Tensile Strength Machineability

[kevian64Participant @kevian64]

Eight, here goes, my very 1st question. I’ve latched onto a really nice guy who I bombard with questions on a daily basis, he’s been really helpful but I feel guilty keep asking him silly, basic questions. He deserves a rest lol.

I’m going to be making myself a little set of ‘lathe levelling screws’ and just wondered if I should get a low or high tensile strength screw? Which is easiest to machine and drill please?

Thank you

[Julie AnnParticipant @julieann]

I used low tensile commercial screws and nuts, unmodified, to set up my ex-industrial 750kg lathe. No point in making life over-complicated.

High tensile materials tend to be more finicky in terms of getting a good finish.

Julie

[kevian64Participant @kevian64]

I was thinking these?

[kevian64Participant @kevian64]

[DiogenesParticipant @diogenes]

Homeland Security worried after rash of people searching ‘M16 Bolt’ on Thursday evening..

[FulmenParticipant @fulmen]

Low strength is simpler to machine to a point. At some point it can turn stringy which is both annoying and a possible hazard. High strength material can give better finish, especially with heavier cuts and suitable carbide inserts. It also tends to break the chips better making less of a mess. But you will need flood coolant and you might want to take a step back cuz those chips are hot. Better left for more experienced machinists.

High grade machine bolts are great for strength, not so much for machining. Especially in the threaded area since it’s been cold worked after heat treatment.

[PeteParticipant @pete41194]

There’s not enough details given for a proper answer. How large, heavy is the lathe? But in reality, it’s a engineering question with fairly easy to find answers. Quality bolts and there various grades have some fairly rigid specifications as far as tensile strength and shear load limits depending on grade, alloy type, thread size etc. In fact most amateurs including myself usually under estimate just how strong they can be. A Google search for bolt and shear load strength should get you the answers though.

For something used to level a lathe and as Julie pointed out, low tensile should be ample. I might go far larger in size than ever needed, but that would be for gaining a larger cross sectional area for better support. My own lathe only weighs about 200 kgs. I still used 3/4″ or in metric, 19 mm sized adjustment bolts at each corner for that reason. And any of the lower tensile bolts should be easily machinable even with decent quality HSS cutting tools. You would be machining heat treatable steel, so keep the speed down and the tool cutting at all times, and use a good cutting oil. Any excess heat is not something you want. Drilling is harder to answer because drill quality varies so much. I’d want to be using a sharp and industrial level brand name HSS drill. Fwiw, I have drilled up to grade 8 imperial bolts with HSS drills.

[JasonBModerator @jasonb]

I’m not sure what the weight of the lathe has to do with it? The jacking screws are likely to be in compression so no tensile loads. So whatever is available and within budget.

If you are going to have the heads downwards then skim off the raise numbers so they turn a bit easier if making fine adjustments.

8.8 is not too bad to machine. I can’t remember the details of why I took this video but probably some saying they cant be turned. Caption should say CCGT 020208 which with a good feed rate gave a finish that is certainly upto standing on a concrete floor. No coolant or flying chips.

[Neil LickfoldParticipant @neillickfold44316]

With the CCGT inserts, or the ground inserts, with a fairly sharp geometry, they will cut quite well even Maraging steels of 1900 MPA and are in the 52-54 Rc range. Avoiding cutting to the centre will reduce insert chipping immensely. I have a small 6mm carbide spotting drill, that I use to relive the centre of stock when facing. Unless it requires being faced to centre, then I spot drill less or travel quite slow as I near the centre.

With hss, these types of materials are very difficult to cut or drill.

[HuubParticipant @huub]

If you are machining bolts and nuts, use a fine thread pitch that makes leveling easier. For such a low load application any metal would do even soft aluminum,  so use whatever is available.

[Martin KyteParticipant @martinkyte99762]

Why don’t you try and make two sets using  high and low strength screws. You will learn more by a practical direct comparison of machineability. As to the end use either will do as has been said.

