Tube Replacement On Osborn Rotary Punch

[TinkerTailor]

I am in doubt that the metric taps are correct, considering the supplier. I would bet they are just using an obscure inch size, or an obsolete thread, like singer did all the time, and Juki did on my 441 clone....

So I did some lookin at charts and things, and came up with this:

m8x1.0 tap hole size 0.2756"

m7x1.0 tap hole size = 0.2362"

mstric thread pitch1.0mm is 25.4tpi.

24tpi= 1.058mm

26tpi = 0.977mm

According to the charts, an m8x1.0 tap has the same hole size within the tolerance range, and might actually be 5/16 24tpi.

Also according to the charts, the closest to an m7X1.0 in drill sizes is 1/4 28tpi,

The m7x1.0 one is quite a bit off in thread pitch from 28tpi and the hole size doesnt match anything i have found around 24tpi

I would not be surprised to see 5/16 26tpi or 1/4 26 tpi. 26 tpi makes its way into the bike world here and there where 24 would be normal. I know they do this in guns and sewing machines as well.

Any chance one of you guys has a micrometer to measure the outside of the threads on the insert, and perhaps a thread pitch gauge....?

[bruce johnson]

Here's what I got on an average of several new tubes in the #3-#6 range that Osborne says are interchangeable tube sizes for the single tube punches.

The outside of the threads is 0.31 inch

With my thread gauges the M 1.0 is a fit as far as I can tell with magnification. My SAE gauge jumps from 24 to 27. The 24 is too coarse and the 27 is too fine.

My experience with the old single tube punches is the threads seem to match interlocked in TPI but the thread height on the old ones is lower. The new tubes do not run into the old holes very often. Run the M8x1.0 tap through and the new tubes go. I take the old tubes out before bead blasting the handles and toss the old tubes so I don't have any right now to check the outside of the old tubes vs. the new tubes. Whether we are dealing with very close but obsolete or propriety threading in the old frames, I don't know but the M8x1.0 makes them work for the new tubes. I am sometimes dealing with 80-100 year old or so frames and last month's replacement tubes.

[TinkerTailor]

I probably would do the same you guys have.

If the metric ones work best, use them. If originally they used an obscure thread pitch like 26tpi, they did it expressly to prevent the user from repairing it and/or using not original replacement parts. I get 3/8 24tpi and 3/8 26tpi bicycle axle nuts in the store. They mark them with a 24 and 26 on the flange on the new ones. I think it was schwinn who used the odd tpi to force you to buy schwinn parts.

There is another reason this is done. Axle nuts are always softer than the axle so they fail first when cross threaded, or over tightened as they are much cheaper and easier to replace than axles. If you put a grade 8 nut on a bike axle, it may strip the axle, The bike designers specd a special thread to prevent you from using over hard nuts from the auto parts store.

There are lots of parts on a brand new metric bike, that measure out at 25.4mm, That is exactly 1 inch... They also use 28.6 and 31.8, which are 1-1/8" and 1-1/4" respectively. And they call it metric.......

In the 70's-90's everybody but the french used a 22.2mm diameter for fork steer tubes and the threads of a headset bearing. The french in their infinite wisdom decided to make it true metric and used 22mm...guess what happens if you use an japanese headset, 22.2mm (by far the most common)of a french bike 22mm? The headset will thread together and adjust up when the parts are brand new, BUT, the reduced thread engagement means the headset lock and bearing race pop up a thread or two on that first big bump.....making the steering really loose all of a sudden. This can cause dental work and wheelchair payments.

Edited January 8, 2016 by TinkerTailor