Lathe Toolpost Stud Thread

[electrosteam]

Aaron,
I worked in the Eighty's with an extremely good Austrian war-time trained mechanical engineer in an Australian aluminium rolling mill plant.
This guy was experienced with European heavy metric plant equipment and when he arrived at the plant was surprised the way the British sourced mills were always suffering from loose fixings.
It was a perennial problem on every scheduled shut to go around flogging up bolts.
In comparison, Japanese sourced mills were regarded as not having loose fixings.
It was not correctly a totally fair comparison as the British were the older, heavier duty, mills whereas the Japanese were newer and handled lighter duty.

But, the claim was that theoretical analysis revealed Whitworth 55 degrees fixings as having less resistance to shock loads when compared with the 60 degrees American or Metric fixings.
The heavy mills suffered impact from 20 T ingots rolled at speed into the bite - unbelievable impacts at times and I have seen a bolt about 1 inch in size exiting the mill horizontally 1500 mm above the floor and travelling more than 30 m before hitting the floor. Perhaps 10 seconds later it could have got me !

Can anyone confirm the theoretical analysis ?

John

[azzrock]

hi john
well that's interesting . i was really just shooting my mouth off. again
the pommy mills im surprised they dint use bsf threads.
i don't know much about the studies .
i just thought the rounded thread form. was stronger than the pointer unc unf type.
ill have to maybe have a look around the innerweb
for some info about the two.

thanks aaron

[Steamwhisperer]

Not 100% sure John but I was always led to believe that loose bolts had more to do with lead angle than thread angle.

Phil

[Oldneweng]

Not 100% sure John but I was always led to believe that loose bolts had more to do with lead angle than thread angle.

Phil

Was my feeling too although that does not mean a heck of a lot. Not a lot of difference between 55 deg and 60 deg really. I like Whitworth thread forms but then I have inherited a P&N Whitworth Tap/Die set about 60yrs old with everything original, with 2 inch dies. An identical set was listed on EBay for $35 this year and I pointed it out in the EBay etc thread. I was surprised when nobody commented on it. A bargain at that price. I would have jumped on it if I didn't already have one. I also have a large collection of Whitworth bolts and nuts that I have collected over the years.

Dean

[Oldneweng]

I despair that Bunnings, and others, continue to display Whitworth fixings enticing the punters to use these for general work.

John

Is there an issue with this other than the fact that Australia is a Metric country now lol. I find it interesting that Whit is the most common thread form used for MS bolts. I have found that metric bolts tend to be more expensive when they are available. Supply and demand.

Dean

[electrosteam]

The new stud is shown in the photo below, together with the old stud, the existing 1/2" W nut and spanner.

New Toolpost Stud 20131119.jpg

Now there is a new problem.
The photo shows the QCTP on the topslide rotated to expose one of the two indexing holes.
This is bad because of the risk of swarf catching whenever the QCTP is rotated.
It is difficult to insert a suitable spacer plate because the QCTP is already too high, caused by the the limited space between the top of the topslide and lathe centerline, 28.5 mm.
The holder has a 1/2" HSS blank set to centre, it is 6 mm above the topslide.

Algra on new stud 20131119.jpg

Any suggestions gladly received.

John

[pipeclay]

Why not just make a slug to fit the hole slightly below the surface.

[electrosteam]

Pipeclay,
Unfortunately, the two index holes exhibit soft edges due to wear, so plugs would leave crevices that will still catch swarf.

I could fill with a composition, like epoxy, that was scraped flat afterwards - but I am not sure this would either be successful intially or that the relatively soft areas would not soon be scraped out by swarf.
My inclination is to introduce a thin steel shim, say 3 mm, and live with the low set of the holders, 3 mm from bottom.
The low set requires the height setting studs on the holders to be removed and replaced with longer ones.
I would take the opportunity to retire the inset square-headed screws that lock the adjustment with hand-operated knurled nuts.

But, a 3 mm shim just sounds too thin to be successful in the long-term.
The existing installation on my Bantam uses a 6 mm aluminium shim, but that lathe has 38.9 mm height from topslide to centreline.

