I've just repaired one of these if it's still relevant!

John

I'm currently adapting the lathe to run from a variable-speed brushless spindle motor. This runs to a maximum of 10,000 rpm and the stated torque is 0.5Nm.

I have a couple of choices of drive belts; so called "Y" section cogged V-belt (6mm top width) or one of the smaller HTD toothed belts.

I'm concious that the lathe is relatively delicate, and that the O-ring drive probably slips under excess load and protects against potential damage? Does this suggest that a small v-belt would be preferable to a toothed belt? Are the latter noisy?

I'd also be interested to hear from any Unimat owners as to the principle speed range(s) which cover a majority of work, I can probably use a 2.5 to 1 reduction which would then replicate the name-plate maximum speed of 4,000 rpm, but the lathe currently seems to run faster by some margin under no load.

Will 1Nm+ torque be sufficient for most turning work?

Many thanks

John

The "pull" of the magnet is actually calculated from the incremental change in stored energy in the air gap as the pole piece (or whatever) is moved towards or away from the magnet. Many non-linearities will render precise calculations of absolute magnetic flux somewhat futile, but the general principle is there, and tells is that the pole piece should have a high saturation figure and should be adequately thick to handle the total flux generated by the magnet (if the objective is to obtain the maximum force). You can observe this phenomena using a magnetic dial-guage holder, first on thick cast iron, and then on a thin plate, where the force is much reduced. The surface roughness / flatness also comes into play when considering the maximum "pul-off" force, as any residual air gap when the parts are touching will impact on the "closed loop" flux density.

BTW, 1.3mm is very close to 16 AWG !

Personally I would forget the filter and just run it at the lower end of the name-plate rating, i.e. 230V delta. With all that mass it will take a long while to get hot!

John

Andrew (T): could you give details of the motor (namplate) and how you intend to operate it? Old (quality) motors are generally quite robust and have some design margins to cope with over-voltage etc.

The principle issues to look out for when operating from a VFD are

- over-heating if continuously run well under normal speed ( fan cooled)

- increased iron losses due to the high frequency switching , so again a thermal issue.

I would say you'll be fine, but if you have some power in reserve and wish to take a conservative approach, set the VFD parameters to output full voltage at, say 55Hz: this will then run the motor 10% under-voltage at 50Hz and reduce the iron losses.

John

Edited By John Sykes 1 on 17/10/2021 10:20:06

Brian:

I think Tom has this sorted . We've established that it's a pole-change two-speed motor, which required a slightly specialised switch to be interposed between the DOL starter & the motor.

John

You already have the DOL.

The switch you need is here:

Ebay item no 202953411153 @ £36 delivered.

John

Having re-examined the Lovato switch data which I mentioned above, it appears that many of the change-over contacts are internally linked, so can't be used as such.

However, on the Lovato website there is a comprehensive list of their motor switches, and there is a three-postion pole-changing switch which does the job: it's schematic 13 and the switch reference is

GX1613U

There's one on ebay at the moment. You could tackle this with a cheaper / simpler switch but you'd then need additional contactors and both the cost & size would escalate.

I've scannned 40 pages of the Brook Motors book which include multiple motor configurations and the schematics of the old Brook control gear. There's a lot more data on their range of motors from the 1960's back, if anyone needs such info.

https://www.dropbox.com/s/z2g2r5ar6ojpkhr/Brook%20Motors%20data_1.pdf?dl=0

John

I have the Broook Motors book on Induction Motors (my father worked for them his entire career).

Pg 199 show precisely the wiring which Tom posted above. It is possible to wire up a star-delta switch to perform the two speed switching. Everything else can be left alone: the switch is interposed between the output of the existing contactor and the new two-speed motor. I can post a schematic if you're interested.

There's a supplier in Italy selling a star-delta rotary switch at a reasonable price

https://www.stockelettrico.com/products/14929-lovato-gx2012u-rotary-cam-switche-3p/

John

Edited By John Sykes 1 on 14/09/2020 17:07:27

Edited By John Sykes 1 on 14/09/2020 17:10:49

Edited By John Sykes 1 on 14/09/2020 17:11:09

I hope this link works:

https://www.dropbox.com/sh/s3gj40jxskg5b4k/AACEh_0P4ZUXnDG7tMUBuRwea?dl=0

John

Edited By John Sykes 1 on 14/09/2020 15:52:35

Not sure if this information is already on this site, but my Google serach yesterday failed to find anything! How do I upload a pdf?

John