[SillyOldDufferModerator @sillyoldduffer]

Putting numbers on the strength of steel may help.

Roughly, given a rod with a sectional area of 1 square inch:

• ordinary Carbon Steel will support a weight of 30 tons.
• a high-tensile Alloy Steel will support about 50 tons.

When choosing materials, the engineer asks ‘what’s the advantage?’   Very often nuts and bolts don’t have to be strong, so something else drives the choice like cheapness or anti-corrosion.   Not smart to hold a garden shed together with expensive High-Tensile steel fasteners when cheapo DIY store galvanised will do a better job!   Also not smart to use ordinary weak bolts to mend vehicle brakes!   When a fastener is safety critical, it may be impossible to make one to specification, so buy the correct spare!

High-tensile steel is often used in construction.  The purpose is to reduce weight: having calculated how strong a ship’s hull needs to be, it could be made from mild-steel or high-tensile steel.   Mild steel is cheap but heavy (more needed to provide strength), leading to poor fuel economy for the entire life of the vessel.   As less high-tensile steel is needed for the same strength, the hull can be made lighter, potentially saving money on fuel.   Warships are often built of high-tensile steel because they place a premium on range and acceleration.  Mild-steel isn’t used much in aircraft – too heavy.

Never say never, but I guess high-tensile steel is rarely deliberately selected in home workshops.  Certainly not needed for lathe levelling, where almost any fine threaded metal will be good enough.    Main exception is modifying a commercial bolt from the junk box that just happens to high-tensile.   Not ideal because machining it will be a mild bother.

The 30 vs 50 ton numbers are indicative, because how metals are processed can radically alter their properties.   As supplied Silver Steel is soft and easily machined, becoming much harder and difficult to machine after heat treatment.  Cold-forming improves strength (Piano Wire), and so does drop-forging (spanners).   The mechanisms are different.

Aluminiums, Alloy Steels, Brasses, Bronzes, Copper, Cast-irons, Carbon Steels, Magnesium, Titanium, Stainless, and Zinc all have useful properties depending on the job.  There are thousands of alloys available for purposes other than turning in a lathe, so don’t expect them all to be suitable.  Avoid scrap metal unless you know what it is.  Manufacturers do not choose metals to suit us!    We want “free-cutting”, they’re just as likely to go for malleability (extrusions & stampings), weldability, corrosion resistance, cheapness, castability, hardness, wear resistance, or some other feature.

Thinking to save money I started by collecting a box full of scrap metal.   By mischance, all of it was nasty, leading me to believe my tools were rubbish!    Not so, eventually coughing up for some machinable mild-steel (EN1A) was a revelation.  Ditto free-cutting Aluminium and Brass.   Now I know what to expect it’s much easier to adapt to difficult materials.  Not wise for a beginner to start with an 8.8 bolt, unless forewarned that they are unfriendly.  Instead. order free-cutting metal from a local stockist (if available), or an internet supplier,  and move on to scrap after building skills with friendly metals.

What’s available in the way of usable scrap depends on where you live.   I’m in the sticks where very little commercial machining goes on.  There are no skips full of nice metal or friendly chaps giving off-cuts away for beer money.   My local scrap yards are positively unwelcoming – angry guard dogs and razor wire.   They sell bulk metal for recycling, not small quantities to casual punters.

Others are still able to pick decent scrap up on the cheap, lucky them!   I get the impression this is ending, perhaps because metal is expensive, and firms have to be cost-concious.  Not like the good old days when they paid someone to take it away…

Dave

 

 

[John HaineParticipant @johnhaine32865]

My Myford S7 on sheet steel stand is mounted on M10 stainless studs, each one loctited into a 50mm square x 12.7mm pad.  These sit on the floor, lathe foot is trapped between a pair of nuts + washers for levelling.  You can easily overthink this!  As the steel is in compression the mildest of steel will do the job.  I just hacksawed the studs from a length of threaded rod and cleaned up the burr.