The thickness of the M250 topslide really is noticeable.
The Bantam has a Tee slot that I have found to be really useful, the complete toolholder assembly can be removed in seconds, and an alternative toolholder system replaced just as quickly - I have 3 that I use interchangeably as required.
The M250 fixed stud is a real disadvantage, and may be the reason for the increased thickness due to the necessity to incorporate a thread for the stud.

John.

[Steamwhisperer]

Hi John,
would an empty toolholder get in the way too much or are you like me and don't have a spare empty one.
Perhaps you could make up a dummy one out of aluminium that was flat on the outside.

Phil

[electrosteam]

Hi Phil,
Large pieces of swarf are easily observed and just as easily brushed away, the real problem is those tiny little bits that you miss, so dummy holders may actually increase the risk.

It is interesting to observe the amount of marking that has been imprinted into the aluminium packer plate on the Bantam and the marks/gouges in the M250 topslide.

I can recommend the aluminium packer plate approach wherever it can be accommodated.

John

[bollie7]

re the exposed indexing hole.
If it was mine I'd just fill the hole with an epoxy and scrape it flat. I really don't think it would be a problem after that. I don't know what your usage patterns for your lathe are but I'm assuming it won't be in use 24/7.
You will probably die from old age before and possible damage from swarf becomes a problem.

bollie7

[Ueee]

When i put the Antrac back together i touched up the top of the compound with the surface grinder to clean up damage from chips under the toolpost. Its been....a couple of months now, if that (6 weeks or so i think) , and the other day i pulled the toolpost off for the fist time to put the TPG on. To my dismay there was already damage to the compound from chips getting squashed under it. To be fair i use the lathe most days, but i also brush all the chips off most days.

I think it is unavoidable really, just fill the hole in and remove the post regularly for a good clean.

Cheers,
Ew

[electrosteam]

Looks like epoxy/scrape is the way forward.

I took the time to get a copy of the Algra Rapidue AR-AP QCTP brochure with dimensions.
It states that this size is suitable for centre height 25 to 41 above the QCTP mounting surface (topslide).
As my situation is 28.5, all should be OK.
But, as tested, the height adjuster studs are too short - so the QCTP does not meet its own sales blurb.

Another very interesting aspect comes to light, the size of the mounting hole.
The photo below shows what looks like a brass insert in the mounting hole, assumed by me to be original, and sized to suit a 1/2" stud.

Algra Bottom View 20131120.jpg

Not so, the Algra brochure quotes a bored hole without insert Dia 18 H7, presumably to fit a stud Dia 18 g6 or g7, a precision fit.
This bored hole has only a short height that increases for most of the QCTP height to "as measured" Dia 22, showing that the brass insert with a neat fit to the stud is wrong in principle.
The Harrison came with a stepped bush located very precisely into the topslide with a Dia 22 projecting above, presumably to engage a Dickson QCTP.
So, I am now considering removing the brass insert from the QCTP and making a stepped bush to suit.

Don't you just love playing with old re-cycled equipment !
John

[scottyd]

On the discussion about thread angle and locking ability, the real world test echos what ive seen documented in engineering texts. The shallower the thread angle, the greater the ability for the thread to lock in place. This is why amce / trapezoidal threadforms have such steep angles, it makes them more suitable for power transmission thanks to their resistance to locking. Likewise, its useful in vices because it allows high clamping forces without making the handle super hard to undo. The locking ability of 60º included angle fasteners will be fractionally better than those with 55º included angle, all other things being the same.

But of course, UNC and whitworth have different pitches for common sizes because screw the english...thats why. everything gets changed with a change in pitch. I can appreciate whitworth for the ease of manufacture, at least on single point threading processes. I think metric is far superior, not only for being based on a nice measurement system that is easy to use and transfer from one field of work to another, but because it is sticks to the one number format and is readily scaleable.

Aaaaaand now that Ive started that ole argument, ill see myself out!

[pipeclay]

If you are refering to 1/2" being the only common size or different pitch then yes to your answer.

If you feel there are other common pitches that differ BSW/UNC you should let us all know.