Cleaning up BSW threads

Having broken down a mid 20th century Italian woodworking bandsaw I discover that all the threads are BSW and many are in need of attention, nuts, screws and studs.

Which tap is best for cleaning up a blind hole and nuts or does will any do? Second, taper, plug, roll? Flutes or no flutes?

Would buying used ones online be a waste of time? In all probability they will only be used the once.

A lot depends on what sort of damage is present. If it is physical damage on either through or blind holes then I would expect the damage to be corrosion or confined to the start of the thread.

For corrosion a plug tap would be best to clear the thread right to the bottom but for damage to the top off the thread then a taper would be best.

I would not go for fluteless unless the damage was to the top of the thread in soft materials.

Previously use taps should be fine as long as there is no serious wear or damage to the tap.

Please let us know how you get on.

Brian

There is no corrosion. It's hard to understand but many seem worn down by repeated removal and insertion, many of the nuts stop after a few turns and it is the nut threads that are damaged. Judging by the state of the bolt heads and the screw slots someone just didn't try very hard.

Hi pgrbff In you case you would mostly use plug taps to clean out threads in holes and nuts and I would have thought standard type and second hand would work in most cases. The only place where you would have to use a first taper tap is if the hole needs plugging and 're tapping from solid.

David

Could be wrong, but I smell a rat! I remember the other forum thread discussed the likelihood of an Italian-made 1950s band-saw being fitted with BSW threads. Feels wrong, though it could happen:

• British-made, but re-badged as Italian. (Re-badging has been common practice since the dawn of time.)
• Faithful copy of a British band-saw, including the fasteners
• It's been bodged by someone in the past.

Looking at the bodge possibility, what diameter are the fasteners? M10- 1.25 and 3/8"-BSF (pitch 1.27) almost fit together, and the result is 'many of the nuts stop after a few turns and it is the nut threads that are damaged'. If a previous owner misidentified the threads and forced a mismatch, the band-saw threads are probably damaged too. Possibly the band-saw is now M10 mangled by BSF, or BSF mangled by M10, hence the confusion.

I think M10 / 3/8" is the only likely modern metric mismatch because the others are all too obviously wrong, but there are other potential near misses between older British threads and the Unified system, and because French, German, Japanese and Italian metric thread systems weren't identical until International Metric was introduced in 1947. I suspect Italy in the 1950's was ankle deep in different thread systems, and it would be easy for the average Joe to get confused. Seventy years later there's still enough thread fog about to catch modern engineers out occasionally.

Nothing can be taken for granted when restoring old kit because it's history is unknown and what's been done in the past makes all the difference. Old gear can be anything between pristine New Old Stock and an overworked, mistreated, badly bodged heap of scrap. When machines get close to end-of-life, there's a tendency for owners to keep them going temporarily by foul means and to tart them up for resale; beware ad-hoc repairs, new paint and obvious recent cleaning! Best to assume previous owners are all untrustworthy idiots until the state of the machine proves otherwise.

Not all is lost if the threads are badly mangled because it's a common problem with many solutions. Simply running a tap down a damaged thread is often enough, or it can be drilled out and re-tapped next size up, or plugged and re-tapped, or repaired with the Helicoil system. Which one is appropriate depends mostly on how strong the fastener needs to be. Unwise to fix a safety critical fastening by bodging a damaged thread just so the bolt screws in! Ask what happens if the joint fails in action?

Dave

Edited By SillyOldDuffer on 21/03/2021 09:55:17

Useful tip: drop a bit of plasticene into the hole before running the tap in; the dirt, etc will be forced into the flutes and come out with the tap.

If you have spare BSW bolts, a hacksaw cut longitudinally on the end on one side converts it into a handy tap for cleaning out dirty and distorted threads like you have.

SOD has it well covered, it could even be american left over from war with UNC or UNF. If using helicoil type repair then one can change the thread type, eg BSW to Metric, which might make getting new bolts or screws a lot easier. A helicoil set is not cheap so it might be that you can standardise on one size. Remember that there are several thread pitches for a given dia in metric, 10mm has 3 (I think) Good luck Noel.

+ for Noel.

Unless you are determined to stay true to prototype, it may well be worth investing in a thread repair kit and converting to Metric coarse, since fasteners will be readily available.

