.

You are right. ………….. Shocking, terrible, awful, horrendous.!!!!

That is if you are in the production of rocket guidance systems. ………. For most model engineers who are being realistic it would be a very good number.

Nick

Hi Joe and welcome.

Yes this is quite uncanny that another lathe from this establishment should surface.

Looking at the spindle limits that you are chasing is taking you into higher end toolroom standards which is where quite a few of these Holbrooks ended up. Not massive swing capabilities given the size and bulk of the machines, but within their limits were very precise and accurate in what they could consistantly produce.

Toolrooms of this era tended to use similar sized machines for the more detailed work and some of the larger DSG's for bigger capacity requirements.

It does go some way to confirming that the PO research facility did in fact have a decent budget for their equipment. Dont know the actual figures are for the weight but at a guess its got to be 1000kgs plus.

This should keep you busy for a while and will no doubt end up a real satisfying piece of kit for you. Such a lot of lathe to digest.

Edited By MalcB on 16/02/2017 07:03:19

Hi Everyone

I was very fortunate and was given a Holbrook C10 lathe which is a beast compaired to my Myford Super 7, it came from a local aerospace company, lathe being 3phase 420v having 220v domestic supply was a bit of a challenge.

Have overcome the problems see write up below picture, the same write up is on the Holbrook web site.

I was in the same situation as some owners of Holbrook C10- I do not have a 3 phase supply or 415V available to power the motor as it is for my home workshop.

Prior to my retirement, I was a maintenance technician at a nuclear power station and asked a good friend who was the chief electrical engineer what to do- his reply was “do you want an honest answer? I don’t know!”

After a long discussion we decided against having the motor rewound as motor rewind companies tend to copy the original windings and do not usually have the expertise to reengineer the motors, without cost, so this was a non-starter.

Another option was to obtain a rotary phase converter. However, there are two reasons not to go down this route. Firstly the cost (again) of the converter and secondly they are not very efficient as the motor has three different windings when changing speed and so there will be imbalance in the system. This problem also applied to a static converter as they are also poorly balanced, which affects the full power of the motor.

We therefore decided the way forward was to replace the motor and use an electronic inverter drive.

I had full confidence in this solution as the power station used electronic inverter drives in many places, being fully programmable with excellent reliability. However, this then required me to buy an inverter drive, a new motor and also an adaptor to make it fit the later.

Motor

First on the list was to look for a replacement – the original motor was 2hp but by choosing a 3hp motor and dropping down to the lower speed there is still plenty of torque available. After a long time spent time on the internet sourcing a 3 phase 220v 3hp 4 pole motor, eBay came up with a brand new Marelli motor and paid £40 which was a good start.

Inverter Drive

The next stage was to look for a AC Inverter Drive –and again after many hours spent searching on the internet and eBay, I took a trip to The Inverter Drive Supermarket Limited, which is in Chipping Campden, Gloucestershire. Once I explained my requirement, they recommended an ‘Altivar 12’ which is made by Schneider for the reasonable sum of £138.

It took an entire evening to configure the drive as the manual was a translation and is not laid out in logical technical English. There were three main changes to the configuration:

• The motor was programmed for a soft start, to change the acceleration characteristics to 3 seconds so to reduce the stress on lathe and motor when starting.
• The drive was programmed for three different frequencies to equate to the three speeds on the lathe speed change.
• The speed change contacts were wired straight to the digital input on the drive, so that the speed change works the same as the original lathe intended. I also wired the stop start reverse lever switch to the drive stop start forward reverse position.

By using an inverter drive, the speed of the lathe goes from the lowest to max 3000 rpm. This meant that with the motor running at max torque, the current would not exceed 10 amps (and therefore not tripping the house electrics!). Another advantage is there is a big gap between 3000rpm and 1492 rpm, but as the drive has a control on the front, any speed can be set manually.

Contunied on next posting

The Schlesinger test for spindle concentricity is 0.01mm or 0.0004" – which applies to both finish turning and toolroom lathes.

It just scrapes in under the wire, so I wouldn't complain too loudly!

Neil

Hello john , i would like to do the same on my c 10 as your solution solve a lot of problems ,

Do you have more info as wirerig diagram ?

Hi guys, I have a Holbrook H20 that I have to move from my dads place as he is now in care and I have the task of clearing out his workshop and yard. The machine was origanly in the toolroom of the long bridge car factory, dad has had it for about 20 years. It runs well and is in reasonable condition it has 3 chucks and a fixed steady with it. has any body any adea what its worth. I am thinking about replacing my Colchester master with it but not yet decided as space is of a premium, I haver not been able to find any for sale to give me an idea of value.

Any comments and advice would be appreciated Mike C

One point to consider. Does the Master do approximate metric threads without changing any wheels as some do? Probably that is more use to an amateur though there are other Holbrook features that might be good to have.

Possibly not, the post is nearly 5 years old and he hasn't posted for 2 1/2 years.

Edited By Bezzer on 30/11/2022 16:15:12

John

Generally when choosing a motor for VFD conversion you are better off going for a 6 pole, 900 nominal RPM, one as this gives better torque at the lower speeds. Or even 8 pole if you don't plan to go fast or your machine large. In a practical world high speed is generally associated with small jobs done with small tools so power loss at the high end is rarely an issue. Its down the bottom where you are swinging large jobs that you want full power.

These days teh price gap between new 4 pole and 6 pole motors has narrowed considerably so 6 pole is economically viable if you decide to go for a new motor.

I'd certainly never choose a 4 pole motor to replace a two speed one if using a VFD to get the required speed range.

The aforementioned Holbrooks, like many high end British machine tools of the era, used a 3 speed compound motor. Basically a two speed motor giving the low and meduim speed range with a single speed motor built on the same shaft for high speed. Wonderfully engineered but monstrously large and heavy. Rewinding costs are basically "take out a mortgage" so pretty much anything is cheaper.

Clive

I agree with Clive on 6 pole motors on VFDs.

And don't forget VFDs allow you to increase the frequency and speed not just reduce it. An "inverter" rated motor may run at several times the nominal 50 Hz speed. The limit is normally the mechanics of the bearings roator and fan. The 1/2 HP Gamak 6 pole motor I bought for the myford has a rated 50Hz speed of 910 RPM (no-load 1000) is rated to tun at up to neary 4 times its nominal frequency,195 Hz or 3500 RPM. Torque will drop off and eventually power too. Clearly however this 6 pole motor can happly run at the nominal speed of a 4 Pole, around 1450-1500 RPM so there is no loss of speed and a gain in reduced torque ripple.
Most "normal" motors are rated at 50/60 Hz so automatically can run at + 20% (~1200 RPM) within their rating and any modern 6 pole motor should handle the 75 Hz required to speed match a 4 pole motor speed.

Robert G8RPI.