Worth it?

Hi All

could somebody please give a `compare and contrast`' of flat bed vs. prismatic lathe beds ?.

I would like to hear the experts opinions.

thanks h.f.

Prismatic may only need one adjustment to keep the saddle smooth without being too loose, flat top and sides requires two adjustments for carriage lift and carriage rotation. Don't know if this is the only advantage.

Martin C

I my view the prismatic vee guide has the advantage of being a narrow guide that is automatically self adjusting for wear.

Whereas a flat bed has a wider guide and has to have means for adjustment to the guideway.

It also suffers in that the ratio of the guide way length versus width for a flat bed cannot match the ratio of a vee guide for the same saddle width.

Alan

You also have Terex-Pegson in Coalville and Red Rhino in Grantham manufacturing plant for mining, quarrying and demolition, and Hitachi's european manufacturing centre between Durham and Sunderland.

It's a myth that the UK doesn't make things anymore, we just make very expensive niche stuff and export it, then export most of the profits too!

I have a real soft-spot for Super-7's, its the lathe I first got to use on a regular basis, I made a variety of really interesting and challenging parts with it, and they are generally a really well made machine which is a joy to use.

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But, unless both space and robustness were both at a massive premium, I wouldn't buy one new or used.

Even then a used Boxford, Smart & Brown, or South Bend would be more attractive, and you'd need to be going into the purchase knowing you were planning to really push the limits of the machine to warrant going for one of those options over a modern mini lathe.

The price premium is impossible to justify when you consider that the functionality on offer is significantly behind other manufacturers, and they're not particularly well equipped to make use of all the modern advances in tooling (although few mini lathes are either in fairness to Myford).

When I was still using the Myford regularly I had bouts running various "full-size" lathes and it was obvious that the core functionality all those lathes shared like a screw-cutting gearbox, lever controlled gears (or variable speed) and sliding/surfacing feeds all made things just so much nicer.

They may not have been as ergonomic or nicely finished as the Myford (although the Lang and DSG put them to shame), but I was rewarded with the joy of getting parts made quickly without fuss or stress, rather than the "joy" of how smoothly the compound slide ball-handle moved perfectly in my hand a zillion times as I painstakingly bored out a taper in stainless steel 0.005" at a time.

Given the choice between a Warco with power-feed and a gearbox, or a Myford without I would go for the Warco every single time.

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IMO, the best lathe purchasing strategy is to set a budget, establish what size of parts you'll be working on and then go search out the most heavily built and feature rich one that has the speed range you will want for your size of parts, and is practical for you to have in the workshop, that will fit your budget.

If you have a concrete floor and good access that's likely to be a small "full-size" lathe either in good used condition or new from the far-east, if you're more constrained for space or in a smaller workshop it's most likely to be a new mini-lathe or if you're lucky enough to run across one a nice condition Boxford or South Bend.

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For me there's a real gap in the market for Myford to undertake some meaningful product development to offer a lathe the size and quality of the Super-7, but refreshed with the features of the 254, and geared to offer speeds appropriate to modern tooling on the size of parts you'd expect to use a 3.5" centre height lathe for; that would actually differentiate them from the competition from abroad.

It's to do with wear and alignment. Trusting to memory, I think I got this summary from a book linked by Michael Gilligan a few years ago.

Alignment: when the lathe is cutting the saddle experiences down and twist forces. Flat and prismatic beds deal with down forces equally well, but the prism provides a simple effective answer to twist without gibs or other complications. Also the prism makes the saddle and tail-stock self-aligning, the latter automatically taking up the correct alignment when it's clamped down.

Wear: prismatic beds last longer. The prism provides more bearing surface compared with a flat bed, and the geometry reduces wear due to twist forces.

For hobby use I don't think bed-type makes much difference, except perhaps it's easier to regrind a worn flat bed.

Whilst the pros and cons of both types rage in amateur circles, industry seems to have abandoned flat-beds in simple form, even though they're a shade easier to make. I suspect it's because individual reports of wear and performance rely on personal experience which is far too limited to draw a sensible conclusion - the sample size is too small. On the other hand industry push machines hard in their thousands and they, and tool manufacturers, get to see the statistics.

If the average prismatic bed lasts 10,000 hours whist an average flat-bed lasts 'only' 9,500, then an individual machinist won't notice the shortfall.  So based on a tiny sample, an amateur might well prefer to die in a ditch rather than admit his trusty flat-bed is inferior! A production accountant is much more likely to spot the difference, because accountants compare cost vs value delivered by machines over a long time, and their figures show that the flat bed costs the firm money.

Whatever the advantages of a prismatic bed, I'd happily buy a flat-bed in good condition. I don't believe the difference between the two types is big enough to matter to me.

Dave

Edited By SillyOldDuffer on 28/04/2023 14:26:43

Hi, I must be one then, as I've got an "M" type one, though it's not in use at the moment.

Regards Nick.

Jelly said:

"... For me there's a real gap in the market for Myford to undertake some meaningful product development to offer a lathe the size and quality of the Super-7, but refreshed with the features of the 254, and geared to offer speeds appropriate to modern tooling on the size of parts you'd expect to use a 3.5" centre height lathe for; that would actually differentiate them from the competition from abroad. "

I could not agree more. They have the name to charge a premium price. It would be so good if they re-engineered it keeping the style but integrating (not scabbing adding on) a 3 phase motor and VFD, deleting the clutch (not needed with VFD), camloc chuck (with adaptor for the old threaded kit), primatic bed etc. Options could be DRO (again properly engineered into the design), ELS (instead of gearbox) and powered cross-slide (possibly leading to CNC).
I recon they would make money on a bit of investment and possibly set the standard for the next generation of small lathes.

