I don’t see a problem with a well designed gap bed lathe, a gap with a removable piece of bed means the gap can be bigger without the saddle overhanging the gap when not in use. Very handy for flywheels and wheels and save having a very large lathe.

Mike

I have a Chester Craftsman gap bed lathe and have no problem with it.

I seem to remember removing the gap piece once, many moons ago to do some job.

I don't think I have ever removed it since, never had the need to, but it is useful to have and it cost nothing extra.

So, I would say, go for it, better to be looking at it than looking for it !

The Craftsman is a good all-round machine, not tool-room, but can still handle fair sized work

I think the Warco machine is very similar.

My Engineers ToolRoom BL12 – 24 is a lookalike of the Chester Craftsman (and the late Warco BH600 )

In the 16 years of ownership, have never needed to remove the gap. But have never had any concerns about rigidity when taking cuts of upto 0.150" deep, or with smaller intermittent cuts. The motor is a 1.5 hp, 3 phase , powered by a VFD.

The Craftsman is a heavy machine, weighing 390 Kg,

I have used it with a Vertical Slide, to flycut the ends of 3" x 1" steel bar, without problems.

When I had a Myford ML7, I did need to use the gap facility of from time to time, but found it not to be quite rigid enough for my needs, especially when using a Rodney milling attachment.

The BL12-24 bolts down using six 1/2" or 12mm fixings, where the ML7 uses four 5/16 or 8mm.

My lathe actually sits on six 1/2 UNF setscrews, with a nut above and below each lathe foot, which are secured to angle irons resting on the beams of ex warehouse staging, rather than the cabinet which comes with the lathe.

The ML7 was bolted to the steel bench.

Hence, I consider it to be much more rigid than the ML7.

In this case there should be no concerns over the bed flexing.

The gap is a useful feature, should you ever need to swing anything larger than 12", or 300mm.

Someone checked his BH600 before and after, having removed and refitted the gap piece. No misalignment was reported in the "refitted" condition, so the alignment seems to give no problems.

The Craftsman should be a versatile machine, given the Norton gearbox and PCF..

Howard

Often very handy on my old Super 7 – where I can swing things that wouldn't fit otherwise, including a large 4-jaw (too big really but used often) as well as a big faceplate (also very useful). There are limits to this (as Dave observes) and care is required when setting up to make sure you don't clip the bed.

With regards to rigidity, I've never noticed a problem with that but I'm a "hobbyist" and don't knowingly abuse my machines – most of which are nearly as old as me and need to be treated gently (like me).

So I'd vote in favour of the extra flexibility a 'gap' provides as I haven't noticed any downsides…

Regards,

IanT

And if a gap bed lathe is chosen, ensure it has a low enough speed. A geared head might be better due to the torque amplification, but I have no experience of variable speed drives (apart from my c300 minilathe).

Bill

Gaps never hindered the popularity of Myford S7 lathes…

Neil

What would you do when a job comes along that would be too big for a non gap machine? Some posters have said they use the gap very rarely but unless you have access to a club workshop with larger machines or a friends machine then you may have to pay a machine shop to do the job, they can be very helpful and do it for a donation to the tea swindle or eye wateringly expensive. I don’t believe the gap has a real downside so why not have one? It could be very useful.

Mike

I see the gap as an asset even if used once in a blue moon.

I would not worry about the bed's rigidity on a properly-made lathe, as the bed will have been designed to cope with the gap both with and without the filler. If removing and refitting the filler compromises the bed's overall accuracy, as Andrew has observed, that seems to me a poorly-designed machine!

If the removed filler is held by screws tapped vertically in the bed (as on my Harrison L5), plug the holes with short screws, as swarf likes burrows.

Mick B1:

You remind me I should examine my L5's gap-filler L5. It does put a tiny step in the V-way, but that might not be the filler's fault. It is made to be easy to remove and replace, being located by two stubby dowels and held by two set-screws, albeit a bit awkward to reach. The mating faces still show their planing-marks, and no damage, so I think bed wear close to the chuck the more likely reason for the step.

The faceplate on that machine will just clear the V on the filler, I think.

It's an interesting question that I think could only be answered by testing.

Old-iron lathes date to a time when stress and strain calculations weren't well understood and the number crunching was too costly to do manually. Lathe designs are based on experience, basically if something broke or bent, more metal was poured next time. Gradually the necessary dimensions became well-known, mostly over-engineered. There's a serious disadvantage: the extra metal adds size and weight and it all costs money owners might have better uses for. The disadvantage becomes painful when competitors use modern techniques to make improved lathes for less money.

Chinese lathes are based on more modern European ideas. Designed to be made at minimum cost , functional without unnecessary material or curlicues. The bed is analysed as a braced girder using methods and understanding not available to the old-iron engineers. No gap in the bed considerably simplifies the analysis.

The build quality of Chinese lathes may not be impressive but the design certainly makes more effective use of materials. They are cheaper to make and there's a good chance they are stronger too. Looking at CNC and manufacturing equipment, it's apparent they are from the same school as Chinese lathes, and they don't resemble traditional old-iron much.

Trouble is no-one knows. Old-iron looks good but the design is probably sub-par. Modern machines look flimsy but were designed 40 years later by advanced engineers. Be interesting to compare the strength of an ML7 bed & headstock with that of a Chinese lathe of the same weight. I don't think it's ever been done.

Possibly lathes are a special case, but old cars, aircraft, ships, locomotives, radios, televisions and most other manufactured goods rarely compare well with their modern equivalents. For example, a WW2 Spitfire IX Fighter had a top speed of 595km/h and a ceiling of 11,125m. A Boeing 737 cruises at 836km/h with a ceiling of 12,500 metres. An ordinary commercial airliner couldn't be intercepted by one of the best fighters of its day. The comparison is even more stark when Boeing's performance is compared with a Sopwith Camel!

Dave

Having read Gray’s comment, it made me think that the initial bed would need to be ‘aged” to ensure no movement after finish machining. That would mean less or no ”twist’ in the bed to be adjusted away by the levelling process.

Nowadays, nothing is aged like castings used to be, and if the bed requires ‘twist’ removal, to cut parallel, the refitting of a gap piece might be more prone to inaccuracy or difficulty.

The origin of Gray’s machine might even be a factor – china or Taiwan? We (all) know that while chinese machines are somewhat better these days, than previously, they are likely using less metal than older products of similar capacity.