order with 4th axis, 30 odd BT40 toolholders. 6:1 speed increaser and 8" vise if you were prepared to strip it to get it out.
The head from a BOSS would be nice but not seen anything from a BOSS listed for some time now, seem to be getting very rare.
Whereabouts are you BTW ? ;)
Yes i decided way back in the beginning to go ahead because I just cant fit anything bigger than a manual BP in the shop - no head room at all. Yes it cost a lot but I have had a blast doing the conversion, learnt a lot and still have a usable machine to play with.
The Quill connection I was not happy with from the outset - its a terrible weak spot, unless a much taller connection is made to the quill to spread the load - this then reduces Z travel respectively and I'm already seeing the bad side of poor Z travel and i only lost 5mm from standard!
I think there is some redemption in using the quill rack/pinion - it's the strongest method and as long as backlash is dealt with should be just as accurate.
Quote:
Originally Posted by Davek0974
Hi Dave,
This company has managed to fit the Z drive on the other side of the shaft and have more mounting plate bolts. The z drive is almost at the end of the video.
https://www.youtube.com/watch?v=6b0Jf-xzE0s
Thanks, yes I've watched that vid a few times ;) Its the same deal really, same shaft in head just different connection styles. Maybe the way to go.
The size and weight is why bigger machines are only a grand. For most garage workshops the 875Kg series 1 manual Bridgeport is probably bigger and heavier than they had wanted to go but they are cheap, lots of info, plenty of spares and the conversions are well documented.Quote:
Originally Posted by John S
Great if you can find one i guess :)
Thinking out loud...
With the drive to the quill rack, probably from the left side as done in the FlashCut kits etc, without measuring i think the quill pinion does 2 full turns for full travel so about 75mm/turn, with a 4:1 or maybe 5:1 belt reduction from servo to pinion shaft, would that give enough resolution/torque - the motor would only ever do 8 or 10 full revs??
I could probably make a bracket pair which could take one or two layshafts which could offer much higher reduction ratios.
Maybe even look into worm-gear reduction.
Just working things through...
Is there much backlash on the quill gear, i have seen a drive with a ballscrew on the front of the head.
No the quill pinion is pretty firm. Yes the screw on the front is a popular method because its the only place you can get a direct connection to the quill, trouble is its an awkward connection and i'm not happy with it yet.
Finally scraped up the cash for proper thrust bearings on the X & Y axes. Got Nachi P4 matched pairs from BearingBoys Ltd
I fitted them in DB or back-to-back style, seemed the best option here - the preload is taken up by the screw nut rather than the bearing retainer.
What a difference, smooth as silk now and no shims needed :)
Will measure backlash again to see what change it has made.
Dave, have you get any pictures of the existing setup/quill?
A few pics here...
Attachment 19490Attachment 19491Attachment 19489
The weak spot is the joint between the coupler and the quill - there is a flat recess milled on the quill about 15mm dia and i picked up on that face, it really needs more contact above and below the bolt but then you lose more z axis travel and thats bad enough already.
Its the little round boss on the right of this part...
Attachment 19492
How much Z travel would you lose, if you bridged between the current single bolt mounting, and the end of the quill (where you currently clamp on the second spindle bracket)?
.
If you were to bridge between the two, then you should get a stable piece to then mount the ball nut to.
I can see where you are coming from here, nice idea and would certain strengthen it 100%.
But as always there is a negative - it would stop me being able to fit the aux spindle.
By having the support on the end of the quill when running as a normal bridgeport, I would maybe lose 12-15mm of travel - not too bad. But to allow me space to fit the aux spindle as well below it, the support would have to be that much further up the quill, probably losing 40mm + of travel permanently - this would cause big issues when doing normal work.
But it is a nice idea though.
Rework the Aux spindle mount, so it attaches to the new adapter?
It's possible, the main draw-back is the loss of the already limited Z travel when doing normal work - this is a big pain in the wotsit really. Not so bad on the aux spindle as all the tools are so short as is the work itself.
To make it really work would need the knee setting up as an axis and diverting all tool-length measurements to that axis - this would mean cutting is done on the quill but the loss of travel would not be as serious.
I still feel the quill rack is a way forwards, won't cost much to try at least.
Maybe a totally stupid off at a tangent idea but could you build an assembly just for that purpose on the other end of the ram, then you could leave it setup and it would not get in the way of normal milling. Sorry, did not see earlier post.
Which purpose?
If you mean the auxiliary spindle - this is only mounted when i need it, that was the whole idea really - its a normal Bridgeport plus a high-speed engraving/milling machine when needed.
The back of the ram was looked at, but adding a full Z-axis of any rigidity would be a considerable task, the aux idea is less cost and means not swivelling the ram.
