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Forum topic by Brad posted 922 days ago 1582 views 0 times favorited 11 replies Add to Favorites Watch
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Brad

807 posts in 1336 days


922 days ago

Topic tags/keywords: rehab tool psw dividers calipers replace screw

While tool-shopping at my favorite Fort Collins flea market, I picked up this 8” pair of PS&W dividers.

I didn’t realize it at the time, but the screw in the hole was not original to the tool. Instead, the dividers should have had a thumb screw like the one pictured below.

Now I tried going to the big box store hardware isle…and the #8 size of thumb screw seemed to be the right diameter, however the threads were not compatible.

Here are my questions:

1. Do these vintage threads have different thread pitches (threads per inch) than bolts that are available today?
2. Where can I find a thumb screw that will fit the threads?

Now I’ll sit back and be awed by your collective knowledge.

Regards,
Brad

-- "People's lives are their own rewards or punishments."


11 replies so far

View Dark_Lightning's profile

Dark_Lightning

1667 posts in 1705 days


#1 posted 922 days ago

Did you try both 8-32 and 8-24? It’s possible to be one or the other. There are also specialty threads, like 8-36, 8-40, etc., but those are usually used for instruments. I’ve used 5/16-40 in some applications (same thread as a micrometer, btw).

View Don W's profile

Don W

14597 posts in 1163 days


#2 posted 921 days ago

I know absolutely nothing about the dividers, but in researching for Stanley planes I’ve discovered its often dependent on where they were made (like US or europe) and when. Most of the threads on a stanley planes are not in any local store, so its reasonable to assume your tool could be the same.

-- Master hand plane hoarder. - http://timetestedtools.com

View Newage Neanderthal's profile

Newage Neanderthal

190 posts in 1146 days


#3 posted 921 days ago

We use 8-40 all the time building guns. I would recommend getting a thumbs screw slightly larger on known threads(I’m thinking 10-32 would be the ticket if an 8 feels right), and tapping the divider.

-- www.newageneanderthal.blogspot.com . @NANeanderthal on twitter

View Dennisgrosen's profile

Dennisgrosen

10850 posts in 1711 days


#4 posted 921 days ago

find a thumpscrew of the next size and make new tread in the devider
if your treads is gone or half gone you have to make new anyway

Dennis

View horologist's profile

horologist

93 posts in 2335 days


#5 posted 921 days ago

Unfortunately, standardized threads are a relatively modern invention. I run into this sort of trouble frequently on old clocks and buy old screw plates, taps, and dies whenever I can get them reasonably.

If someone has already forced an incorrect screw into the hole then your threads may already be damaged and it may be that your best option is to rethread for a slightly larger screw. If you cut a taper on a dowel that is larger in diameter than the hole you can twist it into the hole tightly to mark the dowel. Measure the thread pitch from the marks on the dowel.

The threaded portion looks to be fairly this so getting the correct diameter is much more important than the correct pitch. On thin sheets you can get away with a lot of error in thread pitch.

-- Troy in Melrose, Florida

View BigYin's profile

BigYin

228 posts in 1012 days


#6 posted 921 days ago

if its old and british its almost certainly an odd thread.
Probably BSW BSF or BA

Whitworth Thread
Size (in) Core diameter (in) TPI Pitch (in) Tapping drill size
1/16 0.0411 60 0.0167 Number Drill 56 (1.2 mm)
3/32 0.0672 48 0.0208 Number Drill 49 (1.85 mm)
1/8 0.0930 40 0.025 Number Drill 39 (2.55 mm)
5/32 0.1162 32 0.0313 Number Drill 30 (3.2 mm)
3/16 0.1341 24 0.0417 Number Drill 26 (3.7 mm)
7/32 0.1654 24 0.0417 Number Drill 16 (4.5 mm)
1/4 0.1860 20 0.05 Number Drill 9 (5.1 mm)

BS Thread
BA Outer Diameter TPInch TPmm Tap drill
0 0.2362 in / 6 mm 25.38 1 5.1 mm / 7 gauge
1 0.2087 in / 5.3 mm 28.25 1.112 4.5 mm / 16 gauge
2 0.1850 in / 4.7 mm 31.35 1.234 4.0 mm / 21 gauge
3 0.1614 in / 4.1 mm 34.84 1.372 3.4 mm
4 0.1417 in / 3.6 mm 38.46 1.514 3.0 mm
5 0.1260 in / 3.2 mm 43.10 1.697 2.65 mm / 37 gauge
6 0.1102 in / 2.8 mm 47.85 1.884 2.3 mm
7 0.0984 in / 2.5 mm 52.91 2.083 2.05 mm / 46 gauge
8 0.0866 in / 2.2 mm 59.17 2.330 1.8 mm
9 0.0748 in / 1.9 mm 64.94 2.557 1.55 mm
10 0.0669 in / 1.7 mm 72.46 2.853 1.4 mm / 54 gauge
11 0.0591 in / 1.5 mm 81.97 3.227 1.2 mm
12 0.0511 in / 1.3 mm 90.91 3.579 1.05 mm

-- ... Never Apologise For Being Right ...

View Brad's profile

Brad

807 posts in 1336 days


#7 posted 919 days ago

UPDATE—Closing the loop on your recommendations

The Newage Neaderthal: “I would recommend getting a thumbs screw slightly larger on known threads(I’m thinking 10-32 would be the ticket if an 8 feels right), and tapping the divider.”