Robert.

A nice idea to see an up to date Myford but I doubt that they would be able to make it at a competitive price even if they invested in up to date manufacturing methods . I purchased a new GH660 for less than 1/3 of the price of a new old style Myford . While it lacks the tactile smoothness of my old Super Seven its accuracy and precision are excellent . I can see a few major major issues , economy of scale , the trend to CNC , and the demographic of the model engineer in community .

Brian .

Hi there everyone,

Just a few points to make

A I think Circlip got it just about right ! Full marks !

B I think Chris and I have had similar experiences regarding our "cheap, crappy drills"

I bought mine in 1983 and it cost me 300, I forget was that £ or Euros , needless to say, I was laughed at for buying such a heap of crap. Perhaps they were right, I,m still using that machine and it has well paid for itself at this stage.

I t is a Nu Tool make, not Top-of-the-range perhaps, but it drills holes where I want them, so, what,s not to love ?

C Dave, I,m not sure about these big yellow bikes and the Nortons, where are they to be found ?, not around here anyway. Do they only come out at night, perhaps ? I have met many English lads touring here over the last few years and have NEVER seen them riding English bikes . When I asked why, the answer I got was, "Where are they ?". Nothing but Jap bikes or BMW,s, so there has to be a reason for it.

BTW, what bikes do the police use over your way ?

Fact is, you missed the boat !

Probably cost the thick end of a million to design and develop and the same to set up production. How many would they sell? Not a chance it would make business sense. Might have been a good idea 25 years back to develop a relationship with Sieg and badge Myford version of one of their lathes but too late now.

Edited By John Haine on 28/04/2023 17:10:13

So I had a response to this, but it goes so far off topic that I've forked it into another thread.

(The quoting function does not seem to like pasting between threads however.)

I think that's something of an over-estimate of the development costs, it's ultimately just an integration of various well established solutions to well quantified problems.

Do the initial prototyping in house on a shoestring budget, use that knowledge to do the requirements engineering for any refinements which need "discipline engineering" and let them as work packages to consulting firms on a target cost basis, and then use that to develop the manufacturing program.

From a financial perspective because it's a clearly defined project you can opt to capitalise the development costs under the SSAP 13 or IAS 38 rules as an intangible asset and then write that asset's cost down against tax across the first 15 years of the product lifecycle.

No need to tool up for in-house manufacturing, it's not going to be a volume product, so you can opt for serial production on a JIT model, with small lots sizes for the castings and the machining done externally.

If you know your subbie's capabilities you can also engage in "design for manufacturing" to minimise the setup costs and special tooling requirements.

It then becomes a problem of optimising your cashflows by minimising the "hold-up" in the system.

Ultimately not having to feed a huge production overhead will lower the cost of the product at release as you're not trying to cover financing costs or depreciating assets.

Edit: There's also novel funding streams to consider, traditionally this kind of thing would have to be debt-financed or come from shareholder capital/retained earnings.

However given that it's aimed at a hobby market and if you consider CNC integration is highly appealling to a range of hobbyists who are internet engaged a working prototype can be used to generate a social media buzz which feeds into a crowdfunding effort that effectively de-risks initial production by selling the product before you commit to the spend.

That model has worked for Wazer (desktop water jet cutters) and Markforged (sort-of-affordable metal 3D printing).

Edited By Jelly on 28/04/2023 17:59:04

The two are equal on a machine that is in well-kept or unworn condition. Where the prismatic way wins out is that it can suffer a lot of wear and still be in reasonably good alignment. Gravity does the job of keeping any looseness out of the assembly.

A flat bed way such as the Myford 7 uses will stil wear 'downwards' just like the prismatic one but any wear on the vertical shear translates directly into front/back clearance. This is why many flat bed lathes such as the 7 series and similar Atlas types tend to be loose towards the headstock and tight towards the tailstock - the tailstock end has little or no wear. This can also have an effect that doing any turning away from the chuck will give a drasticlly different cutting depth or level of finish than towards the chuck, something that the prismatic way machine will not suffer to such a great extent because again gravity is causing the saddle to sit down tight on the prisms.

You should not concentrate solely on the bedway in terms of evaluating wear for either types of lathe however. You will find that for any lathe which has significat wear on the bedway, the underside of the saddle will have suffered a much more significant amount. One of the best things you could do to a lathe which is showing signs of wear is remove the saddle, turn it over and scrape the underside ways flat then slightly hollow (less than half a thou, more like a couple of tenths). Saddles are nearly always worn more at the leading edges of travel whoich produces a boat-shaped underside prone to rocking and perfect for trapping grit which will accellerate wear further. Scraping them slightly 'hollow' will allow for oil retention under the saddle where you want it and will let them wear in before they wear out.

Edited By Pete Rimmer on 29/04/2023 12:05:21

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Possibly in 2019, when I wrote:

Recommended reading: **LINK**

https://archive.org/details/lathebeddesign00hornrich

… I’ve mentioned it before

MichaelG.