[PeteParticipant @pete41194]

The size / weight of the lathe is important Jason because the OP was also asking about those M16 bolts. Almost for sure it’s a smaller and more hobby sized lathe, but I still don’t know that with 100% certainty.

For my own lathe, I even thought about just turning, milling my own 3/4″ x 16 mild steel bolts. They would have been more than ample for the intended use. It was just a lot quicker and more efficient to use something that’s easily bought.

[kevian64Participant @kevian64]

<p style=”text-align: right;”>Thank you for all the replies. To clarify, I have a ML7 and am looking for a ‘simple’ levelling system. I was looking on t’internet for set screws and these came up. I’m unsure if set screws are available in mild steel, but I’ve been thinking and contemplating using threaded bar going through the riser blocks, 2 nuts on top of that as the adjusters and nuts top and bottom to fix in place.</p>

[Howard LewisParticipant @howardlewis46836]

As Jason says, levelling bolts will be in compression, so tensile strength is of little or no consequence.

Probably cast iron, being strong in compression, would suffice, and be easy to machine.

To need even low strength M16 fasteners implies a VERY heavy lathe,  a VERY large industrial machine.

Being a 2 mm pitch, the adjustment would be coarse. A quarter turn would change level by 0.5 mm

Which is an enormous amount when trying to take twist out a lathe bed.

That will be difficult to level precisely, since the slightest rotation, or even tightening a locknut will produce a marked change of level.

Many hobby lathe are levelled using one 5/16 BSF bolt at a time, so if the bolts MUST be Metric, M8 would more than suffice.

A quarter turn would change the level of that corner of the lathe by 0.3125 mm, and you will be looking for much less than a tenth of a turn for precise levelling.

Howard

[JasonBModerator @jasonb]

In this day and age metric fine would likely be cheaper than BSF, something like M8 x 1 will be more than upto supporting your Myford.

Not sure I would go with Cast Iron unless it was SG. At the suggested 5/16 or M8 if you were jacking it to also gain a bit of height then due to the length may be prone to fracture if the lathe stand got a knock from the side or just dragging it into position. It is also more expensive than Mild steel.

[kevian64Participant @kevian64]

Thanks JasonB, the difference in cost between Metric and BSF would be negligible so if BSF offers a finer pitch, then BSF it is. I have no intention in gaining height, I’m only a short ar5e anyway, it’s purely for levelling. Do you think my ‘double nut’ idea is suitable for levelling?

[JasonBModerator @jasonb]

M8x1 that I suggested is actually finer than 5/16″ BSF – 25.4tpi vs 22tpi

Yes it would work though personally I’d go with a hex head screw fitted head down and then a nut above and below the hole in the lathe

[kevian64Participant @kevian64]

Apparently one can even get M8 x 0.75 pitch which is 33 threads per inch.

[FulmenParticipant @fulmen]

Yes but that is not something you can pick up at the hardware store. As a general rule metric fasteners will have a finer pitch than their imperial equivalent.

[kevian64Participant @kevian64]

Hi Fulmen, in principle, monetary costs are irrelevant, if it’s the best ‘thing’ for the job, I’ll buy it. However, if it is £000’s per inch, I wouldn’t

[FulmenParticipant @fulmen]

Best or not, it’s just not necessary. There is little in this world that provides more bang for your buck than a modern machine bolt.

[JasonB]

On JasonB Said:

M8x1 that I suggested is actually finer than 5/16″ BSF – 25.4tpi vs 22tpi

Yes it would work though personally I’d go with a hex head screw fitted head down and then a nut above and below the hole in the lathe

Hi Jason,

 

Please excuse my ignorance, but what do you mean ‘fitted head down’?

I can understand fitted head up, with a clearance hole through it so a stud can pass through and a nut beneath the head for adjustment.

Thank you Kev

[JasonBModerator @jasonb]

Like this. The head against the floor/bench will act as a bit of a foot. Nut under the machine to adjust and nut above to lock

[Author]

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