Member postings for Shaun Belcher

Hi Shaun,

Part of the fun is learning the ropes!

An ML7 in good condition is a decent machine, but - like all machines - has to be used within it's limitations. Not serious in practice but the lathe was designed 80 years ago towards the end of an era when HSS tools dominated.

Lathes made before about 1900 were designed to cut with Carbon Steel tools. As Carbon Steels soften at about 200°C, early lathes are spindly affairs that cut rather slowly. No point in putting fast powerful motors on them because their bearings can't take the speed, and their frames bend. But, used slowly they produce accurate work.

Circa 1900, HSS hit the streets. HSS cuts without softening up to about 500°C, and can be worked 5 times faster than Carbon Steel, so 20th Century Lathes designed for HSS are much stiffer, heavier and powerful. During the 1930's it was found that carbides outperform HSS, and today's industrial machines are monsters, removing metal up to 30 times faster than HSS, and able to cut very hard materials. An ML7 isn't in this class, nor does it need to be! It's a precision machine, think scalpel rather than axe, used to make accurate parts rather than hack metal at maximum speed. Power - ¼HP is a bit low, ⅓HP reasonable, ½HP plenty and ¾HP over the top. Substitute patience and skill for brute force!

HSS can be sharpened on an ordinary bench-grinder. Mostly these are sold with grey wheels, coarse on one side, fine on the other, which is fine. Being a clumsy oaf, I'm not good at it, but grinding HSS just needs practice. Carbide inserts are an alternative; you can get HSS inserts, but the sharp carbide intended for non-ferrous metals works well on steel at ML7 speeds. They're available in bewildering variety, but the types sold by hobby suppliers are a good place to start. Inserts remove the need to sharpen, and I value their easy convenience. (About 80%)

Generally easier to get good finish with HSS because it can be sharpened. Carbide likes to cut blunt, and it produces an excellent finish when used to specification. But this is too much for most hobby machines, making it necessary to experiment sometimes.

Experts prefer to buy blanks and particular tools rather than sets, but I found a set to be a good way to start. With hindsight, a tangential toolholder is attractive, and Eccentric's Diamond Type comes with a jig to simplify sharpening even more.

Perhaps the best book on lathes available is Sparey's The Amateur's Lathe. Written in the 1950s, when the ML7 was new, the only disadvantage is it doesn't cover developments like carbide inserts. Highly recommended!

As you suggest, not all QTCP are well-made. My main objection though is value for money. First there's the tool-post itself, then the holders. I'd need 8 or 9 at about £20 each. Say £200, which is a lot of money compared with a handful of shims, especially as I don't change tools much. I've got better things to spend the money on, but others find them indispensable. Not necessary for a beginner, maybe later.

Dave

Not sure of which model ML7 you have , but assume it is the same as the super 7. This is the rating plate of my Super 7 B.

Steve.

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Don’t over-do that speed increase ... The ML7 bearings may not last long

MichaelG.

I remember being confused by lathe tool-sizes too! I assumed that lathes took a particular 'correct' size, but it's rarely so.

All that matters is that the tool can be gripped by the holder with the cutting point at centre height. Oversized tool-shanks are a difficult problem because they have to be reduced to fit. Not worth the bother in my opinion!

Some tool-posts are adjustable. The American's once favoured a sort of tilting boat affair; never used one myself but they're criticised for being fiddly to adjust and not very rigid.

These days, the 4-way tool-post is common. It's a simple flat platform, pretty solid, and tool height is adjusted by shimming under the the tool, as shown in Shaun's photo:

Same idea except I have a collection of shims up to 4mm thick made in a milling machine, short lengths of 1mm steel strip (as used on big packages), and various thicknesses of aluminium strip. For thin shims, cut-up Aluminium Drink cans. I mostly use carbide inserts, and keep a set of pre-sized shims ready to go with each tool; this makes a 4-way tool post almost as fast as a QC type. As always much depends on how you work; frequent fast tool-changing in an HSS shop shouts 'QCTP'. But many HSS users do almost everything with one tool - a tangential tool-holder - see Eccentric's ad on this site. I've not bothered with a QTCP because ready to go shimmed tools are fast enough for me and because the tool does not need to be removed from the lathe for sharpening - changing inserts doesn't mess with the height setting.

The photo shows a second beginner booby trap. Those painted carbide tools! I had nothing but trouble with mine, and it turned out to be because they're not necessarily sharp out of the box. Being carbide, they can't be sharpened on an ordinary grinding wheel, and sharpening skills are needed. Another problem is carbide performs best on fast powerful machines, which the ML7 isn't! So, quite easy for a beginner to get poor results and assume his lathe is at fault, when it's just the cutter. Problem multiplied if a beginner also starts by cutting random scrap metal from his junk box because a metal-lathe will cut metal, right? No! Many metals don't machine well, and quite few are vile. DIY store metal is generally poor. Best to start with metals bought because their specification mentions free-cutting or machinability. EN1A-Pb steel, most Brasses, or an appropriate Aluminium Alloy.

Dave

I was looking at the ones RGDtools sell, they seem to be reasonably priced and good quality, seem lots f myford users buy theirs.

Posted by Clive Brown 1 on 11/05/2020 08:50:51:

1/4" HSS is plenty for a Myford, cheaper and easier to grind than 3/8". Picture shows an arrangement that I copied from a Myford owner and used for years on my Boxford. Cheap as chips. With a selection of home-made holders, tool changing takes seconds. The packer for the Boxford is a piece of 1/4" plate, about 2.5" sq. with a hole drilled for the tool-clamp stud, but might not be needed for the Myford. I later replaced the clamping nut with a permamently mounted handle.

