I’ve seen a few possibilities for purchasing potentially very useful tooling recently but for reasons of economics and priorities I’ve not been able to take them all up. One thing I did do though was to buy a number of collets specific to the Smart and Brown lathes made by Crawford collets. They are numbered 2804 and not easy to find… my lathe was probably made somewhere in the 1950’s.
Anyway, a little advance but since I am spending so much time scraping the slideways (almost 0.010″ off the second top slideway now but a lot of alignment work to go), it’s encouraging to be able to improve the possibilities of it’s usefulness when it’s finally rebuilt.
I’ve been trying to sort a problem out with the website which means that I can’t upload photos. Hopefully I’ll get it sorted out soon but in the meantime I’ll just have to do without.
I was brought up with Smart and Brown lathes; my dad has had a Model A for around 50 years and a 1024 VSL for around 20 years. It wasn’t therefore a huge decision what I would look for when I started to put my workshop together a few years ago. The lathe I bought (unseen off ebay) was a Model M Mk2 which was a very nice 4″ swing tool-room lathe from the late 1940’s to the end of the 1950’s.
It was in a pretty poor state and I think it was a long time since it was a cossetted tool-room machine. Undoubtedly shifted to some unswept corner of the maintenance shop to turn spacers on. I made several other posts about the assessment and strip-down but the most significant matter was the slide-way wear. There was 0.010″ over the length which is quite a lot!
I had wondered about grinding and looked into the costs, but it didn’t seem to be a perfect solution. True it would be a lot quicker than scraping but I could see the possibility of knock-on problems. I wanted to keep the original position of the head, which provided the correct clearance arrangements with the feed drive gears at the rear. One grinder I spoke to suggested that they had ‘shaved’ gears to get over this problem. It just didn’t seem like the right answer. Whatever I did I was going to have to re-establish the original height of the saddle once the work had been completed to ensure that the half nuts still centered on the lead-screw, the feed shaft within the apron, and the main traverse gears had the correct clearance with the rack.
So, to cut a long story short, I decided to scrape the slide-ways using a hardened rail sitting on part of the original head location face and the end of the tail-stock slide as a guide. With a clock stand moving along that whilst clocking the front way, I was not only able to see the initial wear but it gave me a basis from which I could start the work, so that I could start to scrape the worst of it out and establish a reasonable state of parallelism before moving to the next stage.
Months of intermittent scraping have followed. A bit here, a bit there. A few weeks ago, I had arrived at the point of being within 0.001″ over the slide-way according to the clock and so I went to blueing the rail and using it directly on the slide-way to establish a better flatness. Still further hours but at last the front slide is now ‘good enough’ to sit the rail on to start to do the opposite way. There’s a lot of work to come and this is why I haven’t tried to finish the front slide perfectly. When the rear slide is done, then I’ll use a precision level on my datum faces (under the head) to set the bed horizontal and then use some ground V blocks which span the two slide-ways to establish not only the angular alignment to the head face but to ensure, using blue under the v blocks, that the alignment is achieved with faces on the same plane, not just parallel. It’s almost inevitable that after I’ve scraped the rear way, that the two faces will be parallel but not on the same plane. The process to align will mean that at least one of the ways will have to be completely re-scraped again.
Anyway, months of intermittent work ahead but the first stage is complete.
I’ve stripped the saddle off and have had the chance to see the good and the not so good.
The mechanism which shifts the main power travel feed to either the cross slide or the main saddle seems to be in really good condition and is a joy to behold. In fact I think most things seem to be fine although I plan to diss-assemble, clean and lubricate everything even if there’s no actual damage.
Both the top slide operating screws and nuts are very worn though as well as a few other bits and pieces.
Fortunately, I’ve made contact with somebody who has most of the bits I need, which is great.
The saddle is worn though and I imagine the top slides too, so there needs to be some precise measurements of wear and then some decisions made about refinishing work.
This is a fairly big deal, but it can be sorted out.
I think when I’ve got the bits to repair it sorted out, then I’ll put a cover over her and leave her until the end of the season and just do some research on bed repair in the meantime. I don’t want to hurry this as it’s likely that I’ll have this lathe for a very long time. That’s my plan at least. Now I need to get back to the bikes. Really my priority has to be my Super squirrel engine, otherwise I’ll have nothing to ride this year. The Silk Scott racer’s frame is high on the agenda too.
Last week I picked up some 5mm MS plate to make some engine plates out of for the Norton model 18 and I have a plan for the Triumph engine…
Well, It has not been sitting in the corner of someones de-humidified workshop for 60 years with a dustcover on.
The cross slide and compound slide both had a bucketful of backlash, so I took them off last night to check out the leadscrews and nuts. I’ve stripped the cross slide completely and the leadscrew was pretty badly worn, with some damage which actually chased out the brass nut. Amazingly I just found one on ebay(!) and snapped it up. I haven’t stripped the compound slide yet but I’ll probably do it tonight.
