Lathe speed

[sturina]

Hi. Just looking at whether it is possible to slow the RPM of my Carbatec MC900 down slower than 500 rpm? Have a few bits of wood that aren't balanced enough to take that speed without it feeling like I've hit the self destruct button. Eventually I'll upgrade to a better lathe but that is a few years off. Currently running on single phase power but in October the new shed will be finished with three phase.

thanks

[Skew ChiDAMN!!]

Not without fairly major mods.

One of mine has had a lay shaft added but that meant relocating the motor - it now lives on top of the headstock and drives a cluster pulley - and making brackets to support the lay shaft. Which is positioned where the motor used to be... and takes another cluster pulley and the part of the reeve drive that used to live on the motor. So I have both pulley selection to choose a 'range' & the reeves drive for tweaking the speed while I'm working.

I like it. :)

Other options are to replace the motor with an after-market EVS system. But of you want to go that way, it's better to put the $$$ towards a better lathe in the first place, y'know?

[Paul39]

Sturina,

Assuming you have this set up:

http://machines4u.cachefly.net/machinery/52/10052/900mm-Wood-Lathe_67703.jpg

Put a shelf across the bottom and put a couple of 5 gallon buckets of dirt, gravel, etc. on it.

If the out of balance is caused by a section sticking out, cut that off with whatever saw you have.

Put the piece on the lathe and run the tail stock up tight, turn over a few times by hand and tighten the tail stock a bit more.

Stand to the side and turn on the lathe at 500 rpm with your finger over the stop button. If the lathe is not walking around the shed or doesn't spit out the piece, give it a slow count of 15. If how the lathe is behaving is within your level of comfort, proceed, turn off the out of balance first.

Wear your face shield.

[Drillit]

Agree with the Skew - it isnt worth it on that type of lathe. Suggest you "borrow" someone's for those
out of balance pieces or join a local group that may give you access to one that you can turn at less than 500.
Isnt there a Shellharbour woodies group? I have just retro fitted an EVS system to my Durden
and fortunately my electrial engineer mate did the lion's share of the work at cost. Otherwise prohibitive. Drillit.

[chuck1]

I power plane the weighted side off or readjust the centre then bring the lathe up to speed and rough it to true then bump the speed up! as I was taught, have the lathe going as fast as possible with vibration AT A SAFE WORKING LEVEL!

[Pat]

You could wander up here and get them round on the Yellow Peril. 50 rpm vs 500 rpm.

[sturina]

Thanks Pat, the problem is I see the yellow beast and want my own! Will probably take you up on the offer when I get around to it.

[BobL]

. . . . Currently running on single phase power but in October the new shed will be finished with three phase.

thanks

Even without 3 phase you could install a 3 phase motor and a VSD both of which you can also transfer to your next lathe
You might have to look around a bit but a used 1.5 kW or smaller 240V 3 phase motor (it should be wireable in delta mode) should be possible for $35
A new 1.5kW 240V 3 Phase VSD is ~$125 delivered.
If you want remote control of the speed a potentiometer and a switch will be needed (<$10).
I also recommend a big safety switch but you may be able to use the one already on your late
So all up cost will be ~$170

The most tricky part with these (I have no done three) always seems to be converting the pulley from the existing motor to the new one.
You could get lucky and find the old pulley fits the new motor but chances are it won't so some metal work will be needed.
If the pulley hole is too small then you could drill it out but then you won't be able to put it back on your old motor if you want to sell it when you upgrade
If the pulley hole is too big then some sort of bush might fix it - better get it right or it can wobble like crazy.
Also the way the pulley is fixed to the shaft varies - some use keyways, others use woodruff kets some use grub screws, some use taper fits, and some use a simple flattened shaft , Often a completely new pulley that suits the shaft is the best way to go and keep the old one for when you sell the lathe.

I tried to get a new pulley for my Woodfast but I gave up waiting for Woodfast to get back to me so I made my own.
The next head ache is will the new motor fit in the space where the old one is - this is not always the case.

Sometimes you get lucky and it just a simple swap - other times it gets as complicated as Skewies suggestion so it may not be worth doing.

Posts 320 to 319 in this (http://www.woodworkforums.com/f245/bobls-shed-fit-134670/index21.html) thread show how I did mine, new motor new pulley, new motor location.
I really like the final result but it did take a fair bit of effort.

[hughie]

On my old MC1100 which should be very similar I mounted the motor on top. A 3ph 1hp, the only down side was that 1hp lost a lot of torque with the VSD. So I added a set of 4 set pulleys to try and add some mechanical advantage. It did, but not really enough so go for a bigger motor ie 3hp, they are not physically much bigger and should fit ok.

[BobL]

On my old MC1100 which should be very similar I mounted the motor on top. A 3ph 1hp, the only down side was that 1hp lost a lot of torque with the VSD.

Is the motor a 240V 3 phase delta wound? I found a difference at low RPM between this configuration and anything else.
My highly scientific in-house test for torque is what frequencies in the highest and lowest gear can I stall the spindle by hand since this ends up providing a rough guide for my working RPM range.

On my Woodfast mini I can stall the 1/2HP single phase motor at the spindle (or more specifically using the chrome knob on the left hand side of the headstock- whatever that is called) in the highest gear (and of course this is 50Hz).
Using a 1HP 240V 3 phase I can just stall it at ~30 Hz in the highest gear and on the lowest gear I can stall it around 15Hz.
The stall frequencies for the other 4 gears using the 3Phase motor are somewhere in between 15 and 30 Hz.
Using the VSD the highest gear is redundant as I can reach 3200 rpm at just 70 Hz in the second highest gear and the motor is good for another 20 or so Hz after that - whether the Woodfast is, especially for an extended period is another question.
The lowest gear is also (theoretically) redundant because the second lowest gear can reach 300 rpm at 25 Hz - ie well above my in-house stall test frequency.
Of course even lower RPMs are always desirable so the low gear still gets used occasionally because it can get down to 144 rpm at 20 Hz - ie above the stall frequency. Whether 20Hz is good for the motor is another question but I operated at 25Hz (180 RPM) for an extended period without problems.

For most of the stuff I do I tend to use 3rd gear in the 400 to 1600 rpm range and change only when I really need to. For small stuff 5th gear is good for 900 to 3600 rpm.