Edited By Clive Brown 1 on 11/05/2020 08:55:18

They used 3/8" tooling on them. Solid HSS on packing. It was crude.

If you get a QC toolpost it will be to take 8 or 10mm tooling. Others on here can share their QC experiences. I only use the old 4 way.

Standard Myford 4 way toolpost takes 3/8" square tooling. That's about 9.5mm. You can use 8mm quite successfully by packing it up with suitable flat steel packing strips cut from sheet or flat bar etc. If you use modern 10mm carbide insert tooling you will need to machine a bit off either the bases of the tooling (very tough) or off the bottoms of the toolpost slots.

8mm boring bar is held the same way, clamped in the toolpost sitting up on packing strips to get tip to centre height.

If you have the earlier single tool saddle clamp arrangment, 3/8" tooling would have been standard, sat on suitable packing strips.

Edited By Hopper on 11/05/2020 06:08:00

I wouldnt use stainless. Can be a right PITA to machine and no great advantage in this application. Mild steel works just fine, especially with brass nuts. Most of the commercially available threaded bar will have a rolled thread which is left in a work-hardened condition.

If you do use bronze for the nut, make it leaded bronze and not phosphor bronze as the latter will wear non-hardened steel faster. The idea of brass nuts is the same as Myford's orginal Zamak, the nut is sacrificial and wears faster than the leadscrew. So you replace the inexpensive nut, not the expensive leadscrew. Plus its easier to machine.

Don't suppliers of trapezoidal threaded rod also usually supply brass nuts to match? Would be easier, and probably cheaper, to buy the nuts even if you have to machine them down to a sleeve then bore out the original nut and Loctite and pin the sleeve in place.

Edited By Hopper on 28/11/2019 01:04:09

Edited By Hopper on 28/11/2019 01:22:27

I made these square thread serial taps:

to make the nuts for the brake shafts on my traction engines:

After I'd made them I cut a trial thread in brass which was easy. In contrast the bronze I used for the actual nuts was a total PITA.

Andrew

Edited By Andrew Johnston on 27/11/2019 22:22:12

I was surprised by this as I recently had no difficulty in tapping a length of cast iron 1/2" x 10TPI acme. I should add that this was done under power and the tapping hole was slightly oversize. Other materials may well be problematic, of course.

I'm not going to jump into any Square/Acme/Size of Material discussion here Shaun - just wanted to support Hoppers statement (warning) that 'tapping' an Acme tread is not as simple as just buying a single Acme tap and drilling a suitable hole. I think you will find it is very hard (if not impossible) to turn it.

It's either a staged tap (e.g. more than one tap = quite expensive) or an interior thread cutting operation, perhaps using a tap as a finishing touch, if you already have a suitable tap. I've seen YouTubes of folk going straight in with a single Acme tap but I don't know how they do it - because I certainly couldn't when I tried it, albeit on a slightly larger (1/2" x 10tpi) nut.

Of course, if you can purchase a screw & matching nut and modify them to suit your application, then this need not worry you.

Regards,

IanT

Edited By IanT on 27/11/2019 10:22:46

Shaun , a slightly larger diameter screw would still work the same in regard to the dials if the pitch TPI is the same .(as long as everything else is machined to fit (the nut, dials ,handles etc...)

Edited By mark smith 20 on 27/11/2019 09:37:59

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Shaun

This is important ... although sellers all over the world seem to ignore the facts these days:

The ACME thread form is very specific, and has 29° flanks

The Metric equivalent is Trapezoidal, and has 30° flanks

Details of both are readily available.

[sorry for preaching from my soapbox]

MichaelG.

For the sake of clarity [hopefully not for further confusion] regarding the metric screw threads

The aftermarket versions supplied by MyfordSolutions are very clearly stated to be 2mm pitch.

**LINK**

https://myfordsolutions.com/collections/ml7-carriage-assembly

Click the thumbnails for individual descriptions:

” Each rotation of the spindle gives 2 mm displacement. “

MichaelG.

I think you will find Myford uses Acme thread (or maybe trapezoidal for metric?) and not square. But square will certainly work for you if that is what you can buy in threaded rod.

Tracy Tools and others can supply square and Acme thread taps. Many on eBay too. Can be a bit hard to tap large chunky threads like that from scratch so it is common to rough it out by screwcutting in the lathe, even with a steep-sided V tool and finish with the tap. Or buy a set of progressive taps.

I make all my leadscrew nuts from brass, not bronze. Less wear on the leadscrew that way. And easier to machine.

8 tpi would be close to 3mm pitch (actually 3.18). Please do not assume anything - you may well be wrong, so always check it out properly. 2mm pitch is just that - there is no need to try to convert to imperial (it would actually be 12.7 tpi!).

While not standard myford, I would make them in square thread, not acme, although at only 3/8” diameter that may be a little more awkward. Cutters are easily ground in the home workshop for both inside and outside threads.

Myford’s competitor (‘just down the road&rsquo used square threads for feed screws - but 1/2” in diameter. Nothing at all wrong with their feed screws (their lathes were of much higher quality than those of myford). I am currently cutting a new nut in square format for one of those. One only really needs ACME thread for lead screws, that need to be engaged and disengaged with half nuts.

One could always cut the screw easily enough and then make the feed screw nut in acetal. Probably better to cut a piece of extra screw for that, including clearance, as acetal will leave no thread clearance when moulded by the ‘heat and squeeze’ method.