I have even seen a full linear rail Z axis mounted between the ram and the existing mill head - the user locked the quill up all the time and moved the whole head up and down. Sounds nice but to get it working would not be cheap or easy i feel.
Quill drive idea mk1,
gives a 16:1 reduction, takes up little space, mounts to existing threaded holes on left side of head.
Attachment 19498
Should allow both belts to be tightened by having only one moving shaft.
Anyone have a video or link to some pics of a powered knee mill conversion?
Seems a lot of people rate it but i cant find any proof! http://machsupport.com/forum/Smileys/default/smiley.gif
Still deciding which way to go.
What about backlash in the rack and pinion ? ?Quote:
Originally Posted by Davek0974
That is my main issue, its fairly tight but will have some BL in it. I was possibly thinking of some method of applying constant up force to the quill from where the existing drive is now, not sure how or what though.Quote:
Originally Posted by John S
Its a pain really - so close but not there yet, i know for a fact that the existing drive will fail and probably quite soon so doing nothing is not an option.
I have been looking at powering the knee and locking the quill but i still have my doubts about the knee ways and short life etc, plus the cost - ball-screw, bigger servo and drive, hardware, probably going to run about £600 just to do the knee, more if it needs a brake to stop it falling when turned off.
Then there is the speed issue - from what i have read, the knee is slow, peck drilling is going to suck as well as a few other jobs too - V-engraving would take ages due to the thousands of up/down moves used.
Just a bit baffled as to what to do really
This seems a pretty neat way of backlash control - its a brake cable from a motorbike, one end is mounted to quill and the other has an air cylinder on it with variable pressure. The guy that fitted it also fitted a very tidy gear reduction system in the aluminium casing on the left, 15:1 ratio, double reduction. He reports zero backlash and full quill travel :)
Attachment 19502
I think on cost alone, it has to be worth a try to run via the quill rack, powering the knee at any speed is going to take some time to save up for.
Measuring on the adaptor from the Z screw to the quill, near the quill, I have well over 0.5mm of flex - thats a bad figure as it equates to backlash at the tool, so doing nothing here is not an option.
So, looking at the options -
Power the quill via the left side of the pinion shaft, this has slop in it so will need some clever way of preloading the quill upwards - this could lead to rapid rack/pinion wear as it will need enough preload to counter cutting forces from pulling the tool downwards.
Power the knee - this is an option but will cost a lot as it needs a ball-screw, servo, drive plus full tear-down to fit it all.
Alter what i have got - looking at the picture below, is there any harm in removing the web of metal circled?? It would mean i can get a bigger connecting arm in there with much more contact below the bolt to resist the down-forces, without losing any Z travel.
Attachment 19503
After some thought I reckon the easiest option based on what i have going already is to modify the quill housing and build a better connector arm - this should give more rigidity and still maintain the full Z travel.
In the attached picture, on the left is the existing setup, on the right is my next version - as you can see, in the existing one a lot of twisting moment is placed on the bolt when the arm is pushed down (heavy lines).
In the new version, the twist is converted to an axial pull on the bolt and the force transferred to the quill body via the longer contact face below.
Attachment 19505
That was a long day!
Stripped the head, cut away the small web of cast at the bottom of the quill slot, altered the screw connector by welding on a 13mm thick bar underneath, the end of the bar was milled to the curvature of the quill before stripping, fitted up, refitted the Z drive and shimmed the connector, power head back on, motor back on, encoder back on, tested.
The connector now has an extra 25mm of contact below the quill bolt which is a massive improvement over the first attempt, this makes a big difference to the twisting effect on the quill bolt and is now far more rigid in the downward direction which is what matters.
Total backlash is now down from 0.6mm+ to 0.1mm and I also discovered that most of that backlash is caused by the BK screw block not clamping the screw correctly - this was always there but never spotted it before. I will strip that block and see whats wrong with it - either crap bearings or sleeves too short and the nut not reaching properly.
I don't think this one is getting any stiffer (ooh err!) :encouragement:
Attachment 19517
Attachment 19518
Attachment 19519
It's always nice when a plan comes together:toot:
Thanks, it wouldn't have worked without removing that little web of casting though:)Quote:
Originally Posted by Clive S
What can make the tool not follow the path correctly?
Did some work today and as seen here its clearly pulling away from the corners far too early - corner rounding?
Attachment 19725
Not quite so clear here...
Attachment 19724
Cutter was 2mm at 23000rpm, 1000mm/min, X&Y speed set at 3500mm/min and 350mm/s/s in motor tuning.
Your getting because of constant velocity and tight radius most likely caused by low accelleration. Try setting accelration higher and see if better.