The next thing to do is to take the saddle off and look at the underneath. Part of me really wants to strip the thing completely and have the bed re-ground, and scrape the saddle.. but that’s a reasonable amount of work.
Also I’ve found that the brass helical back gear drive from the main spindle is badly worn, but it might be ok. Wonder what the spares situation would be for that?
The more I look at this lathe, the more I like it. The details are superb.
A few extra bits of bracing on Sunday morning and a trip to Screwfix to buy a chain block and Sunday afternoon I lifted the lathe off the trailer! I did have to let the tyres down to get enough clearance to pull the trailer out but actually it all went perfectly. I borrowed some 1/2″ OD stainless rods that we’d had in an auction lot through work and dropped it onto those.
Once down I screwed an anchorage into the floor of the workshop and used the chain block again to drag it in, moving the rollers as necessary. It took a while but it’s now in position. Very satisfying.
I spent an hour or so last night cleaning, lubricating and inspecting it and can see there’s a bit of work necessary. There’s definitely wear on the tenons and the bed but I’m sure that I’ll be able to get it good enough for general work.
The main point of this weekend was to go up to Worcester to pick up the lathe that I bought from a fuzzy picture on ebay. It’s a Smart and Brown Model M Mk2 toolmakers lathe from the 1950s and is soon to be manhandled (400kg?) into my little workshop. I’m going to need to get a phase converter as it’s three phase but I am really pleased. I think you can get much more for your money if you buy three phase. This cost me less than £200 (although a phase converter will probably cost as much). It’s a proper little tool-room lathe and it’s got collets and a three jaw chuck. I’ll just have to start picking bits of tooling up here and there and hope the thing works when it’s all in.
Also, I went up to see my dad to pick up my Scott racer’s cylinder block which he’s had to inspect. I thought I’d bring a few more Triumph bits down too but what I didn’t figure on bringing down was another bike; A Silk Scott.
Ten years ago or more, he bought this Silk Scott from Roy Lambert (not the late John Underhill as I had originally thought. Apparently John had owned it and sold it on previously).
The Silk Scott had been George Silk’s first incarnation of a Scott based motorcycle and had applied 1970’s two stroke tuning theory to the ports and the pipe of an otherwise pretty standard Scott engine. The cranks had been improved and the crank chamber sealing was done with a conventional rubber seal instead of the spring loaded metal to metal gland seal that the original Scott design used. He also created a better oil pump using, I believe, a modified best and lloyd pump design from the vintage period. He had a frame made for it out of Reynolds 531 by Bob Stevenson at Spondon which was basically a copy of the frames Spondon made for the small Yamaha racing bikes.
Here’s a picture of the Silk Scott prototype.
The road bike’s rolling chassis was finished with Spondon 38mm forks, a single sided twin leading shoe front drum and a mechanical disk on the rear. Aluminium rims and a light alloy tank certainly kept the weight down here at least.
Basically it’s a complete racing chassis, built to house an engine which had changed very little from 1928.
George undoubtedly released more power from the engine, but at a cost. Scotts are not a ‘Schnuerle loop scavenge‘ engine, they are a crossflow engine with the exhaust port and transfer ports opposite each other in the cylinder and using a deflector on top of the piston to send the transferred inlet gas into the top of the combustion chamber, thus scavenging the cylinder.
The Scott is notable as a two stroke for having a great amount of torque at low revs, probably because the design does not depend so much on gas velocity to achieve a decent scavenge. Loop scavenge engines, with the transfer ports adjacent to the exhaust port can be susceptible to losing charge directly through the exhaust if the revs aren’t high enough. There are other factors at play, but the torque of the deflector piston Scott really surprises people used to later loop scavenge designs.
If however, as is often done when tuning a loop scavenge engine for greater power, you raise the exhaust port and the transfer and extend the inlet duration, you tend to lose the bottom end. Maybe that’s ok when you’re able to get a engine producing a significant amount of power a bit higher up the rev range, but Scotts aren’t so keen to rev with that massive hump on top of the piston and also have completely unbalanced cranks, relying only on flywheel damping.
Plus the fact that the standard (long stroke) Scott only ever had a three speed box, and the Silk Scott only a four speed box doesn’t enable you to cover a narrower powerband and you start to see where modifications to the original design require an overall consideration of how these things link with each other.
Our plan is to build the Silk up with one of my dads racing engines, which only slight differences to the original port timings but has much better gas flow, and work to make a decent set of exhaust pipes to exploit the low rev range available.
We originally planned to make the Silk Scott a test bed for the engines we built for people so we modified the frame with the intention of doing a detachable front cradle to aid engine swapping.
It’s going to be tight to get it done this year, but I’m going to get on with it and see how it goes.
The virtual oily corkboard of a vintage motorcycle racing family