Harrison L5 Metalworking Lathe (1950) Teardown & Overhaul


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On the subject of cleaning. One of the most useful accessories for a metalworking lathe is a quick change toolpost. With this, tools are clamped into blocks, height adjusted to put the tip on the centre line and then locked off. A part turn of one bolt allows the block to be removed and a different one dropped into place. This is a great time saver as most turning requires a few different tools to be swapped in an out.

The block or QCTP drops on over the post on the top slide where it can be rotated to bring different tools to bear or angled if required.

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A sleeve is often needed to match the post of your lathe to whatever quick chnage or other toolholder you choose.

My L5 came with a popular style of QCTP. A copy of the UK designed Dickson T2, but no holders to fit. It was very gummed up and took most of 5 hours to clean.
There is a lesson in this. The Dickson type block can be disassembled for cleaning in literally seconds with no tools. Simply push in the locking plungers against their springs and the locking cam pulls straight out. If you neglect the cleaning discipline, swarf builds up behind the locking plungers (or top hats) making it near impossible to push them in far enough to pull out the cam pin. Swarf bound up in dried oil and lousy maintenance is why it took 5 hours to clean something that should have taken 2 minutes.
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Although a copy of the Dickson design, my block is labelled "Rapid Benrath"
There were two Italian companies, maybe three, who made quality copies of the Dickson back in the day under the name of Rapid, or similar. You can still buy Rapid toolposts and holders from Italy and I believe the quality is good.

Rapid Benrath however gives me almost nothing. There was a UK importer with the Benrath name back in the 1950's and Benrath is a place in Germany where machine tooling was made. There's likely a connection.
My toolpost is very nice quality. Hardened, ground. Just 2" tall, compared to a Dickson T2 which I think is 2.5" but otherwise dimensions are as close as I can tell and Dickson toolholders drop straight in.

Disckson T2 is a middling size, strictly too tall for my lathe which will only swing 9" work. The upshot is that I cannot use any larger than 16mm shank tools and still get the point low enough to line up with the centreline of the spindle.
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A smaller T1 toolpost would be better suited to the L5. I borrowed a T1 Tall to see how it sat on the lathe. Perfectly good, but even with a T1, the toolholders hang over the end of the top slide.
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It looked such a fragile little thing compared to the T2 that I decided to stick with the excellent Rapid Benrath block even though it's farr too big and several weeks on, I was able to buy some genuine Dickson toolholders to fit it.

Original toolholders are a bit like investing. They cost a mint but tend not to lose value. Good Dickson ones are much more expensive than Chinese or Indian copies. I stumbled onto a set of 5 toolholders on ebay, never unpacked since they were made in the 1970's. They were made by Dickson, boxed up and sent to Harrison who sold them on, probably with a new lathe. They still had the anti rust wax on them. Opening the box which looks like it dates from the 50's never mind 70's , I could imagine what an archaeologist feels like :)

I measured the blocks for reference. Factory new vintage original are pretty scarce, so I photographed everything with zero wear and tear
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Don't think you will have any issues with the overhang on your toolpost, and the holders were quite a find. I have an oversized piston type on mine, purely because the machine came with loads of 7/8 tooling which is too big for the holders on the "correct" size post. It does overhang, but so solid I've never had any problem with it.


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S2/T2 (designation depends on brand) are far too big for the L5, nice fit for the L5A/L6 and 140 but you want an S1/T1 for the L5. Otherwise as you've found you just can't get the centre height low enough. The S1/T1 are designed with 19mm x13mm tooling which is exactly the same as the S2/T2 anyway.

Overhang isn't really an issue, you're going to have that on pretty much any QCTP.
With a proper pin spanner my clutch disassembled easily.

Here are the parts

The outer one of the two "halo" or DC1 friction discs gave me measurements (4" 101.6mm outside, 2" 50.8mm inside) and at 3.7mm thick is clearly worn compared to other owners who have been measuring theirs at 3/16" appx 4.8mm



Here's the side of the drive pulley and the 1/4" brass pegs that should drive another friction disc but have been machined down so the outer friction disc can bear directly on the metal.
This is a bodge because one of the original three friction discs wore out and they couldn't replace it.


The cross pin in the shaft moves left<>right with the operation of the clutch lever to push the outer clutch pad and it's backing plate away from the drive pulley.

Measuring the cross pin in the engaged and disengaged positions, it moves only 3.4 mm



A small steel washer with clear wear marks acts as a shim to position the outer clutch plate at an appropriate position when disengaged. It slips onto the shaft, against the cross pin and the outer clutch plate + backing disc slide upto it and are pressed there by the big spring.

In my case, this shim washer is 1.67 mm thick, bearing in mind I'm missing an entire 4.8mm thick clutch plate !

When the clutch lever is moved to drive, there is 3.4mm of movement in the cross pin and the clutch plates have to achieve full pressure contact within that distance.

The drive pulley has a taper roller bearing so this this is easy to pull off once the belts are removed. The pulley will go on the mill and the brass plugs be drilled out and replaced with new ones that stand about 3mm proud of the surface.

