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QSIMDO
04-26-2006, 10:05 PM
Have they had any problems over the years and how might one determine their conditioin if the machine isn't powered up please?

I seem to remember something about the speed can drift but I don't recall if it was an easy fix or not.

Scishopguy
04-27-2006, 01:21 AM
I have heard that if you don't lubricate the Vari Drive unit regularly they will cause you lots of grief. Some places I worked in had them and never lubed them and didn't have any trouble. I don't know if they were just lucky or what. My BP is a J-head (belt driven) with an inverter drive. To tell the truth I like that arrangement much better than the standard Vari Drive. It has the power at low speed and the spindle stops as if it had a brake, within a couple of seconds.

Jim (KB4IVH)

Schutzhund
04-27-2006, 03:29 AM
Still shoppin huh? ;)

bpsbtoolman
04-27-2006, 06:16 PM
When I bought my Bridgeport without the variable drive a few years ago I looked for one in good condition and had a one shot lube system. I bought one and while there they sold 2 with the variable speed drive for $ 1000 more than mine. They tried running a third one and it growled loudly. I have since put a $ 200 VFD on mine and think I got a better deal having the electronic variable speed and less maintaince and $ 800 more in my pocket.
Walt

QSIMDO
04-27-2006, 06:41 PM
Still shoppin huh? ;)

Insane, isn't it!

I got MARRIED easier than buying a milling machine!

Well...the third time anyway. ;)

Giddyup!

John Stevenson
04-27-2006, 06:57 PM
Valid points about the step speed over the varispeed.
Remember when these were introduced electronic variable spped drives were large and expensive and not that reliable.

With hindsight if a lot of this era machines were redesigned today they would have less speeds and electronic variable.

I converted a mill drill some years ago from the usual three pulley 10 speed that didn't quite work to a three speed toothed belt drive with DC control [ VFD's were still too expensive then ]
In use I found that the three speeds I had designed in were too much as it spent all it's life just using two.

Currently I'm part way thru a Bridgy CNC conversion that has the Varispeed head but I'll find a nice mid point where it makes the least noise and use a VFD for most speed changes controlled by the CNC controller.

.

TECHSHOP
04-27-2006, 08:58 PM
Sir John, Earl of Sudspumpwater:

Ok I'll bite this hook,

"...I'll find a nice mid point where it makes the least noise and use a VFD for most speed changes controlled by the CNC controller."

How do you "know" what RPM the spindle is spinning at?

I understand the CNC program can "change" the VFD, but in general where/how are you going to "factor in" the "RPM correction" between the motor RPM and the spindle RPM?

I am not a CNC machinist at home, and I don't play as one at work.

JCHannum
04-27-2006, 09:57 PM
Allmost all vari-drive sheave drives share the common problem in that if they are not run through their speed range on some regular schedule, they will eventually wear themselves in at the range they are left at.

Bridgeports use plastic bushings on the moveable sheaves, and these do not require lubrication. They will wear, and wobble will develop.

Finding a quiet spot, as Sir John suggests, will delay the inevitable, but eventually, repairs will be necessary.

If the drive is allowed to operate after the plastic bushings have worn out, the shafts and pulleys will be destroyed, and expensive repairs will be needed.

When buying a vari-drive B'port or clone, run the drive through it's entire speed range a couple of times. The motor must be running to do this of course. If it is quiet at all speeds, it is probably OK. If there are problems, speed adjustment will be difficult or "notchy" or the drive will sound like a box of rocks in spots. If you can't run the motor, assume the drive is trashed.

wierdscience
04-27-2006, 11:51 PM
I generally dis-like VS heads,most I have used where noisey and some were down right obnoxious to use.
You can check the belt and pullies on some models by removing one of the vent covers on the side of the drive and trying to wiggle the movable(top)half of the spindle pulley.There shouldn't be any noticable slack in the pulley.

If there is slack in the pulley,don't pass up a good deal just for that reason.I have seen several really nice mills with noisey heads.If it's a deal,buy it,remove all the VS non-sense and replace it with a 2.5:1 micro-vee drive and a VFD.

John Stevenson
04-28-2006, 06:44 AM
Sir John, Earl of Sudspumpwater:

Ok I'll bite this hook,

"...I'll find a nice mid point where it makes the least noise and use a VFD for most speed changes controlled by the CNC controller."

How do you "know" what RPM the spindle is spinning at?

Varispeed head Bridgy's have this rotary dial on the front that displays speed, as you wind the speed up the indicator moves.
High range goes from about 400 to 3,000 max but after about 2,500 it's in the red meaning no prolonged running.
On both of mine between 1600 and 1800 sounds sweetest.
The dial reading with a double check with a tachometer is accurate enough.

I understand the CNC program can "change" the VFD, but in general where/how are you going to "factor in" the "RPM correction" between the motor RPM and the spindle RPM?

Most VFD's can be programmed to produce max and min speeds over the range so if I select say 1500 rpm as my sweet spot on the machine, and then program the VFD to go to 100 Hz max.
On 50 hz [ on UK supply here ] the machine will be running at the normal 1500 rpm and at 100 hz it will go up to 3,000 but the pulleys on the varispeed will still be set for 1500.

By getting to controller to output a 0 - 10v analog signal to the VFD it can them run from 400 to 3,000 under CNC control.

I am not a CNC machinist at home, and I don't play as one at work.

I am not a CNC machinist at home but I do play one at work, playing being the operative word ;)


[ no the message isn't to short - I have replied in quotes]

TECHSHOP
04-28-2006, 09:53 PM
John Stevenson:

This is all an edit, the dang thing launched after I typed John's name.

I couldn't think last night how to ask the question, but you explained.

What I was trying to ask, "How is the combination of a mechanical vari-speed and a VFD going to be idiot proofed"?

If you (alone) are going to use the machine, I can understand the lack of a " RPM interlock"; but the chuckle heads over here just love to push the go button and start twisting dials.

"...but the dial only shows 2450rpm..."

John Stevenson
04-29-2006, 03:54 AM
Take the speed handle off after setting the varispeed head, that should sort them ;)