I learned some time ago, to try the simplest solution first. That lesson involved an Acura Integra I owned and a radiator that I replaced ($165.00) in 10 degree weather but the problem turned out to be a bad radiator cap ($5.00)...but that’s another sad, pour-a-beer-and-sit-back-to-listen story.

So, hoping against hope, I went to Ace Hardware and worked with Patrick to find a screw that would fit the existing hole. He tried a lot of different sizes (the closest were 8-xx size/thread combinations) but to no avail. That told me that, like many screws in vintage Stanley planes, the threads on this vintage PS&W divider were different from the screws available today.

Patrick was greeted by a knowing smile when he said—unprompted—, “Your best bet would be to tap a 10-32NF hole.”

Boy, that sure sounds easy doesn’t it? For me it turned out to be a comedy of errors.

Error #1
I didn’t drill the hole for the tap. I should have used what Irwin calls a #21 drill bit. I got lazy and didn’t want to drive back to the hardware store to get one. In hindsight, I COULD have looked up the appropriate bit site on the US Tap and Drill Bit Size Table, but alas, I had to get Error #2 under my belt before I took that step.

What I did do was use the 10-32 tap I bought and “forced” it through the hole.

Results
This approach stripped the tip of the tap threads because the PS&W metal that I “thought” was soft, wasn’t. So I had to also “force” the 10-32 thumb screw through the very end of the hole, using a wrench to turn it. This also stripped the threads at the end of the screw…which made for a loose, wobbly fit.

More tinkering was required.

Error #2
I “re-tapped” the hole and forced the tap to go a bit further in the hole—meaning that I pushed the tapered tip of the tap against the back of the wing slot. Note that the gap that the wing slides through is only 1/8” wide, so the tap can only advance so far.

Next, I cut the stripped portion of the 10-32 thumb screw off thinking that I had tapped the hole sufficiently to be able to use the thumb screw to tap the last little bit if need be.

Results
Well…using a wrench to apply sufficient force to turn the screw…broke it off in the hole! That’s two steps backwards.

To rectify this, I started drilling out the broken part, starting with a 3/16” bit.

What worked
So now I’m standing there looking at a 3/16” hole through a broken off screw and feeling awfully stupid. The only way forward was to start at square one.

So I looked up the nominal #21 bit size (5/32”), chucked up the proper bit and did what I should have done in the first place by drilling out the hole (and the thumb screw remainder) to the correct diameter.

Then, choosing to learn from my past mistakes, I used my Dremel to cut off the top part of the 10-32 tap (the stripped portion along with the tapered tip). That left me with a tap that would be able to do its work completely through the hole before “bottoming” out in the narrow, 1/8” wing gap.

With the hole drilled, I ever so slowly twisted the tap using a wrench. When I met resistance at the bottom of the hole, I applied downward pressure while twisting. Once the tap cleared the hole it was time to test the thumb screw.

I literally, breathed a sigh of relief and said a short prayer to my creator when it worked. Nice snug fit too. But I wasn’t done.

Tapping the hole had left a burr on the inside of the divider slot which I sanded with 210 grit paper using the head of a small flat-head screwdriver to act as a sanding block.

After all of this, the thumb screw looked like it had been carried by a Marine on Iwo Jima.

I decided that I like it that way because the dings and scratches fit in with the overall vintage look.

Here’s the before/after tapped pics:

…and the ready for use pics:

Success! With help from all of you
Tapping a larger 10-32 hole for a readily available, standard thumb screw was the right answer. And while I initially bungled the execution, I eventually found the right steps to get it to work.

Thank you all for helping me put a beautiful set of dividers back into service!

-- "People's lives are their own rewards or punishments."

View Dennisgrosen's profile

Dennisgrosen

10850 posts in 1711 days


#8 posted 919 days ago

congrat´s by bringing the tool back to life
may it serve you well the next many years

Dennis

View KayBee's profile

KayBee

999 posts in 1842 days


#9 posted 919 days ago

Nice save of an old tool. It looks good.

-- Karen - a little bit of stupid goes a long way

View Newage Neanderthal's profile

Newage Neanderthal

190 posts in 1146 days


#10 posted 918 days ago

That’s what’s so great about this site. We get to help others, and benefit from the help of others; it be great if these kind of threads were the ones with 200 posts. I have learned so much more on threads like these about woodworking than the kind that seem to be popular around here these days.

-- www.newageneanderthal.blogspot.com . @NANeanderthal on twitter

View poopiekat's profile (online now)

poopiekat

3553 posts in 2330 days


#11 posted 918 days ago

Great save! Your item, by the way, was made by ‘Peck, stowe, and Wilcox.’ Famous in an earlier day for metalworking tools, industrial equipment, as well as precision measuring and calibrating tools. In the 40’s and 50’s they shortened their name to “Pexto”, and I recall the well-worn sheetmetal shears and brakes in junior high shop class with that Pexto logo. I’m not sure what era of manufacture the ‘PS&W” logo is, but it must be early, I’d say 20’s-30’s. I wonder if they’re still in business? Anyway, I’d grab any Peck, Stowe and Wilcox hand tools for my workshop that I could find. Good score!

-- Einstein: "The intuitive mind is a sacred gift, and the rational mind is a faithful servant. We have created a society that honors the servant and has forgotten the gift." I'm Poopiekat!!

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