I'll then make some new halo discs once my pad material arrives and will have to re shim the assembly so that the renovated 3 pad clutch is able to open and close correctly.
First a thank you to Fergie. He kindly sent me a new speed chart / gear selector label for the L5 that reflects the increased speeds available with a non original motor. V smart and I'll proudly add it to mine once I have some fresh perspex and a backing plate to do it justice 👍

Next comes a big step on the renovation. My clutch material landed today. Applications of this modern friction material do include machine tool clutches, and it was precision ground to thickness for me based on feedback from other L5 lathe owners.

This is what it looks like ....

There is a strong stink of phenolic which is a good thing as I'm sure that's also a major component of the original halo discs.
It will take a few days to fit it in but I'm really interested to make up the discs and associated parts to try it out.
Long overdue but machine time had to borrowed and other jobs get in the way.
Template made up for the inside and outside diameters and the holes for the driving pegs



Friction material has been routed into plates, Horrid job !

Brass pins turned up and fitted,
The original pins were 1/4" diameter and a slightly loose fit. I made the replacements v slightly bigger and chose a length to give me 3.5mm proud to drive the disc which is 5.5mm thick.



Of course once you start to drive the pegs in, you find that the original holes are tapered and uneven, so precise measurements end up being tweaked in situ with the dremel !

This is the inside. I decided to leave the original phenolic halo disc here as
a) it isn't too worn
b) my new clutch plates are an unknown, so until I know more I'll avoid the risk that they might abrade the cast iron of the pulley more than the original plates.

The new discs fit nicely on the outboard side


The L5 now looks more like it should.

Since the two new outboard clutch plates are much thicker than the single worn original disc, the washer that sits on the cross pin is much too small. I've reassembled without, meaning the clutch lever doesn't work, but I can start and stop the lathe motor so the lathe will work and I can use it to turn up a replacement spacer washer which will be about 8mm thick.
Different design to the 140 clutch. Probably the pins have worn and the matching holes in the plates are oval.
If you have the type with six pins its common for the plates to wear notches in the pins. This causes the rattling and so makes the operation of yhe clutch sticky. If you are lucky then you can take the holes in the plates out slightly oversize to get them round, and fit suitable oversize pins. Not a particularly difficult job.
So many people put so much effort and time into restoring machines which would be best left.
Harrison and Colchester ( and a few others ) are worth every hour of work.
I had an L5 but it ran a little slow for me. I fully restored it about 10 years ago.
Now I have a Colchester Student Square Head - which I also restored - both have advantages over the other.
Congratulations, you have done a fine job.
I have a late Harrison 140 (metric) came out of the college where i worked for a while. Unlike most it still has its original manual & factory test chart plus a large amount of tooling. Lovely lathe to use & still as accurate as the day it was made.
Re toolposts my Harrison has one of the rotating indexing toolposts mounted, I have not seen another one so fitted so its may have been an optional extra. A swift back & forth movement of the top handle spins the toolpost 90degrees & locks it down again. So you can set it up for a job as a 4 tool capstan & is really quick to use. Mine was a box of bits when i got it as it had broken, fixing it & setting it up was a royal pain!
That sounds like an excellent toolpost. I have used one like that sometime back in my youth so I recognise your description.
I very much like the excellent Parat (Germany) quick change system that 600 group still offer as an option on their lathes. That has an integral locking lever (quite long) on top of the block with detents at 90 degrees but not the super fast auto indexing just from using the locking lever.

Still torn between my Harrison L5 and the Colchester Student - square head.
I couldn't keep both even though I fully restored the Harrison. It ran a little slow for some of the work I wanted to do - but it was a beautiful machine.
Having had a Colchester Bantam, and now a Student 1800 - I am still " torn"
It is so great that some very special people appreciate Harrison engineering and are helping to preserve their engineering excellence.
This is a great post, and really stands for what this site is supposed to promote.
Sideways - you should stand proud of, not only your achievement, and skill - but you choice a beautiful piece of engineering to restore.
And like an old car, there is always something new to work on :)
I can see me adding to this thread time and again as years go by !

There is no doubt that the Colchester Students are a far more sophisticated lathe with the benefit of hardened ways and much more, but I have a friend who managed to buy an almost unused Harrison 11" and in that nearly new condition they are a smooth, quiet and quite powerful small lathe.
And like an old car, there is always something new to work on :)
I can see me adding to this thread time and again as years go by !

There is no doubt that the Colchester Students are a far more sophisticated lathe with the benefit of hardened ways and much more, but I have a friend who managed to buy an almost unused Harrison 11" and in that nearly new condition they are a smooth, quiet and quite powerful small lathe.
I've never run a Student lathe. I could have bought many and the newer M series Harrison's as well but I love the clutch on the older Harrison's. Being able to sneak up close to the chuck jaws without pre judging when to disengage the feed, not being frightened of overrunning and colliding with the chuck jaws. My opinion only but I love the clutch it's like driving a car in stop start busy traffic. Check out some of my work on YT EYUP TONY I'm only an amateur but this feature is really beneficial when learning how to run a metalwork engineering lathe.
compliment for good work! I am restoring my grandfather's old l5 lathe. unfortunately the charts for changing the pitch of the metric and whitworth threads have been canceled. could someone send me an image or a manual page where I can see the different combinations of gears? thank you
My metric chart is worn out too but it is in the manual which can be found online and downloaded FOC.

Here's a scan of the imperial and Whitworth charts.


It isn't difficult to make a spreadsheet that shows all of the change wheel combinations and the feeds and threads that they make.
There are many more ways of combining change wheels than in these standard tables.