Standardising on one size will be the cheapest method, unless you don't mind having several spare inserts in stock afterwards.

faced with a choice of insert length, if possible 1.5 D would be my choice.

FWIW I seem to suffer fewer problems with genuine Helicoils and their tooling that some of the "look alikes".

Howard

BSW nuts and bolts are easy to buy online, so replacing the most worn would be a better way, particularly if there is a lot of wear and tear

I had a mowing machine with an Aspera motor made in Italy and all the fastenings were Unified, it was made under licence from the Techumsa USA motor manufacturer.

Edited By old mart on 22/03/2021 15:08:51

Edited By old mart on 22/03/2021 15:10:03

Thanks

I'm pretty sure it is original. In fairly good condition given age, just old and worn. Definitely all BSW and nuts are all similar and pre-war looking, much nicer quality than today. Badged INGmontavoviSOC Milano I'm told this was a large well know Italian manufacturer.

There are relatively few sizes, 1/2" x12, 5/16" x 18, 3/8" x 16. I can see where someone might have tried a metric replacement nut as I was surprised to discover it was BSW. I have been using an ajustable spanner to remove the fastners, must measure heads to see if metric oe Imperial.

If the used British taps and dies I have bought from that well known auction site aren't too knackered I should be OK.

This saw is going to end up costing more than a new one but she is so pretty.

Suspicion of a rat came from 'many of the nuts stop after a few turns and it is the nut threads that are damaged' because that's unusual unless equipment has been repeatedly taken apart and reassembled. Most fasteners are done up once and apart from corrosion are almost immune from wear and tear. But who knows what happened to this saw in the past!

As faults go, mangled threads aren't serious, and it sounds like you're well on track to get the old girl working again. There's a good chance you'll get an above average saw out of it because old kit was often built to last. Well worth trying I think. Please let us know how the story ends. Restorations are always interesting, I enjoy hearing of successes, and there's so much to learn from troubled examples.

Cheers,

Dace

According to the Britool Wrench Comparator Chart, the nominal Wrench opening sizes, or Nut and Bolt sizes Across Flats should be:

5/16 BSW 0.525" (BS 1083 ) or 0.600" (BS 28 and BS 190 )

3/8 BSW 0.600" or 0.710"

1/2 BSW 0.820" or 0.920"

If this is any help.

Howard

the correct spanners are available from the usual auctions sites and are not expensive.

I didn't bother measuring them, I compared two 1/2" nuts from two different assemblies and there is a few mm difference in the diameter of the nuts. Very confusing.

The taps and dies arrived from the UK. The dies can go on one thread fairly easily and stop dead, by hand, on another. I started worrying I'd got the sizes wrong again but they're definitely 12G on the thread gauge.

I wish I had easy access to some bsw nuts and bolts to try.

Edited By pgrbff on 31/03/2021 17:38:15

Edited By pgrbff on 31/03/2021 17:39:30

12 tpi suggests either 1/2 BSW or 9/16 BSW, unlikely to be 3/4 BSF

You now have the means of making some BSW nuts and bolts!

The taps cannot be adjusted, but the internal thread can be used as a gauge of sorts when adjusting the Dies for the external threads.

It is possible that the threads where the Die stops, has been stretched or damaged

Howard

Threads cleaned up nicely. Quite a bit of swarf and it's obvious a few of them are bent.

I'm beginning to wish I'd just put the saw back together as it was.

It is easy to think a 1/2 " thread is Whitworth 12 tpi when it could be UNC which is 13 tpi whereas most of the UNC threads are the same pitch as Whitworth. Could the machine have UNC threads? Colin

Presuming that "diameter of the nuts" is referring to the distance across the flats of the hexagon.Two possibilities there: Either you have a mix of BSW and UNC nuts which have a different "diameter" across the flats. Or you have a mix of pre- and post-war BSW nuts that were two different measurements across the flats as the hexagons were made smaller during the war to save steel and then carried on that way afterwards.

Measuring the distance across the flats will soon tell you. UNC will be a round figure equivalent to a standard fraction to suit wrenches that go up by 1/16" increments. BSW ones will be all over the place with no reference to any known fraction, as Mr Whitworth sized his hexagons across the points to suit the diameter of round bar available from the steel mill in 1066 or whenever he was lathing away.

Edited By Hopper on 01/04/2021 04:23:09