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Davidhcnc
01-21-2009, 02:07 PM
I've taken delivery of a nice Colchester Student Mk 2. The plan is to refit it with a new motor and VFD with a 220v single phase supply.

Driving the spindle directly off some belts.

Here is the problem. The gearbox is a thing of beauty, a work of art. Everything is in spotless condition and it seems such a waste to make it all redundant.



So what should I do? Which is better and for why?

1 drive the gearbox with my motor at a constant speed and use the gearsticks.

2 Make the gears redundant, drive the spindle direclty and fit a knob to the VFD for speed control.


And a pic of the leftovers. Glad to see that lot go!

http://homepage.ntlworld.com/david.hull35/Other%20Images/spaghetti.jpg

John Stevenson
01-21-2009, 02:45 PM
Both, driving the spindle directly with the VFD driven motor will not give you enough torque at low revs in fact you will struggle to go as low as the gearbox.

Just replace the motor if you are doing and fit the VFD.
Then selct a usefull speed say around 600 and use the VFD to vary this ratio to get the best spped for the job.

This way you get the best of both worlds.

.

Daminer
01-21-2009, 07:04 PM
Sir John, as usual, has it right.....

Not having 3PH power when my bridgeport arrived, I bought a VFD to convert my 220 1PH to 3PH.....I still have the original belt change option, so my range of spindle speed is continuous from ~30 RPM on up to as fast as I dare run the spindle.....Keep all the parts and goodies except for the original on/off switch.....VFD's don't like their power switched off under load.....

Jim

Davidhcnc
01-22-2009, 05:29 PM
Thanks for the recomendations.

That is all three of us leaning the same way:) . I'll report the progress.

Silverback
01-23-2009, 12:01 AM
Is that necessary true with newer VFD's that do torque management?

I was thinking that I was going to be in trouble with my VFD and 1hp/pancake motor bridgeport. Initially I tried different things in different belt positions, thought that I would try things like setting the belt in the middle and try running the motor at 2x it's rated speed... but found that if I jacked up the torque management I have yet to run into a situation where I didn't have enough torque for what I was doing... I've had the belt set in the maximum speed setting just controlling speed using the VFD ever since I've tried it, and I've been a lot of larger cutters/mills lately. I figure if I run out of torque I'll probably try the back gear first, but haven't had a reason to yet.

Davidhcnc
03-06-2009, 05:40 PM
All running now, complete with regenerative braking. I am very pleased, bordering on ecstatic, with the soft start and braking... and this forum proved to be an invaluable help.


some pics, old lathes always look like scrap:o

http://homepage.ntlworld.com/david.hull35/Other%20Images/Student%20MK2.jpg

http://homepage.ntlworld.com/david.hull35/Other%20Images/ABB.jpg